Incremental Forming of CP-Al Sheets Using the Helical Tool Path Strategy

Abstract

Incremental sheet forming (ISF) is a novel die-less process for forming sheet metals at very low production time and cost, and is mainly used for small batch type productions. ISF process is usually carried on a 3-axis CNC milling machine using a hemispherical tool. The tool follows a predefined trajectory, created using the CAD geometry of the required component, which greatly influences the formability of the sheet material being formed. Process parameters, such as spindle speed, feed rate and pitch size, also influence the formability of the sheet material. Understanding the influence of these parameters on the formability of the sheet material is vital for improving the formability of the material and the present study is aimed for the helical tool path strategy of the ISF process, as the research in this area is very limited.
In the present study, ISF experiments were performed on 2 mm thick commercially pure Al sheets using the helical tool path strategy. An axisymmetric dome of 80 mm diameter was formed for different combinations of tool speeds (50, 500 and 3000 rpm) and feed rates (50, 1000 and 2500 mm/min) in a CNC milling machine with a 10 mm hemispherical forming tool. The obtained parts were scanned using the FAROARM Laser scanner and analyzed for springback, amount of thinning and maximum forming depth using the Solid Works software. The results showed that when the tool speed was increased by keeping the feed rate constant, the forming depth and amount of thinning were increased. On contrary, when the feed rate was increased by keeping the tool speed constant, the forming depth and thinning were decreased. The forming depth was found to be higher (i.e. 38.83 mm) for the higher tool speed (i.e. 3000 rpm) and lower feed rate combination (i.e. 50 mm/min), and lower (i.e. 33.56 mm) for the lower tool speed (i.e. 50 rpm) and higher feed rate (i.e. 2500 mm/min) combination. The amount of thinning was always higher along the sidewalls of the dome and maximum at the higher wall angle region. Springback increased greatly when the feed rate was increased rather than for the increase in tool speed. Maximum springback of - 17.6% was observed for the higher feed rate (2500 mm/min) and lower spindle speed (50 rpm) combination, and minimum springback value of -4.6% was recorded for the higher spindle speed (3000 rpm) and lower feed rate (50 mm/min) combination. Frictional heating between the tool and sheet metal, and dissipation of heat were found to attribute for the different formability behavior of the material.