Abstract:
A method and apparatus are provided for reducing or eliminating sliver formation during aluminum sheet trimming operations. By controlling parameters such as trimming angle and cutting blade clearance, aluminum sheet can be trimmed while substantially eliminating the formation of slivers which damage the surface finish of the part. Cutting angle and clearance are preferably selected such that a wide range of cutting blade sharpnesses produce satisfactory cuts. The method and apparatus are particularly useful for trimming aluminum autobody sheet.

Description:
FIELD OF THE INVENTION  
         [0001]    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.  
         BACKGROUND INFORMATION  
         [0002]    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.  
           [0003]    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.  
           [0004]    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.  
         SUMMARY OF THE INVENTION  
         [0005]    An object of the present invention is to control the slivering of aluminum sheet during trimming processes.  
           [0006]    Another object of the present invention is to reduce the frequency of tool sharpening required during aluminum sheet trimming operations.  
           [0007]    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.  
           [0008]    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.  
           [0009]    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.  
           [0010]    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.  
           [0011]    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.  
           [0012]    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.  
           [0013]    These and other objects of the present invention will become more apparent from the following description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a partially schematic illustration of a conventional apparatus for trimming steel autobody sheet.  
         [0015]    [0015]FIG. 2 is a partially schematic illustration of an aluminum sheet trimming apparatus in accordance with an embodiment of the present invention.  
         [0016]    [0016]FIG. 3 is a partially schematic illustration of an aluminum sheet trimming apparatus of the present invention, showing the parameters of cutting angle, clearance and tool sharpness.  
         [0017]    [0017]FIG. 4 is a partially schematic illustration of an aluminum sheet being trimmed in accordance with an embodiment of the present invention.  
         [0018]    [0018]FIG. 5 is a photomicrograph of conventional AKDQ steel autobody sheet at a magnification of 250×.  
         [0019]    [0019]FIG. 6 is a photomicrograph of conventional DQIF steel autobody sheet at a magnification of 250×.  
         [0020]    [0020]FIG. 7 is a photomicrograph of Aluminum Association 6111-T4 aluminum alloy sheet which may be trimmed in accordance with the present invention, at a magnification of 250×.  
         [0021]    [0021]FIG. 8 is a photomicrograph of Aluminum Association 6022-T4 aluminum alloy sheet which may be trimmed in accordance with the present invention, at a magnification of 250×.  
         [0022]    [0022]FIG. 9 is a graph showing the effects of cutting angle in trimming steel and aluminum sheet.  
         [0023]    [0023]FIG. 10 is a graph showing the effects of cutting blade clearance in trimming steel and aluminum sheet.  
         [0024]    [0024]FIG. 11 is a graph showing the effects of tool sharpness in trimming steel and aluminum sheet. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    [0025]FIG. 1 schematically illustrates a conventional apparatus for cutting sheet metal such as steel autobody sheet. A metal sheet  10  is sandwiched between a die  12  and a pad  14 . A cutting blade  16  travels in the direction  17  adjacent the die  12  and pad  14  to trim the sheet  10 . In this apparatus, the strain field  18  comprises a shear strain τ with essentially no normal stress. It is known that for steel sheet, a zero degree cutting angle as shown in FIG. 1 produces the most desirable cut edge and generates the least amount of slivers. Conventional trimming apparatus designs therefore minimize any deviation of the cutting angle from zero degrees. Furthermore, when trimming steel sheet, it is critical to maintain sharp tools and keep clearances below about 8 percent of the metal sheet thickness in order to obtain satisfactory cut edges. However, when such conventional steel sheet trimming methods are applied to aluminum sheet, the use of a zero degree cutting angle has been found to produce an unacceptably high amount of slivers for both 6111-T4 and 6022-T4 aluminum alloy sheets.  
         [0026]    [0026]FIG. 2 schematically illustrates an apparatus for trimming aluminum sheet in accordance with the present invention. An aluminum sheet  20  is secured between a die  22  and a pad  24 . A cutting blade  26  travels in the direction  27  adjacent the die  22  and pad  24  to trim the aluminum sheet  20 . The configuration shown in FIG. 2 produces a strain field  28  having a shear strain component τ and a normal stress component σ. In accordance with the present invention, the normal stress component σ is used to improve the cut edge of the aluminum sheet  20  by enhancing ductile fracture.  
         [0027]    As shown most clearly in FIG. 3, the aluminum sheet  20  has a thickness T. The sheet thickness T preferably ranges from about 0.5 to about 1.5 mm, more preferably from about 0.7 to about 1.1. mm. For aluminum autobody sheet, the thickness is typically about 1 mm. The aluminum sheet  20  is positioned with a cutting angle A through use of the die  22  and the pad  24  having opposing angled surfaces which contact the surfaces of the aluminum sheet  20 . The cutting blade  26  is positioned with a clearance C from the die  22  and pad  24 . In accordance with a preferred embodiment, the clearance C is at least about 10 percent of the thickness T of the aluminum sheet  20 . In contrast, the clearance used for trimming steel sheet is conventionally kept below about 8 percent of the steel sheet thickness in order to obtain satisfactory cut edges.  
         [0028]    As shown in FIG. 3, the cutting blade  26  comprises an edge having a tool sharpness R defined as the blade edge radius. During repeated trimming processes, the cutting blade  26  loses sharpness and becomes increasingly dull with values of R ranging from about 0.002 to about 0.75 mm and higher. In accordance with the present invention, the trimming angle A and clearance C are preferably controlled in order to tolerate a tool sharpness R of at least 0.1 mm (0.004 in.), more preferably at least 0.125 mm (0.005 in.), and most preferably at least 0.25 mm (0.01 in.).  
         [0029]    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 FIG. 3 used in accordance with the present invention produces a tensile normal stress component which helps the ductile fracture of the aluminum alloy sheet. The cutting angle A used in the trimming operation of the present invention promotes ductile fracture which involves void nucleation, growth and coalescence, as well as the formation and propagation of a localization zone. However, as the cutting angle A increases significantly, the normal stress component becomes so large that the trimming operation can be adversely effected. As discussed more fully below, depending on the particular cutting blade clearance used, the cutting angle A may preferably be greater than about 10 degrees, and more preferably may range from about 10 to about 25 degrees. Such relatively large cutting angles have been found to substantially reduce or eliminate the formation of slivers during the aluminum trimming operation and to permit the satisfactory use of cutting blades for a relatively long time before sharpening is required.  
         [0030]    As shown in FIG. 3, the clearance C effects the shear strain level in the deformation zone such that the average shear strain in the deformation zone is equal to the blade travel displacement divided by the clearance. Thus, for the same blade travel displacement, a smaller clearance produces a higher shear strain. In conventional trimming of steel sheet, a small clearance is critical because steel has very high ductility. In contrast, the clearance C used in trimming aluminum alloy sheet can be varied within a relatively wide range. The clearance C is typically greater than about 10 percent of the thickness of the aluminum sheet, preferably from about 10 to about 15 or 20 percent of the thickness of the aluminum sheet.  
         [0031]    [0031]FIG. 4 illustrates an aluminum sheet  20  being trimmed. About 80 percent of slivers occur at the blade contact zone  31 , with minor amounts of slivers occurring at the burr area  32  or fracture surface  33 .  
         [0032]    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.  
         [0033]    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 FIGS.  4 - 7 , steel and aluminum alloys have fundamentally different microstructures. The AKDQ steel sheet shown in FIG. 5 and the DQIF steel sheet shown in FIG. 6 have a clean microstructure having very few if any precipitates, dispersoids and constituents. In contrast, the 6111-T4 aluminum sheet shown in FIG. 7 and the 6022-T4 aluminum alloy sheet shown in FIG. 8 contain substantially more precipitates, dispersoids and constituents. These second phase particles make the fracture of aluminum alloys much more sensitive to tensile stresses than steel, which has significantly higher ductility than aluminum alloys. Other microstructural differences between steel and aluminum such as body centered cubic (BCC) and face centered cubic (FCC) crystal structures play important roles in the ductility of the alloys. While trimming of aluminum alloys 6111 and 6022 is primarily disclosed herein, it is to be understood that other alloys may be trimmed in accordance with the present invention. Such additional alloys typically contain similar types and/or amounts of precipitates or dispersoids, and undergo ductile fracture in a manner similar to 6111 and 6022 alloys.  
       EXAMPLES  
       [0034]    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.  
         [0035]    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.  
         [0036]    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.  
         [0037]    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.  
         [0038]    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.  
         [0039]    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.  
         [0040]    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.  
         [0041]    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.  
         [0042]    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.  
         [0043]    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.  
                                                                           TABLE 1                           6111-T4 (BLADE SHARPNESS = 0.0001-0.0004 In.)                0 Degree   5 Degree   10 Degree   15 Degree   20 Degree   25 Degree                         5% Clearance   Significant amount fine   Some fine hairlike   Almost no slivers; very   No slivers; minimal burr   No slivers; minimal burr   No slivers; minimal burr           hairlike slivers; slight   slivers; slight burr on   slight burr on edge   on edge   on edge   on edge           burr on edge   edge       10% Clearance   Some fine hairlike   Some slivers; slight burr   No slivers; slight burr on   No slivers; minimal burr   No slivers; minimal burr   No slivers; minimal burr           slivers; slight burr on   on edge   edge   on edge   on edge   on edge           edge       15% Clearance   Almost no slivers; slight   Almost no slivers; slight   No slivers; slight burr on   No slivers, very slight   No slivers; minimal burr   No slivers; minimal burr           to medium burr on edge   to medium burr on edge   edge   burr on edge   on edge   on edge       20% Clearance   No slivers; medium burr   No slivers; medium burr   No slivers; very slight   No slivers; very slight   No slivers; very slight   No slivers; minimal burr           on edge   on edge   medium burr on edge   burr on edge   burr on edge   on edge       25% Clearance   No slivers; medium burr   No slivers; medium burr   No slivers; slight to   No slivers; slight burr on   No slivers; very slight   No slivers; very slight           on edge   on edge   medium burr on edge   edge   burr on edge   burr on edge                                                          
 
         [0044]    [0044]                                                                           TABLE 2                           6022-T4 (BLADE SHARPNESS = 0.0001-0.0004 In.)                0 Degree   5 Degree   10 Degree   15 Degree   20 Degree   25 Degree                         5% Clearance   Significant amount fine   Many fine hairlike   Little to no slivers; very   Almost no slivers;   No slivers; minimal burr   No slivers; minimal burr           hairlike slivers; slight   slivers; very slight   slight burr on edge   minimal burr on edge   on edge   on edge           burr on edge   burr on edge       10% Clearance   Many fine hairlike   Many slivers; very slight   Almost no slivers; slight   No slivers; minimal burr   No slivers; minimal burr   No slivers; minimal burr           slivers; slight burr on   burr on edge   burr on edge   on edge   on edge   on edge           edge       15% Clearance   A few slivers; slight   A few slivers; slight   No slivers; slight burr on   No slivers, very slight   No slivers; minimal burr   No slivers; minimal burr           to medium burr on edge   to medium burr on edge   edge   burr on edge   on edge   on edge       20% Clearance   Almost no slivers;   No slivers; medium burr   No slivers; slight   No slivers; very slight   No slivers; very slight   No slivers; minimal burr           medium burr on edge   on edge   to medium burr on edge   burr on edge   burr on edge   on edge       25% Clearance   No slivers; medium burr   No slivers; medium burr   No slivers; slight to   No slivers; slight burr on   No slivers; very slight   No slivers; very slight           on edge   on edge   medium burr on edge   edge   burr on edge   burr on edge                                                            
         [0045]    [0045]                                                                                           TABLE 3                                   0 Degree   10 Degree   20 Degree   25 Degree                                    6111-T4 (BLADE SHARPNESS = 0.001 in.)             5% Clearance   Significant amount of long   Some hairlike slivers; very   No slivers; minimal burr   No slivers; minimal burr           hairlike slivers; slight burr   slight burr       10% Clearance   Many hairlike slivers; slight to   A few slivers; slight burr   No slivers; minimal burr   No slivers; minimal burr           medium burr       15% Clearance   Some slivers; slight to medium   No slivers; slight burr   No slivers; slight burr   No slivers; very slight burr           burr       20% Clearance   No slivers; medium burr   No slivers; slight to medium   No slivers; slight burr   No slivers; slight burr               burr       25% Clearance   No slivers; medium burr   No slivers; medium burr   No slivers; medium burr   No slivers; slight burr            6022-T4 (BLADE SHARPNESS = 0.001 in.)             5% Clearance   Significant amount of long   Many hairlike slivers; very   No slivers; minimal burr   No slivers; minimal burr           hairlike slivers; slight burr   slight burr       10% Clearance   Many hairlike slivers; slight to   Some slivers; slight burr   No slivers; minimal burr   No slivers; minimal burr           medium burr       15% Clearance   Some slivers; slight   No slivers; slight burr   No slivers; slight burr   No slivers; very slight burr           to medium burr       20% Clearance   No slivers: medium burr   No slivers; slight to medium   No slivers; slight burr   No slivers; slight burr               burr       25% Clearance   No slivers: medium burr   No slivers; medium burr   No slivers; medium burr   No slivers: slight burr                                                                    
         [0046]    [0046]                                                                                           TABLE 4                                   0 Degree   10 Degree   20 Degree   25 Degree                                    6111-T4 (BLADE SHARPNESS = 0.002 in.)             5% Clearance   Significant amount of hairlike   Many hairlike slivers; very   No slivers; minimal burr   No slivers; minimal burr           slivers slight to medium burr   slight burr       10% Clearance   Many hairlike slivers; slight to   A few slivers; slight burr   No slivers; minimal burr   No slivers; minimal burr           medium burr       15% Clearance   Some slivers; medium burr   No slivers; slight to medium   No slivers; slight burr   No slivers; very slight burr               burr       20% Clearance   No slivers; medium burr   No slivers; slight to medium   No slivers; slight   No slivers; slight burr               burr   to medium burr       25% Clearance   No slivers; medium burr   No slivers; medium burr   No slivers; medium burr   No slivers; slight to medium                   burr            6022-T4 (BLADE SHARPNESS = 0.002 in.)             5% Clearance   Significant amount of hairlike   Some hairlike slivers; very   No slivers; minimal burr   No slivers; minimal burr           slivers; slight to medium burr   slight burr       10% Clearance   Many hairlike slivers; slight to   Some slivers; slight burr   No slivers; minimal burr   No slivers; minimal burr           medium burr       15% Clearance   Some slivers; medium burr   No slivers; slight to medium   No slivers; slight burr   No slivers; very slight burr               burr       20% Clearance   No slivers; medium burr   No slivers; slight to medium   No slivers; slight to medium   No slivers; slight burr               burr   burr       25% Clearance   No siivers; medium burr   No slivers; medium burr   No slivers; medium burr   No slivers; slight to medium                       burr                                            
         [0047]    [0047]                                                                                           TABLE 5                                   0 Degree   10 Degree   20 Degree   25 Degree                                    6111-T4 (BLADE SHARPNESS = 0.005 in.)             5% Clearance   A few hairlike sliver   Almost no hairlike   No slivers; minimal burr,   No slivers; minimal burr,           and some large   slivers, some large   good cutting surface   good cutting surface           peice slivers and particles   pieces slivers and particles;           medium burr, fair cutting   slight burr, fair cutting surface           surface       10% Clearance   Almost no hairlike slivers,   Almost no hairlike slivers;   No slivers, minimal burr,   No slivers; minimal burr,           some large pieces   a few large piece slivers;   fair cutting surface   fair cutting surface           slivers and particles; medium   medium to high burr           burr, fair cutting surface   rought cutting surface       15% Clearance   Almost no hairlike slivers;   No sliver; medium to high burr   No slivers; medium burr,   No slivers; slight to medium burr,           a few large piece slivers;   rough cutting surface   rough cutting surface   rough cutting surface           medium to high burr           fair cutting surface       20% Clearance   No slivers; medium to high   No slivers; high burr, very   No slivers; medium to high burr,   No slivers; medium burr,           burr, rough cutting surface   rouhg cutting surface   very rough cutting surface   very rough cutting surface       25% Clearance   No slivers, high burr,   No slivers, high burr,   No slivers, high burr   No slivers; medium to high burr           rough cutting surface   very rough cutting surface   very rough cutting surface   rough cutting surface            6022-T4 (BLADE SHARPNESS = 0.005 in.)             5% Clearance   A few hairlike sliver   Almost no hairlike   No slivers; minimal burr,   No slivers; minimal burr,           and some large   slivers, some large   good cutting surface   good cutting surface           peice slivers and particles   pieces slivers and particles;           medium burr, fair   slight burr, fair cutting surface           cutting surface       10% Clearance   Almost no hairlike slivers,   Almost no hairlike slivers;   No slivers, minimal burr,   No slivers; minimal burr,           some large pieces   a few large piece slivers;   fair cutting surface   fair cutting surface           slivers and particles; medium   medium to high burr           burr, fair cutting surface   rought cutting surface       15% Clearance   Almost no hairlike slivers;   No sliver; medium to high burr   No slivers; medium burr,   No slivers; slight to medium burr,           a few large piece slivers;   rough cutting surface   rough cutting surface   rough cutting surface           medium to high burr           fair cutting surface       20% Clearance   No slivers; medium to high   No slivers; high burr, very   No slivers; medium to high burr,   No slivers; medium burr,           burr, rough cutting surface   rouhg cutting surface   very rough cutting surface   very rough cutting surface       25% Clearance   No slivers, high burr,   No slivers, high burr,   No slivers, high burr   No slivers; medium to high burr           rough cutting surface   very rough cutting surface   very rough cutting surface   rough cutting surface                                            
         [0048]    [0048]                                                                                           TABLE 6                                   0 Degree   10 Degree   20 Degree   25 Degree                                    6111-T4 (BLADE SHARPNESS = 0.010 in.)             5% Clearance   Almost no hairlike sliver   almost no hairlike slivers,   No slivers, minimal burr,   No slivers, minimal burr,           and may large piece slivers   some large pieces slivers and   good cutting surface   good cutting surface           and particles, high burr,   minimal burr, fail cutting surface           rough cutting surface       10% Clearance   No hairlike slivers, some   No hairlike slivers, a few   No slivers, minimal burr,   No slivers, minimal burr,           large pieces slivers and   large piece slivers; high burr   good cutting surface   good cutting surface           and particles; very high   unacceptably rough cutting           burr, rough cutting surface   surface       15% Clearance   No hairlike slivers, a few   No slivers, high burr,   No slivers, high burr,   No slivers, high burr           large piece slivers; very high   unacceptably rough cutting surface   rough cutting surface   rough cutting surface           high burr, rough cutting           surface       20% Clearance   No slivers, extremely high burr,   No slivers, very high burr,   No slivers, high burr,   No slivers; high burr,           very rough cutting surface   unacceptable rough cutting   unacceptably rough cutting   unacceptable rough cutting               surface   surface   surface       25% Clearance   No slivers, extremely high burr,   No slivers; extremely high   No slivers; extremely high   No slivers, very high burr,           very rough cutting surface   burr, unacceptably rough   burr, unacceptably   unaccetably rough cutting               cutting surface   rough cutting surface   surface            6022-T4 (BLADE SHARPNESS = 0.010 in.)             5% Clearance   Almost no hairlike sliver   almost no hairlike slivers,   No slivers, minimal burr,   No slivers, minimal burr,           and may large piece slivers   some large pieces slivers and   good cutting surface   good cutting surface           and particles, high burr,   minimal burr, fail cutting surface           rough cutting surface       10% Clearance   No hairlike slivers, some   No hairlike slivers, a few   No slivers, minimal burr,   No slivers, minimal burr,           large pieces slivers and   large piece slivers; high burr   good cutting surface   good cutting surface           and particles; very high   unacceptably rough cutting           burr, rough cutting surface   surface       15% Clearance   No hairlike slivers, a few   No slivers, high burr,   No slivers, high burr,   No slivers, high burr           large piece slivers; very high   unacceptably rough cutting surface   rough cutting surface   rough cutting surface           high burr, rough cutting           surface       20% Clearance   No slivers, extremely high burr,   No slivers, very high burr,   No slivers, high burr,   No slivers; high burr,           very rough cutting surface   unacceptable rough cutting   unacceptably rough cutting   unacceptable rough cutting               surface   surface   surface       25% Clearance   No slivers, extremely high burr,   No slivers; extremely high   No slivers; extremely high   No slivers, very high burr,           very rough cutting surface   burr, unacceptably rough   burr, unacceptably   unaccetably rough cutting               cutting surface   rough cutting surface   surface                                    
         [0049]    [0049]                                                                                           TABLE 7                                   0 Degree   10 Degree   20 Degree   25 Degree                                    6111-T4 (BLADE SHARPNESS = 0.020 in.)             5% Clearance   No hairlike sliver, many   No hairlike slivers,   No slivers, minimal burr,   No slivers, minimal burr,           large piece slivers and   a few large piece slivers   good cutting surface   good cutting surface           particles; extremely high   and particles; minimal burr,           burr, unacceptable cutting surface   good cutting surface       10% Clearance   No hairlike sliver, many   No hairlike slivers; a   No slivers, minimal burr,   No slivers, minimal burr,           large piece slivers and   few large piece slivers;   good cutting surface   good cutting surface           particles; extremely high   discontinously high burr,           burr, unacceptable cutting   discontinously rough           surface   cutting surface       15% Clearance   No hairlike sliver, some   No sliver, extremely high   No slivers; minimal burr,   No slivers; minimal burr,           large pieces slivers and   burr, unacceptably rough   fair cutting surface   good cutting surface           particles; extremely high   cutting surface           burr, unacceptable cutting           surface       20% Clearance   No slivers and particles;   No slivers, extremely high   No slivers; discontinously   No slivers; discontinously           extremely high burr,   burr, unacceptably rough   high burr, discontinously   high burr, discontinously           unacceptable cutting surface   cutting surface   rough cutting surface   rough cutting surface       25% Clearance   No slivers and particles;   No slivers, extremely high   No slivers, extremely high   No slivers, discontinously           extremely high burr,   burr, unacceptably rough   burr, unacceptably rough   high burr, discontinously           unacceptable cutting surface   cutting surface   cutting surface   rough cutting surface            6022-T4 (BLADE SHARPNESS = 0.020 in.)             5% Clearance   No hairlike sliver, many   No hairlike slivers,   No slivers, minimal burr,   No slivers, minimal burr,           large piece slivers and   a few large piece slivers   good cutting surface   good cutting surface           particles; extremely high   and particles,           burr, unacceptable cutting surface   discontinously high burr           and rough cutting surface       10% Clearance   No hairlike sliver, many   No hairlike slivers; a   No slivers, minimal burr,   No slivers, minimal burr,           large piece slivers and   few large piece slivers;   good cutting surface   good cutting surface           particles; extremely high   discontinously high burr,           burr, unacceptable cutting   discontinously rough           surface   cutting surface       15% Clearance   No hairlike sliver, some   No sliver, extremely high   No slivers; minimal burr,   No slivers; minimal burr,           large pieces slivers and   burr, unacceptably rough   fair cutting surface   good cutting surface           particles; extremely high   cutting surface           burr, unacceptable cutting           surface       20% Clearance   No slivers and particles;   No slivers, extremely high   No slivers; discontinously   No slivers; discontinously           extremely high burr,   burr, unacceptably rough   high burr, discontinously   high burr, discontinously           unacceptable cutting surface   cutting surface   rough cutting surface   rough cutting surface       25% Clearance   No slivers and particles;   No slivers, extremely high   No slivers, extremely high   No slivers, discontinously           extremely high burr,   burr, unacceptably rough   burr, unacceptably rough   high burr, discontinously           unacceptable cutting surface   cutting surface   cutting surface   rough cutting surface                                    
         [0050]    [0050]                                 TABLE 8                           MAXIMUM CLEARANCE AND BLADE SHARPNESS OF CUTTING DQIF STEEL SHEET            Trimming Angle   Maximum Clearance   Maximum Blade Edge Radius   Remarks               0 Degree   13.80%   0.002 in.   Extremely high and sharp burr, unacceptable                   cutting surface       0 Degree   13.80%   0.005 in.   Extremely high and sharp burr, unacceptable                   cutting surface, significant local bending distortion                   on sheet near the cutting edge       0 Degree   17.20%   0.001 in.   Extremely high and sharp burr, unacceptable                   cutting surface, significant local bending distortion                   on sheet near the cutting edge       0 Degree   17.20%   0.010 in.   Not be able to cut otl the sheet metal       10 Degree    13.80%   0.005 in   Not be able to cut ofi the sheet metal                    
         [0051]    The effects for each individual variable of cutting angle A, clearance C and tool sharpness R are schematically shown in FIGS.  8  to  10 , respectively.  
         [0052]    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 FIG. 9, as the cutting angle increases and when it reaches a certain value, the burr becomes intolerable and the quality of cut surface is unacceptable even though no slivers are generated.  
         [0053]    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.  
         [0054]    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.  
         [0055]    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.  
         [0056]    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.  
                             TABLE 9                           TRIMMING TOOL GUIDELINES FOR 6111-T4 AND 6022-T4            Trimming Angle   Clearance Per Side   Maximum Blade Edge Radius               0 Degree   15%-20%   0.003 in.       0-5 Degree   12.5%-17.5%   0.004 in.        5-10 Degree     10%-17.5%   0.005 in.       10-15 Degree    7.5%-17.5%   0.005 in.       15-25 Degree    5%-20%   0.010 in.                                                                                  
 
         [0057]    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.  
         [0058]    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.  
         [0059]    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.  
                                                                                                       TABLE 10                                   0.001 in.   0.002 in.   0.005 in.   0.010 in.   0.020 In.                                    Burr Height of 6111-T4             5% Clearance   0.05 mm   0.055 mm    0.05 mm    0.06 mm    0.35 mm       10% Clearance   0.10 mm   0.120 mm   0.140 mm   0.183 mm    0.35 mm       15% Clearance   0.133 mm    0.133 mm   0.183 mm   0.233 mm    0.35 mm       20% Clearance   0.15 mm    0.20 mm   0.183 mm   0.233 mm    0.40 mm       25% Clearance   0.167 mm    0.183 mm   0.233 mm   0.317 mm    0.40 mm            Burr Height of 6022-T4             5% Clearance   0.058 mm    0.117 mm   0.133 mm   0.167 mm   0.317 mm       10% Clearance   0.133 mm    0.117 mm   0.142 mm   0.183 mm   0.333 mm       15% Clearance   0.10 mm   0.158 mm   0.183 mm   0.225 mm   0.35 mm       20% Clearance   0.20 mm   0.15 mm    0.167 mm   0.292 mm   0.367 mm       25% Clearance   0.15 mm   0.10 mm    0.225 mm   0.292 mm   0.367 mm                  
 
         [0060]    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.  
         [0061]    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.