Metal Forming Processes & Material Properties

• Permanent deformation requires exceeding the material's yield strength.

Design Considerations

• Feasibility of designing and manufacturing a part depends on:
• Aesthetics
• Cost

Manufacturing Types

• Additive manufacturing builds parts layer by layer.
• Metal deformation shapes metal through processes like:
• Forging
• Burr removal
• Sheet metal forming

Casting

• Involves pouring liquid metal into a mold cavity.
• Used for creating:
• Pumps
• Manifolds
• Street furniture

Subtractive

• Also known as cutting
• Removes material through:
• Drilling
• Milling
• Cylindrical turning

Powder Metallurgy

• Powdered metal is placed in a die.
• Force is applied, often hydrostatically.
• This ensures diffusion and bonding between particles.

Surface Modification

• Includes Painting
• Shot peening involves bombarding a surface with steel balls.
• This creates compressive residual stress, refining the microstructure.

Property Modifications

• Quenching leads to hardening.
• Some materials have crystalline structures such as:
• Body-centered cubic (BCC)
• Face-centered cubic (FCC)
• FCC structures exhibit better stability and can dissolve iron.
• Thermal and mechanical processing alters material properties.

Processing Operations

• Processing operations are divided into:
• Shaping
• Surface processing
• Joining

Shaping Operations

• Shaping operations can be achieved through:
• Deformation
• Casting
• Subtractive methods
• Additive manufacturing
• Powder metallurgy

Surface Processing

• Surface processing techniques include:
• Coating
• Painting
• Anodizing
• Electroplating
• Carburization: Hardens steel by introducing carbon into the surface in a carbon-rich environment at high temperatures.

Assembly

• Joining operations include:
• Welding
• Brazing
• Soldering
• Adhesive bonding
• Fastening methods can be:
• Permanent, like riveting
• Non-permanent, like threaded fasteners
• Annealing restores the material to its original state.

Deformation Processes

• Key points on a stress-strain curve:
• Yield point (1)
• Elastic regime (0 to 1): Deformation is reversible upon load removal.
• Plastic regime (1 to 3): Permanent deformation occurs.
• Necking point (2): Maximum load before fracture.
• Fracture (3)
• Stress is calculated as load (P) divided by the initial cross-sectional area (Ao:)
• Strain is calculated as the change in length (ΔL) divided by the initial length (L).
• Gauge length is the section being measured and not the entire sample.
• Elastic recovery happens when a material is plastically deformed and the load is removed.
• The material partially reverts.
• Key strain measurements:
• Total strain
• Elastic strain (recovered after unloading)
• Plastic strain (permanent strain after unloading)

True Stress and Strain

• Engineering stress (σ) is load (P) divided by initial area (Ao).
• Engineering strain (e) is change in length (ΔL) divided by initial length (L).
• True stress and strain are more accurate for measuring deformation processes.
• True stress is calculated as force divided by the area at a given moment: σ = P/A.
• True strain is calculated as ε=ln(L/Lo), where L is the length at a given moment.
• The relationship between stress and strain is σ= Kε^n
• K is the strength coefficient
• n is the strain hardening exponent,
• Strain hardening is the strengthening of a material through plastic deformation.

Manufacturing Considerations

• Achieving a perfect 90° angle in manufacturing is challenging.
• Annealing softens material by heating it to a high temperature and cooling it slowly.
• This restores the original grain structure after deformation.

Annealing

• Leads to a lowering of strength and an increase in ductility.
• Recovery does not revert the grain structure, only the microstructure.
• Metals are typically multi-crystalline.
• In the annealed state, the crystals are equiaxed with no residual stress.

Steel Hardening

• Involves heating steel to induce a phase transformation from BCC to FCC.
• Followed by quenching in a cool medium.
• FCC (face-centered cubic) allows for more carbon to dissolve.
• BCC (body-centered cubic) is stronger but less ductile.
• Additions to steel are explained via phase diagrams, like the Fe-C diagram.

Tensile Testing

• Tensile testing involves the following:
• Elastic Regime
• Yield point (1)
• Elastic regime (0 to 1) described by Hooke's Law: σ = Eε.
• E is the modulus of elasticity (Young's modulus).
• Uniform plastic deformation regime (1-2)
• Necking point and maximum load (2)
• Ultimate tensile strength or UTS (2')
• Engineering strain (e) is calculated as ΔL/Lo.
• Lo represents the gauge length of the sample.

Plastic Deformation

• In plastic deformation, the stress-strain relationship is σ = Kε^n.
• K represents material properties.
• True stress is calculated as P/A, as opposed to using the original area.
• True strain is calculated as ln(Lo/L).
• Unloading the Sample: When the material is unloaded, it follows a straight line with a slope of E, parallel to the plastic line (from 0↔1).
• Work (strain) hardening can occur (1↔2).
• Increases the yield strength due to plastic deformation.
• This occurs at temperatures below the recrystallization temperature, i.e., cold working.
• A material can exhibit work hardening or not exhibit strain-hardening.

Hot vs Cold Working

• Cold working involves deforming material at a temperature less than its recrystallization temperature
• Atom movement is suppressed
• Hot working is performed above this temperature.
• Benefits of cold working:
• Increased material strength.
• Better control over dimensional and geometrical tolerances.
• Better surface finish.
• Controlled microstructure.
• A primary drawback of hot working is less precise dimensional control
• Disadvantages of cold working:
• Less ductility.
• Requires larger forces and equipment.

Anisotropy

• Plastic anisotropy is induced by plastic deformation in otherwise isotropic materials.
• Isotropy is a condition where the mechanincal proeprties are the same in all directions
• Anisotropy means the mechianl properties will differ.
• Cold working causes grain flattening.
• The material becomes non-isotropic or anisotropic due to the deformation.

Calculations

• n is the strain hardening exponent.
• True strain at necking (εn:) is also the limit before necking and failure.
• Material Behavior: If it is defined by the equation σ=100,000*ε^0.5:
• The limit to which the material can be subjected =TRUE strain @ necking = εn=.5
• Formulas
• Engineering UTS can be figured this way =Pmax/Ao, where Pmax is area at maximum.

Additional Information from Missed Notes

• The true strain at necking is equivalent to the strain hardening exponent.
• Determine True UTS: True UTS = σUTS = 100,000(0.5)^0.5 = 70,710 psi = Pmax/A Find Engineering UTS: Etrue=ln Ao/A.
• In plastic deformation, volume is constant.
• Constant volume condition: ALo=AL therefore Lo/L=A/Ao

Additional Calculations

• εneck=εtrue=n
• σUTS =100,000(ε)^.5 = 70,710 PSI.
• Engineering Stress ~ Suts=Pmax/Ao= 70,710 psi.

Material and Waste

• Assuming no material waste: AoLo ≈ AL
• Volume is constant conditions: AoLo= AL
• But we know that the ε @ ult. Point is εn : ε=ln Ao/ A

Extrusion Calculations

• ε ≈ ln A0/A =ln di0^2/df^2 ≈σ 752.5

Alloys

• In ferrous- alloys are classified: Alloy steel & cust iron (C>42.4 percent)
• Plain carbon steel, steel contains only carbon as its alloying element.

PLAIN CARBON STEEL SUB CATEGORIES

• low carbon steel are [<=. 20% as weight]
• Medium Carbon steel [.20%-3-63%]
• His carbon Steel [.630-4.4%]
• Ferrous alloys share a significant benefit of high tensile strength.
• Alloy steel is steel that only carbon as its alloying clement
• It must withstand higher amounts of tensile strength and extreme temperatures

Tool Steels

• Tool steels feature alloying elements.
• Each grade has a tool steel.
• Examples MI, H2

Other Materials

• Non-creeping, tool steel that maintains high.
• Tungsten-based, high-speed steel- Molybdenum: high-speed steel
• High shock resistance tool steel
• Water hardening tool steel.

Additional Terms to note

• Machinability: refers to being made readily or to wear or wear resistance
• Wrought alloys are shaped or fabricated in the solid state.
• There general properties are higher when they are tough and reliable.
• Cast alloys: shaped casting, cast mold in form

Homework Review

• In plastic deformation, volume is constant.
• In elastic deformation, volume may not be constant.

Bulk Deformation Proces

• Bulk Deformation process, and best process from the material improvement point.
• Forsing: metal by compresive forces
• Reduse & set
• Mechanical Perfomrance typically

1-9 Study Guide points

• Open-Die Forging: Tools and equipment.
• Impressions Die forging gives longer improved set share one steel

Material

• Most of the time it comes from Det.
• It can lead to improve peeling and oxidation can come from the material
• Less control over dimension and beam

Terms

• Eliminate porities/ divert gain flows and the material comes wrought mill to perform better.

Explore metal forming processes like rolling, extrusion, and drawing. Understand how these processes affect grain structure and mechanical properties. Learn about optimizing for strength and flatness in rolled products.