Chip Formation in the Machining of Al-Si / 10 % AlN Metal Matrix Composite by using a TiN-coated Carbide Tool

This paper presents a study on chip formation in the milling process of Al-Si/10% AlN Metal Matrix Composite (MMC). It focuses on the effect of cutting parameters on the formation of the chip. Al-Si/10% AlN MMC reinforced with 10% AlN particle is a new-generation material that is suitable for manufacturing automotive and aerospace components. Several advantageous characteristics of this material include low density, light weight, high strength, high hardness and high stiffness. The milling process was carried out at dry cutting conditions by using TiN-coated carbide tool insert, which was developed by Standards and Industrial Research Institute of Malaysia (SIRIM). The machining parameters were as follows: a constant cutting speed of 230 m/min, feed rates of 0.4, 0.6 and 0.8 mm/tooth and cutting depths of 0.3, 0.4 and 0.5 mm. The analysis of the chip formation was performed using a video microscope (Sometech, SV-35). The chips were formed because of the shear between the work pieces and the cutting chips during dry milling of Al-Si/10% AlN MMC. These chips were small, short and discontinuous with outer face cracks.


INTRODUCTION
AlSi alloy is a Metal Matrix Composite (MMC) that is widely used invarious industrial sectors, such as transportation, domestic equipment, aerospace, military and construction.It is a matrix composite reinforced with AlN particle and transformed into a newgeneration material for automotive and aerospace applications (Said et al., 2014).In general, Al/Si MMCs consist of two chemically and physically distinct materials that are suitably distributed to provide properties that are not obtainable from either the individual phase or fibrous or particulate phase in the form of continuous or discontinuous fiber, whiskers and particles.They are distributed in a metallic matrix containing light metals, such as aluminum, magnesium, titanium and copper and their alloys (Said et al., 2014;Sahin and Sur, 2003;Patel and Patel, 2012;Chawla and Chawla, 2006).Al-Si MMCs materials have increasingly replaced conventional materials in many applications.MMC has a combination of metal and ceramic properties (Abdullah, 2009;Said et al., 2013).
Chip formation is an important index of machining because it directly or indirectly indicates the nature and behavior of work at machining conditions as well as the nature and degree of interaction at the chip-tool interfaces (Radhika et al., 2013).MMC has very good mechanical properties, which are caused by the combination of hard reinforcement, such as SiC and elastic matrix material, such as aluminum or magnesium (Shetty et al., 2008).
To date, only a few reports exist on the use of AlN as a reinforcement to the composite Al alloy.To achieve a longer tool life in the current production practices as well as to enhance our knowledge on tools that can withstand high cutting temperatures, understanding the mechanism of chip formation is a fundamental element that influences tool performance (Said et al., 2014).Models are used to understand the orthogonal cutting chip formation mechanism.The formation mechanism of the pieces depends on the nature of the machined material and the machining parameters.The three types of chips produced in machining (Oxley, 1989;Said et al., 2014) are discontinuous, continuous and continuous with built-up edge.Discontinuous chips are chips formed with multiple segments and produced when machining brittle materials at a low cutting speed.Continuous chips are produced when machining ductile materials at a high cutting speed and at a low feed rate (Groover, 1996).Continuous with built-up edge chips are produced when machining ductile materials at a low cutting speed.The study of chip formation is the cheapest and most effective approach to understand the machining characteristic of a material (Radhika et al., 2013).
Chips produced can be divided into two categories, namely, acceptable and unacceptable chips (Ghani and Yong, 2006).Acceptable chips do not disturb work or machine tool and do not cause problems in chip removal, whereas unacceptable chips disrupt manufacturing operations because they have a tendency to shrink around tools and work piece as well as inflict security problems to workers (Ghani and Yong, 2006).Figure 1 shows the deformation zone during the machining process.A low shear zone extends along the shear plane and represents the boundary between the chip and the work piece material, which is subjected to sheared formation.The secondary shear zone is located along the tool rake surface and is subjected to additional shear to form the chip.The second area includes the interface between the chip and the tool rake face.Some of the shear caused by rubbing off or side face of the tool for the newly generated surface can also be observed.
This study presents chip formation during Al-Si/10%AlN MMC machining on different parameters of feed rate, cutting depth and constant cutting speed by using the TiN-coated insert.The factors that influence chip formation were identified and their effect on improving the machinability of new materials was proposed.Figure 1 shows the major deformation zone in metal cutting.Friction and wear characteristics of the tool or work piece combination were important in this zone.

METHODOLOGY
Experimental machining: Al-Si/10%AlN MMC was produced via the stir casting process in block form with Table 1 shows its composition.The material is reinforced with 10% of small AlN particles with size of <10 µm and purity of >98%.The Al-Si/AlN MMC was fabricated via the stir casting method.The AlSi alloy ingot was heated in a graphite crucible at 750°C and held for 30 min until the material was completely melted.The preheated AlN particles were added to the molten metal, stirred for 5 min (Fig. 2) and immediately casted into a permanent mold via the bottom pour technique.The solidified Al-Si/10%AlN metal matrix composite underwent a heat treatment process to improve its mechanical properties, such as strength and hardness (Tomadi et al., 2013).The three stages of the heat treatments were solution treatment (0 to 540°C for 30 min and 540°C for 4 h), water quenching (60°C) and continuous aging (0 to 180°C for 30 min and 180°C for 4 h). Figure 3 shows the microstructure of Al-Si/10%AlN MMC with 10x magnification after heat treatments Table 2 shows the mechanical properties of 10 wt.% Al-Si/AlN MMC materials.
The milling process was carried out at dry cutting conditions by using the TiN-coated carbide tool insert, which was developed by SIRIM (Advance Materials Research Centre).The TiN films were deposited on the carbide insert at similar physical conditions by using   the Hauzer Techno Coating 9HTC 625/2 ARC coating system.The substrates were cleaned for 30 min in an ultrasonic bath by using a mild, solvent-free, detergent.The substrates were blow-dried using high-pressure nitrogen gas to remove any dust contaminants from the surface and then placed into the coating chamber.Film deposition was carried out with the substrate biased with a DC power source to introduce proper ion bombardment on the growing surface to assist in obtaining a desirable structure, grain size and film density.The chamber was evacuated to a pressure of approximately 4×10 -6 mbar and back filled with nitrogen gas at approximately 10 -3 mbar.The complete deposition procedure has been previously (Mubarak et al., 2008;Mubarak et al., 2005).Table 3 shows the summary of the deposition parameters.This study used a Coro Mill tool holder R390-020C4-11L and an uncoated carbide cutting tool insert with a diameter of Ø20 mm and a nose radius of 0.2 mm (Fig. 4).Table 4 shows the geometry carbide tools used for milling Al-Si/10%AlNMMC.The

RESULTS AND DISCUSSION
Chip formation and different feed rates and cutting depths: The chips were formed because of the shear between the work piece and cutting chips (Ghani and Yong, 2006).Figure 5 to 7 show the chip shapes formed during the dry milling of Al by using the TiN-coated carbide developed by SIRIM.The chips were small, short and d outer face cracks.Ozcatalbas (2003) (2013) also observed this form when machining Al composite materials.
As shown in Fig. 7, the resulting chip was thick with cracks at a cutting speed of 230 of 0.8 mm/tooth and cutting depth of 0.5 result was due to the fact that the increase in feed rate results in the increase in tool-chip contact length, which increases the temperature of the surface of the work piece (Radhika et al., 2013).The band lines affected the three types of body wears during cutting which caused wear on the cutting tools easily and quickly.
These chips were also observed by Ozcatal (2003).He found that chip volume increases with the gross thickness of the segment.He added that these phenomena occurred because of the sheet and the low hardness of the material.According to et al. (1997), low hardness and high to cause adhesion period but reduce the slip period in segment formation.The chip formation changed at a cutting speed of 230 m/min, but different results were obtained for different feed rates and cutting depths Figure 5 illustrates the chip formation 0.4 mm/tooth and a cutting depth of 0.4 illustrates the formation at a feed rate of 0.6 and a cutting depth of 0.3 mm.The Fig. 5 and 6 seemed shorter compared with that in Fig. 7, which shows formation at a feed rate of 0.8 and a cutting depth of 0.5 mm.According Ghani and Yong (2006) microstructure changes in the chip are also affected by the addition of cutting speed, constant chip thickness, or cutting depth and oth hardness of the work piece (Said et al

CONCLUSION
The chips formed during the machining process of Al-Si/10%AlN MMC by using TiN cutting tool insert developed by SIRIM were small, short and discontinuous with outer face cracks mechanism of chip formation involved the initiation of cracking of the outer surfaces, which were chip because of the high shear stress.The chip lengths had different sizes, which were based on feed rate and cutting depth.m/min, feed rates of 0.4, 0.6 and 0.8 and cutting

RESULTS AND DISCUSSION
Chip formation and different feed rates and cutting because of the shear between the work piece and cutting chips (Ghani and Yong, 2006).Figure 5 to 7 show the chip shapes formed during the dry milling of Al-Si/10%AlN MMC coated carbide developed by SIRIM.The chips were small, short and discontinuous with outer face cracks.Ozcatalbas (2003) and Said et al. (2013) also observed this form when machining Al 7, the resulting chip was thick with cracks at a cutting speed of 230 m/min, feed rate mm/tooth and cutting depth of 0.5 mm.This result was due to the fact that the increase in feed rate chip contact length, which creases the temperature of the surface of the work The band lines also body wears during cutting, which caused wear on the cutting tools easily and These chips were also observed by Ozcatalbas (2003).He found that chip volume increases with the gross thickness of the segment.He added that these phenomena occurred because of the sheet-like structure and the low hardness of the material.According to Lin ), low hardness and high ductility are known to cause adhesion period but reduce the slip period in The chip formation changed at a , but different results were for different feed rates and cutting depths.
the chip formation at a feed rate of depth of 0.

CONCLUSION
The chips formed during the machining process of Si/10%AlN MMC by using TiN cutting tool insert developed by SIRIM were small, short and discontinuous with outer face cracks.The main mechanism of chip formation involved the initiation of cracking of the outer surfaces, which were chip-free because of the high shear stress.The chip lengths had different sizes, which were based on feed rate and

Fig. 2 :
Fig. 2: Fabrication of metal matrix composite using the stir casting technique a size of 120 mm long×100 mm wide ×50 mm thick.Table1shows its composition.The material is reinforced with 10% of small AlN particles with size of <10 µm and purity of >98%.The Al-Si/AlN MMC was fabricated via the stir casting method.The AlSi alloy ingot was heated in a graphite crucible at 750°C and held for 30 min until the material was completely melted.The preheated AlN particles were added to the molten metal, stirred for 5 min (Fig.2) and immediately casted into a permanent mold via the bottom pour technique.The solidified Al-Si/10%AlN metal matrix composite underwent a heat treatment process to improve its mechanical properties, such as strength and hardness(Tomadi et al., 2013).The three stages of the heat treatments were solution treatment (0 to 540°C for 30 min and 540°C for 4 h), water quenching (60°C) and continuous aging (0 to 180°C for 30 min and 180°C for 4 h).Figure3shows the microstructure of Al-Si/10%AlN MMC with 10x magnification after heat treatments Table2shows the mechanical properties of 10 wt.% Al-Si/AlN MMC materials.The milling process was carried out at dry cutting conditions by using the TiN-coated carbide tool insert, which was developed by SIRIM (Advance Materials Research Centre).The TiN films were deposited on the carbide insert at similar physical conditions by using

Fig. 5 :
Fig. 5: Elemental chips on cutting conditions V = 230 m/min, F = 0.4 mm/tooth, D.O.C 0.4 mm 4 mm and Fig. 6 a feed rate of 0.6 mm/tooth The chip formations in shorter compared with that in Fig. feed rate of 0.8 mm/tooth .According Ghani and Yong (2006) microstructure changes in the chip are also affected by the addition of cutting speed, constant chip thickness, or cutting depth and other factors such as et al., 2013).

Table 1 :
Chemical composition of materials

Table 4 :
Geometry carbide tools used for milling AL-SI/