Daniel Schaeffler Daniel Schaeffler

Approach Stamping Problems Like a Crime Scene Investigator

April 29, 2021

Prime-time television-viewing options inundate us with police-procedural dramas like CSI: Crime Scene Investigation, and NCIS, among dozens more. In them, we see analysts combing through the area surrounding a mishap and well-meaning people traipsing through crime scenes inadvertently contaminating evidence. 

newspaper-magnifying-glassWhen problems occur in our stamping plants, we should follow similar investigative procedures, while working to maintain the integrity of the data. The first step television teaches us: Define and describe the victim. While a crime-drama detective may start by looking at the information contained on the crime victim’s driver’s license, we can look at the certified sheet metal properties that accompany each material shipment. Here you will find a description of certain material properties that, at one time anyway, provided an accurate representation—yield, tensile and elongation properties from the coil end, for example, much like a person’s height and weight. Because you know the coil number of the shipment, your metal supplier may be able to tell you if other coils in your inventory also are at risk. 

Next, we need to accurately describe the problem. On television, maybe it’s a stabbing or a drowning, each with a different root cause. In our stamping plant, we might have splits, smiles, wrinkles, edge cracking or dimensional issues.

The good crime detective will ask for a toxicology screen, to see if the victim’s blood chemistry meshes with expectations. Chemistry is important for us, as are the material’s tensile properties. Although the metal certs will prove useful, it’s wise to send a material-test coupon from the next blank in the lift to an independent lab for analysis. The certs which came with the shipment were generated from the end of what might be a mile-long coil. Checking a blank near the offending one is a better way to ensure meaningful results.  Be sure to label the sample with the coil number and rolling direction.

Then, a crime-drama detective might check around the victim to look for a weapon that may have caused the wound. Rarely is it something so obvious, like a hatchet. Therefore, good detectives must look carefully and rely on their knowledge of the process involved. They look for fingerprints and stains, for example. Likewise, stamped metal parts will provide clues as to the nature of a problem. Check the underside of the part for scoring, which occurs as the sheet metal flows over a tool radius. If the scoring looks rough and abraded, that may indicate restricted metal flow. And if your part does have stains on it, that may indicate lube puddling in one location and, therefore, not effectively reducing friction across the entire part. 

Also consider the environmental conditions at the time of the mishap. While a detective may want to know if a crime occurred on a dark and rainy night, in our case, confirm that the press line was properly set up according to the recipe, and that tonnage and lubricant monitors were in good working order and reading nominal conditions.  

A crime detective then will check the records to see if crimes had occurred in the past with a similar modus operandi, and if the victims were of similar gender or age, indicating the possibility of a serial killer. Similarities among problem stampings might include material grade or coating. Common patterns in defect parts may lead to a short list of suspects.

A good detective knows to interview witnesses to determine if they saw anything suspicious. In a stamping plant, several production people live with your parts and processes day in and day out. Press operators make great witnesses and can tell the difference between normal and strange behavior. Maybe parts from one run exited the press hotter than usual. This may indicate a lube issue, or that the material lift in question had a greater than typical tensile strength.

Review documents such as operator and maintenance logs to look for any trends that might define the conditions contributing to the problem. These include noting the time or shift when the defects occurred, the position within the coil (since you keep track of which lifts are a problem), and the corner of the part where a problem recurs.

Like bullet fragments at a crime scene, you also might be fortunate to uncover some physical evidence left behind. If, for example, a defective part can be traced to metal flow issues, we can compare a draw panel against the one saved from tooling buyoff when all conditions were sufficient to produce an acceptable panel. In the case of splits initiating at a flanged edge, compare the cut-edge condition against the edge condition from those early buyoff panels. It may indicate improper clearance for the material grade and thickness, or possibly wear or chipping of the cutting knives. 

Finally, confirm that the victim (the problem stamping) was behaving normally at the time of the incident. A metal forming strain analysis prior to the start of production determined that the chosen metal grade was appropriate to form the targeted design. Perform another analysis when you experience defects to confirm if material-flow characteristics have changed.

When evaluating stamping problems, gather evidence and carefully analyze the crime scene like a pro. Don’t be Inspector Clouseau and jump to conclusions. MF

Industry-Related Terms: Blank, Case, Corner, Draw, Edge, Form, Forming, Nominal, Run, Stains, Thickness
View Glossary of Metalforming Terms


See also: Engineering Quality Solutions, Inc., 4M Partners, LLC

Technologies: Materials


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