Major manufacturing processes and its defects
The major materials used for engineering activities are grouped into four classes, namely,
1. Metals and Alloys,
2. Ceramics,
3. Polymers and
4. Composites.
Each of these materials has a distinct property profile.
Pure
metals find limited application, while metals and alloys (ferrous and
Non ferrous) are the most widely used engineering materials. Materials
are subjected to many manufacturing processes to produce not only the
desired shape but also to ensure the design – stipulated physical and
mechanical properties and dimensional tolerances. Further, components
are provided with necessary surface protection from corrosion and
erosion. However, all manufacturing operations and service environments
induce various types of defects in engineering components, which need to
be detected and evaluated.
1. Casting:
Sand casting,
Die casting,
Permanent mold casting,
Investment Casting and
Continuous casting
Defects Encountered during Manufacturing and Service
Inclusions,
Segregations,Gas pockets,
Internal shrinkage,Surface crack,
Pipes,Gas porosity,
Hot tears,
Cold shuts, and
Cavities
2. Welding:
Gas welding,
Resistance welding,
Arc welding,
Friction welding,
Brazing,
Soldering and
Diffusion bonding
Defects Encountered during Manufacturing and Service
Lack of fusion,
Incomplete penetration,Cracks,
Slag inclusion,Gas porosity,
Crack in parent metal,Root undercutting
3. Forming:
Forging,
Rolling,
Wire drawing,
Deep drawing,
Bending,
Extrusion
Defects Encountered during Manufacturing and Service
Inclusion,
Segregation,Pipes,Seams,
Laps,Bursts,
Cracks,Tears,
Lamination,
Flakes,Rolled-in scale,Roll mark,Die-mark,Thermal crack
4. Machining:
Cutting,
Drilling,
Turning and
Milling
Defects Encountered during Manufacturing and Service
Cracks,
Nicks,Scratches and ridges,Tears and laps,Hardness alteration,Residual stress distribution,Deformed debris,Grain size change,Inter-granular corrosion,Embrittlement cracks
5. Powder metallurgy:
Compressing of metal powder into solid mass by application of pressure and heat
Defects Encountered during Manufacturing and Service
Porosity,Cracks,Inclusion,Variation in density distribution
6. Heat treatment:
Specific to alloys to impart desired microstructure, hardness, strength and stiffness
Defects Encountered during Manufacturing and Service
Cracks,Segregation,Grain size changes
7. Surface protection:
Surface protection of components is provided by organic, inorganic and metallic coating:
(i) Organic coating: Paints and lubricants
(ii) Inorganic coating: Phosphating and chromating
(iii)
Metallic coating: Electroplating, coating by diffusion e.g.
galvanizing, aluminizing, metalizing by a spray of partially melted
material
Defects Encountered during Manufacturing and Service
Dents,
Scratches,
Change in thickness of coating,
Insufficient protection of surface, and Erosion of protective
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