Incremental Forming as a Rapid Tooling Process

Product development takes advantage of the use of computer-aided design (CAD) systems to define the geometry and its various dimensional characteristics. Besides, the product’s feasibility can be predicted using computer-aided engineering (CAE) software for the analysis of product performance and for the simulation of manufacturing processes without the need for physical prototypes. While this iteration strongly improves the probability of success, in many cases, a physical assessment of the real component is still needed. This often requires the creation of prototypes and tools to be produced, becoming one of the most time-consuming and costly phases in the development of new products.

The employment of rapid tooling (RT) techniques allows the development of tools for processing different materials by various technologies in a fast and inexpensive way. In such a way, RT offers great advantages both to the product development and production set-up, allowing the achievement of faster and better solutions.

The production of sheet metal parts has long been associated with either skilled manual labour or to the use of expensive tooling for mass production. This led to two classical application fields: the manufacture of unique parts with a high cost and low accuracy, and the mass production of parts after a high tolling investment. The development of incremental sheet metal forming technologies, first introduced as incremental dieless forming in the 1960s and recently studied and developed since the 2000s, has created the opportunity to industrially manufacture unique or low volume sheet metal parts at a low cost and better and repetitive accuracy. Among other applications like prototyping, low volume production and customization, these new processes lead to a new possible method for rapid tooling. To understand the ISF operation principle, as well as limitations, is fundamental to grant a feasible sheet metal part design. These perceptions are indispensable for the process of sheet metal rapid tool development.

Incremental forming alone, as all available manufacturing processes, has limited achievable part in geometry. Thus, to increase the design freedom, it is useful to include other processes in sheet metal tools fabrication. Numerous sheet metal forming processes require the need of dedicated tools, thus not suitable for the manufacturing of unique parts. Nevertheless, some are dieless or use multipurpose tools a could be employed in the manufacturing of sheet metal tools. Apart from the sheet metal forming itself, tool development always requires other processes for preparing blanks, trimming formed parts, linking formed parts into more complex geometry assemblies, and finishing surfaces. A sheet metal tool development results from an ingenious use of a large number of manufacturing technologies, both using state-of-the-art automated processes and long-established metalwork, often very human skill dependent.

Whatever the manufacturing process being used, a correct dimensioning is essential for the development of feasible and reliable tools. Thus, attention must be paid during the tool design for successful use. Generally, tool dimensioning should consider the fulfilment of geometric, mechanical loading and thermal requirements of the process where they are to be used. A sheet metal tool should be designed to mimic the operation of conventional tools. Thus, it must consider both the correct geometry of the target part as well as the possible manufacturing process awarenesses as material shrinkage, demoulding possibilities and clamping and positioning systems. Besides, the geometric possibilities for the sheet metal parts must be considered, exploring not only the potential of ISF processes but also other flexible forming techniques. From the mechanical point of view, the tool development should consider its operation loading in the selection of material and thicknesses, including the possible use of supports and reinforcements. The thermal behaviour of the parts may also influence the tool design. Further, the understanding of thermal behaviour of tools helps to validate their use and defining process cycle time.

The use of sheet metal tools finds its main applicability for processing thermoplastic and thermoset materials, in which the moulding loads and temperature are low. ISF rapid tools have their core parts formed by incremental processes taking advantage of the free-form capability and flexible manufacture. Other complementary operations are used to finish the tools in a fast and low-cost way. A reference geometry has been used to design a set of parts to be manufactured using different manufacturing processes. All parts were detailed to allow a feasible manufacturing process, including the addition of radius between sides and other design features in some walls. The distinct shapes are used in hand moulding operations, vacuum forming, rotational moulding and compression moulding. The proof of concept tests validates the direct rapid tooling techniques using incremental metal forming, although they also confirm the course accuracy reachable which influence the method selection. The tests use a highly available and low-cost 1050 aluminium alloy with 2 mm thickness. This material limits the maximum loading to a significantly low value, although it proves to be adequate for the moulding operations.