Patent Grant
7210323
The present invention generally relates to a binder apparatus for securing the edges of a sheet metal blank in a sheet forming process, especially a hot blow forming or stretch forming process. More particularly, the present invention pertains to a binder apparatus having sequentially movable sheet gripping segments on one side of the sheet metal blank for stepwise stretching of the sheet metal into a product of complex curvature without uneven thinning, tearing, or wrinkling of the sheet material.
In sheet metal stretch forming processes, a hydraulic press machine is often used to support and move opposing forming tools required to form a flat sheet metal blank into a three-dimensional contoured article or product. The press moves the tools from an open position, in which a finished part is removed and a new blank inserted, to a closed position for stretching the sheet metal blank against the tools to form the product. Large presses for shaping large parts typically open and close along a vertical axis. A vertical press, thus, has a lower platen for supporting one of the tools, often a punch or male form tool, and an upper platen for carrying a complementary, opposing tool with a concave cavity, typically a female tool or die. Often the lower platen is raised by a hydraulically actuated ram to close the press. In hot stretch forming, the tools may be individually heated to maintain a suitable forming temperature for the sheet metal blank and the female tool may simply form a closed chamber against an upper surface or side of the sheet metal blank for introduction of a pressurized working gas to stretch the sheet metal blank against the male tool.
In order to stretch the sheet metal blank between the tools, the edges of the sheet metal blank must be gripped so that the interior part of the sheet metal blank is suitably stretched against a forming tool surface. This gripping function is accomplished by opposing binder surfaces. Depending upon the complexity of the shape of the product to be formed, the binding surfaces may be provided on the margins of the opposing tools, or a separate tool sometimes called a binder ring may provided at the margin of a tool to assist the binder function. Such a binder ring may be movable separately from the tool that it surrounds or with which it cooperates.
In operation, the sheet metal blank is placed on top of the contoured surfaces 22a, 22b of the opposed ends 18a, 18b of the lower tool 14. Then, the upper ram of the press drives the upper tool 12 toward the lower tool 14, wherein the sheet metal blank is initially held just between the flat lower surfaces 32a, 32b of the upper tool 12 and the contoured surfaces 22a, 22b of the lower tool 14. As the upper ram of the press continues to drive the upper tool 12 down, the sheet metal blank is first bent into engagement with the flat surfaces 24a, 24b of the lower binder 12 and is eventually bent into complete engagement between the contoured surfaces 22a, 22b of the lower tool 14 and the contoured surfaces 30a, 30b of the upper tool 12. Thereafter, and in accordance with typical Quick-Plastic-Forming (QPF) processes, heating elements (not shown) in the upper tool 12, lower tool 14, and form die 16 heat the sheet metal blank, and pressurized gas is introduced through a port 34 in the side 28a of the upper tool 12. The gas remains pressurized by virtue of a seal created between the upper press platen and an upper surface 36 of the upper tool 12 and by virtue of the seal created by the sheet metal blank which is squeezed between the upper tool 12 and the lower tool 14. As is well-known, the pressurized gas forms the heated sheet metal blank over the form die 16 to create the finished product.
In general, sheet metal that is subjected to a hot gas blow-forming process will undergo thickness reduction, or thinning, depending on factors such as the specific tool surface shape and relative shape and position of the blank. Extreme thinning must be avoided in order for the product to serve its structural purposes. It is also occasionally possible for a complex panel to wrinkle if the blank undergoes compressive stresses sometime during the forming operation. In other words, a finished panel will typically have wrinkles if the surface area of the sheet blank is greater than the final part shape.
In order to avoid the above-mentioned thinning and wrinkling problems, it has been proposed to use more than one forming stage, involving at least one hot blow forming tool. Such an alternative, however, can be cost prohibitive. Also it has been proposed to enlarge an addendum area of the blank, located between the blank holding margin of the blank and the finished component portion of the blank, in order to alleviate the non-uniform stretch condition between the flat clamping surfaces of the lower binder and the contours of the form die. Unfortunately, larger addendum areas increase the size of the blank, thereby leading to increased material costs.
Thus, there is a need to minimize or eliminate wrinkling and thinning conditions in metal forming processes, particularly hot blow forming processes, while avoiding the expense of current solutions to those problems.
The present invention meets this need by providing an improved binder apparatus for bending a sheet metal blank over a form die. The sheet metal blank has first and second opposed surfaces and is generally rectangular in outline and, thus, has opposite side edges and opposite end edges. Likewise, the form die is generally rectangular in outline with opposite sides and opposite ends and has a forming surface thereon.
The binder apparatus includes a first binder tool that is spaced apart from and that faces a second binder tool that generally circumscribes the form die. The first binder tool is generally rectangular in outline and includes a pair of laterally opposed end portions and a pair of laterally opposed side portions. The end and side portions have binder surfaces thereon that face complementary binder surfaces on the second binder tool.
The second binder tool is generally rectangular in outline and includes a pair of laterally opposed end segments that are positioned alongside the opposite ends of the form die and further includes a pair of laterally opposed side segments positioned alongside the opposite sides of the form die. The end and side segments have the complementary binder surfaces thereon that face the binder surfaces on the first binder tool. The binder surfaces on the end segments are elevated with respect to the binder surfaces on the side segments. In other words, the binder surfaces on the end segments are closer to their complementary binder surfaces on the first binder tool than the binder surfaces on the side segments are to their complementary binder surfaces on the first binder tool. Also, the end segments are separately movable with respect to the side segments in a direction that is substantially perpendicular to the opposed surfaces of the sheet metal blank. Preferably, the binder surfaces on the end segments have substantially similar contours, while the binder surfaces on the side segments have different contours from one another that tend to follow the contours on the respective sides of the form die.
In operation, the sheet metal blank is first preheated to a suitable hot blow forming temperature and is then placed against the elevated binder surfaces on the end segments of the second binder tool. Next, the first binder tool is moved toward the second binder tool such that, initially, only the binder surfaces on the end portions of the first binder tool contact the sheet metal blank. The first binder tool continues its movement toward the second binder tool, thereby bending the sheet metal blank into conformity between the complementary binder surfaces on the end binder portions of the first binder tool and the end segments of the second binder tool. Because of the difference in elevation between the end and side segments of the second binder tool, the first binder tool initially bends the sheet metal blank about the binder surfaces on the end segments before ever driving the sheet metal blank into contact with the side segments. Nonetheless, the first binder tool continues to travel toward its closed position against the second binder tool, thereby displacing the movable end segments and thereby driving the sheet metal blank into contact with the binder surfaces on the side segments of the second binder tool. The first binder tool travels even further toward the second binder tool thereby bending the sheet metal blank about the binder surfaces on the side segments of the second binder tool and simultaneously bending a central portion of the sheet metal blank over the forming surface of the form die until, finally, the sheet metal blank is fully clamped between the binder surfaces on the first and second binder tools. Thereafter, the sheet metal blank may be hot blow formed over the forming surface of the forming die in accordance with one aspect of the present invention.
Accordingly, the sheet metal blank is sequentially locked between the first and second binder tools—first between complementary binder surfaces at opposed ends of the first and second binder tools, and then between complementary binder surfaces at opposed sides of the first and second binder tools. This progressive process results in more gradual bending and closer conformity of the shape of the sheet metal blank with respect to the shape of the forming surface of the forming die. Thus, by using a binder apparatus having elevated and movable end segments and having stationary side segments, with contoured surfaces on all of the segments, metal is more easily stretched over a form die so as to minimize thinning and wrinkling.
These and other features and advantages of the invention will become apparent upon reading the detailed description in combination with the accompanying drawings, in which:
Referring now in detail to the drawing figures,
The upper binder 112 is essentially an upper die or pressure flask that has an upper surface 120 adapted for mounting to a flat upper platen of a press (not shown) and that has electrical heating elements (not shown) therein for maintaining a desired forming temperature of the sheet metal blank, which is usually pre-heated. The upper binder 112 is preferably mounted on a load bearing insulation layer (not shown) and a sub plate (not shown) that is attached to the upper platen (not shown). The upper binder 112 includes laterally opposed ends 122a, 122b with contoured lower binder surfaces 124a, 124b and further includes laterally opposed sides 126a, 126b with contoured lower binder surfaces 128a, 128b. Corners 130 of the upper binder 112 are adapted for initial contact with a sheet metal blank (not shown) to be formed. A port 132 is provided through one of the sides 126a to communicate pressurized gas into a cavity defined by the upper platen of the press, the upper binder 112, and an upper surface of the sheet metal blank when the tools are in their closed position. The upper binder 112 is driven by the upper platen of the press in a direction toward the lower binder apparatus 114 and the form die 116.
The form die 116 is preferably fixedly mounted to the upper surface of the lower platen 118 with a layer of insulation (not shown) positioned therebetween. The form die 116 includes a generally convex upper surface 134 having various structural design features 136 therein for embossing or otherwise forming the sheet metal blank. Alternatively, the form die 116 could be movably mounted to the lower platen 118 to provide double-action motion for forming the sheet metal blank. In any event, the form die 116 is generally circumscribed by the lower binder apparatus 114.
The lower binder apparatus 114 basically includes laterally opposed stationary binder segments or sides 138a, 138b on either side of the form die 116, and laterally opposed movable binder segments or ends 140, 140 on either end of the form die 116. The binder segments 138a, 138b, 140, 140 closely circumscribe the form die 116, and are spaced from the form die 116 according to dimensions that are consistent with current one-piece binders known in the art. Uniquely, however, the binder segments 138a, 138b, 140, 140 are contoured, positioned, and mounted in a manner which is heretofore unknown in the art.
The stationary binder sides 138a, 138b are mounted to the upper surface 119 of the lower platen 118 with a layer of insulation 142 therebetween. The stationary binder sides 138a, 138b are generally rectangular in shape, but have contoured upper binder surfaces 144a, 144b that preferably, but not necessarily, conform closely with sides of the form die 116 that are relatively proximate the stationary binder sides 138a, 138b. The contoured upper surfaces 144a, 144b have convex crest portions 146a, 146b, 146c that represent the peak in height of the stationary binder sides 138a, 138b. One of the stationary binder sides 138b has a depression 148 formed in the contoured upper surface 144b that follows a particular contour of the form die 116. To complement the contoured upper surfaces 144a, 144b of the stationary binder sides 138a, 138b, the upper binder 112 is similarly contoured. The sides 126a, 126b of the upper binder 112 include the contoured lower surfaces 128a, 128b that have concave crest portions 150a, 150b, 150c that substantially match the respective convex crest portions 146a, 146b, 146c of the stationary binder sides 138a, 138b. Likewise, one of the sides 126b includes a projection 152 that closely complements the depression 148 of one of the stationary binder sides 138b. Thus, due to the complementary contours, when the upper binder 112 eventually closes down on the stationary binder sides 138a, 138b, the sheet metal blank gets clamped therebetween in a substantially uniform sealing manner. Moreover, seal beads (not shown) may be provided on the lower surfaces 124a, 124b, 128a, 128b of the upper binder 112 to further enable sealing in this regard. Finally, the contoured upper surfaces 144a, 144b of the stationary binder sides 138a, 138b include laterally opposed end portions, or shoulders 154, against which the movable binder ends 140, 140 abut.
The movable binder ends 140, 140 are mounted to the upper surface 119 of the lower platen 118 via cradles 156. The cradles 156 are supported and biased in an upward direction by cushion devices 158 positioned under flange portions 160 of the cradles 156. The cushion devices 158 include pistons 162 that are mounted within cylinders 164, which may be gas, hydraulic, spring, or the like. In any event, the cushion devices 158 provide the means by which the cradles 156 are elevated with respect to the upper surface 119 of the lower platen 118. The cushion devices 158, however, do not support the cradles 156 in a lateral direction. Accordingly, alignment devices 166 are mounted between the upper surface 119 of the lower platen 118 and the flange portions 160 of the cradle 156 to support the cradle 156 in a lateral direction and maintain the cradles 156 in precise relation to the stationary binder sides 138a, 138b and the form die 116 such that a predetermined gap is controlled therebetween. The alignment devices 166 include guide posts 168 that are mounted to the upper surface 119 of the lower platen 118 and are fitted within bearing sleeves 170 that are press fit into the flange portions 160 of the cradles 156. The alignment devices 166 may be any type of bearing device such as a linear bearing assembly and the like.
The movable binder ends 140, 140 are mounted to the cradles 156 with a layer of insulation 172 therebetween. The movable binder ends 140, 140 are generally rectangular in shape, but have contoured upper binder surfaces 174 that preferably, but not necessarily, conform closely with ends of the form die 116 that are relatively proximate the movable binder segments. The contoured upper surfaces 174 have convex crest portions 176 that represent the peak in height of the movable binder ends 140. To complement the contoured upper surfaces 174 of the movable binder ends 140, the upper binder 112 is similarly contoured. The ends 122a, 122b of the upper binder 112 include the contoured lower surfaces 124a, 124b that have concave crest portions 178 that substantially match the respective convex crest portions 176 of the movable binder ends 140. Thus, when the upper binder 112 closes down on the movable binder ends 140, the sheet metal blank gets clamped therebetween in a substantially uniform sealing manner. Again, seal beads (not shown) may be provided on the lower surfaces 124a, 124b, 128a, 128b of the upper binder 112 to further enable sealing in this regard. Finally, the contoured upper surfaces 174 of the movable binder ends 140 include laterally opposed end portions, or shoulders 180, against which the ends 154 of the stationary binder segments abut 138a, 138b. Accordingly, the crest portions 176 and shoulders 180 of the movable binder ends 140 are relatively elevated with respect to the crest portions 146a, 146b, 146c and ends 154 of the stationary binder sides 138a, 138b, to enable sequential clamping or locking of the sheet metal blank between the upper binder 112 and the lower binder apparatus 114, as will be described in more detail below with regard to the method of the present invention.
The method of the present invention is illustrated in reference to
When the blank sheet 182 is in place, the binders 112, 138a, 138b, 140, the form die 116, and the blank sheet 182 itself may be heated such as by electrical resistance elements (not shown), to maintain a desired QPF temperature such as about 500 degrees C. in the forming environment. An upper ram of the press (not shown) then slowly drives or lowers the upper binder 112 toward the lower die platen 118 such that the lower corners 130 of the upper binder 112 engage respective corners in the marginal area 186 of the blank sheet 182. The upper binder 112 continues its downward travel so as to drive the blank sheet 182 downward so that the lower surface 190 of the blank sheet 182 initially engages the crest portions 176 of the contoured upper surfaces 174 of the movable binder ends 140. At this point in the process, the movable binder ends 140 remain in their upwardly biased position, elevated with respect to the stationary binder sides 138a, 138b.
Referring now to
With full closure of the binders 112, 114, the blank sheet 182 is gripped in gas-tight sealing engagement via the lockbeads (not shown) on the upper binder 112. Accordingly, high pressure gas may be admitted against the upper surface 188 of the blank sheet 182 through the port 132 in the upper binder 112, or upper platen, or the like in accord with customary practice in the art. Concurrently, gas may be vented from the opposite side of the blank sheet 182 through similar suitable ports (not shown), as is also known in the art. Thus, the high temperatures and gas pressure combine to stretch the blank sheet 182 into compliance with the contoured convex surfaces 134 of the form die 116.
The sheet metal blank 182 was sequentially clamped, first between ends 124a, 124b, 140 of opposed binders 112, 114 about a first axis 196, and then between sides 128a, 128b, 144a, 144b of the opposed binders 112, 114 about a second axis 198 transverse to the first axis 196. Accordingly, the sheet metal blank 182 is preformed in a compound manner to avoid wrinkling thereof during the forming process, which minimizes wrinkling in the finished component C.
Thinning and wrinkling defects can be avoided by implementing a more complex forming process, wherein a pre-forming stage defines a suitable pre-formed panel shape with relatively even thinning behavior and further wherein the panel is situated against the final forming surface in such a way to guarantee a wrinkle-free final forming process. The pre-forming stage or operation can be achieved by a stamping method or hot gas blow forming. With respect to tool design, the punch can be the only moving element for stretching the blank, or the binder ring can be designed to move around a stationary punch, with an identical effect as the moving punch concept. The functionality of the ring can be substantially increased if the ring is provided in separate sections to enable a sequence of stretching operation to achieve an optimum pre-formed panel shape.
It should be understood that the invention is not limited to the embodiments that have been illustrated and described herein, but that various changes may be made without departing from the spirit and scope of the invention. For example, the present invention could be adapted for use in traditional steel sheet metal stamping if the movable binder segments incorporated a lock bead to control blank draw in. Likewise, the present invention may also be adapted for use in plastic sheet forming. Moreover, the present invention has been described in reference to generally rectangular binders, but is equally applicable to binders of any shape including square, circular, oblong, and the like. Finally, words of orientation such as upper and lower have been used herein to set forth an example of the present invention, but should not be construed as limiting the present invention. In other words, the present invention can be carried out in any orientation. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4090389 | VAN Denderen et al. | May 1978 | A |
| 4754635 | van den Berg et al. | Jul 1988 | A |
| 6880377 | Kim et al. | Apr 2005 | B2 |
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| 7047779 | Kruger et al. | May 2006 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20050126242 A1 | Jun 2005 | US |
