Page 42 - MetalForming-Jul-2018-issue
P. 42

   Tooling by Design
When constructing burnishing punches, always use high-wear-resistant tool steel or consider cemented carbide. The ball-nose radius on the burnishing punch should be highly polished and blend perfectly with the point body, and wear-resistant PVD surface coating is best for tool-steel and carbide burnish- ing punches.
Other Considerations
0.009 in. with the second.
Because a shaving operation acts on
the sheetmetal more like a machining operation (cutting) than a punching operation, consider adding a rake angle to the shave-punch face (Fig. 2) to facil- itate this cutting action. Establishing the proper back-rake angle for each shave application, somewhat of a black art, requires trial-and-error development. Some brass and bronze alloys do not require any back angle at all. Mild steels, depending on hardness, may require 10 deg. or more. And some aluminum alloys have required as much as 45 deg.
The same practices apply to free-edge shaving, although this requires much higher holddown forces to secure the work material while shaving. In addition, preventing deflec- tion due to unbalanced cutting forces requires a heeled and properly supported backside of the shave punch.
Finally, shaving requires a good lubricant. Depending on the type of material and its thickness, a heavy-duty EP lubri- cant used for fine blanking, broaching or in-die tapping operations may be needed. Work closely with your lubricant supplier for best results. MF
August 8-9, 2018
 Shave Punch
         Concave Shape
 In general, material removed by
shaving usually amounts to 10 to 12
percent of stock thickness per side for
most materials. This provides a good
surface finish and leaves enough material in the scrap ring for slug retention, an important consideration because slug retention remains a common problem associated with shav- ing operations.
Shaving thick materials with pronounced die break or taper may require more than one shaving operation. When two shave steps are required, the amount of material shaved in the second step should be one-half that of the first step. For example, if the requirement calls for shaving a total of 0.027 in., remove 0.018 in. with the first shave punch, then
Fig. 2
                 EXPERIENCE AND TECH TOUR DoubleTree by Hilton Hotel Pittsburgh - Green Tree • Pittsburgh, PA
Attendees of the 3D Metal Printing Experience and Tech Tour will come away with an understanding of the trends defining the use of the various metal-AM processes; how to identify suitable applications for metal AM; the top 5 reasons to use hybrid (3D printing + CNC machining) additive systems; and R & D underway for large-scale metal-arc printing of stamping dies and tooling.
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40 MetalForming/July 2018

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