Mold processing and grinding machine processing
Grinding in mold processing involves cutting the surface of mold parts using abrasive tools (grinding wheels, abrasive belts, etc.). It is primarily used to improve the dimensional accuracy, form and position accuracy, and surface quality of parts, making it an important tool for mold finishing. Grinding offers high precision (dimensional tolerances up to ±0.001mm, flatness ≤0.0005mm/100mm) and low surface roughness (Ra 0.025-0.8μm). It is suitable for machining mold working parts (such as punches, dies, and cores) and guide components (such as guide pins and guide sleeves), and is particularly suitable for machining high-hardness materials after quenching. Depending on the surface being machined, grinding can be categorized into surface grinding, external cylindrical grinding, internal cylindrical grinding, jig grinding, and form grinding.
Surface grinding machines are primarily used for machining the flat surfaces of mold parts, such as the upper and lower surfaces of the mold base, the mounting surface of the die, and the surface of the stripper plate. Commonly used equipment includes horizontal and rectangular table surface grinders and vertical rotary table surface grinders. Horizontal and rectangular table surface grinders utilize the grinding wheel’s circumferential surface for grinding, offering high precision (flatness ≤ 0.005mm/300mm) and a surface roughness of Ra 0.4-0.8μm, making them suitable for small and medium-sized flat parts. Vertical rotary table surface grinders utilize the grinding wheel’s end surface for grinding, offering high efficiency (grinding efficiency up to 50-100cm²/min) but lower precision (flatness ≤ 0.01mm/300mm), making them suitable for rough and semi-finish grinding of large surfaces. The process parameters for surface grinding include grinding wheel speed (30-50m/s), feed rate (0.5-5m/min) and grinding depth (0.01-0.05mm for coarse grinding and 0.001-0.01mm for fine grinding). For hardened steel parts, cubic boron nitride (CBN) grinding wheels are required to avoid grinding wheel clogging.
External cylindrical grinding machines are used to machine the external cylindrical surfaces of mold shaft components, such as guide pins, punches, and ejector pins. Commonly used equipment includes conventional and CNC cylindrical grinders. Conventional cylindrical grinders achieve grinding through the rotation of the grinding wheel and the workpiece, rotating and feeding the workpiece. They can achieve precision levels up to IT5 and a surface roughness of Ra0.1-0.4μm. CNC cylindrical grinders, controlled by a CNC system and featuring automatic feed and compensation, are suitable for machining complex shaft components (such as stepped and tapered shafts), achieving dimensional accuracy up to ±0.0005mm. External cylindrical grinding requires the use of a center or chuck for workpiece clamping. For slender shafts with an aspect ratio greater than 10, a steady rest is required to provide auxiliary support to prevent workpiece bending and deformation. Adequate cooling is essential during the grinding process, using an emulsion coolant at a flow rate of ≥20L/min to prevent workpiece burns.
Internal grinding machines are used to machine the internal bores of mold sleeve components, such as guide bushings, die bores, and bearing sleeves. Commonly used equipment includes conventional internal grinding machines and jig grinders. Conventional internal grinding machines are suitable for machining small and medium-diameter internal bores (5-200mm), achieving precision grades of IT6-IT7 and a surface roughness of Ra 0.2-0.8μm. Jig grinders, through spindle rotation and precise table movement, can produce high-precision internal bores and complex shapes (such as round, elliptical, and waist-shaped holes), with positioning accuracy reaching ±0.001mm. They are suitable for finishing mold cavities and bores. The grinding wheel diameter for internal grinding is typically 0.5-0.8 times the bore diameter, with a grinding wheel speed of 15-30m/s and a feed rate of 0.01-0.1mm/r. For internal bores in hardened steel, a vitrified CBN grinding wheel is required to improve grinding efficiency and surface quality.
Jig grinding and form grinding are key machining methods for complex mold parts. Equipped with a precision coordinate positioning system (resolution 0.0001mm), a jig grinder uses the planetary and linear motion of a grinding wheel to produce high-precision circular holes, arcs, and straight contours. These machines are suitable for machining die cutting edges and plastic mold cavities, such as those in mobile phone case molds, with an accuracy of ±0.002mm. Form grinding machines use specialized fixtures or form grinding wheels to machine complex surfaces (such as die cutting edges and gear tooth profiles). The dressing accuracy of the form grinding wheel directly impacts machining quality and requires a diamond stylus or CNC wheel dresser. Profile accuracy is maintained at ≤0.001mm. Grinded parts undergo quality inspection using tools such as micrometers, dial indicators, roughness gauges, and coordinate measuring machines to ensure that all accuracy specifications meet requirements.
The following technical points should be noted when using grinding machines in mold manufacturing: Choose the right grinding wheel type and grit (46-80 mesh for coarse grinding, 100-200 mesh for fine grinding) to avoid deteriorating surface quality due to wheels that are too hard or too soft; control grinding parameters to avoid grinding burns and cracks (for high-carbon steel, the grinding temperature should be kept below 200°C); for thin-walled parts, reduce clamping force and use segmented grinding to prevent deformation; and stress-relieve parts after grinding (such as low-temperature aging at 120-150°C for 2-4 hours) to eliminate grinding stress and ensure dimensional stability. By strictly controlling every step of the grinding process, high precision and surface quality of mold parts can be ensured, providing reliable guarantees for mold assembly and performance.
