Grinding Techniques and Precision Control for Mold Parts Machining
Grinding is one of the most important finishing processes in mold manufacturing and precision machining. It is widely used to achieve tight dimensional tolerances, improve surface finish, and ensure the accuracy of mold components. Common grinding machines include surface grinders, internal and external cylindrical grinders, and tool grinders.
1. Controlling Grinding Deformation and Grinding Cracks
During precision grinding, grinding deformation and grinding cracks must be strictly controlled. Even very small cracks may appear during subsequent machining, polishing, heat treatment, or mold use.
To reduce the risk of grinding cracks and thermal damage:
- Use a small grinding feed during finishing operations
- Provide sufficient coolant throughout the grinding process
- Avoid excessive grinding pressure and heat buildup
- Control workshop and workpiece temperature before precision machining
For mold parts with dimensional tolerances within 0.01 mm, temperature control is extremely important. Steel expands noticeably with temperature changes. For example, a 300 mm steel workpiece may expand by approximately 10.8 μm when the temperature changes by only 3°C. This thermal expansion can directly affect machining accuracy and final dimensional consistency.
2. Choosing the Right Grinding Wheel
Selecting the correct grinding wheel is essential for achieving high surface quality and stable grinding performance.
For high-vanadium and high-molybdenum mold steels, GD single-crystal corundum grinding wheels are often suitable. For carbide materials and hardened steel with high hardness, resin-bonded diamond grinding wheels are commonly preferred.
Resin-bonded grinding wheels provide self-sharpening characteristics and can achieve very fine surface roughness values of up to Ra 0.2 μm.
In recent years, CBN grinding wheels, also known as cubic boron nitride grinding wheels, have become widely used in CNC profile grinding, coordinate grinding, internal grinding, and external grinding applications. Compared with conventional grinding wheels, CBN wheels offer better cutting performance, longer service life, and improved machining accuracy.
During grinding, the grinding wheel should be dressed regularly to maintain sharpness. If the grinding wheel becomes dull, it may rub instead of cut, causing surface burns, reduced hardness, and poor surface quality on the workpiece.
3. Grinding Thin Plate Parts
Surface grinders are commonly used to process flat mold components and plate parts. However, thin and long plate parts are often difficult to machine because magnetic clamping can deform the workpiece during grinding.
When the workpiece is removed from the magnetic table, it may spring back to its original shape, causing parallelism issues even if the thickness appears uniform.
To solve this problem, magnetically shielded grinding methods can be used. Support blocks of equal height can be placed under the workpiece to reduce deformation. Small feed grinding and multiple light passes can further improve dimensional stability and achieve better parallelism.
4. Grinding Shaft Parts and Inner Holes
Shaft parts are usually processed using internal and external cylindrical grinding machines or tool grinders. Because shaft parts rotate during grinding, the accuracy of the headstock and center alignment is critical.
If there is runout in the headstock or center, the finished workpiece may also develop runout, affecting roundness, concentricity, and overall quality.
Before machining shaft parts, the headstock and centers should always be inspected carefully.
When grinding internal holes, coolant should be supplied directly to the grinding area to improve cooling performance and help remove grinding debris efficiently.
For thin-walled shaft parts, clamping force should be minimized. Excessive clamping pressure can deform the workpiece and create an “inside triangle” effect around the circumference, reducing machining accuracy and part quality.
5. Importance of Precision Grinding in Mold Manufacturing
Precision grinding is essential for mold inserts, mold cores, sliders, punches, dies, guide components, and other critical mold parts. Proper grinding methods, suitable grinding wheels, stable temperature control, and correct clamping methods all play an important role in achieving dimensional accuracy, parallelism, surface finish, and long-term mold performance.