Subtractive vs Hybrid CNC-AM for Tool Repair

By PFT, Shenzhen

Keeping production lines running smoothly in 2025 demands maximizing the lifespan of critical, high-cost tooling. Cutting tools inevitably wear down, leading to reduced part quality, increased scrap rates, and costly downtime for replacement. While conventional subtractive CNC machining has long been the standard for tool repair and refurbishment, the emergence of integrated Hybrid CNC-Additive Manufacturing (AM) systems offers a promising alternative. Hybrid systems combine traditional milling/turning with directed energy deposition (DED) AM processes like laser cladding or wire arc additive manufacturing (WAAM), all within a single machine platform.

2 Methods

• Subtractive CNC Repair: Worn areas were machined away on a 5-axis machining center to restore the original geometry. Tool paths were generated from CAD models of the pristine tool.
• Hybrid CNC-AM Repair: Worn areas were first prepared via light machining. Missing material was then rebuilt using laser-based DED (powder feed) on a dedicated hybrid CNC-AM machine (e.g., DMG MORI LASERTEC, Mazak INTEGREX i-AM). Matching tool steel alloy powder was deposited. Finally, the deposited material was finish-machined to the precise final geometry within the same setup. Deposition parameters (laser power, feed rate, overlap) were optimized for minimal heat input and dilution.
• Geometry: Pre-repair and post-repair geometries were scanned using a high-precision optical CMM (Coordinate Measuring Machine). Dimensional accuracy was quantified against CAD models.
• Surface Integrity: Surface roughness (Ra, Rz) was measured perpendicular to the cutting direction using a contact profilometer. Microhardness (HV0.3) profiles were taken across the repaired zones and heat-affected zones (HAZ).
• Material Properties: Cross-sections of repaired areas were prepared, etched, and examined under optical and scanning electron microscopy (SEM) to assess microstructure, porosity, and bonding integrity.
• Process Time: Total machine time for each repair process (setup, machining, deposition for hybrid, finishing) was recorded.
• Reference Data: Results were compared against published benchmarks for tool performance and established repair standards.

3.1 Dimensional Accuracy and Geometric Restoration

• 3.2 Material Properties and Microstructure
• 3.3 Process Efficiency

​4 Discussion

This comparative study demonstrates that hybrid CNC-Additive Manufacturing offers a powerful and often superior alternative to conventional subtractive CNC machining for the repair of high-value cutting tools, particularly those with complex geometries or significant localized damage. Key findings show hybrid CNC-AM:

• Superiority for Complexity: Hybrid CNC-AM's significant advantage lies in repairing tools with complex geometries or localized severe damage (chips, broken edges). The additive capability allows for targeted restoration without compromising the core tool body, preserving more of the original expensive material and geometry – something subtractive methods cannot achieve without fundamental redesign.
• Material Performance: The successful deposition of tool-grade alloys with appropriate hardness and a sound microstructure confirms the technical feasibility of hybrid repair. The controlled heat input minimized detrimental effects on the base material.
• Process Time Trade-off: While subtractive methods are quicker for straightforward wear, hybrid becomes competitive or faster for complex repairs. The value lies not just in time, but in salvaging tools that might otherwise be scrapped using subtractive-only methods.
• Limitations: This study focused on technical feasibility and initial properties. Long-term performance data under actual cutting conditions, including wear resistance and fatigue life compared to new tools and subtractive repairs, is essential. The initial capital cost of hybrid CNC-AM equipment is also significantly higher than standard CNC machines. Powder material cost is a factor, though often offset by material savings on the tool itself.
• Practical Implication: For manufacturers dealing with a high volume of complex, high-value tooling, investing in hybrid CNC-AM repair capability presents a compelling case for reducing replacement costs and tooling inventory. It enables true restoration, not just re-machining. For simpler tools or less complex wear, subtractive methods remain efficient and cost-effective.

While subtractive CNC remains efficient for simpler wear patterns, hybrid CNC-AM unlocks significant value for complex tool repair applications. The recommendation is for manufacturers to evaluate their specific tooling portfolio and failure modes. Implementation should focus on high-value tools with complex geometries where replacement cost is high. Further research should prioritize long-term performance validation in operational settings and detailed cost-benefit analyses incorporating tool life extension.