Precision Grinding Methods for Mold Parts and How to Control Deformation

Grinding is a key finishing process in mold manufacturing and is widely used to achieve high dimensional accuracy, parallelism, roundness, and surface quality. The main machine tools used in grinding include surface grinders, internal and external cylindrical grinders, and tool grinders.

During finish grinding, grinding deformation and grinding cracks must be strictly controlled. Even very small cracks may appear in later processing or during mold service, so precision grinding requires careful control of feed rate, temperature, coolant application, grinding wheel selection, and clamping method.

1. Control Grinding Deformation and Cracks

In fine grinding, the feed rate should be kept small to reduce thermal load and avoid crack formation. Coolant supply must also be sufficient to carry away heat and reduce the risk of surface burning.

For parts with dimensional tolerances within 0.01 mm, ambient temperature must be considered carefully. A small temperature change can affect dimensional accuracy. For example, a 300 mm steel part can change by about 10.8 μm when the temperature difference is 3°C. This level of dimensional change is large enough to influence high-precision finishing results.

2. Choose the Right Grinding Wheel

Grinding wheel selection is critical for both machining quality and surface finish. For high-vanadium and high-molybdenum mold steels, GD single-crystal corundum grinding wheels are often suitable. When machining cemented carbide or materials with very high quench hardness, diamond grinding wheels with organic bond are usually preferred.

Organic bonded grinding wheels have good self-sharpening properties and can achieve surface roughness as fine as Ra 0.2 μm on rough-ground workpieces. In recent years, CBN grinding wheels, or cubic boron nitride wheels, have shown excellent performance in CNC profile grinding, coordinate grinding, and CNC internal and external cylindrical grinding.

During the grinding process, the wheel should be dressed regularly to maintain sharpness. If the grinding wheel becomes dull, it will rub and compress the workpiece surface instead of cutting efficiently, which may cause surface burns and reduce part strength.

3. Grinding Thin Plate Parts on Surface Grinders

Surface grinders are widely used for machining plate-type mold parts. Thin and long plate parts are especially difficult to process because magnetic clamping can deform the workpiece during grinding. After the workpiece is removed from the magnetic table, it may spring back, causing poor parallelism even if thickness measurement appears uniform.

To solve this problem, a magnetic shielding grinding method can be used. Supporting blocks of the same height are placed under the workpiece, and the workpiece is restrained properly from multiple sides. During grinding, small cutting depth and multiple passes should be used. After one side is finished, the part can be turned over and processed again by direct magnetic adsorption. This method helps improve parallelism and overall grinding quality.

4. Grinding Shaft Parts and Internal Holes

Shaft parts are usually processed on internal and external cylindrical grinders or tool grinders. In these operations, the headstock and centers play a critical role in rotational accuracy. If there is runout in the headstock or center, the same error will appear on the workpiece and affect final part quality.

Before grinding shaft parts, the headstock and centers should be inspected carefully. When grinding internal holes, coolant should be delivered directly into the grinding contact area to help remove grinding debris and maintain stable cutting conditions.

For thin-walled shaft parts, special attention should be given to clamping force. It is best to use a suitable fixture or support table, and the clamping force should not be too high. Excessive force can easily cause deformation, including out-of-round conditions such as triangular distortion on the circumference of the workpiece.

Conclusion

Precision grinding of mold parts requires careful control of heat, feed, wheel sharpness, ambient temperature, and clamping method. Proper grinding wheel selection, sufficient coolant, and correct machine setup are essential for avoiding grinding cracks, thermal deformation, and dimensional errors.

By applying the right grinding method for plate parts, shaft parts, and high-hardness mold materials, manufacturers can improve dimensional stability, surface quality, and overall mold performance.