U5 p1 ntm processes
Embed Size (px)
Transcript of U5 p1 ntm processes
- 1. Manufacturing Technology II (ME-202) Nontraditional Manufacturing Processes Dr. Chaitanya Sharma PhD. IIT Roorkee
- 2. Title of slide Lesson Objectives In this chapter we shall discuss the following: Learning Activities 1. Look up Keywords 2. View Slides; 3. Read Notes, 4. Listen to lecture Keywords:
- 3. Nontraditional Manufacturing Processes Necessity to use new materials, demanding functional requirements and miniaturization have led to evolution of modern manufacturing processes. Nontraditional machining refers to a group of processes which removes excess material without a sharp cutting tool by various nontraditional means such as mechanical, thermal, electrical or chemical energy (or combinations) and developed since World War II (1940s). These processes do not use a sharp cutting tool in the conventional sense.
- 4. Why We Need NTM Processes? Nontraditional processes have been developed to meet new and unusual machining requirements of Aerospace and Electronics industries which are either not possible with conventional machining or extremely costly, including the need: 1. To machine new (harder, stronger & tougher) materials. 2. The need for unusual and/or complex geometries. 3. To achieve stringent surface (finish & texture) requirements
- 5. Classification of Non Traditional Manufacturing Based on the principle form of energy nontraditional manufacturing processes can be classified into following groups: 1. Mechanical - Erosion of work material by a high velocity stream of abrasives and/or fluid Example: USM, AWJM, WJM, AFM 2. Electrical - Electrochemical energy removes material Example: ECM, ECD, ECG. 3. Thermal - Thermal energy applied to small portion of work surface, removes material by fusion and/or vaporization Example: EDM, WEDM, EBM, LBM, PAM, IBM 4. Chemical - chemical etchants selectively (using a mask) remove a portion of a workpiece. Example: Chemical milling, Blanking, Engraving and Photochemical machining.
- 6. Principal of NTM Processes Mechanical Energy Methods Chemical Methods Thermal Energy Methods
- 7. General Characteristics of NTM Processes
- 8. Surface Roughness and Tolerances in Machining Fig: Surface roughness and tolerances obtained in various machining processes.
- 9. Application Considerations Workpart Geometry Features Very small holes - (below 0.005 in. in diameter) use LBM Holes with large depth/diameter ratios - (d/D > 20) use ECM and EDM Nonround holes - use EDM and ECM Narrow slots that are not straight - use EBM, LBM, wire EDM, WJC and AWJC
- 10. Work Materials
- 11. Nontraditional processes are generally used when conventional methods are not practical or economical Performance of Nontraditional Processes
- 12. Parts Made by Advanced Machining Processes Figure :Examples of parts produced by advanced machining processes. (a) Samples of parts produced from water jet cutting. (b) Turbine blade, produced by plunge EDM, in a fixture to produce the holes by EDM. (a) (b)
- 13. Material removal is due to abrading action of the grit-loaded flowing slurry. Small amplitudes (1020 m) and high frequency (2040 kHz) of vibrations are given to tool. The hard abrasive particles in the slurry are accelerated towards the workpiece surface by the oscillating action of the tool through repeated abrasions, the tool further machines a cavity of cross section identical to its own. The workpiece shape and dimensional accuracy is directly dependent on the geometry of the tool. The material removal takes place is the form of fine grains by shear deformation. Different mechanisms of material removal include brittle fracture, impact action of abrasives, cavitation and chemical reaction due to the slurry. Ultrasonic Machining (USM)
- 14. Features of Ultrasonic Machining Material removal mechanism: Mechanical - Erosion of work material Tool vibrate at low amplitude (0.05-0.125 mm) & high frequency (20kHz). Vibration amplitude equals to grit size, also determines resulting surface finish. Tool oscillation: Perpendicular to work surface Tool: Formed Stainless steels tool , fed slowly into work. Abrasives BN, BC, Al2O3, SiC & Diamond Abrasive grit size: 100 (rough) to 2000(fine) Abrasives: 20-60 % by volume in water Time of contact: 10-100s. Work materials Hard, brittle materials e.g. ceramics, glass and carbides and stainless steel and titanium Shapes include non-round holes (i.e. along a curved axis) and Coining operations (the pattern on tool is imparted to a flat work surface). Due to the abrasive action of particles, gradually wear of the tool occurs,
- 15. USM: Material Removal Mechanism The impact of abrasives is mainly responsible for the removal of material, in the form of small wear particles which are carried away by the abrasive slurry. Mechanisms responsible for the material removal are: 1. Mechanical abrasion: Occurs due to hammering effect of abrasive particles on work piece through the tool. 2. Impact: Feely moving particles impact with a certain velocity on the work piece resulting in micro chipping. 3. Erosion: Due to cavitation effect of abrasive slurry, erosion of the workpiece occurs. 4. Chemical: Due to fluid employed, chemical effect can come into consideration.
- 16. USM: Advantages, Disadvantages Advantages: 1. Brittle and hard materials can be machined easily. 2. No direct contact of the tool and workpiece. 3. No physical, chemical or thermal changes. 4. W-piece is unstressed, undistorted and free from heat effects. 5. Process is free from burrs and distortions 6. Machine any materials, irrespective of electrical conductivity 7. Process offers good surface finish and structural integrity Disadvantages / Limitations: 1. Can not machine soft & ductile materials 2. consumes higher power and has lower MRR. 3. Fast tool wear. 4. Can not produce deep holes, sharp corners and blind holes.
- 17. USM: Applications 1. USM is used in machining of hard and brittle metallic alloys, semiconductors, glass, carbides and advanced ceramics for applications in auto-engine components. 2. In machining of small dies for wire drawing, punching or blanking. 3. Drilling small holes in helicopter power transmission shafts and gears. 4. For drilling holes in borosilicate glass for the sensors used in electronic industries
- 18. Water Jet Machining (Cutting) Fig. : Schematic illustration of the WJM process The term water jet means a high pressure water stream. WJM uses a water jet cutter, which acts as a tool in the form of a water- saw, for cleaning and cutting applications. This water-jet at a high velocity and pressure is able to slice materials and some metals using some abrasive particles mixed in it. This process resembles natural water erosion phenomenon of soil and rocks. There is no heat-affected zones and process is environmental friendly. Used for cutting, carving and shaping applications in mining to aerospace industries. Fig. : A CNC WJM cutting a granite plate
- 19. Abrasive Water Jet Machining (AWJM) Fig. : Schematic illustration of the WJM process In AWJM processes, which is an extension of WJC, abrasive particles such as Al2O3, SiC are added to water, which further increases the MRR. AWJM is used for machining hard, brittle ceramics and glass and soft metals such as rubber and foam. Fig. : A CNC WJM cutting a granite plate
- 20. 1. Water is forced at high pressure, 180-420 MPa through a small orifice in a nozzle (0.2- 0.4 mm diameter), causing high acceleration of water. 2. Conversion of waters potential energy into kinetic energy yields a very high jet velocity of around 1000 m/s. 3. The impact and high pressure of the accelerating water particles develop fine cracks on the material. 4. These fine cracks propagate further under the impact of high pressure and abrasives to the extent that the material gets cut. 5. The extended version of WJM is AWJM. In AWJM process the particles of abrasives such as sand (SiO2) or beads of glass are added in the water jet in-order to enhance its ability of cutting by many folds. Principle of WJM & AWJM
- 21. WJM :Advantages Advantages of WJM and AWJM No harmful fume, dust or other particles. No need of secondary or finishing operations. In AWJM process, Low cutting forces. Limited tooling requirements and no tool re-sharpening cost. Typical surface finish achieved is in range of 125-250 um Ra. Reduced material wastages due to smaller kerf sizes. There is no heat affected zone and thermal distortion. It can cut metals, plastics, stones, composites, glass, ceramics & rubber.
- 22. WJM: Disadvantages Disadvantages of WJM and AWJM Cannot cut materials which degrades quickly with moisture. Higher cutting speeds (used for rough cutting)degrade the surface finish. Greater chance of cracking in brittle materials. With WJM process, thick parts cannot be cut accurately and economically. The equipment used are quite expensive. There are safety concerns due to noise and high pressures.
- 23. WJM: Applications Fig. : Examples of various nonmetallic parts produced WJM process. Applications of WJM and AWJM Diverse applications in mining to aerospace industries. Primarily used for cutting, carving and shaping applications. WJC is used in cutting low strength materials like plastics, wood and aluminum. AWJM process can be used for stronger materials like tool steels.
- 24. In AJM material removal occurs on account of impact of high velocity air / gas stream of abrasive particles on the workpiece (WP). Abrasives are propelled at a high velocity by gas to erode material from WP. As an outcome of impact of the abrasive particles on WP, tiny brittle fractures occur at the surface of WP and carrier gas carries away the fractured fragments. AJ