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journal of materials processing technology 197 (2008) 200–205 journal homepage: Comparison of slurry effect on machining asonic drilling , Ludhiana 28 May 2007 Accepted 1 June 2007 eviews carbide same quently presented on the production of 5mm diameter holes in pure titanium (TITAN15, ASTM Gr2) and titanium alloy (TITAN31, ASTM Gr.5) using ultrasonic drilling. This entailed the use of a 20kHz piezoelectric transducer with three solid tools of stainless steel, titanium and high-speed steel, operating in silicon carbide, boron carbide and alumina slurry. The data presented includes main effect plots for material removal rate and tool wear rate. The Keywords: Ultrasonic drilling Material removal rate Tool wear rate Silicon carbide Boron carbide Alumina Stainless steel Titanium High speed steel results suggested that boron carbide slurry and stainless steel tool was giving best material removal rate. Also relative hardness of tool–work piece affects the material removal rate in ultrasonic machining. ? 2007 Elsevier B.V. All rights reserved. 1. Introduction Titanium alloys are generally regarded as been amongst the most difficult of work piece materials to machine in spite of their relatively low hardness (e.g. Ti 6/4 annealed ～350HV). This is due to their low thermal conductivity, which con- centrates heat in the cutting zone (Ti 6/4 has a thermal conductivity of 11W/mK for AISI 405 steel), high chemical reactivity at elevated temperature and a tendency to form localized shear bands. Titanium and its alloys are branded as difficult to machine materials (Verma et al., 2003). Unfortu- nately, the machining of titanium is in general more difficult and consequently a significant proportion of production costs ? Corresponding author. E-mail address: rupindersingh78@ (R. Singh). may relate to machining, even though only small volumes of material may be removed. Titanium and its alloys are very popular and are very widely used in aerospace, marine gas turbine engines and surgical applications. Poor thermal con- ductivity of titanium alloys retard the dissipation of heat generated, creating, instead a very high temperature at the tool–work piece interface and adversely affecting the tool life (Dornfeld et al., 1999). Titanium is chemically reactive at elevated temperature and therefore the tool material either rapidly dissolves or chemically reacts during the machin- ing process resulting in chipping and premature tool failure (Verma et al., 2003). Compounding of these characteristics is the low elastic modulus of titanium, which permits greater 0924-0136/$ – see front matter ? 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.06.026 characteristics of titanium in ultr R. Singh a,? , J.S. Khamba b a Mechanical preferably those with low ductility (Koval Chenko et al., 1986; Kremer et al., 1988; Moreland, 1988) and hard- ness above 40HRC (Verma et al., 2003; Dornfeld et al., 1999; Ezugwa and Wang, 1997; Gilmore, 1990), e.g. inorganic glasses, silicon nitride, etc. (Thoe et al., 1998; IMS, 2002; Khamba and Singh Rupinder, 2003; Benedict Gary, 1987; Haslehurst, 1981; Pentland and Ektermanis, 1965). In this process tool is made of tough material, oscillated at frequencies of the order of 20–30Kc/s with amplitude of about 0.02mm. An abrasive filled fluid flushed through the gap between master and work piece. The material removal mechanism involves both erosion and grinding (Benedict Gary, 1987). The principle of stationary ultrasonic drilling has been shown in Fig. 1.The tiny abrasive c The the an this v g Singh r ab n fa glass 2002 drilling ducer e material, in 300 and F ? Three conventional tool materials namely stainless steel (SS), titanium (Ti) and high-speed steel (HSS) have been used as tool combinations with titanium as work material to find out material removal rate (MRRs) and tool wear rate (TWR) at fix slurry concentration and temperature. The slurry concentra- tion was fixed at 15vol.% and slurry temperature at 25.7 ? C (room temperature). An experimental set-up having a provi- sion for variation in the process parameters was designed and fabricated. Fig. 3 shows work piece dimensions. The dimen- sions of the tool were decided keeping in view the limitations of the ‘horn shape’ to economize the machining operation (Fig. 4). 2. Experimentation The experiments have been conducted in six set-ups. In the firstset-up,experimentwasperformedtodeterminetheeffect hip off microscopic flakes and grinds a counterpart of face. work material is not stressed, distorted or heated because grinding force is seldom over 2lb (IMS, 2002). There is never y tool to work contact, and presence of cool slurry makes a cold cutting-process. The tool used for machining has been prepared by sil- er brazing process (Singh, 2002). The amplitude of vibrations iven to the tool also influences the cutting rate (Khamba and Rupinder, 2003). It has been found that the material emoval rate is affected by amplitude of oscillations, size of rasive (Singh, 2002; Singh and Khamba, 2007a). There are umber of applications of ultrasonic drilling, ranging from the brication of small holes in alumina substrates, to engraving ware, to drilling large holes through laser blocks (IMS, ). Fig. 2 shows the three-dimensional view of ultrasonic using either a magnetostrictive or piezoelectric trans- with brazed and screwed tooling. It has been observed in xperimentationusingaluminaasslurryandTITAN15aswork materialremovalratefirstdecreaseswithinincrease power rating (from 150W to 300W) and than increases from W to 450W of ultrasonic drilling machine (USM) (Khamba Singh Rupinder, 2003). ig. 1 – Schematic diagram of ultrasonic drilling, t=penetration in to tool, ?w=penetration in to work piece. Fig. 2 – Three-dimensional pictorial view of USM. In the present experimental set-up the typical value of amplitude and frequency of vibration used were 0.0253–0.0258mm and 20kHz±200Hz. This experimental study has been conducted with the objective to understand material removal rate and tool wear rate comparison of TITAN15 and TITAN31 (having different composition, dif- ferent toughness) when drilled ultrasonically; with three different types of slurries, namely silicon carbide (SiC), boron carbide (B 4 C), and alumina (Al 2 O 3 ) (each of 320 grit size). The pure titanium TITAN15, has ultimate tensile strength of 491MPa (chemical analysis: C, 0.006%; H, 0.0007%; N, 0.014%; O, 0.140%; Fe, 0.05%; Ti, balance) and titanium alloy TITAN31, has ultimate tensile strength of 994MPa (chemical analysis: C, 0.019%; H, 0.0011%; N, 0.007%; O, 0.138%; Al, 6.27%; V, 4.04%; Fe, 0.05%; Ti, balance). The machining was performed on 500W Sonic-Mill, ultra- sonic drilling machine at three different power ratings (i.e. at 150W, 300W and 450W), based upon pilot experimentation. 202 journal of materials processing technology 197 (2008) 200–205 Fig. 3 – Detailed drawing of the work piece. on ‘TITAN15 of SS tool’ using alumina slurry of 320 grit size; at 15% concentration in distilled water as suspension media. The experiment started by setting power rating of the machine at (30% of 500W) 150W of ultrasonic drilling machine. The ini- tial weight of titanium work piece ‘that is of TITAN15’ and tool ‘that is of SS’ was measured. Then machine was allowed to drill for fixed depth of 1mm with constant slurry flow rate Fig. 5 – MRR and TWR vs. power rating using (W/P TITAN15 and tool SS). Fig. 6 – MRR and TWR vs. power rating using (W/P TITAN31 and tool SS). and slurry temperature. The depth was closely watched using dial gauge. Correspondingly, time taken by USM for drilling was measured using stopwatch. After machining was com- pleted, work piece and tool weight was measured for finding difference in weight loss. Corresponding material removal rate and tool wear rate were calculated at 150W, 300W, and 450W (30%, 60% and 90% of 500W). In the first set-up two more experiments were set using ‘TITAN15 work piece SS tool’ with B 4 C slurry and SiC slurry, respectively. Fig. 5 shows the trend of MRR and TWR of TITAN15 work material with SS tool at different power rating of machine used. The second set-up involved machining of ‘TITAN31 work piece by SS tool’ at three settings of ultrasonic power rating Fig. 4 – Detailed drawing of the tool geometry (Singh and Khamba, 2007a,b). with Al 2 O 3 ,B 4 C and SiC slurry. Corresponding MRR and TWR were plotted (refer Fig. 6). The third and fourth set-up covered machining of ‘TITAN15 and TITAN31 work piece by Ti tool’ at three settings of ultrasonic power rating with Al 2 O 3 ,B 4 C and SiC slurry. Corresponding MRR and TWR were plotted (refer Figs. 7 and 8). In the fifth and sixth set-up machining of ‘TITAN15 and TITAN31 work piece by HSS tool’ at three settings of ultra- sonic power rating with Al 2 O 3 ,B 4 C and SiC slurry has been performed. Corresponding MRR and TWR were plotted (refer Figs. 9 and 10). journal of materials processing technology 197 (2008) 200–205 203 Fig. 7 – MRR and TWR vs. power rating using (W/P TITAN15 and tool Ti). 3. Results and discussion From repetitive number of experiments conducted under six different set-ups, the comparative results have been plotted. From Fig.5,ithasbeenobservedthatMRRofTITAN15isoverall lo e similar mac r kinetic piece decr piece F and and tool HSS). Fig. 10 – MRR and TWR vs. power rating using (W/P TITAN31 and tool HSS). wer than TWR while using SS tool with Al 2 O 3 slurry. How- ver trend for MRR in all three experiments of first set-up were . The increase of MRR with increase in power rating of hine is quite obvious because of higher value of power ating abrasive particles strikes with more momentum and energy with work piece. Hence more erosion of work but in certain cases, with increase in power rating, MRR eases which may be because of strain hardening of work . The increase of tool wear rate with increase in MRR and ig. 8 – MRR and TWR vs. power rating using (W/P TITAN31 tool Ti). Fig. 9 – MRR and TWR vs. power rating using (W/P TITAN15 power rating is quite obvious but sometimes TWR decreases withpowerratingincrease/increaseinMRR;thereasonforthis isagainstrainhardeningoftoolsurface.Theselectionofslurry type for MRR of ‘TITAN15’ in this case comes out as unimpor- tant factor. However better tool properties were obtained with Al 2 O 3 slurry. As regards to machining of ‘TITAN31 with SS tool’ the trend for MRR and TWR were different from previous case of ‘TITAN15 with SS tool’ (refer Fig. 6). The main reason for this variation may be strain hardening of work piece/tool material at specific ultrasonic power rating based upon its mate- rial/chemical composition characteristics. The best parameter setting for machining of ‘TITAN31 with SS tool’ has been observed at 300W with B 4 C slurry. 204 journal of materials processing technology 197 (2008) 200–205 compar (Ra references Fig. 11 – Photomicrograph of the machined surface showing machining; magnification: 100×. Ultrasonic machined surface In the next set-up while using titanium tool it has been found that for ‘TITAN15’; MRR showed insignificant effect of slurry type, where as for ‘TITAN31’ choice of slurry has come out as important factor. The best settings have been attained with B 4 C slurry at 300W for ‘TITAN31’. The fifth and sixth set-up highlighted machining with ‘HSS tool’ for ‘TITAN15 and ITAN31’ work piece. The trend obtained for MRR and TWR in fifth and sixth set-ups is almost similar for Al 2 O 3 and B 4 C slurry, but for SiC some variation has been observed. Overall B 4 C slurry comes out as better option. This may be because of better work piece and tool combinations based on relative hardness of tool and work piece for specific machining conditions. Fig. 11 shows the surface of an ultrasonically machined titanium sample exhibits a non-directional surface texture when compared with a conventionally machined (ground) sur- face. These refined grain structure, resulting from ultrasonic machining, can give better strength and mechanical proper- ties. The results agree with experimental observations made otherwise (Singh and Khamba, 2006, 2007b; Jadoun et al., 2006). 4. Conclusions From the experiment following conclusions can be drawn: 1. Titanium is well machinable using ultrasonic drilling machine. It is not always necessary that if work piece with higher toughness value is machined, it will have less MRR rather it is combination effect of material composition (hardness of work piece) relative of tool and work piece. Less TWR and better MRR can be attained by using spe- cific tool, work piece combination at specific power rating values and controlled experimental conditions like slurry type. 2. Best results have been obtained with SS tool and boron car- bide slurry. These results show close relationship between the experimental observations made otherwise (Singh and Khamba, 2007b). 3. No major fatigue problems were encountered with the stainless steel, titanium and high-speed steel tool, any chipping/fracture generally being due to tool/hole mis- alignment during fabrication. ison of the conventional machining and ultrasonic 0.46), conventionally machined surface (Ra 0.8). 4. The verification experiments revealed that on an average there was 34.46% improvement in MRR, for the selected work piece (TITAN15 and TITAN31). Benedict Gary, F., 1987. Non Traditional Manufacturing Processes. Marcel Dekker, Inc, pp. 67–86. Dornfeld, D.A., Kim, J.S., Dechow, H., Hewsow, J., Chen, L.J., 1999. Drilling burr formation in titanium alloy Ti–6Al–4V. Ann. CIRP 48, 73–76. Ezugwa, E.O., Wang, Z.M., 1997. Titanium alloys and their machinability—a review. J. Mater. Process. Technol. 68, 262–274. Gilmore, R., 1990. Ultrasonic Machining of Ceramics, SME Paper MS 90-346, p. 12. Haslehurst, M., 1981. Manufacturing Technology, 3rd ed. Arnold, Australia, pp. 270–271. 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