Urethane Springs Replace Corroding Metal Springs in a Wet Stamping Die
Water-soluble coolant was stress-corrosion cracking chrome-silicon coil springs in a drawing die every 80,000 cycles, scratching panels and stopping the line 18 times a year. Hydrolysis-stable polyether urethane springs eliminated the failures and cut tool operating cost 72%.
PROJECT OVERVIEW
"An automotive body stamper ran a 2-stage draw and trim transfer die producing 1.2 million galvanized chassis reinforcement panels a year. Wet stamping with a water-soluble coolant (95% water, 5% oil) kept the draw ring at an 18,000 daN holding force, delivered by twenty-four heavy-load ISO 10243 coil springs packed in pockets under the ring. The coolant washed away the protective grease, and the chrome-silicon coils started cracking after just 50,000 to 80,000 cycles."
Molded polyether urethane spring blocks rated for continuous coolant exposure
PAIN POINTS
- Stress corrosion cracking (SCC) on the coil surface after 50,000–80,000 cycles, with fragments breaking loose mid-run
- Broken spring fragments scratched drawn panels — 3.1% scrap plus polishing time after every stop
- Emulsified lubricant formed sticky residue that clogged the coils, unbalanced the draw ring and caused wrinkling
- 18 failures a year, each a 2-hour line stop at USD 1,500/hour — USD 54,000 in downtime alone
OUR SOLUTION
- Replaced all 24 coils with custom-cast polyether urethane spring blocks at Shore A90, specified across A70–A95 for different stations
- Polyether chemistry resists hydrolysis — the ether linkage (R-O-R) does not break down in water like polyester-based urethane does
- Hollow cylinder design with a center vent hole, so the block bulges inward and outward under load; pockets widened with ~15% diametral clearance for the bulge
- Blocks drop straight in over the existing guide pins; pocket bores machined to ±0.005 mm with no die base modification
MEASURED RESULTS
| Spring service life | 80,000 cycles (chrome-silicon coil) → 1,200,000+ cycles (polyether urethane) — 15× longer |
| Corrosion / SCC failures | Eliminated — zero spring breakages in 12 months |
| Line stops | 18 per year → 0 per year; 36 hours of downtime saved |
| Downtime + spring cost | USD 54,000 + USD 18,600 → USD 20,300 (maintenance only) — 72% total operating cost reduction |
| Part scrap rate | 3.1% → 0.05% — 98% reduction in scrap and rework |
ENGINEERING NOTE
"Urethane also damps the impact of the draw stroke — the block absorbs energy instead of releasing it, which is why wrinkles disappeared along with the breakages. The blocks are custom cast in-house at Shore A70–A95, and the guide pins they run on are ground to ±0.002 mm, so the fix needed no changes to the die base or the press line."
Polyether urethane blocks cast in Shore A70–A95, drop-in over existing guide pins
YOUR APPLICATION MAY DIFFER
"Send us the spring pocket drawing and the coolant chemistry — we will recommend the Shore hardness, block geometry and bulge allowance for your die, with a 24-hour DFM response under IATF 16949-level process control."