Application and Common Problems of Linear Motor in CNC Busbar Machine
With the continuous development of high-tech industries such as defense, aerospace, automotive, and microelectronics, higher demands are placed on the manufacturing industry. Ultra-high-speed machining and ultra-precision machining have become the two themes of the future development of the machine tool industry. The traditional machine feed drive system is the "rotary motor + ball screw" mechanism. This kind of drive system involves many intermediate components, large motion inertia, and the ball screw itself has physical limitations, so the linear velocity, acceleration and positioning accuracy are limited, which can not meet the needs of ultra-high speed and high precision machining; Linear motor has attracted people's attention. It directly produces linear motion, simple structure, small motion inertia, high system stiffness, good fast response characteristics, precise positioning at high speed, and large thrust, especially moving speed and acceleration higher than ball screw. Several times, the work schedule can be infinitely long, with less maintenance and long life. These advantages make it an ideal component for modern machine tool feed drives.
The key technical problems of linear motors in machine tool applications are mainly AC linear motors for machine tool feed servo systems, which are divided into synchronous and inductive types. With the emergence of rare earth neodymium iron boron (NdFeB) permanent magnet materials and the improvement of cost performance, the development of permanent magnet synchronous linear motors has become the mainstream and the most widely used. Taking the application of such linear motors on high-speed and high-precision machine tools as an example, the key problems to be overcome are analyzed.
I. Thermal insulation and heat dissipation problems When the permanent magnet linear motor is running, the coil will heat up due to copper loss and iron loss, which brings several negative effects:
(1) Old damage or damage to the coil insulation layer, making the coil inconvenient to pass a larger current, so that no greater thrust can be generated.
(2) An increase in temperature changes the operating point of the permanent magnet.
(3) If heat is transferred to the machine? ? Worktables or guide rails, which cause thermal deformation will affect the machining accuracy. Therefore, especially for flat-plate large thrust linear motors, the temperature must be lowered. The maximum temperature of the magnetic steel is not to exceed 70 °C, and the coil temperature is not to exceed 130 °C. For the moving coil and the general moving magnet linear motor, the coil part can be cooled; but the moving magnetic linear motor under the ultra-precision requirement should adopt double-layer water cooling method with temperature sensor monitoring system. . U-shaped linear motors generally do not require cooling measures due to structural causes.
Second, the magnetic separation and protection problems Machine cutting fluid, iron filings, dust, etc. will pollute the motor, and even block the air gap, so the motor must be closed. Permanent magnet steel has a strong attraction to ferromagnetic materials. For safety reasons, it should be magnetically shielded and closed with a stainless steel cover. There should be a shock-absorbing device and an electronic limit switch at both ends of the linear motor to prevent the collision of the mover after the runaway. To protect the cable from the towline, the output signal cable must be shielded.
Third, the linear guide rails are required to bear the load, adapt to high-speed motion and ensure accuracy. The selection of the guide rail should consider the stroke size, mechanical characteristics, precision and speed bearing capacity. Generally, rolling (ball or roller) linear guides are used to ensure parallelism during installation. For ultra-precision requirements, an air static pressure guide can be used.
With the continuous innovation of the linear motor manufacturing process, the scale of production, and the decline in the price of permanent magnet materials and electronic products, the cost of linear motors is decreasing at a rate of 20% per year, and the application prospects on machine tools are broad. But this application is a new thing after all, whether it is a linear motor itself or a matching CNC technology, the potential is great.