Friday, 8 April 2016

GD and T





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

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



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

GD and T