1 Introduction
Our company has imported several ZSTZ315/630 C3 gear grinding machines from the original East Germany, which has good machining accuracy and high efficiency. However, due to the products designed in the 1970s, the relay logic was used in electrical control, which was not only bulky and complicated in structure, but also difficult to maintain. Especially after nearly two decades of use, spare parts were exhausted, and the relay contacts were seriously damaged. The rate is high. Due to sufficient lubrication, the wear of the guide rail, screw, screw nut, sliding table and worktable worm and worm gear of the machine tool is not large, and the machine tool mechanical precision is kept well. Recently, we used the NUM1040 numerical control system and the corresponding drive and servo motor to carry out the numerical control transformation on the indexing worktables 1 and X axis, and mechanically removed all the hanging wheels, which not only made the operation simple, but also improved the transmission accuracy. The electrical control uses PLC to replace the original relay logic, simplifying the circuit structure. The cumulative error of gears detected after machining reaches 0.0052mm, pitch deviation is 0.0038mm, 6 pitch is 0.0046mm, and the jump is 0.009mm. The precision of the processed workpieces is good and the transformation is completely successful.
2. Numerical control reform program
The main parameters of the ZSTZ315/630 C3 gear grinding machine are as follows:
Working table diameter: 315mm/630mm Worktable bearing: 200kg/400kg
X-axis stroke: 360mm Grinding wheel grinding angle: 14~26 degrees Slider stroke length: 20~225mm Stroke times: 75~315/Min
The movement of the original machine tool is accomplished through various mechanical transmissions. The indexing table (B-axis) and X-axis use a three-stage hanging wheel to realize the grinding movement according to the size of the processing gear, the module and the number of teeth. After the transformation, the X and B axis servo motor shafts are directly connected to their respective screw shafts through couplings, eliminating the hanging wheel and reducing the transmission error. In order to reduce the cost of renovation and shorten the renovation cycle, after research and demonstration, the following numerical control transformation plans have been identified:
(1) The NUM1040 numerical control system is used to control the generative motion of the grinding process. The X and B axes are driven by the AC digital drive modules MDLA and BPH servo motors, and a 3032-line encoder is used to form a semi-closed loop control. The use of numerical control system for X and B two-axis linkage and interpolation operations to complete the processing of a variety of gear profiles.
(2) Utilize the built-in PLC function module of NUM1040 system to control the machine operation, hydraulic pressure, cooling, lubrication, wheel start/stop and slide stroke, replacing the relay logic circuit of the original machine tool, which improves the stability and reliability of the machine tool. .
(3) Retain the mechanical part of the original machine tool dresser, and change the original DC motor used for dress dressing to a 3 x 380V, 1200R/Min, 30W AC micro-motor, and add a small commutation contactor to achieve trimming 1 and Trim 2 features.
(4) The grinding wheel drive motor and the slide stroke motor are retained, and the hydraulic pressure, lubrication, and cooling parts are not changed.
3. Configuration of CNC system
(1) The composition of the CNC hardware module
NUM1040 is a full-featured CNC system integrating CNC and PLC. It can control 1-6 axes (4-axis interpolation). The basic configuration of input/output points is 64I/48O (can be extended to 256I/O), 1- 3 handwheels, 8.4 inch LCD color display. It can realize the monitoring from tool path control to external equipment. The CNC system hardware adopts CMOS circuit, optical fiber communication technology and modular design ideas, which reduces the connection between the system and the outside world, and improves the reliability of the entire machine tool electrical system. The system consists of power supply, CNC, and drive modules. The system software has an open and friendly interface, can provide helpful programming methods and powerful communication functions, complete screw pitch error compensation and a variety of interpolation methods, the user can easily write their own fixed cycle according to the processing characteristics need. The hardware configuration of the system is as follows:
(2) Modular design of PLC program
The NUM CNC system is a built-in PLC structure. The machine is equipped with two 32-input/24-output (outputs with relays, and each relay has two pairs of moving/moving open contacts) I/O expansion board. Using ladder programming language, modular programming, according to the control function PLC program is written into multiple modules, each module to complete the specified function, each function module unified by the main task module cycle call. The program thus designed has high readability and high reliability of logic control. The main modules are:
% INI - system initialization module: complete the control system parameter settings and optimization checks. I/O ports, timers, and counter presets. The start address and capacity of the stack, data protection area, and data exchange area are determined.
%TS—Master task module: Complete loop calls to each function module %FP.
%TP1~n—Functional module: Data exchange with the CNC; servo axis feed control; function code processing, wheel dressing control; slide motion control; operation panel processing, alarm text processing, etc.
%TH—Interrupt processing module: Processes random events in real time.
PLC control program flow chart is as follows:
4 Conclusion
The grinding machine is mainly used for grinding involute cylindrical gears. The involute tooth profile was ground using the generative-indexing principle, and the involute tooth profile was generated using the conical grinding wheel according to the meshing principle of the rack and the gear. The two X-axis and B-axis axes are combined to realize the generative movement. At the same time as the generative movement, the rotating grinding wheel reciprocates in the tooth direction together with the sliding table, and once it develops into a cyclic process, an involute tooth surface is generated.
The worktable is a numerically controlled rotary motion. When it develops to the indexing position, the grinding wheel automatically retracts out of contact with the workpiece and the workpiece is indexed to the next tooth slot. The size and accuracy of the indexing are determined by the control system. For gears of different sizes, moduli, and number of teeth, the CNC system automatically calculates and controls the development and indexing movements.
Since the transformation of this machine tool, because of improved mechanical transmission accuracy, plus reasonable use of clearance and pitch error compensation capabilities, workpiece machining accuracy and work efficiency have improved. The machine tool performance is stable and reliable, and no major failure has occurred since the operation. According to preliminary statistics, the failure rate is reduced by more than 80% compared with that before the transformation.
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