Pulley Casting, Machining, Inspection, Mounting Plate Machining, NC 1, Study notes of Manufacturing Processes

Download Pulley Casting, Machining, Inspection, Mounting Plate Machining, NC 1 and more Study notes Manufacturing Processes in PDF only on Docsity! Shop Floor Operation Fundamentals  Engineering Drawing – describes a product to be made (size, shape, material, etc.) o Fabrication – applying a series of manufacturing processes (machining) o Assembly – combining other products together. Engineering Drawing often contains a parts list o Bill of Materials – shows individual items and their relationships  Route sheet – shows operations, sequence of operations, and resources  Task list – specifies assembly activities  Inspection – monitor parts to ensure that drawing requriemtns are being met  Part Inspection Report – documents inspectiosn  Flow Shop – where products are made on one or more flow lines o Flow line – a set of stations (machines, robots, humans) next to one another o each station assigned one operation (fabrication) and one or more tasks (assembly) o investigated with Switch Box – Assembly Lab  Job Shop - products are made by moving parts through different departments for processing. o Each department handles different processing o Batch – set of parts of the same type which are processed together o Work Order – a document which accompanies each batch  Specifies part type, process plan, release date, due date o Investigated with Pulley and Mounting Plate SB-A: Switch Box Assembly (Lab 1)  Precedence diagram – shows order tasks must be completed in  All items are made by assembly o Used when production volume is high  Five objectives for lines where stations are reliable but processing is not: o Maximize Throughput: Parts per hour (pph) o Minimize reject %: Number of good products off the line / hour o Minimize work-in-progress (WIP): avg. number of parts on line o Minimize line imbalance: B = 0: line perfectly balanced o Minimize idle time percentage: extent to which total capacity is utilized  Paced lines – each station allotted the same amount of time to complete task (cycle time) o Throughput – 1/total # of cycles o Reject %: - (# of rejects)/ CTOT o WIP – avg. work in progress – M (one item at each station) o B – Line imbalance –  Bj = total task time at station j for one unit  B is average time for all stations o D – Idle time % -  TTOT – total assembly time for part  Unpaced lines – stations operate independent of each other, moving parts at operator’s pace o Buffer queue – accounts for differences in total task time at each station o Two problems with unpaced lines due to buffer queues:  Blocked station – downstream buffer is full (station forced idle)  Starved station – upstream buffer is empty (Station forced idle) o For M stations operating for T minutes:  Throughput = (# departed items) * 60/T  R = Reject % = (# rejects) / (# departed items)  WIP – Work in progress -  Plot arrival and departure times, integrate under line  B = line imbalance = same as paced line  D = idle time =  Conclusions – paced lines work better where task time is close (predictable output) o Companies that need pre-determined number should use paced P-M: Pulley Machining (Lab 3)  Machining – cutting tool moved relative to stationary workpiece o Create almost any shape or geometric figure o Can be applied to almost all metals and alloys, and many other materials o Produce dimensions to very close tolerances o Produce very smooth finishes o Performed after “bulk deformation process”  Most machining performed on a lathe  Spindle – part affixed  Headstock – motor here rotates spindle  Tailstock – holds end of part opposite spindle  Tool post – holds cutting tool  Compound rest – holds tool post and cross slide, which move tool into workpiece (radially)  Carriage – moves tool parallel to workpiece (axially)  Manufacturing processes performed on lathes:  Three parameters for cutting: o Speed – how fast part surface travels past tool (surface feet per minute, sfpm)  Depends on rotational speed of spindle and diameter of part  We must set rotational speed to get desired speed o Feed – how much tool advances alongside part for each rotation (inches per rev, ipr) o Depth of cut – how much material is removed from the part each revolution (in)  Roughing pass – large depth of cut, remove material quickly  Finishing pass – shallow depth of cut, obtain final dimensions  Tapping – used on drill press to create internal screw threads  Broaching – multiple tooth cutting tool moved linearly through hole, creating a slot  Burrs are undesirable and unavoidable – remove with files, belts, brushes P-I: Pulley Inspection (Lab 4)  Specifications given in engineering drawings  Inspection – process where part attributes are examined for accordance with specifications  Inspection determines quality of product, provides info to improve manufacturing process  Direct measurement – measurement is taken and read with one instrument  Indirect measurement – measurement taken with one instrument, transferred to and read with another  Types of instruments: o Dial caliper – inside, outside, depth o Outside micrometer – thickness, outside diameter o Telescoping Gage – used w/ outside micrometer: inside diameter o Dial Indicator – w/ various fixtures: thickness, straightness, parallelism, roundness, flatness, runout o Gage blocks – used to check or calibrate other instruments, or indirect measurements o Optical comparator – check surface profiles and small dimensions  Projects shadow on a screen, measure image against reference lines  Often used with digital readouts  Disposition values – checked against drawing values  Part Inspection Report Form – records entire inspection procedure MP-M: Mounting Plate Machining (Lab 5)  See Pulley Machining (Lab 3) for details on machining  Milling o Common practice for machining prismatic items o Workpiece is moved relative to a rotating, multiple edge cutting tool o Setup:  Part affixed to work table  Work table sits in saddle  Saddle can move transversely  Part moved relative to tool  Vertical: tool attached to spindle  Horizontal: tool attached to arbor o Horizontal Milling Machines o Vertical Milling Machines o Three cutting conditions:  Speed (V)  Feed (f)  Depth of cut (d) o For measurement units, see Pulley Machining (Lab 3) o Instead of feed, feed rate (fr) is often used  Describes how much tool moves per unit time, rather than tool revolution  Commonly expressed in inches per minute (ipm) o See Pulley Machining (Lab 3) for information on Roughing and Finishing passes o Through holes are common component of prismatic items o Can be drilled  Alternatively, one can shear material by punching  Workpiece placed in die  Punch is brought down with force to shear material  Much faster than drilling  Waste produced is much easier to clean up MP-NC2: Mounting Place NC 2 (Lab 7)  Disadvantages of manual part programming: o Manual calculation and programming line by line are tedious, time consuming, and error prone o Validation takes a long time o Validation must be performed using the actual machine o NC programs are written for a specific machine o Programs are difficult to modify  CAM (Computer Aided Manufacturing) Part Programming o User specifies product geometry o Specifies tool path based on geometry o Part Program – set of coded instructions in non-equipment specific terms o Part programs are POST-PROCESSED to produce instructions on a specific machine o CAD (Computer Aided Design) Model generates product geometry  Validation can be done OFF-LINE (without actually using the machine)  CUTTING EDGE o Eight pre-defined views o Two coordinate systems  WORLD  View o Job – specification of how to create a part  Defining tool path requires  Specifying the necessary tool  View used in specifying tool path  Process – Tool and Tool Path together o Dashed lines denote movement through clearance plane MP-I: Mounting Plate Inspection (Lab 8)  Gaging – comparing the attribute of interest with one or more standards (gages) known to be acceptable or rejectable o Often referred to as Go-No Gages (go or no-go) o Does not give as much information as measuring o Much faster than measuring  Instruments: o Depth Micrometer – depth o Plug Gage – inspecting hole diameters  Two different diameters, one fits, one does not o Hardness Tester – resistance of a material to permanent indentation o Coordinate Measuring Machine – performs variety of inspection tasks  Can be controlled in four ways  Manual – operator physically moves probe, calculates measurements  Manual Computer-Assisted Control – operator moves, computer calculates  Motorized Computer-Assisted Control – operator uses joystick  Direct Computer Control – movement, recording, and calculation done automatically  Used for REVERSE ENGINEERING  See Pulley Inspection (Lab 4) for more information on disposition values and part inspection report forms. MP-W1: Manual Arc Welding (Lab 9)  Arc Welding – electric arc heats area between seams until they melt together o Electrode – Make items part of high-voltage circuit  Shielded Metal-Arc Welding (SMAW) o Flux – covers weld surface to prevent formation of oxides (melts during welding) o Slag – the hardened Flux left over on top of the weld o Shielding Gas – shields the electrode tip from oxygen during welding o Electrodes are consumable – they melt and become part of the weld pool o Filler Metal – additional metal added to a weld joint o Current typically ranges from 50-300 Amps o Power required is less than 10 kW o Simple and versatile welding o Equipment:  Power supply  Cables  Clamps  Electrode holder  Electrode o Angle – about 75 to 80 degrees o Distance – about 1/16 of an inch  Types of Joints and Welds o Double Fillet T-Joint used in this lab o Tack Weld – fusion weld applied to single point to hold pieces together during welding  Properties of welded joints o Fusion – the extent to which the items have fused together  Indicated by lack of discernable line between item and weld pool o Depth of Penetration – the depth to which materials have fused together o Appearance – Good weld bead is characterized by:  Uniform width  Smooth, even ripple pattern  Uniform fillet angle  Weldment – welded assembly  Two methods for striking an arc: o Tapping Motion method: tap against workpiece o Scratching Method: like striking a match  Welding Problems: o Excessive Penetration and burning – moving too slow o Thin bead, weak weld – moving too fast o Poor fusion and penetration – not enough heat due to short arc length o Excessive splatter and irregularly shaped bead – arc length too long F/PM: Sheet Metal Forming, Powder Metallurgy  Used to manufacture automobiles, aircraft panels, appliances, beverages  Benefits: o Good dimensional accuracy o High strength o Good surface finish o Low cost  Deep Drawing o Specialized forming process o Blank – a sheet of metal o Blank is placed over die o Blank is pushed into the die using a punch  One load (Fb) secures blank against blankholder  Separate load (Fp) actually forms the item o Blankholder – holds the blank against the die during the process  Material must be ductile enough to thin and elongate  Limiting Drawing Ratio – formability of a material for deep drawing o The larger the LDR, the higher the formability o Deep Drawing Test – determines LDR  Powder Metallurgy Processing – parts are produced from metal powders o Compacting  Powder placed into a die  Compressed into desired shape  Green compact – compressed part at this stage o Sintering  Heating the green compact  Heat to temperature below melting point, to bond particles via diffusion o Advantages:  Parts produced to final dimensions in one step  Unique alloys can be used  Inherent porosity of parts can be used for self-lubrication  Negligible scrap – about 97% of raw material is used EDM: Electrical Discharge Machining (Lab 13)  Two key process parameters: o Gap Voltage o Working Current  Electrical Discharge Machining: o Electric sparks are created and used to selectively remove material from a workpiece o Workpiece submerged in dielectric fluid o Electrode lowered until it is almost touching part o Electrode and workpiece connected to opposite ends of a DC power supply  Overcut – gap between the electrode and the part o Increases as material is removed o Tool needs to be fed into the workpiece at the required rate to maintain constant gap  Dielectric fluid kept in motion to wash away loose material  Spark Frequency and Discharge current o Increasing either decreases surface roughness, but increases machining time o Spark frequency is directly proportional to Gap Voltage  EDM is a non-traditional machining process used when o The material is extremely hard or brittle o Features are extremely complex, intricate, or small  Temperature rise or residual stresses in workpiece cannot be tolerated  EDM is often used to produce deep, small holes, stepped cavities, narrow slot, or shallow holes A: Geometric Dimensioning and Tolerancing  Two fundamental principles of manufacturing o No specification can be obtained exactly  Any manufacturing process can only be performed to a certain degree of accuracy o No two parts can ever be exactly the same  All manufacturing process is subject to process variability  Interchangeable Parts o Cornerstone of modern society o Only require that all parts are made within a certain range of specifications  Tolerances – acceptable bounds on what is desired when designing products  Dimensional Tolerances – specify bounds on any nominal dimension (length, width, etc.) o Bilateral tolerance – 1.00 ± 0.01 o Unilateral tolerance – 1.00 + 0.00, - 0.01 o Limit Dimensions – 0.99 – 1.01  Geometric Tolerances – used to specify bounds on geometry of part features o Form tolerances – bounds on flatness, parallelism, straightness, circularity, and cylindricity o Location tolerances – bounds on the position of features o Datum references – specified part edges and surfaces upon which tolerances are based.