PSI - Issue 53

Francisco Matos et al. / Procedia Structural Integrity 53 (2024) 270–277 Francisco Matos et al. / Structural Integrity Procedia 00 (2023) 000–000

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1. Introduction

Metal cutting is characterized by high temperatures in the tool-chip interface zone which in turn promote wear and rapid deterioration of cutting tools. Cutting fluids are employed in machining operations to reduce friction, provide cooling, and remove chips from the cutting area. By implementing cutting fluids, tool wear is reduced and the ma chined surface quality is improved. Additionally, lubricants contribute to minimizing cutting forces, leading to energy savings (Dixit et al. (2011)). The considerable potential of additively manufactured cutting tools in terms of enhancing cutting fluid supply and the inherent tribological conditions at the cutting zone is highlighted by the utilization of cutting fluid supplied through targeted channels proved to be significantly more e ffi cient than conventional cooling (Lakner et al. (2019); Rahman et al. (2000); Zachert et al. (2021)). Coolant jets directed towards the cutting zone on the insert tend to act like a hydraulic wedge to lift the chip, shortening the contact length between the insert and the material, reducing cutting forces, temperature and improving chip control. Unfortunately, the design freedom of cooling channels is limited by conventional manufacturing methods, resulting in di ffi cult (often impossible) and time-consuming drilling of bore holes for the cutting fluid throughout the tool. Additive Manufacturing (AM) techniques, such as Laser Powder Bed Fusion (LPBF), are emerging as solution to unlock higher design freedom of internal complex shapes, significantly improving flow conditions while delivering fluid directed to the cutting edge. The ability to fabricate complex parts in one machine and job, made industries to establish AM as a certified end-user product manufacturing technique (Pereira et al. (2019)). In the highly competitive and rapidly evolving automotive industry, the need for e ffi ciency and durability enhance ment of the manufacturing processes is paramount. With the automotive sector increasing its use of parts manufactured from aluminium, the supply chain is challenge to deliver more productive milling operations. Despite 3D printing not being necessarily faster than conventional machining, it reduces the number of machines and processes required given that conventionally machined tool bodies require multiple subtractive operations (i.e. turning, milling, grinding), while post-processing of 3D printed tool bodies is typically limited to brazing the cutting tips into the tool body, followed by calibration of the cutting edges (which are common steps to both additive and subtrative manufacture of tool bodies). High speed machining (HSM) has been one of the most promising technologies in recent decades due to the combi nation of increased productivity and part quality (Gatto et al. (2011)). HSM traditionally makes use of high spindle speeds, specially when machining softer alloys such as aluminium, resulting in high material removal rates (MRR) thus increasing the productivity. Increasing feed rate and cutting speeds leads to a temperature increase at the tool-chip interface which make way to accelerated deterioration of the tool cutting edges (Santos et al. (2016)). The utilization of coolant in machining operations can lead to significant benefits in terms of dimensional accuracy and improved control of heat exchange. The direction of coolant flow must be carefully controlled to ensure it directly engages the cutting zone (Kui et al., 2022), made possible through additive manufacturing. This is especially important in high productivity scenarios allowing for in which spindle speeds and number of teeth are maximized (Singh et al. (2021)), enabling viable (high) table feed speeds while attaining good surface quality. This work explores the feasibility of LPBF in the creation of a complex milling tool geometry with increased number of teeth and conformal cooling chan nels within a compact tool body. To validate geometry and e ff ectiveness of the coolant channels in directing the fluid to the cutting zone, preliminary computational fluid dynamics (CFD) simulations were also performed.

2. Experimental procedure

2.1. Milling tool design

The integration of AM o ff ers a fresh and entirely novel approach to the design of machine tools. In the first step, a milling tool featuring a internal cooling channels, high teeth number relatively to tool size and a hollow interchangeable body was designed, shown in Figure 1. The external dimensions of this cutter are approximately 14 mm in height and 40 mm in diameter. The designed tool teeth number (12) largely exceeds the conventionally manufactured milling tools with similar dimensions since these generally have between 4 to 6 teeth. Each tooth incorporates a slot where a PCD (Polycrystalline Diamond) cutting insert will be brazed in AM post-processing. PCD