Machine Design

Design Process Steps

1. Recognise need

2. Create a Design

3. Prepare a model

4. Test and evaluate model

5. Communicate design

Improve deisgn in steps 2-4

Mechanical vs MAchine Design

Mechanical Design - Involves Energy and structures, all encompassing. (heat exchangers, IC engines)

Machine Design - Focus on structures and motion stems (Gearbox)

Traditional Considerations

• Material

• Geometry

• Operating conditions

• Cost

• availability

• Producibility

• Component Life

Modern Considerations

• Saftey

• Ecology

• Quality of life

Misc Considerations

• Reliability

• Maintainability

• Ergonomics

• Aesthetics

Material Considerations

• Perfect elasticity - return to original shape

• Homogenity - Same properties in entire material

• Isotropy - elastic properties are same in all directions

Saftey considerations

• Awareness

• Imagination

• Guidlines

  • Life cycyle review

  • provisions

  • make it importaint

  • fail safe

  • government

Design for Manufacturing

Focus on making manufacturing easier

• Simple

• Standard components

• Liberal tolerances

• PRocessable materials

• Work with techies

• avoid secondary operations

• understand production capabilities

• Special process characteristics

• avoid restriction

Design for dissasembly

Design to be easily taken apart and re-used or repaired

• Reduce dissasembly operations

• modular design

• removable joints (nuts and bolts)

• Minimise fastener amounts

• standard components

Sustainability Design

minimal environmental and occupational health damages

• LCA

• optimise resource usage

• account for longevity

• DFD

• environment deisgn

• Envrionmentally friendly materials

• circular

Design for environment

ecological considerations

• Economically recyclable

• minimise non-recycled energy sources

LCA

evaluate environmental impact of product throughout its life

• Goal scope

• Inventory

• impact

• Interpreation

Shaft loading types

• Fully reversed

• Repeated

• Fluctuating

Stress relief techniques

• Undercut radius

• relief groove

• radius relief groove

Torque Transmission tehcniques

• Keys

• Pins

• Setscrews

• Splines

• PRess fits and shrinks

• Tapered Fits

Key types

• Square

• Flat

• Round

• Kennedy

• Woodruff

• Gib-head

• Feather

Splines

stubby gear teeth for higher torques. can be made with loose fit

Pins

Simple torque transfer

Set screws

Screw thing in place

Retaining rings

low cost to retain elements and create a shoulder

Interference

Press or shrink fits on shaft

Places of stress concentration

Discontenuities

• Keys

• shoulders

• retaining ring grooves

Bearing Loads

• Radial loads (rotation)

• Axial loads (thrust/linear)

• Combined loads

Bearing types

• Sliding bearings

• Rolling element bearings

  • Roller bearings

  • Ball bearings

Types of ball bearings

• Radial

  • Single row

  • Max capacity

  • sheilded

  • sealed

  • double

• Thurst

• Angular

  • Angular contact

• Self algining

Typers of Roller Bearings

• Straight

• Spherical

• Tapered/Thrust

• Needle

• Tapered

• Steep angled

What are the parameters that govern bearing life

• Number of revelutions until first tangible evidence of fatigue

• Number of hours at standard speed until first signs of fatigue

Rating life and symbol

• number of hours that 90% of a group of bearings will ahcieve or exceed before failiure

• L10

Basic dynamic load rating

• measure of resitance to surface fatigue failiure

Adjustment reliability factors

Take into account if reliability needs to be higher

Failiure modes

• Static - Brinelling

• Dynamic - surface fatigue