Machinery's Handbook, 31st Edition
FINE BLANKING 1415 The clamping elements are sharp projections of 90-degree V-section that follow the outline of the workpiece and are incorporated into each tool as part of the stripper plate with thin material and also as part of the die plate when material thicker than 0.15 inch (3.81 mm) is to be blanked. Pressure applied to the elements containing the V-projections prior to the blanking operation causes the sharp edges to enter the material surface, preventing sideways movement of the blank. The pressure applied as the projections bite into the work surface near the contour edges also squeezes the material, causing it to flow toward the cutting edges, reducing the usual rounding effect at the cut edge. When small details such as gear teeth are to be produced, V-projections are often used on both sides of the work, even with thin materials, to enhance the flow effect. With suitable tooling, workpieces can be produced with edges that are perpendicular to top and bottom surfaces within 0.004 inch (0.1mm) on thicknesses of 0.2 inch (5.0 mm), for instance. V-projection dimensions for various material thicknesses are shown in Table 9. Table 9. Dimensions for V-projections Used in Fine-Blanking Tools
45° 45° A
Stripper Plate
45° 45° A
Stripper Plate
h
r
r
0.004 in.
R R
h
r
r
H
45° 45°
Die Plate V-Projections on Stripper Plate Only
Die Plate V-Projections on Both Stripper and Die Plate
Material Thickness
A
h
r
H
R
V-Projections on Stripper Plate Only
0.040–0.063 0.063–0.098 0.098–0.125 0.125–0.157 0.157–0.197 0.157–0.197 0.197–0.248 0.248–0.315 0.315–0.394 0.394–0.492 0.492–0.630
0.040 0.055 0.083 0.098 0.110 0.098 0.118 0.138 0.177 0.217 0.276
0.012 0.015 0.024 0.028 0.032 0.020 0.028 0.032 0.040 0.047 0.063
0.008 0.008 0.012 0.012 0.012 0.008 0.008 0.008 0.020 0.020 0.020
… … … … … … … … … …
V-Projections on Both Stripper and Die Plate
0.032 0.040 0.047 0.060 0.070 0.087
0.032 0.040 0.047 0.060 0.080 0.118
All units are in inches. Fine-blanked edges are free from the fractures that result from conventional tooling and can have surface finishes down to 80 μ in. (2.0 μ m) Ra with suitable tooling. Close tolerances can be held on inner and outer forms and on hole center distances. Flatness of fine-blanked components is better than that of parts made by conventional methods but distortion may occur with thin materials due to release of internal stresses. Widths must be slightly greater than are required for conventional press working. Generally, the strip width must be 2–3 times the thickness, plus the width of the part measured transverse to the feed direction. Other factors are shape, material quality, size and shape of the V-projection
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