Metal Forming MCQ Quiz - Objective Question with Answer for Metal Forming - Download Free PDF

Explanation:

Upsetting

• Upsetting is a forging process in which the cross-sectional area of a metal piece is increased by compressive forces, which results in a corresponding reduction in its length. This process is one of the fundamental metalworking operations and is widely used in the manufacturing industry to produce components such as bolts, rivets, and other fasteners.
• Upsetting involves applying compressive forces to a heated or cold workpiece, typically using a die or hammer. The material is plastically deformed, causing it to bulge or expand in a specific region. This deformation is achieved without compromising the integrity of the material, and the process is designed to achieve precise dimensional control.

Steps Involved in Upsetting:

1. Preparation: The workpiece is prepared by cutting it to the desired length and heating it to the appropriate temperature (if hot forging is used).
2. Positioning: The workpiece is placed in the die or between the hammer and anvil in the desired position.
3. Application of Force: Compressive force is applied to the end or middle of the workpiece, depending on the design requirements. This force causes the material to expand in the desired direction.
4. Finishing: The deformed workpiece is removed from the die, and any excess material is trimmed or machined to achieve the final shape.

Applications:

• Manufacturing of bolts, rivets, and other fasteners.
• Production of gear blanks and flanges.
• Creation of components for automotive, aerospace, and construction industries.

Explanation:

Sintering:

Definition: Sintering is the process of heating the compacted powder (also known as the green compact) to a temperature below its melting point but high enough to allow the particles to bond together. This process results in a solid, dense structure with enhanced mechanical properties.

Working Principle:

• During sintering, the powdered material is heated in a controlled atmosphere to prevent oxidation or other unwanted reactions.
• As the temperature increases, the atoms of the particles begin to diffuse across the boundaries of the particles, resulting in particle bonding and densification.
• This diffusion process is driven by the reduction of surface energy, leading to a more stable, consolidated structure.

Role in Powder Metallurgy:

• Sintering is a primary process in powder metallurgy because it is a fundamental step that transforms the powder into a solid, usable component.
• It follows the compaction process, where the loose powder is pressed into a desired shape, and precedes any secondary or finishing processes.

Key Benefits:

• Improves the mechanical properties of the material, such as strength and hardness.
• Enhances the density of the component, reducing porosity.
• Enables the production of components with intricate shapes and close tolerances.

In summary, sintering is a crucial, primary process in powder metallurgy and cannot be classified as a secondary process. It lays the foundation for the structural integrity and performance of the final product.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Heat Treatment

Heat treatment is a secondary process in powder metallurgy. After the sintering process, the component may undergo heat treatment to enhance its mechanical properties, such as strength, hardness, or wear resistance. Heat treatment involves heating and cooling the material in a controlled manner to alter its microstructure and achieve desired properties.

Option 2: Impregnation

Impregnation is another secondary process in powder metallurgy. This process involves introducing a lubricant, resin, or other material into the pores of the sintered component to enhance its performance. For example, impregnating a porous part with oil improves its self-lubricating properties. Impregnation is typically performed to improve functionality and extend the component's lifespan.

Option 3: Infiltration

Infiltration is a secondary process in powder metallurgy used to improve the density and strength of a sintered component. It involves introducing a molten metal or alloy with a lower melting point into the pores of the sintered part. As the infiltrant solidifies, it fills the pores and enhances the mechanical properties, such as strength and wear resistance. Infiltration is commonly used for components requiring high density and superior mechanical performance.

Explanation:

Punching force:

The force required to be exerted by the punch in order to shear out the blank from the stock can be estimated from the actual shear area and the shear strength (τu) of the material.

It is given by the formula-

F = τu × shear area

F = τu × perimeter × thickness

F = τu × πd × t     (circle)

F = τu × 4a × t     (square)

F = τu × 2(l + b) × t   (rectangle)

Concept:

Blanking force is given by:

\( F = \tau \times \text{Perimeter} \times \text{Thickness} \)

For a circular blank, perimeter is \( \pi D \) and thickness is \( T \).

Therefore, \( F = \tau \times \pi D \times T \)

Given:

Initial blanking force = 10 kN

Initial diameter = \( D \), Initial thickness = \( T \)

New diameter = \( 1.7D \), New thickness = \( 0.5T \)

Calculation:

New force,

\( F_{\text{new}} = \tau \times \pi \times (1.7D) \times (0.5T) = \tau \times \pi D T \times (1.7 \times 0.5) \)

\( F_{\text{new}} = F_{\text{old}} \times 0.85 = 10 \times 0.85 = 8.5~\text{kN} \)

Explanation:

Cold working:

• Cold working is a metalworking technique in which metal is shaped or deformed at a temperature below its recrystallization temperature. This process is widely used in the manufacturing industry to enhance the mechanical properties of metals, such as strength, hardness, and ductility, while maintaining precise control over the dimensions of the final product. The ability to achieve close dimensional tolerances is one of the primary advantages of cold working, making it an essential process for producing high-quality components with specific dimensional requirements.
• During cold working, the metal is subjected to mechanical forces, such as rolling, drawing, pressing, or forging, which cause plastic deformation. This deformation results in changes to the metal's grain structure, leading to work hardening or strain hardening. As the metal undergoes plastic deformation, dislocations within its crystal structure become entangled, increasing its strength and hardness. However, because the process occurs below the recrystallization temperature, the metal does not undergo recrystallization, and the deformed grain structure is retained.
• One of the critical advantages of cold working is the ability to achieve close dimensional tolerances. Since the process is performed at lower temperatures, there is minimal thermal expansion or contraction of the metal, allowing for precise control over the final dimensions. This is particularly important in applications where tight tolerances are required, such as in the manufacturing of precision components, automotive parts, aerospace components, and electronic devices.

In addition to close dimensional tolerances, cold working offers several other advantages:

• Improved Surface Finish: Cold working processes often result in a smoother surface finish compared to hot working processes. This is because the metal is not exposed to high temperatures that can cause oxidation or scaling, leading to a cleaner and more polished surface.
• Increased Strength and Hardness: The strain hardening effect of cold working enhances the strength and hardness of the metal. This makes the material more resistant to deformation and wear, improving its overall mechanical properties.
• Enhanced Dimensional Accuracy: Cold working allows for better control over the dimensions of the final product, reducing the need for additional machining or finishing operations.
• Cost-Effective: Cold working processes are often more cost-effective than hot working processes because they require less energy and equipment. Additionally, the improved dimensional accuracy and surface finish can reduce the need for secondary operations, further lowering production costs.

Despite these advantages, cold working also has some limitations:

• Residual Stresses: Cold working can introduce residual stresses into the metal, which may affect its performance and stability. These stresses can be relieved through annealing or other heat treatment processes.
• Limited Ductility: Cold working reduces the ductility of the metal, making it less malleable and more prone to cracking during further deformation.
• Work Hardening: The increased hardness and strength resulting from cold working can make the material more challenging to machine or form in subsequent processes.

Lancing - Creating a partial cut in the sheet, so that no material is removed. The material is left attached to be bent and form a shape, such as a tab, vent, or louver.

Parting - Separating a part from the remaining sheet, by punching away the material between parts.

Slitting - Cutting straight lines in the sheet. No scrap material is produced.

Notching - Punching the edge of a sheet, forming a notch in the shape of a portion of the punch.

Concept:

Shearing is a cutting operation used to remove a blank of required dimensions from a large sheet. The shearing operations which make use of a die, include punching, blanking, piercing, notching, trimming, and nibbling.

Punching/Blanking: Punching or blanking is a process in which the punch removes a portion of material from the larger piece or a strip of sheet metal. If the small removed piece is discarded, the operation is called punching, whereas if the small removed piece is the useful part and the rest is scrap, the operation is called blanking.

Piercing: It is a process by which a hole is cut (or torn) in metal. It is different from punching in that piercing does not generate a slug.

Perforating: It is an operation in which a number of uniformly spaced holes are punched in a sheet of metal. The holes may be of any size or shape. They usually cover the entire sheet of metal.

Notching: It is an operation in which a specified small amount of metal is cut from the edges.

Lancing: It is an operation of cutting a sheet metal through a small length and then bending this cut portion.

Explanation:

Methods of powder production:

There are several ways of producing metal powders, and most of them can be produced by more than one method. The choice depends on the requirement of the end product.

Some of the methods are described below:

Atomisation:

• Atomisation involves a liquid metal stream produced by injecting molten metal through a small orifice.
• The stream is broken up by jets of inert gas or air or water.
• The size and shape of the particle formed depend on the temperature of the molten metal, rate of flow, nozzle size and jet characteristics.
• The use of water results in a slurry of metal powder and liquid at the bottom of the atomisation chamber.

Reduction:

• The reduction of metal oxides (i.e. removal of oxygen) uses gases such as hydrogen and carbon monoxide, as reducing agents.
• By this mean, very fine metallic oxides are reduced to the metallic state.
• The powders produced are spongy and porous and have uniformly sized angular shapes.

Electrolytic process:

• Electrolytic deposition utilizes either aqueous solutions or fused salts.
• The powders produced are among the purest available.

Oxidation:

• Oxidation simply means adding of oxygen by use of oxidising agents.
• Chips of heavy metals, obtained during the shaping operation can be transformed into re-usable powder by means of oxidation and heavy reduction.
• The oxidation step leads to a total disintegration of chips into oxide powder.

Shotting:

• It is a mechanical disintegration process for the production of powders.
• In this method, molten metal is poured on a vibrating screen on which disintegrates the molten metal in to a large number of droplets.
• Droplets are allowed to solidify either in the air or neutral gas atmosphere.
• The size and character of the resultant shot depend on the temperature of molten metal, size of openings in the screen and frequency of the vibrations of the screen.

Particles shape in metal powders and the methods by which they are produced are mentioned in the table below.

Explanation:

• Hot extrusion consists of heating suitable metals and alloys to the proper temperature and placing the heated stock in the cylinder of an extruding press.
• The pressure obtained by a moving ram or piston forces the plastic metal through a die of specified shape.
• One of the major problems in hot extrusion is the effect of hot metal on the equipment. Various methods are used to protect the dies. The die may be changed and allowed to cool for each piece.

Explanation:

Roll separating force (F) = Mean flow stress × Projected area

F = σ_o × L_P × b

Where L_p = Projected length = \(\sqrt { {R{\rm{Δ }}h} }\)

where, R is roller radius and Δh = draught = h_i - h_f = initial thickness - final thickness = μ²R

F ∝ LP ∝ R

So by reducing the size of roller or roller diameter, roll separating force can be reduced.

Explanation:

Rolling defects are as follows:

Additional Information

Casting defects is as follows

Welding Defect is as follows.

Explanation:

Blanking: 

• In blanking, the piece being punched out becomes the work-piece and any major burrs or undesirable features should be left on the remaining strip. Blanking is a shearing operation.

Stretch forming: 

• It is a method of producing contours in sheet metal. Thinning and strain hardening is inherent in the process. Stretch forming is a sheet metal forming process in which the sheet metal is intentionally stretched and simultaneously bent to have the shape change. It is a type of cold drawing. Stress-induced is mainly tensile.

Coining:

• It is essentially a cold‐forging operation except for the fact that the flow of the metal occurs only at the top layers and not the entire volume. In the coining process, compressive forces are there.

Deep Drawing: 

• When cup height is more than half the diameter is termed deep drawing. During deep drawing, in the flange of blank, there is bi‐axial tension and compression stresses.

Explanation:

Extrusion:

Extrusion is the process in which the workpiece material is forced to flow through a die opening by applying a compressive force to produce a desired cross‑sectional shape.

In general, extrusion is used to produce long parts of uniform cross-sections.

Extrusion is classified in general into four types. They are Direct extrusion, indirect extrusion, impact extrusion and hydrostatic extrusion. 

Direct extrusion, also called forward extrusion, is a process in which is the billet moves along the same direction as the ram and punch do. Sliding of the billet is against a stationary container wall. Friction between the container and billet is high.

Indirect extrusion (backward extrusion) is a process in which punch moves opposite to that of the billet. Here there is no relative motion between container and billet. Hence, there is less friction and hence reduced forces are required for indirect extrusion. 

In hydrostatic extrusion, the container is filled with fluid. Extrusion pressure is transmitted through the fluid to the billet. Friction is eliminated in this process because there is no contact between billet and container wall.

Impact extrusion: Hollow sections such as cups, toothpaste containers are made by impact extrusion. It is a variation of indirect extrusion. The punch is made to strike the slug at high speed by impact load. Tubes of small wall thickness can be produced. Usually metals like copper, aluminium, lead are impact extruded. This process is used in manufacturing short length components like toothpaste tubes, gun shells etc.

As here impact extrusion is not in option and impact extrusion is a variation of indirect extrusion. ∴ The correct answer will be Indirect extrusion.

Concept:

Rolling: It is the deformation process of a metal that is widely used in the metal forming process. It is done by passing the strip of the metal between the pair of rollers. The thickness is gradually decreased. The cross-section area will be changed but the volume remains constant.

It is classified into two types:

• Cold rolling
• Hot rolling

Cold rolling produces strongest components. 

• If we compare cold forging and cold rolling then cold forging produces stronger components.
• But here only forging is mentioned which means hot forging.
• So the cold rolling will be the answer.

Concept:

In a rolling process, during travel of material through the rollers, a vertical force (compression) and a sliding force (shear force) will act on the grains.