The rudder surface is generally made by 3D printing process, the external size is large, it is an irregular flat space shape, and is composed of thin-walled structures such as upper and lower skins, multiple stringers, and multiple wing ribs, the thickness of the trusses and wing ribs is about 2mm, and the thickness of the skin is about 1mm, which belongs to the thin-walled weak rigid shell structure. The dimensional accuracy, shape and relative position accuracy of the rudder surface and other shafts or bushing fixed parts are required to be high, and there are many counterbores, taper holes, small holes, deep holes, keyways and cavities in the transverse, longitudinal, inclined plane and internal in the structure. The materials are mostly titanium alloys, high-temperature heat-resistant alloys, stainless steel and other difficult-to-machine materials. Fig. 1 shows the local structure of the fixed part of the rudder surface part and other shaft parts, and its main processing features are all on the left and right sides of the U-shaped area, and the space size is small, and the mechanical drilling, milling cutter is difficult to reach, and it is not easy to realize the processing, and the main processing content and technical requirements are as follows. (1) Left: Machining 10 (0 +0.) at a position of 33mm from the m datum015) mm deep 145mm round hole, spacing (15 0..)01) mm position processing 105(0~+0.018) mm, taper 1 20 deep 14mm taper hole, taper hole large diameter port round r05mm。(2) Right: Machining 17 (0 +0.) at a position of 33mm from the m datum018)mm deep 26mm round hole, round hole with width 6 (0 +005) mm deep 26mm keyway, spacing (15 0..)01) mm position processing 105(0~+0.018)mm, taper 1 20 deep 14mm taper, the front end of the taper hole round r05mm。(3) The shape tolerance of the part is required to be 001mm, position tolerance is 0015mm, surface roughness ra 16μm。(4) When clamping and positioning parts, it is not allowed to clamp and bump the skin surface, and the error in all directions of the positioning datum is 001mm。As can be seen from Figure 1, the parts have the following characteristics: the overall size is large (770mm 205mm 30mm), it is a flat structure, and it should generally be placed flat on the workbench for clamping, and the X-axis lateral servo and the shaking of the YOZ plane are used to process each feature size; The processing position is relatively compact, and the space in the U-shaped area is small, which makes it difficult to carry out machining; The processing volume of each processing position is small, and the EDM processing time is short. Based on the above three factors, a multi-posture integrated electrode fixture for EDM was designed, which can clamp different electrodes at both ends of the fixture at one time, and complete the processing of one feature size on the left and right sides at the same time, so as to reduce the processing time and the frequency of manual operation, so as to improve the processing efficiency. 
2.1. Fixture composition and working principleFigure 2 shows a design of a multi-posture integrated electrode fixture for EDM. The special fixture is mainly composed of electrode mounting block, electrode fixing screw, 3R quick-change set (clamp seat, clamping plate), etc., its working principle is to use the advantages of high precision and convenient performance of 3R quick-change set, firstly the designed electrode mounting block is fixed as a whole, and adjust the relative position of the electrode mounting block and the quick-change set, and then the whole is installed on the spindle of the EDM machine tool, and then different electrodes are installed according to the characteristic size for EDM machining. The positioning accuracy and shape and position accuracy of the electrode mounting plate design are all in 001mm. 
2.2. The role of each part of the fixture(1) The electrode mounting block is shown in Figure 3, which is the core part of the fixture design, and the installation mode for the round-shaped and rectangular electrodes is designed, the round-shaped electrode is positioned by using the 90°V-shaped groove, and the rectangular electrode is positioned by using three convex planes perpendicular to each other in the rectangular holes, and three groups of 4 m4mm threaded holes are designed to fix the electrodes from different directions. The shape of the part and the main dimensions of the two mounting parts are processed by high-precision one-way wire EDM wire cutting machine. 
2) The electrode fixing screw is the standard part of the M4mm 10mm cylindrical hexagon socket screw, and the electrode is fixed through the M4mm threaded hole on the electrode mounting block. (3) The 3R quick-change set is composed of a quick-change base and a quick-change clamping plate, and the positioning accuracy and repeated positioning accuracy of the set are high (can be controlled within 2 m), which can not only improve the positioning accuracy of the electrode, but also save the time of installation and disassembly adjustment, and also lay the foundation for the subsequent EDM automatic processing. 3.1 Electrode design10There are 4 electrodes with 5mm taper hole, 10mm and 17mm round hole, and keyway, as shown in Figure 4, and the electrode material is copper. 
3.2 EDM stepsThe EDM steps are as follows. (1) The electrode fixture shown in Figure 2 is installed on the spindle of the EDM machine tool, and the table is calibrated. (2) Compile the relative position program and processing program of each electrode. (3) EDM left 10+00150mm deep 145mm and the right 17+00180mm deep 26mm round hole, the electrodes of Figure 4 (b) and (c) are respectively installed on the left and right sides of the 90 ° V-shaped groove in Figure 3, and fixed with M4mm 10mm cylindrical hexagon screws (the first processing, the dial gauge can be used to correct and confirm), and then the electrode is called to determine the relative position program, the processing position of the left and right electrodes relative to the parts shown in Figure 1 is determined, and the processing program is called after determination to complete the processing of two feature sizes. (4) EDM spacing 15mm left and right 105+0.0180mm, taper 1 20 deep 14mm taper, the same two electrodes shown in Figure 4 (a) are installed on the left and right sides of the 90° V-shaped groove in Figure 3, and the other processes are the same as step (3). (5) EDM right 17mm round hole inner width 6+0050mm deep 26mm keyway, with the help of the electrode positioning block in Figure 4 (d) is installed in the right side of the rectangular hole in Figure 3, and the other processes are the same as in step (3). (6) Using the on-machine detection function of CNC EDM machine tool, on-machine detection of all machining feature sizes should be carried out, and attention should be paid to not disassembling parts after processing, and then testing after cleaning. The proposed multi-posture integrated EDM special electrode fixture is an effective method to realize the processing of rudder surface parts, which has a certain reference effect on the EDM of similar parts, and the following conclusions are drawn through the analysis of processing verification and test results. (1) The characteristics of the multi-posture integrated fixture can realize the fast and accurate positioning and clamping of electrodes with multiple feature sizes, different shapes and different spatial positions, and can also adjust the 90° direction arbitrarily through the micron-level accurate positioning of the 3R quick-assembly fixture, which can realize the processing of XOY plane in 4 directions. (2) With the advantages of the 3R quick-change set, it can be accurately connected with the electrode mounting block, and can also be quickly installed on the machine tool spindle, which simplifies the operation and improves the production efficiency. (3) The fixture can clamp different electrodes at both ends at one time, and complete the processing of one feature size on the left and right sides at one time, which reduces the processing time and manual operation frequency, and can improve the processing efficiency by 30%. (4) Through the verification and test data of EDM, it can be concluded that the designed fixture has achieved the expected purpose, and the test results meet the requirements of the drawings, and have been applied to the processing of a variety of rudder surface parts and similar structural parts. Original authors: Xu Caili, Wang Lidong, Li Jinting, Yang Liguang.
Author's Affiliation: Beijing Dimon CNC Technology Co., Ltd.