Page 28 - MetalForming November 2009

Tooling Technology
Tool Steel Considerations for
Lean Manufacturing
The optimization of tooling per- formance helps metalformers elim- inate waste and improve operations. This requires giving proper considera- tion to the selection and treatment of the tool steel. Users of tool steels are confronted with a range of options rel- ative to heat treatment methods, coat- ings and other special treatments intended to improve tool performance. Rather than rehash such information, the intent here is to suggest how tooling engineers and designers can take a fresh approach to tool steel from the per- spective of lean manufacturing.
The first step: Identify an appropri- ate goal with respect to tooling per- formance. While it might seem desirable for tooling to last forever, this would not be realistic nor would the high costs required necessarily translate into value at the bottom line. From a lean per- spective, tooling should perform reli- ably, consistently and predictably. This allows a metalformer to effectively plan its operations, reduce variation and improve process flow.
Recognize the Factors that Affect Tool Performance
The tool steel often takes the blame for problems that originate elsewhere, such as in the design, manufacture or maintenance of the tooling. From the start, metalformers must ensure that they are not asking more of the tooling that what it can handle—a classic source of waste. Start by selecting the right grade of tool steel as part of the design
Gary Maddock is technical manager, Zapp Tooling Alloys, Summerville, SC: tel. 779/537-0870; www.zapp.com.
Select the correct grade that offers the appropriate balance of wear and toughness for the job at hand.
BY GARY MADDOCK
Comparative Properties of Cold-Work Steels 120
56-58 HRC 60-62 HRC
58-60 HRC
110 100 90 80 70 60 50 40 30 20 10 0
S7 A2
PM-A18 D2
PM-M4 PM-A11
Wear resistance
Toughness
process, and by specifying the heat treat- ment of the tool steel as part of the tool-manufacturing process.
To control metallurgical quality, fol- low these three basic steps:
1) Select the correct grade that offers the appropriate balance of wear and toughness for the job at hand. Tool-steel suppliers can provide data comparing properties on a relative scale. Wear resist- ance generally is associated with longevity —it enables the production of more parts, extends maintenance intervals and minimizes downtime. To some extent, wear life may not seem as much of a con- cern in the age of JIT, short production cycles and more frequent tooling changes. However, achieving adequate wear resistance still is key to producing good parts with minimal variation, and to keeping dies out of the toolroom.
Simply using a more wear-resistant grade may not always be the correct choice. Do not overlook the importance of toughness; nothing spoils reliability
Overly aggressive grinding or EDM machining can cause poor edge reten- tion (shown here), premature wear and an apparent loss of toughness. Care taken during finishing operations to minimize surface damage, remove burrs and maintain good edge quality will provide real value in the end.
and creates waste more quickly than a die component that develops the bad habit of suddenly chipping out a cutting edge (even though it otherwise performs to expectation). And, it is important to have a consistent selection methodology.
26 METALFORMING / NOVEMBER/DECEMBER 2009
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Relative ranking