Patent Application
20220258262
The present invention relates to the field of wirecut electrical discharge machining. More specifically, it relates to wire electrodes for wirecut electrical discharge machining having a carbonaceous surface layer and methods for their preparation.
Wirecut electrical discharge machining is also referred to as WEDM herein. The principle in this technology is to use a wire electrode in continuous movement as the electrode to remove material of a metal work piece by pulsed spark discharges and achieve machine-based shaping of the work piece according to the set trajectory. As compared to other processing methods, WEDM has a better performance in terms of roundness error, linear error and dimensional error, and it is widely applied in aerospace manufacturing. Especially since 1980, with the gradual improvement of the precision of molds for precision machinery parts, home appliances and communication equipment, WEDM has become an indispensible processing method in the mold manufacturing industry. In recent years, automation and artificial intelligence have changed the world. An increasing amount of automation and artificial intelligence equipment has been applied in factories, families, medical institutions, etc. To meet the requirements of such high precision equipments, slow wire-electrical discharge machining has also entered into a new development stage of high dimensional accuracy, high surface finish and high efficiency. In addition to technical innovations related to WEDM machines, wire electrodes for WEDM are also an important motivator for its development. With the development of nearly 40 years, WEDM has witnessed the innovation of products of four generations.
The first generation wire electrode for WEDM is a copper wire. Due to excellent electrical conductivity and processing performance, copper is a preferred choice for wire electrodes for WEDM.
The second generation wire electrode for WEDM is a brass wire. According to related studies, the vaporization performance of a brass wire is superior to that of copper. In other words, under the same discharge intensity, a larger vaporization pressure can be generated, which can better remove the chips (formed in the cutting process), thereby increasing the processing speed. With the discovery of the brass wire characteristics and the maturity of the multi-mode continuous brass wire drawing process, the copper wire electrode has been completely replaced by the brass wire electrode.
The third generation wire electrode for WEDM is a galvanized wire. According to application studies, a pure zinc surface coating can eliminate the capacitive effect generated during the discharge, making the discharge more stable and continuous. Also, the surface finish of the processed work piece is greatly improved compared with the brass wire. For some high-end and high-precision molds and parts, galvanized wire processing is an ideal choice.
The fourth generation wire electrode for WEDM is a coated wire. The coated wire can be divided into a gamma-coated wire, a beta-coated wire and a composite-coated wire. According to application studies, high-zinc alloys (i.e. an alloy having a high content of zinc) on the surface of the wire can achieve higher discharge vaporization pressure. Therefore, a high-zinc alloy, coated on the surface, at a certain thickness helps improving the processing speed.
The wire electrodes for slow wire WEDM have undergone four generations of development. Their application performance has been greatly improved. In particular, the processing precision, surface finish and processing speed have been greatly improved compared with the first generation of copper wires. However, the developments of the industry will never satisfy the ever-changing demands. In the new manufacturing environments, new difficulties and challenges have arisen for users of WEDM processing. For example, further improving the processing speed of a galvanized wire while maintaining the desired precision, increasing the speed and precision of a coated wire, achieving/guaranteeing excellent threading performance of a coated wire, etc. are still technical problems to be solved by the industry to provide wire electrodes for WEDM having greater processing speed, higher processing accuracy, better surface finish and excellent wire feeding performance.
In order to solve the problems associated with of the above-mentioned deficiencies of current technology, the present invention provides a wire electrode for WEDM having a carbonaceous surface layer as defined in claim 1. The present invention also provides a method for preparing such a wire electrode as defined in claim 9.
Preferred embodiments as disclosed in the dependent claims.
As compared to a coated wire, the wire electrode of the present invention is characterized by a special structure that may improve processing speed by over 15%. The processing precision is also superior to that of the coated wire. The wire electrode of the present invention is easy to manufacture, and it exhibits greatly improved performance resulting in stronger market competitiveness as compared a coated wire.
The composition of the carbonization layer of the present invention (also referred to as “carbonized layer”) has a carbon content of 0.1-99.0 wt %, a total content of aluminum and potassium of less than 0.5 wt %, wherein the remainder includes copper and zinc as well as other unavoidable impurity elements (oxygen, hydrogen and nitrogen).
The carbonized layer of the present invention has a thickness of 0.5 to 30 microns and exists on the outer surface of the phase transition layer in a continuous or intermittent (discontinuous) form. The carbonized layer is formed by a carbon precipitation reaction. As the carbonized layer is very dense on the surface of the finished product after being stretched by the drawing die, and the electrical conductivity is improved by 3-8% IACS, the accuracy during the discharge machining can reach up to ±0.002 mm.
The content of the unavoidable impurity elements in the carbonized layer in the present invention is preferably less than 0.5% by weight.
The core material of the present invention is preferably one of brass, copper and carbon steel.
The phase transition layer of the present invention comprises a copper-zinc phase structure composed of one, or two or more metal compounds selecting from the group of CuZn, Cu5Zn8, CuZn3. The reason why the above copper-zinc phase structure is adopted is that the CuZn phase structure has good electrical conductivity, is favorable for improving the positioning accuracy during the processing, and further improves the processing precision. The Cu5Zn8 phase structure has excellent vaporization performance, which is favorable for improving the flushing performance during the processing, thereby improving the processing speed. The CuZn3 phase structure can eliminate the capacitive effect generated during the discharge machining process, and thus improves the discharge stability under the weak current condition, thereby improving the surface finish of the processed workpiece.
Carbon in elemental form is also present in the phase transition layer of the present invention. The composition of the phase transition layer includes a content of elemental carbon of less than 50 wt %, wherein the remainder includes copper, zinc and other unavoidable impurity elements, i.e., oxygen, hydrogen, nitrogen, aluminum and potassium with a total mass percentage of less than 0.5 wt %.
The phase transition layer of the present invention has a thickness of 1 to 40 microns. The phase transition layer structure is prepared according to the different copper-zinc phase structures to obtain wire electrodes with improved processing precision, processing speed and surface finish. Different copper-zinc phase structure combinations will have different application characteristics.
The present invention also provides a method for preparing a wire electrode in accordance with the present invention suitable for slow WEDM having a carbonaceous surface layer, said method including the following preparation steps:
An alternative method for preparing a wire electrode of the present invention comprises the following steps:
Since the aforementioned method only includes three steps, the preparation of the above-mentioned surface carbon-containing wire electrode for slow wire EDM becomes more efficient.
Yet another method for preparing the wire electrode of the present invention comprises the steps of:
The surface roughness of the wire blank ranges from Ra 0.05 to 0.2 μm after coating in accordance with the present invention.
The final product of the present invention has a tensile strength of 500-2,500 MPa and a conductivity of 15-95% IACS. The processing speed of the wire electrode of the present invention is 1.15-1.35 times higher than that of a coated wire as discussed above.
The present invention is associated with the following significant improvements and beneficial effects as compared to wire electrodes for WEDM in the prior art and the preparation methods thereof:
The present invention is described in further detail below by means of the figures and examples. The scope of the invention is not limited by the following illustrative examples.
A wire electrode prepared in accordance with an embodiment of the present invention has a cross section from the inside to the outside as shown in
A wire blank having the brass grade H65 (CuZn35) and a wire diameter of 0.2 mm is prepared. After alkali washing and pickling by pre-plating treatment, the surface of the wire blank is cleaned and then it is delivered to a plating tank. The bath solution is a mixed solution of 1,000 g/L of zinc sulfate, 20 g/L of dextrin having an average length of 3-15 glucose units as CHO organic matter, 15 g/L of aluminum salt and 15 g/L of potassium salt. The production speed is set at 100 m/min. The plating current is set a 900 A and the voltage is set at 8V. The plating thickness of the final electroplated wire blank is 10 μm, and the surface roughness of the electroplated wire blank is Ra 0.12 μm.
The plated wire blank is subjected to carbon precipitation reaction in an annealing furnace with a nitrogen content of 97%. The reaction temperature is 150° C., the reaction time is 10 hours, the cooling temperature is 50° C., and the furnace temperature uniformity is ±10° C.
The wire blank after the carbon precipitation reaction is washed with aviation kerosene, and after washing, it is stretched to a diameter of 0.6 mm, using a tensile speed of 300 m/min, a stress relief annealing voltage of 48 V, and an annealing current of 60 A.
The 0.6 mm diameter wire blank prepared above is treated in an annealing furnace by soft annealing; The annealing atmosphere is nitrogen, the holding temperature is 600° C., the holding time is 30 minutes, the cooling temperature is 80° C., and the furnace temperature uniformity is ±10° C.
The annealed wire blank prepared above is drawn to a finished product of 0.25 mm diameter by multi-mold continuous drawing, and then the wire blank is subjected to stress relief annealing. The process is conducted at a production speed of 1400 m/min, an annealing voltage of 35 V, and an annealing current of 50 A.
The wire electrode prepared by the above process is tested on a Mitsubishi MV1200 WEDM machine. The test work piece is SKD11 die steel having a size of 40 mm (L)×40 mm (W)×60 mm (H). The processings parameter of “one cutting and four trimmings” is selected. The test data is shown in Table 1.
The conductivity, the discharge frequency, phase transition layer thickness and tensile strength of the wire electrode prepared by the above process is determined. The data is shown in Table 2.
A wire blank having the brass grade H65 (CuZn35) and a wire diameter of 0.2 mm is prepared. After alkali washing and pickling by pre-plating treatment, the surface of the wire blank is cleaned and then it is delivered to a plating tank. The bath solution is a mixed solution of 1,000 g/L of zinc sulfate, 20 g/L of dextrin having an average length of 3-15 glucose units as CHO organic matter, 15 g/L of aluminum salt and 15 g/L of potassium salt. The production speed is set at 100 m/min- The plating current is set at 2000 A and the voltage is set at 9V. The plating thickness of the final electroplated wire blank is 20 μm, and the surface roughness of the electroplated wire blank is Ra 0.15 μm.
The plated blank is subjected to a carbon precipitation reaction in an annealing furnace with a nitrogen content of 97%. The reaction temperature is 750° C., the reaction time is 3 hours, the cooling temperature is 80° C. The temperature uniformity in the furnace is ±10° C.
After the carbon precipitation reaction, the wire blank is washed with aviation kerosene, and after washing, it is stretched to a diameter of 0.6 mm using a tensile speed of 300 m/min, a stress relief annealing voltage of 48 V, and an annealing current of 60 A.
The 0.6 mm diameter wire blank prepared above is treated in an annealing furnace by soft annealing; The annealing atmosphere is nitrogen, the holding temperature is 580° C., the holding time is 30 minutes, the cooling temperature is 80° C., and the furnace temperature uniformity is ±10° C.
The annealed wire blank prepared above is drawn to a finished product of 0.25 mm diameter by multi-mold continuous drawing, and then the wire blank is subjected to stress relief annealing. The process is conducted at a production speed of 1400 m/min, an annealing voltage of 35 V, and an annealing current of 50 A.
The wire electrode prepared by the above process is tested on a Mitsubishi MV1200 WEDM machine. The tested work piece is SKD11 die steel with the size of 40 mm (L)×40 mm (W)×60 mm (H). The process parameter of “one main cut and four trim cuts” is selected. The data is shown in Table 1.
Conductivity, discharge frequency, phase transition layer thickness and tensile strength of the wire electrode prepared by the above process are tested. The data is shown in Table 2.
A wire blank having the brass grade H65 (CuZn35) and a wire diameter of 1.2 mm is prepared. After alkali washing and pickling by pre-plating treatment, the surface of the wire blank is cleaned and then it is delivered to a plating tank. The bath solution is a mixed solution of 1,000 g/L of zinc sulfate, 20 g/L of dextrin having an average length of 3-15 glucose units as CHO organic matter, 15 g/L of aluminum salt and 15 g/L of potassium salt. The production speed is set at 100 m/min. The plating current is set at 900 A and the voltage at 8V. The plating thickness of the final electroplated wire blank is 10 μm, and the surface roughness of the electroplated wire blank is Ra 0.12 μm.
The plated blank is subjected to a carbon precipitation reaction in an annealing furnace with a nitrogen content of 97%. The reaction temperature is 750° C., the reaction time is 10 hours, the cooling temperature is 80° C., and the temperature uniformity in the furnace is ±10° C.
After the carbon precipitation reaction, wire blank is washed with aviation kerosene, and after washing, it is stretched to a diameter of 0.6 mm using a tensile speed of 300 m/min, a stress relief annealing voltage of 48 V, and an annealing current of 60 A.
The 0.6 mm diameter wire blank prepared above is treated in an annealing furnace by soft annealing. The annealing atmosphere is nitrogen, the holding temperature is 500° C., the holding time is 30 minutes, the cooling temperature is 80° C., and the furnace temperature uniformity is ±10° C.
The annealed wire blank prepared above is drawn to a finished product of 0.25 mm diameter by multi-die continuous drawing, and then the wire blank is subjected to stress relief annealing. The process is conducted at a production speed of 1,400 m/min, an annealing voltage of 35 V, and an annealing current of 50 A.
The wire electrode prepared by the above process is tested on a Mitsubishi MV1200 WEDM machine. The tested work piece is SKD11 die steel with the size of 40 mm (L)×40 mm (W)×60 mm (H). The process parameter of “one cutting and four trimmings” is selected. The test data is shown in Table 1.
Conductivity, discharge frequency, phase transition layer thickness and tensile strength of the wire electrode prepared by the above process is determined. The data is shown in Table 2.
A wire blank having the brass grade H65 (CuZn35) and a wire diameter of 1.2 mm is prepared. After alkali washing and pickling by pre-plating treatment, the surface of the wire blank is cleaned and then it is delivered to a plating tank. The bath solution is a mixed solution of 1,000 g/L of zinc sulfate, 20 g/L of dextrin having an average length of 3-15 glucose units as CHO organic matter, 15 g/L of aluminum salt and 15 g/L of potassium salt. The production speed is set at 100 m/min. The plating current is set at 2800 A and the voltage at 10V. The plating thickness of the final electroplated wire blank is 30 μm, and the surface roughness of the electroplated wire blank is Ra 0.18 μm.
The plated blank is subjected to a carbon precipitation reaction in an annealing furnace with a nitrogen content of 97%. The reaction temperature is 550° C., the reaction time is 8 hours, the cooling temperature is 60° C. The temperature uniformity in the furnace is ±10° C.
After the carbon precipitation reaction, the wire blank is washed with aviation kerosene, and after washing, it is stretched to a diameter of 0.6 mm using a tensile speed of 300 m/min, a stress relief annealing voltage of 48 V, and an annealing current of 60 A.
The 0.6 mm diameter wire blank prepared above is treated in an annealing furnace by soft annealing; The annealing atmosphere is nitrogen, the holding temperature is 600° C., the holding time is 30 minutes, the cooling temperature is 80° C., and the furnace temperature uniformity is ±10° C.
The annealed wire blank prepared above is drawn to a finished product of 0.25 mm diameter by multi-die continuous drawing, and then the wire blank is subjected to stress relief annealing. The process is conducted at a production speed of 1,400 m/min, an annealing voltage of 35 V, and an annealing current of 50 A.
The wire electrode prepared by the above process is tested on a Mitsubishi MV1200 WEDM machine. The tested work piece is SKD11 die steel with the size of 40 mm (L)×40 mm (W)×60 mm (H). The process parameter of “one cutting and four trimmings” is selected. The test data is shown in Table 1.
Conductivity, discharge frequency, phase transition layer thickness and tensile strength of the wire electrode prepared by the above process are determined. The data is shown in Table 2.
A wire blank having the brass grade H65 (=CuZn35) and a diameter of 1.2 mm is prepared. After alkali washing and pickling by pre-plating treatment, the surface of the wire blank is cleaned and then it is delivered to a plating tank. The bath solution is a mixed solution of 1,000 g/L of zinc sulfate, 20 g/L of dextrin having an average length of 3-15 glucose units as CHO organic matter, 15 g/L of aluminum salt and 15 g/L of potassium salt. The production speed is set at 100m/min. The plating current is set at 900 A and the voltage at 8V. The plating thickness of the final electroplated wire blank was 10 μm, and the surface roughness of the electroplated wire blank was Ra 0.12 μm.
The plated blank is subjected to a carbon precipitation reaction in an annealing furnace with normal atmosphere. The reaction temperature is 200° C., the reaction time is 6 hours, the cooling temperature is 50° C., and the furnace temperature uniformity is ±10° C.
The annealed wire blank prepared above is drawn to a diameter of 0.25 mm by multi-die continuous drawing, and then the wire blank is subjected to stress relief annealing at a production speed of 1400 m/min, an annealing voltage of 35 V, and an annealing current of 50 A.
The wire electrode prepared by the above process is tested on the Mitsubishi MV1200 WEDM machine. The tested material was SKD11 grade die steel with the size of 40 mm (L)×40 mm (W)×60 mm (H). The process parameter of “one main cut and four trim cuts” is selected. The data is shown in Table 1.
Conductivity, discharge frequency, phase transition layer thickness and tensile strength of the wire electrode is determined. The data is shown in Table 2.
A wire blank having the brass grade H65 (=CuZn35) and a wire diameter of 1.2 mm is prepared. After alkali washing and pickling by pre-plating treatment, the surface of the wire blank is cleaned and then it is delivered to the plating tank. The bath solution is a mixed solution of 1,000 g/L of zinc sulfate, 20 g/L of dextrin having an average length of 3-15 glucose units as CHO organic matter, 15 g/L of aluminum salt and 15 g/L of potassium salt. The production speed is set at 100 m/min. The plating current is set at 900 A and the voltage at 8V. The plating thickness of the final electroplated wire blank was 10 μm, and the surface roughness of the electroplated wire blank was Ra 0.12 μm.
The plated blank is subjected to a carbon precipitation reaction in an annealing furnace with normal atmosphere. The reaction temperature is 200° C., the reaction time is 6 hours, the cooling temperature is 50° C. and the furnace temperature uniformity is ±10° C.
After the carbon precipitation reaction, the wire blank is washed with aviation kerosene, and after washing, it is stretched to a size of ϕ 0.6 mm, a drawing speed of 300 m/min, without stress relief annealing.
The drawn blank is subjected to a heat treatment in an annealing furnace with normal atmosphere. The reaction temperature is 400° C. the reaction time is 20 hours, and the cooling temperature is controlled at below 100° C. The furnace temperature uniformity is ±10° C.
The annealed wire blank prepared above is drawn to a diameter of 0.25 mm by multi-die continuous drawing, and then the wire blank is subjected to stress relief annealing at a production speed of 1400 m/min, an annealing voltage of 35 V, and an annealing current of 50 A.
The wire electrode prepared by the above process is tested on the Mitsubishi MV1200 WEDM machine. The tested material was SKD11 grade die steel with the size of 40 mm (L)×40 mm (W)×60 mm (H). The process parameter of “one main cut and four trim cuts” is selected. The test data is shown in Table 1.
Conductivity, discharge frequency, phase transition layer thickness and tensile strength of the wire electrode prepared by the above process. The test data is shown in Table 2.
Comparative Example 1 is selected from commercially available gamma-coated wires.
The gamma coated wire is tested on the Mitsubishi MV1200 WEDM machine. The tested work piece is SKD11 die steel with the size of 40 mm (L)×40 mm (W)×60 mm (H). The process parameter of “one main cut and four trim cuts” is selected. The test data is shown in Table 1.
Conductivity, discharge frequency, the phase transition layer thickness and the tensile strength of the wire electrode is determined. The data is shown in Table 2.
According to the obtained data, the wire electrodes of present invention are superior to the gamma-coated wire in terms of processing speed, processing precision and surface finish. The threading performance is also improved.
Comparative Example 2 is selected from commercially available beta-coated wires.
The beta coated wire is tested on the Mitsubishi MV1200 WEDM machine. The tested material is SKD11 die steel with the size of 40 mm (L)×40 mm (W)×60 mm (H). The process parameter of “one main cut and four trim cuts” is selected. The test data is shown in Table 1.
According to the data analysis, the wire electrodes of present invention are superior to the beta coated wire in terms of processing speed, processing precision and surface finish. The threading performance is also improved.
Comparative Example 3 is selected from commercially available composite-coated wires.
The composite coated wire is tested on the Mitsubishi MV1200 WEDM machine. The tested work piece is SKD11 die steel with the size of 40 mm (L)×40 mm (W)×60 mm (H). The process parameter of “one main cut and four trim cuts” is selected. The data is shown in Table 1.
Conductivity, discharge frequency, the phase transition layer thickness and the tensile strength of the wire electrode prepared by the above process. The data is shown in Table 2.
According to the obtained data, the wire electrodes of present invention are superior to the composite coated wire in terms of processing speed, processing precision and surface finish. The threading performance is also improved.
It can be concluded from the above examples and experimental data that the wire electrode prepared by the method of the present invention has higher processing precision, surface finish and threading performance compared with the conventional wire electrode and has a more ideal electrical conductivity, discharge frequency and tensile strength.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201910396877.X | May 2019 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/059269 | 4/1/2020 | WO |
