- Nov 19, 2024
Selection and functions of wire EDM machine tools
How to choose wire EDM machine tools?
The compilation of models of wire EDM machine tools produced independently in China is carried out in accordance with the provisions of GB/T15375-2008 "Metal Cutting Machine Tool Model Compilation Method". The machine model consists of Chinese pinyin letters and Arabic numerals, indicating the type, characteristics and basic parameters of the machine tool. Taking the model DK7732 wire EDM machine as an example, the meaning of each letter and number in the model is explained as follows:
Wire-cut EDM machine tool manufacturers produced in other countries mainly come from Switzerland and Japan. The main companies are: Swiss Agie-Charmilles Company, Japan's Mitsubishi Electric Company, Sodick Company, Fanuc Company, and Makino Company. The numbers of foreign machine tools are generally compiled based on the series code plus the basic parameter code, such as Sodick's A series/AQ series/AP/AD/ALN series, Mitsubishi Electric Company's FA/BA/MV series, etc. There are many machine tool manufacturers in Taiwan, such as Chmer, ARD, Accutex, JSEDM, JOEMARS, MAXSEE, Sure First and dozens of others. The numbering of its machine tools is not unified and is formulated according to the standards of its own company, but it is generally compiled with the series code plus the basic parameter code of the machine tool. The main companies that introduce production line cutting machine tools in China include Suzhou Electrical Machining Research Institute Zhongte Company, Suzhou Sanguang Science&Technology Co., Ltd, and Hanchuan Machine Tool Group Co., Ltd. The numbering of their machine tools complies with my country's national machine tool numbering standards.
When purchasing a CNC wire cutting machine tool, you can consider the following three aspects: First, whether the machine tool performance can meet your own processing requirements, what is the quality of the machine tool? and whether to choose high-speed wire cutting, medium-speed wire cutting, or low-speed wire cutting. Next is the CNC system. There are many types of CNC systems. Choosing the right system is the key to purchasing CNC machine tools. The last is the drive unit, which is also the key to machine tool control. Different drive units can achieve different machining accuracy. When selecting a drive unit, you must choose an appropriate drive unit according to the accuracy requirements of the workpiece to be processed, such as stepper motor, servo motor or linear motor.
Functions of wire EDM machine tools
1. Common functions of wire EDM machinetools
(1) Travel limit function
At the extreme positions of the X and Y strokes of the worktable and the Z stroke of the column, there are limit travel switches (mechanical limit, electronic limit), which can allow the machine tool table to move within a local range.
Before processing, you can use the mechanical limit function of the machine tool to check whether the processing range of the workpiece is within the cutting stroke. For workpieces that are prone to errors or collisions, the soft limit function of the machine tool can be used for protection.
(2) Backlash compensation function
In the feed transmission system of the worktable in the X and Y directions, there is backlash in both the gears and the ball screws. When an error is caused during cutting, the backlash compensation function of the control system compensates for the reverse backlash, that is, an additional input backlash compensation amount is used in the reverse direction to eliminate the error caused by the backlash. In fact, because the backlash changes throughout the entire stroke, the error caused by the backlash cannot be completely eliminated. If the processed workpiece still cannot meet the dimensional accuracy requirements, you can ask the machine tool manufacturer to perform backlash compensation, and you can use a step gauge or laser interferometer to measure the backlash error.
(3) Offset compensation function
The processing program runs according to the center trajectory of the molybdenum wire (tittle: molybdenum wire edm ) (brass wire). The slit width during wire EDM processing is equal to the diameter of the molybdenum wire (brass wire) plus the discharge gap on both sides. Therefore, it is compiled according to the outline of the processed part. After programming, you need to enter an offset that is half the width of the slit to make the processing trajectory run according to the center trajectory of the molybdenum wire (brass wire). It can be seen that the offset is determined by the diameter of the molybdenum wire (brass wire) and the discharge gap; the diameter of the molybdenum wire (brass wire) is related to the loss of the molybdenum wire (brass wire), and The discharge gap is related to the parameters of the pulse power supply and the concentration of the processing material and working fluid. Therefore, when processing high-precision parts, the slit width needs to be determined through experiments.
For high-speed wire EDM machines, because they only cut once and complete the trajectory once, the offset is usually added to the calculation when programming the program, and the final result is an ISO program or 3B program without G41 or G42 code. Low-speed wire EDM machines cut back and forth multiple times and use the same trajectory, so they generally use the G41/G42 function. The low-speed wire EDM machine tools will provide an offset compensation table. For general cutting, retrieving the processing parameters according to the processing conditions will automatically call the offset compensation; for some precision processing or abnormal state processing, you can manually follow the experience Increase or decrease the offset compensation value.
(4) Any rotation and translation functions
For parts with the same geometric elements on the circumference, the arbitrary rotation function can be used to simplify programming. For example, for gears, if you only program one tooth profile, you can process the entire gear using any rotation function. In the same way, using any translation function to compile a tooth profile program can process the entire rack.
It is important to note that not all programs must use rotation or translation functions. The best processing solution is to first use the CAD function on the computer to draw the entire outline to be cut, and then use the CAM function of the software to automatically generate all NC programs, which is less prone to errors. Because it is much safer to perform rotational flattening on CAD software than directly in the NC program. Rotation or translation in NC is easy to make mistakes if you are not experienced enough.
(5) Automatic centering function
When the part uses holes (round holes, square holes) as the process benchmark, it is necessary to find the X and Y coordinates of the molybdenum wire (brass wire) in the center of the hole. The automatic centering function can position the molybdenum wire (brass wire) in the center of the hole.
Note that the lower the surface roughness value of the hole, the cleaner the hole and the higher the accuracy of the molybdenum wire (brass wire) to the center. If the hole is too small or dirty, it may cause the automatic centering to fail or the found center to be inaccurate.
(6) Reverse processing function
When the processing of the part is more than half or almost complete, if the wire is broken, the reverse processing function can be used to return the molybdenum wire (brass wire) to the starting point of processing. Start from the last section of the program and perform reverse processing to complete the uncut part of the program, which can save time.
This function is mainly used on high-speed wire EDM machine tools, because its tool path is relatively simple and there will be no overcutting in reciprocal machining. Low-speed wire EDM machines generally do not use this function.
(7) Power failure memory function
If there is a power outage during processing, because it has a power outage memory function, you can continue processing from the processing breakpoint before the power outage after the power comes back. This function is very necessary for processing large workpieces, otherwise it will take a lot of time to run the program from the starting point or affect the processing quality.
This function is mainly used for high-speed wire EDM wire cutting machines. It can avoid manual wire threading again, reduce the time when the molybdenum wire (brass wire) does not discharge, executes G00 code or other conditions, and the molybdenum wire (brass wire) moves forward or backward quickly.
(8) Stop function after processing
At the end of processing, the machine tool's wire storage drum motor and water pump motor, control system, pulse power supply, and the entire machine are in an automatic shutdown state. This function is beneficial for multi-machine operation or large workpiece cutting.
2. Special functions of low-speed wire EDM machine tools
In addition to the basic functions of commonly used wire EDM machines, low-speed wire EDM machines also have the following special functions:
(1) Automatic threading and cutting function
Low-speed wire EDM machine tools generally have automatic wire threading and wire cutting functions, and have automatic wire breakage processing functions, which can thread wire in place or return to the starting cutting point.
(2) Motor servo closed loop control function
Low-speed wire EDM machine tools generally use closed-loop control functions, so their processing accuracy will be higher.
(3) Expert system database
Low-speed wire EDM machine tools generally have their own processing conditions database. Users only need to follow the instructions to select data to automatically generate a processing parameter table.
(4) Corner control function
There are two types of corner control functions: one is to automatically change the processing conditions at the corners to ensure the shape accuracy of corner cutting; the other is the automatic corner cleaning function applied to the stamping die to facilitate the loading of inserts.
(5) Arithmetic functions in programs
Low-speed wire EDM machine tools generally have automatic calculation functions in their programs, which can easily insert various mathematical operations.
(6) Coordinate rotation function
In addition to the graphics rotation function, the low-speed wire EDM machine tool also has the coordinate rotation function. That is, there is no need to calibrate the workpiece when clamping, and the brass wire is directly touched at two different points of the workpiece for coordinate rotation positioning.