MACHINE DESIGN SHORT QUESTION ANSWERS CLASS NOTES
MACHINE DESIGN
SHORT QUESTION ANSWERS
Question answers are very helpful
in better understanding. These
improve clarity too. All this is helpful in
design of a component.
Design is process to create an object
/machine. It performs the required
function satisfactorily. It is durable &
have minimum cost. It involves
(i) Selection of material of construction
(ii) Selection of method of manufacture
(iii) Finding sizes on the bases of
(a) Strength
(b) Stiffness
(c) Stability
(d) Wear
Definition of design synthesis
To find various alternatives of a product/mechanism to achieve the desired function satisfactorily over a reasonable period of time.
Definition of design analysis
Process of optimization to decide the best alternative
(i) to achieve the desired objective
(ii) having reasonable life
(iii) with minimum cost.
Q. What is Adaptive Design?
A.
It is copying the existing design. Use it with no chances of further improvement.
Q. Explain the criterion for the SELECTION OF MATERIAL in design.
A.
In engineering, there are two types of materials available. These are brittle and ductile materials. The selection depends upon the various desirable physical, chemical, mechanical and economic properties. Well known properties are easily available in literature.
Physical properties include
(i) Boiling point
(ii) Melting point
(iii) Density
(iv) Dielectric constant
(v) Specific heat
(vi) Thermal conductivity
(vii) Electrical conductivity
(viii) Viscosity
(ix) Magnetic permeability
(x) Refractive index
(xi) Solubility
Chemical properties include toxicity, corrosiveness, inflammability, inertness, stability etc.
Mechanical properties include tensile strength, compressive strength, bending strength, torsional strength, buckling strength, stiffness, ductility, brittleness, malleability etc.
Economical properties include initial cost and manufacturing cost, tendency to contaminate etc.
How do you classify machine design?
A.
(i) Copied design
(ii) Improved design
(iii)Innovative design
Q. List the qualities of a good designer.
A.
The traits of a good designer are
(i) Good communication skill
(ii) good imagination
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Good observation
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Good listener
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Great self confidence
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Love art and nature
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Creative mind
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Flexible
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Cooperative nature
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Technically qualified
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Good clarity about color and texture of materials
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Great visionary
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Problem solver
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Logical thinking and reasoning
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Thick skin to digest criticism
Q. Difference between design synthesis and design analysis.
Design
The process to create
(i) an object/machine
(ii) perform the required function satisfactorily
(iii) over a reasonable period of time (life)
(iv) minimum cost
Q. Explain the Aesthetic design criterion.
Aesthetic design criterion deals with the external shape and physical look of the product. Beautiful product attract customers.
An attractive appearance depends on shape, form, color and surface finish.
Q What is Ergonomics in machine design?
Ergonomics deals with proper and comfortable working conditions for the working persons. It deals with
(i) proper lighting
(ii) ventilation
(iii) air conditioning
(iv) water availability
(v) safety of the human beings using the designed machines and processes
It involves the study and execution of human behavior with the machines to give maximum output. These aspects will enthuse Jeal and interest to give their utmost effectiveness in production.
Q. Enlist the steps in machine design.
A.
Steps in design are
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Write the functional requirement for design.
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Consider all possible mechanisms to give the required purpose or motion.
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Determine forces on each part of the mechanism using statics and dynamics.
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Material selection is based on physical, chemical, mechanical and economical properties of the material.
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Finalize the method of manufacture.
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Propose shapes and configuration of the tentative design.
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Find the sizes of the suggested shape and configuration on the bases of strength, stability, stiffness and wear.
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Select standard dimensions for each part from manufacture’s catalog.
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Make drawing of each part separately. Make the assembled drawing too.
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Mention on the drawing material, method of manufacture, dimensions with upper and lower limits.
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Also mention all other information necessary for manufacture & assembly.
Q. Disadvantages of cast iron from design considerations?
A.
(i) Cast iron is highly brittle.
(ii) Cast iron is very weak in tension.
(iii) Cast iron has almost zero deformability or zero elongation. It is difficult to give the desired shape to cast iron by cold or hot working.
Q. What are the methods to increase the fatigue strength of bolted joints?
A.
Bolted joints are very common in the construction of structures and machines. Bolts in the bolted joints are under fluctuating tension which causes fatigue. These have less fatigue strength. There are bright chances of crack initiation and propagation.
Overcome this difficulty by
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Use rolled threaded bolts
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Rolling of threads done after the HEAT treatment. This heat treatment induces compressive stresses in the roots of the threads which increases the fatigue life.
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Initial compressive stresses are easily achievable by shot peeing on large size bolts. Rolling is more costly on larger size bolts.
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Use multi-start threads in nuts. More distance within threads increase fatigue life. It normally doubles the fatigue life.
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Increase of minimum root radius to 0.15 p increases fatigue life.
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Mounting of bolts straight increases fatigue life. Even a small tilt in mounting, decreases fatigue life abruptly.
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Asymmetric thread profile in the nut increases the fatigue life by 20 %.
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Use of different material of nut with higher Young’s modulus increases the fatigue life.
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Tighten the bolt very firmly to increase fatigue life.
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