20-09-2014, 02:43 PM
DESIGN OF ABRASIVE JET MACHINE
[attachment=68249]
A B S T R A C T
Abrasive Jet Machining (AJM) is the process of material removal from a workpiece by the application of a high speed stream of abrasive particles carried in a gas medium from a nozzle. The material removal process is mainly by erosion. The AJM will chiefly be used to
cut shapes in hard and brittle materials like glass, ceramics etc. the machine will be automated to have 3 axes travel. The different components of AJM are Horizontal motion module (X‐Y Table), Vertical motion module (Z‐ motion), Vibrator, dehumidifier, Pressure Regulator, and Dust filter etc. The different components are selected after appropriate design calculations
1 Introduction :
Abrasive Jet Machining (AJM) is the removal of material from a workpiece by the application of a high speed stream of abrasive particles carried in gas medium from a nozzle. The AJM process differs from conventional sand blasting in that the abrasive is much finer and the process parameters and cutting action are carefully controlled.
The process is used chiefly to cut intricate shapes in hard and brittle materials which are sensitive to heat and have a tendency to chip easily. The process is also used for deburring and cleaning operations. AJM is inherently free from chatter and vibration problems. The cutting action is cool because the carrier gas serves as a coolant
7 Nozzle:
The abrasive particles are directed into the work surface at high velocity through nozzles. Therefore, the material of the nozzle is subjected to great degree of abrasion wear and hence these are made of hard materials such as tungsten carbide or synthetic sapphire. Tungsten carbide nozzles are used for circular cross‐sections in the range of 0.12‐0.8 mm diameter, for rectangular sections of size 0.08 x 0.05 to 0.18 x 3.8 mm and for square sections of size upto 0.7 mm. Sapphire nozzles are made only for circular cross‐sections. The size varies from 0.2 to 0.7 mm diameter. Nozzles are made with an external taper to minimize secondary effects due to ricocheting of abrasive particles. Nozzles made of tungsten carbide have an average life of 12 to 30 hours while nozzles of sapphire last for about 300 hour of operation when used with 27 μm abrasive powder.
The rate of material removal and the size of machined area are influenced by the distance of the nozzle from the workpiece. The abrasive particles from the nozzle follow a parallel path only for a short distance and then the jet flares resulting in the oversizing of the hole. It is observed that the jet
stream is initially a cylinder for about 1.6 mm and then it flares into a cone of 7˚ included angle. The material removal rate initial increases with increase in the distance of the nozzle from the workpiece because of the acceleration of particles leaving nozzle. This increase is maximum up to a distance about 8 mm and then it steadily drops off because of increase in machining area for the same amount of abrasive and decrease in velocity of abrasive stream due to drag.
12.1 ABRASIVE CONTAINER:
The abrasive container was made out of a hollow cylinder. Two iron plates were welded on both ends of the container. On the top plate two holes were drilled and iron pipes were fitted with these holes. The inlet iron pipe is longer so as to make more agitation of the abrasive particles. The outlet pipe is shorter. Both the pipes are clamped with nylon pipes which carries air through them. After removal of moisture by the FRL unit the compressed air goes to abrasive container through inlet, mixes with abrasive particle and then the air with abrasive particles moves through the nozzle to perform the machining action.
14 Advantages:
1. Ability to cut intricate holes shape in materials of any hardness and brittleness.
2. Ability to cut fragile and heat sensitive material without damage.
3. No change in microstructure as no heat is generated in the process.
4. Low capital cost.
5. Depth of damage is low ( around2.5 microns)
6. It provides cool cutting action, so it can machine delicate and heat sensitive material
7. Process is free from chatter and vibration as there is no contact between the tool and work piece
8.Thin sections of hard brittle materials like germanium, mica, silicon, glass and ceramics can be machined.
15 Disadvantages:
1. Material removal rate is low and hence its application is limited.
2. Stray strings can occur and hence its application is limited.
3. Embedding of the abrasive in the workpiece surface may occur while machining softermaterial.
4.The abrasive material may accumulate at nozzle and fail the process if moisture is present in the air.
5. It cannot be used to drill blind holes.
6. Limited capacity due to low MRR. MRR for glass is 40 gm/minute
7 Abrasives may get embedded in the work surface, especially while machining soft material like elastomers or soft plastics.
8. The accuracy of cutting is hampered by tapering of hole due to unavoidable flaring of abrasive jet.
9. A dust collection system is a basic requirement to prevent atmospheric pollution and health hazards. 6. Nozzle life is limited (300 hours) 10.Abrasive powders cannot be reused as the sharp edges are worn and smaller particles can clog the nozzle. 11. Short stand off distances when used for cutting , damages the nozzle.
16 . CONCLUSION
In this project design of the Abrasive Jet Machine is given for different function . The XY motion modules are designed taking in account of currently available components. Design of power screw with appropriate calculation is given.Selection ofmild steel, ball screw with nut bracket of appropriate size and dimensionThe rate of material removal and the size of machined area are influenced by the distance of the
nozzle from the workpiece.The designing and assembling of very large number of components was atremendous task and was completed on time.
[attachment=68249]
A B S T R A C T
Abrasive Jet Machining (AJM) is the process of material removal from a workpiece by the application of a high speed stream of abrasive particles carried in a gas medium from a nozzle. The material removal process is mainly by erosion. The AJM will chiefly be used to
cut shapes in hard and brittle materials like glass, ceramics etc. the machine will be automated to have 3 axes travel. The different components of AJM are Horizontal motion module (X‐Y Table), Vertical motion module (Z‐ motion), Vibrator, dehumidifier, Pressure Regulator, and Dust filter etc. The different components are selected after appropriate design calculations
1 Introduction :
Abrasive Jet Machining (AJM) is the removal of material from a workpiece by the application of a high speed stream of abrasive particles carried in gas medium from a nozzle. The AJM process differs from conventional sand blasting in that the abrasive is much finer and the process parameters and cutting action are carefully controlled.
The process is used chiefly to cut intricate shapes in hard and brittle materials which are sensitive to heat and have a tendency to chip easily. The process is also used for deburring and cleaning operations. AJM is inherently free from chatter and vibration problems. The cutting action is cool because the carrier gas serves as a coolant
7 Nozzle:
The abrasive particles are directed into the work surface at high velocity through nozzles. Therefore, the material of the nozzle is subjected to great degree of abrasion wear and hence these are made of hard materials such as tungsten carbide or synthetic sapphire. Tungsten carbide nozzles are used for circular cross‐sections in the range of 0.12‐0.8 mm diameter, for rectangular sections of size 0.08 x 0.05 to 0.18 x 3.8 mm and for square sections of size upto 0.7 mm. Sapphire nozzles are made only for circular cross‐sections. The size varies from 0.2 to 0.7 mm diameter. Nozzles are made with an external taper to minimize secondary effects due to ricocheting of abrasive particles. Nozzles made of tungsten carbide have an average life of 12 to 30 hours while nozzles of sapphire last for about 300 hour of operation when used with 27 μm abrasive powder.
The rate of material removal and the size of machined area are influenced by the distance of the nozzle from the workpiece. The abrasive particles from the nozzle follow a parallel path only for a short distance and then the jet flares resulting in the oversizing of the hole. It is observed that the jet
stream is initially a cylinder for about 1.6 mm and then it flares into a cone of 7˚ included angle. The material removal rate initial increases with increase in the distance of the nozzle from the workpiece because of the acceleration of particles leaving nozzle. This increase is maximum up to a distance about 8 mm and then it steadily drops off because of increase in machining area for the same amount of abrasive and decrease in velocity of abrasive stream due to drag.
12.1 ABRASIVE CONTAINER:
The abrasive container was made out of a hollow cylinder. Two iron plates were welded on both ends of the container. On the top plate two holes were drilled and iron pipes were fitted with these holes. The inlet iron pipe is longer so as to make more agitation of the abrasive particles. The outlet pipe is shorter. Both the pipes are clamped with nylon pipes which carries air through them. After removal of moisture by the FRL unit the compressed air goes to abrasive container through inlet, mixes with abrasive particle and then the air with abrasive particles moves through the nozzle to perform the machining action.
14 Advantages:
1. Ability to cut intricate holes shape in materials of any hardness and brittleness.
2. Ability to cut fragile and heat sensitive material without damage.
3. No change in microstructure as no heat is generated in the process.
4. Low capital cost.
5. Depth of damage is low ( around2.5 microns)
6. It provides cool cutting action, so it can machine delicate and heat sensitive material
7. Process is free from chatter and vibration as there is no contact between the tool and work piece
8.Thin sections of hard brittle materials like germanium, mica, silicon, glass and ceramics can be machined.
15 Disadvantages:
1. Material removal rate is low and hence its application is limited.
2. Stray strings can occur and hence its application is limited.
3. Embedding of the abrasive in the workpiece surface may occur while machining softermaterial.
4.The abrasive material may accumulate at nozzle and fail the process if moisture is present in the air.
5. It cannot be used to drill blind holes.
6. Limited capacity due to low MRR. MRR for glass is 40 gm/minute
7 Abrasives may get embedded in the work surface, especially while machining soft material like elastomers or soft plastics.
8. The accuracy of cutting is hampered by tapering of hole due to unavoidable flaring of abrasive jet.
9. A dust collection system is a basic requirement to prevent atmospheric pollution and health hazards. 6. Nozzle life is limited (300 hours) 10.Abrasive powders cannot be reused as the sharp edges are worn and smaller particles can clog the nozzle. 11. Short stand off distances when used for cutting , damages the nozzle.
16 . CONCLUSION
In this project design of the Abrasive Jet Machine is given for different function . The XY motion modules are designed taking in account of currently available components. Design of power screw with appropriate calculation is given.Selection ofmild steel, ball screw with nut bracket of appropriate size and dimensionThe rate of material removal and the size of machined area are influenced by the distance of the
nozzle from the workpiece.The designing and assembling of very large number of components was atremendous task and was completed on time.