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-The Project Gutenberg EBook of Die Casting, by Chester L. Lucas
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: Die Casting
-       Dies--Machines--Methods
-
-Author: Chester L. Lucas
-
-Release Date: September 17, 2016 [EBook #53064]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK DIE CASTING ***
-
-
-
-
-Produced by Chris Curnow, Charlie Howard, and the Online
-Distributed Proofreading Team at http://www.pgdp.net (This
-file was produced from images generously made available
-by The Internet Archive)
-
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-
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-
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-
-Transcriber’s Note: Subscripts are preceded by an acute accent mark `;
-italic text is enclosed in _underscores_.
-
-
-
-
-[Illustration]
-
-
-
-
-  MACHINERY’S REFERENCE SERIES
-
-
-  EACH NUMBER IS ONE UNIT IN A COMPLETE LIBRARY OF MACHINE DESIGN
-  AND SHOP PRACTICE REVISED AND REPUBLISHED FROM MACHINERY
-
-
-  NUMBER 109
-
-  DIE CASTING
-  DIES--MACHINES--METHODS
-
-  By CHESTER L. LUCAS
-
-
-
-
-CONTENTS
-
-
-    Die Casting                                      3
-
-    Making Dies for Die-Casting Machines            15
-
-    Van Wagner Mfg. Co.’s Die-Casting Practice      27
-
-
-  Copyright, 1913, The Industrial Press, Publishers of MACHINERY,
-  49-55 Lafayette Street, New York City
-
-
-
-
-CHAPTER I
-
-DIE CASTING
-
-
-Die-casting, a comparatively recent method for producing finished
-castings, is rapidly proving itself an important factor in the
-economical manufacture of interchangeable parts for adding machines,
-typewriters, telephones, automobiles and numerous other products where
-it is essential that the parts be nicely finished and accurate in
-dimensions. The term “die-casting” is self-explanatory, meaning “to
-cast by means of dies”; described briefly, the process consists of
-forcing molten metal into steel dies, allowing it to cool in them, and
-then opening the dies and removing the finished casting. It is the
-purpose of this treatise to give a general outline of the die-casting
-process, showing its possibilities and limitations, and also to give
-a description of the die-casting machinery and its operation, of
-the fundamental principles involved, and of the methods used in the
-die-making. Illustrative examples of the best types of dies, based on
-results obtained from actual experience, will also be given.
-
-
-Origin of Die Casting
-
-The origin of the die-casting process is somewhat difficult to
-ascertain. We may look into the history of type founding and find
-that away back in 1838, the first casting machine for type, invented
-by Bruce, was a machine that involved the principles of die-casting
-as it is practiced to-day. More recently, in 1885, Otto Mergenthaler
-brought out the linotype machine. This machine is a good example of
-a die-casting machine. However, as we interpret the word to-day,
-die-casting is a broader term than type-casting or linotyping, although
-its development without doubt is due to the success of the linotype
-machine. It is doubtful if die-casting, properly speaking, was
-originated until about fifteen years ago, and it is certain that it is
-only during the past few years that the activities in this line have
-been very noticeable.
-
-One of the first experiments in the direction of die-casting was
-undertaken to get out some rubber mold parts cheaply enough to leave a
-profit on a job that was beginning to look dubious from the financial
-side. The molds were for making rubber plates about three inches
-square and one-eighth inch thick, the top side of which was decorated
-with fine raised scroll work; it was this latter feature that gave
-the trouble. After wasting much time and money trying to stamp the
-mold parts, a metal-tight box was made as shown in Figs. 1 and 2 with
-a block screwed in it, the purpose of which was to shape the mold
-impression and impart to it the scroll design. As shown, the ends of
-the box were removable, being screwed on. This box was placed under
-a screw press and a straight plunger that just filled the top of the
-box was fitted to the head of the press. After the two were lined up,
-molten type metal was poured into the box, and as soon as the metal
-had cooled to the “mushy” state, the ram of the press was forced down
-as shown in Fig. 2. Next, the ends of the box were removed, the screw
-holding the block taken out, and the die-casting pushed from the box.
-The object in having the inclined side to the box was to produce a
-piece shaped with the proper inclination for its position in the final
-mold used for casting the rubber plates. The illustrations give an idea
-of the compression that took place. The die-casting was found to be
-sharp at the corners and free from flaws, and the scroll work came up
-in fine shape. Naturally the rest of the mold parts were made in the
-same way and the job turned from failure into success.
-
-[Illustration:
-
-  Fig. 1. An Early Experiment in Die Casting--Before Applying Pressure
-
-  Fig. 2. An Early Experiment in Die Casting--After Applying Pressure
-]
-
-From such simple experiments as these, the die-casting industry has
-developed to its present stage. In view of the advances that have been
-made in die-casting, it is singular that there are to-day only about
-a dozen concerns in the business in this country, but as the subject
-becomes better understood, and the possibilities of the process are
-realized, the demand for this class of castings will result in many
-other firms going into the work, and it is not improbable that a large
-number of factories will install die-casting plants of their own to aid
-them in producing better work in a more economical way.
-
-
-Advantages, Possibilities and Limitations of Die Casting
-
-The greatest advantage of die-casting is the fact that the castings
-produced are completely and accurately finished when taken from the
-dies. When we say completely, we mean that absolutely no machining is
-required after the piece has been cast, as it is ready to slip into its
-place in the machine or device of which it is to be a part. When we say
-accurately, we mean that each piece will come from the die an exact
-counterpart of the last one; and if the dies are carefully made, the
-castings will be accurate within 0.001 inch on all dimensions, whether
-they are outside measurements, diameters of holes or radii. All holes
-are cast and come out smoother than they could be reamed; lugs and gear
-teeth are cast in place; threads, external and internal, and of any
-desired pitch can be cast. Oil grooves can be cast in bearings, and, in
-a word, any piece that can be machined can be die-cast.
-
-The saving in machining works both ways; not only is all machine work
-eliminated by the one operation of casting, but the machine tools and
-the workmen necessary for their operation and up-keep are dispensed
-with, the expense of building jigs and fixtures is stopped; and no
-cutters, reamers, taps or drills are required for this branch of the
-production. In addition, the labor required for operating the casting
-machines may be classed as unskilled. No matter how intricate and
-exacting the machine work on a piece has been, and how skillful a
-workman was required to produce the work when machine-made, the same
-result may be brought about by die-casting, and usually the work is
-excelled, and, excluding the die-making, unskilled men can make the
-parts.
-
-From a metallurgical standpoint a die-casting is superior to a
-sand-casting on account of its density, strength and freedom from
-blow-holes. Also, when the hot metal comes in contact with the cool
-dies, it forms a “skin” similar to the scale on an iron sand-casting.
-As the die-casting requires no machining after leaving the dies, this
-skin increases the wearing qualities of the casting.
-
-The possibilities of die-casting are numerous. By this method of
-manufacturing it is possible and practical to cast pieces that could
-not possibly be machined. It is an every-day occurrence to make
-castings with inserted parts of another metal, as, for instance, a
-zinc wheel with a steel hub. It is also possible to make babbitt
-bearings that are harder and better than can be made in any other way.
-Often there are two or more parts of a device that have formerly been
-made separately, machined and assembled, that can be die-cast as one
-piece. In such cases the saving in production is very great. Figures
-and letters may be cast sunken or in relief on wheels for counting
-or printing, and of course ornamentation may be cast on pieces that
-require exterior finish. As to size, there is no definite limit to the
-work that can be cast. One job that is being done at the present time
-is a disk 16 inches in diameter with a round flange 1 inch in diameter,
-around the rim.
-
-[Illustration: Fig. 3. Examples of Die-castings]
-
-“There is no great gain without some small loss,” is just as true of a
-process like die-casting as it is of anything else. The limitations of
-this work are few, however, and they are here given so as to state the
-situation fairly. Generally speaking, a part should not be considered
-for die-casting if there are but few pieces required, because the cost
-of the dies would usually be prohibitive. Often, however, it happens
-that because of the large amount of accurate machine work being done on
-a machine part, it is economical to make a die for the comparatively
-small number of parts required and die-cast them. A case illustrating
-this phase of the matter recently occurred in actual practice. In
-getting out an order of two hundred vending machines, it was decided
-to try die-casting on a part that was difficult to machine. The dies
-were expensive, costing $200, and as there were only 200 pieces to be
-cast, the die cost per piece was one dollar; but even with that initial
-handicap, it was found that on account of the difficult machining that
-had formerly been required, the die-cast parts effected a large saving,
-and of course the results were superior.
-
-A rough part that would require little or no machining should not
-be die-cast, because pound for pound, the die-casting metals cost
-more than cast iron or steel. The casting machine cannot make parts
-as rapidly or of as hard metals as the punch press or the automatic
-screw machine. For this latter reason a part that necessarily must be
-made of brass, iron or steel, cannot be die-cast, although mixtures
-approximately equal in strength to iron and brass are readily die-cast.
-To give added strength to a die-cast part it is often advisable to
-add webs and ribs or to insert brass or iron pins at points that are
-weak or subject to hard wear. Roughly speaking, it is the part that
-has required a good deal of accurate machine operations that shows the
-greatest difference in cost when die-cast, and sometimes the saving is
-as great as 80 per cent.
-
-
-The Metals used in Die Casting
-
-The metals that produce the best die-castings are alloys of lead, tin,
-zinc, antimony, aluminum and copper, and the bulk of the die-castings
-made at the present time are mixtures of the first four of these
-metals. From them, compositions may be made that will meet the
-requirements of nearly any part.
-
-For parts that perform little or no actual work, save to “lend
-their weight,” such as balance weights, novelties and ornaments for
-show windows, etc., a mixture consisting principally of lead, often
-stiffened with a little antimony, is used. There is but little strength
-to this metal, but it is used because of its weight and low cost.
-For parts that are subject to wear, such as phonograph, telephone,
-gas-meter and adding machine parts, an alloy composed of zinc, tin and
-a small amount of copper is used. This alloy may be plated or japanned,
-and is a good metal to use on general work.
-
-Another metal, used chiefly for casting pieces that have delicate
-points in their design but are not subjected to hard wear, consists
-principally of tin alloyed with lead and zinc to suit the requirements
-of the work. This mixture casts freely, and the finished castings come
-out exceptionally clean. Still another metal, used chiefly for casting
-pieces that have letters and figures for printing, is similar to the
-standard type metal--5 parts lead and 1 part antimony; but if there are
-teeth cast on the sides of the printing wheel a harder mixture will be
-required to give longer life to the gears.
-
-The following mixtures are typical of die-casting or “white brass”
-alloys: copper, 10 parts; zinc, 83 parts; aluminum, 2 parts; tin, 5
-parts. Another is copper, 6 parts; zinc, 90 parts; aluminum, 3 parts;
-tin, 1 part. Another containing antimony is copper, 5 parts; zinc, 85
-parts; tin, 5 parts; antimony, 5 parts. Shonberg’s patented alloy is
-copper, 3 parts; zinc, 87 parts; tin, 10 parts. Alloys containing 15 to
-40 per cent copper and 60 to 85 per cent zinc are brittle, having low
-strength and low ductility. An alloy of 8 per cent copper, 92 per cent
-zinc has greater resilience and strength but not the ductility of cast
-zinc.
-
-Aluminum may be cast, but it is a difficult metal to run into thin
-walls and fine details; it plays, however, an important part in some
-good mixtures used for die casting. Experiments are now being conducted
-for die-casting manganese bronze, and it is said that some very good
-castings have already been made. Its wearing qualities are so valuable
-that it is particularly desirable for making die-castings.
-
-
-The Die-casting Machine
-
-The three important requisites for good die-casting are the machine,
-the dies and the metal. The casting machine is fully as essential as
-either of the other requisites, and although there are a number of
-different styles of casting machines in use, each of which has its
-advantages over the others, especially in the eyes of their respective
-designers, the fundamental principles upon which they all operate are
-the same. In each there is the melting pot and the burner, the cylinder
-and the piston for forcing the metal into the dies, and the dies with
-the opening and closing device. In some machines pressure is applied to
-the metal by hand, in others power is used, and in still another class
-the metal is forced into the dies with compressed air. The provisions
-for opening and closing the dies vary in the different machines; there
-are various means employed for cutting the sprue, and the styles of
-heaters are numerous.
-
-One or two of the largest firms in the die-casting industry have
-automatic casting machines for turning out duplicate work in large
-quantities very rapidly. These machines are complicated and are only
-profitable on large quantities of work, and for that reason their
-use is not extensive. In general, their operating principles are the
-same as in the case of the hand machines, but provision is made for
-automatically opening and closing the dies, compressing the metal, and
-ejecting the castings.
-
-
-The Soss Die-casting Machine
-
-The Soss die-casting machine, manufactured and sold by the Soss
-Manufacturing Co., Brooklyn, N. Y., was the first die-casting machine
-to be placed on the open market. This machine is shown in Figs. 4 and
-5, and in section in Fig. 6. The Soss Manufacturing Co. originally
-manufactured invisible hinges exclusively. At the advent of the
-die-casting era, they commenced to make these hinges from die-castings,
-and placed orders with a leading die-casting concern amounting to
-thousands of dollars each year. After the die-cast hinges had been on
-the market for a short time, complaints commenced to come in, some to
-the effect that the hinges were breaking and others that the hinges
-were corroding. Either of these faults was serious enough to blast the
-reputation of the hinge, but the first trouble, breakage, was the more
-important. Examination of the broken hinges showed that the castings
-were porous and full of flaws, and as the makers of the castings
-could not produce castings sufficiently strong for the hinges, Mr.
-Soss started to experiment for himself. This experimenting led to the
-production of the Soss die-casting machine.
-
-[Illustration: Fig. 4. General View of the Soss Die-casting Machine]
-
-Referring to the illustrations Figs. 5 and 6, _A_ is the base and frame
-of the machine, _B_ is the heating chamber located at one end of the
-machine, and within this heating chamber is the tank _C_, shown in Fig.
-6. This tank contains the metal from which the die-castings are made,
-and the metal is heated by the burners _D_. These burners are fed by
-air and gas through piping on the side of and beneath the furnace. To
-facilitate lighting the burners and inspecting their condition at any
-time, there is an opening (not shown) through the firebrick lining of
-the furnace and the outer iron wall, on a level with the top of the
-burners. There is also another opening through the furnace wall to
-allow the gases due to the combustion to escape. Through the bottom of
-the tank, well to the inner side of the furnace, runs the cylinder _E_.
-Below the bottom of the tank, the cylinder makes a right-angle turn,
-extending through the furnace wall and terminating just outside of the
-wall. The orifice of this cylinder is controlled by gate _F_. In that
-part of the cylinder that extends upward into the tank, there is an
-opening _G_ that allows the molten metal to run into the cylinder from
-the tank. Working in this cylinder, is the piston _H_, that is used in
-forcing the metal into the dies. The compression lever _I_, hinged over
-the inner furnace wall, is kept normally raised by spring pressure, and
-is connected to the piston by means of the link _J_.
-
-[Illustration: Fig. 5. Working Parts of the Soss Die-casting Machine]
-
-At the opposite end of the machine from the furnace, is the mechanism
-for operating the dies. This mechanism consists of a pair of square
-rods _K_, upon which are mounted the sleeves _L_. These sleeves have
-a long bearing surface and are attached to the die-plate _M_. Lever
-_N_ at the end of the operating mechanism controls the movement of
-these sleeves by means of links _O_. Upon these sleeves is mounted a
-secondary set of sleeves _P_, attached to the other die-plate _Q_,
-and whose movement is controlled by lever _R_, through links _S_.
-This second set of sleeves is free to travel with the first set, and
-in addition has an independent movement of its own on the primary
-sleeves. It is the function of lever _R_ to bring die-plate _Q_ up
-to die-plate _M_ by means of links _S_ and sleeves _P_; and it is
-the function of lever _N_ to bring both of the die-plates up to the
-outlet of the cylinder by means of links _O_ and sleeves _L_. This
-system of sleeve-mounting is one of the distinctive patented features
-of the Soss machine. The orifice of the cylinder _E_ is conical in
-shape and exactly fits the cup-shaped opening in die-plate _M_, so
-that when the two are brought together, the joint is metal tight. At
-the center of this opening, and extending through the die-plate _M_,
-is an opening that leads to the dies mounted on the inner faces of the
-two die-plates, and a continuation of this opening extends through
-die-plate _Q_ in which the sprue-cutter _U_ works. Attached to the
-outer side of this die-plate are two slotted brackets. In the slot of
-one of these is pivoted the lever _T_, and in the slot in the opposite
-bracket are bolted two stops that limit the motion of the lever. This
-lever operates the sprue cutter _U_, that works through the opening in
-die-plate _Q_. The sprue-cutting mechanism is best shown in Figs. 5 and
-6. At the left of Fig. 5 may be seen a rubber hose connected to the air
-piping. This hose is used for cleaning out the dies after each casting
-operation.
-
-
-Operation of the Die-casting Machine
-
-The metal for the die-casting machine is mixed in the proper
-proportions for the work in hand by means of a separate furnace, before
-being poured into the tank of the machine itself. The burners are
-lighted and the dies are set up on the two die-plates. As soon as the
-machine has “warmed up,” so that the metal is in a thoroughly melted
-condition, the sprue-cutting lever _T_ is thrown back, leaving a clear
-passageway to the die cavities. Lever _R_ is pulled backward, thus
-bringing die-plate _Q_ up to die-plate _M_, which operation closes
-the two halves of the die. Then lever _N_ is thrown forward, thereby
-bringing the closed die up to the body of the machine, with the nozzle
-in close contact with the outlet of the cylinder. Next, the gate _F_
-is opened, and the man at the compression lever _I_ gives the lever a
-quick, hard pull, forcing the metal in the cylinder downward and into
-the dies. The molten metal literally “squirts” into the dies. Gate _F_
-is now closed; lever _N_ is pulled back to remove the dies from the
-cylinder outlet; and the sprue-cutting lever _T_ is pushed forward,
-cutting off the sprue and pushing it out of the nozzle into the kettle
-placed beneath it. The lever _R_ is pushed forward, and a finished
-casting is ejected from the dies.
-
-An important advantage that this machine has over other die-casting
-machines is the fact that the metal for the castings is taken from the
-_bottom_ of the melting pot, whereas most other machines use metal from
-the top of the tank. At the bottom of the tank the metal is always the
-best, as it is free from impurities and dross; hence, there is little
-chance for the formation of blow-holes. A handful of rosin thrown
-into the melting tank occasionally helps to keep the metal clean,
-but the metal nearest the surface always contains more or less foreign
-matter.
-
-[Illustration: Fig. 6. Section of Soss Die-casting Machine]
-
-While this description of the operation of the die-casting machine may
-convey the idea that the process is a slow one, as a matter of fact,
-the time required is, on the average, not over a minute and a half
-for turning out a finished casting. With the ejection of the casting
-from the dies, the product is completed, in theory; but in practice
-there are always a few small thin fins, caused by the air vents or by
-improperly fitted portions of the dies. It is, however, but the work
-of a few seconds to break off these fins, and unless there are many of
-them, or they are excessively thick, they are detrimental neither to
-the quality nor the quantity of finished castings.
-
-
-Points on the Operation of the Die-casting Machine
-
-We have now taken up the description and general operation of the
-die-casting machine, but like every other machine, there are numerous
-little kinds and practices in its working the observing of which makes
-the difference between good and poor die-casting. Some of these points
-are here given.
-
-The casting machine is best operated by three men, one of whom attends
-to the compression lever and the metal supply in the tank. The other
-two men stand on each side of the die-end of the machine, and it is
-their duty to operate the sprue-cutter, open the dies and remove the
-finished casting, clean the dies with air and close them, throw back
-the die-plates to their casting position over the cylinder outlet, and
-do any other work incident to the operation of the machine. While it
-requires three men to operate a die-casting machine in the best manner,
-the man who attends to the compression lever has a good deal of spare
-time between strokes, and if two or even three of the machines are
-conveniently placed, one man can easily pull levers for all three.
-
-The metal should be kept just above the melting point and at a
-uniform temperature. If the metal is worked too cold, the result will
-manifest itself in castings that are full of seams and creases, and it
-will be difficult to “fill” the thin places in the dies. If, on the
-other hand the metal is allowed to get too hot, the die will throw
-excessively long fins, the castings will not cool as quickly in the
-die, and consequently they cannot be made as rapidly. On account of
-the importance of keeping the metal at a uniform heat, the fresh metal
-that is added to that in the tank from time to time, is kept heated in
-a separate furnace. Therefore, when the metal in the tank gets low, the
-new supply does not reduce the temperature of the metal being worked.
-Some casters use a thermometer to indicate the heat of the metal.
-
-Casting-dies require lubrication frequently. Just how often they should
-be lubricated depends on the shape of the die, the composition of the
-casting metal, and the general performance of the dies. Beeswax is
-the common lubricant, and the lubrication consists in merely rubbing
-the cake over the surfaces of the dies that come in contact with the
-casting metal. In die-casting large parts, the dies must be kept cool
-by some artificial means, for hot dies are conducive to slow work and
-poor castings. To reach this end, large dies are sometimes drilled and
-piped so that water may be circulated through them to keep them cool.
-
-In the Soss machine, the burners are so placed that the metal in the
-cylinder is kept at a slightly higher heat than that in the tank
-proper. This condition is brought about by having the cylinder directly
-over the burners. The value of this feature lies in the fact that
-gas is not wasted in heating the entire tank full of metal to this
-higher heat, but still the metal under compression is at the required
-temperature. The gas consumption of the average die-casting machine is
-about 100 cubic feet per hour.
-
-The speed at which die-castings may be produced varies with the size of
-the castings being made, the composition of the metal being cast, and
-the style of dies that must be employed. In many cases, in die-casting,
-separate brass or steel pieces are used, that must be placed in the
-dies before each operation so that they will be inserted in and become
-a part of the finished casting. The dies may be difficult of operation
-on account of draft problems or pins and screws that must be inserted
-in the dies and removed from each casting before another can be made.
-These different types of dies will be more fully described in the next
-chapter. Taken as a whole, from ten to sixty pieces per hour are the
-maximum limits for speed in die-casting, and with a well-working die,
-of simple construction, a speed of forty pieces per hour is considered
-good production. It is possible, however, when the castings to be
-produced are small in size and simple in shape, to gate a number of
-them together, or rather to construct the dies so that six or more
-castings may be made at once. By this means it is often possible to
-cast five or six thousand pieces per day of ten hours, on a hand
-die-casting machine.
-
-
-
-
-CHAPTER II
-
-MAKING DIES FOR DIE-CASTING MACHINES
-
-
-The making of casting-dies calls for ingenuity and skill of the highest
-order on the part of the die-maker. There is probably no class of
-die-making in which the work produced is more faithful to the dies,
-both in showing up the little details in the making that reflect credit
-on the dies, and in exposing the defects and shortcomings in the
-workmanship, if there be any. The castings from casting-dies or molds
-as they are sometimes called, may be produced in dimensions down to
-ten-thousandths for accuracy if necessary, and once the dies are made
-the castings will not vary in the slightest degree, if the working
-conditions are kept uniform.
-
-In spite of the close work required in making casting-dies, the work is
-very fascinating. Perhaps it is on account of this accuracy; possibly
-it is on account of the fact that they are made from machine steel;
-but most likely it is because there are no hardening troubles to be
-contended with. Another factor that makes the work interesting is the
-ingenuity required in the work, for almost every die-maker, if he is
-worthy of the name, likes to figure out and plan for the best way of
-building a die for a difficult job.
-
-
-General Principles of Casting-die Making
-
-Casting-dies, or molds, have little in common with sand molds. It
-is true that the dies for die-casting are composed of two parts
-corresponding to the cope and nowel of the sand mold, but they are
-so different in every other way that no benefit would result from a
-comparison.
-
-Generally speaking, casting-dies are made of machine steel; the parts
-which are exceptions are the heavy bases and frames, which are made of
-cast iron, and the dowel pins and small cores, usually made of tool
-steel. Except in rare instances, there are no hardened parts about a
-casting-die; this is the case because the melting points of some of the
-alloys that are die-cast are high enough to draw the temper from any
-hardened parts of the dies.
-
-The ideal die is simple in construction, with as few parts as
-practicable; the castings should be easily ejected and should come
-from the dies as nearly free from fins as possible. To meet these
-requirements in the best way is the proposition that confronts the
-ingenuity of the die-maker. As the die is primarily in two parts, there
-must be a parting line on the casting. This line is always placed at
-the point that will permit the casting to be ejected from the dies in
-the easiest manner possible, bearing in mind the effect the joint will
-have on the appearance of the finished casting; this is a point far
-less important than with sand casting, for, if the dies are properly
-made this seam will be barely perceptible. When it is practicable to
-do so, it is wise to have the parting line come on an edge of the
-die-casting. Draft is unnecessary on the straight “up-and-down”
-places, but of course it is impossible to draw any parts that are
-undercut. Means must be provided for ejecting the casting from the
-dies after completion and it is usually done by means of ejector pins,
-though frequently it is better to have the bottom of the die or some
-other section movable and do the ejecting on the same principle that
-is used on drawing dies of the compound type. On close work, shrinkage
-plays an important part, and the amount of shrinkage varies from 0.002
-to 0.007 of an inch per inch. Aluminum shrinks the greatest amount,
-Parsons white brass shrinks considerably, while tin shrinks but little.
-Thus, it may be easily seen that to figure the shrinkage allowance for
-an alloy that contains three or four metals with different shrinkages,
-requires judgment. To prevent the air from “pocketing,” air vents are
-necessary at frequent intervals around the die-cavity. These vents are
-made by milling a flat shallow cut from the die-cavity across the face
-of the die to the outside edges of the block. From ¼ inch to ½ inch
-is the usual width and from 0.003 to 0.005 of an inch, the customary
-depth, varying with the size and shape of the die in question.
-
-[Illustration: Fig. 7. Disk cast in Simple Casting-die]
-
-The dies or molds for die-casting are of various styles, as are also
-punch-press dies, and it would be difficult to lay down specific
-rules for their classification. There are the plain dies, without
-complications of any kind; slide dies with one or more slides; dies
-for bearings, both of the “half-round” and of the “whole-round” types;
-dies for gated work; and many other less important classes. Then there
-are dies that have features that belong to more than one of these
-types, so that it is easily seen that to decide upon the style of die
-that would be best for a given piece of work requires a good deal of
-experience. Some of the most important of these types can best be shown
-by illustrating dies made in the various styles, showing, step by step,
-how the dies are made and assembled. To begin with, consider the making
-of a casting-die of the very simplest form.
-
-In Fig. 7 is shown a plain flat disk made by die-casting. In actual
-practice, a die would not be made for such a simple piece, unless
-there were some features about it that would prevent it being made
-on a screw machine or with press tools. It might have a cam groove
-cut in one of its flat sides, the sides might be covered with scroll
-work, there might be gear teeth around its circumference, or a hundred
-and one other conditions to make die-casting a desirable method of
-manufacturing. All these complications are omitted for the sake of
-simplifying this initial description of a casting-die.
-
-[Illustration: Fig. 8. Simple Casting-die for Casting Block shown in
-Fig. 7]
-
-Fig. 8 shows the die for this piece in plan and sectional elevation.
-_A_ is a square cast-iron frame, made from a single casting. This frame
-or box, as it is generally called, is planed on the top and bottom
-only. Next, the two die-halves _B_ and _C_ are shaped up from machine
-steel. In this casting-die, and in the majority of others, these
-die blocks are square. The lower half of the die _B_ is held to the
-cast-iron frame by fillister head screws, set in counterbored holes,
-thus sinking the screw-heads under the surface of the block. The upper
-half of the die _C_ is located upon _B_ by dowel pins driven into _B_
-which have a sliding fit in the reamed holes in _C_. This being done,
-the die-half _B_ is fixed to the faceplate of the lathe and the recess
-bored for the die-cavity. This operation is a simple one in this case,
-for it is merely a straight hole one-half inch deep and three inches in
-diameter. Of course this recess must be carefully finished with a tool
-that has been stoned up to a sharp edge, using lard oil. Emery cloth
-should be used as little as possible. It is unnecessary to give this
-hole draft, but it must be free from ridges or marks that would prevent
-the casting from being pushed out. If the faces of the dies are spotted
-with a small piece of box wood or rawhide held in the drill press and
-kept charged with flour emery, the die-casting will reproduce this
-“bird’s-eye” finish and the appearance will well repay the few minutes
-additional time that it will take. The spotting should be done with dry
-emery (without oil) to get the brightest finish. The upper die-half _C_
-is simply ground on its working face. The outside corners and edges of
-the faces of both die-halves should be well rounded off so as to insure
-the absence of slight dents or rough places that might prevent the dies
-from fitting perfectly.
-
-The ejecting mechanism must next be considered. Lever _D_, pivoted
-from bracket _E_, has a steel pin _F_ that engages in the elongated
-hole in bracket _G_, so that an upward pull of the lever _D_ raises
-bracket _G_, which is attached to ejector-pin plate _H_. This plate is
-a loose fit over the guide screws _I_ that are attached to the lower
-die-half _B_. The ejector pins _J_, four in number, in this die, are
-riveted into the ejector-pin plate, and they work through holes drilled
-and reamed through the lower die-half. The ends of these pins must be
-finished off so as to lie perfectly flush with the inside of the die
-when ready for operation and, of course, they must be a sliding fit in
-the holes in the die.
-
-An important feature of a casting-die is the sprue cutter, shown in
-this die at _K_. If the disk for which this die was made, had had a
-hole or central opening of any kind, the sprue cutter would best be
-operated at that point; but, as this disk is plain, the sprue cutter
-must be placed at the edge. At the outside of the die-cavity, as shown
-in Fig. 8, the opening for the sprue cutter is laid out, drilled
-and filed to shape. It is obvious that the side of the sprue cutter
-adjacent to the die must fit the outline of the die perfectly, so that
-there will be no break in the appearance of the casting. The opening
-for it is extended through the upper die-half, and from a point ¼ of an
-inch from the inside face of the die this hole is flared out nearly as
-large as the opening through the die-plate of the machine. Of course
-the apperture in the upper die-half must be no larger than the opening
-through the die-plate; otherwise the sprue could not be pushed out. The
-sprue cutter itself is a long rod, whose section is of the same shape
-and size as the openings just made, and it is connected to the sprue
-cutting mechanism of the machine. Of course it is unnecessary to shape
-the entire length of the sprue cutter to size; after the working end is
-milled to shape for a distance of six or eight inches, the rest of the
-rod may be left round. The sprue cutter is finished first, after which
-both the openings in the die are fitted to it; and while the fit should
-be metal tight, it must be perfectly free to slide.
-
-The dies are mounted on the die-plates of the casting machine by means
-of straps, much the same as bolsters are held on punch press beds. The
-position of the die on the die-plate must be such that the opening for
-the sprue cutter will line up with the nozzle at the outlet of the
-cylinder. At the time of casting, the position of the sprue cutter is
-as shown in the illustration of this die, Fig. 8. In this position
-there is room for the metal to enter the die-cavity, and yet there is
-but a small amount of metal to be cut off and pushed back after the die
-has been filled with metal.
-
-With slight modifications, the above style of die may be used for
-die-casting any piece that will draw or pull out of a two-part die. If
-holes must be cast through the piece, it is only necessary to add core
-pins to the lower die _B_, a point that will be more fully described
-later. It is unnecessary to add that both halves of the die may be
-utilized in making the cavity for the die, should they be needed. Also,
-it is often easier to machine out the recess larger than is needed, and
-set in pieces in which parts of the outline of the die-casting have
-been formed. Gear teeth are put in the die in this way; a broach is cut
-similar to the gear desired, then hardened and driven through a piece
-of steel plate which is afterward fitted to its place in the die.
-
-
-Slide Dies
-
-The die illustrated in Fig. 9 is one of the most successful of the
-various types of casting-dies, and if properly made is an interesting
-piece of die work. The principal use of this particular style of die,
-called a slide die, is to cast parts like the one shown in Fig. 10,
-which is a disk similar to the one which the last die described was
-to cast, except that it has raised letters at the edge and a hole in
-the center. It is obvious that the die last described, (Fig. 8), would
-not do for disks or other pieces having projections or depressions
-around their edges, as, for instance, printing or counting wheels with
-raised or sunken characters, or grooved pulleys. Briefly, this style
-of die is similar to the simple casting-die, except that slides are
-provided, to the required number, which form the edge of the casting.
-A die for a plain grooved pulley would require but two slides, while
-a die for a printing wheel with forty letters around its edge would
-necessitate forty slides, one for each of the letters. The die about to
-be described, shown in Fig. 9, was made to cast a wheel with six raised
-letters.
-
-Referring to Fig. 9, _D_ is the cast-iron box or frame, _E_, the lower
-die, and _F_ the upper die. In making the lower die-half, the stock is
-first shaped to size and doweled to the blank for the upper die-half,
-and the holes for attaching to the frame are drilled. For the sake of
-clearness, these holes and screws are omitted from the illustration as
-are also the vents, since they have been fully explained. The lower
-die is next strapped to a faceplate, trued up, and bored out nearly
-to the diameter of the body of the piece to be cast, exclusive of the
-raised letters. The depth of this recess is equal to the thickness of
-the printing wheel plus 3/16 inch to allow for the cam ring _G_ that is
-used to reciprocate the slides of the die. The cam ring is made large
-enough to cover the die-cavity as well as the slides that surround
-it, with an allowance of an inch or two for the cam slots _H_. The six
-slides _I_ are made long enough to have good bearing surfaces. With the
-size of the cam ring determined, the die is next bored out to receive
-this cam ring and the last inch of the recess is carried down to the
-depth of the die cavity so as to make an ending space for the slots
-that the slides are to work in. The die is now taken from the faceplate
-and the slots for the slides laid out.
-
-[Illustration: Fig. 9. Slide Die for Casting the Printing Wheel shown
-in Fig. 10]
-
-These slots may be milled or shaped, but milling is to be preferred.
-The next step is the making and fitting of the slides, which are of
-machine steel, having a good sliding fit in the slots. The six slides
-are fitted in position and left with the ends projecting into the die
-proper. The slots _H_ are next profiled in the cam ring _G_, and the
-pins _J_ that work in them are made and driven into the holes in the
-slides. With the slides and cam ring in place, the cam ring is rotated
-to bring all the slides to their inner position where they are held
-temporarily by means of the cam ring and temporary screws. The die-half
-with the slides thus clamped in the inner or closed position, is set up
-on the lathe faceplate and the die-cavity indicated up and bored out to
-the finish size, which operation also finishes the ends of the slides
-to the proper radius. The die may now be taken down and the slides
-removed to engrave the letters upon their concave ends. The engraving
-can be done in the best manner on a Gorton engraving machine, but if
-such a machine is not available they may be cut in by hand. Stamping
-should never be resorted to for putting in the letters, because the
-stock displacement would be so great that it would be impossible to
-refinish the surface to its original condition. Before fitting the
-cam ring, an opening must be milled in the die to allow the handle to
-be rotated the short distance necessary. After the cam ring has been
-fitted, it is held in by the four small straps _K_, attached by screws
-to the lower die-half at the corners.
-
-[Illustration: Fig. 10. Printing Wheel cast in a Slide Die]
-
-The sprue cutter, which is not shown, is operated through the hole
-in the center of the piece and is, of course, round in this die.
-Its action is the same as was the one previously described, and the
-ejecting device is similar, with the exception that the brackets _L_
-that are attached to the ejector-pin plate M, are widely separated so
-as to make room for the sprue cutter that works through a hole in the
-plate _M_.
-
-
-Die for Casting with Inserted Pieces
-
-For making die-castings that are to have pieces of another metal
-inserted, it is necessary to have a die with provisions for receiving
-the metal blank and holding it firmly in position while the metal is
-being cast around it, and of course the piece must be held in such a
-manner that it can be easily withdrawn from the die with the finished
-casting.
-
-The die illustrated in Fig. 11 is for a part that is used as a swinging
-weight, shown in Fig. 12. The upper part of the piece is made from a
-sheet steel punching, so as to lighten this part of the piece as well
-as to give increased strength, especially at the hole at the pivoted
-end of the work. The cast portion of the piece is slotted lengthwise,
-as the illustration shows; and three holes pass through the casting,
-piercing the sides of the slot. In addition to showing the method of
-making dies for inserted pieces, this die shows the principles of
-simple coring.
-
-[Illustration: Fig. 11. Casting-die for Making Castings with Inserted
-Pieces like that shown in Fig. 12]
-
-In making this die, two machine-steel blanks are planed up for the
-upper and lower halves of the die, _A_ and _B_, the lower die being
-made nearly twice as thick as the upper die because it is in this part
-that the most of the die-cavity will be made. In this lower half of
-the die the stock is milled out to the same shape as the outline of
-the plan view of the casting, being carried down to the exact depth
-of the thickness of the casting. From the wide end of this recess the
-stock is milled or shaped out in a parallel slot to the outside of the
-die-block. At the bottom of the side of this wide slot are T-slots
-to guide the slide _E_ that is to work in this opening. The side is
-milled and fitted to the T-slots and opening in the die, but is left
-considerably longer than the finish size. Next, the slide is mounted
-on the faceplate of a lathe and turned out on the end with the proper
-radius and a tongue to form the slot that is to be in the curved end
-of the casting. At the outer end of the slide is left a lug that is
-drilled and tapped for the operating lever _F_ that reciprocates the
-slide, using the stud in bracket _K_ as a fulcrum.
-
-Two pieces of machine steel are next shaped and finished up to form the
-chamfered part of the casting and to locate the inserted steel punching
-in the die. The combined thickness of these pieces _C_ and _D_ is equal
-to the thickness of the casting, less the thickness of the inserted
-piece. It is now an easy matter to seat section _D_ in the bottom of
-the milled part of the lower die-half, and to locate section _C_ in its
-proper position on the upper half. A pilot pin _M_ is fitted in _D_ to
-hold the steel punching in position by means of the hole that is in the
-extreme upper end of the punching. The pilot pin extends through this
-hole into a corresponding hole in section _C_. At the lower end of the
-steel part that is inserted, there are two holes the object of which
-is to secure the punching to the die-casting, for the molten metal
-runs through these holes, practically riveting the die-casting to the
-inserted piece.
-
-[Illustration: Fig. 12. Die-cast Weight with Inserted Sheet-steel
-Punching]
-
-Provision has now been made for holding the sheet-metal part that is
-to be inserted, and the cavity has been completed for the casting,
-including the tongue at the end; it now remains to describe the manner
-of forming the holes that pierce the casting through the slotted
-portion. In the lower die-half the positions of the three holes _H_ are
-laid out, drilled and reamed. Then, with the two die-halves together
-and the slide clamped at its inner position, the holes are transferred
-through the slide and the upper die. This being done, it is an easy
-matter to make core pins and drive them into the upper die at the two
-end holes, the center hole being taken care of by the sprue cutter _L_
-that will be described later. The core pins should be a nice sliding
-fit through the slide and in the holes in the lower die, into which
-they should extend from a quarter to half an inch. In addition to
-coring the holes, these pins act as a lock to hold the slide _E_ in its
-proper position at the time of casting.
-
-The sprue cutter _L_ is most conveniently operated in the center hole,
-thus doing away with the core pin that would otherwise be required. The
-sprue cutter needs little description in this die, for as in the slide
-die, it is merely a plain round rod that fits closely in the holes
-through the dies and slide. The ejector mechanism is the same in this
-die as in the dies already described; therefore further description is
-unnecessary.
-
-[Illustration: Fig. 13. Casting-die for the Half-round Bearing shown in
-Fig. 14]
-
-The operation of this die is very simple. The sheet-steel piece is laid
-in the recess in the open die, being located by the pin _M_. Slide
-_E_ is thrown in by means of lever _F_, and the dies are closed. At
-the time of casting, the sprue cutter in is the position shown in
-the sketch, being nearly through the die-cavity. As before explained,
-this position admits the molten metal to pass into the die-cavity, but
-still leaves very little sprue to be cut off after the die-casting is
-completed. It should be stated that the steel piece that is inserted
-must be perfectly flat and free from burrs that would prevent the
-die-halves from coming together properly.
-
-
-Bearing Dies
-
-Bearing dies are one of the most important of the various classes of
-casting-dies. The bearings produced by die-casting are so far superior
-to those made by other casting methods and machining that their use is
-now very extensive. Dies are made for “half-round” and “whole-round”
-bearings. There is little out of the ordinary about a whole-round die,
-but the half-round die involves many interesting methods of die-making,
-and for that reason is here described.
-
-Fig. 13 shows a casting-die for half-round bearings. Half-round bearing
-dies are usually made to cast two bearings at a time, for the reason
-that it is just as easy to cast two pieces of such a shape as it is to
-cast one, and, in addition, the die is balanced in a better manner. As
-with other dies, the first step is to machine up the frame _A_ and the
-two die-halves _B_ and _C_. The pieces _D_ and _E_ that are to form
-the insides of the bearings are then turned up and one side of each
-shaped and keyed to fit the slots that have previously been milled in
-die-half _C_. These parts are held in place by dowels and screws. One
-of the bearings produced by this die is shown in Fig. 14, and it will
-be noticed that there is an oil groove within that covers the length
-of the bearing. To produce this groove in the die-castings, a shell
-must be turned up and bored out whose inside diameter is that of the
-inside of the bearing, and whose thickness equals the depth of the oil
-groove. This being done, the oil grooves are laid out upon the shell
-and cut out by drilling and filing. After rounding the outside corners,
-these little strips are pinned to the cores _D_ and _E_ in their proper
-places.
-
-[Illustration: Fig. 14. Die-cast Half-round Bearing, Showing the Cast
-Oil Grooves]
-
-Another little kink in this connection is worthy of noting. So many
-different styles and sizes of bearings are made by a concern doing much
-die-casting that it is essential that the die-cast bearings should
-bear some distinguishing number to identify them. As this number is
-of no consequence to the user it is well to have the number in an
-inconspicuous place, but it must be where it will not be effaced by
-scraping, etc. Bearing in mind that it is much easier to produce raised
-lettering by die-casting than to produce sunken lettering, it will be
-readily seen that the oil groove affords a good place in which to
-put the bearing number. This is easily done by stamping the figures
-upon the narrow strip that forms the oil groove. In this place on the
-bearing it may be easily found if needed, and of course there is no
-danger of its being taken out by machining.
-
-The lower die consists of two blocks _F_ and _G_, each of which
-contains an impression of a bearing. The best way to make these parts
-is to lay out the ends of each of the blocks with the proper radius,
-taking care to have the center come a little below the surface of the
-face of the block. Then the blocks should be shaped out to get the bulk
-of the stock out, before setting up in the lathe. After the lathe work
-is done on each piece, which of course is usually done separately, the
-faces of the two blocks are faced down just to the exact center of the
-impression. It will be noticed that two blocks are used for the lower
-part of the die. The reason is to facilitate the locating of the female
-parts of the die in proper relation to the male parts. After properly
-locating, they may be doweled and screwed to baseplate _B_.
-
-[Illustration: Fig. 15. Interesting Examples of Die-castings]
-
-The sprue cutter _H_, better shown in the plan view, is square in shape
-and connects with the die-cavities in a thin narrow opening on either
-side of the sprue cutter. The ejector pins, _I_, two to each die, are
-at the ends of the bearings. The ejector-pin plate _J_ is necessarily
-large, and is operated by lever _K_.
-
-Fig. 15 shows a number of interesting examples of die-castings.
-
-
-
-
-CHAPTER III
-
-VAN WAGNER MFG. CO.’S DIE-CASTING PRACTICE
-
-
-In 1907, Mr. E. B. Van Wagner, of Syracuse, N. Y., established the
-E. B. Van Wagner Mfg. Co. for the production of die-castings. The
-factory comprises the office section, the machine shop where the dies
-and casting machines are built, the metallurgical laboratory where the
-metals are alloyed, the casting department shown in Fig. 17 where the
-die-castings are made, and the trimming department.
-
-
-Possibilities and Limitations of Die Casting
-
-[Illustration: Fig. 16. Die-casting Constructions to be avoided]
-
-At the outset we may say that it is possible to die-cast almost any
-piece, but it is not by any means practicable to do so. It must be
-remembered that to die-cast on a practical basis the dies must be
-constructed in such a manner that the cost of their operation and
-up-keep will be light, or there will be no profit in die-casting. It
-is impracticable to produce under-cut work, that is, work having no
-draft and which is therefore impossible to draw from the die. Such
-an instance is that illustrated at _A_, Fig. 16, and by the internal
-section of _M_, Fig. 21, and the internal groove in _O_, also shown
-in Fig. 21. If absolutely necessary, work of this kind can be done by
-the use of collapsible cores; but here, again, we meet resistance in
-maintaining the dies in proper condition, and, moreover, this method
-is commercially impracticable, owing to the difficulty of operating
-these cores rapidly. Hollow work, requiring curved cores, like faucets
-and bent piping of the character illustrated at _C_ in Fig. 16, are
-difficult to produce. If, in designing the piece, it can be planned to
-have the parts of such a shape that the cores can be readily withdrawn,
-employing a two-piece core with a slight draft in each direction,
-the division coming as indicated by the core line of _C_ in Fig. 16,
-the problem becomes simpler. Oftentimes this work can best be done
-by casting in a straight piece, afterward bending the die-casting.
-It does not pay to cast rough heavy work that can be made just as
-efficiently by sand casting. Generally speaking, the greatest saving
-can be effected by die-casting small pieces which have previously
-required a large amount of machining to produce. On large plain work
-the amount of metal required for the casting makes the cost excessive
-on account of the difference in cost of the metals. If, however, the
-large work must be finely finished by polishing, etc., it is oftentimes
-found of advantage to die-cast. Corners, especially those joining thick
-and thin sections, as at _B_, Fig. 16, should be heavily filleted
-as shown on one side of this piece. Regarding the casting of thin
-sections, it is not practicable to try to cast sections under 3/64
-inch in thickness, as the metal runs with difficulty into such narrow
-places. A casting having walls 1/16 inch, like that shown at _X_, Fig.
-24, is easily cast. Threaded sections, if the threads are fine, say,
-under twenty-four to the inch, should not be die-cast, because under
-moderate pressure they will strip. A good way to treat constructions of
-this kind is to enclose brass or steel bushings in the die-castings in
-which the threads are required.
-
-[Illustration: Fig. 17. View of the Casting Room]
-
-As to the accuracy with which die-castings may be produced, it is
-possible to keep dimensions within 0.0005 inch of standard size, but to
-do so requires considerable expense in keeping the dies in condition.
-A limit of 0.002 inch, however, is entirely practicable, and can be
-maintained easily. In specifying the accuracy with which die-castings
-are to be made, only those parts which are absolutely essential should
-be held to size, in order to keep the cost of the work nominal. One of
-the great advantages of the use of die-castings is that no finishing is
-required after the pieces leave the molds. Finish requirements should
-be plainly stated in ordering die-castings, as the alloy must be suited
-to these requirements.
-
-[Illustration: Fig. 18. Methods of attaching Die-cast Gears, etc., to
-Shafts]
-
-Another great saving is effected on lettered work, either raised or
-sunken. One of these jobs is illustrated at _Q_, Fig. 22, which shows
-an example of die-cast lettering. Sunken lettering is to be preferred
-to raised lettering, as the latter is more easily injured. Knurled
-work may be produced easily, if straight knurls are used, and threaded
-sections over ¼ inch in size are entirely practicable, either internal
-or external. External die cast threads are illustrated at _R_ and _S_,
-Fig. 22. The casting of gears and segments is a familiar application
-of die-casting; this is illustrated by the large gear at _N_, Fig. 21,
-and the segment at _W_, Fig. 23, which give an idea of the general
-character of this class of work. The casting of pulleys, gears, and
-similar parts on shafts may be easily effected as shown by the gear on
-the shaft at _N_, in Fig. 21. The views shown in Fig. 18 are intended
-to convey an idea of three methods of die-casting around shafts. At
-_D_ is shown a die-casting cast around a steel shaft. If the surface
-of the shaft coming within the pulley has been previously knurled,
-the pulley will grip it much better, but for ordinary purposes the
-shrinkage of the die-cast metal around the shaft is sufficient. If any
-heavy strain is to be imposed on the work, it is better to provide
-anchor holes through the shaft, like those indicated at _E_. It will be
-readily seen that the die-cast metal runs through these holes in the
-shaft, forming rivets which are integral with the casting. For locating
-levers upon the ends of shafts, etc., a good way is to flatten opposite
-sides of the shaft and cast around them, as shown at _F_, Fig. 18. The
-screw seen projecting beneath the piece at _Q_, Fig. 22, was die-cast
-in place. Any of these methods are to be recommended, and a proper
-knowledge of possibilities of this kind will increase the scope of
-die-casting.
-
-[Illustration: Fig. 19. A Few Possibilities of Die Casting]
-
-Another phase of die-casting which can well be borne in mind is the
-possibility of inserting steel or other parts in the die-casting.
-Such an instance is shown at _G_ in Fig. 19--a die-casting which was
-made by the Van Wagner Co. as a part of an electrical apparatus, the
-steel inserts being contact points. Oftentimes it is found advisable
-to include brass bearing rings to give additional durability at points
-where the die-cast metal would not stand up. The die-casting shown at
-_U_, Fig. 23, in which the brass ring at _T_ has been incorporated,
-is typical of such cases. To die-cast pieces like those shown at
-_H_ in Fig. 19, and similarly at _V_ in Fig. 23, having inverted
-conical openings, might at first thought seem difficult, but this is
-entirely practicable. Similarly, split bushings like those shown at
-_I_, Fig. 19, and at _W_, Fig. 23, may be cast with projecting lugs
-for the reception of screws for clamping upon shafts, etc., but this
-construction should not be used if frequent tightening or loosening
-will be necessary.
-
-[Illustration: Fig. 20. Castings which illustrate Points of Shrinkage
-and Draft]
-
-[Illustration: Fig. 21. Die-castings showing Impractical Under-cut
-Sections; also a Large Gear die-cast on Shaft]
-
-[Illustration: Fig. 22. Die-castings which show Lettering and Thread
-Castings]
-
-The shrinkage problem manifests itself in die-casting in the same
-measure that it does in other casting operations. Different metals
-shrink in different degrees, as will be explained later on. However,
-one important point can be mentioned at this time: that is, the amount
-of shrinkage is often dependent upon the shape of the piece. For
-instance, pieces like those shown at _K_ in Fig. 20 or at _X_ in Fig.
-24, will shrink very little on account of the fact that the steel mold
-is of such shape that the central core will prevent the die-casting
-from shrinking. However, pieces like those shown at _L_ in Fig. 20,
-or at _V_ in Fig. 24, which have nothing to hold them from pulling
-together as they cool, will shrink to the greatest extent. All of
-these points must be taken into consideration when designing work for
-die-casting. Practically no draft is necessary on a die-casting, except
-on very deep sections, as indicated at _J_ in Fig. 20, where a draft
-of 0.001 inch to the inch is desirable. Perfectly straight sections,
-however, can be cast, as the shrinkage of the metal is usually enough
-to free it from the die.
-
-[Illustration: Fig. 23. Typical Die-castings illustrating Various
-Points]
-
-[Illustration: Fig. 24. Die-castings illustrating the Extremes of
-Shrinkage]
-
-It is the opinion of the Van Wagner Co. that die-casting costs can
-be materially reduced if designers will bear this point in mind when
-bringing out new designs. Even though it is often possible to cast
-special pieces, incorporating several parts in one, and thereby
-accomplishing what seems to be a great stunt to the designer, it is
-sometimes more practicable to make the piece in several sections and
-later assemble it. Not only is this simpler for the die caster, but it
-is also more economical for the customer. Such points as avoiding thin
-sections, including large fillets at corners, as well as taking account
-of the under-cut problem, are simply matters of common sense, but they
-can profitably be considered by the designer.
-
-
-The Van Wagner Die-casting Machine
-
-The first essential to good die-casting is a good casting machine.
-Perhaps the best known types of casting machines are of the familiar
-plunger type, of which there are several varieties, the pneumatic type
-and the rotary or automatic type. (For descriptions of various types of
-die-casting machines, see “Die Casting Machines,” MACHINERY’S Reference
-Book No. 108.) For the economical production of die-castings, however,
-the hand-operated machines are rather too slow, and automatic machines
-are applicable only to a class of work which may be made in very large
-quantities. For these reasons, therefore, the Van Wagner Co. employs
-the compressed air type of die-casting machine which was patented by
-Mr. E. B. Van Wagner in 1907. In the casting department of the Van
-Wagner shop, illustrated in Fig. 17, there are installed about thirty
-machines. Fig. 27 shows a die-casting machine in the open position.
-Fig. 26 shows a closer view of the die-operating mechanism and Fig. 25
-is presented to give a general idea of the construction of the entire
-machine.
-
-[Illustration: Fig. 25. Drawing illustrating Principle of Van Wagner
-Die-casting Machine]
-
-By referring to the line illustration Fig. 25, which shows the Van
-Wagner pneumatic die-casting machine in part, and comparing this
-illustration with Fig. 26, which shows the general appearance of the
-die-operating and other mechanism of the casting machine, a good idea
-may be obtained of its construction and working. At _A_ may be seen
-the base of the machine in which is located the melting pot _B_. This
-melting pot is heated by means of fuel oil passing through the supply
-pipe _C_ to the burners _C_`1. A vent pipe _D_ is provided to take
-away the gases incident to combustion. The pressure for “shooting” the
-metal into the die cavity is supplied by air through the supply pipe
-_E_. A valve controls this air supply. The pressure is regulated to
-suit the particular casting or die, the proper amount being determined
-by experiment. Similarly, an air exhaust pipe _F_, which may be seen
-directly above the supply pipe, sub-divides into two tubes which
-extend to the die cavity to exhaust the air before the metal is
-admitted. There are two methods of overcoming the presence of air in
-the die cavity--the exhaust method and the venting method, and it is
-the former that is here described.
-
-[Illustration: Fig. 26. View of Machine showing Die-operating Mechanism]
-
-A “goose-neck” _G_, shown in Fig. 25, serves to temporarily contain
-the metal which is forced into the mold. An amount of metal slightly
-in excess of that required for one die-casting is placed in this
-goose-neck with a hand-ladle, previous to each operation of the
-machine. One end of the goose-neck is connected to the air pipe, _E_,
-while the other end terminates in the nozzle _G_`1. This nozzle may
-best be seen by referring to the illustration of the machine shown in
-Fig. 27, in connection with Fig. 25. One of the advantages in using
-this goose-neck is that the entire air pressure is expended upon the
-metal in the goose-neck, and, by reason of its isolated position, the
-goose-neck and its contents are kept slightly hotter than the contents
-of the melting pot.
-
-
-The Die-operating Mechanism
-
-The die-operating mechanism of the machine is contained within a hinged
-framework, shown in position for the removal of the die-casting in Fig.
-27. Referring to Fig. 26, in connection with the line illustration Fig.
-25, it will be seen that the die-holding mechanism is all supported
-upon the lower die-holding plate _H_, which is hinged to the edge
-of the base of the machine. A lock _J_ serves to hold the dies and
-operating mechanism in the upright operating position, and by means
-of a counterbalance, suspended from an overhead rope which connects
-with the top of the mechanism at _P_, the changing of the position of
-this mechanism is easily effected, and when thrown into the horizontal
-position, as indicated in Fig. 27, it rests upon a support while the
-dies are being opened and the castings ejected.
-
-[Illustration: Fig. 27. Die-casting Machine in Position for Removal of
-Casting]
-
-The lower die is shown at _H_`1 and the upper die _K_`1 is mounted
-upon the upper die-holding plate _K_. Four rods _L_ act as guiding
-members for the upper die-holding plate to slide upon. These rods _L_
-are mounted in fixed positions at the corners of the lower die-holding
-plate _H_, and at their upper ends the operating shaft supporting plate
-_M_ is located in a fixed position, serving to support the upper ends
-of these rods. The position of this plate _M_ is adjustable upon the
-rods by means of check-nuts, thus providing for the accommodation of
-thick as well as thin dies. A shaft _O_ is supported in this top plate,
-and by means of the operating lever _N_ working through slotted levers
-_O_`1 and links _O_`2, the upper die-holding plate and die can thus
-be removed from contact with the lower die at will.
-
-The metal enters the die cavity through the nozzle _G_`1 and after
-setting, it is necessary to cut the sprue formed by the surplus metal
-that remains outside the die cavity. For this purpose, a sprue-cutter,
-operated by means of hand-lever _Q_`1, is employed. This sprue-cutting
-lever is hinged in the fulcrumed link _Q_`2, and is held in its
-casting position by means of an adjustable stop on bracket _Q_`3.
-
-[Illustration: Fig. 28. General View of Trimming Department]
-
-In many dies, it is necessary that water be circulated through the
-die-blocks to keep them cool during the die-casting operation. In
-Fig. 26, the water pipe may be seen at _R_, and hose pipes run from
-this supply to each side of the die-blocks, thus providing a cooling
-circulation. In this illustration, the pipes used for exhausting the
-air from the die cavity are apt to be confused with the cooling pipes,
-but by following the two pipes leading vertically down to the machine,
-the exhaust pipes may be seen and kept distinct from the water pipes.
-
-
-Making a Die-casting
-
-In order to clearly understand the operation of the die-casting
-machine, let us follow the sequence of events that takes place in
-producing a casting. Two men are required to operate the machine. In
-Fig. 27, the operators may be seen in their working positions. The
-first step is taken by the operator at the left who, with a hand-ladle,
-dips enough metal for one casting from the melting pot and pours it
-through nozzle _G_`1 into the goose-neck. The second operator in the
-meantime is replacing the cores in the dies, adjusting the position of
-the sprue-cutter and closing the dies preparatory to making a casting.
-This being done, he elevates the dies and their operating mechanism,
-which are hinged and counterbalanced, as previously described, bringing
-them to an upright position. The die operator now mounts the box,
-raises the sprue-cutter to its open position to admit the metal; after
-which the machine operator turns the air valve with his left hand. The
-operation of this air valve admits the air behind the metal, forcing it
-into the die, and the same movement opens the exhaust valve slightly in
-advance. The exhaust valve is located upon the second length of piping
-just above the air valve, and as a link connects the two valves, the
-single motion exhausts the air from the die cavity and immediately
-afterward the air is admitted behind the metal, thereby “shooting” the
-metal into the die. This being done, the air is shut off and the die
-operator cuts the sprue by means of lever _Q_`1, withdraws the cores
-in the die, throws the dies to the open position (which is indicated
-in Fig. 27), and operates the ejecting mechanism, thus removing the
-casting from the die. In the meantime, the machine operator is tending
-to his metal supply and getting a ladle full of metal ready for the
-next die-casting operation. By referring to the machines shown in Fig.
-17, it will be noticed that only a few are provided with exhaust piping
-for venting the dies. Another venting method will be described later.
-
-[Illustration: Fig. 29. Trimming Die-castings on a Filing Machine]
-
-The number of die-castings which can be made on one machine per day of
-ten hours varies with the character of the pieces being die-cast, the
-number of pieces made at each operation of the machine and the ease
-with which the dies may be worked, which depends, of course, upon the
-number of cores and parts to be handled at each die-casting operation.
-The dies shown in the machine in Fig. 26, produce four bearings at each
-operation.
-
-
-Trimming Die-castings
-
-At the end of each run the operators of the machines go over their
-work, breaking the castings from the sprues and throwing out all that
-are defective. No matter how carefully the die-casting molds have been
-made, there is always a certain amount of trimming to be done on the
-finished die-castings, on account of the crevices left in the die for
-air vents, or which exist from improper fitting of the parts of the
-dies. These “fins,” as they are called, are trimmed by hand operators
-in a special department. A general view of this trimming room is shown
-in Fig. 28. Usually it is sufficient to scrape these fins off with a
-scraping knife, but if the casting is especially difficult to produce,
-so that a large opening is required to admit the metal, it is sometimes
-necessary to trim unusually thick sprue sections by filing. Fig. 29
-illustrates the method of trimming such die-castings on a filing
-machine.
-
-[Illustration: Fig. 30. General View of E. B. Van Wagner Co.’s Die
-making Department]
-
-[Illustration: Fig. 31. A Typical Die-casting Mold]
-
-
-The Dies Used
-
-Next to the casting machine, the dies or molds are the most important
-necessary factor. A general view of the Van Wagner Co.’s die-making
-department is shown in Fig. 30. In order to gain a proper conception of
-the work required in producing a high-grade die-casting mold, we will
-follow the different steps which are necessary in making the mold. The
-first and most important step is the proper planning of the die. Before
-any work at all can be done, it is necessary to plan the die, _i. e._,
-to decide just where the parting lines will come; just what method
-will be used for ejecting the piece; what alloy will be used; where
-the casting will be gated; and a hundred and one minor points, all of
-which have a direct bearing upon the performance of the finished dies.
-All these decisions have to be made by the diemaker, and in Fig. 37 he
-is shown, micrometer in hand, computing the shrinkage allowances that
-he will make in the dies. This is a very important factor on accurate
-work as the shrinkage varies from 0.001 to 0.004 inch, according to the
-alloy and the general shape of the piece.
-
-[Illustration: Fig. 32. Die-casting Mold shown in Fig. 31, disassembled]
-
-Before taking up the actual machining operations of the mold-making
-as conducted in this factory, it will be well to take a typical
-die-casting mold and note its general construction. Fig. 31 shows a
-typical die-casting mold closed, while Fig. 32 shows the same mold
-disassembled on the bench to show its construction. The piece for
-which the mold has been made is also shown. Fig. 33 shows a similar
-die in section. From the three illustrations a good idea of an average
-die-casting mold can be obtained. Referring to these illustrations, the
-principal parts of this die are the ejector box _A_, and the ejector
-plate _B_ which is operated by the racks _C_. For operating the ejector
-plate, the pinion shaft _D_ having a handle suitable for turning, is
-furnished. This, of course, fits into a bored hole in the ejector box,
-bringing the pinion into mesh with the racks for raising the ejector
-plate. In the ejector plate are three ejector pins _E_ for removing
-the casting from the mold. The ejector pins operate through holes _F_.
-Beyond the pinion shaft may be seen the casting for which this mold
-has been made. It will be noticed that the top side of the casting has
-three projecting lugs through which are small holes. Provision for
-forming this side of the die-casting is made in the lower half of the
-mold _G_, while the upper half of the die-casting is taken care of
-by the top plate _H_. One of the toggles for operating the core pins
-through these three lugs is shown at _I_. These parts will be described
-more fully later. The sprue cutter is shown in position in the die at
-_J_.
-
-
-Machining the Die Cavities
-
-As will be noticed from Fig. 30, the machinery in the die-making
-department is of modern design, for no other class of work demands as
-good tool equipment and as much skill in the making as die-casting
-molds. The die-blocks are made of machinery steel. Fig. 34 illustrates
-the first step in making a die-casting mold after the die-block has
-been shaped approximately to size. This operation consists in carefully
-facing off the die surfaces on a vertical-spindle grinding machine.
-This, of course, is a quick method of surfacing the die-block, and
-it insures that the top and bottom surfaces of these plates will be
-parallel, permitting the die-faces to come together properly.
-
-[Illustration: Fig. 33. Section through a Die-casting Mold]
-
-The next step consists of laying out the die, as shown in Fig. 36. This
-is done in the usual manner, by working on a coppered surface, using
-dividers, scales, and a center punch. When laying out the die, the
-necessary allowances are made for shrinkage and finish, these points
-having been planned before actual work on the die has been started. As
-in other phases of die-work, the machining operations are performed,
-as far as possible, before any hand-work is done. In Fig. 38 may be
-seen a die-maker turning the cavity in a part of the die-casting mold.
-The highest type of skilled workmanship is called for on this machine
-work, and as may be surmised from Fig. 38, where the die-maker is shown
-measuring the die with a vernier caliper, the measurements must be
-exact, for no grinding operations follow the machine work.
-
-[Illustration: Fig. 34. First step in making the Mold--Grinding
-Surfaces of Blocks]
-
-[Illustration: Fig. 35. A Milling Operation on a Die]
-
-Figs. 35 and 39 show typical milling operations being performed on
-die-casting molds. In Fig. 39 the diemaker is shown indicating a pin in
-one corner of the mold cavity, preparatory to doing additional milling.
-The block is held in the usual manner by being clamped on the bed of
-the milling machine, and after it has been properly located under the
-cutter head, tools are substituted for the indicator and the milling
-of the cavity is completed. Fig. 35 shows one of the sections of the
-die-casting mold which is to be used in producing the casting shown at
-the right of the work. In this case the diemaker is milling the recess
-for the steel arbor which may be seen directly in the foreground. This
-will be fitted in place to provide for the forming of the hole in the
-side of the piece.
-
-[Illustration: Fig. 36. Laying out One of the Mold Parts]
-
-[Illustration: Fig. 37. Planning the Die-casting Mold]
-
-[Illustration: Fig. 38. Turning out a Die-casting Mold]
-
-[Illustration: Fig. 39. Indicating a Mold on the Milling Machine]
-
-Fig. 40 illustrates several important points in the making of a
-die-casting mold. This illustration shows the ejector box with the
-lower half of the mold on it, the ejector plate being held against the
-under side of the die-plate by means of the pinion shaft. The operation
-being done is the drilling of the ejector-pin holes. Referring back to
-Fig. 32, which by the way shows the die here illustrated disassembled,
-the holes being drilled are those shown at _F_ for the reception of the
-pins _E_. The method employed is to drill the holes through the die and
-into the ejector plate, afterward reaming all holes to size and driving
-the pins into position in the ejector plate, while they are allowed to
-slide freely through the die-plate. We will now assume that the ejector
-box and plate have been completed and fitted, a pinion shaft for
-operating this plate also fitted, the lower and upper dies completed
-by the machining operations previously described, and all assembled.
-The final operation of the fitting of the pins is shown in Fig. 41 in
-which the die-maker may be seen filing off the ends of these pins so
-that when dropped to the lower position they will lie flush with the
-surface. If of uneven lengths, these pins will cause irregular spots in
-the casting. It now remains to describe the toggles used for operating
-the cores which form the holes through the three lugs in the casting.
-One of these toggles, of which there are three, is shown at _I_, in
-Fig. 31, and also in Fig. 32. These toggles consist of brackets which
-are attached to the die-plate, and levers which are fulcrumed at the
-ends of the brackets so that their operation works the core pins. It is
-necessary to remove these core pins after each casting has been made
-and position them before another casting can be produced.
-
-[Illustration: Fig. 40. Drilling the Ejector-pin Holes]
-
-The fitting of the parts of a die-casting mold is one of the
-most important parts of the work. It demands the highest type of
-workmanship, for a poorly fitted die means a die which works hard
-in addition to producing poor castings. It is very important that
-all movable parts should work freely. Fig. 42 shows the assembling
-operation on a die-casting mold, the casting which is to be duplicated
-being shown in the immediate foreground. These parts must all be
-screwed into their respective places, making the joints as nearly
-air-tight as possible. One cause of poor die-castings arises from the
-trapping of air in the die, and different methods are employed for
-overcoming this trouble.
-
-
-Venting the Dies
-
-There are two methods of preventing air from being trapped in
-die-casting molds; either by constructing the dies so that the air
-may be exhausted from the mold cavity before admitting the metal, or
-by venting the die so that the air may be forced out by the inrushing
-metal. In the first of these methods it is necessary that the joints in
-the mold be made as close as possible, otherwise it will be impossible
-to produce anything like a vacuum in the mold cavity. If, however, it
-has many parts which must be fitted, it is usually considered advisable
-to provide the die with vents consisting of milled recesses a few
-thousandths inch deep. Several vents are provided, from which the air
-can escape when the metal is admitted to the dies. The hot metal, of
-course, “shoots” through them in thin ribbons, but not enough escapes
-to affect the pressure on the metal which goes into the casting.
-
-[Illustration: Fig. 41. Fitting Ejector-pins]
-
-No matter how carefully a die may have been constructed, or how
-carefully it has been assembled, there is always a certain amount of
-“babying” to be done before it will work satisfactorily. The casting
-may stick a little here, or there may be a rough spot there, and it
-is the successful elimination of these troubles which constitutes the
-production of a good die-casting.
-
-
-Die-casting Metals
-
-One of the purposes of this book is to correct several erroneous
-impressions which are prevalent in regard to die-casting possibilities.
-Many people seem to think that nearly all metals can be die-cast, but
-as a matter of fact, those metals which can be successfully die-cast
-can be numbered on the fingers of one hand, being alloys of lead, zinc,
-tin, copper and antimony. The tin base metals shrink very little, while
-the zinc base metals shrink considerably, and those with a large per
-cent of aluminum have a very high shrinkage. Without doubt, the most
-used die-casting metals are the zinc base metals. A typical metal of
-this class contains about 85 per cent zinc; 8 per cent tin; 4 per
-cent copper and 3 per cent aluminum. The melting point of this metal
-is about 850 degrees F. While this alloy is one of the most common,
-it is not by any means the best, as there is too little tin employed,
-but it is a comparatively cheap metal, which probably accounts for its
-large use. This metal is easily affected by heat and cold, and rapidly
-deteriorates with age. The lead base metals may be typified by an alloy
-containing 80 per cent lead; 15 per cent antimony; 4 per cent tin; and
-1 per cent copper. This composition melts at approximately 550 degrees
-F. and is used for castings subjected to little wear and where no
-great strength is required. The weight of this metal is its greatest
-objection, and it is also quite brittle because of the large percentage
-of antimony.
-
-[Illustration: Fig. 42. Assembling a Die-casting Mold]
-
-For the best class of die-castings, the tin base metals are employed.
-These range from 60 to 90 per cent tin, and from 2 to 10 per cent
-copper, together with a little antimony. The melting point of a
-mixture of this composition is about 675 degrees F. The castings have
-a good color and they are much better in quality than any of the other
-alloys. It is absolutely essential that tin base metals be used for
-carbureter parts or other parts coming in contact with gasoline. Also,
-the tin base metals must be used for parts which come in contact with
-food products, as the lead or zinc alloys have a contaminating effect.
-
-Aluminum alloys have been cast in France and Germany in limited
-quantities, but very seldom in this country on account of their high
-melting point, as well as their effect upon the die. After aluminum
-alloys have been run in the dies for a short time, the surfaces of the
-molds become pitted. Through some unexplained cause, the metal seems
-to flake out particles of the steel in the molds. When an aluminum
-alloy is to be used, a good mixture is 80 per cent aluminum, 3 per cent
-copper and 17 per cent zinc. This alloy has a high shrinkage and it has
-also the same deteriorating effect upon the dies, but to a much less
-degree than pure aluminum.
-
-
-
-
-Transcriber’s Notes
-
-
-Punctuation, hyphenation, and spelling were made consistent when a
-predominant preference was found in this book; otherwise they were not
-changed.
-
-Simple typographical errors were corrected; occasional unbalanced
-quotation marks retained.
-
-Ambiguous hyphens at the ends of lines were retained.
-
-Text uses “die-cavity” and “die cavity”, “die-maker” and “die maker”;
-none changed here.
-
-
-
-
-
-End of the Project Gutenberg EBook of Die Casting, by Chester L. Lucas
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