Tips and tricks
Blanking dies
BLANKING DIESPrinciples of their design and examples from practice.
CONTENTS
- Introduction
- Method of Making Blanking Dies
- Blanking and Piercing Dies for Washers
- Making Blanking Dies to Cut Stock Economically
- Construction of Split Dies
- Stop-Pins for Press-Work
- Practical Examples in Die Design
MACHINERY'S REFERENCE SERIES
The Industrial Press, New York, 1910
DOWNLOAD FREE BOOK: Blanking dies
INTRODUCTION
It is rather difficult to classify and give proper definitions of the many varying kinds and types of dies used on the power press for rapid production of duplicate work. While there are, of course, some general classes into which all tools of this description may be divided, the various types overlap, so to say, and one is sometimes in doubt as to the proper classification of tools which combine the features of different types. In the following, however, the distinctions between the main types have been pointed out in general outlines, the definitions being broad enough to permit of adjustment according to special conditions.
All dies may, in the first place, be divided into two general classes: cutting dies and shaping dies. Cutting dies include all dies which simply cut or punch out required pieces of work from the stock fed into the press, without changing the condition or form of the stock in the plane in which it was located in the material from which it is cut. Shaping dies include all dies which change the form of the material from its original flat condition, producing objects in which the various surfaces are not in the same plane. The last mentioned main division often includes also the characteristics of the first; that is, some shaping dies are, for instance, a combination of cutting and shaping dies, the blank for the work to be shaped or formed being first cut out to the required outline from the stock, and then shaped to the desired form.
The main classes of dies, as will be recognized, are based on the use of the dies. The first of the classes mentioned, cutting dies, may, however, be further subdivided according to the construction of the various types of dies in this class. We then distinguish between four distinct types, plain blanking dies, follow dies, gang dies, and com- pound dies.
Plain blanking dies are the simplest of all types of dies, and are used to cut out plain, flat pieces of stock having, in general, no perforations, the work being turned out complete at one stroke of the press. Follow dies, not infrequently also termed tandem dies, are used for work which must be cut out from the stock to required shape, and at the same time be provided with holes or perforations of any kind. The principle of the follow die is that while one part of the die punches the hole in the stock, another part punches out the work at a place where at a former stroke a hole has already been punched, so that a completed article results from each stroke of the press, but, in reality, two operations have been performed on the work before completion. The follow die cannot be depended upon to turn out very accurate work, because it depends largely on the skill and care of the operator for the production of duplicate work. In both the plain blanking and the follow dies, the punch, or upper member, and the die, or lower member, of the complete tool, are distinct elements, the work being cut out or perforated by the entering of the punch into the holes provided for it in the die.
Gang dies are used when several blanks are punched out simultaneously from the stock. The advantage of the gang die over the plain blanking die is the saving of time. Compound dies differ from plain blanking and gang dies in that the simple punch and die elements are not separated, one in the upper and one in the lower half of the complete tool, but these elements are combined so that both the upper and the lower part contain each a punch and a die. The faces of both punches, dies and strippers are normally held at the same level, and the strippers are spring supported so as to give way when the stock is inserted between the faces, and the press is in action. The springs are so adjusted that they are strong enough to overcome the cutting resistance of the stock, after which they will be compressed until the ram reaches the end of its stroke. A compound die produces more accurate work than the three types previously referred to, for the reason that all operations are carried out simultaneously at one stroke, while the stock is firmly held between the spring-supported opposing die faces. The disadvantage of the ordinary compound die is the difficulty encountered in "setting up," and the complexity of the design, which usually requires more or less frequent repairs.
The second main division of dies, the shaping dies, cannot be subdivided according to the construction of the dies in the same manner as the cutting dies. Shaping dies are usually designed more or less on the compound principle, outlined above, but owing to the great variety of work performed in these dies, the designs vary too greatly for a classification on the basis of constructional features. They may, however, be divided into sub-classes according to the general use to which they are put. We would then distinguish these four main subdivisions: lending dies, forming dies, drawing dies, and curling dies.
Bending dies are used when part of the surface of a piece of work is pushed from its original plane into a new shape in such a manner that the bent work does not form a closed curve. Forming dies are used when the blank is required to be formed into a hollow shape, by being pushed into a cavity in the die. Drawing dies are used for the same purpose as forming dies, but the process differs in that the outer portion of the flat blank to be formed is confined between two rigid flat surfaces, so that, when drawn radially inward from between them, no wrinkles can form. Curling dies are used for bending over the ends or edges of the work into a circular cross section, like the turning over of the edges of hollow objects of sheet metal, etc.
Finally, we must mention the sub-press die, which, however, cannot be defined as a special class of die, but merely as a principle on which all the different classes of dies, cutting as well as shaping dies, may be worked. The sub-press principle is simply that the upper and lower portion of the die, the punch and die, are combined into one unit by guide rods fastened into the lower part of the die and extending through holes in the upper part, or by some other provision for guiding. This construction permits of a high degree of accuracy eliminates the necessity of lining up the punch and the die each time they are set up on the press, and thus saves a great deal of time and cost.
In the following, we shall, however, deal only with the simpler forms of cutting dies, plain blanking and gang dies, except in Chapter VI, where reference will also be made to some of the more complicated types of dies.
METHOD OF MAKING BLANKING DIES
From a mechanical standpoint it can truthfully be said that we are living in an age of dies. Never before has the industrial world made use of the punch and die as it is doing to-day. And no wonder; for this useful tool in all its different phases has proved beyond all reasonable doubt that it can turn out more work in less time than the combined efforts of a room full of milling machines, shapers, and drill presses. To those who are unfamiliar with the die and its work the above may not appear feasible; but one has only to visit a modern sheet metal factory to be convinced of the surprising rapidity with which the power press with its punches and dies will turn out not only work of all kinds of shapes and sizes, but accurate work as well. Of the many different kinds of dies in use, the blanking die is probably the most widely employed. The reason for this is that almost all work that requires the use of various other kinds of dies has its beginning with the blanking die; for it is this die that cuts the work from the flat stock before it is completed by the other dies. In making the blanking die there are a few essential points to be taken into consideration, among which are the following:
1. Use good tool steel of a sufficient length, width, and thickness to enable the die to hold its own.
2. In laying out the die, care should be taken that as little of the stock as possible is left over, as waste, in cutting out the blanks.
3. Be sure not only that the die has the proper amount of clearance (which should be no more than two degrees and no less than one degree.) but also that the clearance is filed straight, so as to enable the blanks to readily drop through.
4. In working out the die, machine out as much as possible; don't let the file do it all.
5. In hardening the die, do not overheat it, as the cutting edge of a die that has been overheated will not stand up to the work, and requires so much sharpening in order to produce perfect blanks, that at its best it is nothing more than a nuisance.
In laying out the blanking die, the face of the die is first polished smooth and drawn to a blue color by heating. This gives better satisfaction by far than using coloring acid, for it gives a clear white line on a dark surface to work to, and is easier on the eyes, particularly when working by artificial light as is often necessary.
DOWNLOAD FREE BOOK: Blanking dies
All dies may, in the first place, be divided into two general classes: cutting dies and shaping dies. Cutting dies include all dies which simply cut or punch out required pieces of work from the stock fed into the press, without changing the condition or form of the stock in the plane in which it was located in the material from which it is cut. Shaping dies include all dies which change the form of the material from its original flat condition, producing objects in which the various surfaces are not in the same plane. The last mentioned main division often includes also the characteristics of the first; that is, some shaping dies are, for instance, a combination of cutting and shaping dies, the blank for the work to be shaped or formed being first cut out to the required outline from the stock, and then shaped to the desired form.
The main classes of dies, as will be recognized, are based on the use of the dies. The first of the classes mentioned, cutting dies, may, however, be further subdivided according to the construction of the various types of dies in this class. We then distinguish between four distinct types, plain blanking dies, follow dies, gang dies, and com- pound dies.
Plain blanking dies are the simplest of all types of dies, and are used to cut out plain, flat pieces of stock having, in general, no perforations, the work being turned out complete at one stroke of the press. Follow dies, not infrequently also termed tandem dies, are used for work which must be cut out from the stock to required shape, and at the same time be provided with holes or perforations of any kind. The principle of the follow die is that while one part of the die punches the hole in the stock, another part punches out the work at a place where at a former stroke a hole has already been punched, so that a completed article results from each stroke of the press, but, in reality, two operations have been performed on the work before completion. The follow die cannot be depended upon to turn out very accurate work, because it depends largely on the skill and care of the operator for the production of duplicate work. In both the plain blanking and the follow dies, the punch, or upper member, and the die, or lower member, of the complete tool, are distinct elements, the work being cut out or perforated by the entering of the punch into the holes provided for it in the die.
Gang dies are used when several blanks are punched out simultaneously from the stock. The advantage of the gang die over the plain blanking die is the saving of time. Compound dies differ from plain blanking and gang dies in that the simple punch and die elements are not separated, one in the upper and one in the lower half of the complete tool, but these elements are combined so that both the upper and the lower part contain each a punch and a die. The faces of both punches, dies and strippers are normally held at the same level, and the strippers are spring supported so as to give way when the stock is inserted between the faces, and the press is in action. The springs are so adjusted that they are strong enough to overcome the cutting resistance of the stock, after which they will be compressed until the ram reaches the end of its stroke. A compound die produces more accurate work than the three types previously referred to, for the reason that all operations are carried out simultaneously at one stroke, while the stock is firmly held between the spring-supported opposing die faces. The disadvantage of the ordinary compound die is the difficulty encountered in "setting up," and the complexity of the design, which usually requires more or less frequent repairs.
The second main division of dies, the shaping dies, cannot be subdivided according to the construction of the dies in the same manner as the cutting dies. Shaping dies are usually designed more or less on the compound principle, outlined above, but owing to the great variety of work performed in these dies, the designs vary too greatly for a classification on the basis of constructional features. They may, however, be divided into sub-classes according to the general use to which they are put. We would then distinguish these four main subdivisions: lending dies, forming dies, drawing dies, and curling dies.
Bending dies are used when part of the surface of a piece of work is pushed from its original plane into a new shape in such a manner that the bent work does not form a closed curve. Forming dies are used when the blank is required to be formed into a hollow shape, by being pushed into a cavity in the die. Drawing dies are used for the same purpose as forming dies, but the process differs in that the outer portion of the flat blank to be formed is confined between two rigid flat surfaces, so that, when drawn radially inward from between them, no wrinkles can form. Curling dies are used for bending over the ends or edges of the work into a circular cross section, like the turning over of the edges of hollow objects of sheet metal, etc.
Finally, we must mention the sub-press die, which, however, cannot be defined as a special class of die, but merely as a principle on which all the different classes of dies, cutting as well as shaping dies, may be worked. The sub-press principle is simply that the upper and lower portion of the die, the punch and die, are combined into one unit by guide rods fastened into the lower part of the die and extending through holes in the upper part, or by some other provision for guiding. This construction permits of a high degree of accuracy eliminates the necessity of lining up the punch and the die each time they are set up on the press, and thus saves a great deal of time and cost.
In the following, we shall, however, deal only with the simpler forms of cutting dies, plain blanking and gang dies, except in Chapter VI, where reference will also be made to some of the more complicated types of dies.
METHOD OF MAKING BLANKING DIES
From a mechanical standpoint it can truthfully be said that we are living in an age of dies. Never before has the industrial world made use of the punch and die as it is doing to-day. And no wonder; for this useful tool in all its different phases has proved beyond all reasonable doubt that it can turn out more work in less time than the combined efforts of a room full of milling machines, shapers, and drill presses. To those who are unfamiliar with the die and its work the above may not appear feasible; but one has only to visit a modern sheet metal factory to be convinced of the surprising rapidity with which the power press with its punches and dies will turn out not only work of all kinds of shapes and sizes, but accurate work as well. Of the many different kinds of dies in use, the blanking die is probably the most widely employed. The reason for this is that almost all work that requires the use of various other kinds of dies has its beginning with the blanking die; for it is this die that cuts the work from the flat stock before it is completed by the other dies. In making the blanking die there are a few essential points to be taken into consideration, among which are the following:
1. Use good tool steel of a sufficient length, width, and thickness to enable the die to hold its own.
2. In laying out the die, care should be taken that as little of the stock as possible is left over, as waste, in cutting out the blanks.
3. Be sure not only that the die has the proper amount of clearance (which should be no more than two degrees and no less than one degree.) but also that the clearance is filed straight, so as to enable the blanks to readily drop through.
4. In working out the die, machine out as much as possible; don't let the file do it all.
5. In hardening the die, do not overheat it, as the cutting edge of a die that has been overheated will not stand up to the work, and requires so much sharpening in order to produce perfect blanks, that at its best it is nothing more than a nuisance.
In laying out the blanking die, the face of the die is first polished smooth and drawn to a blue color by heating. This gives better satisfaction by far than using coloring acid, for it gives a clear white line on a dark surface to work to, and is easier on the eyes, particularly when working by artificial light as is often necessary.
DOWNLOAD FREE BOOK: Blanking dies
Free books category: