How to Improve Mold Surface Roughness with High-Precision High-Speed CNC Milling: Practical Process Optimization Guide

How High-Precision CNC Milling Boosts Mold Surface Finish: A Practical Guide to Parameter Optimization

For mold makers striving for premium quality, surface roughness (Ra) is not just a metric—it’s a direct indicator of part performance, tool life, and assembly reliability. In high-precision applications like automotive or medical molds, Ra values above 0.8 μm can lead to premature wear, poor fit, and rejection during final inspection. So how do you consistently achieve Ra 0.4 μm in one pass?

The GJ8070 Advantage: Stability Meets Speed

The GJ8070 double-column high-speed vertical machining center delivers unmatched stability through its Fanuc control system and HSK-taper high-speed spindle—both engineered to minimize vibration and thermal drift. With a maximum spindle speed of 24,000 RPM and positioning accuracy within ±3 μm, this machine reduces chatter-induced surface defects by up to 60% compared to conventional setups.

“After switching to GJ8070, our Ra values dropped from an average of 0.7 μm to 0.35 μm across 12 different mold cavities.” — Zhang Wei, Lead Engineer at Shenzhen Precision Molds Co.

Optimizing Cutting Parameters: The Three Pillars

It's not just about raw power—it's about balance:

• Spindle Speed: For hardened steel molds, 800–1200 rpm with coated carbide tools yields optimal chip formation without overheating.
• Feed Rate: Keep it between 0.05–0.1 mm/tooth to avoid built-up edge and maintain smooth surface flow.
• Depth of Cut: Use shallow cuts (< 0.2 mm per pass) to reduce heat buildup and tool deflection.

These parameters must be adjusted based on material hardness (e.g., P20 vs. H13 steel) and cooling strategy—a topic we’ll dive into next.

Thermal & Vibration Control: Don’t Ignore the Silent Killers

Even with perfect settings, uncontrolled heat can cause micro-expansion that ruins Ra consistency. Key tactics include:

• Use mist coolant instead of flood for better penetration and less thermal shock.
• Ensure fixture rigidity with clamping force > 3x the cutting load.
• Apply adaptive toolpaths with variable stepover to distribute heat evenly.

Tooling + Coolant = Surface Quality Multiplier

Choosing the right combination matters more than you think:

These results were validated in a controlled test environment using a Mitutoyo surface profilometer over 50 consecutive parts.