Karteikarten
L#18 Advanced Machining Processes
Karten in diesem Stapel (10)
- 1In which cases might mechanical machining processes by unsuitable for manufacturing product components? (5)1. The strength and hardness of the material are very high
2. The workpiece is too brittle to be machines without damage. This is the case with heat treated alloys, glass, ceramics and powder metallurgy parts
3. The workpiece is too flexible to withstand mechanical machining forces
4. The shape of the part is too complex (for example, holes with high length to diameter relationships)
5. Special surface finish and dimensional tolerance requirements that cannot be obtained are uneconomical using other processes
6. The temperature rise or the residual stress developed during the machining process are not desirable or acceptable - 2Summarize the chemical machining process (5)1. Chemical machining (CM) is the process where chemicals attack and etch metals, stones and some ceramics, and remove small amounts of material from the surface
2. These processes are carried out by chemical dissolution using reagents or etchants
3. Typically, shallow cavities are produced on plates, sheets, castings and forgings
4. The profile of the machined area is controlled by the use of masking materials (maskants)
5. CM is used in the aerospace industry to remove shallow layers of material from large aircraft components, missile skin panels and extruded parts for airframes - 3Draw the two annotated diagrams illustrating chemical machining. Also draw a chemically machined missile skin panel (1)See notes (1)
- 4Summarize electrochemical machining. Include the annotated diagram to explain the process (6)1. An electrolyte acts as a current carrier and the high rate of electrolyte movement in the tool washes metal ions away from the workpiece (anode) before they have a chance to plate onto the tool (cathode) as seen in the diagram
2. See notes for diagram
3. The material removal rate (MMR) in electrochemical machining is:
MMR = CI
where I is the current in amperes and C is the material constant
4. This process is used to machine complex cavities in high strength materials
5. For example, in the aerospace industry, ECM is used for mass production of turbine blades, jet-engine parts and nozzles. - 5With use of a diagram, explain electrical discharge machining (EDM) (8)1. Process is based on the erosion of metals using spark discharges
2. When two current-conducting wires are allowed to come into contact with each other, an arc is produced
3. At the point of contact, a small portion of the metal erodes away and a small crater is left
4. See notes for diagram
5. The EDM system consists of an electrode and the workpiece connected to a DC power supply and placed in a dielectric fluid.
6. When the potential difference is high, the dielectirc breaks down and a transient spark discharges through the fluid removing small amounts of the metal.
7. The process can thus be used on materials that are electrical conductors
8. The material removal rate for EDM is estimated by:
MMR = 4*10^4(ITw)^(-1.23)
where:
I is the current in amperes and Tw is the melting point of the material in degrees celsius - 6With use of a diagram, explain wire EDM (4)1. It is an important variation of EDM
2. A slowly moving wire travels along a predefined path through the workpiece and acts as the electrode for the EDM process to create the desired shapes
3. As the wire corrodes in the process, it is continuously pulled from one reel to another to replace the corroded section with fresh wire
4. See notes for diagram - 7With use of a diagram, explain laser beam machining (5)1. A laser beam is used; a highly focused, high density energy source to melt and evaporate portion of the workpiece in a controlled manor
2. The laser may be applied in pulses or continous wave
3. This process is used for drilling and cutting metals, non-metallic materials, ceramics and composites
4. This technology can also be used for welding or additive manufacturing
5. See notes for diagram - 8Explain with use of a diagram water-jet machining (4)1. The force resulting from the change in momentum of a stream of water is used for cutting and deburring operations
2. The water jet essentially acts as a saw and cuts a narrow groove in the material
3. A high pressure level of about 400 MPa is generally used for efficient operation, although pressures as high as 1400 MPa can be generated. Nozzle diameters range between 0.05 and 1 mm
4. See notes for diagram - 9Describe with use of a diagram abrasive jet machining (2)1. A high-velocity jet of dry air, nitrogen or carbon monoxide containing abrasive particles is aimed at the workpiece surface under controlled conditions.
2. See notes for diagram - 10Summarize hybrid machining systems (7)1. A more recent development in manufacturing is the concept of hybrid machining systems
2. Two or more maching processes are combined into one system to take advantage of the capabilities of each process to increase production speed or negate disadvantages of using one of the processes individually
3. Examples of such systems include combinations such as:
4. Abrasive machining and electrochemcial machining
5. Abrasive machining and electrical discharge machining
6. Water-jet cutting and wire EDM
7. Combining additive and traditional manufacturing technologies
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- Beschreibung
- Manufacturing Operations and Technology Karteikarten am L#18 Advanced Machining Processes, erstellt von Block am 05/05/2014.
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- Block
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