Mold Process for Preventing Heat Treatment Cracking

Process for Preventing Heat Treatment Cracking

Cracking of parts (typically core components of a mold, such as cores, cavities, sliders, ejector pins, etc.) after heat treatment has a catastrophic and systemic impact on a mold manufacturing project, far exceeding the scrapping of a single component.

Direct Impact: Failure of Core Function and Loss of Precision

A cracked part is unusable, directly preventing mold assembly or trial. Even microscopic cracks can rapidly propagate under the cyclic high-pressure loading of injection or stamping, leading to catastrophic failure (e.g., cavity fracture). This not only renders the entire mold scrap but also renders hundreds of thousands of dollars' worth of machining hours (precision milling, EDM, polishing) instantly obsolete.

Indirect Impact: Loss of Project Control and Crisis of Trust

Mold manufacturing is a highly sequential process. Heat treatment cracking of a key part disrupts the entire production rhythm. Lead times are typically delayed by weeks or months due to reordering materials, remachining, and repeating heat treatment and finishing processes. This severely impacts the client's product launch schedule, exposes the mold maker to heavy delay penalties, and damages its reputation as a reliable supplier.

Economic Impact: Exponential Cost Increase

The financial impact goes far beyond remaking one part. It includes: The sunk cost of all manufacturing already invested in the failed part; The cost of materials and labor for the second manufacture; Overtime and expediting fees to recover the schedule;  Potential client compensation claims. The total cost is often several times the value of the original part and severely erodes project profitability.

Systemic Reflection: Exposure of Collaborative Design Flaws

Cracking fundamentally exposes a failure in collaboration across the chain from mold design to process planning and heat treatment execution. For instance, design features like sharp corners or abrupt section changes, or rough machining that fails to leave adequate fillets and stock as specified, create stress concentration points during heat treatment. This forces mold makers to treat heat treatability as a core element of front-end design review, promoting integrated collaboration between design, machining, and heat treatment processes.

Heat treatment cracking of parts is one of the most critical defects to avoid in mold manufacturing. It strikes a project on multiple fronts: technical, delivery, economic, and reputational. Successful mold manufacturers must establish systematic prevention mechanisms—through optimizing part design (avoiding stress concentrations), strictly controlling pre-treatment machining processes, and engaging in technical collaboration with heat treatment suppliers—rather than resorting to post-failure remedies.

Process for Preventing Heat Treatment Cracking

Currently, the parts are experiencing cracking after heat treatment, which severely impacts mold delivery schedules and production costs. The primary reason is insufficient understanding of the heat treatment process, leading to such abnormalities. Preventive measures must be implemented in advance for critical processes to ensure no cracking occurs post-heat treatment.

The cause of cracking is the concentration of internal stress or excessive temperature differentials during the heating and cooling stages of the material, leading to molecular-level separation and fracture.

To address the root cause of cracking, the process must ensure that parts after rough machining do not exhibit sharp edges, thin sections, acute angles, or significant thickness variations. Where necessary, the process should incorporate reinforcing ribs in advance to enhance strength.

Illustrated Guide to Preventive Heat Treatment of Parts

1. During rough machining, select tools with a radius greater than R3 and preserve the fillet radius at the root to prevent the formation of sharp corners.

2 . When the thickness variation in the design drawing exceeds more than twice, leave additional stock during rough machining to prevent uneven heat dissipation. Thicker areas dissipate heat slowly, while thinner areas dissipate heat quickly, leading to significant temperature differences and tensile cracking.

3. Ensure the distance from hole-type features to the edge is at least twice the hole diameter.