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What are the steps involved in casting?
What are the steps involved in casting?
Pattern making, Preparation of moulds, Core making, Melting and pouring the molten material, Solidification and further cooling to room temperature, Cleaning, Inspection, and defects if any remove.
Which of the following are advantages of casting? (Select all that apply)
Which of the following are advantages of casting? (Select all that apply)
Dimensional accuracy and surface finish of cast parts always meet specifications.
Dimensional accuracy and surface finish of cast parts always meet specifications.
False
Which materials are commonly used for making patterns in casting? (Select all that apply)
Which materials are commonly used for making patterns in casting? (Select all that apply)
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What is a single piece pattern?
What is a single piece pattern?
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The pattern that is made of two or three pieces for casting intricate shapes is called a ______.
The pattern that is made of two or three pieces for casting intricate shapes is called a ______.
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Match the types of patterns with their descriptions:
Match the types of patterns with their descriptions:
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What is the purpose of machining allowance in casting?
What is the purpose of machining allowance in casting?
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What are some common properties of pattern materials? (Select all that apply)
What are some common properties of pattern materials? (Select all that apply)
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What is a key characteristic of a split pattern in casting?
What is a key characteristic of a split pattern in casting?
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Which of the following is true about a match plate pattern?
Which of the following is true about a match plate pattern?
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What is a disadvantage of using a single piece pattern?
What is a disadvantage of using a single piece pattern?
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What is the primary advantage of using a gated pattern in casting?
What is the primary advantage of using a gated pattern in casting?
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What type of pattern is best suited for producing large symmetrical castings?
What type of pattern is best suited for producing large symmetrical castings?
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Which of the following is a limitation of the casting process?
Which of the following is a limitation of the casting process?
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Which property is essential for the selection of pattern materials?
Which property is essential for the selection of pattern materials?
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What characteristic of cast parts contributes to their high strength?
What characteristic of cast parts contributes to their high strength?
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Which of the following materials is NOT typically used for making patterns in casting?
Which of the following materials is NOT typically used for making patterns in casting?
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What is a consequence of using wood as a pattern material?
What is a consequence of using wood as a pattern material?
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Which of the following is a factor influencing the selection of a manufacturing process?
Which of the following is a factor influencing the selection of a manufacturing process?
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What typically affects the dimensional accuracy and surface finish of cast parts?
What typically affects the dimensional accuracy and surface finish of cast parts?
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Which of the below is NOT an advantage of the casting process?
Which of the below is NOT an advantage of the casting process?
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Which casting method involves the use of a special machine to ensure the formation of the mold?
Which casting method involves the use of a special machine to ensure the formation of the mold?
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What is a typical characteristic of shell moulding?
What is a typical characteristic of shell moulding?
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Which type of riser allows for the easiest flow of molten metal into a casting?
Which type of riser allows for the easiest flow of molten metal into a casting?
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What defect is specifically characterized by an incomplete filling of the mold during casting?
What defect is specifically characterized by an incomplete filling of the mold during casting?
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Which of the following processes uses pressure to fill the mold with molten metal?
Which of the following processes uses pressure to fill the mold with molten metal?
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In which core classification is the core's position critical for achieving the desired internal shapes?
In which core classification is the core's position critical for achieving the desired internal shapes?
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What is the primary purpose of a gating system in casting?
What is the primary purpose of a gating system in casting?
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Which method is utilized to ensure consistent feeding of metal during solidification?
Which method is utilized to ensure consistent feeding of metal during solidification?
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What does the machining allowance compensate for in the casting process?
What does the machining allowance compensate for in the casting process?
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Which type of molding sand is completely dried and used for making large castings?
Which type of molding sand is completely dried and used for making large castings?
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What is the typical draft angle range used for taper allowance in patterns?
What is the typical draft angle range used for taper allowance in patterns?
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Which allowance is specifically provided to compensate for distortion in weaker sections of casting?
Which allowance is specifically provided to compensate for distortion in weaker sections of casting?
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What is the primary component of facing sand used in molding?
What is the primary component of facing sand used in molding?
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What type of pattern allows for large size castings produced in small quantities?
What type of pattern allows for large size castings produced in small quantities?
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Which factor does NOT affect the machining allowance in casting?
Which factor does NOT affect the machining allowance in casting?
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How does rapping and shaking allowance impact the pattern dimensions?
How does rapping and shaking allowance impact the pattern dimensions?
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What characteristic defines green sand used in molding?
What characteristic defines green sand used in molding?
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Which allowance is primarily concerned with the contraction of material during cooling?
Which allowance is primarily concerned with the contraction of material during cooling?
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Study Notes
Manufacturing Process Classification
- Manufacturing processes can be categorized by their method of material removal.
- Common categories include:
- Casting
- Forming
- Machining
- Joining
- Powder Metallurgy
Casting
- Casting is a manufacturing process used to create parts by pouring molten material into a mold.
- Once the material solidifies, the mold is removed, leaving the finished part behind.
Steps in Casting
- Creating the Pattern: A pattern is a replica of the desired part, with allowances for shrinkage and machining.
- Preparing the Mold: The mold is created using a material that can withstand high temperatures and is easily removed from the solidified casting.
- Core Fabrication: If the casting has internal cavities, cores are made from sand or other mold materials and placed inside the mold.
- Melting and Pouring: The casting material (often metal) is melted and poured into the mold.
- Solidification and Cooling: The molten material cools and solidifies within the mold.
- Cleaning and Inspection: The casting is removed from the mold, cleaned, and inspected for defects.
Casting Terms
- Shrinkage: The decrease in the volume of a material as it cools and solidifies.
- Draft: A taper on vertical surfaces of a pattern that helps in removing it from the mold without damaging the mold cavity.
- Core: A mold insert that forms internal cavities in a casting.
- Riser: A reservoir of molten metal that feeds the casting during solidification and prevents defects like shrinkage voids.
- Gate: A channel through which the molten metal flows into the mold.
- Runner: A passage through which molten metal travels from the sprue to the gate.
- Sprue: A vertical channel through which molten metal is poured into the mold.
Selecting a Manufacturing Process
- The choice of manufacturing process depends on several factors, including:
- Part complexity: Some processes are better suited for simple shapes, while others can handle intricate designs.
- Material properties: The chosen process must be compatible with the material’s properties.
- Production volume: High-volume production may require different processes than low-volume production.
- Cost: The cost of each manufacturing process will vary based on the complexity of the part, production volume, and other factors.
Casting Products
- Castings are used in a wide range of applications, including:
- Automotive parts
- Aerospace components
- Machinery parts
- Construction materials
Advantages of Casting
- Complex shapes: Complex shapes, including internal cavities, and hollow sections can be produced with casting.
- Mass production: The casting process is relatively quick, making it suitable for large production runs.
- Size and weight: Parts of any size and weight can be efficiently cast.
- Uniform properties: Casting results in components with consistent properties throughout.
Limitations of Casting
- Dimensional accuracy: Casting may not meet strict dimensional accuracy requirements.
- Surface finish: Casting processes often result in rough surface finishes.
- Defects: Castings can be prone to defects like porosity, inclusions, and shrinkage voids.
- Cost: Casting can be expensive for small parts or low-volume production.
- Labor intensive: Cleaning and finishing cast parts often require manual labor.
Pattern materials
- Wood: Common for small batch production, lightweight, and easy to fabricate but can absorb moisture and change dimensions.
- Metal: Durable, suitable for large castings and high-volume production, but more expensive to manufacture.
- Plastics: Lightweight, corrosion-resistant, and easy to mold, but may require specialized molding techniques.
- Wax: Used for prototype castings, disposable, and easily removed from the mold.
- Gypsum: Durable and resistant to moisture, but may crack or deform under high temperatures.
Selecting Pattern Material
- Factors to consider when picking a pattern material:
- Part Size and complexity
- Desired dimensional accuracy
- Number of castings required
- Casting process (sand casting, investment casting, etc.)
Pattern material Properties
- Important Properties:
- Machinability: The ease with which the pattern can be shaped and finished.
- Wear Resistance: The ability to withstand abrasion during repeated mold filling and stripping.
- Strength: The ability of the material to withstand the forces of handling and molding.
- Dimensional Stability: The ability to maintain its shape and dimensions.
- Resistance to Temperature and Humidity: The pattern material should not warp or deform under different temperatures and humidity levels.
- Repairability: The ability to repair minor defects or damage in the pattern.
Types of Patterns
- Single Piece Pattern: A simple pattern used for casting simple shapes, typically for small quantities.
- Split Pattern: A pattern divided into two or more pieces for easy removal from the mold.
- Loose Piece Pattern: Patterns for complex shapes where the pieces are assembled prior to pouring the molten material.
- Match Plate Pattern: A pattern mounted on a plate with two halves, allowing for efficient casting with a high degree of accuracy.
- Gated Pattern: A pattern that incorporates the gate and runners, allowing for efficient pouring and increased productivity.
- Sweep Pattern: A pattern used to create symmetrical shapes by rotating a template along the axis of the mold.
- Skeleton Pattern: A lightweight pattern made from strips of wood, typically used for large castings in small quantities.
Pattern Allowances
- Allowances are added to the pattern to compensate for:
- Shrinkage: The shrinkage allowance accounts for the decrease in volume of the material as it cools.
- Machining: Machining allowance provides extra material for shaping, finishing, or machining.
- Draft: Draft, or taper allowance, is added to the pattern to simplify the removal from the mold without damaging the mold cavity.
- Shaking: Shaking allowance is extra material for parts that cannot be removed directly from the mold and require shaking to separate.
- Distortion: Distortion allowance is added to compensate for the distortion of the casting during solidification.
Classification of Manufacturing processes
- Casting
- Forming
- Machining
- Joining
- Finishing
- Powder Metallurgy
- Composite Materials
Casting Process
- Liquid metal is poured into a mould
- The molten metal solidifies into the shape of the mould
Examples of Casting Processes
- Sand Casting
- Die Casting
- Investment Casting
- Centrifugal Casting
Steps Involved in Casting
- Pattern making
- Preparation of moulds
- Core Making
- Melting and pouring the molten material
- Solidification and further cooling to room temperature
- Cleaning, Inspection, and defects if any removal
Terms
- Pattern: A model of the casting to be produced, used to create the mould cavity
- Flask: Holds the mould material
- Cope: The top half of a flask
- Drag: The bottom half of a flask
- Parting Line: The line that separates the cope and drag
- Gate: The channel through which molten metal enters the mould cavity
- Riser: A reservoir of molten metal used to compensate for shrinkage during solidification
- Core: A form used to create internal cavities within the casting
- Mould: The cavity in which the liquid metal is poured and solidified
- Casting: The solidified metal product
- Runner: Channels in sand that connect the gate to the mould cavity
Selection of Manufacturing Process
- Factors to consider:
- Production Quantity
- Part Complexity
- Dimensional Accuracy
- Surface Finish
- Cost
Advantages of Casting
- Complex shapes, internal cavities and hollow sections can be produced
- Quick process and suitable for mass production
- No limit on size, shape and weight of the product, very large parts can be produced economically
- High strength and rigid parts obtained as casting exhibit uniform properties in all the directions
Limitations
- Dimensional accuracy and surface finish does not meet exactly
- Presence of defects in cast parts
- Not economical for small parts
- Properties are inferior compared to formed parts
- Labor intensive
Patterns
- Used to create the mould cavity
- Made of wood, metal, plastics, gypsum, or wax
Materials used for Patterns
- Wood
- Metal
- Plastics
- Gypsum
- Wax
Selection of Pattern Material
- Size and shape of the casting
- Dimensional accuracy of casting
- Number of castings required
- Casting process to be used
Properties of Pattern Material
- Machinability
- Wear resistance
- Strength
- Dimensional stable
- Resistance to variation in temp.& humidity
- Repairability
Wood Patterns
- Low cost
- Light in weight
- Easily available
- Ease of fabricating to many shapes
- Absorbs moisture and dimensions change
- Lower life
- Suitable for small quantity castings
Metal Patterns
- Used for mass production
- High strength
- More life compared to wood patterns
- Suitable for the production of large castings
- Example metals for patterns: Aluminum, cast iron, brass
Plastic Patterns
- Low weight
- Easier formability
- Do not absorb moisture
- Good corrosion resistance
Wax Patterns
- Used for prototype castings
- Withdrawal is easy
- Disposable patterns
Types of Patterns
- Single Piece Pattern: Made of wood and inexpensive, used for casting simple shapes, low quantity production
- Split Pattern: Two/Three piece pattern, used for casting intricate shapes, easy removal of pattern from the mould
- Loose Piece Pattern: Used for complex shapes, when it is difficult to withdraw from the mould, two or more loose pieces are assembled together to form a single pattern
- Match Plate Pattern: Both halves of the pattern mounted on a single plate, used for mass production of small castings with accuracy
- Gated Pattern: Made of metal & produce multi-cavity in one mould, gates and runners integral with pattern, productivity is more
- Sweep Pattern: Produces symmetrical shaped large size castings, example shapes include bell and cylindrical shapes
- Skeleton Pattern: Skeleton is made of strips of wood and forms the outline of the desired shape of casting, used for the production of large size castings in small quantities
Pattern Allowances
-
Shrinkage Allowance:
- Compensates for shrinkage of metal during solidification
- Depends on the metal being cast and the design of the casting
- Machining Allowance: Provided to compensate for the rough surface of the cast product when taken out of the mould cavity, excess dimension of casting to be machined/finished
- Draft Allowance: Taper provided on the vertical faces of the pattern to facilitate easy withdrawal of the pattern from the mould
- Shaking Allowance: Compensate for slight enlargement of the mould cavity when the pattern is rapped all around vertical faces before withdrawal
- Distortion Allowance: Compensates for distortion of weaker sections of casting when it solidifies
Moulding Sand
- Used to make moulds and strongly bonded together in the flask
- Components: Base Sand + Binder + water + Additives
Base Sand
- Most commonly used is silica sand
- Requirements include:
- Strength
- Permeability
- Refractoriness
- Thermal conductivity
- Collapsibility
Bindlers
- Responsible for binding the sand particles together
- Types:
- Clay
- Bentonite
- Organic binders
Additives
- Used to modify the properties of the moulding sand
- Types:
- Moisture
- Coal dust
- Cereal binders
- Sea coal
Types of Moulding Sand
-
Green Sand:
- Contains moisture, silica sand + clay
- Used for making small to medium sized castings
- Common and inexpensive
-
Dry Sand:
- Completely dried green sand
- Higher strength than green sand
- Used for medium to large sized castings
- Provides better dimensional accuracy and surface finish to casting
-
Loam Sand:
- Silica sand + clay + water (higher clay %)
- Used for making heavy castings
- Consumes more time
-
Facing Sand:
- Silica sand + clay + coal dust
- Used next to the pattern and in contact with molten metal
- Prevents molten metal from entering the sand
- Produces clean and smooth casting surface
-
Parting Sand:
- Fine dry silica sand. Non-sticky
- Sprinkles on the pattern and parting surfaces of mould halves
- Facilitates easy withdrawal of the pattern and separation of cope and drag
-
Core Sand:
- Silica sand + Oil
- Used for making cores
Types of Sand Moulds
-
Green Sand Mould:
- Most common type of mould
- Made from damp sand with a binder
-
Dry Sand Mould:
- Made from green sand that has been dried
- Stronger than green sand moulds
-
Skin Dried Mould:
- Only the surface of the green sand mould is dried
- Used when a good surface finish is needed
-
No-Bake Sand Mould:
- Does not require baking and is held in a container
- Uses chemical binders
Methods of Sand Moulding
-
Bench Moulding:
- Small castings are moulded on a workbench
-
Floor Moulding:
- Larger castings are moulded on the floor
-
Pit Moulding:
- Mould is made in a prepared pit
- Used for very large castings
-
Machine Moulding:
- Moulds are made using machines
- More efficient and accurate
- Types of machines:
- Jolt Squeeze Machine: A machine that jolts the sand to compact it and then squeezes it to create a firm mould
- Sand Slinger: A machine that uses centrifugal force to sling sand into the flask
-
Shell Moulding:
- A thin shell of sand is created around a pattern
- The shell then is used to create the mould
- Quick and economical
-
Carbon Dioxide Moulding:
- Sand is mixed with a sodium silicate binder and a carbon dioxide gas
- The carbon dioxide reacts with the sodium silicate to harden the sand
- Produces moulds that can be used for making castings with good dimensional accuracy
-
Investment Moulding:
- A wax pattern is coated with a refractory material
- The wax is melted out and the refractory material is baked to form a mould
- Produces castings with very good surface finish and dimensional accuracy
Continuous Casting
- Molten metal is poured continuously into a mould
- The metal solidifies as it moves through the mould
- Produces long, continuous lengths of casting material
Centrifugal Casting
- Molten metal is poured into a rotating mould
- The centrifugal force distributes the metal evenly within the mould
- Used to produce cylindrical castings
Types of Centrifugal Casting
- True Centrifugal Casting: The mould rotates around a horizontal axis
-
Semi Centrifugal Casting:
- Mould rotates partially around a horizontal axis
- This process produces a casting with a thick outer diameter and a thinner inner diameter
-
Centrifuging Casting:
- The mould is rotated about a vertical axis
- This process produces a casting with a uniform thickness
Gravity Die Casting
- The metal flows into the mould by gravity
- Produces castings with good dimensional accuracy and surface finish
Pressure Die Casting
- Molten metal is injected into the mould under pressure
- Produces castings with good dimensional accuracy and surface finish
- Higher production rates and superior mechanical properties
Types of Pressure Die Casting
-
Hot Chamber Pressure Die Casting:
- The molten metal is held in a heated chamber
- The molten metal is forced into the mould under pressure
-
Cold Chamber Pressure Die Casting:
- The molten metal is poured from a ladle into a separate chamber
- Then forced into the mould under pressure
- Squeeze Casting: Similar to pressure die casting, except the molten metal is squeezed into the mould under high pressure
-
Slush Casting:
- Molten metal is poured into a mould
- The metal is allowed to partially solidify
- The excess metal is poured out
- Produces hollow castings with good dimensional accuracy
Green Sand Flask-less Moulding
- A mould is made from green sand without using a flask
- The mould is held together by a special support structure
Plaster of Paris Flask-less Moulding
- Similar to the green sand flask-less moulding process but plaster of paris is used as the mould material
Gating System
- The channel through which molten metal enters the mould cavity
- Requires:
- Proper flow rate
- Minimum turbulence
- Uniform filling of the mould cavity
Types of Gates
-
Top Gate:
- Located at the top of the mould
- Advantages:
- Easy to design and implement
- Produces a faster fill of the mould cavity
-
Bottom Gate:
- Located at the bottom of the mould
- Advantages:
- Reduces the amount of dross and oxides that enter the mould cavity
- Allows for better control of the flow rate
- Parting Gate: A gate that is located along the parting line of the mould
Risering System
- A reservoir of molten metal used to compensate for the shrinkage during solidification
- Requirements:
- Size (depends on the size and shape of the casting and the metal being used)
- Location (placed in the area of maximum shrinkage)
Types of Risers
-
Top (Open) Riser:
- Located at the top of the mould
- Easy to design and implement
- Prone to problems with oxidation
-
Blind (Internal) Riser:
- Located inside the mould cavity
- Less prone to oxidation and turbulence
Cores
- Forms used to create internal cavities within the casting
- Classification based on material:
-
Sand Cores:
- Made from core sand
- Used for making internal cavities
-
Metal Cores:
- Used for making complex cavities
- Can be used in high-temperature casting operations
-
Sand Cores:
- Classification based on position and use:
-
Horizontal Cores:
- Used to create horizontal cavities
-
Vertical Cores:
- Used to create vertical cavities
-
Balanced Cores:
- Used to create cavities that are balanced in the mould cavity
-
Drop Cores:
- Used in gravity casting and are dropped into the mould cavity
-
Kiss Cores:
- Used to create a small cavity, or "kiss", in the casting
-
Ram-Up Cores:
- Used for complex castings where a core has to be positioned and supported
-
Horizontal Cores:
Core Binders
- Used to hold the core sand together
- Types:
-
Oil Based:
- Good strength but can produce smoke and fumes
-
Water Based:
- Less expensive but can shrink the core
-
Oil Based:
Casting Defects
- Shrinkage Defects: These defects occur when the metal shrinks during solidification and can lead to voids, porosity or cracks in the casting
- Porosity Defects: These defects occur when gas is trapped in the metal during solidification. They cause voids or holes in the casting.
- Misrun Defects: These defects occur when the molten metal does not fill the entire mould cavity.
- Penetration Defects: These defects occur when molten metal penetrates into the sand mould, leading to irregular shapes.
- Mould Shift: This defect occurs when the cope and drag of the mould move during casting.
- Cold Shut Defects: These defects occur when two streams of molten metal meet and do not fuse together properly.
- Hot Tears Defects: These defects occur when the metal shrinks during solidification and stresses are placed on the metal, leading to cracks.
Solidification
- Solidification of pure metal: The process by which liquid metal cools and transitions into a solid state.
-
Mechanism of Solidification:
- Nucleation: Formation of stable nuclei in metal
- Grain growth: Nuclei grow to form crystals resulting in grain structure
-
Forms of Nucleation:
-
Homogeneous Nucleation:
- Occurs when nuclei form spontaneously in the molten metal
- Requires higher temperatures and longer solidification times.
-
Heterogeneous Nucleation:
- Occurs when nuclei form on pre-existing surfaces
- Occurs at lower temperatures and faster solidification times
- These surfaces can be:
- Insoluble particles in the melt
- The mould walls
- The cores
-
Grain Size:
- Larger grain size results in:
- Lower strength
- Lower ductility
- Lower toughness
- Smaller grain size results in:
- Higher strength
- Higher ductility
- Higher toughness
- Larger grain size results in:
-
Homogeneous Nucleation:
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Description
This quiz focuses on the casting process within manufacturing classifications. It covers key steps, including pattern creation, mold preparation, and the actual pouring of material. Test your knowledge on how casting is utilized to create parts through these methods.
