NON-CONVENTIONAL CUTTING OF PLATE GLASS USING HOT AIR JET MIXED WITH ABRASIVES PROJECT REFERENCE NO. : 37S1423 COLLEGE : BAPUJI INSTITUTE OF ENGINEERING AND TECHNOLOGY, DAVANGERE BRANCH : MECHANICAL ENGINEERING GUIDE : DR.A.G.SHANKARA MURTHY STUDENTS : KALLANAGOUDA.T.T PAVAN PRASAD.A RAJESH. M VINOD SAJJAN Keywords: Glass, Hot air, abrasives, SOD Introduction: In recent days, industries are facing difficulty in machining materials like alloys, carbides, stainless steels, heat resisting steels, etc. Using nontraditional machining processes. Many of these materials also find important applications in industries owning to their high strength to weight ratio, hardness and heat resisting qualities. In spite of recent technological advancements, nontraditional machining processes are inadequate to machine these materials in view of economic production, besides machining of these materials into complex shapes is time consuming and sometime impossible. Nontraditional machining techniques have emerged to overcome these difficulties. They are classified according to the nature of energy employed in machining. Nontraditional machining process can be classified into various groups according to type of fundamental machining they employ, namely mechanical, chemical, thermo electrical, etc. classification of machining process is based upon the type of energy used, the mechanism of material removal in the process, the source of immediate energy required for material removing and the medium for transfer of energies. Thermal and Electro chemical Chemical and Electro chemical Mechanical 1
In mechanical methods of nontraditional machining, the material is principally removed by mechanical erosion of the work piece material. The mechanical methods include ultra-sonic machining, abrasive jet machining and water jet machining. Objectives: To develop a hybrid non-conventional machining process set up To Produce micro holes on glass plates of various thicknesses To determine the material removal rate and dia of hole produced by varying standoff distance(sod) and thickness of glass plate Methodology: The basic machining principle of AHAJM is that the abrasive are accelerated by a compressed high pressure hot air or gases and are forced through a micro nozzle which collides with hard and brittle work pieces at a very high velocity (80 to 500 m/s) and density. Since the material removal process of AHAJM is performed by an integration of brittle machining based on micro crack propagation, there is very little chipping and crack generation in the work piece. Thus this method is very suitable for the machining of micro shapes of hard and brittle materials (such as glass, ceramics, silicon etc.). In this project, a high velocity abrasive hot air jet called abrasive suspension hot jet which works on the principles of bypass of abrasive and hot air mixture under pressureis developed. The control of mixing process demands experience in fluid high pressure technology. Abrasive hot air jet is generated by the principle as shown in Fig.2.1. Air is pressurized by a compressor and passed through heating chamber where an electric coil is provided to heat the compressed air. The temperature of air is controlled by varying the voltage supplied to the coil. A part of air is lead through a bypass branch and flow through the abrasive chamber, which contains the abrasive material. The abrasive particles are mixed with hot air and it gets recombined with the main flow below hot air vessel through a high pressure hose (mixing head) and then leads to the cutting unit. The suspension is accelerated in a nozzle made up of hard materials (sapphire or tungsten carbide) to get high pressurized jet. The concentration of abrasive particles in the suspension can be adjusted by the amount of air passing through the bypass branch. A valve below the abrasive chamber can control the flow rate. 2
Mechanism of Hot Air Jet In this work, a high velocity hot air jet is used, which is more efficient than others. Here the pressure line is lead through the heating chamber which is bypassed by using the pressure line, flow of the abrasive become easier. This type of hot jet results in higher jet velocity. Fig 2.1 depicts the mechanism of hot air jet. The air compressor is used to compress the air. The compressed air is fed to y=the heating chamber, where air is heated using heating coil and then hot air is passed to mixing chamber and abrasive chamber simultaneously. The control valve present at the inlet of heating chamber is controlled to get the heat inlet pressure equal to 2-4 kg/cm 2. The abrasive control valve is opened to set constant mass flow rate. The abrasive mixed with the compressed hot air is recombined with the main flow in mixing chamber which then leads to the nozzle where the pressure drops and velocity increases. The high velocity hot air jet with abrasives coming out from the nozzle impinges on to the work surface which results in the erosion of the materials. This is repeated for different standoff distance and the temperature is also varied. The temperature of air should be less than the melting point of the work piece (glass). This experiment is carried out on a soda lime glass plate of different thickness viz 1.5, 2.0, 3.0, 5.0mm. Fig: Mechanism of hot air jet 3
Results and conclusions: I. Standoff distance v/s Diameter of hole on glass plate Fig.1 : Standoff distance v/s Diameter for constant thickness of glass 3mm Fig.2: Standoff distance v/s Diameter for constant thickness of glass 4mm 4
Fig3: Standoff distance v/s Diameter for constant thickness of glass 5mm II. Thickness of glass plate v/s Diameter of hole on glass plate Fig4: Thickness v/s diameter for constant standoff distance of 10mm 5
Fig5: Thickness v/s diameter for constant standoff distance of 15mm Fig6: Thickness v/s diameter for constant standoff distance of 20mm Hot air reduces the time taken for producing holes. The material removal rate increases as the nozzle diameter increases. The material removal rate increases with increase in temperature. Smooth surface finish can be obtained by introducing hot air. The material removal rate increases as the thickness of work material decreases. For better flow of abrasive particles, inclination between the abrasive chamber and mixing chamber should be made as less as possible. 6
Heat dissipation in the abrasive chamber and the air vessel is a main problem. Leakage of heating chamber is main problem and should be before every experiment. Continuous cutting cannot be done due to less storage of abrasive particle. Scope for future work: Experimental work may be compared with analytical work by developing a model by using analysis software like ANSYS. 7