Machinability of AISI304 Stainless Steel Using Ethylene Glycol/TiO₂ Nanoparticles Based Coolant

Abstract This chapter discuss the development of linear model order for predicting the milling parameter such as surface roughness, tool life and wear mechanism for end-milling operation of AISI304 stainless steel using TiN coated carbide insert with water soluble coolant and nano particle based coolant (TiO2/EG). The linear model equation of surface roughness and tool life are developed using response surface methodology (RSM). The cutting variables are cutting speed, feed rate, and axial depth.  The developed linear model equations for the surface roughness tool life show that the most significant input parameter is the feed rate, followed by axial depth and cutting speed. The end-milling operation by using nano particle based coolant (TiO2/EG) obtains lower surface roughness and high tool life compared with end-milling operation by using water soluble coolant.  In general, the tool failure for milling with water soluble coolant was flank wear, crater wear, crack, chipping and fracture at cutting distance of 720 mm. But, the milling process with nano particle based coolant (TiO2/EG) obtains a chipping and fracture and cutting distance of 1200 mm. According to ISO 8688-2-1989 (E) the wear criteria for milling with water soluble coolant reached at average of cutting distance of 800 mm but the cutting distance for milling with nano particle based coolant (TiO2/EG) reached the ISO 8688-2-1989 (E) the wear criteria at cutting distance of 1300 mm. The SEM and EDX spectrum shows there are nano layer of Ti nanoparticle from the nanofluid embedded and fills the holes in the insert and for a layer which act as a thermal bridge for the cutting insert. Attrition and oxidation at the cutting edge were the main tool wear mechanism present during end-milling operation nano particle based coolant (TiO2/EG). An oxide layer has been formed during the oxidation wear which shield the cutting tool from the impact during the milling process.

1      Introduction

Coolant is very crucial in all machining process because it can reduce the thermal deformation of the work-piece and produce a fine surface. However, many manufacturing industries are facing a real challenge in the cooling system in the machining process. There are still thermal damages occur on the work-piece surfaces which affect the manufacturing cost of the industry. This is due to the high cutting temperature during the milling process. Many researchers have conducted various researches on alternating the machining coolant. Most of the investigation of alternating the machining coolant is mainly focused on minimum quantity lubricant technique and there are very few research and publication about using nanofluid as a milling machine coolant (Yazid et al., 2011). On the other hand, it is reported that the dispersed nanoparticle additives (TiO2, ZnO, SiC, etc) in the based liquid exhibits higher load carrying capacity, anti-wear and friction reduction properties (Murshed et al., 2008) Therefore, these features can make the nanofluid very attractive in usage of machining coolant.

The concept of nanocoolant or nanofluid is referred to dispersions of nanopaticle into the based liquid which is water or ethylene glycol. Choi et al., 1995 reported that nanofluids are the next generation heat transfer fluid due to their higher thermal conductivity than those of based liquid. From the viewpoints of heat transfer rate, nanofluid are considered as alternatives to conventional coolant for machining. Therefore, ethylene glycol based TiO2 nanocoolant could produce a better surface finish than the conventional coolant. Besides that, the cutting temperature could also be reduced in both work-piece and cutting tools due to its high heat transfer rate. Therefore, the tool life and the surface integrity considered to be much improved compared with normal commercial coolant.

AISI 304 austenite stainless steels are commonly used in manufacturing industries of many component used in automotive department. Furthermore, aircraft industries are also depending on austenite steel to construct part in aerospace engines. AISI 304 austenite stainless steels are grades of chromium-nickel steels. It is very great corrosion resistant and having an outstanding mechanical property which is not exists by other alloy. Besides, this alloy also categorized as non-magnetic and it can only hardened by natural cold working process. However, this alloy is classified as poor machinability material (Novak et al., 1977).

AISI 304 austenite stainless steels are an alloy with high fracture toughness, high tensile strength high ductility, low heat conductivity and high work hardening rates. These undesirable properties contributed to a number of difficulties such as poor surface integrity and short tool life (Shao et al., 2007). Besides that, machining austenite stainless steel comes across with built-up-edge (BUE) on the cutting flank face. BUE will contribute a rises in tool wear and reduce the surface integrity of workpiece. Moreover, having a low thermal conductivity which is 50% lower than normal carbon steel, increases the rates of tool wear and damages on the workpiece due to high absorption of heat in to cutting tool and workpiece (Hossien and Yahya, 2005). One way to reduce the low thermal conductivity effect on tool life is to conduct the milling operation with essential cutting fluid.

The purpose of the milling study is to estimate the usage of ethylene glycol based TiO2 nanocoolant as an alternative milling lubricant when end-mill AISI 304 austenite stainless steel usind TiN coated carbide insert. The objective of this metal cutting study is to found the milling performance consist of tool wear, tool life, wear mechanism and surface roughness. Therefore, the difficulties occur during the milling process can be solved based on the modelling and prediction done on the practical results. Hence, the optimum milling condition can be selected for AISI 304 stainless steel under different milling state.

M.M.Noor