Zhaobing Liu

Vertical Wall Formation and Material Flow Control for Incremental Sheet Forming by Revisiting Multistage Deformation Path Strategies

In this article, multistage deformation path strategies for single point incremental forming (SPIF) are revisited with the purpose of controlling material flow (improving sheet thickness distribution) and forming a vertical wall surface for cylindrical cups. It is noted that stretching and thinning are two main deformation modes during SPIF. How to control material flow in an optimal way is a key point for successful forming. Multistage incremental forming shows more advantages than single-stage forming, especially dealing with shapes with steep walls. In this study, three basic multistage deformation path strategies have been proposed, that is: A. incremental part diameter; B. incremental draw angle; and C. incremental part height and draw angle. Those strategies and their combinations have been evaluated in terms of formability and compared in order to understand the material allocation mechanism and optimize the multistage forming process. In addition, approximate plane-strain analysis models have been given to provide formability predictions between single-stage and multistage strategies, and between strategies B and C, respectively. The prediction results show good agreement with the experimental results. It is demonstrated that the strategic combination A + B is the optimal way to achieve the forming target.

Modeling and Optimization of Surface Roughness in Incremental Sheet Forming using a Multi-objective Function

As a critical product quality constraint, surface roughness is regarded as a weak point in incremental sheet forming (ISF). It is of great importance to identify the impact of forming parameters on the surface roughness and optimize the surface finish at the production stage. This paper proposes a systematic approach to modeling and optimizing surface roughness in ISF. The quantitative effects of four parameters (step down, feed rate, sheet thickness, and tool diameter) on surface roughness are analyzed using the response surface methodology with Box–Behnken design. The multi-objective function is used to evaluate the overall surface roughness in terms of the tool-sheet contact surface roughness, i.e., internal surface roughness and the noncontact surface roughness, i.e., external surface roughness. Additionally, the average surface roughness (R a) on each surface is measured along the tool-path step-down direction taking the impact of sheet roll marks into account. The optimal conditions for the minimization of overall surface roughness are determined as step down (0.39 mm), feed rate (6000 mm/min), sheet thickness (1.60 mm), and tool diameter (25 mm). This study shows that Box–Behnken design with a multi-objective function can be efficiently applied for modeling and optimization of the overall surface roughness in ISF.

Simulation and Experimental Observations of Effect of Different Contact Interfaces on the Incremental Sheet Forming Process

Incremental sheet forming (ISF) is a promising forming process perfectly suitable for manufacturing customized products with large plastic deformation by using a simple moving tool. Up to now, however, the effects of contact conditions at the sheet interface are not well understood. The aim of this work is to study the effect of tool type and size on the formability and surface integrity during the forming process. Experimental tests were carried out on aluminum sheets of 7075-O to create a straight groove with four different tools (ϕ 30,ϕ25.4,ϕ20 andϕ10mm). One tool tip was fitted with a roller ball (ϕ 25.4mm) while the other three were sliding tips. The contact force, friction and failure depth were evaluated. A finite element (FE) model of the process was set up in an explicit code LS-DYNA and the strain behavior and thickness distribution with different tools were evaluated and compared with the experimental results. This study provides important insights into the relatively high formability observed in the ISF process. Microscopic observations of the surface topography revealed that a rolling tool tip produced better surface integrity as compared with a sliding tool tip, wherein, distinct scratch patterns in the tool traverse direction were evident.