Abstract:
A method and a system are disclosed for making an article of manufacture from a blank defining an internal opening. A stack of blanks are aligned and the internal openings of the blanks in the stack of blanks are machined by a rotary cutting tool to a finished dimension. The blanks are clamped together before machining in a numerically controlled machine tool. The blanks are subsequently formed individually in a sheet metal forming operation in which the inner perimeter of the internal openings is expanded as the blank is formed.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a method of manufacturing sheet metal blanks that include an opening subsequently formed in a drawing operation or other type of forming operation. 
       BACKGROUND 
       [0002]    Manufacturing sheet metal parts generally begins with a blanking operation where blanks are cut from coils of rolled steel or aluminum. The outer perimeter and large openings may be trimmed to form a blank that is then formed in subsequent drawing, flanging, punching, piercing and hemming processes. One example of a part that is blanked with a large opening is a body side panel that spans the side of a vehicle and defines the opening that receives the doors in a nesting relationship. One problem with forming precut openings in a blank is that in subsequent forming operations the material around the opening must flow from both the inside of the opening and the areas outside the opening. The precut opening is expanded when the blank is formed and may form splits in the material around the opening. 
         [0003]    With the need to reduce the weight of vehicles to meet fuel economy standards, the development of sheet metal parts made from aluminum or high strength alloys is increasing. Aluminum and high strength steel are less malleable than mild steel and the problems relating to splitting at the inner perimeter of larger openings is more prevalent. Small cracks or small imperfections in the cut edge formed when aluminum blanks are cut out expand to form splits in a subsequent forming operations because additional metal is drawn from the inside of the opening. 
         [0004]    The root causes of splitting at the inner edge of the blank during draw die expansion in subsequent forming operation originates from excessive strain hardening and small imperfections due to rough fracture surfaces, micro-cracks, burrs, and gall marks. Excessive strain hardening and imperfections severely limit the expansion capacity of the metal. Avoiding problems relating to splits caused by imperfections in precut openings in aluminum panels limits opportunities to use aluminum sheet metal parts. Panel splits may cause substantial yield losses in the stamping process due to the need to scrap parts that have splits in critical areas. In addition, problems relating to splits in panels result in cost overruns, supply shortages, potential quality problems, and reduced manufacturing line availability. 
         [0005]    This disclosure is directed to solving the above problems and other problems as summarized below. 
       SUMMARY 
       [0006]    According to one aspect of this disclosure, a method is disclosed for manufacturing a sheet metal part. The method includes the steps of cutting a plurality of blanks defining internal openings from a plurality of sheet metal segments. Stacking the plurality of blanks with the internal openings aligned and machining inner perimeters of the internal openings with a rotary cutting tool to a finish dimension. 
         [0007]    According to other aspects of the method, the method may further comprise clamping the plurality of blanks together before machining. The blanks may be clamped together in a numerically controlled machine tool. The method may further comprise forming the blanks individually in a sheet metal forming operation, wherein the inner perimeter of the internal openings in the blank are expanded as the blank is formed. The rotary cutting tool may be a milling tool. The sheet metal part may be a body side panel for a vehicle that defines a door or window opening or may be another type of panel having an opening or a critical edge area that is expanded in subsequent forming operations. 
         [0008]    According to another aspect of this disclosure, a system is disclosed for manufacturing a sheet metal part from a blank defining an opening. The system comprises stacking a stack of blanks on a base with the openings generally in alignment. A machine tool including a rotary cutter removes material from the openings in the stack of blanks to form a machined blank edge. A forming tool subsequently forms and expands the machined blank edges in each of the machined blanks. 
         [0009]    The system may further comprise a clamping apparatus clamping the stack of blanks on the base while the machine tool cuts material from the openings. The base may include a spacer disposed below the stack of blanks providing clearance for the machine tool to cut material from all of the blanks stacked on the base. 
         [0010]    According to another aspect of the disclosure an article of manufacture is disclosed that comprises a blank defining an internal opening that is initially punched from a sheet metal segment. An inner periphery of the internal opening is formed as a machined surface. The machined surface may be a milled surface. The article of manufacture may be a body side panel for a vehicle and the internal opening may be a door opening, a window opening, or a relief opening. 
         [0011]    According to another aspect of this disclosure, a method is disclosed for manufacturing a sheet metal part by machining inside or outside edges of a blank. The method begins with the step of cutting a plurality of blanks each including a blanked edge from a plurality of sheet metal segments. The blanks are then stacked with the blanked edges generally aligned. The blanked edges of the plurality of blanks are then machined with a machining tool to a finish dimension. 
         [0012]    The above aspects of this disclosure and other aspects will be described below with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1 a    is an exploded perspective diagrammatic view of a blanking press for cutting openings in a blank and stacking a stack of blanks on a pallet or other supporting surface according to one aspect of this disclosure. 
           [0014]      FIG. 1 b    is a perspective view of one example of a body side panel blank. 
           [0015]      FIG. 2  is a perspective view of a numerically controlled machine milling the inner periphery of an internal opening in a plurality of blanks that are clamped in place with the openings in alignment. 
           [0016]      FIG. 3  is a fragmentary cross-section view taken along the line  3 - 3  in  FIG. 2  showing a rotary cutting tool removing material from the inner periphery of the internal openings in the stack of blanks. 
           [0017]      FIG. 4  is a diagrammatic perspective view of a draw die for a body side panel with a blank loaded into the die to be drawn into a desired shape. 
           [0018]      FIG. 5  is a flowchart illustrating the steps of the manufacturing process for forming a sheet metal panel including a large internal opening that is machined to remove edge defects. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The illustrated embodiments are disclosed with reference to the drawings. However, it is to be understood that the disclosed embodiments are intended to be merely examples that may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed are not to be interpreted as limiting, but as a representative basis for teaching one skilled in the art how to practice the disclosed concepts. 
         [0020]    Referring to  FIGS. 1 a    and  1   b,  a blanking press  10  is illustrated that includes an upper blanking die  11  and a lower blanking die  12  that cut large openings, such as a door opening  13 , window opening  14 , or relief opening in a blank  15 . The door opening  13 , window opening  14 , or relief opening are referred to as internal openings. The blank  15  is placed on a stack  16  of other blanks on a pallet  17  generally in alignment with a stack  16  of other blanks  15  when the internal openings are cut out of the blank  15 . The pallet  17  may be of the type used on a stamping press (shown in  FIG. 4 ) or may be a dedicated machining pallet. A space  18  is defined by the supporting member, or pallet  17 , below the internal openings to facilitate machining the internal openings in the stack of blanks  16 . 
         [0021]    Referring to  FIGS. 1   a,    1   b,  and  2 , inner peripheries  20  of internal openings  19  contain a band of highly work hardened material which may include edge defects (not shown) created when the internal openings  19  are blanked. The blanks  15  may be imperfectly stacked with some of the blanks  15  being offset relative to the other blanks  15  in the stack  16 . The blanks  15  are “generally aligned” on the stack meaning that the blanks  15  are stacked within +/−1 mm of the average stack location with the overall stack being +/−1 mm over the height of the stack  16 . 
         [0022]    Referring to  FIG. 2 , a plurality of blanks  15 , or stack of blanks  16 , is shown supported on a pallet  17  and sandwiched between a top plate  21  and the pallet  17 . The internal openings  19  in the stack of blanks  16  are held in place by a plurality of clamping members  22  that are shown engaging the top plate  21 . The top plate  21  functions to distribute the clamping loads applied by the clamping members  22 . Other clamping arrangements may also be used to apply a clamping load to the stack  16 . A numerically controlled machine  24  (herein after a “NC machine”) is shown with a rotary cutting tool  28 , or mill, that machines the inner periphery  20  of the internal openings  19 . 
         [0023]    Referring to  FIGS. 2 and 3 , the stack of blanks  16  is shown being compressed between the top plate  21  and pallet  17 . The rotary cutting tool  28  is shown performing a NC machine controlled milling operation on the inner periphery  20  of the internal openings  19 . The cutter  28  removes material from the inner periphery  20  of the stack of blanks  16  that may be milled as if it was a monolithic metal structure because of the pressure applied by the clamping members  22  to the top plate  21 . The NC machine  24  is initialized by aligning the NC machine  24  relative to the location of the stack  16  on the pallet  17 . The rotary cutting tool  28  includes a plurality of cutter inserts  30  that form a milled surface  32  on the abutting blanks  15  to a finish dimension. The machining operation may be performed with or without a machining lubricant. 
         [0024]    At least one metal thickness of the sheared edge, or blanked edge, is removed to facilitate subsequent hole expansion. The internal openings  19  may be milled up to  4  mm to compensate for stacking tolerance. 
         [0025]    As shown in  FIG. 3 , several machined blanks  34  are illustrated in the top portion of the stack of blanks  16 . The rotary cutting tool  28 , as illustrated, moves from the top of the stack of blanks  16  (as shown in solid lines) to the position shown in phantom lines at the bottom of the stack of blanks  16 . A spacer  36  is placed on the base  17 , or pallet, to allow the rotary cutting tool  28  to mill all of the blanks  15  in the stack of blanks  12  by providing a clearance area  38  defined below the stack of blanks  16  and above the pallet  17 . The spacer  36  and pallet  17  are shown as separate parts in  FIG. 3 . Alternatively, the space  18  may be defined by the pallet as shown in  FIG. 1   a.    
         [0026]    Referring to  FIG. 4 , a blank  15  for a body side panel (not shown) is disposed in a draw die  42  that is part of a press line that forms the body side panel. The sheet metal press  42  expands the internal openings  19  in individual blanks  15 . 
         [0027]    Referring to  FIG. 5  and with continued reference to the other drawings, the process is disclosed with reference to a flowchart  50 . The process begins by producing a blank  15  in a blanking press  10 , or punching operation, to form the outer periphery of the blank and internal openings  19 . At  52 , the blanks  15  are generally aligned and stacked into a stack of blanks  16 , however, some of the blanks  15  may be imperfectly stacked. Imperfectly stacked blanks  15  with misaligned internal openings  19  may be compensated for by subsequent machining to the finish dimension. At  54 , the stack of blanks  16  is clamped in a NC machine  24  that holds the blanks  15  together and generally in alignment. At  56 , the inner periphery  20  of the internal opening  19  is machined to the finish dimension of the milled surface  32 . After machining, the stack of blanks  16  is cleaned by brushing or blowing machining chips off of the stack  16 . At  58 , the blank  15  is separated from the stack of blanks  16  and each individual blank  15  is formed in a sheet metal press  42  to the desired overall shape of the finished part (not shown). 
         [0028]    While the method is described with reference to milling internal openings  19  such as door openings  13  and window openings  14 , the method is also applicable to smaller openings or outside trim edges that are subsequently stretched in the forming process. 
         [0029]    The embodiments described above are specific examples that do not describe all possible forms of the disclosure. The features of the illustrated embodiments may be combined to form further embodiments of the disclosed concepts. The words used in the specification are words of description rather than limitation. The scope of the following claims is broader than the specifically disclosed embodiments and also includes modifications of the illustrated embodiments.