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Manufacturing Science - short answer questions from AMIE exams (Winter 2018)

Answer the following (2 x 10)

What is impact extrusion?

Impact extrusion is a manufacturing-related extrusion process that uses a press, along with a punch and dies set, to form metal slugs. It involves placing a metal slug between a punch and die, followed by engaging the press so that it forces the metal slug through the die.

Define limiting drawing ratio.

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. The limiting drawing ratio (blank diameter/punch diameter) is between 1.6 and 2.2 for most materials.

Define arc length and arc crater.

Arc crater - Depression formed when the arc melts the base metal.
Arc length - Distance between the electrode and the base metal. In SMAW, this distance should be approximately equal to the electrode diameter.

What is directional solidification?

"Directional solidification" is a metal casting term. It refers to the process of controlled feeding of the molten metal into a temperature-controlled mould to produce a part that is free of hollow spots, called shrink defects. 

Shrinkage of metals depends on what factors.

The shrinkage of metal depends upon the following factors:
  • Pouring temperature of the molten metal
  • Design and dimensions of castings
  • Mould material
  • Method of moulding.

Define feed rate in case of turning, milling and drilling operations.

Feed rate is defined as the tool’s distance travelled during one spindle revolution. It determines the rate of material removal, power requirements, and surface finish.

Why do cutting velocity and temperature have an important effect on tool life?

The temperature has a large effect on the life of a cutting tool for several reasons. 
  • All materials become weaker and less hard as they become hotter; therefore, higher temperatures will weaken and soften an otherwise ideal material. 
  • Chemical reactivity typically increases with increasing temperature, as does diffusion between the workpiece and the cutting tool. 
  • The effectiveness of cutting fluids is compromised at excessive temperatures, meaning there is higher friction to overcome, and therefore more tool wear is expected. 
  • In interrupted cutting, there can be an excessive thermal shock if the temperatures are high.

Draw a tool sketch showing the various elements of flank wear and crater wear.

In electron beam machining, why is a high vacuum created in the apparatus?

The vacuum prevents the electrons from scattering, due to collisions with gas molecules. In a vacuum chamber, a beam of high-velocity electrons is focused on a workpiece. The kinetic energy of the electrons, upon striking the workpiece, changes to heat, which vaporizes minute amounts of the material.

Calculate shear angle, when the end of the pipe was orthogonally cut with a tool of 20⁰ rake angle. Assume chip length 85 mm and uncut chip length 202 mm.

Chip thickness ratio (r) = 85/202 = 0.42
tanφ = rcosα/(1 - rsinα)
= 0.42 x cos200/(1 - 0.42sin200)
Solving
φ = 24.740

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