surface quality
(1) Nanosecond level high peak current pulse power supply technology
The erosion of metals during electrical discharge machining can be divided into two types: melting and gasification. The wide pulse width action time is long, which is easy to cause melting processing, resulting in poor surface morphology of the workpiece, thickening of the metamorphic layer, increasing internal stress, and easy to generate cracks. When the pulse width is small to a certain value, the action time is extremely short, forming gasification processing, which can reduce the thickness of the metamorphic layer, improve surface quality, reduce internal stress, and avoid cracks.
The pulse power supply used in the advanced low-speed WEDM machine has a pulse width of only a few tens of ns and a peak current of over 1000 A, forming cavitation erosion, which not only improves the 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 machining. Water has a certain conductivity, and even after deionization treatment, which reduces the conductivity, there is still a certain amount of ions. When the workpiece is connected to the positive electrode, under the action of an electric field, OH ions will continuously accumulate on the workpiece, causing oxidation and corrosion of iron, aluminum, copper, zinc, titanium, and tungsten, and dissolving the binding agent cobalt in the cemented carbide material in an ionic state in water, forming a "softening layer" on the surface of the workpiece. Measures to increase resistivity (from tens of kiloohm? Centimeters to hundreds of kiloohm? Centimeters) have been adopted to minimize ion concentration, which has played a certain role in improving surface quality, but still cannot effectively and thoroughly solve the problem of "softening layer".
Anti electrolysis power supply is an effective technical means to solve the "softening layer" of workpiece. The anti electrolysis power supply adopts alternating pulses with an average voltage of zero, which makes the OH ion electrode wire in the working fluid oscillate with the workpiece and does not tend to the workpiece and electrode wire, preventing oxidation of the workpiece material.
Using an electrolytic proof power supply for wire electrical discharge machining can control the surface deterioration layer to 1 μ Below m, avoid precipitation and dissolution of cobalt in cemented carbide materials, and ensure the service life of cemented carbide molds.
Cutting accuracy
(1) Multiple cutting technology
Multi cutting technology is a fundamental means to improve the machining accuracy and surface quality of low speed wire EDM. It is the scientific integration of design and manufacturing technology, numerical control technology, intelligent technology, pulse power supply technology, precision transmission and control technology. Generally, it is formed through one cut, and the accuracy is improved through two cuts, while the surface quality is improved through more than three cuts. Originally, in order to achieve high-quality surfaces, the number of multiple cuts needed to be as high as 7-9 times, only 3-4 times.
(2) Continuous optimization and improvement of corner processing technology
Due to the hysteresis of the electrode wire when cutting corners, corner collapse can occur. In order to improve the accuracy of corner cutting, researchers have adopted more dynamic corner processing strategies. For example, changing the wire routing; Changing the processing speed (sheet); Automatically adjust the water pressure; Control processing energy, etc.
By adopting a comprehensive corner control strategy, the corner shape error during rough machining is reduced by 70%, and a matching accuracy of 5 μ m can be achieved in one cutting.
(3) Adopt technology to improve flatness
High precision finishing circuits are technologies that improve flatness and are considered significant for thick workpiece processing.
(4) More precise machine tool structure
In order to ensure high-precision machining, many technical measures have been adopted to improve the accuracy of the host machine: ① Controlling temperature. Using a water temperature cooling device, the internal temperature of the machine tool is the same as the water temperature, reducing the thermal deformation of the machine tool Adopt linear motor. High responsiveness, precision positioning can achieve 0.1 μ M-equivalent control, feeding without vibration and noise, increasing discharge frequency, maintaining stable discharge, twice cutting Ry5 μ m。③ Made of ceramic and polymer artificial granite, its thermal inertia is 25 times larger than that of cast iron, reducing the impact of temperature changes on cutting accuracy The fixed workbench and column moving structure are adopted to improve the bearing capacity of the workbench, which is not affected by immersion processing and workpiece weight changes Adopt immersion processing to reduce thermal deformation of the workpiece. ⑥ Motor servo, closed-loop electrode wire tension control. ⑦ High precision tool setting: voltage modulation tool setting power supply is adopted. The knife setting accuracy can reach ± 0.005 mm, without damaging the workpiece, regardless of whether it is dry or wet.
Processing efficiency
(1) Processing efficiency
Due to the development of ns level high peak current pulse power supply technology, detection, control, and anti-interference technology, the processing efficiency of low speed wire EDM machines is also continuously improving.
(2) Machining efficiency of workpiece with larger thickness
When cutting 300 mm thick workpieces, the FA-V series machine tool of Mitsubishi Electric Corporation of Japan has a processing efficiency of 170 mm2/min. This is a significant technical improvement.
(3) Machining efficiency of workpiece with thickness variation
Automatically detect the thickness of the workpiece, automatically adjust processing parameters, prevent wire breakage, and achieve processing efficiency in this state.
(4) Double wire automatic switching technology
ROBOFIL 2030 S1-TW machine tool can automatically perform dual wire switching processing using 0.20 to 0.02 mm electrode wires. Use coarse wire for secondary cutting, generally with a wire diameter of 0.25 mm, to improve processing efficiency, and can be coreless cutting; Then, fine wire is used for trimming, generally using 0.10 mm fine wire to cut small rounded corners and improve accuracy. Overall, it can save 30% to 50% of cutting time.
(5) Rapid automatic threading technology
Automatic threading time<15 s; The threading time is called 13 seconds by Sadik Corporation of Japan. When the plate thickness is 50 mm, the threading time is 10 seconds, and the total time for cutting and threading is 25 seconds.