Presence of waviness in the incremental sheet forming has a detrimental effect on the surface quality of parts, especially on the appearance of those covered with paint. In this paper, the effects of tool diameter, feed rate, spindle speed, and vertical step have been studied on the surface waviness using an innovative method. The proposed method is based on the root mean square deviation of the height of the points located on the wavy surface. In this way, some points are selected on the formed wall and their coordinates are measured using a coordinate measuring machine. Taguchi design of experiments and the analysis of variance are used for studying and optimizing the effects of the four process parameters and their combinations to minimize the waviness of the formed wall. The results show that by reducing the vertical step and increasing the tool diameter, the waviness is decreased. It is also found that the feed rate and the spindle speed have little effect on the waviness. Additionally, from a confirmation test, the results illustrate that the Taguchi method and the analysis of variance provide an efficient and effective method for determination of the optimum level of each process parameter to have the minimum surface waviness.

Flexibility and simple tooling make the incremental sheet forming (ISF) a great process to create complex shapes from mild steel sheets. It is a significant issue to reduce the surface roughness (SR) which is a weakness in the manufacturing of the mild steel parts in ISF process. SR has an adverse effect on the esthetic aspects of the mild steel products or their painting appearance. The purpose of this study is to investigate the effects of the ISF process parameters on the SR of the mild steel sheets. Feed rate, tool diameter, vertical step and spindle speed are chosen as four input variables in the experimental tests. Taguchi design of experiment and the analysis of variance(ANOVA) are used to optimize the SR by investigating the parameters effects and their interactions. According to the obtained results, the vertical step reduction and increase in tool diameter, decrease the roughness on the surface of the mild steel sheets during the single-point incremental forming. In addition, the tool speed (rotation and feed) has little effect on the SR. The results of a validation test demonstrate that the Taguchi technique and the ANOVA, effectively optimize the level of each variable to ensure the best SR.