Wire EDM is a specialty machining technology that originated in the 1940’s. In 1943, BR and NI Lazarenko of the Soviet Union invented EDM, which was initially used for machining hard-to-machine metal materials such as carbide. Today, wire EDM can be used for machining materials as long as they are electrically conductive, and is becoming increasingly important in manufacturing.
Wire EDM has significant advantages over traditional machining methods. It is capable of machining very hard or brittle materials, which often cannot be accurately machined using conventional methods. In addition, WEDM is extremely accurate, which is especially important for machining projects where part quality is critical. Therefore, understanding the machining accuracy of wire EDM is critical to assuring part quality.
Next, we will discuss wire EDM and its accuracy. If you are interested in this field, please follow us for more information!
Table of Contents
What is Wire EDM ?
Wire EDM is a process that removes material by means of a pulsed electrical discharge. It uses a thin wire, which must be electrically conductive in order to work. The cutting is done by discharging electricity between the filament and the work piece being processed. During the discharge, the high temperatures cause localized melting and vaporization of the workpiece. This cutting the material. The electrode wire moves according to a predetermined trajectory under the control of the CNC system, thus cutting the workpiece into the desired shape. Also, during the process, the electrode filament does not touch the material. So, using wire EDM will not create large cutting stress.
Principle of Wire Cutting
There are generally five steps when using a wire EDM machine to process parts.
First, there should be an electrode for discharge. In the wire EDM process, a thin wire (usually molybdenum, copper or alloy wire) is first used as the electrode. This fine wire is secured to the cutting device and serves as the electrode tool for cutting.
Next, an electric spark discharge is performed. The workpiece is connected to the positive pole of the pulsed power supply, while the wire is connected to the negative pole of the high-frequency pulsed power supply as the tool electrode. Between the electrode wire and the workpiece, a high temperature is generated by pulsed spark discharge. This high temperature is sufficient to melt or vaporize the metal locally.
Then, a cutting seam is formed. The melted or vaporized metal is thrown out by the action of the electric spark discharge, thus forming a slit in the workpiece. This kerf is the main result of wire EDM processing.
The CNC programming then controls the movement of the cutting wire. The entire cutting process is programmed by the CNC to precisely control the cutting trajectory of the wire. The ability of wire EDM to process parts of any complex shape is due to the CNC programming control.
Finally, a working fluid is used to remove debris. During the process, a special fluid is used in wire EDM. It removes debris made during processing. It ensures a smooth cut.
What about the accuracy of WEDM?
WEDM is usually categorized into slow-wire and fast-wire. Compared to the fast-feeding wire, the precision of the slow-feeding wire is very high. Its precision can even reach the micron level.
Generally speaking, the machining accuracy of slow-feed wire cutting can reach ±0.002 mm to ±0.005 mm, and the surface roughness can reach Ra0.2 microns or less. The accuracy of FWED is relatively low, usually around ±0.01 mm to ±0.02 mm, and the surface roughness is generally between Ra1.25 micron and Ra2.5 micron. However, its accuracy does not always remain unchanged. Wire-cutting accuracy is affected by many factors. In use, we need to tailor the cutting method to the specific needs and conditions. We must optimize the parameters and processes. Only then can we get better accuracy.
Factors affecting the precision of wire cutting
Wire-cutting with slow-feeding wire makes very precise parts. But, many factors can affect this precision. For example, equipment precision, electrode wire quality, processing parameters, workpiece materials, and working fluid will all affect part precision.
Equipment precision
Equipment precision refers to the machine’s mechanical, motion, and control precision. These factors will directly affect the wire-cutting precision. For example, the straightness and parallelism of the guide rail of the machine tool and the transmission accuracy of the screw. If the machine itself is inaccurate or fails, it will directly affect accuracy. Vibration and deformation can be reduced by improving the structure of the machine tool, so as to improve the machining accuracy.
Electrode wire quality
The quality of electrode wire is also an important factor that directly affects the precision of wire cutting. Generally speaking, high-quality electrode wire material can improve the discharge stability. Thinner electrode wire diameter can cut a narrower gap to improve precision, but the strength will be reduced. If the tension of the electrode wire is uneven or there is excessive loss, this can also lead to a decrease in machining accuracy. For example, molybdenum wire is a common electrode wire material in wire EDM, and with the growth of the use of time, the molybdenum wire will gradually wear out, which will lead to a reduction in machining accuracy.
Processing parameters
The setting of wire cutting processing parameters generally refers to discharge parameters such as pulse current, pulse width and pulse interval. The influence of different parameter settings on the precision of machined parts is also different. Too large pulse current and pulse width may lead to too high discharge energy, causing surface burns and thermal deformation of the workpiece and affecting the accuracy; while too small parameters will reduce the processing efficiency and increase the production cost. Therefore, the machining parameters should be set according to the actual machining materials and electrode wires to choose the right one. In addition, the machining speed will also affect the machining accuracy. For parts with high surface quality requirements, the machining speed cannot be set too high.
Workpiece material
The influence of workpiece material on accuracy is also an important factor that cannot be ignored. Select different workpiece materials, it has different characteristics. The type, hardness, melting point, thermal conductivity and other characteristics of the material will affect the thermal deformation and discharge effect during processing, which in turn affects the accuracy. Materials with high elongation and high thermal conductivity are able to discharge significantly and reduce thermal deformation, thus improving machining accuracy. For example, aluminum alloy conducts heat well and dissipates it fast. It also deforms less. In contrast, titanium alloy conducts heat poorly. Heat builds up when machining, causing slightly more deformation.
Working fluid
Generally speaking, the working fluid is an indispensable part of the wire cutting process. It has the functions of cooling, chip removal and de-ionization, and helps to improve the machining accuracy. The quality and concentration of the working fluid have an important effect on the cutting accuracy. A high-quality working fluid can better perform the functions of cooling, chip removal and deionization. If the fluid is poor, it may have impurities or an unstable composition. These issues will affect the discharge and machining stability, leading to a decrease in precision.
When the fluid’s concentration is too low, cooling and chip removal may be poor. Heat from the discharge process can’t dissipate in time. Chips can’t be removed well. This can easily cause burns, roughness, and deviation. While the concentration is too high, it may affect the fluidity and permeability of the working fluid, which is also unfavorable to heat dissipation and chip removal, and will also adversely affect the cutting accuracy.
In summary, many factors affect wire cutting precision. In addition to the above five, there are clamping and positioning accuracy, and the external environment. Changes in any one of these factors may have an impact on the final accuracy of processing. Therefore, when choosing to use wire-cut processing for parts with high precision requirements, comprehensive consideration should be given to the actual situation.
Methods for improving the precision of wire-cut machining
Improve the performance of machine tool
When processing parts with high precision, we prioritize the selection of high-precision machine tools for processing. However, it is also possible to improve the machining accuracy of WEDM by upgrading the performance of machine tools. On the one hand, the use of high-precision numerical control system can realize more accurate motion control, and then improve the accuracy. On the other hand, regular system maintenance of the control system, and regular calibration to ensure that the control system works properly. In addition, carry out regular inspection and maintenance of the components of the machine tool. At the same time, clean the surface of the machine tool, especially the guide rail and screw, to avoid the influence of accumulated dust or foreign matter on the accuracy.
Choose suitable electrode wire
Before wire-cutting, choose the type of electrode wire to fit the requirements. For example, common ones are molybdenum wire or tungsten wire.
Then, to meet the precision needs, choose high-quality wire. It should have a uniform diameter. This can reduce jitter and loss. After carrying out this operation, it is also beneficial to the improvement of precision.
Reasonable setting of processing parameters
Before the new parts are processed for the first time by wire cutting, the processing parameters can be set initially according to previous experience and methods. The processing parameters contain pulse current, pulse width and pulse interval. Then test or first piece processing, according to the processing results to determine the best pulse current, pulse width and pulse interval and other parameters, in order to achieve stable and efficient EDM.
Optimize workpiece material selection
The material selection of parts is generally determined by mechanical engineers based on product performance. Therefore, if it is determined that the material to be processed by wire EDM is to be used, the hardness of the material needs to be considered first under the premise of prioritizing the satisfaction of product performance. Softer materials, such as aluminum alloys, are relatively easy to machine, but may present some challenges in terms of precision and surface quality. Higher hardness materials, such as mold steel, on the other hand, are more difficult to machine but can yield better accuracy and surface roughness.
Second, the conductivity of the material can also have an impact on wire cutting. Materials with good electrical conductivity can make the discharge process more stable and help improve machining accuracy. Therefore, the selection of materials for wire EDM processing needs to be optimized according to the product, so as to obtain higher machining accuracy.
But, as a parts supplier, the materials for parts should be selected according to the customer’s drawing requirements. Unless the customer has special requirements, the processing material can be replaced only after the customer agrees.
Selection of suitable working fluid
In the wire cutting processing, different processing materials, with the working fluid is not the same. Usually, it is necessary to consider factors such as cooling performance, chip removal ability, insulation performance and anti-rust performance. Common wire cutting working fluids include emulsion, water-based working fluids and so on. In practical application, it is necessary to select the most suitable working fluid according to the specific processing conditions and requirements, through test and experience.
Precautions for using wire-cut processing
When using wire-cut processing, the following points need to be noted in order to obtain ideal processing accuracy:
Accurately clamp and position the workpiece before machining to ensure that it will not loosen or shift during machining.
Check the working fluid often. Replace it to keep it stable while using wire-cutting machining.
After machining is completed, clean up the workpiece and machine tool in time to remove the residual working fluid and chips.
Reasonable arrangement of machining sequence, first roughing and then finishing. For the complex shape of the workpiece, the use of segmented processing or multiple cutting methods to improve machining accuracy.
Conclusion
In this paper, the machining principle of wire EDM and its accuracy have been discussed. Then, we discussed what factors influence wire cutting. We also covered methods to improve wire cutting precision. Finally, its precautions were introduced. Through the above introduction, I believe you have a certain understanding of the precision of wire EDM processing. Afterwards, if you need wire cutting, contact Yonglihao Machinery. We have rich experience in this area. We can provide professional Wire EDM services for you.
FAQ
WEDM is good for materials with good electrical conductivity. These include metals, silicon, and graphite.
WEDM has many advantages. It has high precision and can process complex shapes. It also processes with low stress and has no material hardness limits. The disadvantages are: only conductive materials can be processed. The speed is slow and the cost is high.
WEDM is better for processing small quantities of parts. The parts have complex shapes and need high precision. When dealing with large quantities of simple parts, other more cost-effective machining methods can be considered.