Patent Grant
6976414
The present invention relates to trimming or shearing of aluminum sheet, and more particularly relates to a method and apparatus for reducing sliver production during trimming of sheet such as aluminum autobody sheet.
Automotive manufacturers are seeking ways of replacing steel components with aluminum components in order to gain benefits such as reduced weight and improved corrosion resistance. For example, attempts have been made to replace conventional steel autobody sheet with aluminum autobody sheet.
Trimming is an important operation in the autobody sheet forming process. Such trimming operations have conventionally been used to form steel sheet having adequate edge characteristics. When trimmed with dies conventionally designed for steel sheet, aluminum autobody sheet produces unacceptable cut surfaces having slivers, burrs, surface roughness and the like. Slivers are particularly disadvantageous because they cause damage to both the tooling and surface finish of the part. In addition, slivers contaminate the production line.
Sliver production has been recognized by automotive manufacturers as a critical problem in the utilization of aluminum in the automotive industry. Currently, there is no effective procedure for eliminating sliver production during the formation of aluminum autobody sheet. Instead, hand finishing of the formed aluminum parts and hand removal of the slivers are usually employed in production practice. The present invention has been developed in view of the foregoing and to remedy other deficiencies of the prior art.
An object of the present invention is to control the slivering of aluminum sheet during trimming processes.
Another object of the present invention is to reduce the frequency of tool sharpening required during aluminum sheet trimming operations.
A further object of the present invention is to provide an aluminum sheet trimming operation in which the cutting blade clearance can be varied over a relatively wide range.
Another object of the present invention is to provide a method of trimming aluminum including the steps of cutting the aluminum sheet at a cutting angle and with a cutting blade clearance which substantially eliminate the formation of aluminum slivers.
A further object of the present invention is to provide a method of trimming aluminum sheet including the steps of securing an aluminum sheet at a cutting angle of at least about 10 degrees adjacent a cutting blade, trimming the aluminum sheet at the cutting angle with the cutting blade, and recovering the trimmed aluminum sheet with substantially no slivers.
Another object of the present invention is to provide a method of trimming aluminum sheet including the steps of securing the aluminum sheet between a die and a pad, trimming the aluminum sheet at a cutting blade clearance of greater than about 15% of the thickness of the aluminum sheet, and recovering the trimmed aluminum sheet with substantially no slivers.
A further object of the present invention is to provide an apparatus for reducing sliver production during trimming of aluminum sheet including means for cutting the aluminum sheet, and means for securing the aluminum sheet adjacent the cutting means at a cutting angle of at least about 10 degrees.
Another object of the present invention is to provide a trimmed aluminum sheet substantially free of slivers produced by securing an aluminum sheet at a cutting angle of at least about 10 degrees adjacent a cutting blade, and trimming the aluminum sheet at the cutting angle with the cutting blade.
These and other objects of the present invention will become more apparent from the following description.
As shown most clearly in
As shown in
The cutting angle primarily determines the shear stress and normal stress components on the cutting surface of the sheet. A zero degree cut results in the least amount of normal stress. The normal stress component increases as the cutting angle increases. The cutting angle A shown in
As shown in
In trimming operations, a sharp blade results in more concentrated deformation than a dull blade. The highly concentrated stresses produced by a sharp blade result in highly concentrated strain or strain localization. It has been conventionally recognized that sharper tools perform better in the trimming process than dull tools. However, in accordance with the present invention, the cutting angle A and the clearance C used in trimming aluminum alloy sheet are preferably controlled in a manner that allows relatively dull blades to shear the aluminum sheet satisfactorily.
In accordance with the present invention, the cutting condition for aluminum alloys such as 6111-T4 differs substantially from the cutting condition for conventional steel sheet. As shown in
The trimming variables evaluated include cutting angle, clearance and blade sharpness. The laboratory tooling used to trim each sheet is capable of cutting sheet with 0°, 5°, 10°, 15°, 20° and 25° trimming angles. The clearances evaluated were 5%, 10%, 15%, 20% and 25% of the sheet thickness for 6111-T4 and 6022-T4 sheets with a nominal thickness of 0.040 in. (1 mm). Six blade sharpnesses were evaluated. The blade sharpness is quantified by the cutting edge radius. The sharpest one had a cutting edge radius of 0.0001-0.0004 in. (2-10 μm). Other blade sharpnesses evaluated were 0.001 in. (25 μm), 0.002 in. (50 μm), 0.005 in. (125 μm), 0.010 in. (0.25 mm), and 0.020 in. (0.5 mm). The reason for the sharpest blades not having a definite cutting edge radius is that their edge radii were too small to be exactly quantified on the available measuring device. In addition, such sharp blades would wear after only a few cuts and their sharpnesses would vary.
A total of 130 cutting conditions were evaluated. These conditions included different combinations of cutting angles, clearances and blade sharpnesses. The dimensions of the sheet test samples were 1.5 in.×5.0 in. All samples were tested under unlubricated conditions using straight blades/pads. Within each cutting condition, the effects of sheet orientation were evaluated with samples prepared parallel to and transverse to the rolling direction. About 1,500 samples for each of the two aluminum alloys were tested. For comparison, selected cutting conditions were evaluated for 0.031 in. (0.79 mm) AKDQ steel automotive sheet and 0.029 in. (0.74 mm) DQIF steel automotive sheet.
The observations were focused on the sliver generation. However, the severity of burr formation and the quality of the cut surface are also of concern. The severity of the burr is quantified by the burr height. The quality of the cut surface is represented by its roughness.
Table 1 and Table 2 summarize the results of 6111-T4 and 6022-T4 cut with the sharpest blades which had edge radii R of 0.0001-0.0004 in. (2-10 μm). The cut surface quality is generally acceptable for all cutting conditions with such blade sharpnesses.
As the clearance or cutting angle increases, the burnish area and the secondary-burnish area decrease while the fracture area increases. Hairlike slivers generated by the cuts along the longitudinal (rolling) direction appear longer than those generated by the cuts perpendicular to the longitudinal (rolling) direction. There is no distinguishable difference in burr height and cut surface quality between the cuts along or perpendicular to the longitudinal (rolling) direction.
Table 3 and Table 4 present the results for 6111-T4 and 6022-T4 cut with the blades of cutting edge radii R of 0.001 in. (25 μm) and 0.002 in. (50 μm), respectively. These two blade sharpnesses produce very similar results. The 0.002 in. blade generates slightly bigger (wider) pieces of hairlike slivers and slightly higher burrs than the 0.001 in. blade. The cut surface quality is generally acceptable for all cutting conditions with these two blade sharpnesses. As the clearance C or cutting angle A increases, the burnish area and the secondary burnish area decrease while the fracture area increases. The secondary burnish area eventually disappears as clearance and cutting angle increase. Hairlike slivers generated by the cuts along the longitudinal (rolling) direction appear longer than those generated by the cuts perpendicular to the longitudinal (rolling) direction.
The appearance of slivers changes when the blade edge radius reaches 0.005 in. (125 μm). The amount of hairlike slivers is drastically reduced. However, they are replaced by slivers of large metal pieces and small particles. The cut surface quality declines compared to the cuts by blades with sharpnesses of 0.0001-0.0002 in., 0.001 in. and 0.002 in. Table 5 summarizes the results for 6111-T4 and 6022-T4 for the blades of 0.005 in. With this blade sharpness and small cutting angles (0-10 degrees) and for large clearances (15-25%), the roughness of the cut surface increases significantly as the clearance increases.
Table 6 and Table 7 show the results of 6111-T4 and 6022-T4 trimmed by blades with cutting edge radii of 0.010 in. (0.25 mm) and 0.020 in. (0.50 mm). These blades are considered very dull for cutting sheets of 0.040 in. (1 mm) thick. With these blades, although almost no hairlike slivers are generated, the slivers are in the form of either large metal pieces or small particles. However, with 15-25 degree cutting angles and 5-10% clearances, no slivers in any form are generated and the burr is minimal for blades with edge radii up to 0.020 in. The quality of the cut surface is also very good.
It is observed that the majority of slivers occur during the down stroke. The press used for the testing is a two-step press. It can be interrupted after the down stroke and then resumed for the back stroke. The conclusion that the majority of slivers occur during the down stroke is also reached from intensive micrographic investigations to trace the origin of slivers.
About 150 steel samples were cut under selected combinations of cutting angle, clearance and blade sharpness. The restrictions placed on trimming angle, clearance and blade sharpness for cutting steel sheets are due to concerns about being able to cut off the metal with acceptable burr heights and good cut surfaces. Table 8 shows the representative maximum clearance and blade sharpnesses for cutting DQIF steel sheet.
The effects for each individual variable of cutting angle A, clearance C and tool sharpness R are schematically shown in
The cutting angle required for aluminum sheet differs dramatically from that for steel sheet. The best condition designed for steel results in the largest amount of slivers for aluminum, as shown in FIG. 9. As observed in the present examples, as well as in production trimming lines, slivers are not a problem for steels. A 0° trim gives the best condition to cut off the steel sheets and produces good cut surface quality and the least amount of burr. Therefore, trimming tools conventionally designed for steel sheets require cutting angles as close as possible to 0°. However, the experimental investigation conducted here showed that the 0° cutting generates the largest amount of slivers for both 6111-T4 and 6022-T4. On the contrary, with cutting angles above 15 degrees, slivers were significantly reduced or completely eliminated even with blade radii as dull as 0.020 in. for a wide range of clearances. However, as shown in
For steel it is usually desirable to keep clearances at about 7.5% of metal thickness. Above this value, the burr height and cut surface quality become unacceptable and it may even be impossible to cut off the sheet metal, as shown in Table 8. For 6111-T4 and 6022-T4 sheets, with appropriate cutting angles, the clearance can be 15% of the sheet thickness and result in tolerable burr height and acceptable cut surface quality. Consequently, the clearance for aluminum is less restrictive than that for steels as shown in FIG. 10.
Maintaining sharp tools is critical to trim steel sheets. As exhibited in Table 8, when the radius of the cutting blade exceeds 0.005 in. and the clearance exceeds 10%, high and sharp burrs and unacceptable cut surface quality result. However, with appropriate cutting angles for both 6111-T4 and 6022-T4 the blade edge radius can be as dull as 0.020 in. and still produce little or no slivers, low burrs and good cut surface quality, as shown in FIG. 11.
In accordance with the present invention, with appropriate cutting angles, the trimming/blanking of 6111-T4 and 6022-T4 aluminum sheets can be more robust that the trimming/blanking of steel sheets. For the aluminum alloys, the clearances can be less restrictive and tools may require less sharpening because the cutting is less sensitive to the tool sharpness. In addition, a wide range of cutting angles is possible for 6111-T4 and 6022-T4 sheets.
In accordance with the present invention, improved tool design is provided based on the results shown in Tables 1-7. Tool design guidelines for trimming 6111-T4 and 6022-T4 are shown in Table 9. The guidelines specify the clearance and maximum blade edge radius for different ranges of cutting angles. The lower bounds of the clearances are limited by sliver generation. The upper bounds of the clearances are limited by the tolerable burr height. In general, burr height increases as clearance increases and as blade sharpness decreases. Sharper blade results in lower burrs. Blade sharpness also affects the appearance of slivers. Fine hairlike slivers are generated by sharp blades. When the blade gets dull, it generates large metal pieces and particle-like slivers.
Overall, to get the best results to eliminate slivers and minimize burr height, it is preferred that the lower bounds of clearances be followed. As cutting angle increases, the clearance window opens up and the requirement for blade sharpness becomes less restrictive as shown in Table 9. Cutting angles A of 20±5 degree are the most preferred cutting conditions for trimming 6111-T4 and 6022-T4. Under such conditions, no slivers were generated in the examples and the burr heights were minimal using blades with edge radii up to 0.020 in.
A cutting angle A of zero degrees is possible if the clearance is increased from 7.5±2.5% (designed for steel) to 15% to 20% of the aluminum sheet thickness. Since burr height increases with blade edge radius, the cutting blade needs to be maintained as sharp as possible to reduce the burr height.
For a quantitative indication of burr severity, the burr heights were measured for 0 degree cutting for different clearances with different blade sharpnesses. The burr heights were measured using micrographs of the cross-sections of trimmed samples. The burr heights are given in Table. 10.
In accordance with the present invention, the selection of the appropriate cutting angle A results in improved trimming of aluminum sheet in comparison with steel sheet. In addition, the clearance C used in trimming aluminum sheet can be varied within a relatively wide range in comparison with the relatively small clearance required for trimming of steel sheet. Furthermore, the tools used for trimming require less sharpening and allow the use of a relatively dull cutting blades by adjusting the cutting angle and clearance used to trim the aluminum sheet. These advantages result in a robust trimming operation in comparison with conventional steel trimming methods.
Whereas particular embodiments of the present invention have been described herein, it is to be understood that various changes, additions, adaptations and modifications may be made without departing from the scope of the invention, as set forth in the appended claims.
This is a division, of application Ser. No. 08/742,976, filed Nov. 1, 1996 now U.S. Pat. No. 5,820,999.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2207872 | Ostberg | Jul 1940 | A |
| 2339641 | Jensen | Jan 1944 | A |
| 3215017 | Rutz | Nov 1965 | A |
| 3791248 | Pearson | Feb 1974 | A |
| 3828633 | Klingen | Aug 1974 | A |
| 4043233 | Seki et al. | Aug 1977 | A |
| 4417510 | Sharp | Nov 1983 | A |
| 4485714 | Eriksson | Dec 1984 | A |
| 4569263 | Kravets | Feb 1986 | A |
| 4787542 | Ruff et al. | Nov 1988 | A |
| 4942798 | Taub et al. | Jul 1990 | A |
| 5010795 | Kania | Apr 1991 | A |
| 5103702 | Yannazzone | Apr 1992 | A |
| 5235881 | Sano et al. | Aug 1993 | A |
| 5327806 | Houser | Jul 1994 | A |
| 5373767 | Weisser | Dec 1994 | A |
| 5390576 | Ishibashi | Feb 1995 | A |
| 5458717 | Kurita | Oct 1995 | A |
| 5820999 | Li et al. | Oct 1998 | A |
| 5896795 | Harhay et al. | Apr 1999 | A |
| Number | Date | Country |
|---|---|---|
| 4-59138 | Feb 1992 | JP |
| 4-327322 | Nov 1992 | JP |
| 745608 | Jul 1980 | SU |
| 9014190 | Nov 1990 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20020017173 A1 | Feb 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 08742976 | Nov 1996 | US |
| Child | 08974179 | US |
