ME Session #6 PDS due on Monday –Stay with the suggested format –Cover all items - Use NA, Not known, or None when applicable –Patent search sites: –Patent Number: D (Darren!?) More PDS / Materials / Bad designs

ME Session #6 Auto bike rack –Eric & Merrily –Dave & Serin –Mark & Kareem Home bike rack –Werner & Albert –Scott, Jim, Darren –Mahesh & Chan Cat/Dog Feeder –Clint & Brett –Tony & Bruce –Jim & Jeff –Dana –Tavis Envelope –Shane & Bill –Ceicel, Ben, Brial

Project Timetable

Deliverables Conceptual designs –Include at least 3 different ideas. –Avoid close variations as much as possible. –Each concept should be clearly shown. –Use hand-drawn orthographic-like drawings with correct proportions. –Show details on separate pages if necessary. –Number each major component of the assembly Motor, electronic control box, gear box

Conceptual Designs

Deliverables Final Report Includes –Final PDS –Final design description Assembly drawing. A description of each component in the assembly: –Drawings of designed components. –Complete description of off-the-shelf components including model and brand. Instructions for product assembly. Operations, maintenance, and safety manuals.

Final Report Final Design –Supporting information Other conceptual designs considered. Decision methods used. All major decisions made and reasons for them. – Relate decisions to PDS – Include cost and manufacturing concerns Areas where possible improvements can be made.

Most Commonly used Materials Plain carbon steels –Available in all structural forms, thin sheets, coated or uncoated, cold formed, hot rolled, and free machining. –Use 1006 to 1020 for parts requiring severe forming or welding. Bolts, nails, automobile body panels, brackets, appliance housing, machine bases. –Use 1030 to 1060 for parts requiring higher strength w/o heat treatment. Use only if welding is not required. –Use 1040 to 1060 for parts requiring surface hardening by flame or induction methods. –Use 1080 to 1095 for small parts requiring through hardening. Springs, hammers.

Materail Selection Plain carbon steels have very poor hardenability. Cold finished steels (1006 to 1050) can come in various tempers (hard to skin rolled). They can be strengthened up to 100% with cold working. Cold finished parts are stronger, have better surface finish, are more dimensionally accurate. But, they have less ductility, cost more, are dimensionally less stable in machining, and loose their strength if welded. High sulfur steels are ideal for machining (AISI 1112) as the chips break up easily. High sulfur content, however, causes weld cracking.

Material Selection Alloy steels –AISI 4340 or 4140 (Through hardening grades): Have excellent strength and toughness. Available in most forms in hot rolled form. Designed for high hardenability. Best suited to high stress machine parts - gears, cams, shafting, piston rods, bolts, dies, keys, bending rolls. They can be finish machined but can not be easily welded without special precautions. –AISI 8620 or 9310 (carburizing grades): These steels are designed for case hardening requirements. Deep cases can be created and hardened using carburizing. Used when high wear resistance is required. Suitable for gears, racks, cams, and sliding surfaces.

Alloy Steels High Strength Low Alloy Steels (HSLA) –Used for Structural applications –Stronger than plain carbon steels –Not heat treatable –Corrosion resistant (not as much as stainless steel) –Good weldability (low carbon content) –Good formability –Applications: structural forms, bars, plates. ASTM A36 (most popular), A242

Alloy Steels Ultra-strength steels –High strength and reasonable toughness. –Used for heavily loaded machine parts. –4340 and 4140 are most common Hard to weld but machinable –18% nickel maraging steel Very high strength ( ksi) Good weldability Very expensive

Example Suppose a designer has created a drawing for a shaft of a hypothetical device. The list of operational conditions have been determined as follows: –1.25” diameters are to fit ball bearings –The shaft is subjected to maximum shear stress of 10 ksi –There is possibility of moderate shock load –Small end must resist damage from frequent removal of a keyed gear. –There are no inertial requirements. –Surface roughness to be 32 micro inches max. –Diameters must be concentric to inch.

Example Based on the operational requirements, time constraint, and cost, the following selection factors have been established: –Hardness of at least 30 HRC (285 HB) –Fatigue strength of 30 ksi –Impact strength must be high –Stiffness must be high –The part must not rust in 50% RH room air. –Must be dimensionally stable. –Parts are needed in one week. –Three units are required. –Expected service life is 5 years

Example [ From Budinski ]

Solution ideas What kind of material –Metal? –Plastic? Low stiffness –Ceramic? Low impact strength –Composites? Must be hardenable to 30 HRC –Hardenable steels 1050 or 4340/4140 High fatigue strength –AISI 4340 or 4140 –Must be surface treated (nickel plating)

Cast Irons Grey cast iron (ASTM A 48 grades 20-60) –Easy to cast (excellent fluidity) –Low cost –Low toughness, brittle, no shock resistance –High compressive strength –Not appropriate for parts stresses in tension. –Low to medium tensile strength –Excellent machinability –Superb vibration damping property –Not easily weldable –Low stiffness (30 to 60% of steel)

Cast Irons Gray cast iron –Excellent metal-on-metal wear resistance –Good corrosion resistance in all media Ductile iron (ASTM 536, grade 5 [ ]) –Easy to cast/Low cost. –Much better toughness than gray iron. –Stiffness is about 70% of steel –Yield strengths range from 40 o 90 ksi –Similar to gray cast iron in other properties

Aluminum Alloys General properties –Lightness: 1/3 of steel –Good thermal and electrical conductivity –High strength/weight ratio –Weldable (most alloys) –Atmospheric corrosion resistance (will not rust) –Excellent machinability –Can be die case –Good formability –Non-magnetic –Non-toxic (pots and pans - 25% of all usage)