Materials Fabrication Techniques

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Questions and Answers

What is the primary purpose of annealing glass?

To enhance the mechanical strength of the glass

To change the color of the glass

To remove internal stresses caused by uneven cooling (correct)

To provide decorative features to glass surfaces

Which method is used to create sheet glass through a process of floating?

Floating on water

Floating on mercury (correct)

Floating in air

Floating on resin

What does tempering glass do to the surface of the glass part?

It puts the surface into compression (correct)

It causes the surface to heat up excessively

It alters the chemical composition of the surface

It puts the surface into tension

Which of the following statements accurately describes the sequence of tempering?

The glass is hot, cooled on the surface, and further cooled to achieve compression Signup and view all the answers

What does the term 'gob' refer to in glass fabrication?

Initial molten state of glass Signup and view all the answers

What is one of the effects of surface cooling during the tempering process?

Suppression of growth of cracks from surface scratches Signup and view all the answers

What aspect of glass production involves pressing operations?

Creation of complex shapes and sizes Signup and view all the answers

How does tempered glass behave when subjected to surface scratches?

Scratch growth is suppressed but may still be damaged Signup and view all the answers

What is the initial step in the injection molding process?

Pelletized material is fed into a heating chamber. Signup and view all the answers

In extrusion, what role does the mechanical screw play?

It propels and melts the pelletized material. Signup and view all the answers

How does blow molding operate to create hollow plastic containers?

By blowing air into a semimolten parison inside a mold. Signup and view all the answers

What is a significant advantage of the extrusion process?

It produces continuous lengths with consistent geometries. Signup and view all the answers

What is used to expedite the solidification of extruded plastic?

Blowers, water spray, or bath. Signup and view all the answers

Which of the following is NOT a step in the injection molding process?

Air is used to expand the parison shape. Signup and view all the answers

What material type is primarily involved in the blow molding process?

Thermoplastics and polymer tubing. Signup and view all the answers

What happens to the thermoplastic material during the injection molding process?

It melts to form a viscous liquid before molding. Signup and view all the answers

What is the primary purpose of adding processing aids during sintering?

To enhance neck formation between particles Signup and view all the answers

What type of compression applies pressure through a fluid in a rubber envelope?

Isostatic compression Signup and view all the answers

In the production of Portland cement, which of the following is NOT one of the primary constituents?

Calcium carbonate Signup and view all the answers

What is a key characteristic of thermoplastics?

They become soft when heated and can be reshaped Signup and view all the answers

What is the main method used for casting thin sheets of flexible ceramic tape?

Tape casting from liquid slip Signup and view all the answers

Which method is generally used for forming after hydration begins in cementation?

Forming during the paste state Signup and view all the answers

Which condition does NOT affect the method used for polymer forming?

The optical properties of the polymer Signup and view all the answers

Which of the following statements is true regarding hot pressing in ceramics?

It combines both pressure and heat in the forming process Signup and view all the answers

What is the primary advantage of using the sand casting method?

It is the most common and cheapest method. Signup and view all the answers

In which situation is investment casting most advantageous?

For creating low volume, complex shapes. Signup and view all the answers

Which type of casting is characterized by the use of a wax pattern?

Investment Casting Signup and view all the answers

What is a disadvantage of the sand casting method?

It can result in internal defects. Signup and view all the answers

What is the purpose of using plaster in the investment casting process?

To encase the wax pattern and create a hollow mold. Signup and view all the answers

Die casting is primarily used for which of the following?

High volume, low-temperature alloy parts. Signup and view all the answers

Which application is powder metallurgy best suited for?

Materials with low ductility. Signup and view all the answers

What is a key characteristic of continuous casting?

It creates solidified shapes in real-time. Signup and view all the answers

What is a primary method for shaping metal through deformation using tools such as hammers?

Forging Signup and view all the answers

Which fabrication method involves melting metal and pouring it into a mold?

Casting Signup and view all the answers

What significant temperature difference distinguishes hot working from cold working?

At Tm for hot working, below Tm for cold working Signup and view all the answers

Which of the following processes involves shaping metal by passing it through rolls?

Rolling Signup and view all the answers

During which process are alloying elements typically added to the molten metal?

Casting Signup and view all the answers

What are the characteristics of hot working compared to cold working?

Higher temperatures and larger deformations Signup and view all the answers

Which of the following is NOT typically a method of metal fabrication?

Painting Signup and view all the answers

What is a crucial requirement for the die used in the extrusion process?

It must be well lubricated and clean Signup and view all the answers

What is the purpose of milling and screening in ceramic fabrication?

To achieve the desired particle size Signup and view all the answers

In slip casting, what happens to the slip after it is poured into a mold?

It absorbs water and forms a green ceramic Signup and view all the answers

What is one of the key processes involved in sintering for ceramic fabrication?

Pressing particles at elevated temperatures Signup and view all the answers

Which process is used to form a hollow ceramic component?

Slip casting Signup and view all the answers

At what temperature is aluminum oxide powder typically sintered based on the provided content?

1700°C Signup and view all the answers

What is one initial step in the sintering process?

Grinding ceramic and/or glass particles Signup and view all the answers

Which forming method involves the use of water to create a workable material before shaping?

Hydroplastic forming Signup and view all the answers

What characterizes the 'green' ceramic stage in fabrication?

It is shaped but not yet fired Signup and view all the answers

Study Notes

Fabrication of Materials

Materials fabrication techniques vary depending on the material type, desired shape, and production volume.
Metal fabrication includes techniques like forging, rolling, extrusion, drawing, casting, and welding.
Forming operations reshape raw stock into final shapes using hot or cold working methods. Hot working involves high temperatures for recrystallization and large deformations, while cold working takes place at temperatures below the melting point to achieve work hardening and smaller deformations.
- Techniques like forging (hammering, stamping), rolling, and drawing are used for shaping.
- Casting involves pouring molten metal into a mold to solidify. Common methods include sand casting (large parts), investment casting (complex parts), and die casting, (high volume, low temperature alloys), all useful for large-scale production. Continuous casting creates continuous shapes in the production of slabs.

Casting

Casting is a common method for shaping metals and certain polymers.
In casting, molten material is poured into a mold, where it solidifies into the desired shape.
- Sand casting uses a sand mold and is suitable for large parts, like engine blocks.
- Investment casting uses a mold made from a pattern encased in plaster. It is best for complex parts.
- Die casting involves a metal die mold for high-volume, low-melting-point parts.
- Continuous casting is used for producing cast materials with continuous shapes, such as slabs.

Miscellaneous Metal Fabrication Methods

Welding joins two or more metal pieces by fusion.
Powder metallurgy involves compacting powdered materials under pressure, for components with low ductility.

Ceramic Fabrication Methods

Ceramic fabrication involves pressing, blowing, fiber drawing, and slip casting to shape ceramic components.
- Pressing uses a mold to shape a ceramic, such as plates and dishes.
- Blowing is used for forming hollow ceramic shapes, like dishes.
- Fiber drawing produces fibers or filaments of glass or ceramic.
- Slip casting involves pouring a slip (a mixture of ceramic powder and water) into a mold, allowing the water to drain and leaving a solid ceramic component.
Sintering is a process for improving the properties of ceramic components. This involves producing ceramic and/or glass particles by grinding, placing these particles inside a mold, and pressing at elevated temperatures to reduce pore sizes.

Thermal Processing of Metals

Annealing involves heating a material to a specific temperature then cooling it slowly to relieve internal stresses or alter the microstructure for improved properties. Types of annealing include stress relief, process (recovery/recrystallization), spheroidize, full, and normalize.
Spheroidize is used for making soft steels suitable for machining.
Full annealing produces soft steels good for forming.
Normalizing a material deforms a large grain, then making smaller grains for better properties.

Processing of Plastics

Processing techniques for plastics are influenced by factors like whether the material is thermoplastic or thermosetting, the softening temperature (for thermoplastics), the atmospheric stability of the material, and the geometrical dimensions of the final product.
- Thermoplastics can be repeatedly heated and cooled without significant change, allowing for recycling. Examples of thermoplastics include polyethylene, polypropylene, and polystyrene.
- Thermosets undergo permanent changes when heated and cannot be melted and reshaped. Examples of thermosets include urethane and epoxy.

Plastic Molding

Molding is a common method for shaping plastics. Techniques include compression molding, transfer molding, injection molding, blow molding.
- Compression molding involves placing a plastic compound between mold halves and applying heat and pressure to form the piece.
- Transfer molding is similar to compression molding but uses a separate heated chamber to preform the plastic into a disc.
- Injection molding introduces molten thermoplastic into a mold by forcing it with a moving plunger or ram.
- Blow molding forms hollow plastic products by forcing air into a molten parison inside a mold.

Additional Information

Sheet forming is a continuous drawing technique for creating glass sheets originally by floating on a mercury pool, producing a continuous sheet of glass.
Heat treating glass includes annealing to remove stress from uneven cooling and tempering to compress the glass surface to prevent surface cracks.

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Description

Explore various techniques involved in the fabrication of materials, particularly focusing on metal fabrication methods such as forging, casting, and forming operations. This quiz covers the principles behind techniques like hot and cold working, and the significance of casting in large-scale production.