Application cases of end mills in mold repair processing

Case Studies: Application of End Mills in Mold Repair Machining

Mold repair is a critical process in extending tool lifespan and maintaining production quality, often requiring precise re-machining of damaged or worn areas. End mills are indispensable for tasks such as re-contouring cavities, repairing gate systems, or restoring surface finishes. Below are practical examples demonstrating how end mills are effectively used in mold repair scenarios.

1. Repairing Worn Cavity Surfaces in Injection Molds

Over time, repeated cycles of injection molding can lead to erosion or wear on cavity surfaces, causing dimensional inaccuracies or surface defects. End mills enable localized repairs without replacing the entire mold.

• Challenge: A plastic injection mold cavity showed signs of wear near the gate, resulting in flash formation during production. The goal was to restore the original geometry without altering adjacent features.
• Solution: A carbide end mill with a 2-flute design and a 0.5 mm corner radius was used for precision re-machining. The tool was programmed to follow the original CAD model, with climb milling employed to minimize surface roughness.
• Outcome: The repaired cavity achieved a surface finish of Ra 0.4 µm, eliminating flash and restoring part quality. The process reduced downtime by 60% compared to mold replacement.
• Key Technique: For localized repairs, use a tool diameter slightly smaller than the worn area to ensure controlled material removal. High-pressure coolant was applied to dissipate heat and prevent thermal distortion.

2. Restoring Gate and Runner Systems in Die-Casting Molds

Gate and runner systems in die-casting molds are prone to erosion due to high-velocity metal flow, leading to imbalanced filling or porosity. End mills can reshape these channels to optimize flow dynamics.

• Challenge: A die-casting mold’s submarine gate was eroded, causing uneven metal distribution and cold shuts in the final parts. The repair needed to restore the gate’s original taper and diameter.
• Solution: A 4-flute end mill with a variable helix angle was selected to reduce vibration during machining. The tool performed a roughing pass to remove damaged material, followed by a finishing pass with a 0.2 mm radial stock allowance.
• Outcome: The restored gate achieved a consistent taper of 3°, improving metal flow and eliminating cold shuts. The mold’s operational life was extended by an additional 50,000 cycles.
• Key Technique: For tapered gates, program the tool path to maintain a constant engagement angle, preventing tool overload. A light finishing pass with a polished flute surface ensured smooth gate edges.

3. Fixing Cracks in High-Strength Steel Molds

Cracks in molds made from high-strength steel, such as H13 or S7, can occur due to thermal fatigue or mechanical stress. End mills are used to machine out cracks before welding or filling.

• Challenge: A stamping mold developed a 2 mm deep crack near a critical bending radius. The repair required removing the cracked material without damaging the surrounding geometry.
• Solution: A solid carbide end mill with a 1 mm diameter and a 0.2 mm corner radius was used to machine a V-shaped groove along the crack line. The tool operated at a reduced spindle speed (3,000 RPM) and a feed rate of 0.02 mm/tooth to minimize heat generation.
• Outcome: The crack was fully removed, and the groove was filled with a compatible welding material. Post-weld machining with the same end mill restored the original radius, achieving a surface finish of Ra 0.8 µm.
• Key Technique: For crack repair, use a step-over strategy of 20–30% of the tool diameter to ensure complete material removal. A peck drilling motion can be incorporated for deep cracks to improve chip evacuation.

4. Re-Machining Ejector Pin Holes in Large-Scale Molds

Ejector pin holes can become worn or misaligned over time, leading to sticking or uneven ejection. End mills provide a precise method for re-boring these holes to the correct diameter and depth.

• Challenge: In a 2-ton automotive mold, several ejector pin holes were enlarged due to repeated use, causing inconsistent ejection forces. The repair needed to restore the holes to their original 8 mm diameter.
• Solution: A 6 mm diameter end mill with a 4-flute design was used to pre-drill the holes, followed by a boring operation with a 7.8 mm reamer. The end mill’s high rigidity ensured straight, concentric holes.
• Outcome: The restored ejector pins operated smoothly, eliminating part deformation during ejection. The process was completed in 4 hours, compared to 12 hours for manual reaming.
• Key Technique: For hole repairs, use a drill-and-ream approach to maintain accuracy. Program the end mill to center-cut first, then expand the hole incrementally to avoid tool deflection.

By leveraging end mills for targeted repairs, manufacturers can extend mold life, reduce production downtime, and maintain part quality. Adaptability to different materials, geometries, and damage types makes end mills a versatile solution for mold maintenance challenges.