Study on roughness and form errors linked with tool wear in the drilling process of an Al-Si alloy under high cutting speed using coated diamond-like carbon high-speed steel drill bits

Materials engineering development has led to steel and cast iron replacement by Aluminum-Silicon – Al-Si alloys in various applications due to the adequate good strength-to-weight ratio and corrosion resistance. These features of Al-Si are extremely relevant for the performance improvement of many products by applying this alloy instead of the usual materials. However, studies have shown that the machinability of these materials presents multiple negative aspects, such as adhesion and abrasion. Therefore, optime cutting parameters and tools need to be selected to combine tool life with product quality. Using hard coatings with high chemical inertia, such as Diamond-Like Carbon (DLC), has shown promising results when machining aluminum alloys. Generally, in drilling, roughness, deviations in diameter, circularity and cylindricity represent the quality of a hole. Cutting speed directly influences tool wear and hole quality. Thus, this study aimed to evaluate the quality of holes machined using high-speed steel tools in an Al-Si alloy on the influence of cutting speed and the use of DLC coating. Tools with brazed Polycrystalline Diamond (PCD) are usually chosen for machining aluminum alloys, which can absorb high cutting speeds. In this paper, the replacement of brazed PCD is studied for high-speed steel coated with a thin film that can guarantee the same performance. The tests were carried out varying the cutting speed (V) in 340, 360, and 430 m/min, comparing DLC coated with uncoated tools. Flank wear was analyzed after each machining run using Scanning Electron Microscopy (SEM). The results showed that cutting speed directly influences the roughness, diameter variation, and flank wear. DLC coating did not show hole quality improvements as it presented adhesion problems on the high-speed steel substrate.