A French company developing wireless environmental sensors for agricultural monitoring had designed a custom spring contact to connect their sensor module to a removable battery pack. The contact needed to be formed from 0.15mm thick Stainless Steel 301 and was required to maintain a specific gap between two parallel beams to ensure proper battery insertion force.
The Problem
The initial batch of prototype parts, produced using a simple bending fixture, exhibited significant springback. After the bending force was released, the formed angle opened up by nearly 8 degrees, completely altering the designed gap width and making the battery connection either too loose or impossibly tight. The client needed a reliable, repeatable process for 3,000 pieces.
Understanding Springback in Thin Stainless Steel
Stainless Steel 301 is known for its high strength and excellent corrosion resistance, but it also exhibits considerable elastic recovery after forming. Predicting and compensating for springback is essential, especially when working with material this thin, where small angular deviations translate to large relative changes in the final part geometry.
Our Solution: Coining the Bend Radius
To overcome this challenge, our tooling team employed a technique called coining. Instead of simply air-bending the material (where the metal only touches the punch tip and die shoulders), we designed the die to apply high compressive pressure directly to the bend radius area.
1.Increased Localized Pressure: By squeezing the material at the exact point of the bend, we effectively "set" the new shape and minimized elastic recovery.
2.Over-Bend Compensation: Even with coining, a small amount of springback was predicted. We machined the punch and die angles to be 2.5 degrees more acute than the final desired angle.
Iterative Adjustment: After a short trial run of 50 pieces, we measured the resulting angle and made a final micro-adjustment to the die angle before running the full 3,000-piece batch.
The Result
The full production run of 3,000 contacts exhibited exceptional consistency. The critical gap width was maintained within a tolerance band of ±0.03mm, ensuring uniform battery insertion force across all sensors. The client was able to proceed with their field trials in vineyards across southern France without any reported connection issues.
Takeaway for European Designers
This case highlights a common pitfall in precision metal forming: material behavior matters as much as CAD geometry. At Tingfeng Hardware, we have deep experience compensating for the springback characteristics of various alloys. This expertise ensures that the parts you receive match the dimensions on your drawing, not the approximations of a generic bending calculator.