Development of machine tools made by electric spark

With the development of high precision, diversified materials, and complicated processing in the manufacturing field, higher demands are placed on manufacturing equipment. Therefore, the development of high-speed, high-precision special processing equipment with intelligent control has been The goal people pursue.

Precision CNC special processing machine tools are important equipment for precision machining technology. They are of great significance for precision machinery, automotive, microelectronics, home appliances and aerospace precision parts and precision tooling. At present, China's precision processing level is still quite different from that of developed countries. Some precision products in China still need to be imported (mainly precision machine tools and CNC machine tools). The more sophisticated and ultra-precision processing and manufacturing equipment, foreign mastery The countries with the technology and equipment have imposed embargo and technical blockade policies on China. It is of great significance to develop high-grade precision special processing machine tools and realize their industrialization. It is very important for the level of the whole machine technology of special processing machine tools in China to approach or catch up with the international advanced level. The results of this paper adopt the means of introducing digestion and absorption and independent innovation, and the precision automatic multi-axis numerical control EDM machine tool developed by the company has made certain contributions to China's special processing industry.

I. B-type precision CNC EDM machine tool The B-type precision CNC EDM machine adopts the “C” structure and the center load form, forming the most reasonable wedge structure with bilateral symmetry. The utility model has the advantages of good rigidity, uniform pressure of the guide rail and high precision. The bed and column of the machine tool are made of high-quality cast iron resin sand casting technology. After two times of aging treatment, the machine tool has high static, dynamic rigidity and vibration damping performance, which is the premise of precision CNC machine tool precision guarantee. The machine tool table is made of high-quality granite material, which is made of high-quality granite material. This material has small thermal deformation and can ensure the long-term maintenance of the machine tool. The insulation is good, which can greatly reduce the parasitic capacitance between the two poles during electrical discharge machining. The guarantee of mirror processing. The lead screws and guide rails of the X, Y and Z axes are made of high-precision imported parts. The imported grinding grade (C2 grade) high-precision ball screw, ultra-precision grade (HP grade) linear rolling guide and high precision (P4) Level) Two-way, non-gap back push ball bearings. The advantages are small friction force, high motion precision and good precision retention. In addition, the rigidity and sensitivity are relatively high, and the electromechanical control performance is relatively good. Therefore, the precision of the machine tool is very high, the positioning accuracy is 2μm/arbitrary 100mm, and the repeat positioning accuracy is 2μm. The spindle head adopts high-performance AC servo motor and rolling guide, ball screw straight drag structure, and is equipped with high-precision encoder. Achieving a drive equivalent of less than 0.1 μm/single pulse and a motion with a maximum travel speed of up to 10 m/min enables high-rigidity connections and high-sensitivity motion control. It has the advantages of low friction and small backlash, avoiding low-speed crawling, etc., and improves the servo performance of the spindle. It is a structural diagram of a precision CNC EDM machine tool.

Second, the B-type EDM machine tooling machine with precision indexing axis B-type EDM machine tool precision indexing axis (C-axis, also known as U-axis), can be accurate angular positioning and continuous rotary servo machining. The C-axis and the Z-axis can be used to machine internal and external threads, internal and external helical gears, and the like. The C-axis is linked with the X and Y axes, and can be used for complex parts such as racks, drum molds, and various woodworking tools. Processing. The CNC EDM machine is equipped with a C-axis, which greatly expands its processing range and enhances processing capabilities. Especially when machining a workpiece with a curved or curved shape, the C-axis can be linked with other axes to machine complex cavities and sections, such as worm gears, worms, and threads, in a three-dimensional space. It is equipped with a high-precision built-in C-axis photo of Swiss 3R on the B-type EDM machine. This C-axis can achieve high precision. Its main technical indicators: 1 minimum index (resolution): 12.96" / single step; 2 backlash: 21.6"; 3 positioning accuracy: 21.6"; 4 repeat positioning accuracy: 7.2"; 5 rotation speed: 0 ~ 20rpm / min; 6 maximum processing current: 30A; 7 maximum load weight: 5kg ; 8 chuck clamping range: Ф 3 ~ 20mm.

Built-in C-axis photo 3. Automatic electrode quick exchange jig In order to solve the problems of electrode manufacturing with complex shapes, small size or inability to machine the reference surface, and electrode manufacturing for the tool magazine, it can be fixed in the electrode before processing. Additional reference (carrying clamp), and ensure the connection between the clamp and the electrode is reliable. This is used as the positioning reference for the electrode, the milling, the electric discharge wire cutting and the final EDM forming process. The principle of the benchmark, so the controllability and repeatability is good, that is, the assembly and disassembly process can ensure the positional accuracy and reduce the auxiliary adjustment time without adjustment. This quick-changeable clamp consists of several chucks and chucks. There are at least two chucks, one for electrode manufacturing, one for lathes, milling machines or EDM machines, and the other for EDM. On the machine. There are more chucks and one chuck for each electrode. It is a high-precision quick change fixture photo.

It is composed of a connecting base, a clamping rivet, a positioning piece, four supporting legs and a locking device. The clamp engages the prismatic body on the chuck by positioning the four square holes distributed on the chip as orientation and centering, plus four plane support foot supports, adopting the principle of positioning error compensation, in the flexible positioning piece and Stable positional accuracy is established between the rigid central prisms for precise positioning of the electrodes. When clamping, insert the clamping puller into the hole of the connecting base, tighten the locking screw with a special wrench, and push the self-locking ball locking mechanism to clamp the electrode firmly. The clamping force is 4000N. It will not loosen when there is no external force. The positioning accuracy is high and the installation is simple and convenient. The use of quick change fixtures simplifies the installation calibration process and improves the positioning accuracy. The repeat positioning accuracy can be controlled to about 2 μm.

High degree of automation, reduced clamping and standby time are another feature of quick-change fixtures. Since the electrode and the workpiece are clamped, corrected and machined by the quick-change fixture, the electrode and the workpiece can be clamped, corrected and measured outside the machine. The compensation value can also be measured outside the machine and pre-programmed. For example, after the electrode is formed by car, milling, grinding, and electric discharge wire cutting, the degree of conformity with the pattern is checked in the coordinate measuring machine, and the positioning error in the machining is measured, and the software is transmitted through the programming, and transmitted with the electrode. On the spark forming machine, the machine compensates during machining.

Furthermore, the electrodes and the workpiece are placed in the tool magazine, and the robots can exchange the required electrodes or workpieces according to the instructions, thereby achieving unmanned operation. It can be seen that the quick change fixture not only saves adjustment time, but also is the basis for the automation of the EDM process.

A2 type intelligent precision digital electric spark forming processing pulse power supply pulse power supply is an important part of EDM machine tools, processing performance of almost all EDM machines, for example, processing stability, processing speed, electrodes Loss, surface roughness of the workpiece, surface deterioration layer, etc. are all related to the pulse power supply.

The A2 intelligent precision digitally controlled EDM forming pulse power supply system developed in this paper consists of CNC system and EDM control system, power amplifier unit, main circuit unit, automatic voltage adjustment unit and motion axis drive unit. The EDM control system mainly includes the following parts: clock control and discharge pulse signal generation part, current and voltage parameter setting part, special processing waveform control part (equal pulse width, step wave), lift control part, servo gap and discharge State (voltage and current) detection section, abnormal discharge processing section (increase pulse, cut pulse width, decrease pulse width, increase current), and the like. The main circuit unit includes the following parts: low-pressure processing circuit, high-pressure processing circuit, high-low voltage composite circuit, low-loss circuit, super-precision circuit, special material processing circuit, etc. According to the main circuit and the additional circuit of the pulse power supply provided, a combination of various waveforms can be obtained, which can be arbitrarily selected and superimposed on the discharge gap for different processing technology requirements, so that the processing object obtains the best process effect. The power amplifying unit completes power amplification of the processing pulse voltage and current, and is composed of an IGBT power switch tube and a front drive amplifier circuit. The automatic voltage adjustment unit provides stable processing voltage, which is realized by the thyristor rectification automatic voltage regulation loop, and can realize numerical control and various protection functions.

The structural block diagram of the precision CNC EDM pulse power system is shown in the figure.

V. The main technical indicators independently developed the super-precision discharge circuit, which realized the fine adjustment of the current from IP0.1 to IP0.9. The mirror processing circuit was successfully developed, and the optimal surface roughness was R a≤0.05μm (500mm 2 ). High-precision motor driver system using 17-bit encoder with high positioning accuracy and high machining accuracy; minimum drive accuracy of control system is 0.1μm; positioning accuracy of X, Y, Z axis is 2μm/any? In the sixth phase of 2007, 47 100mm, the repeat positioning accuracy is 1μm (ISO 11090-1:1998 standard); the machining accuracy is ±1μm under certain conditions.

Sixth, typical processing experiment 1. High-efficiency mirror processing The experimental electrode is a copper rod, and the workpiece material is S136.

Input parameters: processing area 79mm 2 (Ф10mm), machining depth 1 mm, machining surface roughness R a 0.05μm and electrode scaling amount 300μm. The experiment uses intelligent automatic processing, input the above processing parameters, the numerical control system calculates the result according to the neural network. Automatically generate machining programs and optimize process parameters to complete the entire process. Processing time is less than 1h.

When the processing area is 314mm2 (Ф20mm) and the processing depth is 0.5mm, the processing time is about 1h40min. When the processing area is 490 mm 2 (Ф 25 mm) and the processing depth is 0.5 mm, the processing time is about 2 h. When the processing area is 706 mm 2 (Ф 30 mm) and the processing depth is 1.0 mm, the processing time is about 4 h. When the processing area is 962 mm 2 (Ф 35 mm) and the processing depth is 1.0 mm, the processing time is about 4 h 20 min. The surface roughness of the above processing can reach R a≤0.1μm.

2. Rod-shaped electrode development processing (three-axis linkage) It is well known that the significance of numerical control of EDM machine tools is mainly manifested in two aspects: First, the automation of operation is realized, the processing precision and efficiency are improved; Application range. The processing of various patterns is performed according to program control using electrodes of a rod shape or a simple shape. It is a photo of a processing example of processing 45 steel with Ф2 copper rod. In the experiment, the processing of linear and circular interpolation was completed, and the processing of different depths, that is, the processing of three-axis linkage, was also performed.

3. The four-axis four-link machining experiment is equipped with the self-developed precision indexing rotary shaft U-axis (C-axis) on the machine tool, and the four-axis four-link machining experiment with the other three linear axes. The machining sample shown in 0 is A schematic diagram of a space-shaped automobile seal forming mold, which uses a sheet-shaped copper electrode having the same shape as the end surface, and a cavity surface built by a servo linkage of X, Y, Z, and U four axes, which is Shaped molds are difficult to machine with.

VII. Conclusion The B-type precision numerical control EDM machine tool and the A2 intelligent precision digital electro-discharge forming pulse power supply system have been developed. The high-precision positioning control with repeatability of 2μm is achieved. The minimum surface roughness of the EDM is R. a ≤ 0.05μm (area 490mm 2), the maximum processing speed of 480mm 3 / min (50A, copper-worked steel), the lowest electrode loss ≤ 0.05%; achieved multi-axis linkage processing (such as four-axis four linkage processing experiments). B-type precision CNC EDM machine tool and A2 type intelligent precision CNC EDM processing pulse power supply have achieved industrial production, and have been well received by users in the mold, military, aerospace, woodworking tools and other industries.

(Finish)

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Luoyang Golden Egret Geotools Co., Ltd , https://www.lygoldentool.com