Metal deforming – With temperature modification of tool or of specified... – Cooling
Reexamination Certificate
2002-10-11
2004-10-05
Tolan, Ed (Department: 3725)
Metal deforming
With temperature modification of tool or of specified...
Cooling
C072S342500, C072S405090, C072S405160, C072S422000, C072S701000
Reexamination Certificate
active
06799450
ABSTRACT:
TECHNICAL FIELD
This invention relates to stretch forming aluminum metal sheets into formed shapes, and more particularly the invention relates to a method of stretch forming an aluminum metal sheet utilizing a removal device such that a formed part is created without distortion.
BACKGROUND OF THE INVENTION
Automobile body panels are typically made by shaping low carbon steel or aluminum alloy sheet stock into desired panel shapes. Sheet panels may be made by using conventional stamping technology or alternative methods such as superplastic forming (SPF) processes and quick plastic forming (QPF) processes. The above-referenced plastic forming processes have the advantage of creating complex shaped parts from a single sheet of material. Such plastic forming processes eliminate the need for joining several panels formed in a stamping process to create an overall panel assembly.
Superplastic forming processes generally utilize a metal alloy, for example, aluminum or titanium alloys that have high ductility when deformed under controlled conditions. Such metal alloys are capable of extensive deformation under relatively low shaping forces. Superplastic alloys are characterized by having tensile ductility in the range of from 200 to 1,000 percent elongation. The plastic forming processes may utilize large aluminum alloy sheets to form outer or inner outer panels of an automotive structure. Such a process involves heating the aluminum alloy sheets to a forming temperature in the range of from 400° C. to 510° C. and then stretch forming the sheet against a forming tool utilizing high pressure gas. The low flow stress of the aluminum alloy at the elevated forming temperature is beneficial when forming the part, but may be a hindrance when removing the part from a die. Removal of the parts at elevated temperatures, particularly utilizing a manual operation, may result in distortion of a part that either requires corrective action to accurately reshape the part, or may result in scraping of the part. Therefore, there is a need in the art for a method of stretch forming an aluminum metal sheet such that accurate part dimensions can be maintained when removing the part from a die.
SUMMARY OF THE INVENTION
There is disclosed a method of stretch forming an aluminum metal sheet including the steps of:
(a) Placing the aluminum metal sheet in a hot forming tool;
(b) Forming a shaped part at an elevated temperature such that the shaped part is hot;
(c) Removing the hot shaped part from the hot forming tool; and
(d) Transferring the hot shaped part to a cooling fixture.
The transfer step is performed at a variable speed based on a correlation of the temperature and strength of the aluminum metal sheet and the speed at which the hot shaped part may be transferred without distortion of its shape. The removal step is performed at a speed and utilizing a removal device, again such that the shape of the hot shaped part is not distorted.
The method disclosed by the present invention has the advantage of providing a method of stretch forming an aluminum metal sheet such that the part shape is not distorted during a removal of the hot shape part from a hot forming tool, and during a transfer step wherein the hot shaped part is placed on a cooling fixture.
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Brinas Nelson T.
Ryntz Edward Frank
General Motors Corporation
Marra Kathryn A.
Tolan Ed
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