TECHNICAL FIELD

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

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.

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.

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.

This disclosure is directed to solving the above problems and other problems as summarized below.

SUMMARY

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.

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.

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.

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.

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.

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.

The above aspects of this disclosure and other aspects will be described below with reference to the attached drawings.

