Design of machine elements of 2

Design of machine elements of 2

 Precisionparts Machine design is a vast field of engineering technology. As such, it begins with the conception of an idea and follows through the various phases of design analysis, manufacturing, marketing and consumerism. The following is a list of the major areas of consideration in the general field of machine design:

  ① Initial design conception;  ② Strength analysis; ③ Materials selection;   ④ Appearance; ⑤ Manufacturing;  ⑥ Safety;  ⑦ Environment effects;  ⑧Reliability and life;                               
   Strength is a measure of the ability to resist, without fails, forces which cause stresses and strains. The forces may be;

 ① Gradually applied;  ② Suddenly applied;  ③ Applied under impact;   ④ Applied with continuous direction reversals;  ⑤ Applied at low or elevated temperatures.       

 Precisionparts If a critical part of a machine fails, the whole machine must be shut down until a repair is made. Thus, when designing a new machine, it is extremely important that critical parts be made strong enough to prevent failure. The designer should determine as precisely as possible the nature, magnitude, direction and point of application of all forces. Machine design is mot, however, an exact science and it is, therefore, rarely possible to determine exactly all the applied forces. In addition, different samples of a specified material will exhibit somewhat different abilities to resist loads, temperatures and other environment conditions. In spite of this, design calculations based on appropriate assumptions are invaluable in the proper design of machine.

  Precisionparts Moreover, it is absolutely essential that a design engineer knows how and why parts fail so that reliable machines which require minimum maintenance can be designed. Sometimes, a failure can be serious, such as when a tire blows out on an automobile traveling at high speeds. On the other hand, a failure may be no more than a nuisance. An example is the loosening of the radiator hose in the automobile cooling system. The consequence of this latter failure is usually the loss of some radiator coolant, a condition which is readily detected and corrected.

 The type of load a part absorbs is just as significant as the magnitude. Generally speaking, dynamic loads with direction reversals cause greater difficulties than static loads and, therefore, fatigue strength must be considered. Another concern is whether the material is ductile or brittle. For example, brittle materials are considered to be unacceptable where fatigue is involved.     
  In general, the design engineer must consider all possible modes of failure, which include the following:

①Stress; ② Deformation;    ③ Wear;  ④ Corrosion;  ⑤ Vibration;    ⑥ Environmental damage;     ⑦ Loosening of fastening devices.                           

   The part sizes and shapes selected must also take into account many dimensional factors which produce external load effects such as geometric discontinuities, residual stresses due to forming of desired contours, and the application of interference fit joints.