Avaliação da retificabilidade de aço inoxidável 316 produzido por manufatura aditiva por deposição a arco elétrico

Abstract

Additive manufacturing (AM) is an alternative manufacturing technique that enables production of raw parts very close to its final desired shape and dimensions, and, in some cases, is faster than other processes such as casting, rolling and machining, for example. However, AM faces some challenges when producing parts with superior surface quality and tighter dimensional tolerances, thereby becoming necessary post-processing stage such as machining operations, like turning and milling, for example. Depending on the project, grinding operations may be required to achieve combination low roughness values (Ra ≤ 1.60 μm) with dimensional deviations that fall within the International Tolerance (IT) ranging from IT3 to IT6 grade. Grinding performance depends on several parameters, such as grinding wheel, dressing operation, radial depth of cut, workspeed, coolant type and delivery, among others. Due to the fact AM is a recent manufacturing process, specific grinding wheels for grinding materials made from AM are not yet commercially available. This highlights the importance of research to evaluate the performance of grinding wheels and understand the mechanism of material removal. Furthermore, it is important to identify the influence of the peculiar characteristics and properties generated from AM process, such as the heat-affected zone and the variation in microstructure and hardness between the deposited layers, on the workpiece surface integrity during grinding. In this context, this study aims to evaluate the grindability of a 316L stainless steel manufactured by wire arc additive manufacturing (WAAM) in comparison with a 316 UF austenitic stainless steel produced by rolling. Two types of white aluminum oxide grinding wheel with different abrasive grain sizes were used: AA46K6V and AA120K8V40K. Radial depth of cut was varied at three levels for each grinding wheel type: 5 μm, 20 μm, and 35 μm for the wheel grain size #46, and 10 μm, 25 μm, and 40 μm for the wheel grain size #120. Also, the workspeed was varied at two levels: 2.7 m/min and 7.5 m/min. The output variables analyzed to assess the grindability were the roughness parameters (Ra and Rz), machined surface images via scanning electron microscopy (SEM), surface and subsurface microhardness, and the main motor power of the grinder. The results pointed out a better grindability of the steel produced by WAAM when using the grinding wheel grain size #120 in terms of roughness, in which a reduction in roughness Ra by up to 52 % was recorded, compared to conventional steel at the same cutting conditions. Also, lower consumption was observed after grinding the steel produced by WAAM with the #46 grain size grinding wheel in most cutting conditions tested, in which a reduction of up to 21 % was observed. However, energy consumption for steel produced by WAAM with the #120 grain size grinding wheel increased by about 85 %. This may be attributed to the #120 grinding wheel which has smaller grit size and consequently higher number of grits edges working at the same time when grinding WAAM material which is harder than the conventional one. This will require more force and power to perform grinding.