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As an important process equipment, mold occupies an important position in industrial industries such as consumer goods, electrical and electronics, automobiles, and aircraft manufacturing. Improving the technical level and quality of mold production is an important factor in the mold manufacturing industry. The use of mold high-speed cutting technology can significantly improve mold production efficiency, mold accuracy and service life, so it is gradually replacing EDM molds, and has been widely adopted by foreign mold manufacturing companies, becoming a major trend in mold manufacturing. The application time of high-speed cutting technology in mold production is relatively short, and the technical requirements in use are relatively high.
High-speed cutting technology
High-speed cutting has the advantages of low temperature rise (the workpiece is only increased by 3°C), small thermal deformation, etc. The metal removal rate per unit power is increased by 30% to 40%, the cutting force is reduced by 30%, and the cutting life of the tool is increased. 70%, the cutting heat left in the zinc alloy die-casting is greatly reduced, and the low-order cutting vibration almost disappears. With the increase of the cutting speed, the removal rate of the blank material per unit time increases, the cutting time decreases, and the processing efficiency increases, thereby shortening the product manufacturing cycle and improving the product’s market competitiveness. At the same time, the high-speed machining of the snack knife and the large feed rate reduce the cutting force acting on the workpiece, and the high-speed discharge of chips reduces the cutting heat transmitted to the workpiece, reduces thermal stress and deformation, thereby improving the processing of zinc alloy die-casting Rigidity, and provides the possibility for the cutting of thin-walled parts. High-speed milling of materials with a hardness exceeding HRC60 can replace the low-efficiency EDM to a certain extent, thus shortening the mold manufacturing cycle to a certain extent. At the same time, the application of high-speed cutting technology can save about 80% of the manual grinding time in the subsequent processing of the mold, save the processing cost by nearly 30%, the surface roughness of the mold can reach Ra0.1, and the cutting efficiency of the tool can be doubled.
Advantages of high-speed cutting applied to mold processing
The characteristics of mold processing are single-piece small batches and complex geometric shapes, so the processing cycle is long and the production efficiency is low. In the traditional mold processing technology, finishing hardened molds usually use EDM and manual polishing technology. Shortening processing time and reducing production costs are the main goals of developing mold processing technology. In recent years, there have been many new technologies in mold processing technology, such as high-speed cutting, CAD/CAE design simulation, rapid prototyping, electrical discharge milling molding and composite processing, among which the most eye-catching and effective is high-speed Cutting process.
High-speed cutting molds use the high speed and high feed rate of the machine tool to complete multiple production processes of the mold by cutting. The advantages of high-speed machining molds are mainly manifested in the following aspects:
①High-speed cutting rough machining and semi-finishing machining greatly improve the metal removal rate.
②Using high-speed cutting machine tools, tools and technology, it can process hardened materials. For small die-casting molds, after the material is heat-treated, roughing and finishing can be completed in one clamping; for large-scale die-casting molds, roughing and semi-finishing are performed before heat treatment, and finishing is performed after heat treatment and hardening.
③High-speed and high-precision hard cutting replaces smoothing, reducing a lot of time-consuming manual grinding, and improving efficiency by 50% compared with EDM.
④Hard cutting process the final forming surface to improve the surface quality and shape accuracy (not only the surface roughness is low, but also the surface brightness is high), which is more advantageous for the mold processing of complex curved surfaces.
⑤It avoids the decarburization, burns and micro-cracks caused by electric spark and grinding, greatly reduces the surface damage of the mold after finishing, and increases the life of the mold by 20%.
⑥ The workpiece has less heat, reduced cutting force, and small thermal deformation. It is used in combination with CAD/CAM technology for rapid processing of electrodes, especially electrodes with complex shapes and thin-walled easily deformable electrodes.
High-speed cutting machine tool for processing molds
When choosing a high-speed machine tool for high-speed cutting molds, pay attention to the following issues:
(1) The main shaft of the machine tool is required to have high power and high speed to meet rough and fine machining. Small-diameter tools should be used for finishing molds, and the spindle speed can reach more than 15,000 to 20,000 rpm. Machine tools with a spindle speed below 10000rpm can perform rough machining and semi-finish machining. If you need to meet both rough and finish machining in the production of large molds, the selected machine tool should preferably have two spindles with two speeds, or two specifications of electric spindles.
(2) The rapid traverse of the machine tool does not require too much rapid idle stroke. But it must have a relatively high processing feed rate (30-60m/min) and high acceleration and deceleration.
(3) It has a good high-speed, high-precision control system, and has the functions of high-precision interpolation, contour forward control, high acceleration, and high-precision position control.
(4) Choose CAD/CAM software that is matched with high-speed machine tools, especially software for high-speed cutting molds.
The application of five-axis machine tools in mold production is gradually increasing, and it has the following advantages to cooperate with high-speed cutting molds:
①The cutting angle of the tool can be changed, the cutting conditions are good, the wear of the tool is reduced, which is beneficial to protect the tool and prolong the life of the tool;
②The processing route is flexible, which reduces tool interference, and can process molds with complex surface shapes and deep cavity molds;
③Large processing range, suitable for processing various types of molds.
(Five-axis linkage high-speed milling machining center)
Five-axis machine tools usually have two types: table type and milling head type, which can be selected according to the type of mold.
Tool technology of high-speed cutting die
High-speed machining needs to be equipped with suitable tools. The application of hard alloy coated tools and polycrystalline reinforced ceramic tools makes it possible for tools to have both a high-hardness blade and a high-toughness matrix at the same time, which promotes the development of high-speed machining. The hardness of polycrystalline cubic boron nitride (PCBN) blades can reach 3500～4500HV, and the hardness of polycrystalline diamond (PCD) can reach 6000～10000HV. Especially coated tools play a huge role in the semi-finishing and finishing of hardened steel.
Generally speaking, when the acceleration of the tool and the tool holder is above 3g, the radial runout of the tool should be less than 0.015mm, and the length of the tool should not be greater than 4 times the diameter of the tool. The experience of domestic high-speed precision machining of molds, when using small-diameter ball-end milling cutters for mold finishing, the linear speed exceeds 400m/min. This has high requirements for tool materials (including hardness, toughness, red hardness), tool shape (including chip removal performance, surface accuracy, dynamic balance, etc.) and tool life. Therefore, in the high-speed hard cutting and finishing of molds, not only high-speed machine tools must be selected, but also cutting tools and cutting processes must be selected reasonably.
When processing molds at high speeds, the following aspects should be paid attention to:
①According to different processing objects, reasonably select carbide-coated tools, CBN and diamond sintered tools.
②Small diameter ball-end milling cutter is used to finish the mold surface, usually the diameter of the finishing tool is less than 10mm. Depending on the material to be processed and the hardness, the selected tool diameter is also different. In the selection of tool materials, TiAIN ultra-fine grained carbide-coated tools have good lubrication conditions. When cutting die steel, they have better wear resistance than TiCN carbide-coated tools.
③Select appropriate tool parameters, such as negative rake angle. High-speed machining tools require higher impact resistance and thermal shock resistance than ordinary machining.
④ Adopt a variety of methods to improve tool life, such as appropriate feed rate, feed method, lubrication method, etc., to reduce tool costs.
⑤Using high-speed tool holder. At present, HSK tool holders and hot press clamping tools are the most widely used. At the same time, attention should be paid to the overall dynamic balance of the spindle system after the tool is clamped.
Post time: Aug-03-2021
