Rapid Prototyping for Sheet Metal Products

Nguyen Duc-Toan and Hoang Long

## Abstract

The aim of this chapter is to evaluate and predict forming limit and then to improve and develop the incremental sheet metal forming (ISMF) processes for complex surface products of sheet metal. The theoretical study was first overviewed and synthesized in order to recognize the effect of geometry, technology parameters, and processing conditions on ISMF process. Finite element method (FEM) simulation study was then used to compare the accuracy of constitutive material models and fracture criteria and propose new equations in order to improve the prediction of FEM simulation for incremental sheet metal forming process. To develop a new technique for improving the formability of sheet metal using ISMF, FEM was also adopted to reduce the cost and time of research. The basic experimental studies were performed to determine the input data for FEM simulation such as tensile data, fracture parameters, and so on. To investigate and compare the simulation results, the incremental sheet metal forming processes for complex shapes were also conducted.

Keywords: rapid prototyping, ISMF, tool path generation, FEM simulation

#### 1. Introduction

In recent years, various methods for sheet metal deformation have been developed including incremental sheet metal forming (ISMF). ISMF has been bringing about many effects for small series production and in rapid prototyping of products. ISMF now becomes the leading research and development (R&D) topics in the manufacturing industry. ISMF is a sheet deformation method that uses simple settings: the deformation tool is a spherical round cylinder without a blade, and the metal sheet is fastened on a support to allow the sheet to deform according to the supported mold. The supported mold can be made of simple materials such as wood, plastic, composite, and so on, so that there is no need for expensive specialized molds. To receive tool paths for a complex shape, the CAD 3-D model of the finished part must be designed. The 3D model will be transferred to the CAM environment to simulate a reasonable tool path. Depending on the shape and complexity of the forming part, the machining process may or may not need a support mold. Table 1 lists the practical applications of the ISMF method that has been manufactured in different countries around the world. Figure 1 illustrates the rapid prototyping products of this technology [1].

ISMF processing is a continuous forming process until plastic deformation occurs locally in a small area beneath the forming tool. The deformed shape is a


2. Incremental sheet metal forming

Rapid Prototyping for Sheet Metal Products DOI: http://dx.doi.org/10.5772/intechopen.88435

ISMF is an innovative process for manufacturing sheet metal products by numerical control machines (CNC) based on simple forming tools for plasticity deformation to form metal sheets according to the desired shape. The controllable motion of the forming tool allows deforming three-dimensional profiles. This forming method offers many advantages in rapid prototyping of sheet metal products, which were directly constructed from CAD 3-D models to a complete traditional product without middle stages for designing and manufacturing molds. There are two main deformations of ISMF according to concave surfaces (Figure 2a) and convex surfaces (Figure 2b). They show the workpiece surface where the tool is shaping motion. The actual experimental setup used in ISMF is shown in Figure 3. The forming limit curve (FLC) of ISMF process is much higher than the forming limits calculated from the theory of plasticity as well as obtained from traditional test [2]. The forming limit curve from conventional deformations is V-shaped. But, recently studies have shown that ISMF process achieved greater formability and FLC shape almost like a straight line with negative slope in the principal limit strains (major strain, ε1, and minor strain, ε2). In order to estimate the forming limit curve

at fracture (FLCF) in ISMF for a cold rolled, Nguyen et al. [3] proposed the combination method for predicting FLC based on in-plane test (M-K model) and ductile fracture criterion of Clift et al. [4]. In the previous study [5], cold rolled steel sheet improved formability by ISMF process and is also used to manufacture automotive structure [6] as shown in Figure 4. In ISMF process, the effects of parameters such as size-step, tool-down step, tool radius, etc. on formability are very

2.1 Basic concepts

Figure 2.

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Forming concave surface (a) and convex surface (b).

Table 1.

Potential application areas for ISMF [1].

#### Figure 1.

Rapid prototyping products from ISMF: (a) dental, (b) medical, (c) headlight, (d) sculpture, (e) automotive cover.

combination of forming movements in the local plastic deformation region. The deformation process is slow and time-consuming, so it is only suitable for rapid prototyping of products or in series production. However, this method allows for greater formability than conventional deformation methods of material sheet. Forming tools are simple and inexpensive and develop products in a short time.

This method contains new and creative contributions in sheet metal forming such as:

