Our client’s product contained brass pins formed from wire, then electroplated with nickel and gold, then annealed, and finally bent to the final shape. Pins were breaking during the bending step. The scrap rate was 21%. This prevented meeting delivery schedules and resulted in high scrap costs.
The pin breakage indicated a problem with the anneal process. Annealing is used to improve metal ductility. It also results in reduced strength and hardness. Sufficient ductility was needed to enable bending the pins. But losing too much strength was a concern.
We performed metallurgical examinations of broken and intact pins. This included looking at grain structure and measuring hardness. The broken pins showed no signs of having been annealed. Intact pins showed signs of partial anneal. This data indicated two causes of the problem: non-uniform furnace temperature and annealing temperature too low.
We made temperature measurements and found the temperature was not uniform throughout the furnace. That was fixed by installing a fan in the furnace.
Then we ran experiments to see the effects of annealing temperature on pin microstructure, hardness, and ductility. The data indicated that increasing the temperature 25 degrees gave the best combination of ductility and strength. This was still a partial anneal.
The higher temperature was implemented and the pin breakage stopped.
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Michael Pfeifer, Ph.D., P.E. is President of Industrial Metallurgists and a metallurgical engineering consultant with more than 30 years of experience in product design, manufacturing, failure analysis, and metallurgy training. He helps clients worldwide solve design and manufacturing problems and is the author of Materials Enabled Designs.
