Manuf PPT notes( except CNC programming) PDF

Preview

Summary

it has short notes regarding the corresponding course. Except for the topic CNC programming...

Description

Manufacturing notes Intro to Manufacturing Manufacturing: Process of producing merchandise by using labor, machines, tools, raw materials chemicals etc. Raw material is used to generate output (goods only). Production: Process to make something used for consumption by combining various resources. Converts input to outputs (Goods and services) Types of substances:      

Pure Alloys Ceramics Plastics Composites Miscellaneous

Classification of processes: Primary: Raw material/scrap to basic shape & size. Can’t provide exact same product. Close dimensional tolerance unachievable. Surface finish and integrity is poor. Allows for further processing in secondary process. 1. Casting 2. Forming (Forging, Rolling, Extrusion etc.) 3. Joining (Brazing, Welding, Soldering etc.)  Secondary: Further modify output of primary manufacturing processes. Improves material properties, surface quality, finish, integrity, dimensional tolerance. Input material must have certain shape and size. 1. Machining 2. Surface Working(Heat Treatment, Coating etc.)  Tertiary: Grinding and Abrasive processes, NTM processes 1. Grinding 2. Honing, Lapping, Super Finishing, Polishing, Buffing etc.



CASTING: Means pouring molten metal into a mold with a cavity of the shape and allowing it to solidify. Object is obtained by either breaking the mold or taking it apart. Solidified object is called casting. ADVANTAGES Very thin/intricate shapes can be made Any material can be cast Large saving in metal weight Simple and inexpensive Size and weight isn’t a limitation TERMINOLOGY

DISADVANTAGES Dimensional inaccuracy Poor Surface finish High rejection rate Automation is $$



              

Flask: Moulding flask holds sand mould intact. 1. Drag: Lower moulding flask 2. Cope: Upper moulding flask 3. Cheek: Intermediate moulding flask used in 3 piece moulding Pattern: Replica of final object with some modifications. Parting Line: Dividing line btw. 2 mldng flasks Bottom board: Wooden, used at start of mould making Core: Used to make hollow cavity in casting Core print: Used to support core weight Pouring Basin: Funnel shaped cavity at top where metal is poured Sprue: Passage through which metal reaches to mould cavity Runner: Passageways in parting line which regulate metal flow en-route to cavity Gate: Actual Entry Point where metal enters cavity Riser: Reservoir of molten metal in casting to account for any shrinkage during cooling Chills:Metal object placed in mould to increase cooling rate for uniform cooling Chaplet: Used to support core which may sag/sink and prevent it from floating Facing sand: Small amount of carbonaceous material sprinkled on inner surface of moulding cavity. Moulding sand: Freshly prep. Material to make mold cavity. Silica+ Clay+ Moisture Backing sand: It is most of the refractory material in the mould.

Cope and drag are prepared such that on aligning them, we get the requisite pattern. STEPS IN SAND CASTING 1. 2. 3. 4. 5. 6. 7.

Molding (Pattern making, Core Making, Gating System) Sand around finished mould Pouring molten metal into mould (Solidification) Casting (Shakeout, Removal of risers and gates) Heat Treatment (Optional in some cases) Cleaning and Finishing (Possible additional heat treatment) Inspection ( Check 4 defects, Pressure, tightness, Dimensions)

MOLD MATERIALS: Should retain shape till solidification. 1. Permanent Molds: Made of Fe and alloys. Costly. Used for low m.pt. materials. High Quality and accuracy. 2. Temporary: Made of refractory sands and resins. MOLDING SANDS:    

Sources: River Beds, Sea, Lakes, Deserts Types: Natural, Synthetic, Loam Ingredients: Refractory sand grains, Binders, Water, Additives Refractory sands: Silica/zircon/magnesite/dolomite/graphite etc.

1. Natural sands: Contains binding material, only need H 2O to mix, maintains moisture content for long time, permits easy finishing, less refractory compare to synthetic. Used to cast Fe and non-Fe metal alloys, less costly, needs less control, easy repair. 2. Synthetic sand: Natural sand + Binder (say bentonite) + moisture. Formulation done to get desired properties. Used to cast steel and other alloys 3. Loam sands: >50% clay. Fine sands+clay+graphite etc. Dries hard. Used to cast large bells. Sweep/skeleton patterns may be used. PATTERNS FOR CASTING: Model of casting which makes impression in molding sand. It is the replica of final object. Factors on which selection of pattern material depends: 1. No. of castings to be made 2. Size, complexity and shape of casting 3. Type of molding method Types of pattern 1. 2. 3. 4. 5. 6. 7. 8. 9.

Single Piece Split/Two Piece Gated Cope and drag Match plate Loose piece Follow board Sweep Skeleton

Types of mold: Open-simply a container in shape of desired part. Closed: mold geometry is more complex and requires a gating system. Types of molding processes: 





According to method 1. Floor molding 2. Bench molding 3. Pit molding 4. Machine molding Acc. To mold materials 1. Green sand molding 2. Dry sand molding 3. Loam sand molding 4. Core sand molding Other molding process 1. Shell molding 2. Permanent mold casting 3. CO2 molding

TYPES OF ALLOWANCES: 









Shrinkage allowance: Occurs in 3 stages. All metals shrink (except Bi, cast Fe). Rate of contraction is material dependent. Pattern dimensions differ from final dimensions. 1. Contraction of liq. from pouring to freezing temp. (taken care by riser) 2. “ “ “ “ “ due to change of phase (taken care by riser) 3. “ “ “ of casting from freeze to room temp(shrinkage allowance) Draft allowance: Occurs during withdrawal of pattern from mold. Due to contact of vertical surface of pattern with mold. Draft angle varies with complexity. Inner details are given higher draft from outer surfaces. Finishing/machining allowance: Finish and accuracy in casting is poor. Scale deposition takes place on Fe materials. To get desired dimensions, machining is done. Shake allowance: Pattern is rapped all around vertical faces to enlarge cavity to facilitate removal. Final casting is enlarged, thus og pattern dimensions are reduced. Negative allowance. Distortion/Camber allowance: Solidified material gets weak. Shape of pattern should be itself given distortion in opp. direction.

Riser: Acts as reservoir to the liquid and solidification shrinkages. It provides passage for gases to escape. Works as an indicator of complete mold filling. TYPES OF CASTING:    

Slush casting: Makes hollow component without use of core, molten metal solidifies up to req. thickness. Lost wax casting: Jewelry, ornaments Centrifugal casting Die casting

MAJOR CASTING DEFECTS: 



Gas defects 1. Blowholes: Due to excess gas content in metal bath & rejection of dissolved gases. Produced btw. growing crystals. 2. Air inclusion: Unescaped gases absorbed by molten metal in surface during flow into metal. 3. Pin holes: Numerous holes on surface due to rxn. btw. mold n metal. 4. Shrinkage cavity: Dip in casting during solidification. Has angular edges. Molding material defects 1. Cuts and washes: flowing molten metal erodes the surface, called cuts. 2. Scab: Place from where sand is cut is occupied by molten material. 3. Fusion: sand fuses and sticks to casting surface. Results in glossy surface due to lack of refractoriness of sand. 4. Runout; Molten metal leaks from mold 5. Rat tail: Slight compression failure of thin layer of molding sand. 6. Swell: enlargement of mold cavity due to molten metal pressure.





Pouring metal defects: 1. Misrun: metal cools down after gate but b4 filling cavity. 2. Cold shut: metal solidifies btw. gates preventing further flow 3. Slag inclusions Metallurgical defects: 1. Hot tears: internal/external cracks on casting due to solid shrinkage 2. Hot spots: Sections of casting that have cooled slowly. Results in porosity and cracks.

FORMING: Shaping of materials in hot/cold state by mechanical means. Doesn’t include casting, machining or grinding. Improves mechanical properties. Saves material, costs and time. TERMS FOR METAL BARS:    

Ingot: Formed by injecting/pouring molten liquid into a mold. Can be cat into size and shape that is convenient to store, transport and work into a product. Billet: square cross sectional are less than 36 sq. inches Slab: Rolled from ingot or bloom. Rectangle cross section of 250mm x 40mm Blooms: Rectangular cross section > 36 sq. inches

Increase in temperature decreases strength and increases ductility. This increases chances of deformation. Deformation occurs due to slip and twinning. Forming can be cold, hot or warm. COLD FORMING Below recrystallization temp. Temp. of deformn0.6*(m.pt temp in K) Surface finish isn’t good Formation of new crystals Residual stress Less force is required

Warm forming occurs in btw. given temp. range. Hot Working ADVANTAGES Any amt. of deformn can be done High ductility Less force required Favorable grain size is achieved

DISADVANTAGES Some metals can’t be hot worked due to brittleness Results in scaling-poor surface finish Inaccurate dimensions due to expansion Handling hot material is difficult

Cold working ADVANTAGES Strength and hardness of material

DISADVANTAGES For material with high yield strength,

increases Better dimensional accuracy Easy handling No oxide formation

deformation is limited Strain hardening results in limited deformation Brittle materials can’t be worked

FORGING: Involves application of force on metal to cause plastic deformation to get req. final shape. Generally hot working. Done in two ways 

Drawing out: Increase length with reduction in area by using force perpendicular to longitudinal axis. Upsetting: Increases cross sectional area of stock at cost of length by applying force parallel to length axis.

Advantages of forging 1. By mechanically deforming the heated metal under tightly controlled conditions, forging produces predictable and uniform grain size and flow characteristics. Forging stock is also typically preworked to refine the dendritic structure of the ingot and remove porosity. These qualities translate into superior metallurgical and mechanical qualities, and deliver increased directional toughness in the final part. 2. Forging also provides a degree of structural integrity that is unmatched by other metalworking processes. Forging eliminates internal voids and gas pockets that can weaken metal parts. By dispersing segregation of alloys or non-metallic, forging provides superior chemical uniformity. 3. Parts can also be forged to meet virtually any stress, load or impact requirement. Proper orientation of grain flow assures maximum impact strength and fatigue resistance. The high-strength properties of the forging process can be used to reduce sectional thickness and overall weight without compromising final part integrity. Types of forging: 1. Smith Forging: Involves heating stock over hearth and beating it over the anvil. Component is manipulated btw. Blows to get desired shape. 2. Drop Forging 3. Press Forging 4. Machine Forging Smith forging operations:      

Fullering: Used to add depression to a section of the material Flattening Bending Upsetting Swaging: Used to give a constant diameter to the material. Edging: Used to add swelling to a section of the material.

Forging Operations on basis of dies;

  

Open Die forging Close Die forging Impression Die forging

Forging Defects  



Unfilled sections: poor metal flow due to Poor design of forging Die or Faulty Forging Techniques. (Soln. - use forging press to complete power) Cold shut: Cracking occurring at the Corners of the Forging caused by poor ductility under forging conditions and improper near corners owing deficient die design (Increase fillet radii) Scale pits: Irregular Depressions on the Surface of the Forging due to improper Cleaning of the Stock, formation of Oxide and Scale.

ROLLING: Material is compressed btw. 2 rotating rolls to reduce cross-sectional area. Widely used due to high productivity and low cost. Normally hot working. Material fed into rolls by friction. Material entering has lesser speed than spinning roll; opposite for exiting materials. ROLL PASS SEQUENCE: 1. Break Down Pass a. Used to reduce cross sectional area nearer to desired region. b. First in sequence 2. Roughing Pass: Area reduces, also shape of material is closer to final shape. 3. Finishing Pass: Final step. Gives required shape. Roll deflections: Occur in flat rolling. Causes a barrelling effect. Requires rolls with camber. Rolling Defects:     

Edge Cracks Cracks in inner region Wavy edges Alligatoring (splitting of material exiting rolls in outwards fashion) Internal defect

EXTRUSION: Material confined in closed cavity and forced to flow from only one opening so material takes shape of opening (like tube of toothpaste) Possible to make components with constant cross-section Parts more complex than rolling can be obtained bc die is easy to make Single Pass process unlike rolling Large amt. of reduction possible Brittle materials are easily extruded Forward Hot Extrusion a. Direction of flow of material is same as ram b. Friction is imp. Due to relative motion btw. Hot billet and cylinder walls i. Lubes are used to reduce this friction 2. Backward Hot Extrusion

     1.

a. Ram compresses material against the container, forcing material to flow backwards through the die in the ram b. Billet remains stationary-no friction c. Not used extensively due to problem of handling extruding material coming out through the moving ram 3. Impact Extrusion (Backward Cold extrusion) a. Extrusion occurs due to impact force of punch b. Slug for making component is kept on the Die. 4. Hydrostatic Extrusion a. Billet is compressed from all sides by liquid rather than ram b. Lube is not needed due to presence of liquid. Also compression is more uniform. Pressure range is 1110-3150 MPa. c. Brittle materials like grey cast Fe can be extruded d. Set-up is very important. Billet must be tapered to prevent water leaking. Buckling chance is reduced. Ductility is increased. e. Not used much due to complicated equipment, work prep, long cycle times and dangers of working with hot, high pressure liquid. Wire Drawing: aim is to get wire from rod of > diameter Wire has circular cross-section with small diameter so it’s flexible. It is a cold working. Material drawn must be ductile. Wire Drawing Machine:     

Die is of conical shape. Multiple dies may be used End of rod is reduced to conical shape to insert through die opening End is gripped on other side with gripper and pulled through the die Wire thus drawn is coiled in a reel Die/s are well lubed

Bar Drawing:   

Involves stock too large in cross-section (d=1-10 cm). Must be drawn straight. Single draft operation- only one die opening is used Beginning stock has large dia and is a straight cylinder

Rod Drawing:  

Dies are bigger than for wires as rod is > than wire If rod drawn is in coiled form, it is straightened and cut.

Tube Drawing:  

Mandrel of requisite diameter is used to form internal hole. Remaining process is similar to bar drawing

Sheet Metal Operations: Sheet is a plate with thickness < 5mm. Some ops areSTRESS INDUCED Shearing

OPERATIONS Shearing, Blanking, Piercing, Trimming, Shaving, Notching, Nibbling

Tension Compression Tension and Compression

Stretch- Forming Ironing, Coining, Sizing, Hobbing Drawing, Spinning, Bending, Embossing, Forming

1. Shearing: Sheet is brought to plastic stage by pressing it btw. two shearing blades so that fracture occurs at cutting points. 2. Blanking: Removing a portion of the material from the stock by a punch. Removed material is called Blank and used as work piece. 3. Punching: Identical to Blanking but punched out piece is scrap. 4. Shaving: removal of thin strip of metal along the edge to obtain smooth and straight edges. 5. Slotting: Punching but rectangular holes 6. Notching: Punching edge of sheet. Forms a notch in the shape of the punch. 7. Nibbling: Punching overlapping slits/holes to cut out a larger shape 8. Lancing: Creating a partial cut such that no material is removed. Material left can be bent to form a shape like tab/vent/louver 9. Slitting: Cutting straight lines in the sheet 10. Parting: Separating part from the sheet, by punching material btw. the parts Ironing Process: If thickness of sheet as it enters die cavity > clearance btw. punch and die, thickness will be reduced. This effect is called ironing. It produces cup with constant wall thickness. < the clearance, > the ironing. Spinning: axially symmetrical part is gradually shaped over rotating mandrel using a rounded tool or roller. Used in automobile parts, utensils, aerospace parts. Embossing: Creates indentations in sheets, like raised lettering or strengthening ribs. Coining: Squeezing operation. Metal flows into cavity btw. pinch and die. Coins, medals etc. JOINING: Comprises large no. of processes to assemble parts into a complex component. Parts meet at joints. Joints transmit/distribute forces generated during service from one part to another. Process of joining called fabrication. MECHANICAL Bolts, screws- temporary Rivets, stitches, staples, shrink fits- semi temporary

ADHESIVE Less strength Used for Thin sheets

WELDING,SOLDERING, BRAZING Permanent joints High Strength

WELDING: Process of joining two metal pieces using coalescence  

Fabrication process that uses high temp. to melt and fuse parts together Pressure can be used to aid or even used exclusively to produce welds

Types of welded joints: Butt Joint, Corner Joint, Lap Joint, Tee Joint, Edge Joint

Edge prep for butt welds: Single (Square, Bevel, V, J, U), Double(all except square) Types of welding positions: Groove weld (Flat, Vertical, Horizontal, Overhead), Fillet weld (Same) Types of Welding: Arc, Gas, Resistance, Projection, Flash, Upset, TIG, MIG 1. ARC WELDING  Arc generated btw. two conductors of electricity  Current flow occurs when separated by small gap  This causes arc(plasma) formn btw. electrodes  Heat of 6000○ C  e-s collide with ionized gas particles btw. electrodes thus continuous flow of arc Equipment: AC/DC machines (transformer+ engine driven alternator), electrode holder, electrode, safety equipment, metal table. Transformer is used in AC welding. Rectifier used to supply DC power. DC welding preferred due to better heat control. Electrode: Consumable and Non-consumable. Consumable electrodes melt along with weld metal. Molten metal from electrode and base material mix and solidify. Electrode is moved constantly to maintain constant arc length. Electrode can be bare or coated. Purpose of coating in electrodes:  Coatings give off inert gases which shields molten metal pool  Provides flux which lowers cooling rate and avoid cracking  Stabilisation of arc Manual Metal Arc Welding (MMAW):  Also known as shielded metal-arc welding  Extensively used in India, Cheap equipment  Welds can be made in any position  Both AC, DC source works. I=50-500A. V=20-40V.  Slow Speed due to low deposition rate  Wastage in form of unused end of electrode, slag, gas.  Chance of slag inclusions and moisture pick-up in coating 2. GAS WELDING  Also called oxy-fuel gas welding  Heat is derived from combustion of gases like oxyacetylene with O2  Fusion welding process where joint is completely melted to get fusion Equipment: Pressure Regulators, O2 hose+ cylinder(black), Acetylene hose+ cylinder(Red), needle valves, torch. Types of flame: REDUCING/CARBURIZIN G