Conventional sheet metal-forming technologies are mainly suitable for mass production due to the requirement of specific and complicated mechanical tools, which inevitably incurs a long lead time and high material and process costs. Since the 1980s, great effort has been made to meet the demand for the small-lot production of sheet metal parts, and a variety of fast or dieless sheet-forming methods have been proposed and studied extensively. For example, He et al. (2000)  discussed the explosive forming of thin-wall semispherical parts, and the design principles of such shell structures and related technological parameters were introduced. Yarlagadda et al.  used a combination of stereolithography and nickel eletroforming processes to develop a rapid tool (RT) for the production of sheet metal drawing. The tools were then evaluated by forming components with 0.8-mm aluminum sheets. Yoo and Walczyk  studied the design and development of an RT called profiled edge laminate tool, involving the assembly of an array of laminates, with the top edges being simultaneously profiled and beveled according to a CAD model of the intended surfaces. Zhang et al.  investigated rapid hard tooling by plasma spraying for injection molding and sheet metal forming. To improve the durability of the tool, composite materials made of ceramic and metal powders were used as the sprayed original mold materials. Male et al.  studied plasma-jet forming, and a robotic system was used to manipulate a nontransferred arc plasma torch to locally heat sheet metal. Thermal conductivity was the principal physical property affecting the bending behavior. Lasers can also be used as controllable heat sources to bend metal plates into complex 3D shapes by generating thermal stress in the materials. Kyrsanidi et al.  proposed an analytical model for predicting the distortions caused by the laser forming process. Bachmann et al.  stated that laser forming can address two notable shortcomings of metal 3D printing, namely, large structures and thin structures. This method has been applied to shell fabrication in the shipbuilding industry. Shulkin et al.  developed an eight-point blank holder force control system in a viscous pressure forming (VPF) machine, and Liu et al.  confirmed that the formability of a sheet stretched with VPF is higher than that of a sheet stretched with a hard punch due to the lower interface friction. Liu et al.  optimized cushion conditions in micro multipoint sheet forming to obtain better surface quality and thickness distribution. Li et al.  used a sparse multipoint flexible forming tool to obtain doubly curved shapes of AA2050-T34 plates in creep age forming.
In recent years, flexible forming methods based on CNC technologies, especially incremental sheet forming and its variations, have received widespread attention. For example, Wu et al.  proposed a multistep strategy to solve the local thinning problem of parts with steep walls in single point incremental forming (SPIF); Milutinovic et al.  studied the geometric and physical properties of a stainless steel denture framework made by SPIF; Wen et al.  modified bar tools in SPIF to form thin-walled parts with nonbiaxial stretching deformation features; Jurisevic et al.  applied laminated supporting tools in water jet incremental sheet metal forming; Cui et al.  studied electromagnetic incremental forming (EMIF), where the part is shaped by accumulating the local deformations caused by the small discharge energy at high speed. Wang et al.  investigated the friction stir-assisted SPIF of aluminum alloy sheets to achieve higher formability and surface quality.
In the existing technologies for rapid and economical sheet metal forming, stamping with soft tools has the same deformation mode as conventional stamping processes, and it is one of the few methods that can meet the quality and precision requirements in industrial fields such as automobile manufacturing. This is important for sheet metal parts that need functional testing, since they must be representative of the actual performance. Various materials are used in soft tooling, including low-melting-point alloys, resins, and concrete. For instance, Durgun et al.  utilized bismuth MCP 137 alloy, a recyclable low-melting-point alloy, to manufacture rapid tools for producing sheet metal parts. More inaccuracies occurred during the tool-making stage rather than during press forming, and the usable tool life was significantly shortened by harder and thicker steel sheets.
The lack of strength of soft tools makes it difficult to form the required clear and delicate geometric features, and the usability is limited. In this situation, much work has been done to improve the strength and durability of soft tools. For example, Kuo and Li  examined the effect of ZrO2 addition on the mechanical properties of epoxy resin dies for sheet metal forming. They confirmed that an epoxy resin material filled with 30 wt% ZrO2 particles had the highest wear resistance. Kleiner et al.  investigated sheet metal hydroforming dies made of ultrahigh performance concrete (UHPC) with a compressive strength of approx. 250 MPa and a Young’s modulus of approx. 50 GPa. Although the formed parts had good shape accuracy, the required internal pressure could not be withstood by the UHPC die in the case of small part radii.
Overall, as Schuh et al.  summarized, “currently there is no suitable technology for the economic production of deep drawn parts in low quantities” due to the various drawbacks of existing technologies for rapid sheet metal forming. To improve the usability of soft tools, this paper proposes a new structure of a zinc alloy die by combining traditional soft tooling and additive manufacturing (AM) or 3D printing (3DP) technologies. A technical route for developing the new tool was constructed, and a W-shaped part with sharp corners was formed to evaluate the feasibility of the method.