Experimental Investigation of a Backing Sheet Stiffener in Incremental Forming of Polycarbonate

Single point incremental forming (SPIF) is a dieless forming process for sheet materials. This process forms materials with a hemispherical forming tool which locally deforms the sheet at incremental depths. The freeform nature of this process promises significant efficiency improvements within small and medium volume industries where stamping is traditionally used. However, several drawbacks currently inhibit its widespread use. One of these drawbacks is springback or elastic recovery resulting in reduced geometrical accuracy. An existing approach to counter this involves using a dedicated backing die, increasing the cost of the forming apparatus and the overall energy input per part. Other springback reduction methods involve the direct addition of energy to the workpiece through electrical or heat input. This study investigates the use of sacrificial steel blanks as backing dies for incremental forming of polycarbonate sheets, to overcome the loss in geometrical accuracy affiliated with forming geometries with a relatively large distance between the geometry periphery and the clamped edge. The blanks were not bound to each other, but rather clamped along their edges. In this study, polycarbonate blanks were tested using a three-factorial design of experiments, with relative plate thicknesses of 0.4, 0.5, and 0.6, and wall angles of 15°, 30°, 45°, and 60° as independent factors. The test geometry used was a straight walled pyramid with a square base. Using the backing sheet, a reduction in the springback was observed, demonstrating the effectiveness of sacrificial backing blanks. Particularly, the ‘pillow effect’ at the base of the geometry was reduced. This is attributed to the higher stiffness of the steel plates, increasing the plastic strain on the polycarbonate. However, the formability is found to decrease for higher values of the backing plate thickness due to premature steel failure. In future studies, this work will be expanded to include additional thickness ratios, geometries, toolpath types, step sizes and materials to form a more complete trend.

Numerical Determination of Unconstrained Area Effect on Springback in Incremental Forming of 5052-H32 Aluminum

Incremental forming (IF) is a novel sheet material forming process which promises significant energy savings within the low and medium volume sheet production industries. This advantage stems from IF’s dieless forming nature, which alleviates the need for time and energy input towards die fabrication and offers significantly greater flexibility. However, a distinct disadvantage of this process is its relatively low forming rate compared to conventional stamping, which reduces its feasibility of use in higher volume productions. Springback is one disadvantage of incremental forming which has hindered its implementation within industry. Spring-back reduction methods, as well as springback characterization, can be found throughout literature. However, very few publications disclose the clamping dimensions used for fixturing work-pieces. This study numerically determines the springback effect of utilizing various clamping structures and presents an empirical solution for determining the springback of truncated pyramid geometries for various constraining areas. The resulting equation was found to have an acceptable degree of error relative to experimental analysis.

Shape Indexes for Dieless Forming of the Elongated Forgings with Sharpened End by Tensile Drawing with Rupture

The criteria for the assessment of the form change in the process of direct profiling of workpieces , applying the stretching method with a rupture are developed, methods for their calculation are proposed with allowance for the volume of the redistributed metal and energy costs for deformation. The nature of the functional connection of these criteria of shape change assessment with the work of deformation is determined.

A Mixed Double-Sided Incremental Forming Toolpath Strategy for Improved Geometric Accuracy

Double-sided incremental forming (DSIF) is a relatively new dieless forming process which uses two hemispherical ended tools, one on each side of the sheet, moving along a predefined trajectory to locally deform a peripherally clamped sheet of metal. DSIF provides greater process flexibility, higher formability, and eliminates the tooling cost when compared to conventional sheet forming processes. While DSIF provides much improved geometric accuracy compared to other incremental forming processes, current toolpath planning strategies suffer from long forming times. A novel mixed double-sided incremental forming (MDSIF) toolpath strategy is proposed in the present study. It simultaneously reduces the total forming time by half while preserving the best currently achievable geometric accuracy. The effect of the forming parameters, i.e., of the incremental depth and of tool positioning on the geometric accuracy of the parts formed with MDSIF was investigated and compared to those formed by traditional DSIF strategies.

A New Incremental Sheet Forming Process Based on Layer Manufacture

Sheet dieless digital forming is a new sheet metal dieless forming technology. This paper introduced the fundamentals of the Sheet dieless digital forming process. Based on the principle of “layered manufacture” in rapid prototype technology, this process resolves the intricate three-dimensional geometry information of the workpiece into a series of two-dimensional data, which can be used by an NC system to control a forming tool to make a curvilinear movement over the raw sheet metal layer by layer until the component wanted is formed. This paper introduced the Sheet dieless digital forming system and metal digital forming technology.