Machinery's Handbook, 31st Edition
Steel Rule Dies
1457
D
A B C
Fig. 65. Cutting Edges for Steel Rule Dies The thickness and hardness of the material to be blanked also must be considered when choosing rule thickness. Making of Steel Rule Dies: Die making begins with a drawing of the shape required. Saw cutting lines may be marked directly on the face of the die block in a conventional layout procedure using a height gage, or a paper drawing may be pasted to or drawn on the die board. Because paper stretches and shrinks, Mylar or other nonshrink plastics sheets may be preferred for the drawing. A hole is drilled off the line to allow a jig saw to be inserted, and jig saw or circular saw cuts are then made under manual control along the drawing lines to produce the slots for the rules. Jig saw blades are available in a range of sizes to suit various thicknesses of rule and for sawing medium-density Lignostone, a speed of 300 strokes/min is recommended, the saw having a stroke of about 2 inch (50.8 mm). To make sure the rule thickness to be used will be a tight fit in the slot, trials are usually carried out on scrap pieces of die block before cuts are made on a new block. During slot cutting, the saw blade must always be maintained vertical to the board being cut, and magnifying lenses are often used to keep the blade close to the line. Carbide or carbide-tipped saw blades are recommended for clean cuts as well as for long life. To keep any “islands” (such as the center of a circle) in position, various places in the sawn line are cut to less than full depth for lengths of 1 ∕ 4 – 1 ∕ 2 in. (6.4–12.7 mm), and to heights of 5 ∕ 8 to 3 ∕ 4 in. (16–19 mm) to bridge the gaps. Slots of suitable proportions must be provided in the steel rules, on sides away from cutting edges, to accommodate these die block bridges. Rules for steel rule dies are bent to shape to fit the contours called for on the drawing by means of small, purpose-built bending machines, fitted with suitable tooling. For bends of small radius, the tooling on these machines is arranged to perform a peening or hammering action to force the steel rule into close contact with the radius-forming component of the machine so that quite small radii, as required for jig saw puzzles, for instance, can be produced with good accuracy. Some forms are best made in two or more pieces, then joined by welding or brazing. The edges to be joined are mitered for a perfect fit, and are clamped securely in place for joining. Electrical resistance or a gas heating torch is used to heat the joint. Wet rags are applied to the steel at each side of the joint to keep the material cool and the hardness at the preset level, as long as possible. When shapes are to be blanked from sheet metal, the steel rule die is arranged with flat, 90 ° edges ( B , in Fig. 65 ), which cut by pushing the work past a close-fitting counter-punch. This counterpunch, shown in Fig. 64, may be simply a pad of steel or other material, and has an outline corresponding to the shape of the part to be cut. Sometimes the pad may be given a gradual, slight reduction in height to provide a shearing action as the moving tool pushes the work material past the pad edges. As shown in Fig. 64, punches can be incorpo rated in the die to pierce holes, cut slots, or form ribs and other details during the blanking operation. These punches are preferably made from high-carbon, high-vanadium, alloy steel, heat treated to 61 to 63 RC (Rockwell C scale), with the head tempered to 45 to 50 RC.
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