Overview
For manufacturers supplying precision components into the automotive sector, achieving and sustaining high process capability (CPK) is not optional—it’s a requirement. This case study outlines how a specialized garter spring manufacturer significantly improved CPK across its product lines through process simplification, standardization, and deep operational expertise.
With over 63 years of experience exclusively producing garter springs, the organization leveraged its niche focus to refine every aspect of production—from APQP documentation to machine utilization.
The Challenge
Automotive garter springs are critical components in sealing systems, where dimensional variation directly impacts performance. The company faced several challenges common in high-mix, precision manufacturing environments:
- Complex and redundant APQP documentation across similar parts
- Inconsistent operator interpretation of “best practices”
- Variation in CNC coiling programs between similar designs
- Lack of standardized stress relief parameters across materials
- Inefficient machine allocation for similar part families
These issues contributed to unnecessary variation, limiting achievable CPK levels.
Solution Strategy
1. Streamlined APQP Through Family-Based Schema
Instead of managing individual APQP documentation for each part number, the company transitioned to a family-based APQP schema.
Parts with similar:
- Wire diameters
- Coil diameters
- Materials
- Functional requirements
were grouped into standardized families.
Impact:
- Reduced documentation redundancy
- Improved consistency in control plans and PFMEAs
- Faster onboarding of new part numbers within existing families
- Reduced risk of oversight in quality planning
2. Converting Best Practices into Preventative Controls
Historically, many process “best practices” existed as tribal knowledge or informal guidelines. These were formalized into:
- Preventative controls within quality work instructions
- Visual pictograms to eliminate ambiguity
Examples included:
- Proper handling techniques for springs to avoid deformation
- Standardized inspection points during coiling and assembly
- Visual defect criteria for operators
Impact:
- Reduced operator-to-operator variation
- Improved training efficiency
- Stronger alignment with IATF 16949 requirements
- Increased process repeatability, directly improving CPK
3. Custom Garter Spring CNC Programming
Rather than relying on generic or legacy CNC programs, the company developed custom CNC programs specifically tailored for garter spring geometry.
These programs accounted for:
- Material springback behavior
- Loop formation consistency
- Tension control during coiling
Impact:
- Reduced variation in critical characteristics
- Improved first-pass yield
- Greater consistency across production runs
4. Standardized Stress Relief Temperatures
Material variation was addressed by implementing standardized stress relief temperatures for key materials:
- ASTM A227 (hard-drawn spring wire)
- ASTM A313 (stainless spring wire)
Instead of adjusting temperatures ad hoc, fixed, validated temperature ranges were established for each material type.
Impact:
- Reduced variability in mechanical properties
- Improved dimensional stability post-processing
- Enhanced consistency in final spring tension and geometry
5. Optimized Machine Utilization with Simplex Rapid Equipment
All production was standardized on Simplex Rapid coiling and assembly machines.
With 26 coilers available, the company implemented a strategic machine allocation approach:
- Parts are grouped by similarity (geometry, material, setup requirements)
- New jobs are assigned to machines already running comparable parts
Impact:
- Reduced setup variation
- Shorter changeover times
- Increased process stability
- Higher sustained CPK due to consistent machine conditions
Results
By implementing these initiatives, the company achieved measurable improvements:
- Increased CPK across critical characteristics
- Reduced process variation at both coiling and assembly stages
- Improved repeatability across shifts and operators
- Faster APQP deployment for new programs
- Higher customer confidence and reduced PPAP issues
Key Takeaways
- Standardization drives capability – Whether in documentation or processing, consistency reduces variation.
- Visual controls outperform written instructions alone – Pictograms significantly improve operator execution.
- Process specialization matters – 63 years focused solely on garter springs enabled deep process optimization.
- Machine strategy is as important as machine capability – Grouping similar jobs stabilizes output.
- Material control is critical – Standardized stress relief removes a major source of variation.
Conclusion
Improving CPK in automotive garter spring manufacturing is not the result of a single breakthrough, but rather the accumulation of disciplined improvements across documentation, process control, equipment strategy, and material handling. By aligning these elements under a unified, experience-driven approach, the company transformed variability into consistency—delivering the level of precision the automotive industry demands.