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Discussion On The Methods Of Improving The Precision And Efficiency Of Precision High-speed Stamping Equipment For Motor Iron Cores

Large-tonnage, wide-table, double-drive, four-point ultra-precision high-speed press and matching demoulding cylinder device, automatic detection and automatic handling device can meet the needs of precision stamping and automatic unmanned production of motor iron cores, and will be obtained in the future.

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With the advent of Industry 4.0 and the continuous development of automation and informatization, the use of motors is becoming more and more extensive, and the requirements for motors are also getting higher and higher.

Faced with the increasing shortage of petroleum resources, the severe challenges of global warming caused by the increase in carbon dioxide emissions, and the increasingly fierce competition in the automobile industry, the world’s major automobile producing countries have raised the development of electric vehicles or hybrid new energy vehicles into national strategies. , and actively meet the challenge to the commanding heights of future competition.

The prime mover of electric vehicles or hybrid new energy vehicles is a high-power motor with high speed, low consumption and wide speed regulation range. At the same time, in the compressor industry, due to the national regulations that refrigeration and air-conditioning compressors need to meet the second-level energy consumption standards, the silicon steel of compressor motors Sheet thickness from 0,5mm down to o. 35mm, and there is a trend of continuing to thin.

Requirements For Precision High-Speed Punching Machines

As the core component of the motor, the quality of the motor core will directly affect the quality of the motor. The thinner the core material, the smaller the gap between the concave and convex dies in the mold must be, and the corresponding precision requirements for the press are also higher.Due to the constraints of cost and stamping equipment, industrial motors used composite dies to stamp silicon steel sheets in the past, but the efficiency of composite dies is low, and product quality is difficult to control, the overall labor cost is high, and the safety is low. It is gradually being replaced by multi-row progressive dies. It also puts forward higher requirements for the accuracy of the press

In order to meet the needs of the above-mentioned motor iron core stamping, there are the following requirements for stamping equipment

  • The press slide must be wider. The shape of the iron core of the new energy vehicle motor is large (the outer diameter of the stator is up to 300mrn), the shape is complex, and the geometric accuracy is high, which makes the step distance of the progressive die increase and the number of working steps increase.In order to save materials and improve efficiency, the shape of the stator and rotor molds must also be longer, and the sliders of high-speed punches using this mold must also be wider.
  • The precision of the press requires higher requirements. During the iron core stamping process, the lamination of the stator and the rotor needs to be completed (that is, the previous silicon steel sheet is protruded by a few points through the die, and the next silicon steel sheet is embedded to connect them to the required number. fall later). The repeatability of the bottom dead center of the slider will affect the consistency of the gap between the silicon steel sheets and cause the change of the magnetic flux when the motor is working. The verticality, stiffness and thermal deformation of the slider movement will affect the concentricity of the inner and outer holes of the silicon steel sheet, increase the motor noise, and affect its performance.This requires the high-speed press slider to have higher rigidity, smaller table verticality, smaller integrated clearance and higher slider bottom dead center repeatability
  • The energy consumption of the press is low. Sustainable development is the common goal of human society, and energy conservation and emission reduction is an urgent requirement of the manufacturing industry. Effective control and reduction of energy consumption not only meets the requirements and goals of national energy conservation and environmental protection, but also brings significant economic benefits to enterprises.Energy saving and consumption reduction also put forward higher requirements for the lightweight and high-speed movement of the slider of the press.

In a word, under the premise of ensuring quality, achieving central control with higher speed, higher efficiency, smaller energy consumption, more convenient operability and central control is the development trend of the stamping industry and the pursuit of stamping equipment manufacturing enterprises. Target

Methods To Improve The Performance Of Precision High-Speed Presses

In response to this situation, there are four aspects to be solved:

  • Improve the technical level of press equipment, including accuracy, operability, etc.
  • Improve the multi-column of the mold,
  • Automate your stamping process
  • Realize informatization and intelligent control, and finally reach the unmanned level.

On the premise of studying the development level of domestic and foreign presses, the GD320t wide table, ultra-precision new high-speed presses developed by Jingda Company meet the needs of the new energy automobile industry, integrated compressor motors and other high-end motor manufacturing industries for ultra-precision high-speed stamping. requirements, and provide stamping equipment reserves for product upgrading, energy saving and consumption reduction of small and medium-sized motor parts manufacturing industries.The technical indicators of the new high-speed press have reached the international advanced level, with independent intellectual property rights, and mastered the core technology of the new high-speed press, which has been practically applied in high-end motor core manufacturing enterprises

The core technology of the punch press includes dual-drive four-point force application, four-column overhead oil cylinder slider closed height adjustment, ultra-precision guidance and bottom dead center precision repeat control, etc. In terms of wide table, the length of the mold reaches 23m, so the stamping table of the press has different specifications such as 1.7m, 2.0m, 2.3m and 2.7m to meet the requirements of different molds.

The Punching Speed Of The Press Can Reach 400 Times/Min.

The punch adopts a two-sided drive four-point force application structure, that is, a motor and a clutch on the left and right are used for driving, and a four-point force application method for the slider is used. The reason is that the wide table press must have a large aspect ratio. The two-point force application structure of the drive and the slider makes it difficult to ensure the accuracy of the bottom dead center of the slider. Due to the long spindle, the span between the two force application points of the slider is relatively large, and the unilateral drive will cause a large phase difference between the two force application points.

The driving torque cannot be transmitted to the two application points of the main shaft at the same time, and the slider will tilt, as shown in Figure 1.The new type of press adopts the double-side drive form of the main shaft, so that the driving torque can be transmitted to the connecting rod force point of the main shaft at the same time (Figure 2), which effectively solves this problem

High rigidity is another important sign of the development of punch presses. The use of multi-row progressive dies puts forward higher requirements for the rigidity of punch presses. The design stiffness of ordinary presses is generally within the range of 1/60m to 1/8000. Some enterprises have adopted 1/10000, but in the process of large tonnage and high-speed stamping, such rigidity is still not enough. During the stamping process, due to insufficient rigidity of some presses, the riveting stack in the middle row will appear uneven.

At the same time, due to the large span of the force application point of the connecting rod, in order to achieve high rigidity of the slider, the design of the slider must be cumbersome, and it is difficult to achieve light weight. To achieve lightweight, high stiffness is difficult to guarantee. The use of four-point force application mechanism can realize the lightweight and high rigidity of the ultra-wide slider at the same time. At the same time, due to the lightweight of the slider, the inertial force during the movement can be reduced, and the motor energy consumption of the large-tonnage punch can be improved. By testing the press of Japan AIDA company, it is found that the stiffness of its SPM series press is 1/25m0, which is much higher than the standard of ordinary presses. The GD320t press is designed according to the stiffness of 1/30000. After the actual test, the stiffness value is 1/31m0, which fully meets the design requirements.

There are many factors affecting the repeatability of the bottom dead center. One of the main factors is the temperature rise generated during the movement. If the temperature rise is large, the thermal deformation will be large. A good lubrication system can effectively control the temperature rise. The flow rate at the point and the cooling temperature of the circulating oil are used to minimize the temperature rise of the press. On the other hand, the stiffness of the slider also affects the accuracy of the bottom dead center.

As mentioned above, the four-point force application mechanism and the finite element analysis of the slider are used to ensure the rigidity of the slider during the movement. Acceleration generates inertial force. On an automatic press with excellent performance, when the slider reaches the bottom dead center, the inertial force will be very large. In order to reduce the influence of inertial force and mechanism deformation on stamping accuracy, it needs to be balanced by reasonable mass. Balance the acceleration generated by the weight of the slider part and the upper die to improve the motion accuracy and the repeatability of the bottom dead center, and at the same time reduce the vibration and noise of the press.

The precision requirements of the press are also constantly improving. Several key indicators of the precision high-speed press, such as verticality, parallelism, and bottom dead center repeatability, have clear requirements. For example, according to the precision index of Japan’s sB6402 special grade, the verticality is required to be between 0 and 0165mm. In the actual measurement of AIDA’s SMP press, the verticality is between 0003 and 0,004mm.

In terms of improving the verticality, the upper part of the slider is guided by a four-point guide column guide sleeve, and the lower part of the slider is guided by an octagonal column guide pair (Fig. 3) On the one hand, the guiding position and the material in the die stamping process can be on the same horizontal line , improve the guiding accuracy, on the other hand, the rolling friction structure is used to replace the sliding friction to achieve zero-gap friction and further improve the guiding accuracy. The rolling friction force is smaller than the sliding friction force, so the design of this structure can reduce the energy consumption of the press and achieve the purpose of energy saving.

At the same time, the press guide is subjected to eccentric load, which causes the friction of the guide pair to generate heat, the guide is heated to expand, and the wear of the guide pair increases. , which affects the guiding accuracy. Due to the wider die, the eccentric load on the wide table is more complicated, and the frictional heat generated by the guiding pair is larger. Therefore, the structure of the octagonal prism has a higher heat dissipation efficiency and improves the guiding precision. In the actual test and use, it is found that the verticality of this guiding method can also reach 0003mrn, which can meet the requirements of precision high-speed stamping.

On the one hand, the design of the overhead cylinder can realize the overload protection of the press during the stamping process. When the overload occurs, the cylinder drives the upper beam to automatically rise to protect the punch and die, especially for large-tonnage dies. It is easy to test the die at low speed. The phenomenon of jamming occurs. On the other hand, due to the use of large-tonnage punches, the size of the mold is getting larger and larger. The disassembly and assembly of the mold requires a lot of physical strength for the operator. Since the stroke of the press is only about 30mm, it is difficult to see It is not easy to remove the waste after cleaning the inside of the mold. The overhead oil cylinder can lift the upper beam by 150mm, which greatly facilitates the operation.

The traditional slider closed height adjustment and overload protection mechanism are all set on the connecting rod. The connecting rod adopts a segmented ball head structure, which increases the link that generates the gap and the weight of the slider. Its structure is complex, and the thread at the adjustment place bears alternating loads , The use of large pitch threads increases the height adjustment error and the mechanism distribution spacing is small, and the height adjustment is prone to errors, which will lead to poor parallelism retention of the press. The closed height adjustment of the worm-gear-sleeve type slider has the advantages of simple connecting rod structure, light weight of the slider, large spacing distribution of the adjustment mechanism, small adjustment error, and can well solve the problems of overload protection and limited adjustment range of the slider. ,As shown in Figure 4.

With the improvement of the precision of the press, in the actual stamping process of thin materials (ie, silicon steel sheets with a thickness of 0,35mm), it is found that only relying on the improvement of the precision of the die and the press cannot solve all the problems. The company has newly designed a demoulding cylinder system. The main principle of this system is passive pressure relief. The product is pressurized at the moment of the finished product through the upper and lower pressure, and the product is pressurized during the whole process, thereby improving the concentricity and end face of the product. Beating precision. First set a reasonable system oil pressure (less than the punching shear force of the punch), the cylinder piston rises, the cylinder head stands against the product, the magnetic induction receives the signal and the punch starts to run, each punching time, the oil cylinder drops a little (passive pressure relief) each time the downward stroke is about consistent with the material thickness. When the product reaches the desired height, the cylinder is cut, the cylinder supports the product and descends to the plane of the mold platen, and the cylinder pushes out the product.

Practice has proved that this structure can effectively improve the flatness and concentricity of the iron core. At present, the well-known compressor factories in China are basically using this system, such as Meizhi, Mitsubishi, Panasonic, Hitachi, Chunlan and so on. Taking Meizhi as an example, the iron core product with a thickness of 85mm is not subjected to hydraulic shaping, and the concentricity is detected at 3 points. Each point of the rotor is within 0.04mm, and the stator is within 0.06mm.

The stamping of the iron core of the motor realizes automatic riveting and stacking, and the discharge of waste material realizes automatic hydraulic shaping of the stator and rotor through the conveyor belt. Automatic detection is realized by height detection or weighing. The handling manipulator carries out automatic handling and automatic stacking to achieve an unmanned production method. As shown in Figure 5, some external dimensions are identified by the image recognition system. At the same time, through the computer control system, the stamping running time, failure time and production speed are analyzed. Automatic recording, realizing central control, no need for manual statistics and calculations, and truly unmanned production.

Concluding Remarks

From the above analysis, we can draw the conclusion that the current large-tonnage, wide-table, double-drive, four-point ultra-precision high-speed press and the matching demoulding cylinder device, automatic detection and automatic handling device can realize the precise high-speed stamping and The need for automated production will surely be further applied and promoted in the future.

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