Automotive High-Load Compression Spring: Oil-Tempered Wire, 5M-Cycle Fatigue, PPAP Documentation
Compression springs in automotive chassis and driveline are parts that live and die by fatigue life: tens of thousands of cycles a day, a design life of five million, and a failure is a safety incident. What this demands from a supplier is not just "can you coil it" - it is controlled material sourcing, traceable heat treatment parameters, and fatigue verification data that maps to a specific heat number for every batch.
Project Background & Challenge
A Tier-1 automotive parts supplier was qualifying a local source for a suspension assist spring: oil-tempered spring wire, 2.5mm diameter, 22mm OD, 80mm free length, 5-million-cycle fatigue at working stress, and a complete PPAP package. They had been importing with 10-week lead times, annual price increases, and no capacity in the supplier's quarterly plan.
The challenges: oil-tempered wire consistency directly drives fatigue life; the stress-relief temper window after coiling is narrow and mishandling causes early fracture; and automotive documentation - material certificates through process control records - is non-negotiable.
BQUQ Process Solution
Material & Coiling Control
Wire is sourced from a major mill with incoming verification of diameter, tensile and decarburization. Coiling runs on closed-loop tension machines for stable pitch and free length; stress-relief temper temperature and time are documented per batch after coiling, fully traceable.
Fatigue Verification & Documentation
Fatigue testing to 5 million cycles is sampled per batch with life curves issued; hardness, salt spray and surface quality are sampled per batch. Documentation is compiled to PPAP requirements - material certificates, process parameter records, inspection reports and packaging specs - and delivered with the first shipment.
Key Specifications
| Item | Specification |
|---|---|
| Material | Oil-tempered spring wire (55CrSi / 60Si2MnA options) |
| Wire diameter | φ1.0-6.0mm |
| Fatigue life | 5M cycles, batch sampling with curves |
| Surface | Black oxide / zinc / Dacromet (per drawing) |
| Inspection | Hardness + salt spray + fatigue + full dimensions |
| Volume | From 50K pcs/batch, PPAP package included |
| Delivery | PPAP samples 4 weeks, production 3 weeks per batch |
Quality Control & Delivery
From wire heat number to finished batch, everything is traceable. First article is fully verified before production and process records are archived. PPAP samples ship in 4 weeks; after the customer's bench validation the program rolls batch to batch with documentation included.
Related Products & Resources
To see more parts in this category and how we scale them, browse the Compression Springs category page, or these related products:
Related Q&A: Which Spring Wire Is Better: Music Wire or Oil-Tempered Wire? More Q&A is in our FAQ Center.
For our capabilities, equipment and quality system, visit About BQUQ and Factory Strength.
FAQ
How do you guarantee automotive fatigue life?
Three gates: incoming verification of oil-tempered wire from a major mill, documented and controlled coiling/temper parameters, and 5-million-cycle fatigue sampling per batch. The curves ship with the parts.
Can you deliver a complete PPAP package?
Yes. Material certificates, process parameter records, dimensional and hardness reports, salt spray results and packaging specs are compiled to PPAP level requirements and shipped with the first samples.
Do you have automotive supply history?
Our springs and stampings supply automotive electronics and parts customers on a long-term basis under ISO9001:2015. Specific OEM system requirements are handled per your drawing and agreement, with upfront documentation support at no extra charge.
