The influence of tool coatings in machining of magnesium

Magnesium is the lightest metal used in construction and therefore offers the greatest potential for weight reduction. The automotive industry in particular has an upcoming interest in the use of magnesium alloys. To observe the interactions between workpiece material and tool material and coating, respectively, turning experiments were carried out machining the alloy AZ91 HP. When machining magnesium dry, flank build-up due to adhesion between cutting tool and workpiece can occur at cutting speeds of v c = 900 m/min and more for uncoated and TiN-coated cemented carbide tools. Tools with either polycrystalline diamond (PCD) insert or coating can be used to reduce friction and adhesion in the tool-workpiece contact resulting in low machining forces as well as a superior surface quality even at high cutting speeds of v c = 2400 m/min. PCD coatings can also be applied to complex tool geometries. As tool wear can hardly be observed when machining magnesium alloys, a magnesium-based metal matrix composite (MMC) is machined to combine the adhesive effects of magnesium with the abrasive load caused by a reinforcement component. Excessive tool wear can be observed for TiN-coated carbides even at low cutting speeds of fv c = 100 m/min. PCD coatings show better results but cannot compete with tools having a PCD insert if a low film thickness is chosen.