STAMPING/PIERCING
A key to efficient cutting or penetration of workpiece material is edge retention, i.e. to maintaining the geometry of the cutting edge of the tool. The cutting edge can lose its geometry by deformation (flattening), abrasion (rounding), chipping or cracking. Any of these problems can cause part tolerance problems or burr conditions. In addition, wear or galling can ruin the edges or flanks of tools. Each of these is caused by a different mechanism and relates to a different property of the tool steel.

• Deformation of the cutting edge results in flattening (rollover or peening). To minimize deformation, consider tool steels with high hardness and therefore high compressive yield strength. High hardness is usually the first consideration for cutting type tooling. However, hardness is not a highly distinguishing factor as most of the tool steels have similar working hardness ranges.

  A2 or D2 cutting dies which experience rollover or peening may suggest higher hardness is necessary. CruWear, M2, CPM M4, or CPM T15 may offer the required attainable hardness. See Working Hardness Range table and Hardness vs. Compressive Yield Strength chart for information about high hardness.

• Abrasion of the tool involves actual metal loss and results in rounding of the edge. To minimize abrasion consider tool steels with high wear resistance.

  A2 or D2 tools which are experience premature wear may benefit from higher alloy tool steels, which offer better wear resistance, even at similar hardness. Grades such as CPM 10V, 15V, or M4 may be appropriate. See the discussion of wear properties of tool steels.

• A chipped or cracked edge results in a worthless tool, often beyond repair. To minimize chipping or cracking, consider tool steels with high toughness.

  Tools which chronically crack, or cutting edges that chip, require higher toughness tool steels. In many cases, lower wear resistance tool steels (A2, S7) are selected in order to avoid brittleness problems. Depending on the application, CPM 3V may offer an advantageous combination of high toughness and wear properties. See the discussion of toughness issues with tool steels.

• Galling is not generally easily solved by a change of tooling materials, as most tool steels have similar physical surface properties. Certain tool steels may be beneficial in some cases. Coatings or surface treatments may be helpful.