Page 26 - MetalForming December 2010

Tooling Technology
Peter Ulintz has worked in the sheetmetal-forming industry since 1978. His background includes tool and die making, tool and process engineering, engineering management and product devel- opment. Peter also operates the website ToolingbyDesign.com, a source for the transfer of modern metalforming and tool-and-die technology, and which promotes the use of “Performance-Based Die Engineering Strategies.”
Peter speaks at PMA seminars and roundtables focusing on tool and die design, die maintenance, deep drawing, stamping simula- tion, tooling for stamping high- strength steels and problem solv- ing in the press shop.
Peter Ulintz pete.ulintz@toolingbydesign.com www.toolingbydesign.com
Stamping dies are subjected to an array of stresses, strains, tempera- tures, chemicals, fluids, dynamic shock and vibrations. As a result, it is not at all surprising that dies can be prone to all kinds of in-process failures.
A complete analysis and proper iden- tification of the failure mode(s) is nec- essary in order to repair the tooling properly and maintain optimum per- formance. Although the following sequence may vary depending on the failure type(s), the specific procedures for any failure analysis—including stamping dies—should include some or all of the following steps:
• Collect samples—broken die com- ponents, progressive die strips, etc.
• Compile background data.
• Visually examine the failed part, and document findings.
• Nondestructive-test surface finish, dimensional specifications, etc.
• Mechanically test—hardness, toughness, etc.
• Examine fracture surfaces, cracks and other surface anomalies.
• Determine the failure mode(s).
• Test under simulated service con- ditions.
• Analyze the evidence.
• Develop a conclusion.
The failed die component (broken,
twisted, bent, galled, chipped, scored, etc.) is the primary failure sample because it is, or it contains, the actual failure site. A sample part of a similar component that has not failed, prefer- ably one that has run successfully in production, also is desirable. If replace- ment parts are generally produced in batch lots, a sample also should be taken from the replacement parts bin for com- parative analysis.
Unfortunately when a failed die
PETER ULINTZ
component is discovered, the immedi- ate response is to repair or replace the damaged or broken component so pro- duction may resume. Most attempts at a failure investigation end here unless the failure was catastrophic or it con- tinues to repeat throughout the pro- duction run.
If the failure continues to repeat during production, manufacturing will demand that the problem be fixed—not necessarily solved—because it causes excessive downtime and jeopardizes timely shipments to the customer. Under these time-pressured conditions a properly devised investigation pro- cedure will not be employed, which usually results in important evidence being discarded or destroyed.
The time employed collecting back- ground data is vital to the success of any failure analysis. A thorough under- standing of the entire manufacturing process, the service histories of the failed component(s), and reconstructing, at least as much as possible, the entire sequence of events leading up to the fail- ure are all necessary steps.
Getting acquainted with the manu- facturing process requires, at minimum: die detail drawings, technical specifica- tions, component process flow diagrams and all relevant fabrication information including the die materials used, machin- ing methods employed, heat treatment process and surface treatment data including the application methods.
The ability to accurately complete a service history will depend on how detailed the record keeping in the plant was prior to the failure. In collecting service histories, environmental details are of particular importance. These include normal and abnormal load- ing, accidental overloads, cyclic load-
24 METALFORMING / DECEMBER 2010
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TOOLING BY DESIGN Stamping-Die Failure Analysis