Die Design Fundamentals. Vukota Boljanovic
3.7) in a cut-off die. At view A, the part is positioned the wide way in the strip. The edges of the strip are notched at the first station and a rectangular hole is punched. The blank is cut off from the strip at the second station. At view B, the part is positioned the narrow way in the strip. Observe how notching punches are sectioned. The heels C, which prevent deflection of the punches, are shown, but not sectioned. At D, short 45 degree lines and a long vertical line represent the “cut off” line.
Figure 3.7 Typical part for production in cut-off die.
Figure 3.8 Blank layout for part shown in Figure 3.7 run, either the wide (A) or narrow (B) way.
Blank layouts are drawn to explain the proposed operation of a die to others. When die designers are given a part print of a stamping for which a die is to be designed, they proceed to lay out a suitable scrap strip. Then they section significant punches and add cut-off lines to make the proposal layout clearer. This is the blank layout, and it must be approved by the group leader or chief engineer before design of the die is begun. When an outside engineering office is doing the work for a manufacturing company, the blank layout is submitted to the customer for approval.
3.4.2 Stripper Sheet
Sizes of sheets as they are manufactured by the mill are given in steel catalogs. Here is a representative list for #18 Gage (0.0478 in. or 1.2 mm) cold-rolled steel:
30 in. × 96 in. (762 mm × 2438 mm)
30 in. × 120 in. (762 mm × 3048 mm)
36 in. × 96 in. (914 mm × 2438 mm)
36 in. × 120 in. (914 mm × 3048 mm)
48 in. × 96 in. (1219 mm × 2438 mm)
48 in. × 120 in. (1219 mm × 3048 mm).
Figure 3.9 Number of strips obtainable with wide strip blank layout.
Figure 3.10 Strips per sheet with wide strip blank layout for production in a cut-off die.
The next step is to select the sheet that will be most economical, that is, the sheet from which a maximum number of strips can be cut, leaving a minimum amount of waste.
a) Wide Run
Strip width is taken from the blank layout. Divide the value given into the values for “width of sheet” in the steel catalog, and compare to determine which sheet leaves the smallest remainder. Figure 3.9 shows a sheet 48 by 120 inches (1219 mm × 3048 mm) divided into strips when the typical representative blank is run the wide way.
Figure 3.10 shows the sheet divided into strips for producing parts in a cut-off die when the blank is run the wide way.
Figure 3.11 Number of strips obtainable with narrow strip blank layout.
Figure 3.12 Strips per sheet with narrow strip blank layout for production in a cut-off die.
b) Narrow Run
Next, we must know how many blanks are produced per sheet with the blanks positioned the narrow way in the strip. With blanks arranged the narrow way, more strips are cut from the sheet, but fewer blanks are contained in each strip.
Figure 3.11 shows the same sheet divided into strips when the typical representative blanks are to be run the narrow way. More strips are produced from the same size of sheet.
Figure 3.12 shows the sheet divided into strips for producing a part in a cut-off die when the blank is run the narrow way.
3.4.3 Strip Layout
After it has been decided how the blanks are to be run (wide or narrow way), a stock layout is prepared complete with the following dimensions:
•Strip width. This dimension is used in selecting the proper width of sheet from which strips are to be cut.
•Feed. This is the amount of travel of the strip between stations. This dimension is used in selecting the proper length of sheet.
Figure 3.13 Complete strip layouts for blanks run either the wide (A) or narrow (B) way.
Figure 3.13 shows complete strip layouts for the typical representative blanks run either the wide (view A) or narrow (view B) way. Two views are applied, ordinarily. These are exactly the views of the strip that will be drawn on the die drawing except that an end view of the strip is added to the die drawing. The die is then actually designed around these views.
View A illustrates a strip layout for a blanking die in which the blank is run the wide way. View B shows a layout in which the blank is run the narrow way. For this particular job, more blanks per sheet are produced when the blanks are positioned the wide way and there is less waste. Therefore, all else being equal, this method of positioning the blanks would be selected.
Figure 3.14 Strip layouts for blanks run either the wide (A) or narrow (B) way.
Figure 3.14 shows strip layout for production of parts in cut-off die. The strip layout is prepared and copies are sent to the purchasing department and to the shear department. From the layout, sheets are ordered and, upon delivery, they are sheared to the strip width given on the layout. View A shows a representative strip layout for a blank for a cut-off die positioned the wide way, and view B shows a layout for a blank positioned the narrow way.
For this job we find that exactly the same number of blanks are produced with blanks positioned the narrow way as for wide-run positioning; there is no waste in either method. When blanks can be run either way, select the wide run method for three reasons:
•Fewer cuts will be necessary for producing the strips.
•The feed is shorter when running strips through the die, thus reducing the time required.
•More blanks are produced per strip and fewer strips have to be handled.
Figure 3.15 Strips ready for feeding either the wide (A) or narrow (B) way.
Figure 3.16 Strips ready for feeding either the wide (A) or narrow (B) way in a cut-off die.
3.4.4 Strips
Figure 3.15 shows a strip ready