The instant disclosure is related to an apparatus and/or process for reducing springback in sheet metal forming and in particular to using electrically-assisted manufacturing for reducing springback in single point incremental forming of sheet metal components.
The use of single point incremental forming (SPIF) for forming sheet metal into a desired shape is known. Such forming typically places on a piece of sheet metal in a clamping fixture where it is held while SPIF processing is executed thereon. In addition, it is known that springback of the sheet metal can be present after SPIF manufacturing, and thus a less than desired shape can be present after the formed piece is removed from the clamping fixture. Therefore, an improved apparatus and process that reduces springback of a piece of sheet metal that has been formed by SPIF would be desirable.
A process for forming a piece of sheet metal is provided. The process includes providing the piece of sheet metal and a clamping fixture. The piece of sheet metal is rigidly clamped to the clamping fixture. Then, the piece of sheet metal is plastically deformed while it is rigidly clamped to the clamping fixture and a shaped component is formed during a first manufacturing step. Also, the shaped component has a first amount of springback.
During a second manufacturing step, a pair of electrodes configured to pass electrical current from one electrode to another electrode is used to apply one or more pulses of electrical current at one or more locations on the shaped component while the shaped component is still rigidly clamped to the clamping fixture. The one or more pulses of electrical current applied to the shaped component provide an electrically-assisted manufactured (EAM) shaped component that has a second amount of springback that is less than the first amount of springback.
The first manufacturing step can be an incremental forming process such as a single point incremental forming (SPIF) deformation process that uses an arcuate tipped tool to incrementally deform the piece of sheet metal and form the shaped component. The clamping fixture with the piece of sheet metal can be rigidly secured to an SPIF machine at a first workstation where the first manufacturing step forms the shaped component. Then the clamping fixture with the shaped component can be unsecured from the SPIF machine and moved to a second workstation where the second manufacturing step using the pair of electrodes is applied to the shaped component to form the EAM shaped component. In the alternative, the clamping fixture with the shaped component can remain rigidly secured to the SPIF at the first workstation while the pair of electrodes apply the one or more pulses of electrical current at one or more locations on the shaped component during the second manufacturing step to form the EAM shaped component.
The one or more locations on the shaped component where the one or more electrical pulses are applied can be locations that are proximate and/or adjacent to areas of maximum residual stress in the shaped component, such areas being locations or regions of plastic deformation of the shaped component. The shaped component has a thickness and the pair of electrodes can be oppositely disposed across the thickness of the shaped component and the one or more pulses of electrical current pass through the thickness of the shaped component from one electrode to another electrode.
The second amount of springback is less than 25% of the first amount of springback, preferably less than 40%, and more preferably less than 50%.
As such, a process for forming a sheet metal component is disclosed. The process includes providing a piece of sheet metal having a thickness; providing a clamping fixture and rigidly clamping the piece of sheet metal to the clamping fixture; providing a single point incremental forming (SPIF) machine and rigidly securing the clamping fixture with the piece of sheet metal to the SPIF machine; plastically deforming the piece of sheet metal while the clamping fixture is rigidly secured to the SPIF machine and forming a shaped component from the piece of sheet metal during a first manufacturing step, the shaped component having a first amount of springback; providing a pair of electrodes configured to pass electrical current from one electrode to another electrode; and applying one or more pulses of electrical current at one or more locations on the shaped component while the shaped component is still rigidly clamped to the clamping fixture using the pair of electrodes during a second manufacturing step, the one or more pulses of electrical current applied to the shaped component providing an electrically-assisted manufactured (EAM) shaped component, the EAM shaped component having a second amount of springback that is less than the first amount of springback.
The process can also include the pair of electrodes being oppositely disposed the thickness of the piece of sheet metal during applying the one or more pulses of electrical current at one or more locations on the shaped component. The second amount of springback is less than 25% of the first amount of springback, preferably less than 40%, and more preferably less than 50%. The process can include the first manufacturing step being executed at a first workstation and the second manufacturing step being executed at a second workstation. In the alternative, the process can include the first manufacturing step and the second manufacturing steps being executed at a first workstation.
An apparatus and a process for reducing springback of a piece of sheet metal that has been subjected to incremental forming are provided. In some instances, the incremental forming is single point incremental forming (SPIF), however this is not required. For the purposes of the instant disclosure, the term “springback” is defined as the amount a work piece, e.g. a piece of sheet metal, that has been plastically deformed while rigidly clamped in a clamping fixture, reverts back to its original form or shape before being plastically deformed, after the work piece is removed from the clamping fixture.
It is appreciated that incremental forming typically uses a rounded or arcuate tipped tool to form simple and complex shapes. Limits in incremental forming are usually caused by the material being formed, the wall angle of the part to be formed and the springback of the formed piece. The springback is due to or caused by residual stresses which occur during the forming process. Also, the residual stresses discussed herein do not cause visible springback until the work piece, i.e. the piece of sheet metal, is unclamped from its clamping fixture.
The process disclosed herein takes a piece of sheet metal, clamps it to a rigid clamping fixture and then rigidly secures the rigid clamping fixture with the piece of sheet metal to an incremental forming machine at a first work station. The piece of sheet metal is subjected to incremental forming while clamped to the clamping fixture in order to produce a shaped component. Also, the clamping fixture requires an outer periphery of the piece of sheet metal to remain stationary or fixed relative to the clamping fixture during plastic deformation of the piece of sheet metal. Residual stress is created in the piece of sheet metal during the plastic deformation and if the piece of sheet metal is removed from the clamping fixture, a first amount of springback is present.
In some instances, and before the shaped component is removed from the clamping fixture, i.e. while the plastically deformed piece of sheet metal is still rigidly clamped to the clamping fixture, a pair of electrodes apply one or more pulses of electrical current at one or more locations on the shaped component and thereby produce an electrically-assisted manufactured (EAM) shaped component. The EAM shaped component is then removed from the clamping fixture and exhibits a reduced amount of springback, i.e. when the EAM shaped component is removed from the clamping fixture, a second amount of springback that is less than the first amount of springback is present. In this manner electrically-assisted manufacturing provides an EAM shaped component with less springback and thus a more desired shape compared to a similarly shaped component that is not subjected to electrically-assisted manufacturing. Stated differently, the problem of springback in incrementally formed components is reduced and/or eliminated using apparatus and/or process described herein
Turning now to
The forming machine 120 can be a computer numerical controlled machine that can move the arcuate tipped tool 100 a predetermined distance in a predetermined direction. For example, the forming machine 10 can move the arcuate tipped tool 100 in a generally vertical (e.g. up and down) direction 1 and/or a generally lateral (e.g. side to side) direction 2. In the alternative, the support structure 130 can move the clamping fixture 132 with the piece of sheet metal 110 rigidly clamped thereto in the generally vertical direction 1 and/or the generally lateral direction 2 relative to the arcuate tipped tool 100. The arcuate tipped tool 100 can be rotationally fixed, free to rotate and/or be forced to rotate. After the clamping fixture 132 with the piece of sheet metal 110 has been attached to the support structure 130, the arcuate tipped tool 100 comes into contact with and makes a plurality of single point incremental deformations on the piece of sheet metal 110 and affords for a desirable shape to be made therewith.
The clamping fixture 132 with the shaped component 110a still rigidly clamped therein illustrated in
The springback exhibited by the EAM shaped component can be less than 25% of the shaped component, preferably less than 40 springback, and more preferably less than 50% springback.
Turning now to
Turning now to
At step 440, the shaped component, while still being rigidly clamped to the clamping fixture, is then subjected to one or more electrical pulses at one or more locations during a second manufacturing step and an EAM shaped component is produced. The application of the one or more electrical pulses at the one or more locations on the shaped component can be executed while the clamping fixture with the shaped component rigidly clamped thereto is still rigidly secured to the incremental forming machine. In the alternative, at step 450, the clamping fixture with the shaped component rigidly clamped thereto can be removed from the incremental forming machine and placed at a different workstation where, at step 440, the one or more electrical pulses at the one or more locations on the shaped component is applied to the shaped component.
In order to better explain the teachings of the instant disclosure but not limit its scope in any manner, one or more examples with experimental data and results is provided below. Experimental Setup
Samples for testing were cut from a 2024-T3 aluminum sheet that was 0.5 millimeters (mm) thick using a sheet metal shear. The samples were square shaped and had dimensions of 280 mm×280 mm. During incremental forming a sample was clamped into a clamping fixture and then incrementally formed using a HAAS VF3 mill. The desired shaped component was a pyramid with a 178 mm square base, a 38 mm square top and walls with a 29° angle relative to a vertical axis. The pyramid was formed using an out-to-in forming technique with a step down size of 0.25 mm and a step over size of 0.46 mm.
After forming, the clamping fixture with the shaped component still rigidly clamped thereto was removed from the mill and set onto an electrode assembly. An electrical power supply in the form of a Lincoln R35 Arc Welder with a thermally controlled variable resistor was connected to the electrode assembly to supply electric current to a pair of oppositely disposed electrodes. One of the electrodes was on one side of the piece of sheet metal and the other electrode on an opposite side, i.e. across the thickness of the piece of sheet metal.
Tests were run with 4 different current densities (40, 50, 60, 70 A/mm2), 4 different time intervals (1, 2, 3, 4 seconds), and a varying number of applied current locations based on a finite element analysis (FEA) which showed high stress concentrations in the corners of the formed pyramid close to the edge of the shaped component. The clamping fixture with the shaped component, also referred to as the work piece, was clamped into the electrode assembly and then one or more pulses of electrical current was applied through a location with a high stress concentration. The part was then rotated and current was pulsed through another location. This process was repeated until the desired number of stress concentrations had been pulsed with current. The pulsed current was applied to the shaped component in a clockwise direction, i.e. current pulses were applied at one corner of the shaped component and then the clamping fixture with the shaped component was turned or rotated clockwise to the next corner where the pair of electrodes applied pulses of electrical current.
After testing, the specimens were painted white on 1 side and scanned with a Zscanner 700 hand held 3D scanner. The scanned data was imported as CAD files for comparison with a desired shape CAD model.
FEA Model and Theory
A FEA simulation model of the experiment was developed with the ANSYS® software. The final formed part exhibited two plane of reflective symmetry, so a three-dimensional, quarter-symmetry model was developed for this study. The model used a lower-order, four-node quadrilateral-shaped, structural shell finite element formulation to represent the sheet metal part. While the forming process itself had no symmetry, using the symmetry approximation yields significant savings in simulation time and resulting file storage demand. The piece of sheet metal was assumed to be of uniform thickness and the material was isotropic and homogeneous. The forming tool was modeled as a series of rigid spheres which contact the piece of sheet metal to create the intended shaped component. A series of forming tools was used since it saved simulation time by starting a new tool for each pass over the plate rather than moving the original tool to a new starting position after the previous forming pass was completed. In the ANSYS software the spherical tool was modeled using a rigid “target” element and the corresponding surface of the metal plate was skinned with matching “contact” elements to detect the interference between the tool and the plate and to transmit forming forces to produce the final part shape.
The aluminum material properties were defined at room temperature as:
The effects of current density, duration of the current pulse and the number of areas that electric current was pulsed were examined. To determine the springback of the formed pyramid shape the 3D scan data was imported into Geomagic Control along with a CAD model of the desired shape.
Geomagic control created 3D deviation plots and gave average differences between the test shape (scanned data) and the reference shape (CAD model). The 3D deviation in Geomagic control was the distance between a point on the reference model and the closest corresponding point on the test model. The deviation plot was always plotted on the reference model.
Current Density and Pulsed Locations
In one test, four (4) different current densities, all with a time period of 4 seconds, at a varying number of spots or locations were applied to test samples. The current densities tested were 40, 50, 60 and 70 A/mm2 and at 4, 8 and 12 stress concentration locations.
The number of locations or places pulsed with electric current had a larger impact on the springback of the pyramid shape than the range of current density. When only 4 spots were pulsed, one in each corner of the pyramid, the average deviation difference was approximately 1 mm when compared to the control specimen. However, when the number of locations was increased to 8 the average deviation dropped from 6.25 mm to 2.64 mm. Also, increasing the number of locations to 12 did not appear to increase the average deviation. The data also showed that pulsing electrical current at multiple locations adjacent to a deformed corner, i.e. to the side of the corner had a greater effect in reducing springback than applying electrical current directly in or on the corner of the formed specimen.
The disclosure provides various examples, aspects, etc., but the scope of the disclosure is not limited to such teaching. Changes, modifications, and the like will occur to those skilled in the art and yet still fall within the scope of the instant disclosure. Therefore, it is the claims, and all equivalents thereof, which define the scope.
This National Phase application claims priority to International Patent Application No. PCT/US2015/054520 filed on Oct. 7, 2015, which claims priority to U.S. Provisional Patent Application No. 62/060,607 filed Oct. 7, 2014, both of which are incorporated herein by reference in their entirety.
This invention was made with government support under Grant No. DE-EE0005764, awarded by the Department of Energy. The Government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US2015/054520 | 10/7/2015 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2016/057688 | 4/14/2016 | WO | A |
Number | Name | Date | Kind |
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6047582 | Daehn | Apr 2000 | A |
7467532 | Golovashchenko | Dec 2008 | B2 |
8021501 | Roth | Sep 2011 | B2 |
8534109 | Golovashchenko | Sep 2013 | B1 |
Number | Date | Country |
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2646623 | Nov 1990 | FR |
2194588 | Dec 2002 | RU |
2002026414 | Apr 2002 | WO |
Entry |
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Romanovskiy V.P. Spravochnik po kholodnoy shtampovke. Leningrad, 1971, “Mashinostroenie”, pp. 242-243; concise explanation of the relevance: Claim No. 1-3, 12-15 per International Search Report and Written Opinion for International Application No. PCT/US2015/054520, dated Jan. 28, 2016. |
International Search Report and Written Opinion for International Application No. PCT/US2015/054520, dated Jan. 28, 2016. |
Romanovskiy V.P. Spravochnik po kholodnoy shtampovke. Leningrad, 1971, “Mashinostroenie”, pp. 242-243 with English translation. |
Number | Date | Country | |
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20180264538 A1 | Sep 2018 | US |
Number | Date | Country | |
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62060607 | Oct 2014 | US |