The effect of tool wear on tool life of alumina-based ceramic cutting tools while machining hardened martensitic stainless steel

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Abstract

Tool life is an important parameter in evaluating the performance of the cutting tools. Tool wear affects dimensions and surface quality of the workpiece and it is also one of the important criteria in determining tool life. When the tool reaches the tool wear criterion, the cutting edge fails and cannot be used further. Machining studies have been conducted on hardened martensitic stainless steel (HRC 60) to analyse the effect of tool wear on tool life of alumina ceramic cutting tools. The tool wear such as flank wear, crater wear and notch wear are noted. These wear data are used to develop mathematical tool wear models using multiple regression analysis (MRA). Tool life of the alumina-based ceramic cutting tools is evaluated from these tool wear models and the effect of various types of wear on tool life is analysed while machining hardened martensitic stainless steel.

Introduction

Alumina-based composite ceramic cutting tools are widely used for machining hard materials such as cast irons having wide range of hardness, plain carbon steels and alloy steels having a hardness range of HRC 34 to HRC 66, stainless steels and high temperature alloys as they have high hot hardness and very good chemical stability [1]. Aluminium oxide-based ceramic cutting tools are mainly classified as plain oxide alumina ceramic cutting tool, mixed alumina ceramic cutting tool and whisker reinforced alumina ceramic cutting tool. When zirconium oxide is added to the aluminium oxide matrix, the resulting ceramic tools are called plain oxide ceramic cutting tools. The fracture toughness of the ceramic composite increases by the addition of zirconia in alumina matrix [2]. When non-oxide particles like TiC and TiN are added in the aluminium oxide matrix, they are called mixed alumina ceramic cutting tools. The addition of TiC and TiN in the alumina matrix increases hardness and thermal conductivity [3]. When whiskers like silicon carbide are reinforced in the aluminium oxide matrix, they are called whisker reinforced alumina ceramic cutting tools. SiC whisker reinforcement in alumina matrix increases the fracture toughness of the composite. The main advantage of the whisker reinforcement is the improved strength and toughness [3].

The alumina-based ceramic cutting tools are subjected to not only flank wear but also to crater wear and notch wear, especially where machining hard and tough materials. Xiao [4] has observed that zirconia toughened alumina ceramic cutting tools and TiC mixed alumina ceramic tools are more suitable for machining hardened steel than other ceramic tools because of their superior flank wear resistance. Brandt and Mikus [5] have observed that the crater wear in alumina-based ceramic tools also affects the performance of the ceramic tools and crater wear in these tools is predominantly dependent on superficial plastic deformation when machining steel. Richards and Aspinwall [6] have observed that the tool life of mixed alumina ceramic tool is severely limited due to excessive notching, when machining nickel-based alloys. Thangaraj and Weinmann [7] have studied the wear behaviour of SiC whisker reinforced alumina ceramic tools when machining Inconel 718 and they observed that the flank wear plays a larger role at lower speeds and notch wear is significant at higher speed. It is evident that, though the flank wear is the predominant wear in determining the tool life of alumina-based ceramic cutting tools; the other types of wear also affect the tool life. The effect of the various types of wear on the tool life of alumina-based ceramic cutting tools has to be thoroughly investigated for their effective utilisation. For this purpose, detailed tool wear studies were carried out using the alumina-based ceramic cutting tools while martensitic stainless steel.

Section snippets

Tool wear studies

Tool wear studies have been performed on martensitic stainless steel (SS 410 grade), which was previously heat treated to obtain the hardness value of HRC 60. In our present study four types of alumina-based ceramic cutting tools such as zirconia toughened alumina (tool A), Ti[C, N] mixed alumina with zirconia addition (tool B), Ti[C, N] mixed alumina (tool C) and SiC whisker reinforced alumina (tool D) have been used. The details of composition and properties of the cutting tool materials are

Tool life analysis

Tool wear is generally a gradual process and wear rate depends on tool and workpiece materials, tool shape, cutting fluids, process parameters and machine-tool characteristics. Tool wear in turn adversely affects tool life and it is one of the important criteria in determining tool life. Apart from gradual tool wear, tool fracture or excessive chipping and surface roughness also affect tool life. The tool rejection criteria for rough machining operation are employed and the following values are

Results and discussion

The effect of various types of tool wear on tool life at different cutting speeds is analysed. The maximum allowable machining time is calculated from the flank wear, crater wear and notch wear models using the respective tool rejection criterion and plotted against the cutting speed for the alumina-based ceramic cutting tools in Fig. 5a–d. From these figures, it can be noted that the tool life of the alumina-based ceramic cutting tools is affected by flank wear at low speeds, and it is

Conclusion

Tool wear studies wear have been conducted on martensitic stainless steel (60 HRC) using alumina-based ceramic cutting tools and various types of wear were observed. Tool life models are developed using the wear data. The effect of various types of wear on tool life is analysed. Flank wear affects the tool life at lower speed, however, crater wear or notch wear affects the tool life at high speed, i.e. above 200 m/min. The tool life of Ti[C, N] mixed alumina ceramic cutting tools (tools B and C)

Industrial summary

Machining of hard materials is found to be difficult, especially in its hardened condition. However, with the development of new harder work materials, the necessity arises for the industry to machine such hard materials. The tool materials technology is advancing at a fast rate to enable machining of these materials at higher removal rate with reliability of performance. In the machining of hard materials, cutting tools made of ceramics, cubic boron nitride (CBN) and poly crystalline diamond

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