An investigation on use of colemanite powder as abrasive in abrasive waterjet cutting (AWJC)

Transcription

1 Journal of Mechanical Science and Technology 26 (8) (2012) 2371~ DOI /s An investigation on use of colemanite powder as abrasive in abrasive waterjet cutting (AWJC) Gulay Cosansu 1 and Can Cogun 2,* 1 TAI (Turkish Aerospace Industries Inc.), Kazan 06980, Ankara, Turkey 2 Mechanical Engineering Department, Faculty of Engineering, Middle East Technical University, Ankara, Turkey (Manuscript Received August 24, 2011; Revised January 9, 2012; Accepted April 3, 2012) Abstract In the present study, the cutting performance outputs (surface roughness, surface waviness and kerf taper angle) of colemanite powder as abrasive in abrasive waterjet cutting (AWJC) with varying traverse rate and abrasive flow rate were investigated experimentally. The performance outputs were compared to that of garnet which is in common use in industry as abrasive in AWJC industry. Al7075, marble, glass, Ti6Al4V and a composite material were selected as sample materials in the experiments. Furthermore, colemanite powder was mixed with garnet powder at certain proportions and the obtained surface characteristics were compared with those cut with pure garnet powder. It is found experimentally that in spite of higher amount of colemanite powder consumption with respect to garnet to perform the same cutting action, the colemanite powder could be an alternative powder for AWJC process. Keywords: Abrasive waterjet cutting (AWJC); Colemanite powder; Garnet powder; Surface characteristics; Kerf taper angle Introduction Abrasive waterjet cutting (AWJC) is one of the extensively used non-traditional machining processes in industry to cut different types of materials [1]. In AWJC, water is used as the medium for transferring the momentum of abrasive onto the workpiece to enhance material erosion process. The abrasive such as garnet (Fe 2 O 3 Al 2 (SiO 4 ) 3 ), aluminum oxide (Al 2 O 3 ) or silicon carbide is accelerated by a thin stream of high velocity waterjet and directed through a nozzle towards to the target material [2]. The mixing between abrasives, waterjet and air takes place in the mixing chamber and the acceleration process occurs in a focusing tube. After the mixing and acceleration process, a high-speed three phase suspension leaves this tube at velocities of several hundred meters per second [3]. The process offers possibilities to cut difficult-to-machine materials, such as ceramics, reinforced and composite materials and heat sensitive alloys [4]. The obtained cutting surface without any heat affected zone and residual stress is the advantage of AWJC [5]. Although olivine (Fe 2 SiO 4 ), aluminum oxide (Al 2 O 3 ), silica sand (SiO 2 ), glass bead, silicon carbide (SiC) and zirconium are the other abrasives used, the garnet (7.5-8 Mohs hardness) is the most commonly used abrasive in AWJC with the user rate of 90% [6]. Its high cost compared to * Corresponding author. Tel.: , Fax.: address: cogun@metu.edu.tr Recommended by Associate Editor Haedo Jeong KSME & Springer 2012 Fig. 1. General characteristics of cut surface (a = thickness of workpiece, hrf = region of finish cutting, hrb = region of rough cutting, n = trail back) [7]. the others is the main disadvantage of the powder. Authors of this paper believe that an alternative abrasive powder which is vastly available and has a lower cost than garnet would contribute greatly to reduce the costs of the AWJC process. Surface roughness, surface waviness and the kerf taper angle are the basic performance measures that characterize the AWJ cut surface topography. The surface topography of a cut by AWJC (Fig. 1) is well characterized by Guo et al. [7]. The kerf geometry starts with a small rounded corner at the top edge due to the plastic deformation of material caused by jet bombardment. As the kerf is wider at the top than at the bot-

2 2372 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~2380 Fig. 2. Schematic definition of kerf geometry [8]. Fig. 3. AWJC zones defined by Hashish (dj = incoming water jet diameter, x = deformation zone lateral axis, h = deformation zone depth axis) [9]. Fig. 4. Striations at the jet exit. tom due to the decrease in water pressure, a taper is produced (Fig. 2). When cutting ductile materials, burrs occur at the jet exit due to rolling over of the plastically deformed material [8]. Hashish [9] defines the cutting process of abrasive jets with two zones, namely cutting and deformation wear zones (Fig. 3). In the first, cutting occurs when particles impact the cutting surface at shallow angles. In the second, a step is formed and removed, and striations occur by particles striking at large angles of impact. Fig. 4 shows striations formed at the jet exit. AWJC performance is related to hydraulic, mechanical, mixing (concentration) and abrasive parameters [10]. One of the important parameters that effect AWJC performance is hardness of the abrasives used in the process. Ohman [11] stated that the harder abrasive assures faster and deeper cutting. In the experimental study of Axinte et al. [12], the AWJC trials on PCD (polycrystalline diamond) grades with different types of abrasives proved the effect of abrasive hardness on AWJC. The results revealed that while garnet can be considered as ineffective in achieving through cut even in PCD grades with lower intergrowth, the jet penetration significantly improves with the increase of abrasive hardness and sharpness (Al 2 O 3 to SiC); spectacular increase of traverse rate (125 times faster than SiC) can be achieved with a diamond abrasive (10 Mohs hardness). Diamond abrasives also enhance highly acceptable kerf taper angle and surface roughness values. However, the use of diamond as an abrasive in AWJC is not cost-effective. Also, the utilization of Al 2 O 3, SiC and especially diamond abrasives increased the wear rates of the focusing nozzle compared to the similar values obtained in garnet abrasives [12]. The increase in wear rate of the focusing nozzle also affects the economics of AWJC negatively. Khan and Haque [5] also performed an experimental work for cutting glass workpiece by using garnet, Al 2 O 3 and SiC abrasives. Results indicated that garnet abrasive produced the largest kerf taper angle followed by Al 2 O 3 and SiC abrasives. The authors of the work also found that the taper of cut increases with increase in traverse rate and stand of distance (SOD), and decreases with increase in water jet pressure. In the Azmir and Ahsan study [1], the effect of abrasive material, hydraulic pressure, abrasive flow rate, traverse rate, cutting orientation on the surface roughness and kerf taper angle for glass/epoxy composite laminate workpiece were investigated. It was found that Al 2 O 3 abrasive gave a better surface finish and smaller kerf taper angle than the garnet abrasive which has a lower hardness than Al 2 O 3. Increase in the hydraulic jet pressure and abrasive mass flow rate and decrease in the SOD and traverse rate resulted in better surface roughness and kerf taper angle. Colemanite (CaB 3 O 4 (OH) 3 H 2 O, 4.5 Mohs hardness) is a raw boron containing mineral. Approximately 64.4% of Turkey s boron reserve is comprised of colemanite. Currently, it is used as raw material in production of boric acid, borax and sodium perborate chemicals. The comparably high hardness and low price of the colemanite powder, in particular, make the powder a candidate for AWJC purposes. In this paper, colemanite powder was tested as abrasive in AWJC for various workpiece (sample) materials. The performance outputs (surface roughness, surface waviness and kerf taper angle) of colemanite powder were evaluated for varying traverse rates and abrasive flow rates in comparison to garnet powder s. Colemanite powder was also mixed with garnet powder at certain proportions and the resulting surface characteristics of cut samples were compared with those obtained in pure garnet powder tests. 2. Experimental work 2.1 Abrasives used Garnet (Fe 2 O 3 Al 2 (SiO 4 ) 3 ) is the most commonly used abrasive in AWJC. Its hardness is Mohs. Chemical composi-

3 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~ Table 1. Chemical composition of garnet powder. Chemical composition SiO 2 36% FeO 30% Al 2 O 3 20% MgO 6% Fe 2 O 3 2% CaO 2% TiO 2 1% Others 1% Table 2. Chemical composition and physical characteristics of Bigadiç (Turkey) colemanite. Chemical composition B 2 O 3 35% CaO 27% SiO 2 8% SO 4 0.7% Crystal system Monoclinic Hardness 4.5 Mohs Density 2.42 g/cm 3 Table 3. Mechanical properties and thicknesses of sample materials. UTS (MPa) tion of garnet is given in Table 1. It s mostly supplied from Australia and India by industrialists with a price of $/ton. The average size of garnet abrasive used in the tests is 80 mesh ( µm). The colemanite (CaB 3 O 4 (OH) 3 H 2 O) powder (4.5 Mohs hardness) used in the tests is provided by ETI Mine Works Technology Development Department in Turkey in form of mm rocks. The domestic sale price for Bigadiç (Turkey) colemanite is $/ton. The average size of colemanite abrasive used in the tests is 80 mesh. The chemical composition and physical characteristics of the powder are summarized in Table Sample (workpiece) materials Density (g/cm 3 ) Thickness (mm) Al Composite Marble Ti6Al4V Glass The mechanical characteristics and thicknesses of the sample (workpiece) materials (Al7075, composite material, marble, Ti6Al4V, glass) cut in the tests are given in Table 3. The composite material is AS4 carbon fiber (carbon prepreg/epoxy laminates) of Hexcel Company with 7.1 µm fiber diameter, 94% carbon content, 40 plies, 60% fiber content and direction Fig. 5. Cut samples and cutting paths. of lay +45/0/-45/0/-45/90/+45/0/+45/90/+45/90/+45/0/-45/90/ 90/-45/0/ Method Colemanite material, originally in mm size of rocks, was crushed and ground to average 80 mesh size which is almost equal to the grit size of garnet used in the tests. The AWJ cutting path designed for the cutting trials is illustrated in Fig. 5. The reason for designing the cutting path in linear, radial and angular forms is to observe effect of jet cutting characteristics at different paths. The machine used in the tests was a 3 axis CNC controlled machine (Cutting Technologies & Machines Inc.) with Uhde HP 19/45-S pump. The machining (cutting) parameters kept constant throughout the experiments were hydraulic jet pressure (450 MPa), orifice diameter (0.25 mm), nozzle diameter (1.02 mm), standoff distance (SOD) (2 mm), abrasives grit size (80 mesh) and jet impact angle (90 o ). Three different traverse rate and abrasive flow rate settings were selected for the abrasive types. The cutting parameters used are summarized in Table 4. Initial AWJ cuts for all samples were performed by garnet powder. The cutting parameter levels selected in the experiments were compatible with the values common in industrial applications. Based on Table 5, the traverse rates for colemanite are lower than the ones with garnet. Since the hardness

4 2374 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~2380 Table 4. Cutting parameters used in the experiments. No Abrasive Workpiece Cutting parameters material Traverse Abrasive 1 Al Composite Garnet Burdur beige Glass Ti6Al4V Colemanite Al Colemanite Composite Burdur beige 17 Colemanite (marble) Colemanite Glass Colemanite Ti6Al4V Al % Colemanite + 70% Composite Burdur beige Garnet 24 (in volume) Glass Ti6Al4V Al % Colemanite + 50% Composite Burdur beige Garnet 29 (in volume) Glass Ti6Al4V 80 5 Table 5. Cost of colemanite powder in Turkey. Domestic (Turkey) sale price of raw colemanite ($/ton) Electricity cost (crushing, grinding) ($/ton) 3.50 Consumable materials cost ($/ton) 1.00 Dehydration cost ($/ton) 1.00 Labor cost ($/ton) 6.00 Overhead cost ($/ton) 2.00 Profit ($/ton) Cost of colemanite powder ($/ton) of colemanite powder is lower than that of the garnet powder, it requires more time to cut the same length. Second and third levels of traverse rates and abrasive flow rates were determined after the initial trial cuts. Totally, 30 experiments were conducted. Surface roughness and surface waviness measurements were performed by using Marsurf M300 portable surface measuring instrument. The Fig. 6. AWJ cut surfaces of Al7075 with colemanite powder for varying abrasive flow rates (the photographs are taken from 40 mm straight cutting path (demonstrated in Fig. 5). surface roughness and surface waviness were measured over the edge of the cut specimen (across the thickness of the test sample surface) at 2, 4, 6 and 8 mm depths in material thickness direction. The surface roughness, waviness and kerf taper profiles were taken between 2 mm above the bottom surface and 2 mm below the top surface in order to avoid the effects of jet exit and entry, respectively. Due to the variability of surface data (i.e. surface roughness, surface waviness and kerf taper angle) three different measurements were taken at each sample along the linear cutting path at 10, 20 and 30 mm positions so that averages could be calculated. 3. Results and discussion 3.1 Experiments with colemanite powder Colemanite powder succeeded in cutting Al7075, composite material and marble (Burdur Beige) materials. In spite of using lower traverse rate (50 mm/min) and higher abrasive flow rate (10 g/s) with respect to garnet powder (300 mm/min, 5 g/s), frequent occurrence of cracks were observed during the cut trials of glass Al7075: The experiments of Al7075 with colemanite powder were started at 80 mm/min traverse rate and 5 g/s abrasive flow rate. Due to intensive striation formation at the jet exit zone, abrasive flow rate was increased to 7.5 and 10 g/s levels. Fig. 6 shows the surface textures taken from 40 mm straight cutting path (illustrated in Fig. 5) for various abrasive flow rates. Based on the figure, it is obvious that the increasing abrasive flow rate leads less striation at the bottom of the cut surface. Fig. 7 illustrates the variation of surface roughness, surface waviness and kerf taper angle with varying abrasive flow rate at 2, 4, 6 and 8 mm depths (in material depth direction). The figure shows that increasing abrasive flow rate decreases surface roughness, surface waviness and kerf taper angle values. Especially, in the deformation wear zone, the decrease in surface roughness and waviness is evident (Figs. 6 and 7). Increase in abrasive flow rate also reduces the jet deflections and burr formation at the jet exit region (Fig. 8). This is mainly due to the improved cutting ability of the jet with increasing amount of abrasive impinges to the work surface in

5 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~ Fig. 7. Effect of abrasive flow rate on: (a) surface roughness; (b) surface waviness; (c) kerf taper angle for Al7075 with colemanite powder. (a) (b) Fig. 8. The burr formations (circled with white color) and jet deflections (circled with black color) for varying colemanite abrasive flow rates for Al7075 material. unit time. In the second set of experiments, the traverse rate was increased gradually (40 mm/min, 80 mm/min and 100 mm/min) to observe the variation in cutting performance with colemanite powder. Throughout the experiments, abrasive flow rate was kept constant (7.5 g/s). The colemanite powder was successful in cutting Al7075 even for traverse rates higher than 100 mm/min. However, the traverse rate was limited by 40 mm/min, since the higher values resulted in poor surface roughness, high surface waviness and high kerf taper angle (Fig. 9) which weren t comparable to those obtained with garnet abrasive. Increase in traverse rate, resulting in less overlapping machining action of the jet and less abrasive particles impinging to surface [13], increases the surface roughness and kerf taper angle (Figs. 9a and 9c) as well as jet deflections and burr formations (Fig. 10) Comparison of Al7075 cutting costs for colemanite and garnet powders: The surface roughness values obtained through the depth of cut by using garnet and colemanite powders at different cutting conditions are illustrated in Fig. 11. At 2 mm and 4 mm depth of cuts, the colemanite powder gives a little better surface quality. At higher depth of cuts (6 mm and 8 mm) the obtained surface roughness values are almost equal. For the sake of convenience of cost comparisons, the obtained surface roughness values for the both powders are considered equal. The experimental findings (Fig. 11) reveals that the (c) Fig. 9. Effect of traverse rate on: (a) surface roughness; (b) surface waviness (c) kerf taper angle for Al7075 with colemanite powder. Fig. 10. The burr formation and jet deflections for varying traverse rates for Al7075 with colemanite powder. surface roughness values obtained with garnet powder can be accessible with colemanite powder at 60% lower traverse rate and 100% higher abrasive flow rate settings. It is clear that more amount of colemanite powder should be used to get the same surface quality obtained with garnet powders.

6 2376 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~2380 Table 6. Comparison of Al7075 cutting (machining) costs for colemanite and garnet powders. Abrasive Garnet Colemanite Traverse rate (mm/min) Abrasive flow rate (g/s) 5 10 Length of cut (m) 1 1 Cutting time (min) Spent abrasive (g) Cost of abrasive ($/ton) 700 (India price) Machining cost ($/m) Fig. 12. AWJC surfaces of composite material with colemanitepowder for varying abrasive flow rates. Fig. 11. Surface roughness values obtained by using colemanite and garnet powders under different cutting conditions for Al7075 material. (a) (b) (c) Fig. 13. Effect of abrasive flow rate on: (a) surface roughness; (b) surface waviness; (c) kerf taper angle for composite material with colemanite powder. The possible use of colemanite as an abrasive in AWJC must also be discussed in terms of comparative costs of garnet and colemanite powders to get similar cut surface characteristics. Table 5 summarizes cost elements (raw material cost, electricity cost for crushing and grinding, consumable materials cost, labor cost, dehydration (heating) cost, overhead and profit) of producing per ton of colemanite powder in Turkey. Consumption costs of garnet and colemanite powders are listed in Table 6 for the machining settings given in Fig. 11. Machining cost term in the paper defines the cost of abrasive amount consumed in cutting per meter length of workpiece material. The cost of electricity consumed during cutting and other facility utilization costs were neglected. The nozzle wear rate (i.e. nozzle cost) is expected to be higher in use of hard garnet abrasive than the colemanite in AWJC. In the present study, the preliminary tests indicated that higher amount of colemanite use than the garnet powder for realizing the same cutting effect balances the nozzle wear for both cases. Considering this finding and the long life of nozzles as well in AWJC, the nozzle cost is neglected in machining cost calculations. Based on the table, five times more amount of colemanite powder is required for obtaining the same surface quality, leading to higher consumption cost of colemanite, even though the cost of per ton colemanite powder is about the one third of the garnet. For cutting Al7075, the consumption cost of colemanite powder is 1.8 times higher than that of garnet powder use Composite Material: The composite material cutting tests were performed at 250 mm/min traverse rate for 5, 7.5 and 10 g/s flow rate settings using colemanite abrasive. Ruptured cut surfaces were observed in the jet exit side at 5 g/s abrasive flow rate setting (Fig. 12). The rupturing was eliminated by increasing the abrasive flow rate to 7.5 g/s. Increasing abrasive flow rate also reduced striation occurrences and surface roughness, surface waviness and kerf taper angle values (Fig. 13).

7 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~ Table 7. Comparison of composite material cutting costs for colemanite and garnet powders. (a) Abrasive Garnet Colemanite Traverse rate (mm/min) Abrasive flow rate (g/s) 5 10 Length of cut (m) 1 1 Cutting time (min) Spent abrasive (g) Cost of abrasive ($/ton) Machining cost ($/m) (b) Fig. 15. Surface roughness values obtained by using colemanite and garnet powders under different cutting conditions for composite material. (c) Fig. 14. Effect of traverse rate on: (a) surface roughness; (b) surface waviness; (c) kerf taper angle for composite material with colemanite powder. Since the performance of colemanite powder for composite material cutting was not satisfactory at traverse rates higher than 250 mm/min, experiments were performed at lower settings (Fig. 14). As illustrated in the figure, an increase in traverse rate increases surfaces roughness, surface waviness and the kerf taper angle. This is attributed to the impingement of fewer abrasive particles to the surface in unit time as also the case in Al7075 tests Comparison of composite material cutting costs for colemanite and garnet powders: Surface roughness values obtained by colemanite and garnet powders use at different cutting conditions for composite material are illustrated in Fig. 15. Experiments with colemanite powders performed at three times slower traverse rates than garnet powder (at the same abrasive flow rates) to achieve resembling surface roughness characteristics. Although, the calculated machining costs for both abrasives were very close to each other (Table 7), the surface roughness values obtained with colemanite powder was still little higher than that of garnet. However, the obtained average surface roughness (Ra) values, ranging μm, with use of colemanite powder was highly acceptable for composite cutting applications. In order to obtain very close surface roughness values, the traverse rate of cutting with colemanite powder must be reduced by 20% resulting in 20% increase in colemanite powder consumption as well as machining cost Burdur beige (marble): The experiment with Burdur beige (marble) was conducted initially at 50 mm/min traverse rate and 10 g/s colemanite flow rate settings. Poor cutting performance was experienced despite of using maximum abrasive flow rate setting. Throughout the experiments, traverse rate was also set to 40 and 60 mm/min (at 10 g/s flow rate). Increasing traverse rate increased the surface roughness, surface waviness and kerf taper angle (Fig. 16) and resulted in heavily fractured cutting edges leading poor cutting details (Fig. 17) Comparison of marble cutting costs for colemanite and garnet powders: The surface roughness values obtained with colemanite powder at traverse rate of 40 mm/min, abrasive flow rate of 10 g/s and with garnet powder at traverse rate of 300 mm/min and abrasive flow rate of 5 g/s are given in Fig. 18. The traverse rate and abrasive flow rate were set to 1/7.5 and twice of the garnet, respectively, to obtain similar surface characteristics in colemanite powder trials with garnet. At 2, 6 and 10 mm depth of cuts, the colemanite powder enhances even better surface roughness values. At 15 and 18 mm depth of cuts, the surface roughness values obtained from garnet are

8 2378 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~2380 Table 8. Comparison of costs of colemanite and garnet powders for marble cutting. (a) Abrasive Garnet Colemanite Traverse rate (mm/min) Abrasive flow rate (g/s) 5 10 Length of cut (m) 1 1 Cutting time (min) Spent abrasive (g) Cost of abrasive ($/ton) Machining cost ($/m) (b) Fig. 18. Surface roughness values obtained by colemanite and garnet powders under different cutting conditions for marble. 3.2 Experiments performed using mixture of colemanite and garnet powders Fig. 16. Effect of traverse rate on: (a) surface roughness; (b) surface (c) Fig. 17. Effect of traverse rate on fracture of marble material with colemanite powder. 30%-50% better than that of colemanite. Based on Table 8, the machining cost of colemanite powder for cutting marble was 5.7 times higher than that of garnet due to low traverse rate and high abrasive flow rate requirements. The authors of the present study expected to get better surface quality by creating polishing effect on the cut surface by the addition of softer colemanite powder into harder garnet powder. In this direction, tests were performed for all sample materials by using abrasive mixtures containing 30% and 50% colemanite powders (in volume). The cutting parameter settings mentioned before for the garnet powder experiments were used for the mixed powder experiments. Referring to Figs. 19(a), 19(c) and 19(d), the addition of 50% colemanite compared to 30% colemanite addition did not have a significant effect on the surface roughness for Al7075, marble and glass tests. For composite material cutting (Fig. 19(b)), the deterioration of surface roughness with an increase of colemanite addition was more evident. Although, the abrasive mixture containing 30% colemanite was successful in cutting Ti6Al4V material, the surface quality was slightly lower compared to the one obtained with pure garnet powder (Fig. 19(e)). The abrasive mixture containing 50% colemanite powder wasn t even successful in cutting Ti6Al4V material (Fig. 20). 4. Conclusion This paper reports the results of an investigation on the performance of colemanite powder as candidate abrasive for AWJC process. Summarizing the main features of the results, the following conclusions may be drawn:

9 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~ (a) (b) (c) (d) (e) Fig. 19. Effect of colemanite addition to garnet powder on surface roughness for (a) Al7075; (b) Composite; (c) Burdur Beige (marble); (d) Glass; (e) Ti6Al4V materials. Fig. 20. Jet exit side view of the Ti6Al4V material (poorly cut path is the below one) cut with abrasive mixture containing 50% colemanite and 50% garnet. (1) The tests performed by using garnet and colemanite powders with different traverse rates revealed that increase in traverse rate increases surface roughness, surface waviness and kerf taper angle. Burr formation for ductile materials and fracture occurrences for brittle materials increase with increasing traverse rates. The increase in abrasive flow rate reduces surface roughness, surface waviness and kerf taper angle due to the impinging of more powder particles to the surface in unit time. (2) Colemanite powder succeeded in cutting Al7075, composite and Burdur beige (marble) materials. The surface roughness values obtained with colemanite powder in cutting Al7075 material could approach to that of garnet when using the 40% lower traverse rate and twice abrasive flow rate of garnet tests. In cutting composite material with colemanite powder, in spite of using very low traverse rates compared to garnet powder the surface roughness values were still little higher. The results indicated that lower hardness of the colemanite powder compared to that of garnet reduced the cutting

10 2380 G. Cosansu and C. Cogun / Journal of Mechanical Science and Technology 26 (8) (2012) 2371~2380 performance measures (surface roughness, waviness and kerf taper angle) significantly. The tests performed by using mixed powder (containing 30% and 50% colemanite powder in volume) weren t successful in creating polished cut surfaces. (3) Higher amount of colemanite powder consumption with respect to garnet powder (1.8 times higher for cutting Al7075 and 5.7 times higher for cutting Burdur beige marble) leads higher machining cost. In spite of this, cutting test confirms that the colemanite powder is an alternative powder for AWJC processes in case of garnet or other high hardness powder shortages in the world. The cutting performance and the cost-effectiveness of colemanite powder can be improved by using different powder particle geometries, different size of powders, chilled water jets and different water jet nozzle geometries to whirl the emerging jet. References [1] M. A. Azmir and A. K. Ahsan, A study of abrasive water jet machining process on glass/epoxy composite laminate, Journal of Materials Processing Technology, 209 (2009) [2] R. Kovacevic, R. Mohan and H. Beardsley, Monitoring of thermal energy distibution in abrasive water jet cutting using infrared thermography, ASME, Journal of Engineering Industry, 118 (1996) [3] A. W. Momber, Energy transfer during the mixing of air and solid particles into a high-speed waterjet: an impact-force study, Experimental Thermal and Fluid Science, 25 (2001) [4] A. W. Momber, I. Eusch and R. Kovacevic, Machining refractory ceramics with abrasive water jets, Journal of Material Science, 31 (1996) [5] A. A. Khan and M. M. Haque, Performance of difference abrasive materials during abrasive water jet machining of glass, Journal of Materials Processing Technology, 191 (2007) [6] G. A. Mort, Results of abrasive water jet market survey, Proc. of 8th American Water Jet Conference, Vol. 1, Houston, Texas, USA (1995). [7] N. S. Guo, H. Louis and G. Meier, Surface structure and kerf geometry in abrasive water jet cutting: formation and opti- mization, Proc. of 7th American Waterjet Conference, Seattle, USA (1993). [8] L. F. Chen, J. Wang, E. Lemma and E. Siores, Striation formation mechanism on the jet cutting surface, Journal of Process Technology, 141 (2003) [9] M. Hashish, A modeling study of metal cutting with abrasive waterjets. ASME, Journal of Engineering Industry, 106 (1984) [10] A. W. Momber and R. Kovacevic, Principles of Abrasive Waterjet Machining, Springer-Verlag, London, UK (1998). [11] J. L. Ohman, Abrasives: Their characteristics and effect on waterjet cutting, Proc. of 7th American Waterjet Conference, Seattle, USA (1993). [12] D. A Axinte, D. S. Srinivasu, M. C. Kong and P. W. Butler-Smith, Abrasive waterjet cutting of polycrystalline diamond: A preliminary investigation, International Journal of Machine Tools and Manufacture, 49 (2009) [13] A. Hascalik, U. Caydas and H. Gurun, Effect of Traverse Speed on Abrasive Waterjet Machining of Ti6Al4V Alloy, Materials and Design, 28 (2007) Gulay Cosansu graduated from Gazi University Mechanical Engineering Department (Ankara, Turkey) in She completed her master degree in 2010 at the same department. She worked as manufacturing engineer in an automotive industry company for 4 years and she is currently working as design specialist at TAI (Turkish Aerospace Industries Inc.). Can Cogun is currently teaching in Mechanical Engineering Department of Middle East Technical University in Ankara (Turkey). His research and teaching activities are on nontraditional machining processes (especially, electric discharge machining (EDM) and wire EDM), machining theory, conventional machine tools, manufacturing systems, manufacturing automation.