Scuffing in High-Pressure Die Casting Molds
As aCatTech, specializing in high-pressure die casting molds and casting production for the automotive sector, we have gained profound insights through years of practice that scuffing and heat checking are common and challenging issues in high-pressure die casting mold production.
These issues not only affect casting quality but also shorten mold lifespan and increase production costs. Based on our experience, we will elaborate on the causes, prevention strategies, emergency treatment, and lifespan restoration solutions for these two major issues, and provide professional recommendations.
Scuffing in High-Pressure Die Casting Molds
In the high-pressure die casting production of automotive components, mold scuffing is a frequent issue encountered by aCatTech. Through extensive practical summary, we have identified the main causes as follows.
Core Cause Analysis of Scuffing Issues
- Mold Design Defects
In our production practice, we have repeatedly encountered scuffing caused by mold design flaws. For example, insufficient draft angles (less than the industry standard of 3°, or even negative draft angles) directly lead to significantly increased ejection resistance, thereby causing scuffing. When cavity surface roughness exceeds standards (Ra > 0.8μm), micro-protrusions form mechanical interlocking points, resulting in scuffing during ejection. Improper fit clearance of inserts/slides—clearance < 0.02mm easily causes extrusion scuffing, while clearance > 0.1mm leads to flash tearing and subsequent scuffing.
- Material and Processing Issues
We have found that insufficient die steel hardness (HRC < 46) accelerates surface wear, easily forming erosion grooves and causing scuffing. Improper heat treatment leading to surface decarburization reduces the mold’s anti-adhesion properties, increasing the likelihood of scuffing. Additionally, unpolished EDM (Electrical Discharge Machining) surfaces leave residual discharge erosion marks, which serve as starting points for scuffing—this has been repeatedly verified in our production.
- Improper Process Parameters and Maintenance
Excessively high injection speeds (> 50m/s) cause molten metal to scour the cavity at high speed, resulting in surface damage and subsequent scuffing. Uneven or ineffective release agent spraying leads to local lubrication loss, causing sticking and scuffing. Insufficient mold preheating (< 150℃) exacerbates cooling shrinkage of molten metal, increasing ejection resistance and scuffing risks.
Design of Systematic Prevention Measures
- Design Stage Optimization
In the design phase, aCatTech uses CAE simulation for the ejection process to ensure critical draft angles ≥ 5°, reducing ejection resistance from the source. For scuffing-prone areas (e.g., deep cavities, thin-walled structures), we install removable inserts for easy later maintenance and replacement. Meanwhile, we strictly control cavity surface roughness to Ra ≤ 0.4μm and mating surface precision to IT6 grade, reducing the formation of mechanical interlocking points.
- Material and Manufacturing Control
We select high-quality hot-work die steels such as H13 and 8407, and reduce sulfur content (≤ 0.005%) through electroslag remelting to enhance die steel performance. In heat treatment, we perform high-temperature quenching (1050℃) + triple tempering (560℃) to control surface hardness at HRC 48-52, enhancing mold wear resistance. After finishing, mirror polishing is conducted to completely eliminate machining marks and avoid scuffing initiation points.
- Production Process Control
During production, we implement staged control of injection speed: ≤ 30m/s in the filling stage and ≥ 80m/s in the boosting stage to reduce molten metal erosion on the cavity. Water-based release agents (5%-8% concentration) are used with automatic spraying systems to ensure uniform coverage and effective lubrication. Molds are preheated to 180-220℃, and oil temperature machines maintain mold temperature fluctuations ≤ ±10℃ to reduce scuffing caused by temperature changes.
