CN104084654B - Six-axis linkage space shake electric discharge machining method - Google Patents

Abstract

A six-axis linkage space shaking electric discharge machining method in the field of numerical control machining technology, by classifying the margin of the workpiece after preliminary machining, that is, the margin between the workpiece surface and the surface to be processed is divided into multi-level shaking surfaces and graded. Reduce the discharge standards between the levels, and then convert the pose data corresponding to the reference plane obtained from the equidistant planes at all levels to obtain the NC machining code of the electrode movement, and smooth the surface of the workpiece to the design requirements by shaking the electrode. Dimensional accuracy and surface roughness. The invention uses CAD/CAM software to analyze shaking errors, plan shaking trajectories, generate corresponding shaking data, and realize shaking processing involving up to six axes at the same time.

Description

Six-axis linkage space shaking EDM method

technical field

The invention relates to a processing technology in the technical field of mechanical automation, in particular to a six-axis linkage space shaking EDM method capable of improving the processing effect during the EDM process.

Background technique

EDM is a special processing method that uses the electric erosion effect generated when the pulse discharge between the two electrodes immersed in the working fluid is used to erode conductive materials. EDM has many advantages, mainly in: no cutting force during processing, it can process materials and complex part shapes that are difficult to process by ordinary processing methods, and the hardness of the tool electrode material can be lower than that of the workpiece material. Therefore, EDM is widely used in aerospace and mold making industries.

A relatively big problem faced by EDM is that the processing efficiency is not high. To obtain better surface quality means to adopt finer discharge calibration, and the problem of low efficiency is even more prominent. For this reason, in the process of processing, EDM generally adopts the method of rough, medium and finishing classification. Rough machining uses high-energy discharge pulses to quickly remove the allowance, and the corresponding surface quality is poor. In the middle processing and finishing stages, lower energy discharge pulses are used to remove less allowance, thereby improving the surface quality after processing. In the EDM process, the material removal efficiency is directly proportional to the discharge power, resulting in that although the machining allowance is small in the finishing stage, it still takes a long time. Moreover, corresponding electrodes need to be replaced for rough, medium and finish machining, which leads to an increase in electrode manufacturing cost, and also increases the corresponding electrode replacement time and labor costs.

In order to solve the above problems, in the field of mold processing, the surface of the cavity is usually quickly repaired by the numerical control shaking method, that is, the worktable of the numerical control EDM machine tool (sometimes the tool electrode will also participate) makes a small amount of additional movement along a certain trajectory To lighten the side walls. Rely on the worktable to carry the workpiece to gradually expand outward, cooperate with the movement of the spindle and the step-by-step conversion of the discharge standard to realize the processing of different specifications of the cavity. By shaking, the side of the cavity can be gradually smoothed only through the additional movement of the machine tool without adding the finishing electrode, so that the surface roughness can reach a higher level (such as R _a 0.8μm and below), and can Process the side walls and bottom edges with clear edges and corners.

The essence of shaking is to increase the slight relative motion between the tool electrode and the workpiece, thereby improving the discharge state of the side wall and improving the processing efficiency. The shaking machining function is usually built into the EDM CNC system by the machine tool manufacturer, and is called in the machining code through special instructions. EDM shaking has many advantages. For example, the electrode can not be replaced when the machining allowance is not large, and the semi-finishing and finishing of the cavity of the part can be completed at one time by using EDM shaking. In this way, repeated positioning errors of multiple clamping can be reduced. At the same time, through shaking processing, chip removal during processing can be improved and stable processing can be achieved. The shaking functions of the machine tool mainly include plane shaking and spherical shaking. Plane shaking means that the shaking track is located in the XY plane or XZ plane or YZ plane (generally choose the plane perpendicular to the main motion direction), and the shaking forms generally only have several forms such as circle, square, rhombus, star and cross. Spherical shaking is to add a small spherical motion to the main machining direction of the electrode, but currently there are few machine tools that support spherical shaking.

However, these shaking functions are all aimed at the needs of mold processing, and are mainly applied on three-axis or four-axis EDM machine tools. However, the existing five-axis or even six-axis linkage CNC EDM machine tools are usually developed on the basis of four-axis linkage machine tools. Generally, only one or two rotary axes are added to meet the complex path feeding requirements of the electrode space. needs. However, the shaking function of the machine tool is mostly directly inherited. Obviously, the simple plane shaking can no longer match the movement on the rotary axis. Five-axis or six-axis EDM machine tools are generally used to process complex parts, and the closed integral blisk of aerospace engines is one of the key parts. However, due to the particularity of the processing of closed blisk parts, the original shaking function can no longer support the five-axis or even six-axis simultaneous processing mode.

After searching the existing technology, it is found that the Chinese Patent Document No. CN1290583A, the date of publication (announcement) is 2011.04.11, discloses a method of electrode compensation for electric discharge machining based on numerical control technology. This technology first uses the existing CAD/CAM software Generate the CNC tool path for processing electrodes, and then use the corresponding algorithm to compensate the CNC tool path according to the shaking mode of the electrode in EDM, such as vector shaking or plane circular shaking and the amount of shaking. The complex free-form surface processing problem encountered in the electrode correction is transformed into a simple processing of the numerical control tool path, thus greatly simplifying the theoretical model of the electrode correction. However, this method only compensates the electrode model, and the shaking methods used are still vector shaking and plane shaking. The shaking motion is still concentrated in the plane, and the movement axis of the machine tool is less used, and the shaking motion method is not changed. In the multi-axis simultaneous machining of complex parts, especially in the machining process with many rotating axes involved, the application will be limited.

Contents of the invention

Aiming at the above-mentioned deficiencies in the prior art, the present invention proposes a six-axis linkage spatial shaking EDM method, using CAD/CAM software to analyze shaking errors, plan shaking trajectories, generate corresponding shaking data, and realize up to six axes Simultaneously participate in the shaking process.

The present invention is achieved through the following technical scheme. The present invention classifies the margin between the workpiece surface and the surface to be processed by dividing the margin between the workpiece surface and the surface to be processed into multi-level shaking surfaces and gradually reducing the gap between each level. Then according to the position and orientation data corresponding to the reference surface obtained from the equidistant surfaces at all levels, the numerical control machining code of the electrode movement is obtained, and the surface of the workpiece is polished to the dimensional accuracy and surface roughness required by the design through electrode shaking. Spend.

The multi-level refers to: divide the shaking processing allowance into several levels of shaking surfaces, each level corresponds to a kind of electric spark discharge standard, and keep the discharge standard decreasing step by step to obtain the final position of each level of processing surface;

The reference surface is obtained by the following method: a number of equidistant surfaces inserted with the smallest shaking step length between each level of shaking surface and the next level of shaking surface, and the surface of the discharge gap bias electrode shaken according to this level is the reference noodle.

The pose data refers to: during the shaking process of the same level, take the two adjacent shaking surfaces as the starting point and the end point in turn, move the reference plane, and select several equidistant planes at the position where the reference plane coincides with the equidistant plane Move the reference plane in the tangential direction of , and the moving step is the shaking step. At the same time, fine-tune the attitude of the rotation axis to ensure that the maximum normal distance between the two surfaces is less than the tolerance requirement. Otherwise, give up the current moving vector and re-select. And record the reference surface pose data after fine-tuning.

The conversion refers to converting the pose data of the reference surface into the motion posture of each axis of the electrode, forming a shaking trajectory and outputting a numerical control machining code.

technical effect

Compared with the prior art, the shaking trajectory involved in the present invention is no longer limited to the plane, but a multi-axis linkage micro-motion in the three-dimensional space according to the needs, and can support six-axis linkage shaking at most. For EDM Processing will be more beneficial. The shaking trajectory involved in the present invention is more flexible and can be adjusted according to the shape of the electrode and the workpiece. It can also be used for workpiece processing on free-form surfaces. The trajectory is smoother than the traditional shaking method, and movement in a small space can make the discharge easier. Stablize. At the same time, the shaking step size involved in the present invention is controllable, generally at the micron level, and can be adjusted according to the shape of the electrode and the workpiece. Secondly, the shaking method involved in the present invention uses CAD software to analyze the shaking error, which can ensure that the shaking error meets the tolerance requirement.

Description of drawings

Fig. 1 is a schematic diagram of the definition of each motion axis of electric discharge machining in a specific embodiment of the present invention;

Fig. 2 is a flow chart of obtaining multi-axis shaking tracks in a specific embodiment of the present invention;

Fig. 3 is an equidistant plane and a reference plane in a specific embodiment of the present invention;

Fig. 4 is the tangential movement on the equidistant plane in the specific embodiment of the present invention;

In the figure: 1 machine tool spindle, 2 rotary table, 3 working fluid tank, 4 electrode, 5 blisk blank, 6 reference plane, 7 equidistant plane, 8 equidistant plane tangent.

detailed description

The embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

Example 1

As shown in Figure 1, it shows the definition of each coordinate axis of the six-axis linkage EDM machine tool in the closed integral blisk EDM. Fig. 2 is a flow chart of acquisition of multi-axis spatial shaking trajectory. The method uses CAD/CAM software to analyze shaking errors, plan shaking trajectories, generate corresponding shaking data, and realize shaking processing involving up to six axes through a numerical control system. The specific method is: divide the total margin of shaking machining into series, and each level corresponds to a gradually decreasing electric spark discharge standard. Insert an equidistant surface with the minimum shaking step between adjacent final configuration surfaces, and form a reference surface according to the offset electrode surface of each level of discharge gap, move the reference surface with the equidistant surface as the end point, and get close to the reference surface The position of the isometric surface, select the tangential direction of several isometric surfaces to move the reference surface, fine-tune the attitude of the isometric surface along each linear axis and rotation axis, so that the normal distance between the reference surface and the isometric surface is the smallest, specifically for:

In order not to lose generality, equidistant surfaces with the minimum shaking step length (generally micron level) are evenly inserted between the i-th stage shaking and the i+1th stage shaking final surface, as shown in Fig. 3 . The surface of the electrode is also offset by the distance of the discharge gap as a reference plane. Move the reference plane with the equidistant plane as the end point, and select several tangent vectors on the equidistant plane as the moving direction of the reference plane at the position where the reference plane is close to each equidistant plane, as shown in Figure 4. Move the reference surface along these directions with minimum shaking steps, and then adjust the attitude on the rotation axis to ensure that the maximum normal distance between the two surfaces is less than the tolerance requirement. If the maximum normal distance is greater than the tolerance requirement, you need to re-select the tangential vector for movement. Record the pose data of the movement on the reference surface, and convert it into the output of the movement posture of each axis of the electrode, become the electrode shaking trajectory, and output the corresponding numerical control code.

Finally, the surface of the workpiece is smoothed to the dimensional accuracy and surface roughness required by the design through electrode shaking.

From the actual processing effect, in the present embodiment, the workpiece material is selected as nickel-based superalloy Inconel718, and the electrode material is selected as PCO EDM-C3 copper-infiltrated graphite, which is carried out by two-stage shaking (i.e. adopting the middle processing standard and the finishing standard respectively) Shaking), the surface roughness after rough machining can be increased to Ra1.184μm, and the surface roughness Ra of the workpiece processed with the same parameters without shaking is 2.227μm. It can be seen that the effect of multi-axis shaking processing on surface smoothing is obvious. At the same time, the same electrode is used for two shakes, which requires three types of electrodes for rough, medium and finish machining compared with that without shaking, which can reduce the number of electrodes.

Claims (5)

1. A six-axis linkage space shaking electric discharge machining method is characterized in that, by carrying out margin grading to the rough-machined workpiece, the margin between the workpiece surface and the surface to be machined is divided into multi-stage shaking surfaces and gradually reduce the discharge standards between the stages, and then convert the pose data corresponding to the reference surface obtained from the equidistant surfaces of each stage to obtain the NC machining code of the electrode movement, and smooth the surface of the workpiece to the design requirements by shaking the electrode dimensional accuracy and surface roughness. 2. The method according to claim 1, characterized in that, said multi-level refers to: divide the shaking processing allowance into several levels of shaking surfaces, each level corresponds to a kind of electric spark discharge standard, and keeps the discharge The norm is reduced step by step to obtain the final position surface processed at each level. 3. The method according to claim 1, wherein the reference surface is obtained by: inserting several equidistant surfaces with minimum shaking steps between each level of shaking surface to the next level of shaking surface , according to the level of shaking the discharge gap biases the electrode surface to obtain the reference surface. 4. The method according to claim 1, wherein the pose data refers to: during the shaking process of the same level, take the two adjacent shaking surfaces as the starting point and the ending point in turn, move the reference plane, and The position where the reference plane coincides with the equidistant plane, select the tangential direction of several equidistant planes to move the reference plane, the moving step is the shaking step, and fine-tune the attitude of the rotation axis at the same time to ensure the maximum normal distance between the two planes If it is less than the tolerance requirement, otherwise the current movement vector is discarded, re-selected, and the pose data of the reference surface after fine-tuning is recorded. 5. The method according to claim 1 or 4, wherein the conversion refers to converting the pose data of the reference surface into the motion posture of each axis of the electrode, forming a shaking trajectory that supports up to six axes participating simultaneously and Output CNC machining code.