Chapter 05: Materials & Manufacturing

Why Materials Matter

Material selection is one of the most critical decisions in industrial design. It affects:

• Function: strength, durability, weight
• Aesthetics: appearance, feel, quality perception
• Manufacturing: process options, cost, speed
• Sustainability: environmental impact, recyclability
• Cost: material price, processing cost, waste

"Materials don't limit design; they enable it." Industrial design principle

Core Material Categories

Plastics (Polymers)

Advantages:

• Lightweight
• Design flexibility (complex shapes)
• Low cost at volume
• Color variety
• Good chemical resistance

Disadvantages:

• Environmental concerns
• Lower strength than metals
• Temperature limitations
• Can feel cheap

Common Types:

Metals

Advantages:

• High strength
• Premium feel
• Excellent thermal/electrical conductivity
• Precise tolerances
• Recyclable

Disadvantages:

• Heavy
• Expensive
• Limited shape complexity
• Can corrode (except stainless)
• Requires more machining

Common Types:

Natural Materials

Wood:

• Warm, natural aesthetic
• Renewable (if sourced responsibly)
• Easy to work
• Varies by species
• Examples: Furniture, handles, accessories

Leather:

• Durable, ages well
• Premium feel
• Natural variations
• Requires animal source
• Examples: Bags, upholstery, grips

Stone:

• Permanent, luxurious
• Heavy, difficult to work
• Natural variations
• Examples: Countertops, decorative objects

Bamboo:

• Fast-growing, sustainable
• Strong, lightweight
• Warm appearance
• Examples: Furniture, cutting boards

Glass

Properties:

• Transparent/translucent
• Hard, scratch resistant
• Chemically inert
• Brittle (can break)
• Recyclable

Types:

• Soda-lime glass: common, inexpensive (windows, bottles)
• Borosilicate: heat resistant (Pyrex, lab equipment)
• Tempered: impact resistant (phone screens, car windows)
• Gorilla Glass: strengthened, scratch resistant (smartphones)

Textiles

Properties:

• Soft, flexible
• Breathable (can be)
• Wide aesthetic range
• Requires cleaning

Types:

• Natural: cotton, wool, silk
• Synthetic: polyester, nylon, spandex
• Technical: Gore-Tex, Kevlar, Dyneema

Uses:

• Upholstery, bags, wearables, soft goods

Composites

What Are They? Combination of two or more materials to achieve superior properties.

Examples:

Manufacturing Processes

Understanding how things are made shapes design decisions.

Plastic Manufacturing

1. Injection Molding

Process:

1. Plastic pellets heated to liquid
2. Injected into metal mold under pressure
3. Cooled and ejected
4. Cycle time: 30 seconds to 2 minutes

Best For:

• High volume (thousands to millions)
• Complex shapes
• Consistent quality

Design Considerations:

• Draft angles (1-3°) for part ejection
• Uniform wall thickness (2-4mm typical)
• Avoid undercuts (or use slides/lifters)
• Fillets at corners (reduce stress)
• Gate placement (affects aesthetics)

Cost:

• Tooling: $5,000-$100,000+ per mold
• Part cost: $0.50-$5 at volume

Examples: Phone cases, toys, appliance housings

2. Blow Molding

Process:

1. Heated plastic tube (parison)
2. Placed in mold
3. Air blown in to expand against mold
4. Cooled and ejected

Best For:

• Hollow objects
• Bottles and containers

Examples: Water bottles, shampoo bottles, jerry cans

3. Rotational Molding

Process:

1. Plastic powder in mold
2. Mold rotated and heated
3. Powder melts and coats interior
4. Cooled while rotating

Best For:

• Large, hollow objects
• Low volumes
• Uniform wall thickness

Examples: Kayaks, playground equipment, tanks

4. Thermoforming

Process:

1. Plastic sheet heated
2. Vacuum or pressure formed over mold
3. Trimmed to shape

Best For:

• Large, shallow parts
• Lower volumes
• Rapid prototyping

Cost:

• Low tooling cost
• Limited to simple geometries

Examples: Packaging, trays, interior panels

Metal Manufacturing

1. Die Casting

Process: Similar to injection molding but with molten metal.

Best For:

• Complex metal parts
• High volume
• Thin walls

Materials: Aluminum, zinc, magnesium

Examples: Engine blocks, enclosures, hardware

2. Machining (CNC)

Process: Material removed by cutting tools.

Types:

• Milling: rotating cutter removes material
• Turning: part rotates, tool cuts
• Drilling: creates holes

Best For:

• Low to medium volume
• High precision
• Complex geometries
• Prototypes

Cost:

• No tooling cost
• Expensive per part ($50-$1000+)
• Slow (hours per part)

Examples: Prototypes, low-volume products, precision parts

3. Sheet Metal Forming

Process: Flat sheet bent, stamped, or cut into shape.

Operations:

• Bending: brake press bends along lines
• Stamping: die stamps features
• Laser cutting: cuts complex profiles

Best For:

• Enclosures, brackets
• Medium to high volume
• Cost-effective

Examples: Computer chassis, appliance panels, brackets

4. Extrusion

Process: Material pushed through shaped die.

Best For:

• Constant cross-section profiles
• Long lengths

Materials: Aluminum, plastic

Examples: Aluminum channels, window frames, pipes

5. Casting (Sand, Investment)

Process: Molten metal poured into mold.

Types:

• Sand casting: cheap, rough finish
• Investment casting: precise, smooth finish

Best For:

• Complex shapes
• Low to medium volume
• Art objects

Examples: Engine blocks, jewelry, sculptures

Additive Manufacturing (3D Printing)

1. FDM (Fused Deposition Modeling)

Process: Plastic filament melted and extruded layer-by-layer.

Best For:

• Prototyping
• Low-volume production
• Complex geometries

Materials: PLA, ABS, PETG, TPU, nylon

Cost:

• Printer: $200-$5,000
• Material: $20-50/kg
• Time: Hours to days

Limitations:

• Layer lines visible
• Lower strength
• Support structures required

2. SLA/DLP (Resin Printing)

Process: UV light cures liquid resin layer-by-layer.

Best For:

• High detail
• Smooth finish
• Small parts

Cost:

• Printer: $300-$10,000
• Material: $50-150/L

Limitations:

• Brittle materials
• Post-processing required
• Toxic uncured resin

3. SLS (Selective Laser Sintering)

Process: Laser fuses powder particles together.

Best For:

• Functional prototypes
• Complex geometries
• No support structures

Materials: Nylon, TPU

Cost:

• Very expensive ($100,000+ machines)
• Used via service bureaus

4. Metal 3D Printing (DMLS, SLM)

Process: Laser melts metal powder layer-by-layer.

Best For:

• Complex metal parts
• Low volume
• Aerospace, medical

Cost:

• Extremely expensive
• Service bureau only for most

Assembly Methods

Fasteners:

• Screws: disassemble-able, visible or hidden
• Snap fits: no fasteners, design-intensive
• Rivets: permanent, strong
• Magnets: easy assembly, premium feel

Adhesives:

• Epoxy: very strong, permanent
• CA glue (superglue): fast, brittle
• Hot glue: weak, temporary
• VHB tape: strong, vibration resistant

Welding:

• Plastic welding: ultrasonic, heat staking
• Metal welding: TIG, MIG, spot welding

Design for Manufacturing (DFM)

Key Principles

1. Design for the Process Each process has unique requirements and limitations.

Example (Injection Molding):

• Constant wall thickness
• Draft angles
• Avoid sharp corners
• Consider parting line

2. Minimize Part Count Fewer parts = lower cost, faster assembly, fewer failures.

Example:

• Replace 5 screws with snap fits
• Combine two parts into one molding

3. Use Standard Parts Off-the-shelf components are cheaper than custom.

Examples:

• Standard screws, nuts, bolts
• Catalog electronics (buttons, switches)
• Stock materials (rod, sheet, tube)

4. Tolerance Stack-Up Accumulated variations can cause assembly problems.

Solution:

• Design for larger tolerances
• Use alignment features
• Adjust critical dimensions

5. Minimize Secondary Operations Every additional step adds cost.

Examples:

• Paint/coating
• Assembly
• Post-machining
• Inspection

Material Selection Framework

Ask These Questions:

1. Functional Requirements:

   • What loads will it experience?
   • What temperatures?
   • Chemical exposure?
   • Wear resistance needed?

2. Aesthetic Requirements:

   • What feel/appearance?
   • Color options?
   • Texture?
   • Premium vs. value perception?

3. Manufacturing Constraints:

   • Production volume?
   • Complexity of shape?
   • Tolerance requirements?
   • Assembly method?

4. Cost Targets:

   • Material cost per part?
   • Tooling budget?
   • Processing cost?
   • Acceptable waste?

5. Sustainability:

   • Recyclable?
   • Renewable source?
   • Energy to produce?
   • End-of-life disposal?

Cost Estimation

Rule of Thumb:

Total Cost = Material + Processing + Tooling + Assembly + Overhead

Material: Volume × Material cost/volume
Processing: Machine time × Rate
Tooling: Amortized over production quantity
Assembly: Time × Labor rate
Overhead: 20-50% of above

Example (Injection Molded Part):

Material: 50g × $2/kg = $0.10
Processing: 45 sec × $60/hr = $0.75
Tooling: $20,000 / 10,000 parts = $2.00
Assembly: 30 sec × $30/hr = $0.25
Subtotal: $3.10
Overhead (30%): $0.93
Total: $4.03 per part

At 100,000 parts: ~$1.25 per part (tooling amortized)

Material Testing & Selection

Testing Methods

Physical Tests:

• Tensile test: pull until it breaks
• Impact test: drop or strike
• Fatigue test: repeated loading
• Hardness test: resistance to deformation

Environmental Tests:

• UV exposure: sunlight resistance
• Salt spray: corrosion resistance
• Temperature cycling: expansion and contraction
• Chemical exposure: solvent resistance

Material Databases

Online Resources:

• MatWeb: free material property database
• Material Connexion: innovation library (subscription)
• McMaster-Carr: stock materials with specs
• Supplier datasheets: specific product data

Key Properties to Compare:

Case Study: Water Bottle Design

Requirements:

• Hold 24 oz (700ml)
• Dishwasher safe
• Leak-proof
• Durable (drops)
• Target retail: $15

Material Options:

Manufacturing Process:

• Blow molding (body)
• Injection molding (cap with silicone seal)
• Pad printing (logo)

Estimated Cost:

• Material: $1.50
• Processing: $0.75
• Tooling: $1.00 (amortized)
• Assembly: $0.25
• Total: $3.50 → Retail $14.99 (4.3× markup) ✅

Key Takeaways

1. Material choice affects everything: function, aesthetics, cost, sustainability
2. Design for your process: each manufacturing method has rules
3. Volume determines process: low volume = machining/3D printing; high volume = molding/stamping
4. Simplicity saves money: fewer parts, standard components, loose tolerances
5. Test materials early: don't assume; validate properties
6. Consider lifecycle: from manufacturing through disposal
7. Work with manufacturers: they know what's possible and cost-effective

What's Next

In Chapter 06: Ergonomics & Human Factors, you'll learn how to design products that fit the human body and mind.

Exercise: Choose a simple product (e.g., spatula, flashlight):

1. Identify all materials used
2. Why was each material chosen?
3. What manufacturing process created it?
4. Sketch an alternative design using different materials
5. Compare cost, weight, durability, aesthetics