2. Material Behavior and Cutting Techniques

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Questions and Answers

What effect does an increase in cutting speed have on surface roughness?

It has no effect on surface roughness.

It decreases surface roughness. (correct)

It increases surface roughness.

It causes irregular surface patterns.

Which of the following materials is categorized as isotropic?

Pure metals like lead.

Composite materials.

Ceramics like glass and zirconia. (correct)

Wood-based materials.

What property is measured by the integral of deviation from the mean value known as Ra?

Surface roughness. (correct)

Material strength.

Surface lay.

Surface hardness.

How does the use of cutting fluids during machining processes affect surface roughness?

It decreases surface roughness by reducing tool temperature. Signup and view all the answers

Which of the following statements about the effect of increasing feed on average roughness is true?

It corresponds to an increase in average roughness. Signup and view all the answers

What is the primary material recommended for the fishing reel to withstand salt-water use?

Aluminum Signup and view all the answers

Which manufacturing method is deemed most cost-effective for producing an aluminum fishing reel?

Stamping Signup and view all the answers

In the redesign of the truck sheet metal fan cover, what was the impact on material costs?

Decreased from 75.1 kr to 56.3 kr Signup and view all the answers

What is one benefit of designing different parts to have the same initial geometry for milling operations?

Reduces variation in material supply Signup and view all the answers

Which part of the robot arm gripper is made using casting with nylon material?

Gear 1 Signup and view all the answers

What design change resulted in a 17% reduction in machining time for a sophisticated bracket?

Using a larger tool Signup and view all the answers

Which of the following best describes the term 'design for manufacturing'?

Consideration of manufacturing throughout the product design process Signup and view all the answers

What is a key drawback of using 5-axis CNC milling for bracket production?

Long cycle times Signup and view all the answers

Which parameters are required to describe linear elastic material behavior?

Young’s modulus and Poisson’s ratio Signup and view all the answers

What stress condition is analyzed under a Brazilian test?

Tensile stress in rocks Signup and view all the answers

What effect does cyclic loading have on materials, compared to static loading?

Potential for damage in both types of materials Signup and view all the answers

What does the factor of safety represent in engineering design?

The strength of the material divided by equivalent stress Signup and view all the answers

Under the Von Mises criteria, which type of materials is the equivalent stress primarily applied to?

Ductile materials Signup and view all the answers

Which material is considered isotropic?

Glass Signup and view all the answers

Which test measures shear strength in a material?

Torsion of a pipe Signup and view all the answers

What happens to the fatigue strength of a material when heat treatment is applied?

It increases Signup and view all the answers

In linear elastic material testing, which materials can be characterized from brittle to ductile?

Glass and concrete Signup and view all the answers

What is the role of Finite Element Method (FEM) in product design?

It performs structural analysis and simulates loading conditions Signup and view all the answers

Study Notes

Surface Characteristics

Surface roughness is impacted by cutting speed, depth of cut, and feed rate
Increased cutting speed results in less surface roughness
Increased depth of cut leads to an increase in maximum roughness depth
Higher feed rate corresponds to greater average roughness
Cutting fluids reduce surface roughness by decreasing tool temperature and reducing friction

Material Behavior

Isotropic materials have consistent properties in all directions
- Examples: Aluminum, steel, magnesium, copper, glass, zirconia, concrete, clay, basalt, epoxy, rubber, polycarbonate
Anisotropic materials have varying properties depending on direction
- Examples: Copper at microscopic scale, fiber-reinforced composites, natural wood

Isotropic Material Behavior (Linear Elastic)

Requires two material parameters to describe: Young's modulus ( E ) and Poisson's ratio (ν)
Young's modulus and shear modulus (μ) are also used
Linear elastic materials are suitable for Finite Element Method (FEM) simulations to determine equivalent stress

Stress-Strain Relation

Brittle materials exhibit a linear elastic behavior followed by fracture
- Examples: Glass, concrete, and cast iron
Ductile materials exhibit linear elastic behavior followed by yielding and then failure
- Examples: Some metals

Measurement of Limit Stress

Uniaxial tensile tests measure the ultimate tensile strength and yield strength of materials for casting and machining
Three point flexural tests are used for composite materials
Brazilian tests are used for measuring the tensile strength of cylindrical materials like concrete and rocks
Torsion tests are used for measuring the shear strength of materials
Box tests are used for granular materials and rocks
Iosipescu tests are used for measuring the shear strength of thin materials

Fatigue Strength

Cyclic loading can cause fatigue damage, leading to fracture in brittle materials and rupture in ductile materials
Fatigue strength is the stress level at which a material can withstand a specified number of cycles before failure
Heat treatment can significantly impact fatigue strength

Equivalent Stress

Equivalent stress is a single value that represents the combined effect of multiple stress components
Von Mises criterion is used for ductile materials
Tresca criterion is used for brittle materials

Factor of Safety

Factor of safety is the ratio of the material's strength to the equivalent stress
It provides a margin of safety to account for uncertainties and variations in material properties and loading conditions
The required factor of safety depends on the application, material reliability, and environmental conditions

Design for Manufacturing

Design for manufacturing considers manufacturability during the design process
It focuses on minimizing costs, maximizing production efficiency, and ensuring product quality
Key considerations include material selection, manufacturing methods, assembly, and cost analysis

Design for Manufacturing Examples

Fishing Reel:
- Initial design: plastic injection molding for affordability, but market research showed preference for metal
- Revised design: aluminum or stainless steel for saltwater use, die casting or stamping for cost-effectiveness
- Final design: aluminum stamping for the lowest cost
Robot Arm Gripper:
- Components: aluminum body, nylon gears, aluminum linkage, base plate, off-the-shelf pins and fasteners
- Manufacturing methods: milling, casting, stamping
Truck Sheet Metal Fan Cover:
- Redesigned to reduce costs by using the same material and sheet bending process
- Achieved 25% cost reduction despite a small increase in labor costs
Bracket Design:
- Redesigned for 3-axis milling instead of 5-axis CNC machining
- Sand casting considered as an even more affordable option
- Achieved a cost saving of approximately 2000 kr per 300 parts annually
Sophisticated Bracket:
- Redesigned for larger radius to allow the use of larger tools, reducing machining time by 17%

Material Supply Reduction

Design parts with the same initial geometry for consistent milling operations and material procurement, reducing variations in material supply and costs

Tool Reduction in Milling

Design parts for compatibility with the same tools in machining, minimizing tool changes and reducing variation in used tools, which lowers costs

Design for Manufacturing Conclusion

Design for manufacturing involves a systematic approach to product design that considers manufacturability and cost-effectiveness
It is an ongoing process with no single solution, requiring a conscious effort to balance functionality, cost, and producibility.

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Description

Explore the principles of surface characteristics and material behavior in manufacturing processes. Understand how cutting speed, depth of cut, and feed rate affect surface roughness, and discover the differences between isotropic and anisotropic materials. This quiz covers essential concepts related to linear elastic materials and their properties.