Patternmaking Techniques and Materials Quiz

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Questions and Answers

Which of the following properties of investment wax contributes to its usability in creating complex shapes?

High melting point

Poor surface finish

High ash content

Low viscosity and high flowability (correct)

What is a key reason for using old castings as patterns in emergency situations?

They do not require cleaning before use

They lack oxidation resistance

They can be quickly modified and reused (correct)

They are always larger than required

What type of machine is specifically designed to perform operations efficiently in patternmaking?

Woodworking lathe

Joiner

Band saw

Pattern miller (correct)

In patternmaking, what does lagging with thin strips of wood or leather help achieve?

Increase dimensions to account for various allowances Signup and view all the answers

What is a characteristic of special waxes used for dip coatings, patching, and adhesives?

Unfilled wax compounds Signup and view all the answers

Which property of pattern materials makes them dimensionally unstable when exposed to moisture?

Presence of hydroxyl groups in cellulose Signup and view all the answers

What are the main constituents of wood that contribute to its absorption of moisture?

Cellulose and lignin Signup and view all the answers

Which of the following is NOT a requirement for suitable pattern materials?

Low abrasion resistance Signup and view all the answers

At what moisture content does the fibre saturation point of wood typically occur?

25-35% Signup and view all the answers

What is one of the main drawbacks of using wood as a pattern material?

Susceptibility to moisture Signup and view all the answers

Which material is least likely to be affected by variations in temperature and humidity as a pattern material?

Metals and alloys Signup and view all the answers

Which property is critical for a material to be classified as suitable for repeated usage in pattern making?

Can be repaired or reused Signup and view all the answers

What is the main advantage of using LM 25 WP in casting compared to other materials?

Good strength and high wear resistance Signup and view all the answers

Which treatment enhances the properties of LM 25 WP?

Solution heat treatment and precipitation heat treatment Signup and view all the answers

What is a primary limitation of using brass and bronze for pattern work?

High cost Signup and view all the answers

Which alloy has a melting point of approximately 138°C?

Cerro-alloy containing tin and bismuth Signup and view all the answers

What is the role of the mandrel in the electro-deposition process?

To serve as a conductive template for metal deposition Signup and view all the answers

Why is the coefficient of expansion for certain cerro-alloys significant?

It impacts the precision of the final shape Signup and view all the answers

What does the 'Mercast' process predominantly utilize for producing castings?

Frozen mercury Signup and view all the answers

What is a potential drawback of using cerro-alloys in casting?

High cost and poor availability Signup and view all the answers

For intricate shapes, what process has recently gained application in pattern and die work?

Metal electro-deposition or electro-forming Signup and view all the answers

What is the main benefit of using low melting point alloys for dies?

Easy and quick melting Signup and view all the answers

What factor primarily determines the equilibrium moisture content (EMC) of wood?

Relative humidity and temperature Signup and view all the answers

What happens to wood dimensions when the moisture content is below the fibre saturation point?

Wood experiences swelling and shrinkage Signup and view all the answers

Which of the following statements correctly describes the growth pattern of wood in temperate climates?

Growth occurs in two distinct stages: rapid in spring and slow in summer Signup and view all the answers

What is the primary function of medullary rays in wood?

Store and distribute food material Signup and view all the answers

What is the purpose of seasoning timber?

To minimize the effects of moisture variations Signup and view all the answers

Why does heartwood differ from sapwood?

Heartwood is older, stronger, and more durable Signup and view all the answers

Which of the following accurately characterizes the cellular structure of spring wood?

Thinner cell walls and an open texture Signup and view all the answers

What type of wood results from the aging process of trees, providing better strength and durability?

Heartwood Signup and view all the answers

Which method of seasoning involves exposing wood to ambient environmental conditions?

Natural seasoning Signup and view all the answers

What is the primary method of removing a polystyrene foam pattern from a sand mold?

Breaking it manually Signup and view all the answers

Which property is NOT desired in a good wax pattern for investment casting?

High shrinkage Signup and view all the answers

What is the primary benefit of using polystyrene patterns in investment casting?

Extremely low ash content Signup and view all the answers

Which type of material is described as having low thermal conductivity and high strength for die forming?

Urethane elastomers Signup and view all the answers

For which type of casting is the polystyrene pattern used as a full mould?

Sand casting Signup and view all the answers

Which wax is commonly not used for making investment casting patterns?

Polyethylene wax Signup and view all the answers

What happens to the polystyrene pattern during the pouring of molten metal in casting?

It vaporizes Signup and view all the answers

Which of the following is a characteristic of urethane elastomers used in casting?

Low shrinkage Signup and view all the answers

Which specification provides standards for expanded polystyrene in pattern making?

IS: 10094-1981 Signup and view all the answers

What is the role of polymerizing agents in wax patterns for investment casting?

Stabilize the wax blend Signup and view all the answers

Study Notes

Technology of Patternmaking - Requirements

Patterns are the primary tools in the casting process.
Casting quality heavily relies on the pattern's material, design, and construction.
Expensive patterns are justified for high-volume casting needs.
Inexpensive wooden patterns suffice for small-quantity casting.
Metal or epoxy resin patterns are used for large-scale, repeated production, mounted on plates for moulding machines.
Much preparation precedes pattern creation, including material type, mould method, core box construction, allowances, and gating details.
Patternmakers need to interpret engineering drawings and translate them into precise patterns, including gating details, risers, and tooling.
Patternmakers require a working knowledge of computer-aided design and drafting.

Pattern Materials

Pattern material selection depends on service requirements, design changes, production type, and repeat orders.
Suitable pattern materials should be easily worked, light, strong, resistant to wear, corrosion, and dimensional changes, and affordable.
Wood and wood products are the most common pattern material.
Wood's main characteristics are its workability, light weight, affordability and susceptibility to moisture.
Wood comprises cellulose, lignin, carbohydrates and mineral matter and contains, 50-60% cellulose and 20–35% lignin.
Wood swells and shrinks with moisture content changes.
Moisture content in raw wood includes; water in cell cavities and absorbed in cell walls.
Fibre saturation point: 25-35% moisture resulting in stability of wood.
Equilibrium Moisture Content (EMC) varies with humidity and temperature
Seasonal growths cause differences in wood structure (sapwood and heartwood).
Wood seasoning aims to stabilize dimensions, increase strength, reduce susceptibility to decay, and facilitate easy finishing, through natural or artificial methods.
Other pattern materials include metals (aluminium alloys, cast iron, steel, copper alloys, such as brass and bronze), and waxes(paraffin wax, carnauba wax, shellac wax, beeswax, cerasin wax), used for investment casting.
Metal patterns are used for high-volume production, offering advantages like availability, better castability, machinability and surface finish, though they are heavier and more costly than wooden patterns.
Compressed wood laminates, including plywood and veneered boards, are stronger, denser, dimensionally stable, and more durable and more expensive than plain wood.
Wood-plastic composites (WPC) combine the qualities of wood with the strength and resistance offered by plastics, ideal for automotive casting and some other applications.
Metal-coated patterns use bismuth, zinc, or aluminium coatings to enhance the pattern's durability and finish.

Patternmaking Machines and Tools

Many woodworking machines used for creating wooden patterns; a lathe, circular saw, band saw, jig saw, jointer, planer, shaper, milling machine, and disc and bobbin sanding machines are typical.
These machines allow for accurate and efficient shaping and cutting of the pattern. Other tools include measuring and marking tools (ruler, calliper, scribes), sawing tools (hand saw, tenon saw), plane tools (jack plane), boring tools (drill), and clamping tools (carpenter's vice, bar clamp).
Specific pattern shop tools for creating patterns with complex shapes include pattern milling machines, capable of various cutting and shaping operations.
Machinery for metal patterns include moulding machines, drill presses, lathes(turning, boring, etc.) milling machines(vertical or horizontal), grinding machines, and other similar equipment for quality machining and finishing.

Pattern Allowances and Considerations

Pattern allowances compensate for shrinkage of the casting during solidification.
Machining allowances are provided for finishing the casting to the correct size
Draft allowances are provided to facilitate the removal of the pattern from the mold without causing damage and tearing.
The amount of allowances depends on factors such as type of casting (method of molding/casting), size and shape of the casting, casting orientation, and characteristics of the material, as well as the functional needs of the casting.
Core prints are designed to hold the cores in the mold, addressing irregularities, support, and dimensions/exact shapes and sizes of the core itself (vertical, horizontal, balanced).
The proper design of the Core prints and boxes ensures the accuracy of the finished castings.
Patterns can be arranged and supported with loose pieces for intricate shapes.
Types of pattern construction include ring construction, tongue-and-groove, header and stave, and disc constructions.

Pattern Storage and Repair

Proper storage is crucial for pattern preservation.
Identifying patterns (numerical storage identifiers) , storage conditions (shelving, fireproofing) , repair and maintenance (record keeping) are considered.
Pattern repair and maintenance procedures (quality control, recording, maintenance, and storage).

Rapid Prototyping (RP) Techniques

Rapid prototyping enables quicker creation of prototypes and patterns.
Techniques include stereolithography (SLA), fused deposition modeling (FDM), selective laser sintering (SLS), and laminated object manufacturing (LOM).

Pattern Types

Pattern types include loose patterns, gated patterns, special patterns, and match-plate patterns.
Each type is chosen based on casting requirements and complexity.

Manufacturing of Gauges and Templates

Template and gauge creation is an important initial step.
Tools are used for marking out templates, which are used as models to achieve accurate measurements and shapes.

Summary of Processes

Manufacturing metal patterns involves design, marking, machining, and assembly.
Suitable metal is chosen, along with consideration for allowances and procedures, such as fixing.

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Description

Test your knowledge on the properties and techniques used in patternmaking. This quiz covers the characteristics of different materials, including waxes and wood, and their usability in creating complex shapes. Explore various factors that affect pattern materials and their applications in casting.