Metal Forming MCQ Quiz in मल्याळम - Objective Question with Answer for Metal Forming - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept:

In punching and blanking, the shearing action on the sheet takes place which will depend on the shear strength of the metal.

Punching force F = Lt τ

Where L is Length of the periphery, t = thickness, τ = Ultimate shear strength

For circular section L = πd

Explanation:

Forging:

Forging may be defined as a metal-working process by which metals and alloys are plastically deformed to the desired shapes by the application of a compressive force.

Basic forging operation:

Explanation:

Hot extrusion:

• Hot extrusion involves prior heating of the billet to a temperature above its recrystallization temperature, lubrication is critical hot extrusion for certain metal’s (eg. steels) and special lubricants have been developed that are effective under harsh conditions in hot extrusion. 
• The lubrication reduces the friction between the billet and the container to such an extent that it can approximately be assumed that friction has no influence on the material flow. 
• This should, on one hand, have sufficient lubrication properties to completely separate the material being extruded from the container wall and the die and, on the other hand, the lubricant should also have a low thermal conductivity in other words, provide thermal isolation.
• Glass and combinations of grease, oil, and graphite are used as lubricants.
• Glass provides very good lubrication and simultaneously excellent insulation.
• Direct hot extrusion of steel is, therefore, usually lubricated with glass.

Explanation:

Forging is the process by which a metallic part is deformed to final shape with the application of pressure and with or without the application of heat. Forging involves the application of compressive stress which exceeds the flow stress of the metal. This stress is applied either quickly or slowly.

Advantages of Forging

• Strength and toughness are high
• As forged parts have a high strength to weight ratio, the material required to produce a component is less
• Internal defects like segregation, cracks, and porosity are eliminated
• Forged parts have the ability to withstand higher loads during service
• Components can be produced to close tolerances
• Machining time after forging is reduced considerably

Disadvantages of Forging

• Brittle materials like cast iron cannot be forged
• The cost of forging dies is high
• Complex shapes can easily be produced by casting and not by forging
• Small components can easily be machined from regular sections

Explanation:

Toothpaste tube can be produced by backward hollow extrusion also known as impact extrusion.

In impact extrusion, a heavy punch is allowed to fall over the material/billet and the material/billet takes the shape of the die. Collapsible tubes are made by this process. This process is limited to soft and ductile materials.

Explanation:

Extrusion:

Extrusion is any process in which material is forced through shape orifice, with the material solidifying immediately to produce a continuous length of constant cross-section. Squeezing toothpaste from a tube is a familiar example of extrusion.

Various factors on which an extrusion process depends are die design, extrusion ratio, billet temperature, lubrication, extrusion speed and metal properties. Among these, the most important factor is metal property.

For successful extrusion to happen the metal should be plastic.

Plasticity:

Plasticity is the ability of a material to undergo some degree of permanent deformation without rupture or failure. Plastic deformation will take place only after the elastic range has been exceeded. Forming, shaping extruding and many other hot and cold working processes requires metal to be plastic. 

Ductility:

Ductility is the property of the material that enables it to be drawn out or elongated to an appreciable extent before rupture occurs.

The percentage elongation or percentage reduction in the area before the rupture of a test specimen is the measure of ductility.

Toughness:

Toughness is defined as the ability of the material to absorb energy before fracture takes place.

This property is essential for machine components which are required to withstand impact loads.

Malleability:

Malleability is the property of a metal by which it can be beaten into thin sheets without breaking or damaging it.

Concept:

The extrusion ratio \(R = \frac{{{A_i}}}{{{A_f}}} = {\left( {\frac{{{d_i}}}{{{d_f}}}} \right)^2}\)

And the extrusion pressure is P = σ_m ln R

The plastic work involved in the extrusion process will be:

\(W = P \times \;{V_i} = P\; \times \frac{\pi }{4}d_i^2L\)

Calculation:

\(R = {\left( {\frac{{{d_i}}}{{{d_f}}}} \right)^2} = {\left( {\frac{{20}}{{16}}} \right)^2} = 1.5625\)

Extrusion pressure \(P = 40\ln 1.5625 = 17.85\;MPa\)

The work involved is:

\(W = 17.851 \times \frac{\pi }{4} \times {20^2} \times 100 = 560805.7046\;N.mm = 560.805\;Nm = 560.8\;J\)

Concept:

• Powder metallurgy is a process in which metallic powders are heated below their melting temperatures to achieve bonding.
• It involves metal or alloy powders to be compacted into the desired shape after blending, and then to be heated in a controlled atmosphere at a temperature below their melting points in order to achieve bonding of the particles to get the desired properties.
• The powder metallurgy process enables to produce parts in their final shape, thus eliminating the need for any additional machining.

Basic steps of the manufacturing of parts by powder metallurgy are

• Production of metal powders
• Blending and mixing of powders
• Compaction
• Sintering
• Finishing operation

Blending and Mixing:

• In this process, metallic powders in the required proportion are mixed uniformly. Binders are added to develop the required green strength.
• Lubricants are added to reduce interparticle friction and to reduce die wall friction.

Compacting: 

• In compacting, loose powder is compressed into a shape known as a green compact, which is a very important step in powder metallurgy.
• The desired characteristics to be achieved by compacting are high product density and uniformity of that density throughout the compact.

Sintering:

• Sintering is the process of heating the green compact at a high temperature below the melting point in a controlled atmosphere.
• Sintering increases the bond between particles and increases the strength of the powder metal compact.

Secondary Operations: 

• Generally, some optional Secondary Operations are performed on the sintered part to achieve the final dimensions and properties of the part.
• Example: Repressing, Sizing, Coining, Heat treatment, Finishing operations.

Concept:

Degree of drawing (D) is given by:

\(D = \frac{{{A_0} - {A_f}}}{{{A_0}}}\)

Calculation:

Given:

d₀ = 18 mm

Since degree of drawing (D) is given by:

\(D = \frac{{{A_0} - {A_f}}}{{{A_0}}}\)

\(0.36 = 1 - \frac{{{A_f}}}{{{A_0}}}\)

\(\frac{{{A_f}}}{{{A_o}}} = 0.64\)

\(\frac{{\frac{\pi }{4}d_f^2}}{{\frac{\pi }{4}d_0^2}} = 0.64\)

d_f = 0.8 × 18

= 14.4

% reduction in diameter \( = \frac{{{d_0} - {d_f}}}{{{d_0}}} \times 100\)

= \(\frac{{18 - 14.4}}{{18}} \times 100\) 

= 20%

Explanation:

Cold working or Cold Forming:

• Cold working is the plastic deformation process where metal is processed below the re-crystallization temperature.
• Most of the time cold forming is done at room temperature.
• The major cold-working operations can be classified basically as rolling, squeezing, bending, shearing, and drawing.

Advantages: 

• No heating required.
• The better surface finish obtained.
• Superior dimension control.
• Better reproducibility and interchangeability of parts.
• Improved strength properties like fatigue strength and tensile strength.

Disadvantages: 

• Higher forces required for deformation
• Heavier and more powerful equipment required
• Less ductility available
• Metal surfaces must be clean and scale-free
• Strain hardening occurs

Materials used for cold working

• Low and medium carbon steels, low alloy steels, copper and light alloys, Titanium and beryllium