Paper on EDM technology

EDM cutting is widely used in practical production and processing, especially in stamping die processing, and it is the most ideal processing equipment. Adjusting the processing parameters in the processing process is an important factor affecting the quality of the workpiece. I hope you like the paper on EDM technology that I compiled for you.

Paper on EDM technology 1

Discussion on WEDM processing technology

This paper analyzes the WEDM process, the pretreatment of workpiece materials and the processing of wire piercing holes, and defines the pretreatment method of workpiece before WEDM, which has a guiding role in the WEDM route design of actual workpiece.

Keywords: demagnetization treatment; Pretreatment; Threaded hole; Wire cutting; electrosparking

China Library Classification. : TG66 1 document identification code: a article number:1009-2374 (2014) 22-0131-02 EDM is a kind of electrical discharge machining which uses high energy density to melt, vaporize and evaporate workpiece materials. WEDM is a kind of EDM, which uses metal wire as line electrode to cut the workpiece. The following technological problems of WEDM are analyzed.

1 workpiece material pretreatment

Forging and quenching workpiece materials need pretreatment before processing. Forging and quenching materials will have different residual stresses. In large-scale cutting and cutting, because the relative balance of residual stress is destroyed, the stress will be released during the machining process, resulting in the deformation of the workpiece, which can not meet the requirements of dimensional accuracy. Incorrectly quenched materials will also produce cracks during processing. Therefore, this kind of material should be tempered at low temperature before on-line cutting.

After heat treatment, it is necessary to remove the heat treatment residue, scale and rust spot at the cutting position of the electrode wire on the workpiece. Because these residues are not conductive, the electrode wire is very easy to burn off, or leave deep marks on the surface of the workpiece. In severe cases, the electrode wire will leave the machining track, leading to the scrap of the workpiece. If the workpiece needs machining methods (such as turning, milling, etc. ) processing shape and positioning surface, pay attention to edge chamfering and orifice chamfering. In order to grind the locating surface, it is necessary to demagnetize the workpiece material.

2. Machining of threaded holes

The threading hole is the starting point of the movement of the electrode wire relative to the workpiece and the execution of the program, and is generally selected as the datum point on the workpiece.

2. 1 function of threaded hole (also called process hole)

(1) is used to process the concave die. The closed workpiece of the female die must have threaded holes before cutting to ensure the integrity of the workpiece. (2) Reduce the deformation of stamping process and prevent wire from being pinched off due to material deformation. (3) As a positioning benchmark, ensure the position accuracy of machined parts and other parts. For the first two functions, the machining accuracy of wire piercing holes does not need to be too high. But for the third function, its machining accuracy must be considered.

2.2 Location of threading holes

The minimum distance between the contour of the threaded hole and the contour of the machined part is related to the thickness of the workpiece. The thicker the workpiece, the greater the minimum distance, generally not less than 3 mm For punch and die workpiece, what is the shortest distance from the thread hole profile to the workpiece machining profile? 3 mm. For stamping workpieces, in order to reduce deformation, what is the distance from the machining profile of the workpiece to the side of the blank? 5mm, the distance from the machining contour of the workpiece to the sharp corner of the blank? During the heat treatment of 8 mm WEDM blank, the surface cooling is fast, but the internal cooling is slow. After heat treatment, the metallographic structure of the blank is inconsistent, resulting in internal stress, and the closer to the corner, the greater the stress change. Therefore, the graphic outline of wire cutting should try to avoid the corner of the blank, so as to avoid deformation affecting the accuracy of the workpiece. Generally, 8 ~ 10 mm should be given, and enough clamping allowance should be reserved for the punch.

The following principles should be followed when selecting threading holes:

Machining female die (die hole workpiece): (1) cut small die hole and set a threaded hole in the center of the die hole. It is most convenient to select the threading hole in the center of the die when cutting the small hole-shaped die. Because this can not only make the machining position of threaded hole accurate, but also facilitate the calculation of control coordinate trajectory. (2) For large die hole cutting (or convex workpiece), the wire threading hole is set near the corner of the machining path or at the intersection of known coordinate sizes to simplify the calculation process. When cutting a convex workpiece or a concave workpiece with a large hole, it is not appropriate to choose the center of the concave hole as the threading hole, because this will make the cutting path of useless stroke longer. Therefore, it is generally better to choose the vicinity of the cutting point for this kind of cutting. (3) Multi-hole cutting, each hole has its own independent threaded hole.

Machining punch (contour workpiece): (1) cutting punch (or large hole), and the thread-through hole is near the corner of the machining trajectory, that is, near the cutting point. The position of the thread hole can be selected near the corner of the machining pattern to simplify the programming operation and shorten the cutting stroke during cutting. (2) closed cutting, not open cutting, otherwise it will destroy the balance of residual internal stress and cause deformation. As shown in figure 1(a), when cutting the workpiece with the outer contour of the punch, many modelers often cut directly from the side of the material, resulting in a cut at the cut-in place, and the residual stress is released from the cut, which is easy to deform the punch. In order to avoid deformation, a wire threading hole with a diameter of 3 ~ 10 mm is punched on the die blank before quenching, and the cutting punch is closed from the inside of the die blank after the workpiece is quenched. (3) cutting from outside to inside. As shown in figure 1(b), for parts, especially stamping workpieces, the cutting direction can be from outside to inside. The cutting direction should be conducive to ensuring the rigidity of the workpiece during cutting and avoiding the influence of stress and deformation. Cutting from outside to inside is adopted, that is, cutting the machining track far from the clamping part first, and then cutting the machining track near the clamping part. If cutting from inside to outside is adopted, the main connecting parts between the blank and the workpiece are cut off prematurely, and the remaining materials are sandwiched in fewer parts, which greatly reduces the rigidity of the workpiece and easily leads to deformation, thus affecting the machining accuracy.

(a) closed cutting (b) cutting from outside to inside.

When choosing the position of threading hole, we should also pay attention to the following problems: (1) hole may be crooked. As shown in Figure 2, if the minimum distance between the thread hole profile and the machined profile of the workpiece is too small, the workpiece may be scrapped. On the contrary, if the minimum distance between the wire piercing hole and the workpiece machining trajectory is too large, the cutting stroke will increase. (2) Clean up burrs. After the wire piercing hole is processed, it needs pretreatment and deburring just like the workpiece to avoid short circuit and abnormal processing.

(a) The threaded hole is too close to the machining track; (b) The threaded hole is too far away from the machining track.

2.3 Size of threading hole

In order to facilitate processing, the diameter of threaded hole should not be too small or too large, and 3 ~ 10 mm is generally selected. It is best to choose an integer value for the aperture, so as to use it as a machining reference to simplify the operation.

If the diameter of the threading hole must be very small due to the machining contour of the part, be careful when threading, try to avoid skewing or minimize the depth of the threading hole. As shown in fig. 3, in fig. A, it is difficult to directly punch holes with an electric spark punch. Figure B shows the design of milling a larger bottom hole at the bottom, which can reduce the depth of the wire hole without affecting the use, thus reducing the difficulty of drilling. This method is often used to process parts such as push rod hole of injection mold.

2.4 Manufacturing of threading holes

The threading hole can be milled and drilled by milling machine and drilling machine to process the workpiece before quenching, or it can be machined by EDM punch to process the workpiece with small aperture and high hardness after quenching.

When the wire piercing hole is used as the machining benchmark, its position accuracy and size accuracy should be equal to or higher than the accuracy required by the workpiece. Therefore, drilling, milling, boring, reaming and other precision machining methods should be used to process the wire piercing hole, and it should be processed on a machine tool with a precision coordinate table to ensure its position accuracy and dimensional accuracy.

When the material allowance is very small, the size of the thread hole is limited, and it cannot be machined by mechanical method, it can be machined by EDM high-speed punch. Generally, the diameter of the threaded hole is 0.5 ~ 3 mm, and the depth-diameter ratio can reach more than 20.

3 Conclusion

Through the pretreatment of workpiece materials and the analysis of the function, position, size and manufacturing method of wire piercing holes, the pretreatment method of workpiece before WEDM is expounded, which has guiding significance for the setting of WEDM path elements of actual workpiece.

refer to

[ 1]? Operation and example of high-speed WEDM [M]. Beijing: National Defense Industry Press, 20 10.

[2]? Wang Min. Analysis on the application of project teaching method in the teaching of die fitter [J]. Modern communication, 20 13, (3).

[3]? Special processing technology [M]. Xi An: xidian university Publishing House, 20 1 1.

About the author: Liang Tianyu (1978―), female, Siping, Jilin, lecturer of Dalian Vocational and Technical College, master's degree, research interests: stamping die, die-casting die, electro-machining technology, etc.

The second paper on EDM technology

Analysis of WEDM processing parameters

[Abstract] EDM is widely used in actual production and processing, especially in stamping die processing, and it is the most ideal processing equipment. Adjusting the processing parameters in the processing process is an important factor affecting the quality of the workpiece. This paper mainly summarizes practical experience and analyzes the adjustment and setting of electrical parameters and non-electrical parameters in order to achieve more reasonable processing quality.

[Keywords:] mass electrical parameters non-electrical parameters

Electro-machining, also known as EDM, also known as electric pulse machining, is a process that directly uses thermal energy and electric energy for machining. The principle of EDM is completely different from that of metal cutting. In the process of machining, the tool does not contact with the workpiece, but the pulse spark discharge between the tool and the workpiece produces local and instantaneous high temperature to gradually remove metal materials. Because sparks can be seen during discharge, it is called electric spark. There are many factors that affect the machining quality of workpieces in the machining process, among which machining parameters are the main factors that affect the machining quality. Below, I mainly analyze the electrical parameters and non-electrical parameters from two main aspects:

I. Electrical parameters

Electrical parameters mainly include: pulse width, pulse interval, open-circuit voltage, short-circuit peak current, discharge waveform, machining polarity and feed speed. 1, pulse width Ti, increasing pulse width, increasing cutting speed, and deteriorating surface roughness. (When the pulse width increases, the energy of single pulse discharge increases. When Ti >: 40? S, the machining speed does not increase much, but the electrode wire loss increases). [Usually Ti is 1 ~ 60? S, the pulse frequency is 10 ~ 100 kHz]

2. Due to the influence of pulse interval, the pulse interval is reduced, the cutting speed is increased, and the surface roughness is slightly increased, but it is too small to eliminate the discharge products, the ionization between gaps cannot be completely eliminated, and the insulation state is not restored, which is easy to cause workpiece burns or broken wires. [Generally, to = 4 ~ 8ti, the workpiece thickens and to increases] The pulse width is 5 ~ 9 times, and the short-circuit current changes with the pulse width. The thicker the cutting, the greater the inter-pulse frequency doubling, reaching 9 times when it exceeds 300mm; 3. Due to the influence of the open-circuit voltage Ui, the peak value of the open-circuit voltage increases, the machining current increases, the cutting speed is accelerated, and the surface roughness is poor (high voltage increases the machining gap, which is beneficial to the discharge products, improves the machining stability and pulse utilization, but causes the electrode wire to vibrate, reduces the machining accuracy and increases the electrode wire loss). Voltage: general metal 1H, only the semiconductor material is cut for 2 hours or many times with small current;

4. The influence of short-circuit peak current is that increasing the short-circuit peak current will increase the cutting speed and worsen the surface roughness. (Short-circuit peak current is large, corresponding machining current is large, pulse energy is large, discharge trace is large, and electrode wire loss is large, thus reducing machining accuracy.

(Generally speaking, yes.

5. Due to the influence of discharge waveform, the leading edge of voltage waveform rises slowly and the electrode wire loss is small, but it is not conducive to the narrowing of pulse width, the waveform is not easy to form and the cutting speed is reduced.

6. Due to the influence of machining polarity, WEDM uses positive electrode for machining because of its narrow pulse width, that is, the workpiece is connected to the positive electrode and the electrode wire is connected to the negative electrode (choose positive pulse wave). The reverse connection will slow down the cutting speed or even make it impossible to cut, and the electrode wire loss is large.

Second, non-electrical parameters

Non-electrical parameters mainly include: the influence of mechanical transmission accuracy, electrode wire and wire speed, workpiece thickness, workpiece material, working fluid, guide wheel parameters and position on taper machining accuracy;

1, the influence of mechanical transmission precision, high transmission precision and good processing effect;

The transmission accuracy of coordinate table largely determines the dimensional machining accuracy of wire cutting, and its influence mainly depends on four factors:

(1) Accuracy of transmission mechanism components (screws, nuts, gears, worms, guide rails, etc.). );

(2) Fit clearance (fit clearance of screw pair, gear pair, worm gear pair, key, etc.). );

Assembly accuracy (mainly three-line alignment of lead screw and nut, even gear matching, tangency of turbine and worm, parallelism of lead screw and guide rail of two vertical and horizontal carriages, verticality of guide rail of two carriages);

(3) The working environment of the machine tool (temperature, humidity, dustproof, vibration, etc.). ). The poor transmission accuracy of the coordinate table leads to large floating amount, which often leads to short circuit or open circuit in the discharge gap, making the machining unstable, often leaving discharge traces on the machined surface, and even jagged stripes, resulting in poor machining accuracy and surface roughness. At the same time, the pulse utilization rate is low, which reduces the processing speed and will cause wire breakage in serious cases.

2. The influence of transmission accuracy of wire feeder mechanism. The stability of electrode wire movement in EDM area depends on the transmission accuracy of wire feeder mechanism. Uneven wire feeding affects the processing effect and the service life of wire. The faster the wire feeding speed, the greater the influence on processing.

The moving position of the electrode wire is determined by the guide wheel, which is mainly caused by three aspects:

(1) The guide wheel has radial or axial runout, which causes the electrode wire to vibrate, and the amplitude is positively related to the guide wheel runout or runout. In fact, the jumping (jumping) of the upper and lower guide wheels may exist at the same time, and the action is relatively complicated. However, it can be judged from the upper and lower taper of the workpiece whether the guide wheel jumps or not, which guide wheel or which direction jumps greatly (the guide wheel at the smaller end of the workpiece at the inner side of the electrode wire cutting direction jumps more or more), and similarly, the guide wheel at the outer side of the electrode wire cutting direction jumps more or more).

(2) When the fillet radius of the V-shaped groove of the guide wheel exceeds the electrode wire due to wear, the accurate position of the electrode wire will not be guaranteed. Usually, the wear is asymmetric, and the deeper the wear, the greater the jitter; The axes of the two guide wheels are not parallel, or the V-shaped groove is not in the same plane, and the electrode wire is not inclined on the same side when moving, so that the positive and negative directions of the electrode wire are not inclined on the same side, resulting in reverse stripes on the machining plane. The main reasons for the wear of V-groove are: the electrode wire moves forward and backward at high speed; The installation of the guide wheel bearing is not flexible, the seal is not good, and the movement resistance is large; In the reverse direction, the guide wheel cannot immediately follow the reverse direction; The hardness of discharge products is high;

(3) The wire storage drum vibrates, which leads to the vibration of the electrode wire. The concentricity of the drum must be ensured.

3. The influence of electrode wire and linear velocity.

(1) The commonly used electrode wire materials are molybdenum wire, tungsten wire and tungsten-molybdenum wire, and the commonly used specifications are Ф 0.10 ~ 0.30 mm. 。

(2) Due to the influence of the diameter of the electrode wire, if the diameter of the electrode wire is small, it will bear less current and narrow slit, which is not conducive to chip removal and stable machining, and the cutting speed is low; The electrode wire diameter is too large, the slit is large, the erosion amount is large, and the cutting resistance increases accordingly, which is not conducive to improving the speed. Therefore, the diameter of electrode wire should be moderate. The most commonly used is Ф 0.12 ~ 0.18 mm.

(3) The influence of winding and tightening on the electrode wire, and the quality of winding and tightening directly affects the tension of the electrode wire. The electrode wire is too loose and the jitter is large; Too tight, large tension, small vibration, high discharge efficiency, which can improve the speed, but it is easy to break the wire.

(4) The influence of wire feeding speed. When the wire feeding speed is high, the thermal stress of the electrode wire is small, which reduces the probability of wire breakage and short circuit and can correspondingly improve the cutting speed. However, the electrode wire jitter is large, which causes great wear on the V-groove of the guide wheel, affects the cutting accuracy and shortens the service life of the electrode wire.

4, the influence of the thickness of the workpiece, the workpiece cutting thickness is thin, which is beneficial to chip removal and ionization, and the machining stability is good, but the workpiece is too thin, the utilization rate of discharge pulse is low, the efficiency is low, and the electrode wire is easy to shake, which affects the accuracy; Thick workpiece, working fluid, difficult to enter and fill the discharge gap, poor chip removal, easy short circuit, affecting accuracy, poor machining stability and reducing cutting speed; However, the electrode wire jitter is small, which is beneficial to improve the machining speed and accuracy. Therefore, pay attention to the selection of pulse interval and pulse width according to the thickness of the workpiece.

5, the influence of workpiece materials, different workpiece materials, its melting point, vaporization point, thermal conductivity, cutting speed is different.

6, the influence of the working fluid, increase the pressure and flow of the working fluid, and easily eliminate the etchant; Too high will cause the vibration of the electrode wire; Too low is not conducive to chip removal, easy to short circuit, unable to take away the eroded heat in time, burn the workpiece, break the wire and so on. Maintain laminar flow (DC).

7. Influence of guide wheel parameters and position on taper machining accuracy

During taper machining, the parameters of the guide wheel and the position of the guide wheel relative to the workpiece will directly affect the machining accuracy (cutting position deviation). Including the distance (Z-axis height) between the upper and lower guide wheels, expressed by Hc-c; Distance from the center of the lower guide wheel to the bottom surface of the workpiece, HB; Workpiece thickness; Radius of guide wheel r

About the author: Zhang Dongwei, male, Han nationality, from Baicheng City, Jilin Province, graduated from Taiyuan University of Science and Technology in 2009 with a bachelor's degree in engineering and an assistant lecturer.

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