The service life of trimming dies in cold forging processes depends on multiple interrelated factors, including the material of the die, the complexity of the forged part, the type of fastener being produced (bolts, studs, screws, or nuts), and the maintenance practices employed. In general, a well-designed and properly maintained trimming die can last anywhere from 50,000 to over 500,000 strokes, but this range is influenced heavily by the operational and material conditions present in the manufacturing environment.
1. Role and Stress Factors on Trimming Dies
Trimming dies are used at the final stage of the cold forging process to remove excess flash and ensure a precise outer profile of the forged part. These dies endure repeated impact loads, high contact pressures, and frictional forces, especially when working with high-strength steels or stainless steel fasteners.
The mechanical and thermal stresses in trimming operations are significant. Since the die must shear hardened or work-hardened material at the parting line, the die edge experiences high wear and may suffer from chipping or cracking if the material or heat treatment is inadequate.
2. Material and Heat Treatment Influence
The choice of die steel has a major impact on trimming die life. Common materials include:
- SKD11 (D2 Tool Steel): Excellent wear resistance, commonly used for high-volume production.
- DC53: An improved version of SKD11 with higher toughness, better suited for complex profiles or high-speed trimming.
- Powder metallurgy steels (e.g., ASP23, CPM10V): Offer superior wear and chipping resistance for extremely high-volume operations.
Proper heat treatment—typically through vacuum hardening followed by multiple tempering cycles—ensures an optimal balance of hardness (typically HRC 58–62) and toughness, extending die life and reducing early failures.
3. Part Geometry and Forging Complexity
Fasteners with simple head profiles (e.g., standard hex bolts) exert less stress on the trimming die than those with complex, multi-lobed heads or special contours. Parts with greater flash volume require more energy to trim, increasing wear. Additionally, if the trimming operation must also deburr or chamfer, die life will typically decrease.
4. Die Maintenance and Lubrication
Regular polishing, inspection, and preventive maintenance are essential to achieving longer die life. Even high-quality dies will experience premature failure if neglected. Maintenance practices include:
- Checking for micro-cracks and edge rounding.
- Regrinding and resharpening of the trimming edges.
- Applying appropriate lubricants or anti-galling coatings to minimize adhesion and wear.
Some plants also implement die rotation strategies, where dies are swapped before they wear out completely, allowing them to be refurbished and reintroduced into the production line, further extending their total life cycle.
5. Typical Service Life Ranges
Below are rough benchmarks for trimming die life based on material and process quality:
| Fastener Material | Die Material | Expected Die Life (Strokes) |
| Low Carbon Steel | SKD11 | 100,000 – 300,000 |
| Alloy Steel | DC53 | 80,000 – 250,000 |
| Stainless Steel | ASP23 | 50,000 – 150,000 |
| High-Volume Production | PM Steel | 300,000 – 500,000+ |
Note: These values assume proper die design, fitment, and lubrication.
Conclusion
Trimming die life in cold forging is not fixed but rather a variable metric influenced by die material, part complexity, forging load, and shop-floor practices. With the correct combination of material selection, heat treatment, precision machining, and preventive maintenance, trimming dies can deliver high productivity and long service life, making them a critical cost and quality factor in the fastener production industry.