BASICS OF DESIGNING PARTS AND NODES OF MECHANISMS...

BASICS OF DESIGNING PARTS AND NODES OF MECHANISMS

After studying the chapter 4 the bachelor must:

know

- concepts and classification of parts and mechanisms;

- the basic requirements for operation, production, economy, etc.;

- influence on mechanisms of mechanical, climatic and other influences;

- the construction of the simplest gear, worm, planetary, belt, lever and other gears

- types of connections of parts (threaded, riveted, welded, soldered, etc.);

- design and purpose of couplings, elastic elements;

be able to

- calculate and construct the simplest kinds of transmissions;

- it is reasonable to assign the material of parts to meet various requirements;

- calculate the technical characteristics of the mechanisms, determine their dimensions, mass, efficiency;

- competently apply the basics of design in self-development mechanisms;

- to design and execute the design documentation;

own

- technique of calculating the basic parameters and characteristics of the mechanisms;

- methods of calculation and design of parts and components of transmission mechanisms;

- skills in the design of graphic and text design documentation.

Structural Materials

The responsible moment of the design process is the selection of materials for the parts and nodes of the mechanisms, which is carried out by the designer. It is necessary to provide ra

Awareness, reliability and fulfill some special requirements. For example, for the mechanisms of aviation and space technology, the main requirements are to ensure minimum weight and overall dimensions; for details, working in sliding friction - wear resistance, at elevated temperatures - heat resistance, etc. Technological characteristics of materials should correspond to the methods of obtaining blanks (casting, stamping, cutting) and the type of production (serial or mass). The cost of the selected material is important.

The main characteristics of structural materials:

• mechanical characteristics , which include the strength indexes - the ultimate strength , the yield strength σТ, and the endurance limit ; stiffness characteristics - modulus of elasticity E and shear modulus G; characteristic of resistance to contact stresses - surface hardness НВ, HRC; the plasticity indices are the relative elongation and the relative transverse narrowing ; impact strength a;

• weights: density , the specific strength and the specific rigidity;

• properties of materials, associated with the operating conditions of parts: wear resistance, indirect indicators of which are the surface hardness of HB, HRC and allowable pressure P ; frictional properties characterized by a coefficient of friction f , permissible pressure P and relative sliding speed corrosion resistance; thermophysical properties determined by the temperature coefficient of linear expansion a, the thermal conductivity , the specific heat c;

• technological characteristics - casting properties, machinability by cutting, the possibility of punching and welding;

• economic indicators - cost and scarcity of materials.

Structural materials include steels, cast iron, light alloys based on aluminum and magnesium, copper alloys, alloys based on refractory metals - titanium, nickel, tungsten and molybdenum, babbits - alloys based on soft metals, lead and tin, composite materials, plastics, rubber.

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