Dry Machinability of Aluminum Alloys

Adverse effects of the use of cutting fluids and environmental concerns with regard to cutting fluid disposability is compelling industry to adopt Dry or near Dry Machining, with the aim of eliminating or significantly reducing the use of metal working fluids. Pending EPA regulations on metal cutting, dry machining is becoming a hot topic of research and investigation both in industry and federal research labs. Although the need for dry machining may be apparent, most of the manufacturers still consider dry machining to be impractical and even if possible, very expensive. This perception is mainly due to lack of appropriate cutting tools that can withstand intense heat and Built-up-Edge (BUE) formation during dry machining. The challenge of heat dissipation without coolant requires a completely different approach to tooling. Special tooling utilizing high-performance multi-layer, multi-component, heat resisting, low friction coatings could be a plausible answer to the challenge of dry machining. In pursuit of this goal Argonne National Labs has introduced Nano-crystalline near frictionless carbon (NFC) diamond like coatings (DLC), while industrial efforts have led to the introduction of composite coatings such as titanium aluminum nitride (TiAlN), tungsten carbide/carbon (WC/C) and others. Although, these coatings are considered to be very promising, they have not been tested either from tribological or from dry machining applications point of view. As such a research program in partnership with federal labs and industrial sponsors has started with the goal of exploring the feasibility of dry machining using the newly developed coatings such as Near Frictionless Carbon Coatings (NFC), Titanium Aluminum Nitride (TiAlN), and multi-layer multicomponent nano coatings such as TiAlCrYN and TiAlN/YN. Although various coatings are under investigation as part of the overall dry machinability program, this extended abstract deals with a systematic investigation of dry machinability of Aluminum 6061 and 2024 using uncoated carbide, TiN coated carbide, and TiAlN coated carbide inserts. Central Composite Design (CCD) is used to study the effect of speed, feed, depth of cut, workpiece material, and cutting tool material on the resulting forces, surface finish, temperature, chip morphology and tool wear. Each of the machining responses is measured and compared under 15 different machining conditions. Results from CCD experiments have been used to develop linear and logarithmic models for forces (Fx, Fy, Fz, & Fr) surface finish (Ra), and temperature. Furthermore, chip morphology and tool wear have also been compared. From the comparison of forces, surface finish, temperature, chip morphology, tool wear and the corresponding statistical models, it is clear that in general TiAlN results in lower forces, better surface finish, greater fragmented chips, and lesser tool wear.