In the past ten years, due to the continuous advancement of cutting tools, drives, controls and machine tools, high-speed machining and high-efficiency machining, especially high-speed hard milling, have been widely used and promoted in the mold manufacturing industry. Traditional EDM machining Many occasions have been replaced by high-speed hard milling. Through high-speed hard milling, the integrated processing of the mold blank under one clamping not only greatly improves the processing precision and surface quality of the mold, greatly reduces the processing time, and simplifies the production process, thereby significantly shortening the manufacturing of the mold. Cycles reduce mold production costs.
The ever-increasing performance of high-speed machining centers is an important prerequisite for the mold manufacturing industry to process molds efficiently and with high precision. In recent years, driven by the drive technology, many different types of high-speed machining centers with structural innovation and excellent performance have emerged. The three-axis high-speed machining center that appeared in the mid-to-late 1990s (such as the HSM700 high-speed machining center introduced by Mikron in Switzerland in late 1996) has now developed into a five-axis high-speed machining center. In the drive mode, the linear motor (X/Y/Z axis) servo motor and ball screw drive have been developed to the current linear motor drive, and the rotary motion (A and C axis) uses a direct drive torque motor. Some companies have developed the machining center into a five-axis machining center that uses direct drive through linear motors and torque motors. Significantly improved the travel speed, dynamic performance and positioning accuracy of the machining center.
Structural Features and Advantages of High-Speed ​​Machining Centers A high-speed machining center for mold processing, a common structural feature is the use of a gantry frame structure to enhance the rigidity of the machine tool and to make full use of the space in the processing area. The material of the machine bed is mostly made of polymer concrete. Because of its good damping performance and low thermal conductivity, it is beneficial to improve the machining accuracy of the mold.
At present, according to the configuration of the coordinate axes, the five-axis machining center can basically be divided into two structural types. One is that three linear axes (X/Y/Z) are used for the tool movement and two additional rotary axes (A and C) for the structural version of the workpiece's swivel and swivel. This type of high-speed machining centers, such as RXP500DS/RXP800DS from Röder, Germany, GS1000/5-T from Alzmetall, Germany, HSM400U/HSM600U from Mikro, Switzerland, and XSM400U/XSM600U from ultra-high-speed machining centers, and Germany Hermle's C30U/C40U/C50U and so on. The other is that one of the five coordinate axes (A) is arranged on the spindle head, and the spindle cutter is swung by the fork spindle head, and the swing spindle head can also be firmly clamped. Position at any position within the range of the swing angle.
This type of machine tools are DMC75V linear/DMC105V linear from DMG, Germany, HPM1850U from Mikro and GAMMA605/1200 from Germany Rolf Wisser. Some machine tools have a swing axis and a rotary axis on the spindle head, such as the G996V/BSH/5A high-speed milling center of Parat, Germany, and the 5-axis or six-axis gantry milling machine of Edel, Germany.
The five-axis high-speed machining center is much higher in price than the three-axis machining center. According to the price comparison between the five-axis machining center of the DMG 75V series and the three-axis machining center, the five-axis is about 50% higher than the price of the three-axis. The five-axis high-speed machining center is expensive, but this high-end machine is especially suitable for machining complex molds. When machining a deeper and steeper cavity, the five-axis machining center can create the best process conditions for the machining of the end mill by the additional rotation and swing of the workpiece or the spindle head, and avoid the tool and the shank and cavity wall. Collision occurs, reducing the risk of tool shake and tool breakage, which helps to improve the surface quality, machining efficiency and tool durability of the mold. When purchasing a machining center, the user selects a three-axis machining center or a five-axis machining center, which should be determined according to the complexity and precision of the mold cavity geometry.
From the continuous innovation process of high-speed machining centers, it can be seen that making full use of the latest achievements in today's technology fields, especially the latest achievements in the use of drive technology and control technology, is the key to continuously improve the high-speed performance, dynamic characteristics and machining accuracy of the machining center. .
Electric Spindle The high-speed electric spindle is the core component of the high-speed machining center. In the processing of free-form surfaces and complex contours of molds, 2 to 12 mm smaller diameter end mills are often used, and in the processing of electrodes for EDM of copper or graphite materials, high cutting speed is required, therefore, electricity The spindle must have a very high speed. At present, the spindle speed of the machining center is mostly 18000~42000r/min. The spindle speed of XSM400U/XSM600U of Mikro, Switzerland has reached 54000 r/min. For micro-milling of the mold (the diameter of the milling cutter is generally 0.1 to 2 mm), a higher rotation speed is required. For example, the 5-axis high-precision milling machine from Kugler, Germany, has a maximum spindle speed of 160,000 r/min (with air bearing). This high speed can reach 150m/min when machining a steel mold with a 0.3mm diameter milling cutter. Cutting speed. At present, the Fraunhofer Institute of Production Technology in Germany is developing a spindle supported by an air bearing with a speed of 300,000 r/min.
When machining molds, high speeds are always used, and the heat generated by high speed and the vibration that may occur during cutting are important factors affecting the precision of mold processing. In order to ensure the stability of the high-speed electric spindle work, sensors for measuring temperature, displacement and vibration are installed on the spindle to monitor the temperature rise, axial displacement and vibration of the motor, bearing and spindle. This provides correction data for the CNC system of the high-speed machining center to modify the spindle speed and feed rate to optimize the machining parameters. When the spindle produces an axial displacement, it can be compensated by zero correction or trajectory correction.
Linear motors At present, most of the high-speed machining centers or milling machines used for mold processing use servo motors and ball screws to drive linear axes. However, some machining centers have adopted linear motors, such as the RXP500DS/RXP800DS high-speed milling machine from Röders, Germany. Dejima's DMC75V linear high-speed machining center (with an axial acceleration of 2g and a fast stroke speed of 90m/min). Since the linear drive eliminates the transmission element that converts the rotary motion into a linear motion, the dynamic performance, the moving speed and the machining accuracy of the shaft can be significantly improved.
Machines driven by linear motors can significantly increase productivity. For example, when processing electrodes for electrical discharge machining, the processing time is reduced by 50% compared to the conventional high-speed milling machine.
Linear motors can significantly improve the dynamic performance of high-speed machine tools. Since most of the molds are three-dimensional surfaces, the tool axes are constantly braking and accelerating while the tool is machining the surface. Only with a high axial acceleration is it possible to ensure that a given contour is tracked with a constant feed per tooth on a shorter path path at very high path speeds. If the radius of curvature of the surface profile is smaller, the higher the feed rate, the higher the required axial acceleration. Therefore, the axial acceleration of the machine tool largely affects the machining accuracy of the mold and the durability of the tool.
Torque Motor In the high-speed machining center, the swing of the rotary table and the swinging and turning of the fork-shaped spindle head have been widely implemented using torque motors. A torque motor is a synchronous motor whose rotor is directly fixed to the component to be driven, so there is no mechanical transmission component, and it is a direct drive like a linear motor. The angular acceleration that can be achieved by a torque motor is six times higher than that of a conventional worm gear, and the acceleration can reach 3g when swinging a forked spindle head. Due to the extremely high static and dynamic load stiffness of the torque motor, the positioning accuracy and repeatability of the rotary and swing axes are improved.
At present, some manufacturers of high-speed machining centers have used linear motors and torque motors to drive linear axes (X/Y/Z) and rotary swing axes (C and A), respectively. Such as R?er's RXP500DS/RXP800DS, DMG's DMC75V linear and Edel's CyPort five-axis gantry milling machine.
It should be mentioned that the direct drive linear axis is combined with the directly driven rotary axis to give the machine a high dynamic performance and adjustment characteristics for all motion axes, thus freeing the mold for high speed, high precision and high surface quality. Surfaces provide the best conditions.
Control System The CNC control system is an important part of the high-speed machining center, which determines the speed, accuracy and surface quality of the machine tool to a large extent. Therefore, the performance of the numerical control system is of particular importance for high-speed machine tools that process free-form surfaces of molds.
When machining high-precision free-form surfaces, the tool path consisting of micro-segment lines and arcs creates a huge part program. These data streams need to be stored and processed by the machine control system. Therefore, the length of the block processing time determines the CNC control system. An important indicator of work efficiency. At present, the processing time of the high-end CNC control system is generally 0.5ms (such as HEIDENHAIN's iTNC530 CNC system), and the processing time of the individual CNC system has been shortened to 0.2-0.4ms.
Modern CNC CNC systems for high-speed machining of molds, in addition to the short program processing time necessary to ensure high-speed feed rates, should also have Nurbs and spline interpolation functions, and can work at nano resolution. In order to achieve high machining accuracy and surface quality in the case of high speed machining.
At present, high-end CNC systems can also be connected to CAD/CAM systems from different manufacturers, and data is transferred from the CAD/CAM system to the control system via Ethernet at a very high speed. The integration of CAD/CAM into the control system can, to a large extent, achieve good results in the processing of complex contours of the mold, and contributes significantly to shortening the adjustment time and programming time.
In the above-mentioned five-axis high-speed machine tool, except for R?er, which uses its own CNC system, the other mainly uses Siemens 840D and HEIDENHAIN iTNC530 CNC system.
Conclusion In the past decade, the advancement of drive technology and control systems has driven the continuous innovation and performance improvement of the machining center structure. The application of electric spindles, linear motors, torque motors and rapid CNC systems has played a decisive role in improving the high speed, high dynamics and high machining accuracy of machining centers. In many structural innovations in mold processing machines, torque motors play a particularly important role. It is applied not only to the rotary and oscillating drives of the rotary table, but also to the swinging of the forked spindle head or the swinging and slewing drive of the spindle head, thereby constituting various types of five-axis machining centers. The application of the rotary and oscillating spindle heads provides technical support for the development of five-axis gantry high-speed precision milling machines for machining large molds.
In the future, further improvement of spindle speed, dynamic performance and stroke speed is still the focus of high-speed machining center development, which not only depends on the further development of drive technology and numerical control technology, but also depends on the development of lightweight components of machine tools and parallel machine tools. Development. It can be expected that in the next five years, the axial acceleration of high-speed machining centers or high-speed milling machines is expected to reach 3 to 4 g, and the rapid stroke speed of the coordinate axes reaches 100 to 140 m/min.
The ever-increasing performance of high-speed machining centers is an important prerequisite for the mold manufacturing industry to process molds efficiently and with high precision. In recent years, driven by the drive technology, many different types of high-speed machining centers with structural innovation and excellent performance have emerged. The three-axis high-speed machining center that appeared in the mid-to-late 1990s (such as the HSM700 high-speed machining center introduced by Mikron in Switzerland in late 1996) has now developed into a five-axis high-speed machining center. In the drive mode, the linear motor (X/Y/Z axis) servo motor and ball screw drive have been developed to the current linear motor drive, and the rotary motion (A and C axis) uses a direct drive torque motor. Some companies have developed the machining center into a five-axis machining center that uses direct drive through linear motors and torque motors. Significantly improved the travel speed, dynamic performance and positioning accuracy of the machining center.
Structural Features and Advantages of High-Speed ​​Machining Centers A high-speed machining center for mold processing, a common structural feature is the use of a gantry frame structure to enhance the rigidity of the machine tool and to make full use of the space in the processing area. The material of the machine bed is mostly made of polymer concrete. Because of its good damping performance and low thermal conductivity, it is beneficial to improve the machining accuracy of the mold.
At present, according to the configuration of the coordinate axes, the five-axis machining center can basically be divided into two structural types. One is that three linear axes (X/Y/Z) are used for the tool movement and two additional rotary axes (A and C) for the structural version of the workpiece's swivel and swivel. This type of high-speed machining centers, such as RXP500DS/RXP800DS from Röder, Germany, GS1000/5-T from Alzmetall, Germany, HSM400U/HSM600U from Mikro, Switzerland, and XSM400U/XSM600U from ultra-high-speed machining centers, and Germany Hermle's C30U/C40U/C50U and so on. The other is that one of the five coordinate axes (A) is arranged on the spindle head, and the spindle cutter is swung by the fork spindle head, and the swing spindle head can also be firmly clamped. Position at any position within the range of the swing angle.
This type of machine tools are DMC75V linear/DMC105V linear from DMG, Germany, HPM1850U from Mikro and GAMMA605/1200 from Germany Rolf Wisser. Some machine tools have a swing axis and a rotary axis on the spindle head, such as the G996V/BSH/5A high-speed milling center of Parat, Germany, and the 5-axis or six-axis gantry milling machine of Edel, Germany.
The five-axis high-speed machining center is much higher in price than the three-axis machining center. According to the price comparison between the five-axis machining center of the DMG 75V series and the three-axis machining center, the five-axis is about 50% higher than the price of the three-axis. The five-axis high-speed machining center is expensive, but this high-end machine is especially suitable for machining complex molds. When machining a deeper and steeper cavity, the five-axis machining center can create the best process conditions for the machining of the end mill by the additional rotation and swing of the workpiece or the spindle head, and avoid the tool and the shank and cavity wall. Collision occurs, reducing the risk of tool shake and tool breakage, which helps to improve the surface quality, machining efficiency and tool durability of the mold. When purchasing a machining center, the user selects a three-axis machining center or a five-axis machining center, which should be determined according to the complexity and precision of the mold cavity geometry.
From the continuous innovation process of high-speed machining centers, it can be seen that making full use of the latest achievements in today's technology fields, especially the latest achievements in the use of drive technology and control technology, is the key to continuously improve the high-speed performance, dynamic characteristics and machining accuracy of the machining center. .
Electric Spindle The high-speed electric spindle is the core component of the high-speed machining center. In the processing of free-form surfaces and complex contours of molds, 2 to 12 mm smaller diameter end mills are often used, and in the processing of electrodes for EDM of copper or graphite materials, high cutting speed is required, therefore, electricity The spindle must have a very high speed. At present, the spindle speed of the machining center is mostly 18000~42000r/min. The spindle speed of XSM400U/XSM600U of Mikro, Switzerland has reached 54000 r/min. For micro-milling of the mold (the diameter of the milling cutter is generally 0.1 to 2 mm), a higher rotation speed is required. For example, the 5-axis high-precision milling machine from Kugler, Germany, has a maximum spindle speed of 160,000 r/min (with air bearing). This high speed can reach 150m/min when machining a steel mold with a 0.3mm diameter milling cutter. Cutting speed. At present, the Fraunhofer Institute of Production Technology in Germany is developing a spindle supported by an air bearing with a speed of 300,000 r/min.
When machining molds, high speeds are always used, and the heat generated by high speed and the vibration that may occur during cutting are important factors affecting the precision of mold processing. In order to ensure the stability of the high-speed electric spindle work, sensors for measuring temperature, displacement and vibration are installed on the spindle to monitor the temperature rise, axial displacement and vibration of the motor, bearing and spindle. This provides correction data for the CNC system of the high-speed machining center to modify the spindle speed and feed rate to optimize the machining parameters. When the spindle produces an axial displacement, it can be compensated by zero correction or trajectory correction.
Linear motors At present, most of the high-speed machining centers or milling machines used for mold processing use servo motors and ball screws to drive linear axes. However, some machining centers have adopted linear motors, such as the RXP500DS/RXP800DS high-speed milling machine from Röders, Germany. Dejima's DMC75V linear high-speed machining center (with an axial acceleration of 2g and a fast stroke speed of 90m/min). Since the linear drive eliminates the transmission element that converts the rotary motion into a linear motion, the dynamic performance, the moving speed and the machining accuracy of the shaft can be significantly improved.
Machines driven by linear motors can significantly increase productivity. For example, when processing electrodes for electrical discharge machining, the processing time is reduced by 50% compared to the conventional high-speed milling machine.
Linear motors can significantly improve the dynamic performance of high-speed machine tools. Since most of the molds are three-dimensional surfaces, the tool axes are constantly braking and accelerating while the tool is machining the surface. Only with a high axial acceleration is it possible to ensure that a given contour is tracked with a constant feed per tooth on a shorter path path at very high path speeds. If the radius of curvature of the surface profile is smaller, the higher the feed rate, the higher the required axial acceleration. Therefore, the axial acceleration of the machine tool largely affects the machining accuracy of the mold and the durability of the tool.
Torque Motor In the high-speed machining center, the swing of the rotary table and the swinging and turning of the fork-shaped spindle head have been widely implemented using torque motors. A torque motor is a synchronous motor whose rotor is directly fixed to the component to be driven, so there is no mechanical transmission component, and it is a direct drive like a linear motor. The angular acceleration that can be achieved by a torque motor is six times higher than that of a conventional worm gear, and the acceleration can reach 3g when swinging a forked spindle head. Due to the extremely high static and dynamic load stiffness of the torque motor, the positioning accuracy and repeatability of the rotary and swing axes are improved.
At present, some manufacturers of high-speed machining centers have used linear motors and torque motors to drive linear axes (X/Y/Z) and rotary swing axes (C and A), respectively. Such as R?er's RXP500DS/RXP800DS, DMG's DMC75V linear and Edel's CyPort five-axis gantry milling machine.
It should be mentioned that the direct drive linear axis is combined with the directly driven rotary axis to give the machine a high dynamic performance and adjustment characteristics for all motion axes, thus freeing the mold for high speed, high precision and high surface quality. Surfaces provide the best conditions.
Control System The CNC control system is an important part of the high-speed machining center, which determines the speed, accuracy and surface quality of the machine tool to a large extent. Therefore, the performance of the numerical control system is of particular importance for high-speed machine tools that process free-form surfaces of molds.
When machining high-precision free-form surfaces, the tool path consisting of micro-segment lines and arcs creates a huge part program. These data streams need to be stored and processed by the machine control system. Therefore, the length of the block processing time determines the CNC control system. An important indicator of work efficiency. At present, the processing time of the high-end CNC control system is generally 0.5ms (such as HEIDENHAIN's iTNC530 CNC system), and the processing time of the individual CNC system has been shortened to 0.2-0.4ms.
Modern CNC CNC systems for high-speed machining of molds, in addition to the short program processing time necessary to ensure high-speed feed rates, should also have Nurbs and spline interpolation functions, and can work at nano resolution. In order to achieve high machining accuracy and surface quality in the case of high speed machining.
At present, high-end CNC systems can also be connected to CAD/CAM systems from different manufacturers, and data is transferred from the CAD/CAM system to the control system via Ethernet at a very high speed. The integration of CAD/CAM into the control system can, to a large extent, achieve good results in the processing of complex contours of the mold, and contributes significantly to shortening the adjustment time and programming time.
In the above-mentioned five-axis high-speed machine tool, except for R?er, which uses its own CNC system, the other mainly uses Siemens 840D and HEIDENHAIN iTNC530 CNC system.
Conclusion In the past decade, the advancement of drive technology and control systems has driven the continuous innovation and performance improvement of the machining center structure. The application of electric spindles, linear motors, torque motors and rapid CNC systems has played a decisive role in improving the high speed, high dynamics and high machining accuracy of machining centers. In many structural innovations in mold processing machines, torque motors play a particularly important role. It is applied not only to the rotary and oscillating drives of the rotary table, but also to the swinging of the forked spindle head or the swinging and slewing drive of the spindle head, thereby constituting various types of five-axis machining centers. The application of the rotary and oscillating spindle heads provides technical support for the development of five-axis gantry high-speed precision milling machines for machining large molds.
In the future, further improvement of spindle speed, dynamic performance and stroke speed is still the focus of high-speed machining center development, which not only depends on the further development of drive technology and numerical control technology, but also depends on the development of lightweight components of machine tools and parallel machine tools. Development. It can be expected that in the next five years, the axial acceleration of high-speed machining centers or high-speed milling machines is expected to reach 3 to 4 g, and the rapid stroke speed of the coordinate axes reaches 100 to 140 m/min.
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