Tips and tricks
Punch and die work
PUNCH AND DIE WORK
CONTENTS
- Principles of Punch and Die Work
- Suggestions for the Making and Use of Dies
- Examples of Dies and Punches
MACHINERY'S REFERENCE SERIES
The Industrial Press, New York, 1911
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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 1/4 to 3/8 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.
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.
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 high-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 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, 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 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.
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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 1/4 to 3/8 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.
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.
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 high-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 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, 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 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.
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