No abstract

The present paper deals with incremental sheet forming (ISF), a metal forming process developed in the last 20 years. Main advantages characterising this technology are its high flexibility and the possibility of reducing development times and costs. ISF consists of a simple hemispherical tool, moved by a CNC machine or a robot, which locally deforms a metal sheet moving along a defined path. The desired part profile can be obtained using three ISF techniques: single point incremental forming (SPIF) and two points incremental forming (TPIF) with either negative or positive die. In this work, a part, whose geometry was chosen to be representative for sheet formability through ISF, was formed considering the different ISF techniques. Moreover, the influence on the produced part of the adopted tool path step depth increment was investigated. Experimental tests were conducted and the results were analysed in terms of forming forces, material formability, process accuracy and final part thickness.

Incremental sheet forming is a technique that allows locally deforming a sheet by means of a movable punch. Even if it requires longer forming time and higher part geometrical tolerances with respect to traditional sheet forming techniques, it does not need dedicated devices and its accuracy can be improved adopting low cost full or partial dies. For these reasons, it results to a flexible technology and economically suitable for low volume batch productions such as pre-series, prototypes or high customised parts. These characteristics well fit with prosthesis manufacturing where each part is a unique product, indeed its geometry needs to meet the patient's physical characteristics. In the present paper, titanium ISF formed parts will be studied, in particular surface anodising pre-treatment effects on part finishing and biocompatibility are investigated.

Tube hydroforming (THF) technology is receiving much interests in automotive and pipe industry thanks to its advantages in terms of final part quality and manufacturing costs. In THF a tube is placed in a die and is expanded by means of high pressure filled-in media. The sealing and the material feeding are guaranteed by two punches that plastically deform and then push the tube edges. To obtain sound parts, the tube expansion zones still represent a criticalness in THF, in fact the severe thinning the tube can undergo in those areas leads to bursting before the die is completely filled. Consequently, the high friction acting on the tube prevents the material flow towards the expansion zones. In this work, an experimental test campaign will show how unbalanced friction conditions can influence the material flow and the geometry of the expanded material in Y-Joint pipes hydroforming. In fact, studying a semi-free expansion of the tubes using different feeding zones length, the tube expansion will follow its free evolution that depends on the imposed unbalanced conditions at the tube edges.

In addition to its technical and economical advantages, Incremental Sheet Forming (ISF) has been recognized as an environmentally friendlier process in comparison to its conventional counterparts. As a result, during the past two decades ISF has been the central topic of different research groups trying to overcome the barriers limiting its use as a widespread manufacturing process. Aiming to improve the geometrical accuracy of ISF, University of Brescia has been working with TPIF using both experimental and numerical approaches. Among others, an ISF process representative geometry has been the focus of previous studies where different parameters were varied in order to quantify their influence in the results. Besides the insight obtained from this strategy, a rich database of experimental results has been generated which allows to validate numerical models. Following this trend, the present work presents recent advances in the simulation of TPIF. Initially, numerical results were compared to experimental measurements in order to assess the robustness of the modeling technique. Finally, as a first step to improve the accuracy of numerical predictions, the influence of modeling parameters in the force results was investigated.