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How to improve the precision and smoothness of WEDM
[Abstract]:
First, improve the deformation process
Before wire cutting, due to the hot working and cold working of the metal plate, the stress is produced in the material, and the stress in different directions and sizes can be balanced or not released in a short time. Even after stress relieving annealing, residual stress exists. When a large amount of material is removed, the original balance is broken, and the material will deform. Therefore, the workpiece must be tempered or artificially treated before cutting.
Improved process of 1.1 cutting cavity
(1) rough and fine processing method. Before machining on the workpiece machining to remove a large number of material cutting online, leaving deformation allowance (usually 0.51mm) can be made of gold or wire cutting processing, the internal stress is released to generate deformation, and then finishing once or twice, so that the processing to reduce the amount of deformation is also reduced.
(2) use closed cut cavity as far as possible (i. e. internal cavity and external boundary not cut). Because there is residual stress inside the material, if the cutting cavity is not closed will be distorted, the result is poor and in cutting near the end due to the deformation of the workpiece is easily broken workpiece deformation.
Improved process of 1.2 cutting core
(1) the cut line should choose the tangent line along the arc edge or the straight edge. Due to lack of rigidity of molybdenum wire, cutting the core of thick, strong discharge corrosion and friction force caused by molybdenum wire twisting machine, clearance screw nut, the workpiece should be cut off when the connection stiffness is insufficient, often make the core surface bulge or groove, this will affect the size of precision molds. The cutting plane is cut off along the long line of the cutting line, so that the processing error is concentrated in the direction of the cutting line, and the defects are greatly improved.
(2) multiple point cutting. The core of high precision, even with closed cutting, because the gap between the workpiece and the material (molybdenum wire diameter of 0.18 m m+ 0.02 M discharge gap of 0.2 m m m), there will be some deformation, to eliminate deformation, can use multiple point cut, each segment left a small amount of support (as far as possible, so that the workpiece symmetric distribution) will be difficult to deformation, finally cutting or manually remove the pliers for repairing surface.
(3) pay attention to the running stability of wire feeding system (wire guide wheel, conductive block, etc.) of wire cutting machine tool. If the wire is round wire and conductive block check and change the jitter response, not easy to loose wire, wire frame from the workpiece appropriate, the purpose is to reduce the wire vibration when running. The diameter of the wire is measured, especially for a long time. The diameter of the loss wire becomes smaller due to the long time drawing, abrasion and discharge, so as to offset the offset. For the workpiece to be polished, according to the nature of the material should be retained polishing margin.
Two. The process method to improve the shape and position accuracy
Control of verticality of cavity and core of model 2.1
Tighten the molybdenum wire, adjust the verticality of the wire with the regulator, and also manually adjust the wire rack with the two base plane of the standard template (verticality is better) until the spark is uniform. The verticality of the cavity is very important. It is generally used as the datum of the core. The core is inlaid in the cavity groove which is cut first. As long as the verticality of the cutting hole meets the requirements, the cavity can be used as the benchmark for grinding or other cutting process.
2.2 position control
Wire cutting multi cavity mold, can use the jump function to ensure the position of the (automatic control), but sometimes to find a reference center or reference edge, to accurately find on the edge or center, first to tension the molybdenum wire, good verticality adjusting wire, in addition to the workpiece burr, debris, and find it a few times, the numerical difference can be. Write down the coordinates of each jump position to check the accuracy of the broken wire retraction.
2.3 action fixed mould matching processing
The fixed mold cavity and core and the dynamic model of the need to work together, the best use of templates and the dynamic template with guide column positioning together with cut, so even if the alignment is perpendicularity deviation or wire cutting wire does not affect the matching precision, if the fixed template separately cut, will affect the fit in the precision alignment and the verticality of silk and other factors, and even produce burr.
Three. Improve the surface finish process
3.1 main factors affecting the surface finish of the machined surface
(1) the wear of guide wire wheel and bearing makes the machined surface fringe pattern.
(2) the electrode wire loss is too large, so that the electrode wire moves in the guide wheel.
(3) the movement of the electrode wire is not stable, or the tension of the electrode wire is not enough.
(4) improper selection of electrical parameters, improper feed rate adjustment, to the processing instability.
3.2 overcome the factors of machine tools
Check the machine tool stepper motor gear meshing clearance and the upper and lower guide pulley and conductive block wear strictly, wear seriously should be replaced, otherwise the wire will run beating, the use of qualified electrode wire, the surface without oxidation. With special cutting fluid for wire cutting, the new cutting liquid is best to be used in finishing.
3.3 adopt reasonable process method
The tension electrode wire, according to the height of the workpiece to adjust the distance between the upper and lower guide wheel, so as to reduce the vibration of molybdenum wire. Selecting appropriate electrical parameters, increasing pulse voltage and pulse width, and increasing feed rate can improve machining efficiency, but surface roughness will become worse. On the surface of high quality should be used repeatedly processing, use the pulse voltage and pulse width, increasing the feed rate of rough machining efficiency, redundancy using pulse voltage and pulse width of small, decreasing the feed rate of repeated finishing, but also pay attention to the machining process
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