Die Design Fundamentals. Vukota Boljanovic
were not inverted, most lines representing punches would be hidden and the drawing would contain a confusing maze of dotted lines.
Figure 1.10 A die set.
Another reason for inverting the punch holder is that this is actually the position assumed by the die holders and punch holders on the bench as the die makers assemble the die, and it is easier for die makers to read the drawing when the views have been drawn in the same position as the die on which they perform assembly motions.
1.2.2 The Die Block
Figure 1.11 shows the die block of the die shown in Figure 1.2. The die block is made of hardened tool steel into which holes have been machined, before hardening, at the piercing station and also at the blanking station. These are the same size and shape as the blank holes and contour. Other holes are tapped holes used to fasten the die block to the die holder, and reamed holes into which dowels are pressed to fix the block’s location relative to other die parts.
Figure 1.11 The die block.
The top view is a plan view of the die block. The lower left view is a section through the holes machined for piercing and blanking. Lines drawn at a 45-degree angle, called “section lines,” indicate that the die block has been cut through the center, the lines representing the cut portion. Similarly, the end view is a section cut through the die block at the blanking station. A tapped hole is shown at the left and a reamed hole at the right side. These are for the screws and dowels that hold the die block to other die components. Sectioning a die, that is, showing the die as if portions were cut away to reveal the inside contours of die openings, is a very common practice. In fact, practically all dies are sectioned in this manner. The die maker can then “read” the drawing far more easily than he could if outside views only were shown because these would contain many dotted or hidden lines.
Always remember that all drafting is, in a sense, a language. A die drawing is a sort of shorthand, which is used to convey a great deal of information to the die makers. Anything that can be done to make it easier for them to read the drawing will save considerable time in the shop.
Now refer back to Figure 1.2 and see how easily you can pick out the three views of the die block. That is exactly what the die maker has to do in order to make the die block.
1.2.3 The Blanking Punch
The blanking punch (Figure 1.12) removes the blank from the strip. The bottom, or cutting edge, is the shape and size of the part. A flange at the top provides metal for fastening the blanking punch to the punch holder of the die set with screws and dowels. Two holes are reamed all the way through the blanking punch for retaining the pilots, which locate the strip prior to the blanking operation. Locate the views of the blanking punch in the die drawing, Figure 1.2, to improve your ability to read a die drawing.
1.2.4 Piercing Punch
A piercing punch (Figure 1.13) pierces holes through the material strip or blank. It is usually round and provided with a shoulder to keep it in the punch plate. When a piercing punch penetrates the strip, the material clings very tightly around it. A way must be provided to strip or remove this material from around the punches. The means employed to remove such material is called a “stripper.”
Figure 1.12 The blanking punch.
Figure 1.13 A piercing punch.
1.2.5 Punch Plate
The punch plate (Figure 1.14) is a block of machine steel that retains punches by keeping the punch heads against the punch holder of the die set. The punches are held in counterbored holes into which they are pressed. Four screws and two dowels retain the punch plate to the punch holder of the die set. The screws prevent it from being pulled away from the punch holder. Dowels, which are accurately ground round pins, are pressed through both the punch plate and punch holder to prevent shifting. Locate the front view and plan view of the punch plate in the die drawing Figure 1.2.
Figure 1.14 A punch plate.
Figure 1.15 A pilot.
1.2.6 Pilot
Pilots (Figure 1.15) are provided with acorn-shaped heads, which enter previously pierced holes in the strip. The acorn shape causes the strip to shift to correct register before blanking occurs.
1.2.7 The Back Gage
The back gage (Figure 1.16) is a relatively thin steel member against which the material strip is held by the operator in its travel through the die. The front spacer is a shorter component of the same thickness. The strip is fed from right to left. It rests on the die block and is guided between the back gage and front spacer. The distance between the back gage and front spacer is greater than the strip width to allow for possible slight variations in width.
Figure 1.16 The back gage.
Figure 1.17 A finger stop.
1.2.8 The Finger Stops
The finger stop (Figure 1.17) locates the strip at the first station. In progressive dies having a number of stations, a finger stop may be applied at each station to register the strip before it contacts the automatic stop. Finger stops have slots machined in their lower surfaces to limit stop travel.
1.2.9 Automatic Stops
Automatic stops (Figure 1.18) locate the strip automatically while it is fed through the die. The operator simply keeps the strip pushed against the automatic stop toe, and the strip is stopped while the blank and pierced slugs are removed from it, then it is automatically allowed to move one station further and stopped again for the next cutting operation.
1.2.10 The Stripper Plate
The stripper plate (Figure 1.19) removes the material strip from around blanking and piercing punches. There are two types of stripper plates: spring-operated and solid. The one illustrated is solid. The stripper plate has a slot A machined into it in which the automatic stop operates. Another slot B at the right provides a shelf for easy insertion of a new strip when it is started through the die.
Figure 1.18