What Are The Steps Involved In Designing A Machine Component? & Types Of Loads Acting On A Machine Element - SKengineers

 

WHAT ARE THE STEPS INVOLVED IN DESIGHNING A MACHINE COMPONENT?

Ø  GENERAL PROCEDURE OR STEPS INVOLVED IN DESIGHNING A MACHINE COMPONENT –

1.      Recognition of need –

First of all make a complete statement of problem, indicate the need, aim or purpose, for which the machine is to be designed.

2.      Mechanism –

Select the possible mechanism or group of mechanism, which will give the desired motion.

3.      Analysis of forces –

Find the forces acting on each member of machine.

4.      Material selection –

Select most suitable material for each member.

5.      Design of machine elements –

Find size of each member by considering forces acting on the member and permissible stress value for the selected material from design data book.

6.      Modification –

Modify size of member to agree with past experience and judgement to reduce the overall production cost. This will benefit the manufacturer.

7.      Detailed drawing –

Draw detailed drawings of each component and assembly of machine with complete specifications for the manufacturing process suggested.

8.      Production –

Each component is manufactured according to drawings and specifications of designs in production department.

Ø  GENERAL CONSIDERATIONS IN MACHINE DESIGN –

1)     Type of externally applied loads and stresses induced in machine component –

                   Externally applied loads, on a machine component may act in several ways component tries to resist these loads, due to which, internal stresses are induced in component.

2)     Mechanism –

Successful operations of any machine depends largely upon the simplest arrangement of parts, which will give the required motion.

3)     Selection of material –

Designer should have a deep knowledge of properties of materials and their behaviour under working conditions, i.e. strength, durability, flexibility, weight, resistance to heat and corrosion, castability, weldability, hardenability, machineability etc.

4)     Convenient and economical features –

Machine designed must be convenient to operate and cost wise economical for the customer to purchase.

5)     Use of standard part –

Use of standard part reduces the overall cost.

6)     Safety of operation –

To avoid accidental hazards, care should be taken by designer, against all possibilities of dangerous situations.

7)     Workshop facilities –

A design engineer should be familiar with limitations of his employers workshop, in order to avoid the necessity of vendors.

8)     Number of machines to be manufactured.

9)     Cost of production –

Design engineer should always try to design a part product or machine, in such a way that, production cost will be less. This benefits manufacturer as well as customer.

10)  Ease in assembly –

All the components should be easy to assemble for creating a machine. Simplicity in design should be top priority for any design engineer.

11)  Frictional resistance and lubrication –

Designer should provide necessary lubrication to all moving parts of machine. Movements may be sliding, rolling, rotary reciprocating etc.

Ø  BASIC DESIGN REQUIREMENT –

Sr. No.	DESIGN REQUIREMENT	DESCRIPTION -
1.	Strength	A machine part should not fail under the effect of externally applied loads or forces acting on it. It should have sufficient strength to avoid failure either due to fracture or due to general yielding.
2.	Rigidity	A machine component should be rigid, i.e. it should not deflect or bend too much due to forces or bending moments acting on it.
3.	Wear resistance	Machine parts worn out very early as compared to their expected life due to wear, also leads to the loss of accuracy of machine tool wear resistance of any machine part can be increased by increasing its hardness. EXAMPLE – case hardening of gear and cams.
4.	Manufacturability	Manufacturability is the ease of production, fabrication and assembly. Shape and material of machine part should be selected in such a way that, it can be produced with minimum labour and material costs.
5.	Safety	Shape and dimensions of machine parts should ensure safety to the operators of machine.
6.	Standardization	A machine part should conform to national or international standards covering its profile, dimensions, grade and material used.
7.	Reliability	Reliability is defined as the probability of a machine part that it will give satisfactory performance over sufficient time period. Any machine part can be called as reliable, if the performs its intended functions under desired operating conditions over a specified period of time.
8.	Maintainability	A machine part should be maintainable. Maintainability is the ease, with which a machine part can be serviced or repaired. Maintainability is defined as, the probability that a product will be restored to its operational effectiveness within the given period. When maintenance action is carried out as per the prescribed procedure mentioned in service manual.

·        In addition to above, other desired requirements are durability, size and shape, efficiency, lubrication, cost etc.

Ø  TYPES OF LOADS –

1.      DEAD OR STEADY LOAD –

2.      VARIABLE OR FLUCTUATING LOAD –

3.      IMPACT LOAD –

4.      SHOCK LOAD –

Ø  DEAD LOAD –

·        It is the gradually applied load, which does not change in magnitude, direction or point of application with respect to time.

·        It can be a force, torque or twisting moment, bending moment or combination of these.

·        EXAMPLE – load acting on a column or strut.

Ø  VARIABLE LOAD –

·        It varies in magnitude, direction or point of application with respect to time.

·        It is also called as fatigue load.

·        Types of fatigue load are reversed, repeated, and completely reversed.

·        EXAMPLE – force in I.C engine valve spring. Bending moment on rotating shaft.

Ø  IMPACT LOAD –

·        It is suddenly applied with initial velocity.

·        EXAMPLE – blows of a hammer.

Ø  SHOCK LOAD –

·        It is applied or removed suddenly.

·        EXAMPLE – leaf spring of automobile.