Sheet metal forming is a manufacturing process
Adaptation of a new die set for repetitively metal stamping sheet metal parts to a part design specification is simplified by using a math-based simulation of the metal stamping operation under specified engineering metal stamping conditions for the specified part. The metal stamping simulations are used to create an engineered draw-in map comparing selected locations on the peripheral edge of the stamped part with corresponding locations on the peripheral edge of its original sheet metal blank.
The resulting map of sheet metal draw-in dimensions reflect suitable displacements of the metal sheet between the binder ring and binder surface of the female die member at all such locations as the punch member of the die set executes its metal stamping operation. The engineered draw-in dimensions for a simulated part identify specific locations for adjustment of the binder ring/binder surface system in adapting the die set for production of parts.
A conventional three-component die set for metal stamping sheet metal parts consists of a punch, a binder ring and a female die. Such die sets are used to make many strong and light weight articles of manufacture. These articles include, for example,automotive body panels and other structure parts; aircraft and appliance sheet components; and beverage cans. Families of formable ferrous and aluminum sheet metal alloys have been developed for these manufacturing processes.
In a typical sheet metal forming operation, a flat blank of the metal is held at its periphery over the shaped cavity surface of a female die and the sheet is pulled into the cavity and against the shaped surface using a punch with a formingsurface complementary to that of the female die. The sheet is drawn and stretched between the tools and assumes a desired shape. In making stamped parts such as automotive body panels, often characterized by deep pockets and small radii bends, thepanel may be formed in stages using two or more sets of metal stamping dies each operated in a suitable hydraulic press.
In sheet metal stamping operations the blank is clamped at its periphery against the marginal surface of the female die cavity with a blank holder called the binder ring. The interaction between the binder ring, the interposed sheet and thebinder portion at the margin of the female die is critical to making a part that is formed free of wrinkles or tears. The binder ring has a bead that presses adjacent sheet metal into a complementary depression, a trough, in the binder portion of thefemale die to create proper restraining forces that prevent the sheet metal from being drawn to the die cavity too freely or too restrictively.
In a traditional die development and making process, a die is designed based on previous experience, and the die is validated through a series of physical tryouts. These tryouts are time consuming and costly and cannot guarantee the success ofthe die developments. For a typical automotive body panel, say a fender, the tryout alone could last twelve months and cost more than one million U.S. dollars. Today in math-based die development practice, the design of a die can be evaluated andreshaped through electronic tryout via advanced metal stamping simulation technology that consists of metal stamping CAE (computer aided engineering) programs, sheet metal forming simulation software (e.g., Pamstamp? and Dyna3D?) and high performancecomputers.
After the die sets for a vehicle body panel, for example, are designed or developed successfully in the digital world, the dies are constructed and tried out in a tooling shop. However, there are differences between the engineering of a die setand its everyday use in a manufacturing operation. And there are differences in results obtained between digital simulation of die operation and physical parts produced in a metal stamping plant. One aspect of the problem is that die makers are not sofamiliar with math-based die engineering principles that they can make good use of the math-based work in tuning actual dies for everyday metal stamping operations and ordinary sheet metal material. Therefore, physical tryout periods for each set ofmanufacturing dies can still take weeks or months because there has been no robust procedure by which manufacturing people can detect and correct differences between an actual die set and the math-based simulation from which it was built.
It is an object of this invention to provide a process for conforming actual sheet metal metal stamping experience using a specific die set with state-of-the-art math-based simulation of the die set and metal stamping operation. It is a more specific objectof this invention to provide a process for using the exact amount of sheet metal drawn in over the binder ring at selected locations around the periphery of the blank as a practical and effective basis to conform the operation of the physical die set tothe simulated performance of the virtual die set.
Die tryout workers can use the engineered draw-in map as a basis for correcting actual draw-in of the blank on the real die set. Where the sheet metal draw-in distance on the trial part is larger or smaller than the map dimensions suitablecompensation adjustments are made to the bead shapes to reduce or increase sheet metal flow. Invariably, as the actual draw-in values around the periphery of formed parts are brought into conformity with the simulated metal stamping draw-in values, good partsare produced.
The advantage of this invention is that die tryout workers can focus on draw-in of the sheet metal as the part is formed, one of the occurrences that they regularly observe in the making of each metal stamping. Now, with the use of the engineereddraw-in map, die tryout workers can more efficiently approach the die tryout process by conforming actual sheet metal draw-in dimensions with the math based simulation draw-in map and, where necessary, making adjustments to the beads at specificlocations identified from the draw-in map.