AHSS Properties & Blank Die Standards
With the continuing Government requirements to produce safer and more efficient vehicles, the demand for stronger and lighter components will continue to increase. Advanced High-Strength Steels (AHSS) are filling this demand. While these materials are great for increasing our EV range, stamping and blanking these materials will require adherence to die standards and die maintenance practices. Maintaining uptime and part quality could challenge tooling PM Budgets if these standards are not followed.
Understanding just a few of the major differences between traditional sheet steel and AHSS will help in maintaining robust KPIs. One of the most prevalent AHSS’s we deal with is Dual-phase (DP). DP steels are made up of ferrite and martensite. The martensite content in DP steels can be high, up to 20%. This is noteworthy because martensite is extremely hard and is the same phase that makes up our hardened tool steels.
Challenges in AHSS Blanking
Another consideration is AHSS’s susceptibility to localized failure. Most notably, trim edge failure. Problems such as inadequate punch entry, double shear, and rough fracture area can lead to a lessened edge stretchability in later operations. Aiming for the standard 8-10% roll over, 10-25% Burnish and a fracture length of 60-80% is a good place to start. Keep in mind – with stronger AHSS, this may be hard to hit due to quicker crack initiation.
Die Maintenance & Challenges
One of the most common problems we see in plants new to AHSS blanking is a drastic reduction in tool life. Typical inconsistencies found in traditional blanking tend to have serious consequences when cutting AHSS. Varying punch and die clearances can exponentially increase required cutting forces – increasing wear. Large shim packs under cutting steel mushrooms under increased pressure and increase the surface area from dirt and silvers to hind. Both these events can lead to movement in the details – increasing wear. Subpar surface finishes increase friction on the cutting steels – increasing wear. While milder blanking operations can absorb some of these shortcuts, high-strength cutting is not as forgiving.
Tackling Excessive Wear in AHSS Blanking
Persistent Problem – Excessive Wear
We frequently see stampers struggling to reach 50,000, with many of the modern high-strength steel on the market today. Many end up with sharpening details after just a couple of runs. This leads to excessive shimming or welding, which exacerbates the problem.
Analyzing & Addressing Wear Issues
Methodical and systematic solutions can typically be implemented at relatively low costs. To do this, we must have sufficient data to improve tool life to support our hypotheses.
- How many hits are we getting out of the tool?
- What type of wear is breaking down the tools?
- Is tool wear consistent, or does failure happen at unpredictable intervals?
- What are the material’s incoming mechanical properties?
- What are the mechanical properties of the cutting steels?
These questions do not cover all the variables that may cause excessive wear, but they help show the bigger picture.
For example, corrective actions to fix deformation wear are likely different from punch chipping. Changing tool steels, trim die clearances, or coatings without analyzing the variables involved is a shot in the dark. While these changes may show marginal results, the costs involved in finding a substantial solution are typically inconsequential.
Types of Wear & Solutions
One of the essential questions to answer is what type of wear is seen. Some of the most frequent failure conditions are abrasive, adhesive, chipping, galling, deformation, and cracking. Most commonly, excessive tool wear is caused by a combination of abrasive and adhesive wear. These two conditions also tend to lead to the latter failure modes.
Different wear conditions may necessitate distinct corrective actions, emphasizing the importance of analyzing variables before making changes to tool steels, trim die clearances, or coatings.
Improve the Blanking Process for AHSS with Help from Phoenix
Mastering the blanking process for Advanced High-Strength Steels involves a deep understanding of material properties, die standards, and systematic approaches to address wear issues, ultimately enhancing the overall efficiency of automotive manufacturing processes.
Understanding the intricacies of the blanking process for AHSS is vital for improving throughput and die work efficiency. The Phoenix Group, with a proven track record of success, offers expertise to leverage your establishment’s effectiveness.
If you’re interested in learning how The Phoenix Group can drive improvement at all levels of your organization, contact us today.