Slow silk processing accuracy and factors that affect processing accuracy
Time:2022-10-18
Views:3294
1. The precision of slow wire walking is related to the model of the machine tool and the level of the operator. At present, the precision of the processing industry can reach 0.005mm.
2. Slow wire walking is a kind of numerical control machining tool that uses continuously moving thin metal wires as electrodes to conduct pulse spark discharge on the workpiece, generating a high temperature of more than 6000 degrees, eroding metal and cutting into workpiece.
3. The surface roughness of workpiece processed by slow wire cutting machine can generally reach Ra=0.8 μ M and above, the roundness error, straightness error and size error of slow wire cutting machine are less than those of fast wire cutting machine, so it is widely used.
Processing characteristics of slow wire walking
surface quality
(1) Nanosecond high peak current pulse power supply technology
The metal removal in EDM can be divided into melting and gasification. The wide pulse width has a long action time, which is easy to cause melting processing, make the surface morphology of the workpiece worse, thicken the metamorphic layer, increase the internal stress, and easily produce cracks. When the pulse width is small to a certain value, the action time is very short, forming gasification processing, which can reduce the thickness of the metamorphic layer, improve the surface quality, reduce the internal stress, and avoid cracks.
The pulse power supply adopted by the advanced low-speed wire edm machine has a pulse width of only tens of ns and a peak current of more than 1000 A, forming gasification erosion, which not only has high processing efficiency, but also greatly improves the surface quality.
(2) Anti electrolysis (BS) pulse power supply
Water quality working fluid is used for low-speed wire EDM. Water has a certain conductivity. Even though the conductivity is reduced after deionization, there is still a certain amount of ions.
When the workpiece is connected to the positive electrode, under the action of electric field, OH ions will continuously gather on the workpiece, causing oxidation and corrosion of iron, aluminum, copper, zinc, titanium and tungsten, and dissolving the bond cobalt in the cemented carbide material in ionic state in water, forming a "softening layer" on the workpiece surface.
The measure of increasing resistivity (from tens of kiloohm cm to hundreds of kiloohm cm) has been adopted to reduce the ion concentration as much as possible. Although it has played a certain role in improving the surface quality, the problem of "softening layer" cannot be effectively and thoroughly solved.
Anti electrolysis power supply is an effective technical means to solve the "softening layer" of workpiece. The anti electrolysis power supply adopts alternating pulse, and the average voltage is zero, so that the OH ion electrode wire in the working fluid is in an oscillating state with the workpiece, and does not tend to the workpiece and electrode wire, so as to prevent the oxidation of the workpiece material.
The anti electrolysis power supply is used for WEDM, so that the surface deterioration layer can be controlled at 1 μ Below m, the precipitation and dissolution of cobalt in cemented carbide materials shall be avoided to ensure the service life of cemented carbide dies.
Cutting accuracy
(1) Multiple cutting technology
Multiple cutting technology is the fundamental means to improve the machining accuracy and surface quality of low-speed WEDM. It is the scientific integration of design and manufacturing technology, numerical control technology, intelligent technology, pulse power technology, precision transmission and control technology.
Generally, the precision is improved by one cutting, two cutting and more than three cutting to improve the surface quality. In order to achieve high-quality surface, the number of times of multiple cutting should be as high as 7-9 times, only 3-4 times.
(2) Continuous optimization and improvement of corner machining technology
Because the electrode wire lags behind when cutting corners, it will cause corner collapse. In order to improve the corner cutting accuracy, researchers have adopted more dynamic corner processing strategies. For example, change the wire path; Change the processing speed (sheet); Automatically adjust water pressure; Control processing energy, etc.
By adopting the comprehensive corner control strategy, the corner shape error during rough machining can be reduced by 70%, and the fitting accuracy can reach 5 μ m at a time.
(3) Adopt technology to improve flatness
High precision finishing circuit is a technology to improve the flatness, which is considered to be of great significance for thick workpiece processing.
(4) More precise machine tool structure
In order to ensure high-precision processing, many technical measures have been taken to improve the accuracy of the host machine:
① Control temperature. The water temperature cooling device is used to make the internal temperature of the machine tool the same as the water temperature, reducing the thermal deformation of the machine tool.
② Linear motor is adopted. High responsiveness, precision positioning can achieve 0.1 μ Control of m equivalent, feeding without vibration and noise, increase discharge frequency, maintain stable discharge, and cut Ry5 twice μ m。
③ Using ceramic and polymer artificial granite parts, its thermal inertia is 25 times greater than that of cast iron, reducing the impact of temperature changes on cutting accuracy.
④ The fixed worktable and column moving structure are adopted to improve the bearing capacity of the worktable, which is not affected by immersion processing and workpiece weight changes.
⑤ Immersion processing is adopted to reduce the thermal deformation of the workpiece.
Reference source: Baidu Encyclopedia -- Slow Moving Silk
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