Form
|
Straightness
|
Controls the straightness of a feature in relation to
its own perfect form
|
Flatness
|
Controls the flatness of a surface in relation to its
own perfect form
|
|
Circularity
|
Controls the form of a revolved surface in relation to
its own perfect form by independent cross sections
|
|
Cylindricity
|
Like circularity, but applies simultaneously to entire
surface
|
|
Profile
|
Profile of a Surface
|
Controls size and form of a feature. In addition it
controls the location and orientation when a datum reference frame is used.
|
Profile of a Line
|
Similar to profile of a surface, applies to cross
sections of a feature
|
|
Orientation
|
Perpendicularity
|
Controls the orientation of a feature which is
nominally perpendicular to the primary datum of its datum reference frame
|
Angularity
|
Controls orientation of a feature at a specific angle
in relation to the primary datum of its datum reference frame
|
|
Parallelism
|
Controls orientation of a feature which is nominally
parallel to the primary datum of its datum reference frame
|
|
Location
|
Position
|
Controls the location and orientation of a feature in
relation to its datum reference frame
|
Concentricity
|
Controls concentricity of a surface of revolution to a
central datum
|
|
Symmetry
|
Controls the symmetry of two surfaces about a central
datum
|
|
Runout
|
Circular runout
|
Controls circularity and coaxiality of each circular
segment of a surface independently about a coaxial datum
|
Total runout
|
Controls circularity, straightness, coaxiiality, and
taper of a cylindrical surface about a coaxial datum
|
Mechanical Design Tutorial
Friday, 8 April 2016
GD and T
Tuesday, 8 March 2016
Material Selection
The selection of a
material for a machine part or structural member is one of the most important
decisions of the designer. There are
systematic and optimizing approaches to material selection. Here, we will only
look at how to approach some material properties. One basic technique is to
list all the important material properties associated with the design,(
strength, stiffness, and cost). This can be prioritized by using a weighting
measure depending on what properties are more important than others. Next, for
each property, list all available materials and rank them in order beginning with
the best material; e.g., for strength, high-strength steel such as 4340 steel should
be near the top of the list. For completeness of available materials, this
might require a large source of material data. Once the lists are formed,
select a manageable amount of materials from the top of each list. From each
reduced list select the materials that are contained within every list for
further review. The materials in the reduced lists can be graded within the
list and then weighted according to the importance of each property.
Choosing material for any product in design stage, should analyses the product.
What does it do, who uses it, what should it cost?
How do the mechanical parts work and interact
What does it do, who uses it, what should it cost?
How do the mechanical parts work and interact
Selection of Material Depends on following factors,
• Function• Material Properties
• Failure mode
• Material Cost and Availability
Material must be priced appropriately (not cheap but right)
Material must be available (better to have multiple sources)
• Processing / Manufacturability
Must consider how to make the part, for example:
Casting
Machining
Welding
• Working Environment and Serviceability
Wear and Corrosion
• Durability and Maintenance
Materials Selection Methodology
1. Identify the design requirements, The design requirements include the following items:• Performance requirements
• Reliability requirements
• Size, shape, and mass requirements
• Cost requirements
• Manufacturing and assembly requirements
• Industry standards
• Government regulations
• Intellectual property requirements
• Sustainability requirements
2. Translate the design requirements into materials specifications. It should take into consideration the design Objectives, Function, Constraints and Free variables.
(Objectives- to make it as cheap as possible, or as light as possible, or as safe as possible, or combination of all)
(Function- to support load, or to contain pressure, or to transmit heat)
(Constraints- dimensions are fixed, or withstand load without fail, or it should function in a certain temperature range)
3. List the constraints (e.g. no buckling, high stiffness) of the problem and develop an equation for them, if required.
Develop an equation of the design objective in terms of functional requirements, geometry and materials properties (objective function)
4. Define the unconstrained (free) variables. Substitute the free variable from the constraint equation into the objective function.
5. Group the variables into three groups, functional requirements (F), geometry (G) and materials functions (M), to develop the performance metric (P)
6. Screening out of materials that fail the design constraints and other variables. And Ranking the materials by their ability to meet the requirements.
7. Search for supporting information for the material candidates/Attributes. Analyze and select the appropriate material for safe design.
Some Material And Its Application
Material
|
Applications
|
Ferrous
|
|
Cast irons
|
Automotive
parts, engine blocks, machine tool structural parts, lathe beds
|
High carbon steels
|
Cutting
tools, springs, bearings, cranks, shafts, railway track
|
Medium carbon steels
|
General
mechanical engineering (tools, bearings, gears, shafts, bearings)
|
Low carbon steels
|
Steel structures (mild
steel)—bridges, oil rigs, ships; reinforcement for concrete; automotive
parts, car body panels; galvanized sheet; packaging (cans, drums)
|
Low alloy steels
|
Springs,
tools, ball bearings, automotive parts (gears connecting rods, etc.)
|
Stainless steels
|
Transport, chemical and
food processing plant, nuclear plant, domestic ware (cutlery, washing
machines, stoves), surgical implements, pipes, pressure vessels, liquid gas
containers
|
Non-ferrous
|
|
Aluminum alloys
/
Casting alloys
|
Automotive parts (cylinder
blocks), domestic appliances (irons)
|
Non-heat-treatable alloys
|
Electrical conductors, heat
exchangers, foil, tubes, saucepans, beverage cans, lightweight ships,
architectural panels
|
Heat-treatable alloys
|
Aerospace engineering,
automotive bodies and panels, lightweight structures and ships
|
Copper alloys
|
Electrical conductors and
wire, electronic circuit boards, heat exchangers, boilers, cookware, coinage,
sculptures
|
Lead alloys
|
Roof and wall cladding,
solder, X-ray shielding, battery electrodes
|
Magnesium alloys
|
Automotive castings,
wheels, general lightweight castings for transport, nuclear fuel containers; principal
alloying addition to aluminum alloys
|
Nickel alloys
|
Gas turbines and jet
engines, thermocouples, coinage; alloying addition to austenitic stainless
steels
|
Titanium alloys
|
Aircraft turbine blades;
general structural aerospace applications; biomedical implants.
|
Zinc alloys
|
Die castings (automotive,
domestic appliances, toys, handles); coating on galvanized steel
|
Polymers: Elastomer
|
|
Butyl rubber
|
Tyres, seals,
anti-vibration mountings, electrical insulation, tubing
|
Ethylene-vinyl-acetate
|
Bags, films, packaging,
gloves, insulation, running shoes
|
Isoprene
|
Tyres, inner tubes,
insulation, tubing, shoes
|
Natural rubber
|
Gloves, tyres, electrical
insulation, tubing
|
Polychloroprene (neoprene)
|
Wetsuits, O-rings and
seals, footware
|
Polyurethane elastomers
|
Packaging, hoses,
adhesives, fabric coating
|
Silicone elastomers
|
Electrical insulation,
electronic encapsulation, medical implants
|
Polymers: Thermoplastic
|
|
Acrylonitrile butadiene styrene
|
Communication appliances,
automotive interiors, luggage, toys, boats
|
Cellulose polymers
|
Tool and cutlery handles,
decorative trim, pens
|
Ionomer
|
Packaging, golf balls,
blister packs, bottles
|
Polyamides (nylons)
|
Gears, bearings; plumbing,
packaging, bottles, fabrics, textiles, ropes
|
Polycarbonate
|
Safety goggles, shields,
helmets; light fittings, medical components
|
Polyetheretherketone
|
Electrical connectors,
racing car parts, fiber composites
|
Polyethylene
|
Packaging, bags, squeeze
tubes, toys, artificial joints
|
Polyethylene terephthalate
|
Blow molded bottles, film,
audio/video tape, sails
|
Polymethyl methacrylate (acrylic)
|
Aircraft windows, lenses,
reflectors, lights, compact discs
|
Polyoxymethylene (acetal)
|
Zips, domestic and
appliance parts, handles
|
Polypropylene
|
Ropes, garden furniture,
pipes, kettles, electrical insulation, astroturf
|
Polystyrene
|
Toys, packaging, cutlery,
audio cassette/CD cases
|
Polyurethane thermoplastics
|
Cushioning, seating, shoe
soles, hoses, car bumpers, insulation
|
Polyvinylchloride
|
Pipes, gutters, window
frames, packaging
|
Polytetrafluoroethylene (teflon)
|
Non-stick coatings,
bearings, skis, electrical insulation, tape
|
Polymers: Thermoset
|
|
Epoxies
|
Adhesives, fiber
composites, electronic encapsulation
|
Phenolics
|
Electrical plugs, sockets,
cookware, handles, adhesives
|
Polyester
|
Furniture, boats, sports
goods
|
Polymers:Polymer foams
|
|
Flexible polymer foam
|
Packaging, buoyancy,
cushioning, sponges, sleeping mats
|
Rigid polymer foam
|
Thermal insulation,
sandwich panels, packaging, buoyancy
|
Composites
|
|
Alumina
|
Cutting tools, spark plugs,
microcircuit substrates, valves
|
Aluminum nitride
|
Microcircuit substrates and
heat sinks
|
Boron carbide
|
Lightweight armor, nozzles,
dies, precision tool parts
|
Silicon
|
Microcircuits,
semiconductors, precision instruments,
|
Silicon carbide
|
High temperature equipment,
abrasive polishing grits, bearings, armor
|
Silicon nitride
|
Bearings, cutting tools,
dies, engine parts
|
Tungsten carbide
|
Cutting tools, drills,
abrasives
|
Ceramics
|
|
Borosilicate glass
|
Ovenware, laboratory ware,
headlights
|
Glass ceramic
|
Cookware, lasers, telescope
mirrors
|
Silica glass
|
High performance windows,
crucibles, high temperature applications
|
Polymer
|
|
CFRP
|
Lightweight structural
parts (aerospace, bike frames, sports goods, boat hulls and oars, springs)
|
GFRP
|
Boat hulls, automotive
parts, chemical plant
|
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