Manufacturing Considerations

The subject relates with the designer's intimate knowing of methods of manufacturing. Any designed object can be described required shape by various methods of manufacturing and thus the designer will have to identify the methods wherever he prefers a specific method. The selected material will have to be described a renewed consideration for manufacturing. For illustration, from stress consideration a gear wheel made in stainless less steel might be better and smaller, however its machining and teeth cutting will cost more like compared to medium carbon steel. Modify of tools during machining operation may cost. Even in modern computer or pc numerically controlled machines bringing needed tool in position will not be cost free besides adding cost at programming stage. Therefore it is, to be considered by the designer if the radit of fillets and shoulders might be kept similar or they must be not same. If the keyways can be cut in one setting in more than one place or location the cost may be decreased for shaft manufacturing. The pulleys can be cast or fabricated. The process requires to be examined on the basis of weight and cost. Sometimes in raise cost may be tolerated if weight is reduced. Similarly a welded structure from mild steel for the housing of a gear reducer may have to be compared along with the cast structure either in cast iron or steel.

Casting in sand mould or permanent might be a question before designer in many cases. Though a permanent mould may appear to be a better choice for large number yet the employ of pressure and conditions of melting from batch to batch and high initial cost might be prohibitive. Casting generally may pose some problems concerning rate of cooling, change of thickness, intricate nature of product and any subsequent machining require to be considered. The designer must consider that in casting metal at every location that is a flat wall and a corner does not cool at the same rate. If material in adjacent location cools differentially residual stressed are produced. They may even reason cracking. Such consideration may need basing thicknesses and radii not merely on strength but also upon rate of cooling. The residual stress may not only purpose reduction of strength but may result into undesirable deformation throughout subsequent machining. Large diameter or thicknesses in casting solidify over a much longer period and thus are prone to have coarse structure and lesser strength. The designer may have to allocate a proper heat treatment to refine internal grain structure.

The designer ought to take note of the fact that in forging the deformation is concentrated more on the surface and inner material is not worked. Therefore in hot forging process the structure of material is more liable to be refined on the surface creating non-uniformity of structure in the entire body. The refinement is often advantageous with enhanced strength, though defects are also some times created in severely worked mater. On the other hand process like rolling, extruding and pressing is not confined to merely surface in their effects. They result in uniform structure in the last. Cold processes are performed on softer alloys but stronger materials as like steel are often worked hot. Cooling will eventually follow which if not controlled and slow can result in residual stresses. Anticipating the cooling stresses the designer may recommend the rate of cooling.

Plastic parts are often cast in modules made individually or in pressure die case. The design must keep minimum thickness within limit, not underneath 4.5 mm. The pressure die case plastic may not require finishing by machining but cast parts need machining and hence proper thicknesses are to be provided. Very few parts of plastic are made by machining but designer should take care of temperature rise during cutting process. Slight rise in temperature may purpose material to join by the side of machine surface. Internal threading has to be performed much more carefully. They can be better made during casting thirteen threats per cm can be cast easily. The colour of casting is not easy to maintain which created problem in assembling parts. To ignore mismatch the surfaces may be spotted as streaked.