I.
Introduction
In the modern mold production, with increasing high aesthetics and functional requirements of the plastic parts, plastic parts internal structure is designed to be more and more complex, the exterior design of the mold are becoming increasingly complex, free-form surface increasing proportion corresponding mold structure is also designed to be more and more complicated. Mold Accessories processing technology put forward higher requirements, should not only ensure the manufacture of high precision and surface quality, but also to the pursuit of the beauty of the machined surface. With the deepening of the high-speed processing technology, especially in promoting the development of machine tools, CNC system, tool systems, CAD / CAM software and other related technology, high-speed processing technology has been increasingly used in the mold cavity processing and manufacturing.
CNC high-speed machining as the most important one in the mold manufacturing advanced manufacturing technology, is a set of efficient, high-quality, low power consumption at an advanced manufacturing technology. Compared to conventional machining, the cutting speed and feed speed has been greatly improved, and the cutting mechanism is not the same. Cutting speed cutting essential leap unit power metal removal rate of 30% to 40%, a 30% reduction in cutting forces and tool cutting life expectancy has increased by 70% to stay in the workpiece, cutting heat The amplitude decreased low-level cutting vibration almost disappeared. With the increase in cutting speed, rough material removal rate per unit time, cutting the time to reduce the processing efficiency, so as to shorten the product manufacturing cycle, improve the market competitiveness of the products. At the same time, high-speed processing of a small amount of fast-forward the cutting force reduces the chip's high-speed discharge to reduce the the workpiece cutting forces and heat stress deformation, increase the possibility of poor rigidity and thin-walled parts machining. Due to the reduction of the cutting forces, the speed increases so that the cutting system frequency away from the low-order natural frequency of the machine, while the surface roughness of the workpiece is most sensitive to low-level frequency, thereby reducing the surface roughness. Electrical processing and the step of grinding and polishing can be substituted in the mold high-hardened steel (HRC45 ~ HRC65) during processing, the use of high-speed cutting, thereby avoiding the manufacturing of the electrodes and time-consuming electrical processing, significantly reduce the fitter grinding and polishing amount. A growing need in the market for thin-walled mold workpiece, high-speed milling can also be successfully completed, and in high-speed milling CNC machining centers, a mold clamping can complete the multi-step processing.
High speed machining of the mold process to produce a huge impact, changing the traditional mold used annealing → milling machining → heat treatment → grinding or EDM → hand sanding, polishing "complex and lengthy process, and can even be used to replace all of the original high-speed machining process. High-speed machining techniques can be applied to the the hardened mold cavity directly processing (especially semi-finishing and finishing), EDM electrode machining, Rapid Prototyping Manufacturing has also been widely used. Mass production practice shows that the application of high speed cutting technology can save about 80% of the mold in the subsequent processing manual grinding time, saving nearly 30% of the processing costs, the mold surface machining accuracy of up to 1 m, the tool cutting efficiency can be increased by 1.
Second, high-speed milling machine
Speed cutting technology is one of the main development direction of cutting technology to a higher level with the development of the basic technology of CNC technology, microelectronic technology, new materials and new structure. Due to the mold special processing and high-speed processing technology, the technology and process systems for high-speed machining of molds (machine tools, CNC system, tool, etc.) put forward higher requirements than the traditional punch and die.
A high stability of the machine tool support member
High-speed cutting machine tool bed support member should have a good dynamic and static stiffness the the hot stiffness and damping characteristics. Most of the machines are high-quality, high rigidity and high tensile gray iron as a support member material, add some machine tool companies still base a high damping characteristics of polymer concrete to increase its vibration resistance and thermal stability This will not only ensure the machine accuracy and stability, but also prevents the cutting tool chatter. The closed bed design, overall casting bed, symmetrical structure of the bed with clouds of ribs is also an important measure to improve machine stability. The company's R & D departments of some machine tools in the design process, but also using modal analysis and finite element structural calculations to optimize the structure of the machine more stable and reliable support member.
2. Machine spindle
The performance of high-speed machine tool spindle is an important condition for achieving high-speed machining. High-speed cutting machine tool spindle speed range to 10000 ~ 100000m/min, and 15kW spindle power greater than. Axial gap between the shank and spindle control spindle compressed air or cooling system is not greater than 0.005mm. Also requires the spindle performance (that has a very high angular acceleration and deceleration) with rapid acceleration, rapid accurate stop at the specified location, high-speed spindle often hydrostatic bearings, aerostatic bearing, hot-pressed silicon nitride (Si3N4) ceramic bearings magnetic bearing type structure. Lubrication to use more oil lubrication and jet lubrication technology. Spindle cooling generally use the spindle internal water-cooled or air-cooled.
3. Machine drive system
To meet the needs of high speed machining of the mold, the high speed machining machine tool drive system should have the following characteristics:
(1) a high feed rate. Studies have shown that, for small diameter tool to improve the speed and the amount of feed per tooth helps reduce tool wear. The feed rate range of 20 ~ 30m/min, such as the use of a large lead ball screw drive, feed rate up to 60m/min; linear motor allows speeds of up to 120m/min feed.
(2) a high acceleration. Three-dimensional complex surface contour of the high-speed machining requirements drive system has good acceleration characteristics, to provide high-speed feed drive (fast forward speed of 40m/min, 3D contouring speed of 10m/min) to provide 0.4m/s2 to 10m/s2 acceleration and deceleration.
Most machine manufacturers closed loop position servo control lead to large-size, high-quality ball screw or lead screw bulls. With the development of motor technology, advanced linear motor has come out, and successfully applied to theCNC machine tools. No mass inertia advanced linear motor driven CNC machine tools, advanced, hysteresis and vibration problems faster servo response speed and improve the the servo control accuracy and precision machining.
4. CNC system
Advanced CNC system is a key factor to ensure the quality and efficiency of high-speed machining of mold complex surface, the basic requirements of the numerical control system of high-speed machining of the mold:
(1) high-speed digital control loop (Digital CONTROL loop), including: a 32-bit or 64-bit parallel processor and 1.5Gb more hard disk drives; very short sampling time of a linear motor
(2) the velocity and acceleration feedforward control (Feed forward control); crawl control of the digital drive system (Jerk control).
(3) advanced interpolation method (based on NURBS spline interpolation), to obtain a good surface quality, precise dimensions and high geometric accuracy.
(4) pretreatment (Look-ahead) function. Requires a large capacity buffer register, pre-reading and checking more than one block (such as DMG machine can block up to 500 the Simens block system up to 1000 to 2000), in order to be processed surface shape (curvature) occurs change to take timely measures to change the feed rate to avoid excessive cutting.
(5) error compensation function, including fever caused by thermal error compensation due to the linear motor spindle quadrant error compensation, the measuring system error compensation. In addition the requirements of high-speed machining of the mold on the data transmission speed is also high.
(6) data interface, such as RS232 serial port transmission speed of 19.2kb, while many state-of-the-art machining centers have adopted Ethernet LAN (Ethernet) for data transfer speeds of up to 200kb.
5. Cooling lubrication
High-speed machining using coated carbide cutting tools without cutting fluid, in the case of high-speed, high-temperature, efficient cutting. This is because: the high speed rotation of the milling spindle, cutting fluid to reach the cutting area must first overcome a great centrifugal force; even if it overcomes the centrifugal force into the cutting area, may also be due to the high temperature of the cutting area and immediately evaporated, the cooling effect is small even not; cutting fluid causes the intense temperature changes of the cutter blade, easily lead to cracks, so dry cutting oil / gas cooling and lubricating. This manner can be provided with high pressure gas quickly blown away by the cutting of the cutting zone, so that the large amount of cutting tropical go, while the atomizing the lubricant can be provided in the the tool blade portion and the workpiece surface to form a thin layer of micro-protective film, can be effectively extend tool life and improve the quality of the parts of the surface.
In the modern mold production, with increasing high aesthetics and functional requirements of the plastic parts, plastic parts internal structure is designed to be more and more complex, the exterior design of the mold are becoming increasingly complex, free-form surface increasing proportion corresponding mold structure is also designed to be more and more complicated. Mold Accessories processing technology put forward higher requirements, should not only ensure the manufacture of high precision and surface quality, but also to the pursuit of the beauty of the machined surface. With the deepening of the high-speed processing technology, especially in promoting the development of machine tools, CNC system, tool systems, CAD / CAM software and other related technology, high-speed processing technology has been increasingly used in the mold cavity processing and manufacturing.
CNC high-speed machining as the most important one in the mold manufacturing advanced manufacturing technology, is a set of efficient, high-quality, low power consumption at an advanced manufacturing technology. Compared to conventional machining, the cutting speed and feed speed has been greatly improved, and the cutting mechanism is not the same. Cutting speed cutting essential leap unit power metal removal rate of 30% to 40%, a 30% reduction in cutting forces and tool cutting life expectancy has increased by 70% to stay in the workpiece, cutting heat The amplitude decreased low-level cutting vibration almost disappeared. With the increase in cutting speed, rough material removal rate per unit time, cutting the time to reduce the processing efficiency, so as to shorten the product manufacturing cycle, improve the market competitiveness of the products. At the same time, high-speed processing of a small amount of fast-forward the cutting force reduces the chip's high-speed discharge to reduce the the workpiece cutting forces and heat stress deformation, increase the possibility of poor rigidity and thin-walled parts machining. Due to the reduction of the cutting forces, the speed increases so that the cutting system frequency away from the low-order natural frequency of the machine, while the surface roughness of the workpiece is most sensitive to low-level frequency, thereby reducing the surface roughness. Electrical processing and the step of grinding and polishing can be substituted in the mold high-hardened steel (HRC45 ~ HRC65) during processing, the use of high-speed cutting, thereby avoiding the manufacturing of the electrodes and time-consuming electrical processing, significantly reduce the fitter grinding and polishing amount. A growing need in the market for thin-walled mold workpiece, high-speed milling can also be successfully completed, and in high-speed milling CNC machining centers, a mold clamping can complete the multi-step processing.
High speed machining of the mold process to produce a huge impact, changing the traditional mold used annealing → milling machining → heat treatment → grinding or EDM → hand sanding, polishing "complex and lengthy process, and can even be used to replace all of the original high-speed machining process. High-speed machining techniques can be applied to the the hardened mold cavity directly processing (especially semi-finishing and finishing), EDM electrode machining, Rapid Prototyping Manufacturing has also been widely used. Mass production practice shows that the application of high speed cutting technology can save about 80% of the mold in the subsequent processing manual grinding time, saving nearly 30% of the processing costs, the mold surface machining accuracy of up to 1 m, the tool cutting efficiency can be increased by 1.
Second, high-speed milling machine
Speed cutting technology is one of the main development direction of cutting technology to a higher level with the development of the basic technology of CNC technology, microelectronic technology, new materials and new structure. Due to the mold special processing and high-speed processing technology, the technology and process systems for high-speed machining of molds (machine tools, CNC system, tool, etc.) put forward higher requirements than the traditional punch and die.
A high stability of the machine tool support member
High-speed cutting machine tool bed support member should have a good dynamic and static stiffness the the hot stiffness and damping characteristics. Most of the machines are high-quality, high rigidity and high tensile gray iron as a support member material, add some machine tool companies still base a high damping characteristics of polymer concrete to increase its vibration resistance and thermal stability This will not only ensure the machine accuracy and stability, but also prevents the cutting tool chatter. The closed bed design, overall casting bed, symmetrical structure of the bed with clouds of ribs is also an important measure to improve machine stability. The company's R & D departments of some machine tools in the design process, but also using modal analysis and finite element structural calculations to optimize the structure of the machine more stable and reliable support member.
2. Machine spindle
The performance of high-speed machine tool spindle is an important condition for achieving high-speed machining. High-speed cutting machine tool spindle speed range to 10000 ~ 100000m/min, and 15kW spindle power greater than. Axial gap between the shank and spindle control spindle compressed air or cooling system is not greater than 0.005mm. Also requires the spindle performance (that has a very high angular acceleration and deceleration) with rapid acceleration, rapid accurate stop at the specified location, high-speed spindle often hydrostatic bearings, aerostatic bearing, hot-pressed silicon nitride (Si3N4) ceramic bearings magnetic bearing type structure. Lubrication to use more oil lubrication and jet lubrication technology. Spindle cooling generally use the spindle internal water-cooled or air-cooled.
3. Machine drive system
To meet the needs of high speed machining of the mold, the high speed machining machine tool drive system should have the following characteristics:
(1) a high feed rate. Studies have shown that, for small diameter tool to improve the speed and the amount of feed per tooth helps reduce tool wear. The feed rate range of 20 ~ 30m/min, such as the use of a large lead ball screw drive, feed rate up to 60m/min; linear motor allows speeds of up to 120m/min feed.
(2) a high acceleration. Three-dimensional complex surface contour of the high-speed machining requirements drive system has good acceleration characteristics, to provide high-speed feed drive (fast forward speed of 40m/min, 3D contouring speed of 10m/min) to provide 0.4m/s2 to 10m/s2 acceleration and deceleration.
Most machine manufacturers closed loop position servo control lead to large-size, high-quality ball screw or lead screw bulls. With the development of motor technology, advanced linear motor has come out, and successfully applied to theCNC machine tools. No mass inertia advanced linear motor driven CNC machine tools, advanced, hysteresis and vibration problems faster servo response speed and improve the the servo control accuracy and precision machining.
4. CNC system
Advanced CNC system is a key factor to ensure the quality and efficiency of high-speed machining of mold complex surface, the basic requirements of the numerical control system of high-speed machining of the mold:
(1) high-speed digital control loop (Digital CONTROL loop), including: a 32-bit or 64-bit parallel processor and 1.5Gb more hard disk drives; very short sampling time of a linear motor
(2) the velocity and acceleration feedforward control (Feed forward control); crawl control of the digital drive system (Jerk control).
(3) advanced interpolation method (based on NURBS spline interpolation), to obtain a good surface quality, precise dimensions and high geometric accuracy.
(4) pretreatment (Look-ahead) function. Requires a large capacity buffer register, pre-reading and checking more than one block (such as DMG machine can block up to 500 the Simens block system up to 1000 to 2000), in order to be processed surface shape (curvature) occurs change to take timely measures to change the feed rate to avoid excessive cutting.
(5) error compensation function, including fever caused by thermal error compensation due to the linear motor spindle quadrant error compensation, the measuring system error compensation. In addition the requirements of high-speed machining of the mold on the data transmission speed is also high.
(6) data interface, such as RS232 serial port transmission speed of 19.2kb, while many state-of-the-art machining centers have adopted Ethernet LAN (Ethernet) for data transfer speeds of up to 200kb.
5. Cooling lubrication
High-speed machining using coated carbide cutting tools without cutting fluid, in the case of high-speed, high-temperature, efficient cutting. This is because: the high speed rotation of the milling spindle, cutting fluid to reach the cutting area must first overcome a great centrifugal force; even if it overcomes the centrifugal force into the cutting area, may also be due to the high temperature of the cutting area and immediately evaporated, the cooling effect is small even not; cutting fluid causes the intense temperature changes of the cutter blade, easily lead to cracks, so dry cutting oil / gas cooling and lubricating. This manner can be provided with high pressure gas quickly blown away by the cutting of the cutting zone, so that the large amount of cutting tropical go, while the atomizing the lubricant can be provided in the the tool blade portion and the workpiece surface to form a thin layer of micro-protective film, can be effectively extend tool life and improve the quality of the parts of the surface.
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