Mold processing and milling machine processing
Milling, a process used in mold manufacturing, utilizes milling cutters to perform surface machining on mold components, including flat surfaces, curved surfaces, grooves, and cavities. This method boasts a wide range of machining capabilities and strong adaptability, making it widely used in roughing, semi-finishing, and even partial finishing stages of mold manufacturing. Milling removes material through the rotary motion of the cutter and the feed motion of the workpiece. It can produce a variety of complex mold components, such as the flat surfaces of the mold base, the cavities of the die, and the working parts of the punch. It is an essential and fundamental process in mold manufacturing.
Milling machines can be categorized by structure and function into horizontal, vertical, gantry, and universal milling machines. Each type of milling machine is suited to different mold processing scenarios. Vertical milling machines, with their vertical spindle arrangement, are easy to operate and suitable for machining flat surfaces, steps, and cavities in small and medium-sized mold parts. Common models, such as the X5032, have a worktable measuring 320×1250mm and a spindle speed of 30-1500 rpm, meeting the rough machining needs of general molds. Gantry milling machines, with their excellent rigidity and large travel range, are suitable for machining flat surfaces and profiles in large molds (such as automotive panel molds). With worktables up to 2000×6000mm and the ability to process multiple toolholders simultaneously, they offer 3-5 times higher efficiency than vertical milling machines. Universal milling machines, with both spindle rotation and worktable swivel, are suitable for machining complex angled surfaces, such as inclined guide post holes and inclined slider work surfaces in molds.
Milling machine tools come in a wide variety of types. Based on the surface shape, they can be categorized as face mills, end mills, keyway mills, and form mills. Face mills are primarily used for flat machining of mold components. They range in diameter from 50-300mm, have 4-16 teeth, and utilize carbide inserts. They operate at cutting speeds of 100-300m/min and have surface roughnesses of Ra 3.2-6.3μm. End mills are suitable for machining cavities, grooves, and steps. They range in diameter from 3-50mm and have either straight or tapered shanks. High-speed steel end mills are used for low-speed machining, while carbide end mills are used for high-speed machining. Form mills are used for machining surfaces with specific shapes (such as arcs and tooth profiles in molds). Their tooth shape aligns with the workpiece surface, ensuring precise machining. For example, a 20mm diameter end mill, using circular interpolation, can produce the contour of the mold in a single pass, achieving an accuracy of ±0.02mm.
Milling machine process parameters are determined based on the tool material, workpiece material, and machining accuracy, primarily including cutting speed, feed rate, and cutting depth. During roughing, a larger cutting depth (2-10mm) and feed rate (0.1-0.5mm/r) are used, along with a lower cutting speed (30-50m/min for high-speed steel tools) to quickly remove stock. During semi-finishing, a cutting depth of 1-2mm, feed rate of 0.05-0.1mm/r, and cutting speed increased to 50-100m/min are used. For surfaces with higher precision requirements (Ra 1.6-3.2μm), a smaller cutting depth (0.5-1mm) and feed rate (0.03-0.05mm/r) are used, along with a cooling lubricant (such as an emulsion) to reduce surface roughness. For example, when using a carbide face milling cutter to process the 45 steel die seat plane, the cutting depth is 5mm, the feed rate is 0.3mm/r, and the speed is 150m/min during rough milling; the cutting depth is 0.5mm, the feed rate is 0.1mm/r, and the speed is 200m/min during fine milling, and the flatness can reach 0.05mm/1000mm.
Milling machines offer flexibility and cost-effectiveness in mold manufacturing, making them particularly suitable for small- and medium-volume mold production and the initial forming of complex parts. In mold cavity machining, milling machines can gradually approximate the cavity shape through layered milling. For simple cavities (such as rectangles and circles), machining efficiency is 2-3 times higher than that of EDM. When machining flat surfaces on mold parts, a milling machine, combined with a flat-nose vise or clamping plate, ensures that flatness and perpendicularity meet requirements, laying the foundation for subsequent grinding. Milling machines are also used for mold repair and modification, such as re-milling worn surfaces on old molds to restore dimensional accuracy. With the integration of CNC technology, CNC milling machines have significantly improved machining accuracy and efficiency. Compared to traditional milling machines, they can reduce the time required to machine complex cavities by over 60% and improve dimensional consistency by 50%, making them the mainstream equipment for modern mold milling. By properly selecting the milling machine type, tooling, and process parameters, the advantages of milling can be fully utilized to reduce mold manufacturing costs and improve production efficiency.
