In the prior art, various methods and apparatus have been proposed to shape or form metals, both in the hot or cold state. When forming sheet metal, often times a press is used. The press is usually driven by mechanical or hydraulic action and contains a male die or punch and a female die. In use, a metal blank is placed between the dies and subjected to mechanical or hydraulic press forces by one die being driven against the other die. The dies are appropriately shaped to impart a given shape or form to the metal blank. One particular application of this type of metal forming entails manufacturing the internal and external plates for stamped mufflers.
In place of mechanical or hydraulic forces, high pressure fluid can be employed to form a given metal part. U.S. Pat. No. 5,435,163 to Schafer discloses an apparatus for hydraulically shaping a hollow body. The apparatus includes a stationary base, a die fixed on the base and formed with a cavity having an inner surface and axially oppositely open ends so that a tubular workpiece can be held in the cavity with ends of the workpiece exposed at the cavity ends. A pair of pistons fittable with the workpiece ends are arranged at the cavity ends. Actuators are provided which can displace the pistons toward each other and against the ends of the workpiece in the cavity. The hydraulic liquid is fed at high pressure through one of the pistons to an interior of the workpiece in the cavity to deform the workpiece. The hydraulic shaping described in the Schafer patent is commonly referred to as hydroforming and is often used in the manufacture of exhaust system components, particularly, tubular components.
The metal forming methods described above are not without their disadvantages. First, metal forming presses are extremely expensive, costing as much as $500,000 or more. With this expense, it is often necessary to operate these presses in a batch manner. That is, the presses are employed to produce a large number of pressed parts at one time. The pressed parts are subsequently integrated into a continuous manufacturing line to assemble and/or manufacture a desired component. As an example, stamped mufflers may comprise two internal plates and two external plates. When using a mechanical or hydraulic press, a large number of each of the muffler components are stamped in a batch operation. The stamped plates are then later assembled to form the stamped muffler. With the combination of a batch operation and a continuous operation, manufacturing productivity is compromised. Moreover, given the high rate of speed of mechanical presses, it is difficult to perform a quality control operation after each stamping, i.e., stampings may be done at the rate of one per second. Consequently, total quality control may require intermittent checks at the batch pressing operation and subsequent checks as part of the continuous manufacturing operation, thereby slowing down overall productivity.
Methods and apparatus employing hydroforming techniques are also disadvantageous. Many times, due to the high pressures required to form metal parts, an external force must be applied to the hydroforming dies to assure that they do not separate from the part to be formed. However, since the pressures used in hydroforming are extremely high, e.g., 1500 bar, it is difficult to keep the die halves together without resorting to complex and expensive devices.
The hydroforming and mechanical or hydraulic presses described above also require complex tooling. This tooling not only contributes to increases machinery cost, but requires longer lead times prior to initiating production runs.
In view of the drawbacks of the above-described prior art apparatus used to shape metal, a need has developed to provide an improved metal forming apparatus and method which overcomes the aforementioned disadvantages.
In response to this need, the present invention provides a metal forming apparatus and method which is low in cost so it can be integrated in a continuous production or manufacturing line effectively. The inventive apparatus and method also require simpler tooling to minimize cost and does not require long lead times or the use of external forces other than those required for metal shaping.