ULTRA-HIGH-SPEED FORMING METHOD USING ELECTROPLASTICITY EFFECT

Abstract

A method for forming or deforming a workpiece at a high speed using electroplasticity effect includes: applying a first level of pulse current to the work piece to cause the electroplasticity effect and lower a flow stress of the work piece; and applying a first level of electromagnetic force to the workpiece for 150˜300 μs to form or deform the work piece in a desired shape while the flow stress of the work piece is maintained at the lowered level, wherein the first level of electromagnetic force is lower than a second level of electromagnetic force which is required to form or deform the workpiece in the desired shape without applying the first level of pulse current.

Claims

1. A method for forming or deforming a workpiece at a high speed using electroplasticity effect, comprising: applying a first level of pulse current to the work piece to cause the electroplasticity effect and lower a flow stress of the work piece; and applying a first level of electromagnetic force to the workpiece for 150˜300 μs to form or deform the work piece in a desired shape while the flow stress of the work piece is maintained at the lowered level, wherein the first level of electromagnetic force is lower than a second level of electromagnetic force which is required to form or deform the workpiece in the desired shape without applying the first level of pulse current.

2. The method of claim 1, wherein the first level of pulse current varies depending on the workpiece.

3. The method of claim 2, wherein the flow stress of the workpiece varies depending on the workpiece.

4. The method of claim 1, wherein the first level of electromagnetic force is Lorentz force.

5. The method of claim 1: wherein the first level of electromagnetic force is applied using a high-capacity capacitor.

6. The method of claim 1, wherein the first level of electromagnetic force is generated using a forming coil.

7. The method of claim 6, wherein the forming coil discharges currents, changes a magnetic flux, and applies an induced electromotive force to the workpiece.

8. The method of claim 7, wherein the forming coil creates a strong magnetic field, and wherein the strong magnetic field applies an induced current to the workpiece by Faraday's Law.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0046] FIG. 1 is a graph showing electroplastic effects on steels with a high ultimate tensile strength and Al5000 Family automotive body products in an electrically assisted forming process. The gragh shown in FIG. 1 is found in 2014 Korean Society of Manufacturing Technology Engineers Spring Conference journal at page 61.

[0047] FIG. 2 to FIG. 4 are schematic illustrations to explain a concept of an electromagnetic forming process.

[0048] FIG. 5 is an embodiment of a formed coil in use for an electromagnetic forming process.

[0049] FIG. 6 is a perspective view of a forming coil insulated by Epoxy.

[0050] FIG. 7 shows an exemplary arrangement of equipment for an electromagnetism forming process in which awork-piece is located between a die and an electromagnetism forming coil.

[0051] FIG. 8 shows a concept of charging and discharging circuit in use for an apparatus for an electromagnetic forming process.

[0052] FIG. 9 to FIG. 10 are schematic illustration explaining an electromagnetic forming method using electroplastic effect according to an embodiment of the present invention.

[0053] FIG. 11 is a schematic illustration explaining an electromagnetic forming process according to an embodiment the present invention.

EMBODIMENTS

[0054] Hereinafter, the present invention will be described in more detail referring to the drawings attached hereto

[0055] High speed forming method using electroplastic effect according to the present invention is configured to a step of electroplastic effect on work piece and a step of high speed forming on work piece.

[0056] 1. First, a step of generating electroplastic effect will be explained.

[0057] Electroplastic effect generating step is a process of lowering flow stress of a work-piece below a certain level by applying a certain amount of electric current to the work-piece. As is well known, when a certain level of electric current is applied to a workpiece, flow stress of the workpiece drops below a certain level for a short time period.

[0058] When a certain amount of plasticity is applied to the workpiece while the flow stress of the workpiece is maintained at a reduced level, it is possible to form or deform the workpiece with a relatively lower level of plasticity compared with a case where no electroplastic effect is employed.

[0059] 2. Next, a step of performing formation or deformation at a high speed will be explained.

[0060] The time when the flow stress of work piece gets lower by the aforementioned electroplastic effect varies depending on workpieces, but, in general, the time is very short.

[0061] To use electroplastic effect, it is necessary to apply a certain amount of plasticity while a flow stress of the workpiece is maintained low. Thus, the timing of applying the plasticity to the workpiece is desirable to be synchronized with the timing when the flow stress is maintained low.

[0062] For example, if the time duration when the flow stress is maintained low by electroplastic effect is A seconds, it is preferred that the time duration when the certain amount of plasticity is applied to the workpiece is A seconds or less.

[0063] Any conventional forming method can be employed since the time duration when the electroplastic effect lasts is very short. Therefore, in the present invention, a method should be selected which is capable of providing plasticity during such a short time period electroplastic effect lasts. An explosive forming method or an electromagnetic forming method may satisfy such condition.

[0064] Either the explosive forming or the electromagnetic forming method may apply a certain level of plasticity to the workpiece at a high speed. Hereinafter, an embodiment of the present invention employing an electromagnetic forming method will be explained. The method may provide plasticity during such a short time period and while the low-flow stress of the workpiece is maintained.

[0065] The present invention is not limited to be applicable to or combinable with an electromagnetic forming method (EMF) which is performed at a high speed using the electroplastic effect. Instead, the present invention is also applicable to or combinable with an explosive forming method.

[Embodiment Employing an Electromagnetic Forming Method (EMF)]

[0066] As is known in the industry, an electromagnetic forming method (EMF) is a technology for forming or deforming metals at high speed, e.g., at 15˜300 m/s, by using a high strength magnetic field. In the electromagnetic forming method (EMF), induced electromotive force applies onto the workpiece due to current discharged by a forming coil and due to a change of magnetic flux. When the induced current flows on the workpiece, the workpiece is subject to formation or deformation by Lorentz force.

[0067] The electromagnetic forming method (EMF) is performed without a physical contact with the workpiece and this is advantageous in that surface defects can be prevented, lubrication issues, abrasion issues, etc. can be prevented. Thus, a repetitive forming process is possible without deterioration in quality.

[0068] As shown in FIG. 8, an apparatus for performing an electromagnetic forming method may include a resistance, an inductor, a high-capacity capacitor, a formed coil, charging/discharging switches, etc. All components or parts shown in FIG. 8, except for a formed coil, are charging and discharging circuits for providing a certain amount of current to the formed coil. See the charging/discharging circuit shown in FIG. 9.

[0069] Although not shown in FIG. 8, the electromagnetic forming apparatus may further include a control circuit for controlling the charging and discharging switches, a power supply, a mold, etc.

[0070] A high-capacity capacitor connecting to power supply unit is charged through the charging switch. The capacitor is charged up to a targeted energy level and then be abruptly discharged during a very short time period through discharging switch so that an impulsive current starts to flow to the forming coil.

[0071] The current applied to the coil decays within hundreds of μs, thereby applying a strong magnetic field onto the forming coil. The strong magnetic field applies an induced current to the workpiece in the opposite direction by Faraday's Law, generating Lorentz force which serves as a plasticity force to the workpiece. To form or deform the workpiece, the plasticity force applied to the workpiece should be above a certain level. Thus, the electromagnetic forming method consumes a considerable amount of energy.

[0072] To reduces power consumption, in an embodiment of the present invention relatively the electromagnetic forming process is performed in in a state when the flow stress of the workpiece is lowered.

[0073] FIG. 9 and FIG. 10 are illustrations of an apparatus performing an electromagnetic forming method according to an embodiment. Referring to (a), (b) of FIG. 9, a process of forming a workpiece (10) is performed when current is supplied to a forming coil. Referring to (a) of FIG. 10, current is supplied to the workpiece (10) for obtaining electroplastic effect by connecting the workpiece (10) to a pulsed current generator. Referring to (b) of FIG. 10, a multiple number of charging and discharging circuits each of which may be identical or similar to what is shown in FIG. 8 are connected to the forming coil.

[0074] Although not shown in FIG. 9, a pulsed current generator and the charging and discharging circuit shown in FIG. 10 are connected respectively to the workpiece (10) and the forming coil shown in FIG. 9.

[0075] First, an apparatus for performing an electromagnetic forming method is prepared. As shown in FIG. 9, the forming coil tis placed on the right position and a certain shape of mold is placed over the forming coil.

[0076] Next, the work piece (10) is placed over the forming coil. In another embodiment, an intermediate member of ferromagnetic material may be additionally located between the forming coil and the workpiece (10).

[0077] Next, electroplastic effect is obtained by applying a certain amount of pulsed current using a pulsed current generator, for example, as shown in FIG. 10.

[0078] As is known, the time necessary for a flow stress of the workpiece to reach down to a certain level varies depending on the kinds of workpieces, intensity of the current that is applied to, a duty ratio of the pulsed current, etc.

[0079] Next, in an embodiment of the present invention, a certain level of current is provided to the forming coil to drop a flow stress of the workpiece to a certain level. Then, the electromagnetic forming apparatus controls the charging and discharging circuits so that the timing of providing a certain amount of pulsed current onto the workpiece is synchronized with the timing at which the flow stress of the workpiece is maintained at the reduced level.

[0080] FIG. 11 is a schematic illustration explaining an electromagnetic forming process according to an embodiment the present invention. A certain level of electromagnetic force is intermittently and repeatedly applied to the workpiece to form or deform the workpiece in a desired shape.

[0081] According to an embodiment of the present invention, the charging and discharging circuits is synchronized with the timing at which the flow stress of the workpiece is at a reduced level. Thus, the workpiece can be more easily formed or deformed.

[0082] The present invention using electroplasticity is not limited to a combination of the electroplasticity effect with electromagnetic force. Instead, the electroplasticity effect according to the present invention can be combined with any kind of methods, for example, an explosive forming method that can apply a certain amount of force to a the workpiece. The timing of applying the certain amount of force is synchronized with the timing at which a flow stress of the workpiece is reduced to a certain lower level and maintained at the certain lower level. Thus, the scope of the present invention should not be interpreted to be limited to the combination of the electroplasticity effect and the electromagnetic force.