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I. Introduction
The piston is a key component of the car engine. The quality and output of the piston directly affects the quality and output of the car. At present, China's car industry is developing very rapidly. Take the development of Shanghai Volkswagen Santana sedan as an example. In 1994, the production program was 100,000 vehicles per year. In 1995, it was 150,000 vehicles. In 1996, it reached 200,000 vehicles. In 1997, it reached 250,000 vehicles. At the end of the century, it will reach 500,000. Shanghai's new SGM company will launch new mid-to-high-end cars by the end of 1998, so the demand for pistons will be even greater. Shanghai Piston Factory is a professional factory that can directly produce pistons with cars. In order to cooperate with Santana car production, the factory has gradually introduced more than 10 million US dollars of key processing equipment for piston processing from abroad in the mid-1980s. The first car uses a piston production line, but its production capacity can only provide an annual service cost of 100,000 to 200,000 Santana sedan. To produce pistons with an annual output of 500,000 Santana cars, it is necessary to introduce tens of millions of dollars of key equipment, which is unbearable for enterprises. In order to reduce the cost of piston manufacturing and develop China's advanced manufacturing technology, it is imperative to develop key process equipment for piston processing. To this end, in 1994, Shanghai Piston Factory proposed the localization of imported equipment according to the needs of production development. After more than half a year of investigation and research, Shanghai Jiaotong University and Shanghai Piston Factory signed a fully automatic CNCé•— with the support of Shanghai Key Office, Shanghai Santana Car Localization Office, Shanghai Automotive Industry Corporation, and Shanghai Santana Car Research Project Office. The research and development agreement for the special machine tool for cutting the pin hole of the piston, and the team composed of Shanghai Jiaotong University, Shanghai Piston Factory and related machine tool factory, formulated a detailed research plan. After more than two years of hard work, the fully automatic CNC boring piston pin hole special machine tool was finally developed, and was delivered to the Shanghai Piston Factory in August 1997 for production.
It has been tested and produced by the Shanghai Branch of the Machine Tool Product Quality Supervision and Inspection Center of the Ministry of Machinery Industry. The machine has stable performance and reliable quality. In January 1998, it passed the appraisal jointly organized by the Ministry of Machinery Industry and Shanghai Automotive Industry Corporation.
Second, the requirements of the parts being processed
The boring of the piston pin hole is a more complicated process in the piston machining process, including the machining of the five parts of the boring hole, the outer ring opening, the cutting ring groove, the inverted inner angle and the inverted outer angle. Figure 1 is a simplified view of the machined part. The material is silicon-aluminum alloy, the processing size requirements are: pin hole diameter is φ19.5+0.050mm, the distance from the end face of the port to the inner surface of the pin hole is 19.24±0.03mm, and the diameter of the ring groove is φ21.7+ 0.13-0.05mm, width 1.6+0.10mm, radius of the bottom of the groove is R0.8mm, outer diameter is φ22.2+0.40mm, arc radius is R0.5mm, inner arc radius is R0.5mm, The width is 0.8+0.2-0.1mm, the outer taper is 40°±10′, the distance between the outer faces of the two holes of the pin hole is 60+0.20mm, and the distance between the two outer corners is 62.15±0.2mm. The distance between the two is 65 ± 0.2 mm. The position requirement is: the symmetry requirement of the retaining ring groove, the outer port and the outer corner to the center line of the piston is 0.2 mm, and the perpendicularity between the end faces of the two inner corners and the center line of the pin hole is required to be 100:0.8, and the retaining ring groove is opposite to the pin hole. The radial runout of the centerline is 0.1 mm, and the pinhole centerline is not coplanar with the piston centerline, and the pitch is 1.2±0.75 mm. All of these processing requirements are guaranteed by one-time processing in one installation, no downtime, and no change of position.
Figure 1 Schematic diagram of the machined parts
Third, the working principle of the machine tool
The characteristics of piston machining are large batch size, high processing precision, fast production tempo, high degree of automation and good processing stability. In response to these characteristics, this project designed a fully automatic CNC boring piston pin hole special machine as shown in Figure 2. (The D-cylinder and E-cylinder-driven gear alignment mechanism in the figure is aligned with the rear part of the piston to be machined at O1, G Align the front and rear of the piston to be machined at O2 with the F cylinder. The whole machine consists of bed, spindle system, eccentric mechanism, knife row, automatic loading and unloading mechanism, pneumatic system, numerical control and servo system. The following describes the principle of automatic loading and unloading and numerical control multi-knife double eccentric boring.
Figure 2 Schematic diagram of the special CNC machine for boring the piston pin hole
1. Feeding trough 2, 3. Servo motor 4. Spindle motor 5. Spindle 6. Eccentric sleeve 7. Robot 8. Knife 9. Feeding trough 10. Console
(1) Fully automatic loading and unloading
The automatic loading and unloading mechanism has the functions of automatic detection, fault diagnosis and alarm, which is the key to realize high-volume, fast-beat and automatic processing. It can increase labor productivity, reduce labor intensity, ensure consistency of processing accuracy and coordination of automated production lines. The working process is as follows: the piston automatically input by the previous process (automatic CNC fine-engine piston stopper special machine tool) is stored in the loading trough 9. After the pressing cylinder A is released, the piston automatically rolls down to the blocking material. The cylinder B is blocked (the distance between the retaining cylinder B and the pressing cylinder A can only accommodate one piston); then the pressing cylinder A returns to the pressing state, preventing the rear piston from rolling down; then the retaining cylinder B is released The piston is rolled into the V-shaped block, and the retaining cylinder B is reset; after that, the pushing cylinder D pushes the piston into the robot 7; at this time, the positive cylinder E is rotated to perform the orientation correction; after the alignment, the D and E cylinders are aligned. Reset; then the loading cylinder C pushes the robot 7 to the front end of the positioning member socket; the top cylinder G pushes the piston into the socket and tightens; then the loading cylinder C is reset; then the machining is started. At the same time of processing, the A, B, D and E cylinders are operated for feeding, which can reduce the feeding assist time. After the machining is completed, the top-cylinder cylinder G is relaxed, and the discharge cylinder F pushes the piston to eject from the stopper seat, and the material is slid down through the guide rod.
The coordination of the above actions is done by the numerical control system and the PLC control system, and the reliability of the action is completely dependent on the performance of the pneumatic system.
(B) the principle of CNC multi-knife double eccentric boring
Since the piston is mass-produced, efficient processing equipment and a reasonable processing process are required. CNC technology and online inspection technology are key technologies for efficient and flexible automated production. The relative concentration of the process is beneficial to reduce the number of workpiece installations, avoid installation errors, reduce the number of machine tools and tooling, reduce floor space and auxiliary time, and reduce the probability of failure and improve machining accuracy. To this end, the machine adopts CNC multi-knife double eccentric boring technology to realize the piston pin hole, outer port, ring groove, inner and outer chamfer in one installation, no tool change, no stop, no change of position. Efficient and fully automatic processing.
As shown in Fig. 1, the piston pin hole is divided into two sections, each of which has five processing parts, namely an outer port, an outer chamfer, a pin hole, a ring groove and an inner chamfer. The CNC multi-knife double eccentric boring technology adopts numerical control technology and eccentric mechanism to control two spindle heads at the same time under the premise of ensuring the coaxiality requirement. Each spindle head is equipped with a cutter row, and each cutter row is equipped with five tools, which respectively complete the processing of five parts such as the boring hole, the outer ring opening, the cutting ring groove, the inverted inner angle and the inverted outer angle. The working principle is shown in Figure 2: the spindle motor drives the spindle through the belt pulley together with the eccentric rotary drive shaft, the coupling, the eccentric sleeve, the eccentric shaft and the cutter row to rotate together for the main cutting movement, the center line of the eccentric sleeve and the spindle rotation center line There is an eccentricity e1 between them, and there is another eccentricity e2 between the center line of the blade mounting hole and the center line of the eccentric shaft, which is generally designed as e1=e2. In the initial position, the center line of the knife row coincides with the center line of the spindle rotation. When the eccentric rotary drive shaft drives the eccentric shaft in the eccentric sleeve through the coupling and the cutter row fixed thereto rotates by 180°, the distance between the center line of the cutter row and the center line of the spindle rotation is e1+e2. When the knife row returns to 0°, the center line of the knife row and the center line of the spindle rotation coincide.
According to the processing requirements of the piston, the boring knife, the outer knives and the grooving, the inverted inner angle and the inverted outer knives are respectively arranged at the symmetrical positions of the knives. First, when the center line of the cutter row coincides with the center line of the spindle rotation, the inner hole and the outer port of the outer ring are turned to the size, and the servo motor 3 drives the eccentric shaft to rotate along the direction of the spindle rotation. Due to the eccentric action, the boring knife and the outer edge of the boring tool The radial retraction, while the remaining three knives (grooving knives, inverted outer knives and inverted inner knives) are fed in the radial direction to complete the work of cutting the groove, the outer corner and the inner corner. The axial feed is realized by the servo motor 2 driving the ball screw pair and the linear guide, mainly completing the feed of the bore and the fast forward and reverse movement of the spindle box. In this way, efficient automatic machining of the five parts of the piston pin hole is realized in one installation, no change of the tool row, no stop, and no change of the work position.
Fourth, the machine tool control system
The control system of the fully automatic CNC boring piston pin hole special machine tool is mainly composed of numerical control system, servo system and pneumatic system. The numerical control and servo system adopts the products of Siemens AG of Germany, which consists of 810M numerical control system, 611-AIRF drive power supply, spindle motor, AC servo feed motor and servo drive module. The 810M CNC system is a compact CNC control system for milling machine tools. It consists of CNC, PLC, operation panel and display. The CNC is the control center of the entire machine tool, which can be used for NC programming. During the machining process, the CNC receives information about the position and status of the machine and issues various commands to control the machine to perform the desired action. The PLC (Programmable Logic Controller) is integrated inside the CNC controller. It is the interface between the CNC and the machine tool. It is responsible for the exchange of information between them. It controls the machine from automatic loading and execution of various auxiliary actions to automatic Material and other action processes to achieve sequential control of the machine. The PLC is programmed in STEP5 language and can be written in three expressions: “statement tableâ€, “control system flow chart†or “ladder diagramâ€. The spindle motor adopts Siemens' two-speed motor, and the speed is changed by Y-Δ switching. The spindle is driven by the belt pulley together with the eccentric rotary drive shaft, the coupling, the eccentric sleeve, the eccentric shaft and the cutter row to rotate as the main cutting motion. The four servo axes are driven by SIMODRIVE 611-A servo drive module and its AC servo motor. The servo drive module mainly controls the synchronous linear feed and eccentric feed of the left and right files according to the information sent by the CNC. The servo motor is equipped with a speed encoder and position encoder for precise control of tool feed. The pneumatic system adopts the valves, cylinders and sensors produced by Germany FESTO Company, which are managed by PLC and have the characteristics of reliable action and stable performance.
Fifth, the main features of the machine tool
(1) The standard is unified, with automatic positioning and automatic pressing function. It can realize the processing of the five parts of the piston pin hole, the outer hole, the cut ring groove, the inverted inner angle and the inverted outer angle efficiently and automatically in one installation, no stop, and no change of the knife row. Benchmark uniformity can reduce installation times, installation errors and installation time, save tooling fixtures and machine footprint, reduce failure probability and improve machining accuracy.
(2) The double-head, double eccentric, multi-tool spindle system and symmetrical servo drive structure can realize the relative concentration of the process and improve the machining accuracy of the machine tool.
(3) Fully automatic loading and unloading mechanism with automatic detection and fault alarm. It is the key to achieving high volume, fast beat and automated processing, which can improve labor productivity, reduce labor intensity, ensure consistency of processing accuracy and coordination of automated production lines.
(4) Pneumatic, electrical and numerical control systems with high stability and reliability, easy operation and convenient maintenance. As mentioned above, all pneumatic, electrical and CNC components are products of a reputable company in the world. Therefore, the quality is reliable, the performance is stable, and the interchangeability is good.
The whole machine tool fully embodies the organic combination of machine, electricity, gas, PLC control technology and numerical control technology, and is a typical application of advanced manufacturing technology.
Conclusion
The above special machine tool realizes fully automated processing of the piston pin hole. In the case of one installation, no stop, no change of position, from loading, processing to unloading fully automatic. The machine has been put into production at the Shanghai Piston Factory, and it has been connected with the previous fully automatic CNC finishing piston valve special machine to realize the automatic production of wiring. Through the inspection and actual production assessment of the Shanghai Branch of the Machine Tool Product Quality Supervision and Inspection Center of the Ministry of Machinery Industry, the performance indexes of the machine tools have met the design requirements. The processing cycle is: the processing time of each piston is less than 20 seconds.
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