Manufacturing Science - short answer questions from AMIE exams (Winter 2016)

Answer the following (10 x 2)

Negative rake angles generally are preferred for ceramic, diamond and cubic boron-nitride tools. Why?

Although hard and strong in compression, these materials are brittle and relatively weak in tension. Consequently, negative rake angles (which indicate the larger included angle of the tooltip) are preferred mainly because of the lower tendency to cause tensile stresses and chipping of the tools.

If a drill bit is intended only for woodworking applications, what material is it most likely to be made from?

Because of economic considerations, woodworking tools are typically made of carbon steel, with some degree of hardening by heat treatment.

Tool life can be almost infinite at low cutting speeds. Would you then recommend that all machining be done at low speeds?

This reason alone would not justify using low cutting speeds. Low cutting speeds remove less material in a given time which, unless otherwise justified, would be economically undesirable. Lower cutting speeds also often lead to the formation of a built-up edge and discontinuous chips, thus affecting the surface finish.

Define Limiting Drawing Ratio (LDR).

The limiting drawing ratio (LDR) test evaluates the deep drawability of sheet metals. It indicates the maximum ratio of circular blanks to the diameter of the die, by deep-drawing the blank into a cup, without crack formation.

Define Nibbling.

Nibbling is a cold-cutting process which uses a punch to cut multiple holes in the workpiece. These holes overlap, meaning that larger areas of material can be removed by nibbling along the desired profile outline.

Modulus of rupture

The flexural strength or modulus of rupture of the material is defined as the maximum bending stress that can be applied to that material before it yields. 

Why does grey iron undergo expansion, rather than contraction, during solidification?

During solidification of some grades of graphitic cast irons, contraction followed by expansion occurs due to the graphitization reaction which is accompanied by swelling. This swelling mainly depends on some factors like cast iron chemical composition (high carbon Equivalent), casting modulus ( high modulus, thick section), and pouring temperature.

What are the different types of electrode coating in welding?

In industry, the following four major types of welding electrode coatings are the most commonly used. 
  • Rutile Coating
  • Basic or low H2 Coating
  • Cellulosic Coating
  • Iron oxide Coating

Define warm working.

Warm working (also known as warm forming) is defined as a metal forming process in which the plastic deformation of metals takes place above room temperature but below their recrystallization temperature.

What is upset forging?

Upset forging involves locally heating a metal bar and then while holding it firmly with special tooling, applying pressure to the end of the bar in the direction of its axis to deform it. The process allows the production of long parts with a forged end.

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