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A curved surface mold, in simple terms, is a perfect three-dimensional curved surface replicated on a solid material. It is a complex system engineering that involves digital design, CNC machining, and material mechanics.

1. Curved Surface Modeling and Parting Surface Design

The curved surface needs to be created in the computer using CAD software. The difficulty lies in the fact that the surface must be smooth - even a tiny imperfection that is invisible to the naked eye can cause a noticeable blemish on the product's surface after processing. What's more troublesome is the parting surface. It is no longer a flat surface but a complex curved surface. Poor design can result in the product either sticking to the mold or having sharp edges with burrs.

2. CNC Machining Process Planning

The core task during the CAM programming stage is to generate collision-free and high-precision tool paths. Therefore, during processing, the following issues will arise:

• Tool path parameter selection: The setting of the stepover (the distance between tool paths) and the step length (the length of each tool path) directly affects the surface quality. An excessively large stepover will result in obvious tool marks (increased surface roughness), while an excessively small stepover will significantly prolong the processing time.

• Interference and collision risks.

• Material deformation control: The mold blanks are mostly made of steel or aluminum. After removing a large amount of material during rough machining, the residual stress in the workpiece re-distributes, which may cause unexpected deformation of the mold. In addition, during the fine machining process, the cutting heat will cause local thermal deformation, and the size will deviate after the workpiece cools down.

3. Measurement and Mold Repair

The detection of curved surface molds usually uses a three-coordinate measuring machine to sample the curved surface at multiple points and compare it with the design model. Unlike flat or cylindrical surfaces, the measurement of free-form surfaces cannot be accomplished using simple measuring tools. The sampling strategy and evaluation methods have specific requirements. If the product size exceeds the tolerance after trial molding, the defect location and attribution are relatively complex, and the repair work often requires reprogramming and machining, resulting in high costs.