DRY TURNING OF COMMERCIALLY PURE ALUMINIUM WITH CARBIDE TOOLS

Dry turning test was performed on commercial pure aluminum Al1100 with two grades of carbide (WC-Co) tool, fine and coarse grained grades. Because of the tiny amount of abrasives in Al1100, the resulting tool wear is mainly sliding wear on flank surface. In our experiment, the fine grain carbide tool has more wear than coarse grain carbide tool despite of the miniscule wear on both carbide grades tools. Notably, the micro fracture was only observed on the fine grain carbide tool's nose due to the low fracture resistance of fine grain carbide. Using Confocal Laser Scanning Microscopy (CLSM) and wavelet filtering, the built up edge (BUE) and tool wear evolutions were analyzed. The volume of BUE becomes the maximum at the beginning of the machining and diminishes as the cobalt was worn down from the tool surface, eventually reaching a relatively steady state after half hour's turning. The fine grain carbide tool have more built up edge than coarse grain carbide tool because of the higher cobalt content with the fine grain carbide. Oxygen from the air may play a very important role in the adhesion between aluminum and carbide tool. Two types of built up edge was found in the experiment. The first type BUE is huge and covers whole tool surface, which is mainly aluminum. The second type BUE is very thin (similar to 1-2microns), which covers relatively small area of tool surface. This location is characterized by both high temperature and the presence of the oxygen from the air trapped between tool and work material. This second type of BUE has much better resistance to the NaOH solution, which is metal oxide (Aluminum oxide or complex oxide such as spinel), and it could increase the adhesion between tool and work material. Mainly, in dry turning commercial pure aluminum, the larger carbide grain size has a better wear performance.