Manufacturing Processes

Manufacturing transforms raw materials into finished products. Understanding manufacturing is essential for designing parts that can actually be made economically.

Design for Manufacturing (DFM)

Key Principle: Design parts that are easy and economical to manufacture.

DFM Guidelines

1. Minimize part count: fewer parts = lower assembly cost
2. Use standard materials: readily available, lower cost
3. Standardize features: same hole sizes, radii, etc.
4. Avoid tight tolerances: unless necessary for function
5. Design for process: match design to manufacturing method
6. Minimize machining: near-net-shape processes save time
7. Consider assembly: easy access, self-locating features

Material Selection

Common Engineering Materials

Selection Factors

1. Mechanical properties (strength, stiffness, toughness)
2. Physical properties (density, thermal, electrical)
3. Manufacturing (formability, machinability, weldability)
4. Cost (material + processing)
5. Environment (temperature, corrosion, wear)
6. Availability (standard stock vs custom)

Example: Material Selection for Bike Frame

Requirements: Lightweight, strong, corrosion resistant, weldable

Options:

• Steel: Strong, heavy, weldable ✓
• Aluminum: Light, strong, weldable, corrosion resistant ✓✓✓
• Titanium: Excellent properties but expensive ✗
• Carbon fiber: Very light, strong, but expensive and not repairable ✓✗

Choice: Aluminum for performance bikes, steel for budget/touring bikes

Primary Manufacturing Processes

Casting

Pour molten metal into mold cavity, let solidify.

Types:

Advantages:

• Complex shapes
• Large parts possible
• Good for mass production (die casting)

Disadvantages:

• Poor surface finish (sand)
• Porosity issues
• High tooling cost (die casting)

Design Tips:

• Uniform wall thickness
• Generous fillets and radii
• Draft angles for mold removal
• Consider parting line location

Forging

Shape metal by compressive forces (hammering, pressing).

Types:

• Open-die forging: Simple shapes, low tooling cost
• Closed-die forging: Complex shapes, high tooling cost
• Hot forging: High temperatures, easier to form
• Cold forging: Room temperature, better finish and properties

Advantages:

• Excellent mechanical properties (grain flow)
• High strength
• No porosity

Disadvantages:

• Limited complexity
• High tooling cost
• Material waste (flash)

Applications: Crankshafts, connecting rods, gears, hand tools

Extrusion

Force material through die opening.

Types:

• Hot extrusion: Metals (aluminum, steel)
• Cold extrusion: Soft metals, plastics

Advantages:

• Consistent cross-section
• Good surface finish
• Efficient for long parts

Disadvantages:

• Constant cross-section only
• High die cost

Applications: Aluminum profiles, window frames, pipes, railings

Rolling

Reduce thickness by passing between rollers.

Products:

• Sheet metal
• Plates
• Structural shapes (I-beams, channels)
• Rails

Advantages:

• High production rate
• Good surface finish
• Continuous process

Machining Processes

Remove material to create features and achieve precision.

Turning (Lathe)

Rotate workpiece, feed cutting tool to remove material.

Operations:

• Facing (flat end surface)
• Turning (reduce diameter)
• Boring (enlarge hole)
• Threading (cut threads)
• Grooving

Tolerances: ±0.01-0.05 mm
Surface finish: Ra 0.4-6.3 µm

Design Tips:

• Minimize tool changes
• Avoid internal corners (tool radius needed)
• Standard thread sizes

Milling

Rotate cutting tool, feed workpiece.

Types:

• Face milling: Flat surfaces
• End milling: Pockets, slots, profiles
• Slot milling: Keyways, grooves

Tolerances: ±0.02-0.1 mm
Surface finish: Ra 0.8-6.3 µm

Design Tips:

• Standard tool sizes (avoid custom cutters)
• Adequate corner radii (match tool radius)
• Minimize tool depth (avoid long, thin tools)

Drilling

Create holes using rotating drill bit.

Standard drill sizes:

• Metric: 1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 20 mm
• Imperial: fractional (1/16", 1/8", etc.), number, letter

Depth limitation: Typically L/D < 10 (length/diameter ratio)

Design Tips:

• Use standard drill sizes
• Flat bottom requires end mill (drills leave conical point)
• Through holes easier than blind holes
• Chamfer or radius hole entrance

Grinding

Precision finishing process using abrasive wheel.

Tolerances: ±0.001-0.01 mm
Surface finish: Ra 0.1-1.6 µm

Applications:

• Precision shafts
• Bearing surfaces
• Tool and die finishing

Joining Processes

Welding

Fuse materials using heat.

Common Types:

Advantages:

• Permanent joint
• High strength
• No fasteners needed

Disadvantages:

• Thermal distortion
• Requires skilled operator (TIG, stick)
• Difficult inspection

Design Tips:

• Accessible joint locations
• Appropriate joint type (butt, lap, T, corner)
• Consider weld shrinkage and distortion
• Material must be weldable

Brazing and Soldering

Join using filler metal with lower melting point.

Brazing: T > 450°C (silver, brass filler)
Soldering: T < 450°C (lead-tin, lead-free)

Advantages:

• No melting of base metal
• Join dissimilar metals
• Less distortion

Disadvantages:

• Lower joint strength than welding
• Requires cleanliness

Applications:

• Plumbing (solder)
• HVAC (brazing)
• Electronics (solder)

Mechanical Fastening

Bolts, rivets, screws, pins, etc.

Advantages:

• Disassembly possible
• No heat required
• Simple equipment

Disadvantages:

• More parts
• Potential for loosening
• Stress concentration

Adhesive Bonding

Join using structural adhesives.

Advantages:

• Uniform stress distribution
• Seals joint
• Join dissimilar materials

Disadvantages:

• Surface preparation critical
• Curing time required
• Difficult to disassemble

Sheet Metal Processes

Bending

Deform sheet metal to desired angle.

Bend allowance:

BA = θ(π/180) × (R + K × t)

Where:
- θ = bend angle (degrees)
- R = inside bend radius
- t = material thickness
- K = K-factor (≈ 0.33 for 90° bend)

Design Tips:

• Minimum bend radius: R ≥ t (usually R = 2-3t safer)
• Bend perpendicular to rolling direction for strength
• Account for springback (material elastic recovery)

Punching and Blanking

Shear material using punch and die.

Tolerances: ±0.1-0.25 mm

Design Tips:

• Minimum hole diameter: d ≥ t
• Edge distance: ≥ 2t from edge to hole
• Hole spacing: ≥ 3t between holes

Deep Drawing

Form 3D shapes from sheet metal (cups, cans).

Limitations:

• Drawing ratio: diameter/height typically < 2
• Multiple draws for deep parts
• Requires annealing for ductility

Plastic Manufacturing

Injection Molding

Inject molten plastic into mold cavity.

Advantages:

• High production rate
• Complex shapes
• Excellent surface finish
• Minimal post-processing

Disadvantages:

• High tooling cost
• Not economical for low volumes

Design Tips:

• Uniform wall thickness (1.5-3 mm typical)
• Draft angles (0.5-2° for mold release)
• Avoid undercuts (or use slides/lifters)
• Generous radii (avoid stress concentrations)

Extrusion

Continuous profiles (pipes, channels, etc.)

Applications: Pipes, window frames, profiles

Blow Molding

Hollow parts (bottles, containers)

Process: Heat plastic tube, inject air, expand against mold

3D Printing (Additive Manufacturing)

Build part layer by layer from digital model.

Technologies:

• FDM: Extrude plastic filament
• SLA: UV cure liquid resin
• SLS: Laser sinter powder
• Metal: Laser melt metal powder

Advantages:

• No tooling (direct from CAD)
• Complex geometry
• Rapid prototyping
• Low-volume production

Disadvantages:

• Slow (compared to traditional)
• Surface finish varies
• Material properties may be anisotropic
• Size limitations

Tolerances and Fits

Geometric Dimensioning & Tolerancing (GD&T)

Precise language for specifying tolerances on drawings.

Common symbols:

• ⊥ Perpendicularity
• ∥ Parallelism
• ⌭ Flatness
• ○ Circularity
• ⌀ Diameter
• ⟂ Position

Tolerance Grades

ISO 2768 standard for general tolerances:

Fits

Clearance fit: Hole always larger than shaft (loose)
Interference fit: Shaft always larger than hole (tight, press fit)
Transition fit: May be clearance or interference

ISO fit system:

• H7/g6: Clearance fit (sliding)
• H7/h6: Transition fit (locating)
• H7/p6: Interference fit (press)

Cost Estimation

Factors Affecting Cost

1. Material (volume × material cost)
2. Processing (setup + cycle time × rate)
3. Tooling (amortized over production volume)
4. Finishing (painting, plating, heat treat)
5. Quality control (inspection, testing)
6. Assembly (labor + fixtures)

Production Volume Impact

Practice Problems

Problem 1: Bend Allowance

Calculate bend allowance for 90° bend, R = 3 mm, t = 2 mm, K = 0.33.

<details> <summary>Solution</summary>

BA = 90(π/180) × (3 + 0.33 × 2)
BA = 1.571 × 3.66 = 5.75 mm

</details>

Problem 2: Process Selection

Part: 1000 aluminum brackets, complex shape, tight tolerances. Which process?

<details> <summary>Solution</summary>

Die casting or machining from stock. Die casting preferred if sufficient volume to justify tooling cost and shape is suitable. Otherwise, CNC machining from extruded or rolled stock. </details>

Key Takeaways

✓ Design for Manufacturing: Make parts easy and economical to produce
✓ Material selection: Balance properties, cost, and manufacturability
✓ Process selection: Match process to part requirements and volume
✓ Tolerances: Specify only as tight as necessary for function
✓ Cost drivers: Material, tooling, setup, cycle time, volume
✓ Standard features: Use standard sizes to reduce cost

Next Steps

Complete your foundation with the reference chapter:

• Chapter 09: Reference: quick formulas and conversions
• Learn CAD (SolidWorks, Fusion 360)
• Study GD&T in depth
• Visit manufacturing facilities to see processes firsthand

Pro Tip: Always talk to manufacturing engineers early in design. They know what's actually makeable and economical.