Prediction of Cutting Forces in Micro Milling of p-20 Steel by TiAln coated wc tool: An Analytical Approach
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cagan2020
| 1 Introduction Extensive applications of micro features in aerospace, microelectronics and biomedical field spur the development of several micro fabrication processes. Among various micro fabrication processes, micro milling is one of the facile manufacturing approach due to its enhanced characteristics such as higher material removal rate, applicability to wide range of engineering materials, capability towards producing three dimensional complex and precise micro-features [1,2]. Usually, it is considered that micro milling tool (Figure a) is just the down scaling of conventional milling cutter. However, due to this scaling effect, chip formation process encounters severe problem as edge radius of the cutting tool comes in the range of uncut chip thickness (Figure b. This scaling effect is also commonly known assize effect [3]. Because of the size effect, chip formation is not possible when uncut chip thickness is smaller than minimum chip thickness. This leads to rubbing and ploughing followed by elastic recovery rather than shearing of workpiece material. In addition, various undesired phenomena come into picture like higher force generation, worse surface quality, burr formation, tool wear and tool breakage [1, 4]. Again, edge radius of the micro tool is comparable to the grain size of the workpiece material and sometimes feed and depth of cut are in the range of the grain size, so the chip formation is not isotropic and homogeneous like macro milling process [3]. As a consequence, the performance of micro end mill becomes more critical compared to conventional scale end mill cutter. Tool wear and tool breakage are major impediments in micro scale milling [5]. Especially these phenomena are prone to be more critical during machining of hard materials such as hardened tool steel, titanium alloy and nickel based super alloy. Among such hard materials, P steel which is a type of tool steel has enormous applications in micro mould and die preparation due to superior characteristics such as wear resistant, higher toughness and hardness [6]. To meet the desired surface quality criteria, minimization of burr formation and tool wear and enhancement of the micro tool performances, hard coating is generally implemented on the tool surface [4]. Aramcharoen et al. [6] reported the effect of ultra- thin coating of TiN, TiCN, TiAlN, CrN and CrTiAlN on tungsten carbide (WC) micro end mill cutter for machining of hardened tool steel. Their research concluded that all coated tool enhanced the performance in comparison to uncoated tool in terms of edge chipping and flank wear. TiAlN coated tool was established as the flagship among all coated tools. Thepsonthi and Ozel [4] examined the effect of CBN coating in micro end mill cutter for machining of Ti-6Al-4V by both FEM simulation and experimental method. Their study revealed the improved characteristics of CBN coated tool in terms of burr formation, tool wear, surface roughness and temperature generation. Furthermore, effects of various types of coated tools such as diamond like carbon (DLC), Al- TiN, AlCrN and TiAlN+AlCrN in micro milling of Inconel-718 has been performed by Ucun at al. [5]. Their study showed that coated tools outperformed the uncoated tool by reducing surface roughness, burr formation, flank wear, edge chipping and edge rounding. The above literature concludes the improvement in performance of the coated tool for machining of hard and difficult to machine material. Although, tool wear and tool breakage can be reduced by coating but can’t be eliminated completely due to increase in cutting force due to increase in edge radius by application of coating material. So prediction of cutting forces is much requisite to control the surface quality and tool 3 failure by optimizing the machining parameters in advance. Many researchers showcase their work in modelling of cutting forces, some of them are described in this section with brevity. Bao and Tansel [7] reported the analytical modelling for the prediction of cutting forces in micro milling by differentiating the total cutting zone into three parts and added size effect with tool run out in their model. Jun et al. [8] proposed a cutting force model by incorporation of effective rake angle, ploughing, rubbing and elastic recovery. They developed two separate mechanistic models for shearing dominant region and ploughing dominant region, respectively. Lu et al. [9] proposed an analytical cutting force model by incorporating flank wear during micro milling. Srinivasa and Shunmugam [10] reported purely analytical model for force prediction in micro milling by considering material strengthening effect, edge radius effect and basics of oblique cutting. Further, with recent advances in hardware and software, an Arbitrary Lagrangian-Eu- lerian (ALE) formulation is used by most of the software packages such as ABAQUS, Ansys and DEFORM for modelling material removal processes. Jin and Altintas [11] reported the fine element method (FEM) based simulation for calibration of cutting coefficient in turning of brass. Further, they implemented the cutting coefficient results to find the force value in micro milling by aggregating the effect of tool run out and helix angle. FEM simulation for the prediction of cutting forces, temperature and stress with their experimental validation for micro milling of Ti-6Al-4V has been presented by Ucun et al. [12]. However, they did not consider the effect of minimum chip thickness, tool run out, elastic recovery, etc. which are very significant parameters associated in micro milling. Download 1.01 Mb. Share with your friends:
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