Abrasive water jet machining

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1. PRESENTED BY : P.AKHIL KUMAR ABRASSIVE WATER JET MACHENING

2. CONTENTS INTRODUCTION WORKING PRINCIPLE BASIC MECHANISM OF METAL REMOVAL PROCESS PRINCIPLE APPROACHES EQUIPMENT DESCRIPTION CUTTING GEOMETRY PROCESS PARAMETERS PROCESS CAPABILITIES ADVANTAGES & DIS -ADVANTAGES APPLICATIONS AWJM vs. OTHER MODERN PROCESS COCLUSION

3. Abrasive Water Jet Machining (AWJM) is non-traditional or non-conventional machining process. In these processes , the mechanical energy of water and abrasive phases are used to achieve material removal or machining. Abrasive water jet machining – Developed in 1974 to clean metal prior to surface treatment of the metal. INTRODUCTION

4. WORKING PRINCIPLE OF AWJM The cutter is commonly connected to a high pressure water pump where the water is then ejected from the nozzle, cutting through the material by spraying it with the jet of high speed water. Additives in the form of suspended grit or other abrasives, such as garnet and aluminum oxide can assist in this process.

5. BASIC MECHANISM OF MATERIAL REMOVAL

6. Process Principle • An abrasive jet starts out the same as a pure water jet. • As the thin stream of water leaves the nozzle, abrasive is added to the stream and mixed. • The beam of water accelerates abrasive particles to speeds fast enough to cut through much harder materials. • Silicon carbides, sand (SiO 2 ), corundum, and glass beads of grain size 10 to 150 μm are often used as abrasive materials.

7. Process Principle • The mixing of abrasive particles in water jet is in such a manner that water jet’s momentum is transferred to the abrasives. • The coherent, abrasive water jet that exits the AWJM nozzle has the ability to cut various materials, such as metals, glass, ceramics and composites. • Generally, AWJM cuts 10 times faster than the conventional machining methods of composite materials.

8. APPROACHES Different approaches IN AWJM • AWJM – entrained – three phase (water + air + abrasives) • AWJM – suspended – two phase (water + abrasives) • Direct pumping • Indirect pumping • Bypass pumping

9. APPROACHES

10. Schematic Setup of AWJM

11. Schematic Setup of AWJM

12. EQUIPMENT DESCRIPTION

13. EQUIPMENT DESCRIPTION

14. EQUIPMENT DESCRIPTION Pumping system : Identical as WJM A brasive F eed System: Purpose : Controlled flow of abrasive particles to the abrasive jet nozzle. AWJM abrasive feed systems deliver a stream of dry abrasives to the nozzle . Drawback with dry abrasive delivery systems is that the delivery of abrasives over long distances is difficult.

15. EQUIPMENT DESCRIPTION Typical work materials involve soft metals, paper, cloth, wood, leather, rubber, plastics, and frozen food. If the work material is brittle it will fracture, if it is ductile, it will cut well . Abrasive Water jet Machining consists of: Hydraulic Pump Intensifier Accumulator High Pressure Tubing Jet Cutting Nozzle Catcher

16. HYDRAULIC PUMP • Powered from a 30 kilowatt (kW) electric motor • Supplies oil at pressures as high as 117 bars. • Compressed oil drives a reciprocating plunger pump termed an intensifier. • The hydraulic pump offers complete flexibility for water jet cutting and cleaning applications. • It also supports single or multiple cutting stations for increased machining productivity.

17. INTENSIFIER • Intensifier – driven by a hydraulic power pack. • Heart of hydraulic power pack is a positive displacement hydraulic pump. • The power packs in modern commercial systems are often controlled by microcomputers to achieve programmed rise of pressure, etc.

18. INTENSIFIER Hy draulic power pack – delivers hydraulic oil at a pressure p h to Intensifier. CONDITIONS: Ratio of cross-section of the two cylinders, A ratio =A large /A small Thus, pressure amplification at the small cylinder takes place as follows: Thus, if the hydraulic pressure is set as 100 bar and area ratio is 40, p w = 100 x 40 = 4000 bar.

19. INTENSIFIER By using direction control valve, the intensifier is driven by the hydraulic unit. The water may be directly supplied to the small cylinder of the intensifier, Or it may be supplied through a booster pump, which typically raises the water pressure to 11 bar before the intensifier. Sometimes water is softened or long chain polymers are added in “additive unit”. Thus, as the intensifier works, it delivers high pressure water.

20. ACCUMULATOR • As the larger piston changes direction within the intensifier, there would be a drop in the delivery pressure • To counter such drops, a thick cylinder is added to the delivery unit to accommodate water at high pressure which is called as “Accumulator”. • Maintains the continuous flow of the high-pressure water and eliminates pressure fluctuations. • It relies on the compressibility of water (12 percent at 3800 bar) in order to maintain a uniform discharge pressure and water jet velocity, when the intensifier piston changes its direction.

21. HIGH PRESSURE TUBING • Transports pressurized water to the cutting head. • Typical tube diameters are 6 to 14 mm. • The equipment allows for flexible movement of the cutting head. • The cutting action is controlled either manually or through a remote-control valve specially designed for this purpose.

22. Injection & Suspension Heads

23. JET CUTTING NOZZLE Purpose of the abrasive jet nozzle is to provide efficient mixing of the abrasives and the water jet and to form the high-velocity abrasive water-jet combination

24. JET CUTTING NOZZLE There is a difference between a pure water nozzle and an abrasive jet nozzle. With the abrasive jet nozzle, an opening in the side of the nozzle allows for the introduction of the abrasive to the high-pressure water stream. The two are mixed in a mixing tube and then exit the nozzle. With a pure water jet nozzle, there is no opening and no mixing tube and the high-pressure water is directed to the material after it exits the jewel.

25. 25 Mixing Chamber • Abrasive particles during mixing try to enter the jet, but they are reflected away due to interplay of buoyancy and drag force. • They go on interacting with the jet and the inner walls of the mixing tube, until they are accelerated using the momentum of the water jet. • In entrained AWJM, the abrasive water jet, which finally comes from the focussing tube or nozzle, can be used to machine different materials .

26. ABRASSIVE MOVEMENT

27. WORKPIECE CUTTING

28. b t Jet affected zone Jet affected zone burr Outer dia Inner dia CUTTING GEOMETRY TOP VIEW BOTTOM VEIW Rough surface

29. Cutting Geometry Stand off diameter

30. Cutting Geometry

31. EFFECT OF FEED RATE

32. EFFFECT OF FEED RATE

33. ROUGHNESS

34. To minimize abrasive wear, the nozzle is usually made from either tungsten carbide or boron carbide. Two major design concepts are currently used for the design of abrasive jet nozzles . They are : Single-jet side feed nozzle Multiple jet feed nozzle JET CUTTING NOZZLE

35. JET CUTTING NOZZLE Single-jet side feed nozzle This design is based on a central water jet with abrasives fed into the mixing chamber from the side . This configuration is easily machined and can be made quite small, which is an advantage when cutting in tight locations . But this concept does not provide for optimal mixing efficiency and usually experiences rapid wear of the exit section . The major advantage with this system is this that, it incorporates a central, conventional water jet, the abrasive flow can be stopped and the system will function as a conventional WJM system .

36. JET CUTTING NOZZLE Multi jet feed nozzle : While cutting the same type of material, one can choose the nozzle that works best for that material . This type of nozzle is used for cutting materials like Hardened tool steel, Titanium, Aluminium,Hard Rubber,Stone , Inconel , mild steel ,Stainless Steel

37. JET CUTTING NOZZLE Limitations of abrasive jet nozzles Despite their simple design, abrasive jet nozzles can be troublesome at times. There are many designs, but they share the same problems which are listed below. Short life of the mixing tube Occasional plugging of mixing tube Wear, misalignment, and damage to the jewel

38. CATCHER • “Catcher” is used to absorb the residual energy of the AWJ and dissipate the same. • Acts as a reservoir for collecting the machining debris entrained in the water jet. • Moreover, it reduces the noise levels [105 decibels (dB)] associated with the reduction in the velocity of the water jet from Mach 3 to subsonic levels • Catcher is of two types (a)Pocket type: The catcher basin travels along the jet (along X&Y) . (b)Line type : The catcher basin travels along one axis and its length covers the entire width of the other axis of the CNC table.

39. 39 CATCHER

40. PROCESS PARAMETERS

41. WATER JET PRESSURE: • Pc is the minimum critical pressure required to cut the material.   • A minimum critical pressure Pc exits because of the minimum abrasive particle velocity required to cut specific materials. PROCESS PARAMETERS

42. PROCESS PARAMETERS • fig . Shows the depth of cut is affected by varying the water flow rate (increasing the nozzle diameter) while maintaining the constant pressure. •   As the flow rate increases, the slope of the curve decreases because the saturation point is reached . • As the nozzle diameter increases and the water flow rate increases, the rate of increase in the particle velocity is reduced, thus reducing the depth of cut. WATER FLOW RATE & NOZZLE DIA

43. PROCESS PARAMETERS Abrasive flow rate: Abrasive flow rate versus depth of cut is a linear relationship up to a point Above a critical flow rate, the cutting efficiency decreases . This is because of the fact that, as the abrasive flow rate increases( with a fixed water flow rate), particle velocity begins to decrease faster than the rate at which the number of abrasive particle impacts increase.

44. PROCESS PARAMETERS Abrasive Particle Size: The most common abrasive particle sizes used for AWJM range from 100 to 150 grit An optimum abrasive particle size also exists for each particular nozzle mixing chamber configuration.

45. PROCESS PARAMETERS Abrasive T ype: The type of abrasive used is also an important parameter . Garnet(30% more efficient than sand), silica and silicon carbide are the most commonly used abrasives . Selection of abrasive type is usually determined by the hardness of the material that is being cut.

46. PROCESS PARAMETERS Abrasive Type: • Steels & Non-ferrous alloys • Ti alloys, Ni- alloys • Polymers • Honeycombs • Metal Matrix Composite & Ceramic Matrix Composite • Concrete • Stone – Granite • Wood • Reinforced plastics • Metal Polymer Laminates • Glass Fibre Metal Laminates

47. PROCESS PARAMETERS Traverse Rate: When traverse rates are increased the depth of cut decreases . There is also a minimum critical traverse rate below which further increases in depth of cut are not obtained .   If the traverse rate is not maintained at a relatively uniform velocity, a rough edge will result because of the nature of the process.

48. PROCESS PARAMETERS Stand-off-Distance: Data generated by some researchers indicate that depth of cut is approximately linear relative to SOD . Increasing SOD decreasing the depth of cut . When mixing is efficient and process parameters are correct, a deviation in SOD of up to +-12.7mm can be tolerated without degradation of the cut quality . If SODs are increased to a distances of about 80mm, the process will no longer cut but will efficiently clean and de-scale surfaces.

49. PROCESS PARAMETERS Surface Roughness: • Surface roughness depends on the workpiece material, grit size, and type of abrasives. • A material with a high removal rate produces large surface roughness. • Fine grains are used for machining soft metals to achieve better roughness • The decrease in surface roughness by using smaller grain size is related to the reduced depth of cut and the undeformed chip cross section.

50. PROCESS PARAMETERS Surface Roughness: • A carrier liquid consisting of water with anticorrosive additives has higher density and contributes to higher acceleration of the grains. • This results in higher grain speed and increased metal removal rate. Moreover, the carrier liquid spreads over the surface filling its cavities and forming a film that impedes the striking action of the grains. • Therefore, peaks in the surface irregularities are the first to be affected and the surface quality improves.

51. Typical Parameters in Entrained AWJM Orifice – 0.1 to 0.3 mm Focussing Tube– 0.8 to 2.4 mm Pressure – 2500 to 4000 bar Abrasive – garnet and olivine - 125 to 60 micron Abrasive flow rate - 0.1 to 1.0 kg/min Stand off distance – 1 to 2 mm Machine Impact Angle – 60 o to 90 Traverse Speed – 100 mm/min to 5 m/min Depth of Cut – 1 mm to 250 mm

52. PROCESS CAPABILITIES AWJM can be thought of as a combination of WJM and AJM principles . But in terms of capability, AWJM combines the best of both processes, resulting in a new process that can cut materials whether they are hard or soft at high rates and in very thick sections . AWJM can cut materials as thick as 200mm and still maintain a comparatively narrow kerf . Kerf width is a function of the material thickness and usually is between 1.5 and 2.3mm.

53. PROCESS CAPABILITIES The resulting taper on the cut edge is a function of the material hardness. Where hard materials have the widest kerf at the top of the cut and Soft materials have the widest kerf at the bottom of the cut.

54. Advantages 19-01-2017 Cut virtually any material. Cut thin or thick stuff. Make all sorts of shapes with only one tool No heat generated. Leaves a smooth finish, thus reducing secondary operations. Modern systems are now very easy to learn and safe. Unlike machining or grinding, cutting does not produce any dust or particles that are harmful if inhaled. Abrasive Water jet cutting can be easily used to produce prototype parts very efficiently This part is shaped with waterjet using one tool. Slots, radii, holes, and profile in one 2 minute setup.

55. DISADVANTAGES COST DIMENSIONAL ACCURACY

56. APPLICATIONS Paint removal Cleaning Cutting soft materials Cutting frozen meat Textile, Leather industry Peening Pocket Milling Drilling & Turning Nuclear Plant Dismantling

57. AWJM vs. OTHER MODERN PROCESS 19-01-2017 57 After laser cutting After Abrasive waterjet cutting Abrasive Water jets are much faster than EDM. After plasma cutting After waterjet cutting

58. CONCLUSION In technical field technology plasma arc , laser welding e.t.c has been huge success due to their flexibility and adaptability. AWJ has also attracted the vision of entrepreneur by their capabilities. Advanced AWJ machines are now available where the computer loads a CAD drawing from another system which increasing its eco-friendly .