Mechanical Design

Material Science

Composition

Elemental Composition: All physical materials are made of elements.

Molecular Structure: One or more elements chemically bond into molecules.

Crystal Structure: Molecules are scattered randomly (amorphous) or organized to some pattern (crystalline) based on intermolecular dynamics.

Example: steel

Cutouts, Infill, Porosity: Internal geometry can include various forms of material removal/absence such as slots (strength-weight optimizing) and voids (open-cell, closed-cell).

Composite Structure: Different materials can be combined at the geometric level.

Example: reinforced concrete

Residual Stress: Uneven changes in temperature/microstructure causing spring-like internal tension.

Example: hot-rolled steel

Properties

Yield Strength: Permanent deformation limit.

Ultimate Tensile Strength: stretch-break limit (MPa)

Fracture Strength: stress at break

Thermal Expansion

Galvanic Corrosion

Resonant Frequency

Selection

6061-T6 Aluminum

A4 (SAE 316) Stainless Steel

A2 (SAE 304) Stainless Steel

3D Printing Filaments:

Prototyping: Precision PLA (±20um DIA) based on Natureworks 3D870

Fasteners

Standard

Our fastener standard is passivated stainless steel (A2/A4; 304/316) in metric sizes (generally hex-socket/hex-head coarse-threaded M2 thru M12). We often use M2x0.4, M3x0.5, M4x0.7, M6x1, M8x1.25, M10x1.5, M12x1.75; we rarely use M2.5x0.45 and M5x0.8.

M2 and M3 for micromechanical/electronic (ex. car remote, phone)
M4 for light structural (ex. VESA mounting standard)
M6 and M8 for medium structural
M10 and M12 for heavy structural

M6 is a particularly good general-purpose size with over 5kN proof load (500kg). It has good compatibility (dimensionally close to the 1/4-20 imperial size) and universality (standard thread for aluminum breadboards).

Screw Thread	Common Lengths (mm)
M2
M2.5	6, 8, 10, 12, 16
M3	6, 8, 10, 12, 16, 20, 25, 30
M4	10, 14, 16, 20, 25, 30, 35, 40, 50
M5
M6	12, 16, 20, 25, 30, 35, 40

Tensile Load and Proof Load Charts (engineeringtoolbox)

For improved reliability, we like to use:

stainless steel self-locking nuts (nylon-insert or metal-tension)
stainless steel threaded-insert nuts for plastic designs

We use: IUTC-M2, IUTC-M3, IUTC-M4, IUTC-M6 (DISTR: Hi-Tech Fasteners, Bisco Industries)

Special

Specialty fasteners help in plastic, sheet metal, laminate, ceramic, composite, and exotic applications.

Specialty Fastener Catalog (Pemnet)

Geometry

Common Issues

all corners/edges are not deburred/radiused/chamfered

Resources

Description	Link
History of the jerry can	https://web.archive.org/web/20070524182038if_/http://www.americanheritage.com/articles/magazine/it/1987/2/1987_2_62.shtml

Additive Manufacturing, CCAT Shop Tour, 2022: Youtube Link

Forums:

https://www.reddit.com/r/IndustrialDesign/

Aesthetic-Functional Design

(industrial design, product design)

Form and Function:

Form follows function: Durable, Comfortable, Compact (priorities)
Form adds function: Improvised Table, Handle, Mounting Point (examples)
Form has function: Aesthetic (ex. feelings), Intuition (ex. learning how to use something without instructions)

Principles:

Consistent Design Language
Aesthetic-Conceptual Alignment
Easy-to-Use During Emergencies

Acoustics

Basic Acoustic Theory:

Sound waves propagate through a medium (ex. air)
When sound waves contact a different medium (ex. air to wall), some waves are reflected by the new medium; some waves are absorbed in the new medium (as heat or kinetic resonance); some waves propagate through the new medium.

The industry-standard for acoustic insulation is mass-loaded vinyl (MLV). We don't like its PVC base because the plasticizer off-gas causes reduced longevity and health risks (ok but not ideal). It seems a more durable and safe alternative is mass-loaded EVA.

Pneumatics

Basic Pneumatics (PDF, SMC, 2005)

SMC, 2022 New AFF/AM/AMD Series

Compressed Air Purity Standard: ISO 8573

Air Pre-Filters
Air Compressors (ex. 4x pumps, paired 50% duty cycle)
Inline Filters (ex. 15um)
Check Valves
Aftercooler
Auto Drain
Relief Valve (ex. 1 MPa)
Water Separator
Main Line Filter (ex. 1um)
Mist Separator (ex. 0.1um)
Micro Mist Separator (ex. 0.01um)
Purge Valve
Tank (with ball-valve + auto-drain bottom)

The North American pipe thread standard is NPT. Our pipe/tube fitting standard is 1 inch NPT (thread size) and 316/A4 stainless steel (material), providing over 2500 LPM (90 CFM) flow capacity at 60 psi.

Pipe Air Flow (PDF, Parker)