CN105930589A - Data processing method of multi-axis linked electric discharge machining feeding speed postprocessor based on spatial mapping - Google Patents

Abstract

The invention relates to the data processing method of a multi-axis linked electric discharge machining feeding speed postprocessor based on spatial mapping. With respect to electric discharge machining participated by a rotation axis, a control object is a relative distance between an electrode and a workpiece. According to the method, through start from a model of the electrode and the workpiece, displacements of each line of G codes under a machine tool coordinate system and a workpiece coordinate system are solved through spatial mapping; the ratio of the displacements is solved; the ratio is multiplied by an originally planned feeding speed of each line of G codes; and a machining program is updated. According to the method, speed fluctuation resulting from spatial transformation can be greatly reduced; the discharge state of movement participated by the rotation axis is protected from instability; occurrence of open circuit and short circuit states can be reduced; and the electric discharge machining efficiency can be improved.

Description

Data processing method of multi-axis linkage electric discharge machining feed rate post-processor based on space mapping

technical field

The invention relates to electric spark process control, belongs to the technical field of special machining, and specifically relates to a data processing method of a multi-axis linkage electric spark machining feed rate postprocessor based on space mapping.

Background technique

Modern CNC machining includes several typical links of CAD (Computer Aided Design), CAM (Computer Aided Manufacturing), post-processing, and CNC machining, as shown in Figure 1. CAD designs the workpiece, CAM simulates the processing process to generate processing trajectory information, and the post-processing process optimizes the processing code for equipment or process to generate processing G code files, and the CNC processing system follows the G code for processing to obtain better results. Processing effect.

EDM is a process of removing material from a workpiece by a series of spark discharges between the workpiece and the electrode. EDM is widely used in molds, aerospace, medical equipment and other fields. Compared with traditional milling, EDM has many differences. For example, EDM is non-contact machining, multi-axis linkage EDM can process very complex cavities, and copy the surface shape of the machining tool electrode to the workpiece. For example, the closed overall blisk is processed by a six-axis linkage EDM machine tool as shown in Figure 2. Using the synthetic motion of three linear axes X, Y, Z and three rotational axes A, B, C, the machining tool electrode can be Feed to the inside of the closed blisk, copy the surface shape of the electrode to the closed blisk, and complete the processing of the blisk, as shown in Figure 3. In the case of multi-axis linkage, the relative motion between the discharge point on the electrode and the corresponding point on the workpiece is the result of the synthetic motion. In the numerical control system of the EDM machine tool, the speed of the linear axis and the rotation axis The angular velocity is synthesized, that is, the respective velocity values of the N axes are orthogonally synthesized. Due to the different dimensions of linear velocity and angular velocity, the direct synthesis without considering the radius of rotation of the rotating shaft will inevitably cause a speed mismatch, thereby affecting the processing effect. In EDM, different from the fixed speed feed in milling, the machining direction is determined according to the measured inter-electrode state: forward or backward, and according to the difference between the currently measured inter-electrode voltage and the set servo voltage The value determines the forward or backward speed. According to the different discharge states between the electrode and the workpiece, it can be divided into four states: open circuit, normal discharge, short circuit and arc. The servo control system estimates the discharge state by collecting information such as voltage and current, and then determines the feeding speed of the electrode according to the empirical formula. In the empirical formula, the feed rate refers to the relative speed of the discharge point on the electrode relative to the discharge point on the workpiece. In the multi-axis linkage servo control with the participation of rotating axes, the numerical control system performs extended line displacement synthesis calculation displacement in the machine tool coordinate system space according to the displacement of each coordinate axis, and this displacement is different from the concept of the workpiece coordinate system space displacement of the electrode relative to the workpiece. This creates a gap between the actual feed rate and the feed rate required by the empirical formula. In this case, with the same coordinate increment, the actual feed amount of the workpiece in different poses relative to the electrode is different.

Since the multi-linkage EDM involving the rotating shaft is necessary for complex cavity machining, in this case, it is necessary to correctly handle the synthetic motion involving the rotating shaft. Since the workpiece and the electrode are in surface-to-surface contact, the reference points on the electrode and the workpiece should be reasonably selected first. With the location information of the reference point, post-processing planning can be carried out.

Contents of the invention

In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a design method of a feed speed post-processor for linked EDM, which can greatly reduce the speed fluctuation caused by spatial mapping, and avoid the instability of the discharge state of the motion involving the rotating shaft , reduce the occurrence of open circuit and short circuit state, and improve the efficiency of EDM.

Technical solution of the present invention is as follows:

A data processing method of a multi-axis linkage electric discharge machining feed rate postprocessor based on space mapping, the method includes the following steps:

Step 1: Select the reference point of the machining tool electrode and the workpiece, and measure the position information such as the radius of rotation of the reference point relative to the rotation center;

Step 2: Open the G code file and read the first line of G code;

Step 3: Read the next line of G code. If it is in absolute mode, subtract the coordinates of the previous line of G code from the coordinate of the G code in this line to obtain the displacement increment of the coordinate axis; if it is in incremental mode, read the G code in this line. Coordinate increment of the code

Step 4: Calculate the displacement Δs of the extension line of the coordinate space of the machine tool, taking a 6-axis machine tool as an example;

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&Delta;x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;z</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; .</span>$

Step 5: Calculate the displacement δs of the reference point on the space electrode in the workpiece coordinate system relative to the reference point on the workpiece Its three direction components δx, δy, δz can be obtained through space mapping.

Step 6: Multiply the feed speed originally planned by this line of G code by Δs/δs, and replace the original feed speed;

Step 7: Determine whether there is a next line of G code, if yes, go to step 3, if not, go to step 8.

Step 8: Save the G code after changing the feed speed and pass it to the CNC system. The CNC system will process according to the changed G code, so as to reduce the instability of the discharge state of the motion involving the rotating axis and reduce the risk of open and short circuits. occurs, increasing the effective discharge rate.

Principle of the present invention is as follows:

For multi-axis linkage EDM with the participation of rotating axes, the object of control is the relative distance between the electrode and the workpiece. Since the coordinate axis motion of the machine tool is to synthesize the linear axis velocity and the rotational axis angular velocity by means of extended linear displacement in the multi-dimensional machine coordinate system, the respective velocity values of the N axes are orthogonally synthesized. The feed rate in the CNC system is no longer equal to the feed rate of the electrode relative to the workpiece in the workpiece coordinate system.

In order to solve this problem, it is necessary to separately calculate the displacement of the expansion line corresponding to a line of G code and the actual displacement of the electrode relative to the workpiece. Take the six-axis linkage of three linear axes and three rotary axes participating in the movement as an example. The three linear axes are defined as X, Y, and Z axes, and the three rotary axes are defined as A, B, and C axes.

The selection of reference points for machining tool electrodes and workpieces is based on their CAD models. Generally speaking, the part that participates in the discharge is most likely to generate discharge concentration is selected as the reference point, so the point corresponding to the maximum rotation radius of the machining tool electrode and the workpiece along the motion axis is selected as the reference point.

Define the displacement of each coordinate axis in the first line of G code as Δx, Δy, Δz, Δa, Δb, Δc, then the displacement of the machine tool coordinate space extension line Δs is:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&Delta;x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;z</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

The actual displacement of the reference point on the electrode relative to the reference point on the workpiece is a displacement δs in the Euclidean space, and the projection components in three directions in the three-dimensional Euclidean space are defined as δx, δy, and δz, which can be obtained through space transformation. δx, δy, δz are the space transformation of the coordinate value and coordinate increment corresponding to the line of G code, and g represents the space transformation function.

(δx, δy, δz) = g(Δx, Δy, Δz, Δa, Δb, Δc, x, y, z, a, b, c)

After calculating δx, δy, and δz, δs can be calculated by the following formula.

$\mathrm{<span\; class="notranslate">\; \&delta;</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&delta;x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&delta;y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&delta;z</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Assuming that the originally planned feed speed of this line of G code is f, then to realize the feed speed f of the reference point on the electrode relative to the reference point on the workpiece, the feed speed F set by the CNC system according to the machine tool coordinate system is:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; \&delta;</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}$

After getting the modified feed speed of the line of G code, save it and pass it to the numerical control system, and carry out EDM according to the modified G code.

Compared with the existing technology, the unprocessed machining code has larger speed fluctuations, and in this case, it is impossible to maintain a continuous and stable EDM. It is possible that due to the complexity of the synthetic motion, the feed rate in a single cycle is too large or too small, resulting in frequent short circuits and arcing, which not only reduces the processing efficiency, but also produces adverse processing consequences caused by short circuit arcing, such as surface Ablation, metal modification. By adopting the multi-axis linkage EDM feed speed post-processor based on space mapping of the present invention, the speed planning is carried out according to the actual displacement of the workpiece coordinate system, which can basically eliminate speed fluctuations, realize a more stable EDM state, and reduce The probability of bad machining states such as short circuit, open circuit, and arcing improves the efficiency of EDM.

Description of drawings

Fig. 1 is a schematic diagram of several typical links of numerical control machining in the implementation system in the prior art.

Fig. 2 is a flow chart of the data processing method of the multi-axis linkage EDM feed rate post processor of the present invention.

Fig. 3 is a schematic diagram of a six-axis linkage EDM machine tool on the platform of the present invention.

Fig. 4 is a schematic diagram of multi-axis linkage feed trajectory in the present invention.

Fig. 5 is a schematic diagram of selection of reference points according to an embodiment of the present invention, where a is the reference point of the electrode and b is the reference point of the workpiece.

detailed description

The specific embodiment of the present invention is implemented in the G code of the electrode machining closed integral blisk shown in Fig. 3 and carried out on the HE 70 electric discharge forming machine produced by Shanghai Hanba Electromechanical Co., Ltd. The reference point of the selected workpiece has a rotation radius of 120mm around the rotation axis of the installation workpiece, and the angle between the initial position and the coordinate axis Z is 0 degrees. The rotation radius of the reference point on the processing tool electrode around the rotation axis of the installation electrode is 27.5714mm. The angle between the position and the coordinate axis Y is 21.75 degrees.

Example:

According to the measurement, the reference point on the selected workpiece is 120 mm away from the center of rotation of the workpiece, and the reference point on the selected electrode is 27.5714 mm away from the center of rotation of the electrode, as shown in Figure 5.

Read the first line of code, then start to read the G code line by line from the second line, and calculate the displacement of the second line of G code relative to the first line in each movement axis Δx, Δy, Δz, Δa, Δb, Δc. Calculate the amount of displacement Δs of the extension line of the coordinate space of the machine tool. Calculate the displacement δs of the reference point on the space electrode in the workpiece coordinate system relative to the reference point on the workpiece. Multiply the originally planned feedrate of the diverted G code by Δs/δs, and replace the original feedrate.

The original processing feed speed is planned to be f10 according to the empirical formula, and the feed speed value after calculation of each line of G code optimization produces different changes, and its range is: F4.775 to F320.010. (Feedrate in G code)

Then use the above-mentioned G code after changing the feed speed to pass to the numerical control system to conduct the processing experiment of the closed blisk, and conduct a comparative experiment with the code that uses the constant feed speed F10 throughout the process. The electrode material of the processing tool used in the experiment is POCO EDM-C3, and the workpiece material of the closed blisk is C45E4 steel. The processing conditions are shown in Table 1 below:

Table 1-Experimental parameters of closed blisk processing

workpiece polarity open circuit voltage peak current Pulse Width pulse interval Knife lift height Lifting cycle negative electrode 120V 36A 80μs 8μs 1mm 5s

Each method uses one processing tool electrode to process three times, and the specific processing results are shown in Table 2:

Table 2 - Comparison of machining results of two feed speed control methods

It can be seen from Table 2 that the results obtained by using the multi-axis linkage EDM feed speed control method based on space mapping are better than the constant feed speed in terms of processing time and tool electrode loss.

The preferred specific embodiments of the present invention have been described in detail above. Those skilled in the art should understand that many modifications and changes can be made according to the concept of the present invention without departing from the scope of the present invention. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention by changing materials or characteristics on the basis of the prior art should be within the scope of protection defined by the claims.

Claims (4)

1. A data processing method based on a multi-axis linkage electric discharge machining feed rate postprocessor based on spatial mapping, it is characterized in that the method comprises the following steps: Step 1: Selection of processing tool electrode and workpiece reference point, measuring the position information of the reference point relative to the rotation radius of the rotation center; Step 2: Read the first line of G code; Step 3: Read the next line of G code, and calculate the displacement increment of each coordinate axis of the machine tool; Step 4: Calculate the displacement Δs of the machine tool coordinate space expansion line; Step 5: Calculate the displacement δs of the reference point on the space electrode in the workpiece coordinate system relative to the reference point on the workpiece; Step 6: Multiply the feed speed originally planned by this line of G code by Δs/δs, and replace the original feed speed; Step 7: Determine whether there is a next line of G code, if yes, go to step 3, if not, go to step 8. Step 8: The G code after changing the feed speed is saved and transmitted to the CNC system, so as to reduce the instability of the discharge state of the motion involving the rotating axis, reduce the occurrence of open circuit and short circuit state, and improve the effective discharge rate. 2. The data processing method of the multi-axis linkage electric discharge machining feed rate post-processor as claimed in claim 1, characterized in that, the electrode and the workpiece reference point described in step 1 are the most likely to generate discharge concentration on the electrode and the workpiece s position. 3. The data processing method of the multi-axis linkage electric discharge machining feed rate postprocessor as claimed in claim 1, wherein the displacement Δs of the machine tool coordinate space expansion line described in step 4 is the square of the displacement of each coordinate axis The arithmetic square root of the sum. 4. The data processing method of the multi-axis linkage electric discharge machining feed rate post-processor as claimed in claim 1, characterized in that, the displacement δs of the reference point on the electrode described in step 5 is in three dimensions relative to the reference point displacement δs on the workpiece The three-direction projection components of Euclidean space are the spatial transformation of the coordinate value and coordinate increment corresponding to the line of G code.