Nonconventional cutting of plate glass using hot air jet: experimental studies

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1 Mechatronics ) 595±615 Nonconventional cutting of plate glass using hot air jet: experimental studies E.S. Prakash a, *, K. Sadashivappa a, Vince Joseph b, M. Singaperumal c a Department of Mechanical Engineering, Bapuji Institute of Engineering and Technology, Davangere , India b Department of Mechanical Engineering, University BDT College of Engineering, Davangere , India c Precision Engineering and Instrumentation Laboratory, Indian Institute of Technology, Madras, Chennai , India Received 6 December 1999; accepted 11 February 2000 Abstract Glass is an important engineering material used in several applications because of its attractive look, chemical stability towards environment, nonporosity, and transparent nature. Its application is widely found in optomechatronic systems, windows of buildings, art work, etc. Glass cutting is the rst step in the fabrication for any of its applications. Conventionally, plate glass soda lime glass) is cut by a diamond point tool or a diamond wheel. The cut surfaces by this method are rough and wavy. Microcracks, which a ect the life and quality of glass, may develop during cutting. It is di cult to cut nonstraight pro les by the conventional method and glass wastage is more. Curved pro les cannot be cut in a single step. Recently, glass cutting using laser and abrasive waterjet have been developed. Laser cutting is very costly, unsafe and leaves a heated-a ected zone. Researchers have used laser cutting on glasses of thicknesses lesser than 1 mm. Abrasive waterjet requires de-ionized very high pressure water with entrained garnet abrasive. This method produces rough cut surfaces and causes wear of diamond nozzles. A novel method is developed which uses a low cost, simple, hot air jet to cut any complex pro le with ease. Experimental studies are conducted to determine the variation of the cutting speed for various values of the stand-o distance, glass thickness, air temperature, and air ow rates. Glasses in the thickness range of 2±20 mm are used for the experiments. The roughness of the * Corresponding author. Fax: addresses: es_prakash@usa.net E.S. Prakash), mech2@iitm.ernet.in M. Singaperumal) /01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S )

2 596 E.S. Prakash et al. / Mechatronics ) 595±615 Nomenclature D nozzle diameter at exit, mm f 1 low air ow rate setting f 2 high air ow rate setting h stand-o distance SOD), mm L length of cutting, mm t plate glass thickness, mm T a air temperature at the nozzle exit, C V glass cutting speed, mm/min maximum glass cutting speed, mm/min V m cut surfaces using the hot air jet and the diamond point tool is compared. The new method has produced cut surfaces of relatively higher surface nish. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Nonconventional cutting; Plate glass cutting; Thermal cutting; Pro le cutting; Hot air jet; Crack propagation 1. Introduction Glass has been one of the important engineering materials used by man since ancient times. People rst used natural glass to make hunting tools. With the advances made in the glass industry in recent times, it has become the most versatile engineering material for use in both domestic and modern, industrial and laboratory applications. Glass is chemically stable in the environment. It has an excellent property to resist attack by water vapour, carbon dioxide, and bacterial and plant organisms. An increase in the diversi ed use of man-made glass, from decorative toys to astronomical mirrors and telescopes to microscopes, has given enough scope for research on this versatile material. Plate glass is used for windows i.e., in buildings, ships, automobiles, locomotive cars, and microwave ovens. It is also used for tableware, art glass, partition walls, interior decoration and a variety of other applications. Glass, for a speci c application, needs to be fabricated to the required size and shape. Glass cutting is inevitably the rst step in any fabrication method Conventional and other glass cutting methods Conventionally, plate glass cutting is usually done by using a diamond point tool. The steps followed are: a) marking and scribing shallow cutting) on the plate glass surface as per the desired pro le using a diamond point tool, and b) application of an external force on the glass with extreme skill so that the glass breaks along the scribing. The cut surface obtained by the above method, is always irregular, wavy and with poor surface nish, in spite of the amount of skill used and the care taken. Hence, grinding and polishing are required to bring the glass to the required size,

3 E.S. Prakash et al. / Mechatronics ) 595± shape and surface nish. But this increases the fabrication cost and is highly timeconsuming. The glass damages are more likely during cutting. Also, it is impossible to cut complex pro les shapes other than a straight line) in a single step with the conventional cutting. These disadvantages are very much inherent in the cutting method itself. The size and shapes obtained are always unpredictable. Fig. 1 shows the steps followed for cutting a circle by the conventional method. A lot of damage can occur in this method and the damage is cumulative if the number of steps taken to give the nal shape is more. During the conventional cutting process there is a possibility of developing internal aws and small cracks, which reduce the life and quality of the plate glass. Owing to the inherent uncertainty, repeatability is very poor. Researchers have developed other glass cutting methods such as laser and abrasive waterjet. Laser cutting of glass has many advantages: it is a noncontact process, amenable to computer control, and is able to produce complex shapes. Two laser shaping methods, termed controlled fracture and scribing are used. These do not involve full through-section cutting. In the controlled fracture method, the laser is used to produce large local thermal stresses which cause fracture. The fracture path Fig. 1. Steps for cutting a circle by conventional method.

4 598 E.S. Prakash et al. / Mechatronics ) 595±615 follows the beam as it traverses the specimen and leads to separation of the material. This method has been used on a variety of ceramics and is reported to be di cult to reproduce. In scribing, the laser is used to produce a line of partially penetrating holes along which separation of the material takes place on the subsequent application of a low stress. This method is widely used for ceramic substrates in the electronics industry. The cutting mechanism involves melting and some resolidi cation. Further work is required to determine the mechanisms of material loss from processes such as evaporation and dispersion of the melt pool by the gas jet pressure before resolidi cation can occur. A 2 kw continuous wave) CO 2 laser with varying beam diameter and power are used for a thickness up to 0.9 mm [1]. In another method of laser cutting of plate glass, channels of microcracks are formed using a Nd:YAG laser. The channel of microcracks is then grown from pulse to pulse in the direction inside and ended on the face side. The discharge of this stress results in the formation of a large common crack along the set of channels. This method di ers from the traditional methods of cutting using laser. But this needs a polished face side of the specimen to let laser radiation into the bulk of the glass. The speed of the channelõs development is frequency-dependent. This method needs focusing of laser by a lens [2]. Cutting of plate glasses of higher thickness range larger than 2 mm) using laser is doubtful. Laser cutting of plate glass causes some fracturing of the edges, which could continue to grow and crack even days after the original cut. However, a sample testing of plate glass of a higher thickness range is under progress [3]. Laser scribing has proven advantageous for many applications. Such equipment, however, do leave a heat-a ected zone in the glass at the cut edge which can produce local thermal stresses causing fracture or other undesired e ects. High initial capital investment is required for laser cutting systems. Waterjet cutting has been developed for cutting glass and does not produce a heat-a ected zone in the workpiece material. Two variations of the waterjet cutting method are used to cut the glass: abrasive and nonabrasive. Cutting is done on a glass of 1 mm thickness using either pure de-ionized high pressure water at 380 MPa with a jet velocity of 915 m/s or de-ionized water with entrained garnet abrasive with the same high pressure and velocity). The major cost factors in the operation of abrasive waterjet systems are the capital cost of the equipment and the cost of power, abrasive material, and the nozzles due to wear). Both straight lines and holes can be cut. Some surface damages are likely to occur around the smaller holes. The cut section using abrasive material is smoother than that produced by the water stream alone. As the cutting rate is increased, the roughness of the cut section increases. The roughness of the cut surface varies from 9.2 to 14.5 lm r.m.s.) for the cutting speed range of 127±1270 mm/min. This method is free from thermal or deformation stresses [4] The novel method A novel plate glass cutting method by the above authors has been reported earlier [5,6]. In this method, the hot air jet issuing from a nozzle is impinged on the plate

5 E.S. Prakash et al. / Mechatronics ) 595± glass to be cut. The hot air jet or the X±Y coordinate table, on which the plate glass is placed, can be moved at the required speed. Any complex pro le could be easily and economically generated in a single step by this method. Fig. 2 shows a typical circular cutting by the novel method in a single step. The disadvantages of the available methods of glass cutting are listed in Table 1. The new method hot air jet) overcomes the disadvantages faced by the conventional and other glass cutting methods. This method is relatively a simple one and has several comparable advantages. It makes use of a low cost, simple, electronic Fig. 2. Typical circular cutting by nonconventional method in a single step. Table 1 Disadvantages of the available glass cutting methods Sl. no. Cutting method Disadvantages 1 Diamond point tool Time consuming process Di cult to maintain close tolerance More wastage of glass Nonstraight pro les cannot be cut in a single step 2 Laser cutting Very high initial capital equipment Microcracks at the cut surface Evaporation and resolidi cation at the cut edge Leaves a heat-a ected zone 3 Abrasive waterjet cutting Very high initial capital equipment Surface nish varies with the cutting speed Nozzle wear Requires de-ionized high pressure water

6 600 E.S. Prakash et al. / Mechatronics ) 595±615 hot air blower and an X±Y table for glass movement, for its operation. The process is safe: does not involve very high pressure or high temperature. Plate glass upto a thickness range of 20 mm can be easily cut. The process is clean i.e., does not generate glass powder or does not involve melting since the operation is carried out at moderate temperature 200±280 C). It is easy to cut any complex shape to very close tolerance. The process is noncontact and amenable to computer control. The cutting can also be done economically using a pantograph mechanism. This method does not require a lens system or a high pressure power pack for its operation. The surface nish of the cut section is smoother than the one obtained by diamond tool or abrasive waterjet. The surface nish is independent of the cutting speed and material thickness. But this method has a limitation, i.e., it is impossible to cut interior holes. The cutting process has to start at the glass edge and requires a scratch for quick crack initiation. The in uence of a hybrid jet a cold and hot air jet combination) on the cutting speed is under investigation. 2. Nonconventional cutting 2.1. The principle of thermal cutting The method of thermal cutting of plate glass consists of a) a crack initiation at the scribed glass edge, and b) propagation of the crack in glass owing to thermal stresses set up by the hot air jet. For an easy initiation of crack, a scratch or a shallow cut is required at the starting edge. The scratch at the starting edge acts as a region of stress concentration. Hence, the plate glass may break or fail easily under the in uence of the stress concentration as well as the thermal stresses caused by the hot air jet. The e ect of the scratch size on the air temperature and crack initiation time dwell period) requires further investigation. Heating a moving plate glass by a stationary hot air jet causes thermal stresses in glass due to nonuniform heating. With rising temperature, the localized elements of the glass expand. As the glass under the stationary jet is moved along the desired path, crack propagates in the direction of the jet. This is due to the fact that the thermal stresses are maximum at the zone of the jet impingement [7±9]. This is called the fatigue failure due to temperature gradient. The theoretical aspects of failure due to the thermal stresses are available elsewhere [10±15]. The localized regions on the glass surface below the jet expand due to heating by the hot air jet. The posterior region of the crack tip experiences a fall in temperature resulting in contraction of the expanded elements and hence the crack advances at the tip. A contraction in the localized posterior region sets up a cracking couple, which favours the crack propagation. Fig. 3 shows the schematic of the crack opening mode due to setting up of the thermal stresses. The crack propagation is quicker if the posterior crack tip region is subjected to a wet environment such as application of water using a cotton wick). This is due to acceleration of contraction.

7 E.S. Prakash et al. / Mechatronics ) 595± Fig. 3. Schematic diagram of the crack opening mode due to thermal expansion and contraction The cutting procedure For an easy initiation of cutting, a shallow cut or scratch of approximately 2 mm length) on the glass surface at the starting edge is required. The scratch can be made using a diamond point tool or a hacksaw. The plate glass to be cut is placed on the X±Y coordinate table such that the scratch starting edge) is below the stationary hot air jet. A rotary table can be used for the circular cutting. The stand-o distance SOD) and the air temperature are adjusted. A crack in glass appears after an initial dwelling period a few seconds). The crack propagation in the desired path can be achieved by moving the table with plate glass mounting, at the required speed, under the stationary hot air jet as per the required pro le. The schematic diagram of the crack propagation in plate glass is shown in Fig. 4. Glass cutting using a CNC X±Y coordinate table gives a better pro le than a manual table. This is because of the

8 602 E.S. Prakash et al. / Mechatronics ) 595±615 Fig. 4. Schematic diagram of the crack propagation. controlled and uniform motion of glass with the CNC table. It is also possible to cut repetitive pro les using the CNC table. But it is di cult when it is done using a manual table The key parameters in uencing the cutting process The thermal energy is required to induce thermal stresses. The amount and pattern of the thermal energy input on the glass surface in uences the crack initiation and propagation rates. The thermal energy input is dependent on the air ow rate and its temperature. The thermal energy input required varies with the thickness and the composition of the glass to be cut. However, the present work deals only with the plate glass soda lime glass) and ophthalmic lens. Increasing the air pressure and air temperature favour the cutting process. The nozzle diameter also plays an important role on the pattern of thermal energy input, thereby in uencing the cutting process. The nozzles of smaller diameter 1.5± 2.5 mm) give a ner air jet and hence, the cutting process is e ective and quicker. The nozzles of diameter larger than 2.5 mm produce a jet of larger diameter causing the

9 E.S. Prakash et al. / Mechatronics ) 595± hot air to spread over a larger area and hence the heat is distributed over a larger area making the cutting process di cult. The SOD is another important parameter in uencing the cutting action. The smaller SODs create a back pressure and causes reduction in the air ow rate. The thermal energy input obtained with the smaller SODs is insu cient for the crack to progress. Increasing the SOD beyond a certain value causes diverging of the air jet and hence, the cutting process becomes di cult. Hence, an optimum SOD should be maintained. 3. Experiments 3.1. The hot air jet A hot air jet is produced by using a) a glass tube, b) a compact hot air gun or c) an electronic hot air blower. In the preliminary experiments, a glass tube and a compact hot air gun are used. The schematic diagram and the photograph of the glass tube are shown in Figs. 5 and 6, respectively. The glass tube, made of a suitable composition, consists of three openings: two for inserting electric heating coil Fig. 5. Schematic diagram of the glass tube.

10 604 E.S. Prakash et al. / Mechatronics ) 595±615 Fig. 6. Photograph of the glass tube. terminals and one for inserting a thermometer. The compressed air is passed through the inlet passage of the glass tube and the hot air jet is obtained at the nozzle exit. The air temperature is adjusted by adjusting the voltage supply to the electric coil with the help of a dimmerstat. The glass tube used for producing the jet can withstand temperatures upto 400 C. The air ow rate and the velocity can be varied by varying the supply air pressure. The hard rubber stoppers prevent the air leakage at the three openings. The glass tube, being a transparent material, provides for a visual control on the performance of the heating coil. Also, it is advantageous to use a glass tube, because it is a bad conductor of heat and electricity. A metallic tube is not preferred, as it does not o er these advantages. Air pressure ranges from 0.25 to 0.5 bar gage). The use of a glass tube carries the risk of breakage due to over-heating during prolonged hours of usage. Therefore, a compact hot air gun is designed and developed for obtaining the hot air jet. The schematic diagram of the compact hot air gun is shown in Fig. 7. It consists of an inner metallic casing and an outer sheet metal pipe tted between the upper and the lower end caps. A thick steam gasket with an electric heating coil insertion is placed at the centre of the gun. The glass wool and asbestos layers prevent the heat loss outside and also prevent heating of the sheet metal pipe. The compressed air is passed through the inlet passage and a hot air jet is obtained at the nozzle exit. The nozzles of di erent diameters are tted one at a time) at the outlet of the gun by varying the jet diameter. The required air ow rates and velocities are obtained by varying the supply air pressure. The designed hot air gun can be used for longer hours without any problem during its operation. A photograph of the disassembly of the hot air gun is shown in Fig. 8. Both the glass tube and the compact hot air gun require an air compressor for the supply of air. The hot air blower is used in the continued experiments. It can supply hot air without the requirement of a separate air compressor. Hence, the set-up becomes very compact and portable. The schematic diagram of the experimental set-up used for glass cutting using the manual X±Y coordinate table and the hot air blower is shown in Fig. 9. The blower has the provision of a two-stage air ow control f 1 ± low and f 2 ± high). A constant electronic, in nitely variable temperature control 100±600 C) is provided inside the blower. An adapter with a nozzle of required diameter is tted in the blower. The vent holes are provided on the adapter to avoid back pressure in the apparatus and excess heating of the blower. Only a small amount of air will come out of the nozzle and impinge on the glass surface. The air ow rate through the nozzle is lesser than 10 lpm.

11 E.S. Prakash et al. / Mechatronics ) 595± Fig. 7. Schematic diagram of the compact hot air gun The X±Y coordinate table In the preliminary investigations, the manual X±Y coordinate table is used to mount the glass. This is suitable for straight cutting rather than exact-curved and irregular nonstraight) pro les such as circle, wavy, sinusoidal, etc. A two-axis CNC coordinate table attached to the centre lathe), with a suitable attachment for xing the blower, is used for moving the plate glass in the continued

12 606 E.S. Prakash et al. / Mechatronics ) 595±615 Fig. 8. Photograph of disassembly of the hot air gun. Fig. 9. Schematic diagram of the experimental set-up for glass cutting using manual table). experiments. The attachment has a provision for varying the SOD. The part programs for the pro les to be cut are fed to the CNC controller having linear and circular interpolation facilities. The controller controls the X±Y table movement. Fig. 10 shows a photograph of the experimental set-up using the CNC X±Y table and the hot air blower. A few two-dimensional pro les of various shapes are cut on the plate glass of di erent thicknesses. Figs. 11 a)± e) show photographs of a few pro les cut using the above set-up. A straight and circular cutting is also successfully made on an ophthalmic lens and an art glass using the novel method. The thermal cutting can also be used on

13 E.S. Prakash et al. / Mechatronics ) 595± Fig. 10. Photograph of the experimental set-up for glass cutting using CNC table). glasses for partition and interior decoration purposes. Alpha numerals can also be cut on a plate glass by this method. 4. Results and discussion 4.1. The e ect of the nozzle diameter on the exit air temperature Nozzles of di erent diameters and the adapter are shown in Fig. 12. Each nozzle 1.5, 2.0, 2.5 and 3.0 mm diameter) is tted into the adapter in the hot air blower. The temperature of the hot air emerging at the nozzle exit, for low air ow rate setting and at a distance of 2 mm below the nozzle tip, is recorded using a thermometer. Fig. 13 shows the variation of the hot air temperature with the nozzle diameter. It is observed from the gure, that the air temperature at the nozzle exit is maximum 280 C) for a nozzle diameter of 2.5 mm. The nozzles of 2.0 and 2.5 mm diameters are selected for conducting further experiments Comparison of the diamond cut edge surface with the thermal cut surface The surface nish measurements of both the diamond and the thermal cut surfaces for a plate glass specimen of 20 mm thickness) are made, using Taylor Hobson Talysurf-4 Instrument no. 1) and Portable Taylor Hobson Surtronic-3 Instrument No. 2) surface testers. These measurements are made on the cut surface at 0.5±1 mm distance from the edge. The surface nish results are shown in Table 2.

14 608 E.S. Prakash et al. / Mechatronics ) 595±615 Fig. 11. Photograph of a few pro les, cut using CNC table: a) a typical complex pro le; b) sinusoidal; c) step; d) circular; e) straight. For the diamond cut surface, the surface nish varies between 2.73 and 3 lm Ra value). The surface nish of a thermal cut surface is higher and Ra value varies from 0.3 to 0.62 lm. A photographic comparison between a diamond cut surface and a thermal cut surface is shown in Fig. 14. The arrow mark in Fig. 14 a) shows the cut

15 E.S. Prakash et al. / Mechatronics ) 595± Fig. 12. Photograph of nozzles and adapter. Fig. 13. Variation of the hot air temperature with nozzle diameter h ˆ 2 mm, f 1 ). Table 2 Comparison of surface nish on the cut surfaces Sl. no. Cutting method Surface nish instrument no. 1 Diamond point tool Meter cut-o value mm) Hot air jet Surface nish Ra value in lm)

16 610 E.S. Prakash et al. / Mechatronics ) 595±615 Fig. 14. Photographic comparison of the cut surfaces of glass of thickness 20 mm: a) by conventional method; b) by nonconventional method using CNC table). edge using the diamond point tool and the surface nish is measured on that side of the cut surface. Fig. 14 b) shows the thermal cut surface. The surface nish is same on either side of the cut surface and it is di cult to identify the cut edge exposed to the hot air jet as the surface nish and appearance do not vary over the entire cut surface. It can be noticed in the photograph that the surface waviness of a) is more as compared to b). This is due to the unpredictable breaking of glass along the scribed mark during conventional cutting The e ect of SOD on the cutting speed Experiments are conducted to determine the variation of the cutting speed with the SOD on two plate glasses of thicknesses 2 and 3 mm. A nozzle of 2.5 mm diameter is used and the air temperature is 280 C. Fig. 15 shows the variation of the cutting speed with SOD. From the gure, it is seen that: i) for a glass of 2 mm thickness, higher cutting speeds 143±167 mm/min) are observed for SODs ranging from 7 to 11 mm. For SODs higher than 11 mm, the cutting speed gradually decreases. The increasing cutting speeds are observed, with the increase of SOD from 3 to 7 mm. ii) For a glass of 3 mm thickness, higher cutting speeds of 129 and 120 mm/ min are observed, for SODs of 2 and 4 mm, respectively. The cutting speeds are almost constant for SODs above 6 mm. The cutting speed for a 3 mm glass is lower indicating that 3 mm thick glass requires relatively more thermal energy input than

17 E.S. Prakash et al. / Mechatronics ) 595± Fig. 15. Variation of the cutting speed with SOD D ˆ 2.5 mm, L ˆ 100 mm, t ˆ 2 and 3 mm, T a ˆ 280 C, f 1 ). that required for a 2 mm to maintain a higher cutting speed. This is also observed in the experiments discussed in Section 4.5. Also, any value of SOD from 6 to 15 mm may be used for a glass of 3 mm thickness, which will give almost the same cutting speed The e ect of glass thickness on the maximum cutting speed Some experiments are conducted on glasses having thicknesses of 2, 3, 5, 10, 12 and 20 mm to study the e ect of the plate glass thickness on the maximum cutting speed. The nozzle diameter, SOD, and air temperature are 2.5 mm, 1.5 mm and 232 C, respectively. The cutting is made for a 100 mm length. The CNC table and the hot air blower experimental set-up with low air ow rate setting f 1 ) is used for these experiments. The experiments are conducted for various increasing values of cutting speed and thus, the maximum cutting speed is determined. The results are shown in Fig. 16. From the gure, it is clear that the cutting speed decreases with an increase in the glass thickness. The maximum cutting speed was 140 and 6 mm/min for a glass thickness of 2 and 20 mm, respectively. The cutting speeds higher than these values were not possible for the given set of conditions. By increasing the

18 612 E.S. Prakash et al. / Mechatronics ) 595±615 Fig. 16. Variation of the maximum cutting speed with the glass thickness using CNC table, D ˆ 2.5 mm, h ˆ 1.5 mm, L ˆ 100 mm, T a ˆ 232 C, f 1 ). thermal energy input it may be possible to increase the cutting speed for thicker glasses The e ect of the air temperature on the cutting speed Some experiments are conducted to study the e ect of the air temperature on the cutting speed on a plate glass of 3 mm thickness. Both the nozzle diameter and the SOD are 2 mm. The blower is set to low air ow rate. The air temperature is varied by operating the miniature electronic rheostat in the blower and the cutting is done for di erent values of air temperature. Fig. 17 shows the variation of the cutting speed with the air temperature. From the gure, it is seen that the cutting speed increases with an increase in the air temperature. This is because the higher thermal energy input is obtained at higher temperatures, which favours the cutting process. The cutting speeds are 42 and 67 mm/min at 210 and 240 C, respectively. Beyond 240 C, there is a steep increase in the cutting speed. At 280 C, the cutting speed is 400 mm/min. Similar trends are observed in the experiments conducted on a glass having a thickness of 2 mm The e ect of the air ow rate on the cutting speed Some experiments are conducted to study the e ect of two di erent air ow rate settings f 1 ± low and f 2 ± high) on the cutting speed. The nozzle diameter, SOD, and

19 E.S. Prakash et al. / Mechatronics ) 595± Fig. 17. Variation of the cutting speed with the air temperature D ˆ 2 mm, h ˆ 2 mm, L ˆ 100 mm, t ˆ 3 mm, f 1 ). Fig. 18. Variation of the cutting speed with the air ow rate D ˆ 2.5 mm, h ˆ 2.0 mm, L ˆ 100 mm, T a ˆ 295 C).

20 614 E.S. Prakash et al. / Mechatronics ) 595±615 air temperature are 2.5, 2 mm and 295 C, respectively. The plate glasses of thicknesses 2, 3, 4 and 5 mm are cut for a length of 100 mm and the results are shown in Fig. 18. From the gure, it is observed that i) the cutting speed for a 2 mm plate is 143 mm/min at f 1 and it increases to 150 mm/min at f 2, ii) similar trends are observed for 3, 4, and 5 mm thicknesses, and iii) the cutting speed decreases with an increase in glass thickness similar observation is made in Section 4.4). 5. Conclusions The novel method of glass cutting makes use of the hot air jet produced by a low cost, simple, electronic hot air blower, for its operation. This nonconventional glass cutting is successfully used to cut plate glass in the thickness range of 2±20 mm. It is also possible to cut nonstraight pro les on mirrors and ophthalmic lens. The hot air jet method has several advantages over other comparable methods such as the laser and waterjet. It does not require very high pressure or high temperature for its operation. There is no melting or wear of the glass at the cut edge. The process does not generate glass powder or fumes. It requires a simple arrangement to produce a hot air jet, which does not require high initial capital equipment. The surface nish of the cut section is smoother than those obtained by the diamond tool and waterjet cutting. No microcracks are developed at the cut edge. The process is amenable to computer control and is able to produce complex shapes. It is a noncontact process. Thus, the process is simple, clean, safe and economical. An experimental set-up is developed for cutting plate glass using a hot air jet and a CNC coordinate table. The e ects of various parameters such as SOD, thickness of glass, air temperature, nozzle diameter, and air ow rate on the cutting speed are studied. This is very useful for plate glass fabrication in various applications. With the CNC table set-up very close tolerances can be achieved. Acknowledgements The authors wish to thank The All India Council for Technical Education AICTE), New Delhi for sponsoring this research work. The authors gratefully thank Prof. Y. Vrushabhendrappa, Principal, Bapuji Institute of Engineering and Technology, Davangere for his support and encouragement. The authors also thank Prof. K.S. Eshwarappa, DRM Science College, Davangere for the critical reading of this manuscript. References [1] Ridealgh JA, Rawlings RD, West DRF. Laser cutting of glass ceramic matrix composite. Mater Sci Technol 1990;6:395±8.

21 E.S. Prakash et al. / Mechatronics ) 595± [2] Strigin MB, Chudinov AN. Cutting of glass by picosecond laser radiation. Optics Commun 1994;106:223±6. [3] Private correspondence with Sinrad Inc., Harbour Heights Parkway, Mukilteo, WA 98275, USA. [4] Fang Yuan, Johnson JA, Allred DD, Todd RH. Waterjet cutting of cross-linked glass. J Vac Sci Technol A 1995;13 1):136±9. [5] Sadashivappa K, Bhaskar Dixit CS, Singaperumal M. Thermal cutting of plate glass. In: Proceedings of the 11th Annual Meeting, ASPE, Monterey, CA, USA. 1996;14:551±56. [6] Sadashivappa K, Prakash ES, Singaperumal M. Compact portable air jet gun for thermal cutting of plate glass. In: Proceedings of the 13th Annual Meeting, ASPE, 1998 Oct 25±30; St. Louis, MO, USA. [7] Prakash ES, Sadashivappa K, Joseph V, Singaperumal M. A study on thermal strains in plate glass during thermal cutting using hot air jet. In: Proceedings of the 14th Annual Meeting, ASPE, Oct 31± Nov 5; Monterey, CA, USA. 1999;20:184±7. [8] Prakash ES, Sadashivappa K, Joseph V, Singaperumal M, Strain measurement in plate glass during thermal cutting. In: Proceedings of the First National Conference on Precision Engineering, COPEN 2000, 2000 Jan 12/13; Indian Institute of Technology, Madras, India. p. 117±22. [9] Prakash ES, Sadashivappa K, Joseph V, Singaperumal M. Experimental study on glass cutting speed using hot air jet. In: Proceedings of the Fourth International Conference on Optoelectronics, Optical sensors & Measuring Techniques Special Session on Innovative Products, Lecture S10), accepted for presentation at OPTO 2000, 2000 May 9±11; Germany. [10] Boley BA, Weiner JH. Theory of thermal stresses. 2nd printing. USA: Wiley; [11] Hellan K. Introduction to fracture mechanics. International student ed., rst printing. Singapore: McGraw-Hill; [12] Barsoum MW. Fundamentals of ceramics, material science series. Singapore: McGraw-Hill; [13] Bobcock CL. Silicate glass technology methods. New York: Wiley; [14] Kingery WD, Bowen HK, Uhlmann DR. Introduction to ceramics, 2nd ed. Singapore: Wiley; [15] Timoshenko SP, Goodier JN. Theory of elasticity, 3rd ed. Singapore: McGraw-Hill; 1970.