Machinery's Handbook, 31st Edition
Classification of Dies 1455 Progressive Die: A progressive die (Fig. 63) is used to transform coil stock or strips into a finished part. This transformation is performed progressively by a series of stations aligned in a row; the workpiece is fed from station to station with each stroke, by being attached to the scrap skeleton. Force for the movement is applied to the incoming sheet metal strip or coil and outgoing scrap skeleton by means of rolls.
Fig. 63. Progressive Die The cost of a progressive die is high, so it is best used for high-volume production. Transfer Die: In transfer die operations, individual stock blanks are mechanically moved from die station to die station within a single die set. Large workpieces are done with tandem press lines, in which the stock is moved from press to press where specific operations are performed. Steel Rule Dies.— Steel rule dies (or knife dies) were patented by Robert Gair in 1879, and, as the name implies, have cutting edges made from steel strips of about the same proportions as the steel strips used in making graduated rules for measuring purposes. According to J. A. Richards, Sr., of the J. A. Richards Co., Kalamazoo, MI, a pioneer in the field, these dies were first used in the printing and shoemaking industries for cutting out shapes in paper, cardboard, leather, rubber, cork, felt, and similar soft materials. Steel rule dies were later adopted for cutting upholstery material for the automotive and other industries, and for cutting out simple to intricate shapes in sheet metal, including copper, brass, and aluminum. A typical steel rule die, partially cut away to show the construction, is shown in Fig. 64, and is designed for cutting a simple circular shape. Such dies gener- ally cost 25 to 35 percent of the cost of conventional blanking dies, and can be produced in much less time. The die shown also cuts a rectangular opening in the workpiece, and pierces four holes, all in one press stroke. The die blocks that hold the steel strips on edge on the press platen or in the die set may be made from plaster, hot lead or type metal, or epoxy resin, all of which can be poured to shape. However, the material most widely used for light work is 3 ∕ 4 -in. (19.05 mm) thick, five- or seven-ply maple or birch wood. Narrow slots are cut in this wood with a jig saw to hold the strips vertically. Where greater forces are involved, as with operations on metal sheets, the blocks usually are made from Lignostone densified wood or from metal. In the 3 ∕ 4 -in. thickness mostly used, medium- and high-density grades of Lignostone are avail able. The 3 ∕ 4 -in. thickness is made from about 35 plies of highly compressed lignite wood, bonded with phenolformaldehyde resin, which imparts great density and strength. The material is made in thicknesses up to 6 in. (15.24 cm), and in various widths and lengths.
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