Factors Affecting Surface Finish of Abrasive Water Jet ... · Surface roughness of carbides...

International Journal of Modern Trends in Engineering and Research

www.ijmter.com e-ISSN No.:2349-9745, Date: 28-30 April, 2016

@IJMTER-2016, All rights Reserved 859

Factors Affecting Surface Finish of Abrasive Water Jet Machining- A Review

K.Arunkumar1, M.Navaneethbalaji2, G.Praveenkumar3, R.Venkatesan4. 1*Assistant Professor, Dept. of Mechanical Engineering Sri Ramakrishna Engineering College,

Coimbatore, India .E Mail: [email protected] 2.Final Year Student ,Dept. of Mechanical Engineering, Sri Ramakrishna Engineering College,

Coimbatore, India,E Mail: [email protected]

3.Final Year Student ,Dept. of Mechanical Engineering, Sri Ramakrishna Engineering College, Coimbatore, India,E Mail: [email protected]

4.Final Year Student ,Dept. of Mechanical Engineering, Sri Ramakrishna Engineering College, Coimbatore, India,E Mail: [email protected]

–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Abstract— The Abrasive Water Jet Machining (AWJM) is used for cutting materials in precision machining [1].The process represents cold, precise cutting with minimal thermal load. This technology covers requirements for quality and manufacturing productivity [2].In manufacturing process high quality products are improved by dimension, shape accuracy and surface roughness of the products is observed [3].Various machining technologies of high speed cutting by using water jets can be used for the betterment of surface finish and accuracy. The effective machining process and to predict the optimal choice for each parameters such as transverse speed, abrasive flow rate and standoff distance respectively [4].It is based on significant analysis of quality and technical of surface finish its main process is to check accuracy of the most precise components [5].The quality of surface roughness is expressed through the abrasive materials. The quality terms is based on the composite materials in which that has been differing according to several components and its material characteristics [6].This technology is widely used in manufacturing sectors for irregular surface and polishing hard materials, cleaning constrained surfaces on surface roughness. The results show that a smooth surface finish is more easily obtained on hard materials under the operation of abrasive water jet machining. Keywords- Transfer speed, Stand off distance, ANNOA, abrasive water jet, Surface roughness

I. INTRODUCTION

It is one of the fast growing non traditional machining techniques of abrasive water jet technology. This process having good adaptability to various composite materials also having low impact force of the products to friendly environment. This application and techniques mainly involves in improving competitiveness for modern manufacturing and technology [1].The process of machining work piece material through high pressure water jet mixed with abrasive particles. The abrasives are helps us to reduce surface roughness of aluminium cutting surface in machining process. Machining of surface roughness in particulate reinforced conventional machining process such as turning, drilling. The surface finish of the machined surface acts as a major role in dimensional accuracy. The proper selection of this process is important in achieving of better surface finish [8].The parameters

International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 3, Issue 4, [April 2016] Special Issue of ICRTET’2016


of machining process such as water pressure, standoff distance and transverse speed were considered on the machining process. It has become highly developed industrial technology for the proper surface finish and accuracy with material properties.

II. LITERATURE SURVEY

Surface roughness of carbides produced by abrasive water jet machine. In this article the work aims to evaluate the effect of jet of pressure, abrasive flow rate and work feed rate on smoothness of the surface produced by abrasive water jet machining of carbide of grade P25 is a very hard and cannot be machined by conventional machining techniques Cutting was performed on a water jet machine model WJ 4080. The abrasive used in investigations was garnet of mesh size 80. It was found from the investigations that with increase in jet pressure the surface becomes smoother due to higher kinetic energy of the abrasives. But the surface near the jet entrance is smoother and the surface gradually becomes rougher downwards, and the roughest near the jet exit. Increase in abrasive flow rate also makes the surface smoother which is due to the availability of higher number of cutting edges per unit area per unit time. Feed rate didn’t show any significance influences on the machined surface, but it was found that surface roughness increase drastically near the jet entrances. Finally they have concluded that A jet Pressure And Abrasive Flow rate are the Most influencing parameter on the surface roughness, the work feed rate is less insignificant as compared to jet pressure and abrasive flow rate. Experimental investigations were found the influence of Abrasive Water Jet Machining (AWJM) process parameters on surface roughness (Ra) and kerf taper ratio (TR) of aramid fiber reinforced plastics (AFRP) composite. The approach was based on Taguchi’s Method and Analysis of Variance (ANOVA) to optimize the AWJM process parameters for effective machining. It was found that traverse rate was considered to be the most significant factor followed by hydraulic pressure in influencing the Ra quality criteria. In case of TR, traverse rate showed the greatest influence by standoff distance. It was also confirmed that increasing the kinetic energy of water jet may produce a better quality of cuts. It was confirmed that determined optimal combination of AWJM parameters satisfy the real need for machining of AFRP composites in practice. They have concluded that Traverse rate is the most significant factor on surface roughness during AWJM while standoff distances and abrasive mass flow rate are the insignificant control factor on surface roughness (Ra). By applying the optimal setting to the Experiments there are considerable improvement in the process. A study of the depth of jet penetration (or depth of cut) in abrasive water jet (AWJ) cutting of alumina ceramics with controlled nozzle oscillation is presented and discussed. An experimental investigation is carried out first to study the effects of nozzle oscillation at small angles on the depth of cut under different combinations of process parameters. Depending on the other cutting parameters in this study, it is found that a high oscillation frequency (10-14 Hz) with a low oscillation angle (4-61) can maximize the depth of cut. Using a dimensional analysis technique, predictive models for jet penetration when cutting alumina ceramics with and without nozzle oscillations are finally developed and verified. An experimental investigation of the depth of jet penetration in AWJ cutting of alumina ceramics with controlled nozzle oscillation has been carried out and reported. Hence oscillation frequencies (10-14 Hz) and small oscillation angles (4-61) are recommended for maximizing the depth of cut in nozzle oscillation cutting.



III. FACTORS AFFECTING SURFACE FINISH

Table 1-Parameters and levels Level Water pressure, MPa (A) Standoff distance, mm (B) Traverse speed, mm/s (C)

I 200 2.5 1.0 II 250 5.0 1.5 III 300 7.5 2.0

Table 2-ANOVA analysis for surface roughness

Parameters DOF Seq.SS Adj.MS F value P value Pc

Water pressure, MPa (A) 2 27.1107 13.5553 50.98 0.019 74.083

Standoff distance, mm (B) 2 2.6294 1.3147 4.94 0.168 7.185

Traverse speed,mm/s (C) 2 6.3231 3.1615 11.89 0.078 17.278

Table 3- Measured values and S/N ratios for surface roughness of composite

ExpNo

Water pressure, MPa (A)

Standoff distance, mm (B)

Traverse speed, mm/s (C)

Surface roughness, microns

S/N ratio

1 200 2.5 1.0 8.20 -18.2763 2 200 5.0 1.5 10.56 -20.4733 3 200 7.5 2.0 11.96 -21.5546 4 250 2.5 1.5 7.05 -16.9638 5 250 5.0 2.0 8.62 -18.7101 6 250 7.5 1.0 7.60 -17.6163 7 300 2.5 2.0 6.60 -16.3909 8 300 5.0 1.0 5.23 -14.37 9 300 7.5 1.5 6.20 -15.8478

Under the chosen experimental conditions. In light of this, it is reasonable to use the estimate of water-hammer pressure as the appropriate impact pressure. Similarly, the average surface roughness value with respect to the three different traverse speeds at optimum water pressure of 300 MPa and traverse speed of 1mm/s. It demonstrates that a decrease in traverse speed decreases the surface roughness of the machined surface of the composite. Surface roughness decreased from 6.6 μm to 4.7 μm when traverse speed was decreased from 2 mm/s to 1 mm/s. It can be noted that the considerable reduction (29%) in surface roughness is achieved by decreasing the traverse speed. It can be revealed that the lower traverse speed enhance easier removal of material within a short time, resulting in considerable improvement in surface finish. The results revealed that the surface roughness decreased by 19 % when the standoff distance was decreased from 7.5 mm to 2.5 mm at optimum traverse speed (1 mm/s) and water pressure (300 MPa). A lower



standoff distance ensures the smoother surface roughness due to increased kinetic energy of the abrasive- water stream.

Table 4- Technical ParametersTechnical

Parameters Images Technical Parameters Images

v = 350mm/min ma = 250 g/min

v = 350 mm/min ma = 400 g/min





Similar observation was made by John Kechagias and they reported that when the standoff distance was increased, the surface roughness increased considerably in machining of TRIP sheet steels. It can be seen from the high magnification SEM image that de-bonding between the graphite particles and Al –Si alloy matrix occurred on the cutting surface where the soft graphite particles pulled out and form a valley on the machined surface of the Al –Gr composite. This could be the cause for higher surface roughness values while machining graphitic reinforced composites.

Figure 1: variations of graph and micro structure zone

Figure 2:Heterogeneous surface with highlighted initial zones Surface profile parameters Ra and Rq in entry area of sample (initial zone is highlighted) High-magnification SEM imaging was conducted in order to better understand the initial mechanisms of damage illustrate the damage initiation at the boundary between _ grains and the matrix at the lower water hammer pressure (0.94 GPa), whilst show some fracture features of the damage associated with impact at the higher water hammer pressure (1.24 GPa). Following a single jet pass at the lower water hammer pressure, initial damage over the jet footprint can be seen in some of the grain boundaries exhibiting contrast in the SEM images, a feature which was not observed before the PWJ exposure. A few isolated micro pits can be observed indicating regions where material has been



removed. It is not clear from such images whether these micropits were formed within grains or located along the grain boundaries. Higher magnification imaging on the same surface indicates some slight damage to the grains themselves, in the form of micro voids and micropits with much smaller sizes than the grains. However, it is unlikely that these features result directly from plastic deformation as they have angular shapes.

Figure 3: Surface roughness in initial zone Ra(MI) and Ra(MII)

Figure 4: Micro structure analysis When water is pressurized to a high pressure and discharged from a small orifice, a water jet with high velocity is generated which can cause damage to the target materials by means of erosion. The loss of jet velocity and breakdown of jet into droplets start occurring once the jet departs the nozzle exit due to aerodynamic interaction, turbulence and cavitation.Described that the initially coherent jet fully breaks up to form droplets as air is entrained into the jet. Sohr and Thorpe argued that this breakdown into droplets occurred at a critical distance (SODc) which is approximately 175 orifice diameter from the orifice. In this work, the SODs reported are the distances from the nozzle exit to the work piece the true SODs are the distances from the orifice to the work piece (i.e. an additional 76 mm due to the length of the nozzle). Thus, both of the SODs examined are above the SODc indicating droplet work piece impacts represent the conditions experienced during the erosion process

IV. ADVANTAGES

Possible to cut materials having higher hardness value, that cannot cut in other machining process. • There is no cutting force during and after cutting operation, there is no more strain on the material. • Production operations such as deburring, cutting, drilling, turning, milling can be done easily with

multiple machining mode of water jet lathe. • There is no need to use edges of cutting tools so no loss of time in changing tools. • It is efficient and economic since it has high rate of machining. • It is possible to machine materials in macro and micro sizes. • It is environmental friendly since there is no burning, oxidizing or toxic slag during machining

operation.



CONCLUSION

Results showed that surface roughness of composite decreased with increasing water pressure. The lowest surface roughness values occurred at the lowest traverse rate and the standoff distance. The outcomes of investigation show that the water pressure (74.08 %) has the highest influence on surface roughness followed by traverse speed (17.28 %) and standoff distance (7.18 %) in machining of Al-Gr composite. Obtained mathematical modeling can be successfully employed to predict the surface roughness of composites.

REFERENCES

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Factors Affecting Surface Finish of Abrasive Water Jet ... · Surface roughness of carbides...

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