Assistant Design Engineer

The thing to remember when you’re answering this question is that there’s no right or wrong answer. The employer is looking for your insight into the industry – and they’re really trying to determine how much you know – and whether you have enough knowledge to try and forecast trends. As I said, with this one, there’s no one ‘correct’ answer – so the best way to really answer this one is to again be honest.

Think about what has happened in the design industry over the last few years ( Ways of design technique has been changed, great designs according to the request of the client can be made in less number of time ) – and think realistically about what might happen in the next few years. Whatever answer you give, make sure you can justify your answer.

Brakes can be classified on the basis of their medium used to brake, they are as follows:

☛ > Hydraulic Brakes: These brakes as their name suggest use a fluid medium to push or repel the brake pads for braking.

☛ > Electric Brakes: These brakes use electrical energy to deplete or create a braking force.

☛ Both the above types of breaks are used primarily for applications where a large amount of energy is to be transformed.

☛ > Mechanical Brakes: They can be further classified on the basis of the direction of their acting force: Radial Brakes: As their names suggests the force that acts on the brakes is of radial direction. They can further be classified into internal and external blades. Axial Brakes: In these types of brakes the braking force is acting in an axial direction as compared to radial brakes.

Some of the points that must be kept in mind during the process of cast designing are as follows:

☛ > To avoid the concentration of stresses sharp corners and frequent use of fillets should be avoided.

☛ > Section thicknesses should be uniform as much as possible. For variations it must be done gradually.

☛ > Abrupt changes in the thickness should be avoided at all costs.

☛ > Simplicity is the key, the casting should be designed as simple as possible.

☛ > It is difficult to create true large spaces and henceforth large flat surfaces must be avoided.

☛ > Webs and ribs used for stiffening in castings should as minimal as possible.

☛ > Curved shapes can be used in order to improve the stress handling of the cast.

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

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.

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.

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.