1. Tell us what do you enjoy least as Assistant Design Engineer?
Guess what? You need to be honest with this answer too – but be careful not to be too negative – or you might talk yourself out of the job altogether! With this answer, ‘safe' answers might include you hate the fact that sometimes designing particular part may take some time. Sometimes the quality doesn't meet the numbers, these comments that most people in the design industry would agree with- so they may give you common ground with you interviewer.
2. Tell me what is the use of mechanical engineer's scale?
This is flat or triangular shape and used for making drawings of machines and structural parts in 1/8, 1/4, 1/2 or full size.
3. Tell me some methods of reducing stress concentration?
Some of the methods are:
☛ Avoiding sharp corners.
☛ Providing fillets.
☛ Use of multiple holes instead of single hole
☛ Undercutting the shoulder parts.
4. Tell me what do you mean by First Aid?
First Aid is immediate and temporary care given to a person who affected accidental injury or a sudden illness before the arrival of doctor.
5. Tell us the difference between brittle fracture and ductile fracture?
In brittle fracture, crack growth is up to a small depth of the material.
In ductile fracture large amount of plastic deformation is present to a higher depth.
6. Tell me what is principle stress and principle plane?
A plane which has no shear stress is called principle plane the corresponding stress is called principle stress.
7. Tell me what is a Centre line?
Centreline is a thin line in the form long and short dashes. It indicates area of symmetrical parts, circles and path of motion.
It is a graphical representation of a real thing to define and specify the shape and size of a particular object by means of lines.
9. Explain me stress concentration and stress concentration factor?
Stress concentration is the increase in local stresses at points of rapid change in cross section or discontinuities.
Stress concentration factor is the ratio of maximum stress at critical section to the nominal stress
10. Tell me what are the various phases of design process?
The various phases of design process are:
☛ Recognition of need.
☛ Definition of problem
☛ Synthesis
☛ Analysis and optimization
☛ Evaluation
☛ Presentation
11. Tell me what are the precautions to be taken to avoid fire?
☛ 1) The buckets along with sand should be placed inside the workshop.
☛ 2) Switches and other electrical parts must be made of fireproof material.
☛ 3) Carbon dioxide gas should be place at required points in special containers.
☛ 4) Fire extinguishers of suitable type should be placed at accessible places.
12. Explain me what is Drafting machine(Mini Drafter)?
It is a device to do drawing work neatly and quickly.An attachment provided to move any position and may be adjusted at any required height.
13. Explain me what are the points that should be kept in mind during forging design?
Some of the points that should be followed while forging design are:
☛ > A radial flow of grains or fibers must be achieved in the forged components.
☛ > The forged items such as drop and press forgings should have a parting line that should divide the forging into two equal halves.
☛ > The ribs in a forging should not be high or thin.
☛ > In order to avoid increased die wear the pockets and recesses in forgings should be minimum.
☛ > In forgings the parting line of it should lie as far as possible in a single plane.
☛ > For ease of forging and easy removal of forgings the surfaces of the metal should contain sufficient drafts.
14. Tell me what are the types of fracture?
The two types of fracture are
☛ Ductile fracture
☛ Brittle fracture
Endurance limit is the maximum value of completely reversed stress that the standard specimen can sustain an infinite number (106) of cycles without failure.
16. Can you please explain the difference between repeated stress and reversed stress?
Repeated stress refers to a stress varying from zero to a maximum value of same nature.
Reversed stress of cyclic stress varies from one value of tension to the same value of compression.
It is the property of the material, which refers to a relative ease with which a material can be cut. It is measured in a number of ways such as comparing the tool life for cutting different material
18. Tell me what is an accident?
An accident is a unexpected and unforeseen event which may or may not injury to a person or a machine tool.
19. Tell me what is Representative Fraction?
It is the ratio of drawing to the object. R.F=Length of the object in the drawing /Actual length of the object.
20. Explain me what is Engineering Drawing?
A drawing which is worked out an engineer for the engineering purpose is known as Engineering Drawing.
21. Explain me what is curved beam?
In curved beam the neutral axis does not coincide with the centroidal axis.
22. Explain me what is impact load?
If the time of load application is less than one third of the lowest natural period of vibration of the part, it is called an impact load.
23. Tell me some example for curved beam?
C frame, crane hook
24. Tell me what is a sketching?
This is freehand expression of the graphic language.
25. Tell us briefly the following lines used in Engineering drawing?
☛ (a)Dimension Lines
☛ (b)Extension Lines
☛ (c)Leaders
Dimension lines are the thin lines used to indicate extents and direction of dimension. These are terminated with arrowheads.
Extension lines are also thin lines and it used to indicate the termination of a dimension.
Leaders are used to direct notes or identification symbols to feature on the drawing.
26. Explain me what is heat treatment and why is it done?
Heat treatment can be defined as a combination of processes or operations in which the heating and cooling of a metal or alloy is done in order to obtain desirable characteristics without changing the compositions. Some of the motives or purpose of heat treatment are as follows:
☛ > In order to improve the hardness of metals.
☛ > For the softening of the metal.
☛ > In order to improve the machinability of the metal.
☛ > To change the grain size.
☛ > To provide better resistance to heat, corrosion, wear etc.
Heat treatment is generally performed in the following ways:
☛ > Normalizing
☛ > Annealing
☛ > Spheroidising
☛ > Hardening
☛ > Tempering
☛ > Surface or case hardening
27. Tell me what are various theories of failure?
The failure theories are:
☛ Maximum principal stress theory.
☛ Maximum shear stress theory.
☛ Maximum principal strain theory.
28. Tell me which designing tools do you use- and how effective do you think they are?
This question should be a relatively simple one to answer because it all comes back to your previous experience. With this one, the interviewer is interested in your history with designing tools and what your personal opinions are regarding these tools so you've really got nothing to lose by just being honest. With this one, they're also looking to see if you use any tools which they use – and how you find them/how familiar you are with them.
Again, with this one, it's all going to come down to personal experience but some designing tools which you might like to mention if you've had experience with them- mechanical / civil design using AutoCAD for 3D design.
29. Tell us what are the different types of loads that can act on machine components?
Different loads on machine components are:
☛ Steady load.
☛ Variable load.
☛ Shock load
☛ Impact load.
30. What is size factor in endurance strength?
Size factor is used to consider the effect of the size on endurance strength. A large size object will have more defects compared to a small one. So, endurance strength is reduced. If K is the size factor, then
Actual endurance strength = Theoretical endurance limit x K
31. Tell me during the design of a friction clutch what are the considerations that should be made?
In order to design a friction clutch the following points must be kept in mind:
☛ > The material for the contact surfaces must be carefully selected.
☛ > For high speed devices to minimize the inertia load of the clutch, low weight moving parts must be selected.
☛ > The contact of the friction surfaces must be maintained at all the times without the application of any external forces.
☛ > Provisions for the facilitation of repairs must be there.
☛ > In order to increase safety the projecting parts of a clutch must be covered.
☛ > A provision to take up the wearing of the contact surfaces must be present.
☛ > Heat dissipaters to take away the heat from the point of contacting surfaces must be there.
32. Explain me what are the different theories of failure under static load?
The main theories of failure of a member subjected to bi-axial stress are as follows:
☛ > Maximum principal stress theory ( Rankine's theory): This theory states that failure occurs at a point in member where the maximum principal or normal stress in a bi-axial system reaches the maximum strength in a simple tension test.
☛ > Maximum shear stress theory ( Guest's or Tresca's theory): This theory states that failure occurs when the biaxial stress reaches a value equal to the shear stress at yield point in a simple tension test.
☛ > Maximum principal strain theory ( Saint Venant theory): This theory states that failure occurs when bi-axial stress reaches the limiting value of strain.
☛ > Maximum strain energy theory ( Haigh's theory): This theory states that failure occurs when strain energy per unit volume of the stress system reaches the limiting strain energy point.
☛ > Maximum distortion energy theory ( Hencky and Von Mises theory): This theory states that failure occurs when strain energy per unit volume reaches the limiting distortion energy.
33. Explain me what are the different types of fits?
On the basis of Indian standards fits can mainly be categorized into three groups:
> Clearance Fit: These types of fits are characterized by the occurrence of a clearance between the two mating parts. The difference between the minimum size of the hole and the maximum size of the shaft is called the minimum clearance, the difference between the maximum size of the hole and the minimum size of the shaft is known as maximum clearance.
> Interference Fit: In these types of fits the size of the mating parts are predefined so that interference between them always occurs. The tolerance zone of the hole is completely below the tolerance zone of the shaft.
> Transition Fit: As the name suggests these type of fit has its mating parts sized limited to allow either clearance or interference. The tolerance zone of the hole and the shaft overlaps in case of such fits.
For a shaft designated as 40 H8/f7, calculate the tolerances.
Given: Shaft designation = 40 H8/f7
The shaft designation 40 H8/f 7 means that the basic size is 40 mm and the tolerance grade for
the hole is 8 ( i. e. I T 8) and for the shaft is 7 ( i. e. I T 7).
Since 40 mm lies in the diameter steps of 30 to 50 mm, therefore the geometric mean diameter,
D = Square root of (30 x 50) = 38.73 mm
We know that standard tolerance unit,
i = 0.45 x Cube root of (D) + 0.001 D
i = 0.45 × 3.38 + 0.03873 = 1.559 73 or 1.56 microns
i = 1.56 × 0.001 = 0.001 56 mm ...(1 micron = 0.001 mm)
The standard tolerance for the hole of grade 8 (IT8)
= 25 i = 25 × 0.001 56 = 0.039 mm
The standard tolerance for the shaft of grade 7 (IT7)
= 16 i = 16 × 0.001 56 = 0.025 mm
34. Explain me briefly the different cold drawing processes?
Some of the important cold drawing processes are as follows:
☛ > Bar and Rod Drawing: In the case of bar drawing the hot drawn bars are at first pickled, washed and coated to prevent oxidation. Once this is done a draw bench is used for the process of cold drawing. In order to make an end possible to enter a drawing die the diameter of the rod is reduced by the swaging operation. This end is fastened by chains to the draw bench and the end is gripped by the jaws of the carriage. In this method a high surface finish and accuracy dimensionally is obtained. The products of this process can be used directly without any further machining.
☛ > Wire Drawing: Similar to the above process the bars are first pickled, washed and coated to prevent any oxidation. After this the rods are passed through several dies of decreasing diameter to provide a desired reduction in the size ( diameter ). The dies used for the reduction process is generally made up of carbide materials.
☛ >Tube Drawing: This type of drawing is very similar to the bar drawing process and in majority of cases it is accomplished by the use of a draw bench.
Notch sensitivity (q) is the degree to which the theoretical effect of stress concentration is actually reached.
The relation is, Kf = 1 + q (Kt-1)
