Punch and die work

Contents

Principles of Punch and Die Work, by E. R. Markham 3 Suggestions for the Making and Use of Dies - - 31 Examples of Dies and Punches, by F. E. Shailor - 41

The Industrial Press, 49-55 Lafayette Street, New York Publishers of MACHINERY

i^V,^___^^5 COPYRIGHT, 1911. THE INDUSTRIAL PRESS, NEW YORK

Chapter I Principles Of Punch And Die 'work*

Under the head of punch and die work is generally included all the various tools used in blanking pieces from commercial stock; bending stock to shape; drawing out articles from sheet stock; and all the different operations performed with punching, drawing and forming presses. The most common forms of tools to be considered are the dies used for blanking articles from sheet stock, called blanking dies.

Blanking Dies

A set of blanking dies consists of a male die, or punch, as it Is generally termed, and a female die, or die block. These terms are generally abbreviated and the set is called a punch and die. Blanking dies are generally considered as belonging to one of three classes: First, plain (or simple) dies; second, gang dies; and third, compound dies.

When punches and dies are used in a punch-press, and are to constitute a part of the regular equipment of the shop, they are held in suitable permanent fixtures. Dies are held in position on the bed of the press by means of a "holdfast," the name of which differs in different shops. Some of the more common names are chair, chuck, bolster, and die holder. Dies large enough to warrant it are clamped to the bed of the press, thus doing away with the necessity for holders. Dies are fastened in place in the die holder by several methods, the most common of which is by means of screws, as shown in Fig. 1, in which a is the die and & the holder. Having screws on both sides, it is an easy matter to adjust the die, loosening the screws on one side, and forcing the die over by those on the opposite side.

When the die is small, it is generally held in a shoe, as shown In Fig. 2. The manner of fastening the die in the shoe usually depends on the designer. In some shops the shoe is dove-tailed as shown, the angle being from 10 degrees to 15 degrees less than a right angle; the slot is made somewhat tapering. The die is given a corresponding taper and angle on its sides, and, to fasten it in position, it is driven securely in place. The amount of taper given the slot in the shoe must not be great, or the die will jar loose when in use. A taper of one-half inch per foot of length answers nicely. In other shops the shoe is made with a groove, as described above, only it is from \i to % inch wider than the dies, which are held in place by means of a taper key or wedge, as shown in Fig. 3. When making this form it is necessary to make the dies of equal width on their ends. This method does not require so great a degree of accuracy when machining the die block.

• Machinery, July, August and September, 1906.

A third method consists in making a shoe having the back of the slot planed at the angle mentioned, while the front wall is made square with the bottom, the die being held with setscrews, as shown in Fig. 4. If this form is used, care must be exercised when laying out the screw holes, so that they do not come in line with the screws in the bolster when the shoe is in its proper place; and, again, the screws must not press on any portion of the die immediately in line with the opening, or it will be closed somewhat when pressure is applied to the screws. Fig. 4 shows the screws pressing on the solid portion of the die.

Fig. 3

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Figs. 1 to 4. Various Methods of Holding Work

Dies which are fastened in bolsters without using a shoe must have their sides machined at an angle, as in Fig. 1, to prevent them lifting from the strain incident to removing the punch when it has pierced the stock. The angle should be from 10 degrees to 15 degrees, some mechanics- claiming best results with 20 degrees. The latter, however, seems greater than there is any necessity for on ordinary work. Kind of Steel Used for Die Work

For most work the stock used in making punches and dies should be a good quality of tool steel. A die that has cost from 5 dollars to 100 dollars for labor is as liable to crack when hardening as though the same steel had been made into any other form of tool; and in fact its shape and irregular thickness of stock at various points, together with numerous sharp corners that are liable to be present, make a tool that requires extreme care in handling when hardening. A good grade of tool steel, free from harmful impurities, is less liable to crack then an inferior grade, and the slight difference in cost is offset many times by the cost of labor in the die construction. This does not necessarily mean that a higli-priced steel must be used for this class of work; simply a good quality of steel, low in percentage of those impurities which cause trouble when the steel is hardened. When we speak of good, reliable steels, we do not necessarily mean high-priced steel.

If best results are desired when hardening, the steel should be annealed after the outer surface of the piece has been removed and the opening blocked out somewhere near to shape.

In all shop operations true economy should always be practiced, and many times this may be done by a saving of tool steel. If a die is

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. 5. Cast Iron Body Die, used with Tool Steel Bushings

. 7

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Figs. 6 and 7. Method of Removing the Stock in a Solid Die like Fig. 5, a saving may be effected by making the body of cast iron and inserting bushings of tool steel; and if we wish at any time to make a new die, we simply make the bushings, and if ordinary care is taken, the holes will be concentric and consequently the proper distance apart, so there will be no necessity of altering the location of the punches, as might be the case if a die made of a solid piece was hardened.

General Principles of Die Making

When a number of dies are to be made to fit the same holder, they may be planed to size in the bar and then cut apart by means of the cold-sawing machine. It will be necessary to plane again the side of dies that must fit a shoe of the style shown in Pig. 2, as one end must be wider than the other. This may be effected very readily by having a strip of cast iron planed to the proper taper to place the die on when planing or milling. The face of the die must be smooth in order that the outline traced on it may closely correspond to the templet. If the surface is a succession of ridges, the scriber will not closely follow the edges of the pattern, and the figure traced will be larger than desired. After the face has been made smooth by planing, grinding or filing, the surface may be coated with blue vitriol solution, or it may be heated until it assumes a distinct straw or blue color, and the outline of the piece to be punched laid out.

If the die is what is known as a solid die, that is, made from one piece of stock, it may be laid off and prick-punched as in Fig. 6, after which holes may be drilled, leaving the face of the die as in Fig. 7,

Machi-iify, S.T.

Fig. 8. Die Milling Machine

after which the core may be removed. When drilling for the opening, first drill any portions which are to be left circular or semi-circular in shape. These are then reamed from the opposite side with a taper reamer that will give the desired amount of clearance. When drilling to remove the core mentioned, some tool-makers use drills of sizes that break into the next hole. After drilling all way round, the core drops out of its own accord. If this method is adopted, best results follow the use of the straight-fluted drill. Fig. 9. Others drill with drills of the size of the pilot of a counterbore, and after drilling all the holes, the counterbore is run through. Of course, it is understood that in laying off for the holes, they are located so that the counterbore breaks into the next hole. A third method consists of laying off and drilling holes so that there is a little stock between the holes after drilling, which is broken out by means of a drift driven in from each side until the cuts meet. In this way the stock is cut away and the core removed.

After taking out the core, the die may be placed in a die milling machine, or a die sinking machine, and by the use of a tapered milling cutter the stock may be removed and the desired angle of clearance given the walls of the hole. The angle of clearance necessary for best results cannot be arbitrarily stated, but varies according to the character of the work to be done with the die. In the absence of either of the milling machines mentioned, a universal or a hand miller may be used. There are various slotting devices which may be attached to universal milling machines which are used advantageously on work

Machinery, N. V,

Fig. 11

Fig-s 9, lO and 11. Tools used in Die-making' Machines

of this character. During the past few years several vertical filing machines have been placed on the market which are recommended highly for the purpose of working the openings of dies to shape. If a die milling machine. Fig. 8, is used, the form of taper milling cutter shown in Fig. 10 is employed. As the milling cutter is driven by a spindle beneath the die, the cutting portion extending up through the opening, with the face of the die uppermost, the small part of the cutting portion should be at the end of the cutter. If a die-sinking machine, Fig. 12, is used, a cutter like Fig. 11 is employed. After working the opening to shape and size as nearly as possible with the milling cutter, it may be finished by filing.

Clearance When finishing the opening to shape and size it is necessary to get the desired clearance and to have the walls of the opening straight, as at o a in Fig. 13, rather than rounding as represented at a a in Fig. 14. The amount of clearance differs for various work and ranges from one-quarter to three degrees. The greater amount is seldom given unless it is necessary that the blank fall from the die each time one is punched. Another instance where it is desirable to give excessive clearance is where a punch with a crowning face, as in Fig. 15^ is used for punching stiff stock.

When a milling machine with a slotting attachment, Fig. 17, is used, sharp corners may he cut to the line, as may certain irregular sur-

Fig. 12. Die-sinking Machine

Fig. 17. Die-slotting Attachment for Milling Machine

Fig. 13

Fig. 14

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Figs 13 and 14 Correct and Incorrect Relief. Fig. 15. Punch Crowned for Stiff Slock. Fig. 16. Templot for Gaging Relief

faces which could not be shaped with milling cutters. Of course, it would be necessary to have cutting tools of the proper shape to machine the forms mentioned, the advisability of making which would depend on whether it would be cheaper to make the necessary tools and to do the machining, or file to the desired shape. A fixture known as a die shaper, whose action resembles the slotting device described above, is made to attach to a milling machine and works the same as the other attachment.

In order to gage the angle of clearance it is advisable to have angle gages. Several of these may be made and kept in the tool chest and should be of the more common angles used. They may be of the form shown in Fig. 16, with the angle stamped on the heavier portion.

Shear of Punches and. Dies

The cutting faces of dies are given shear for the same reason that the teeth of milling machine cutters are cut helical or spiral. The shear makes it possible to cut the blank from the sheet with less expenditure of power; it also reduces the strain on the die and punch. While it is customary to shear the face of the die when possible, there are instances when it is advisable to leave the face of the die

Fig. 18. A Piece of Work for

■which the Punch Should be

Provided with Shear

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Fig. 10. A Case where the Shear should be on the Die flat and shear the punch. The shear is given to the punch when the stock around the hole is the desired product and the stock removed is scrap, as in Fig. 18. The face of the die is sheared when the portion pressed through the die is the product, as at a a in Fig. 19, which also illustrates the shear of the die.

The amount of shear necessary to give a die to obtain best results depends a great deal on the thickness of the stock to be punched, and also on the length of the piece to be removed, and on the power of the press. The shear of a die usually commences at the center and extends toward each end, as in Fig. 19, the punch being left flat on its face. When the punch descends, the cut commences at the highest point of the die, which is in the center, and continues toward each end. The portion at the center will have been removed from the stock before the cut has progressed very far toward the ends, and in this manner the cut is distributed over the length of the piece, reducing the strain on the press and tools.

The diemaker, if he works to drawings furnished him by the draftsman, makes the thickness of die and length of punch to correspond with dimensions. However, it is customary in shops where few dies are made and no draftsman is employed, to give the diemaker or toolmaker an idea of the shape and dimensions wanted, or possibly a templet, and he is required to go ahead and "work out his own salvation." In such cases the workman must first find the dimensions of the press to be used, the distance from the bed to the ram, the length of stroke of the ram, the amount the ram may be adjusted, the thickness of the bolster, and particulars about any shoes that are to be used. These things should be carefully set down and kept where the workman may have access to them at any time. If there are several presses, each should be marked and the dimensions of each carefully recorded, according to the work of the individual machine. If this precaution is followed and the dimensions taken into consideration when machining the die and punch, there need be none of the trouble sometimes experienced, such as a die too thick or a punch too long, or the reverse, for the press in which they are to be used.

Stripping the Stock

When articles are punched from sheet stock, or in fact from any stock where the scrap is around the punch, the stock will be carried

Fig. 20. Example of Stripping Plate upward when the punch ascends, unless some device is furnished to prevent its doing so. Fig. 20 shows an arrangement o called a stripper, or stripping plate, the opening in this being a trifle larger than the punch. The stripper plate must be securely fastened to the die, or the die holder, and must be stiff enough to prevent its springing when in use. Between the stripper and the die (at 6) is a guide against which the stock being operate! on rests, and which determines the amount of scrap at the back edge of the sheet. This guide is made of a thickness that insures the space between the die and stripper being somewhat greater than the thickness of the stock used; in fact, the space must be sufficient to allow the stock to move along easily even when the surface is made somewhat irregular by the operation of punching. At c is a guide pin or stop against which the stock is placed to determine the endwise setting.

Templets

When dies are made for producing pieces that must be of a given size and shape it is necessary to have a piece of the same shape and size to work to; this is called a templet. At times it requires a considerable degree of skill to make a templet that will answer for the work in hand. As an example, the templet shown in Fig. 21 may be referred to. After blanking and turning the ear at the top of the piece to be made, it was to be closed on a groove in an axle, as shown in Fig. 22. After closing, the outside of the washer was supposed to run about true. The die was made to a templet and it was found less difficult to make the die than the templet. In this instance it was necessary to make two pieces of the desired shape exactly alike, one of which was closed on the model axle and tested. The points that were not right were located on the one that had not been closed up. Then others were laid out from it, due allowance being made for the im-

Fig. 2»

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Figs. 21 to 24. Example of Templet Making

perfections of the first. When making, two pieces of stock v/ere placed together, and one half was worked to the laying out lines as in Fig. 23. After the other half had been blocked out somewhere near the line, the pieces were reversed and each half that had been blocked out was finished to the finished half, as indicated. In this way the ends were exactly alike and the two being machined, or filed together, were, of course, alike. When one was forced down or closed on the axle and was found correct, the other answered for the templet to be used in laying out the die, and afterward to fit the opening, too. While the example related was comparatively simple, it did not appear altogether simple to one not accustomed to that class of work, and it serves to illustrate the idea brought out.

In order that templets may be easily handled, it is customary to attach some form of handle to them, which is sometimes done by drilling and tapping a hole in the templet, and cutting a short thread on a piece of wire which is screwed into the tapped hole. Another common method is to attach a piece of wire by means of a drop of solder, as shown in Fig. 24. This method is open to the objection that the wire must be removed from the templet when it is used in laying out the punch, as it is necessary, when the templet differs in shape on two edges, to lay opposite sides of the templet against punch and die.

Sectional Dies

Dies are many times made in two or more sections in order to facilitate the operation of working the opening to shape. In other cases the die, if solid, would be so large as to render it well-nigh impossible to harden it in a shop with only the usual facilities for doing work of this class. And then again if it should go out of shape in hardening, it would be a difficult task to remedy the defect. If made in sections, as shown in Fig. 25, it would be possible to peen or grind to the original shape with little trouble.

A die of the design shown in Fig. 26 may be made sectional because It is much easier and cheaper to make than if solid. The sec-

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Fig. 25. Sectional Dio held by Screws

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Fig. 26 Sectional Die Located by Taper Pins

tions are held in their proper location by dowel pins. They are held together by the shoe which secures them in the press. If the die is comparatively small, the circular shapes at each end and center are produced by first drilling, and then reaming from the back, with a reamer of the proper angle. The sections may be separated and the balance of the stock removed in a shaper, planer or milling machine. When this stock is removed the die may be held at the proper angle to produce the desired clearance. After machining as close as possible, the surfaces may be finished with a file and scraper.

When the opening has been finished to the templet, the top may be giren the proper shear. In order to facilitate the operation of grinding -when the die is dull, the stock may be removed, as in Fig. 27, leaving about 1/4 inch on each side of the opening at the narrowest portion.

There are certain forms of dies where it is not feasible to cut away a portion of the top, as shown, but where it can be done it saves much time when grinding.

Correcting- Mistakes Made in Dies

Should the workman, through misunderstanding or carelessness, make the opening too large at any point, he should not attempt to

Machinery^ iV. K.

Fig. 27. Method of Cutting away the Top of Die to Facilitate Grinding

peen the stock cold, as is sometimes done, for while it is possible to do this and then finish the surfaces in such a manner that it will be scarcely noticeable, the stock directly below where the peening took place will almost surely crack during the life of the die.

Should the mistake referred to occur, heat the die to a forging heat, when the stock may be set in without injury to the steel. When set-

Machineryj N. V, Fig. 28. Closing up a Die which is too Large

ting in, a blacksmith's fulling tool may be used, this placed on the face of the die and struck with a sledge, as in Fig. 28. If there is objection to disfiguring the top surface of the die, this method can, of course, not be used, but if the top is to be cut away, as shown in Pig. 27, the depression made by the fulling tool would be entirely cut away. It is never good practice to bend, set in, or otherwise alter the form of steel when cold, if it is to be hardened, as such attempts nearly always end in a manner entirely unsatisfactory.

Re'working' Worn Dies

When a die becomes worn so that the opening is too large, or the top edge of the -walls of the opening are worn so that the die is "bell muzzled," it may be heated to a forging heat, set in with a fulling tool, or a punch of the desired shape, after which it is reheated to a low red and annealed. After annealing it is reworked to size. This reworking, care and judgment being- used, gives excellent results, and effects a considerable saving, as otherwise it would be necessary to make new dies, while the die may be reworked at a fraction of the expense of a new one.

When making a sectional die, it is possible in case the opening is a trifle too large, to work a little stock off the faces that come together, provided the outer edges have not been planed to fit the holder; also,

JiJriclMiri/iKy, Fig. 29. Arrangement of Oil Cooling Bath

if it is allowable, these surfaces may be cut away the desired amount, and a strip of stock of the proper thickness placed between the die and holder. Considering the liability of a mistake taking place when the beginner is doing work of this kind, it is, generally speaking, advisable to leave the fitting of the die to the holder until the opening has been worked to size.

Hardening' Dies

There is probably no one article the hardener is called on to harden that he dreads any more than a die. If he succeeds in bringing it out of the bath without a crack, he gives the credit to "luck"; and if it cracks, it is almost what he was looking for. This is an unfortunate condition, as there is no need of losing dies in the operation of hardening. Of course, if a piece of imperfect steel is used, it is almost sure to go to pieces in the bath; but if the steel is of the proper quality and in good condition, there need be no trouble when hardening.

When handling work so diversified in character as the class under consideration, the operator should not assume that it is possible to adopt any set method which is not to be deviated from, as there is no one class of work that calls for a greater exercise of skill and common sense than the proper hardening of punch-press dies, unless it be the hardening of drop-forging dies. For most dies of this character, however, and especially for those complicated in form, and which must retain as nearly as possible exact measurements, there is no method that will give the satisfaction derived from the method known as "pack-hardening."

Pack-hardening'

When pack-hardening such pieces, best results are derived from the use of a bath of raw linseed oil of the type shown in Pig. 29, in which the oil is kept from heating by being pumped through a coil of

Fig. 30. Dipping the Work in the Bath

pipe in a tank of water, and then forced into the bath and through the opening as shown. If such a bath is not at hand, good results can be obtained where the oil is not agitated but the die is swung back and forth and moved up and down somewhat in the oil. If many dies are to be hardened this way, however, it is necessary to have a bath of generous proportions, or, else several smaller baths, as it would not do to use the oil after it becomes hot, although oil that is heated somewhat will conduct the heat from steel more rapidly than would be supposed, and is better adapted for hardening than if it is extremely cold.

General Directions for Hardening-

The secret of success in hardening dies by the ordinary method consists in getting as nearly as possible a uniform heat. To accomplish this the die cannot be heated very rapidly, as the edges and lighter portions would heat more rapidly than the balance of the piece. Unequal contraction, when quenching in the bath, follows uneven heating, and unequal contraction causes the die to crack. High heats cause cracks in steel. Then, again, high heats render the steel weak, and as a consequence it cannot stand the strain incident to contraction of one portion of the steel when another portion is hard, and consequently rigid and unyielding. Steel is the strongest when hardened at the proper temperature, known as the refining heat.

Cold baths are a source of endless troubles when hardening dies. They will not make the steel any harder than one that is heated to a temperature of 60 or 70 degrees, or even warmer than this, but they will cause the die to spring or crack where the warmer bath would give excellent results. A bath of brine is to be preferred to one of water for this class of work, the brine being heated to the temperature mentioned above.

Have the bath of generous proportions. When the die is properly heated, lower it into the bath as shown in Fig. 30, moving it slowly back and forth to the positions shown, which causes the liquid to circulate through the openings, thus insuring the walls of the opening hardening in a satisfactory manner. Then again, moving back and forth brings both surfaces of the piece in contact with the liquid, causing them to harden uniformly, and ]>pe,vent-jing an undue amount of "humping," as would be the case if one side hardened more rapidly than the other. The workman must, of course, exercise common sense when doing this class of work. If he were to swing a die containing sharp corners, intricate shapes, and fine projections as rapidly in the bath as it would be safe to do were the opening round or of an oval shape, it might prove disastrous to the die, as such a shape would give off its heat very rapidly, and as a result the fine projections and sharp corners would harden much quicker than the balance of the die; and as they continued to contract, the projections would fly off, or the steel would crack in the corners. To avoid this, have the bath quite warm, move the die slowly, and as soon as the portions desired hard are in the proper condition, remove the die and plunge it in a bath of warm oil, where it may remain until cooled to the temperature of the oil.

Most of the trouble experienced when hardening dies is occasioned by one of two causes — possibly both. The first cause is uneven heating, the second, cold baths.