ISyE 415 Midterm 2
COLLET
Pressed into a "sleeve" to hold smaller workbar
Workholding Methods - Collet
Pressed into a "sleeve" to hold smaller workbar
Cutting Condition - Speed (v)
Primary Motion
DRILL PRESS
machine tool for drilling holes, set on a fixed stand
Positional Weight
the sum task A's time and the times of all tasks with A as a predecessor -First task in process will have highest positional weight
Conventional abrasives
aluminum oxide or silicon carbide
Boring option - Rotating workpiece
cantilevered boring bar feeds into it
Advantages of Metal Machining
Can make complex part geometries, wide variety of shapes, hold tight tolerances, and smooth surface finish
Process Description - Thermoforming Process
-A shaping process in which a thermoplastic sheet is heated to its softening point and then pressed against the contours of a mold and allowed to cool until it retains the shape of the mold -Vacuum, air, or mechanical means used to press the heated sheet against the mold
Process Description - Rotational Molding Process
-A thin walled metal mold is made in two pieces and is designed to be rotated about two perpendicular axes -A pre-measured quantity of powdered plastic is placed inside the warm mold. -The mold is heated and rotated continuously about the axes. The powder tumbles against the mold and fuses the powder without melting it -Trash cans, buckets, and plastic footballs can be made by this process
GATE
-After Runner & before Mold
RUNNER
-After Sprue & before Gate
Description - Reaming
-An operation that enlarges and more accurately sizes an existing hole -Improves surface finish & tolerance
Electrical Discharge Machining - Advantages
-Any level of material hardness can be cut -High accuracy and good surface finish are possible, no cutting forces are involved -Intricate shaped cavities can be cut with modest tooling costs -Holes complete in one pass
Vertical Machining Centers - Disadvantages
-As work piece size increases, it becomes more difficult to conveniently look down into the cut -Extensive chip build up obstructs view of the cut -On large verticals, head weights and distance from the column can cause head drop, loss of accuracy and chatter -Not suitable for large, boxy, or heavy parts
A Perspective on FMS Adoption - Lessons
-At one time, the answer to the productivity crisis was believed to be in automation. However, the answer lies in organization and management and not in technology and automation alone. -Automation can support these strategies, but relying on automation alone typically leads to glorious failures. Companies also learned that automated systems require more planning, analysis, modeling and simulation... here is where Industrial Engineers provide a lot of value.
Honing - Facts
-Creates a highly precise and uniform surface -Minimizes heat and distortion with lower cutting speeds than grinding -Lubricants are used to flush chips and remove heat -Surface finish can be controlled by the type and size of abrasive used, pressure, and speed Produces a cross hatch surface pattern
Slab milling
-Cutter is longer than the width of the cut •Cutters may have straight or helical teeth, helical teeth are preferred
Advantages of SINGLE POINT TOOL
-Design & Fabrication is simple & less time consuming -Cheaper
Cutting Fluid - Common Problems
-Difficult to deliver to point of cutting action -Possibly solved by: Some drills have internal holes that allow cutting fluid to be pumped to the drill point OR "Pecking" procedure - Periodically withdrawing the drill from the hole & clearing the chips
Horizontal Machining Center - Disadvantages
-Difficult to load and unload large, flat, plate type work pieces -High thrust must be absorbed by tombstones, fixtures, or right angle braces -Heavy tools can deflect -Generally more costly
Conventional or Up Milling
-Direction of cutter motion opposite of feed direction •Piece is fed against the rotation of the tool •Maximum chip thickness is at the end of the cut as the tooth leaves the workpiece surface •Tooth engagement is not a function of the workpiece surface characteristics •Starting forces are lower, produces a slightly wavy surface
Centering (or center drilling)
-Drills a starting hole -Accurately establishes location for subsequent drilling
Flute
-Drills have two spiral flutes that act as passageways for extraction of chips from hole -sharp slots that corkscrew upwards along the length of a milling bit. They are responsible for doing the cutting work when the bit is spinning
Thread Designation - Ex: 3/8 - 16
-First Value: The nominal size of the OD in inches -Second Value: The number of threads per inch
Types of End Mills
-Flat (square) end mills -Ball nose mills -Hollow end mills -High speed end milling
Products Made by Injection Molding
-For thermoplastics, pellets or powder material heated above the melting point. Mold is at a cooler temperature than the barrel. 2-6 cycles per minute are possible -For thermosets, liquid or pre-formed material heated just enough to allow material to flow. Mold is at a hotter temperature, high enough to cure the parts. Cycle times range from 1-5 mins
FMS Components
-Hardware components •Workstations: CNC machines (typically) •Material handling system: Conveyors, Automated Vehicles •Central control computer: To coordinate the activities of the components for smooth operation -Software and control functions -Human labor
ELASTOMER
-Have extreme elastic behaviors when subjected to small mechanical stresses -Manufacturing processing similar to thermoset plastics -Heating & cross-linking -No reheating possible Examples: Polyurethane, silicone rubber
Polymer Types - Elastomers (rubbers)
-Have extreme elastic behaviors when subjected to small mechanical stresses -Manufacturing processing similar to thermoset plastics =Heating & cross-linking =No reheating possible -Examples: Polyurethane, silicone rubber
Three ways to stimulate cross-linking
-Heat -Catalyst -Mixing of two chemicals
HOT-RUNNER MOLD
-Heaters are placed to keep the sprue & runner material melted during solidification of the parts
Hot-Runner Molds
-Heaters are placed to keep the sprue & runner material melted during solidification of the parts
Disadvantages of SINGLE POINT TOOL
-High wear rate -High friction/temperature (can lead to low precision) -Low Material Removal Rate
DEPTH OF CUT
-How far into workpiece the cut will go -Used for many cutting calculations
Layouts of Automated Production Lines
-In-line layout -Circular around a dial indexing machine
Polymer Types - Thermosetting polymers (thermosets)
-Initial heat softens material, allows it to flow -Higher temperatures produce a chemical reaction (cross-linking) =Material hardened into a solid -Reheating causes degradation & charring - NOT able to re-melt -Examples: Melamine formaldehyde, glass filled polyester
Chemical Machining - Advantages
-Low capital cost once basic equipment is installed -Many work surfaces can be machined simultaneously -No cutting forces, so no distortion or thermal stresses (good for delicate parts) -No edge deburring
Lapping - Facts
-Low speed and pressure result in finely finished surfaces of extreme flatness -Contact points between tool and workpiece are constantly changed through relative motions -The rotating tool is of soft metal, so the abrasive is pressed into it
CROSS-LINKING
-Material hardened into a solid -Higher temperatures produce a chemical reaction -Irreversible process where long chains of polymers are linked together
Thermoforming Process - Facts
-Material is heated by radiant or convection heat -Can produce simple shapes, with large radii and no undercuts
Lathe Specifications - Swing
-Maximum workpiece diameter that can be rotated in the spindle -Twice the distance between the center line of the spindle and the ways of the machine -Actual maximum size is smaller than the swing because the carriage & cross-slide assembly get in the way
ELECTRODE
-Medium for conducting or detecting electrical current -Used in EDM •Can use a new electrode for finishing and an old one for roughing -Can be constructed in different shapes -Poked down into workpiece -Can rotate to make circularly milled openings
DIELECTRIC FLUID
-Mineral Oil -Workpiece submerged in oil during electric discharge machining -At low voltage, acts as insulator
Tool Description - Reamer
-Multi-point, fluted, rotating cutting tool -May be adjustable to cover large range of hole sizes -Creates close tolerance holes
Description - Knurling
-Produces regularly shaped roughness on surfaces. Generally used for non-slip surfaces, such as knobs or grips -Uses a wheeled tool that imprints the pattern of the tool on the workpiece; not technically machining since material is not removed
ROUGHING
-Remove large amounts of material quickly -One or more -Faster feeds & greater depths (0.1 to 0.75 inches) -Lower speed
Drilling - Common Problems
-Rotating chisel edge wanders over the surface at the beginning of the operation --> lose positional accuracy -Friction between the tool cutting edge & the workpiece, also from rubbing between the OD of the drill bit and the newly formed hole -Heat, temperature of both workpiece and tool rise
Description - Threading
-Similar to turning but at a faster feed rate -Produces a helical thread of uniform section on the internal or external surface of a cylinder or cone -Allows connection to other parts by a screwing operation -Requires multiple threading cuts (passes) to reach full thread depth -Positional relationship must be held constant between tool, workpiece and lead screw
Three types of Assembly line
-Single model line -Batch model line -Mixed model line
Polymer Types - Thermoplastic polymers
-Solid at room temperature -Viscous liquids when heated to a few hundred degrees -Can be heated and cooled repeatedly without significant degradation -Examples: ABS, nylon, acrylic, polycarbonate, polyethylene (HDPE, LDPE), polyvinyl chloride (PVC)
THERMOPLASTIC
-Solid at room temperature -Viscous liquids when heated to a few hundred degrees -Can be heated and cooled repeatedly without significant degradation -Examples: ABS, nylon, acrylic, polycarbonate, polyethylene (HDPE, LDPE), polyvinyl chloride (PVC)
Abrasive (Water) Jet Machining
-Sprays water at workpiece at an angle -Requires Hood & Exhaust system
Conventional Molds (for Thermoplastics)
-Sprue & runners are waste material -Can often be reground and reused •A portion of regrind goes into the mix
Horizontal Machining Center - Advantages
-Table indexing capability enables multiple sides of a work piece to be machined in one program & clamping -Chips drop out of the way during machining providing an uncluttered view of the cut and preventing re-cutting of chips -Operator's station is to one side of the column, providing good line of sight control -Pallet shuttle/exchange mechanisms are open, accessible, and easy to service
SPEED
-The speed of rotation of the milling cutter or of the workpiece (if on a lathe) -Measures the rate at which metal is removed perpendicular to the tool's travel -Referred to as Rotations Per Minute (RPM) is based off of the SFM and the cutting tool's diameter,
Computer-Integrated Manufacturing (CIM)
-The uniting of computer-aided design with computer-aided manufacturing. -link these CNC machines to improve coordination among these CNC machines. This was also coupled with growth in GT, which focused on parts similarity. This similarity in parts simplified the computer coordination of CNC machines in terms of planning, scheduling and execution.
Process Description - Transfer Molding
-Thermoset or elastomer material (pre-form) loaded into a transfer pot then pushed by a ram into the hot mold -Produces simple part geometries -Has a sprue & runner system (or cull) -Mold produces 1 or multiple parts per cycle
Process Description - Compression Molding
-Thermoset or elastomer material loaded into a hot mold =Powders or pellets =Liquid =Pre-form -Produces simple part geometries -No sprue & runner system -Mold produces 1 or multiple parts per cycle
Vertical Machining Centers - Advantages
-Thrust absorbed directly into the machine table during deep tool thrust operations such as drilling or pocketing -Ideal for large, flat plate work piece or single surface, three axis contouring -Heavy tools can be used without concern about deflection -Generally less costly
Chemical Machining - Disadvantages
-Undercutting of masked areas a problem -Sharp corners not possible -Workpiece material must be homogeneous -Disposal of chemical etchant is expensive -Operators require special protection against chemical spillage
SLURRY
-Used in Lapping -Mixture of abrasive material (e.g. silicon carbide and boroncarbide) suspended in water or oil. The vibration causes the abrasive particles in the slurry between the tool and the workpiece to impact the workpiece surface, causing material removal by micro-chipping
Surface Grinding
-Uses a grinding wheel to produce flat or formed surfaces. •Grinding wheel may be shaped to form a variety of workpiece geometries. Usually requires a coolant. •Produces a high surface accuracy as it removes small amounts of material. •Workpiece may be held by magnetic chucks, vacuum chucks or vises
Disadvantages of Metal Machining
-Very time consuming -Requires high skill level for operator/programmer -Creates waste -Doesn't change grain flow
Applicability of Compression Molding
-Widely used for thermosets & elastomers -Rarely used for thermoplastics -Produces electric plugs, sockets, pot handles, keypads, etc.
Process Description - Milling
-Workpart is fed past a rotating cylindrical tool (milling cutter) with multiple cutting edges (called teeth or flutes or inserts, depending on tool style) -Axis of rotation of tool is perpendicular to the direction of feed -Large variety of possible shapes/geometries
Advanced Machining Processes - Why we need advanced machining processes:
-Workpiece material is too brittle to be conventionally machined without damage -Workpiece is too flexible or slender to withstand machining forces -Shape of the part is too complex -Surface finish and dimensional tolerance requirements cannot be obtained by other processes -Temperature rise during processing and residual stresses developed are not acceptable
Electrochemical Machining - Disadvantages
-Workpiece must be electrically conductive -Equipment is expensive -Tooling costs are high
Electrical Discharge Machining - Disadvantages
-Workpiece must be electrically conductive -Process is slow, especially if good surface finish and accuracy are required -Dielectric vapor can be dangerous -Electrode (tool life) is limited, wire scrapped after one pass -Heat Affected Zone (HAZ) near cutting edges
EJECTOR PINS
-components used to (automatically) remove the part from the mold in an injection molding process -Eject the part when finished -Leave impressions on hot part
Batch Model Line
-produces more than one model, but in batches (changeover needed in between)
Automated Production Line Two Basic Types
1.Lines that perform processing operations •Example: transfer line 2.Lines that perform assembly operations •Example: automatic assembly machine
Minimum number of workstations Formula
=Total work time/Required Cycle Time
Start of Boring process requires?
A hole in workpiece
THROUGH HOLE
A hole that goes completely through the workpiece
Lapping - Process Description
An abrasive process in which a rotating lap charged with loose abrasive slurry removes small amounts of material from flat metallic or non-metallic surfaces
Description - Tapping
An operation that produces uniform, internal, helical threads in an existing hole with a multi-point tool
Process Description - Extrusion Blow Molding
A tube of thermoplastic material (parison) is extruded, a die shuts immediately sealing one end, then air pressure is used to inflate the tube to match the inner contours of the mold
Boring & Boring Mill - Surface Finish
Accurate internal cylindrical surface or conical surface, less accuracy than what can be achieved on a lathe
Counterboring
Adds a "step" leading in to the hole
Countersinking
Adds a tapered lead-in to the hole
Rotary tables
Allow multiple pieces to be ground simultaneously
Components of Lathe - Feed rod
Allows continuous feed motion
Electrochemical Machining - Advantages
Any level of material hardness can be cut, no physical contact with workpiece, so no cutting or thermal stresses, long tool life, no edge burrs, holes complete in one pass
Dimension - A
Approach allowance
Ranked positional weight technique
Assign tasks sequentially to stations in the order of the ranking making sure the precedence constraints are not violated.
Abrasive materials hardness
Considerably harder than conventional cutting tool materials
SINGLE-POINT TOOL
Consists of only one main cutting edge that can perform material removal action at a time in a single pass
MULTI-POINT TOOL
Contains more than two main cutting edges that simultaneously engage in cutting action in a pass
MASKING
Covering some surface of a part during Chemical Milling to protect it from etchant
Description - Drilling
Creating a hole with a multi-point, fluted, cutting tool (drill); drill held in the tail stock of the lathe. May be followed by boring to improve the accuracy and surface finish -Most common hole making process
CURING
Cross-linking of Thermosets -NOT DRYING - No liquid removed -Heated, Catalyst, or Mixing of chemicals
PRE-FORM
Crucial step that helps to improve the performance of the finished part. The pre-formed part is inserted into the heated mold -Plastic preform is the process of forming sliced fiber threads, usually made of glass, into mats that will serve as reinforcements for a plastic molding procedure -"Mini" version of final product
Describe Typical Parts Machined on a Lathe
Cylindrical parts or features with rotational symmetry
Gun Drill
Deep hole drilling. Historically used to bore gun barrels. Requires slow feeds and high cutting speeds. Hole depth to diameter ratio can be 300 or more
Radial Drill
Designed for large work pieces that are not feasible to move. The spindle is mounted on a moveable area that can be swung over the work piece
Dimension - Theta
Drill point angle
Lathe Cutting Operations - Multipoint tools/Special Tools
Drilling/Form Turning, Cutoff, Kurling
FLASH
Excess material on a moulded part, forming a thin fan where two parts of the mould meet. -Minimal in blow molding if trimming works well -Potential defect in injection molding
Machining - Finishing Cuts
Final dimensions, tolerances, surface finish, slower feeds + smaller depths, higher speed
Cutting Condition - Cutting Fluid
For cooling & lubrication
Purpose of Workholding Methods
Grasp the work, center & support it in position along the spindle axis & rotate it
Tapping - Equipment Options
Hand tap, drill press, lathe, tapping machine, mill
Trepanning Drill
Has no dead center and leaves a solid core of metal. The core acts as a continuous center guide at the point where the cutting is done.
Crankshaft Drill
Have good centering ability, and because chips tend to break up easily, these drills are suitable for producing deep holes
Common Problems - Tapping
Heavy friction (need cutting fluid!), difficult chip removal, taps easily broken
Flexible Manufacturing Systems
Highly automated cell, consisting of a group of processing stations (usually CNC machine tools), interconnected by an automated material handling and storage system, and controlled by an integrated computer system
CHUCK
Holds cylindrical work piece
Workholding Methods - Faceplate
Holds rectangular shape
FACEPLATE
Holds rectangular work piece for turning operation
Workholding Methods - Chuck
Holds spherical shape
Components of Lathe - Tailstock
Holds the center
Components of Lathe - Tool post
Holds the tool
Components of Lathe - Carriage
Holds the tool post and moves it (on the ways) along the length of the work piece
Superfinishing
Honing with very light pressure and a short stroke
UNDERCUT
In Chemical Milling, part of workpiece under mask becomes removed
A Perspective on FMS Adoption p2
Industry has found more productivity improvements via strategies such as Just in Time, Total Quality Management, Lean Manufacturing, Quick Response Manufacturing
Boring & boring Mill - Applications
Large and heavy parts, generally with small length to diameter ratio
LATHE
Machine for shaping metal by means of a rotating drive which turns the piece being worked on against changeable cutting tools
MILL
Machine tool in which a horizontal arbor or vertical spindle rotates a cuttingtool above a horizontal table, which is used to move a workpiece
FINISHING
Machining a surface to size with a fine feed produced in a lathe or milling machine
Grinding Wheels
Made with conventional abrasives. Note that each wheel has a specific grinding face; grinding on other surfaces is improper and unsafe
SPRUE
Main channel through which molten plastic enters system -Between Nozzle & Runner
Lathe Specifications - Maximum distance between centers
Maximum length of a workpiece that can be mounted between the headstock and tailstock centers
Gang Drill
Multiple spindle drills that allow flow line material handling.
Multi-spindle
Multiple spindles operate simultaneously for faster production rates. Long setup times and/or dedicated tooling are common.
Extrusion Die Geometries
Nonuniform recovery of the part after it exits the die. (Piece widens more than die diameter)
Turret Drill
Overcomes the floor space restrictions of a gang drill by using a turret as described for use on a lathe
Cutting Condition - Depth of Cut (d)
Penetration into workpiece
Types of Production Lines: Product Variety
Production lines can be designed to cope with variations in product models so long as product variety is limited
Melt Spinning Process Use
Production of polymer fibers used in clothing, carpeting, fabrics, rope and packaging
Machining - Roughing Cuts
Remove Large amounts of material quickly, faster feeds & greater depths, lower speeds
Coated abrasives Examples
Sandpaper (developed in the 16th century) and emery cloth
Cutting Condition - Feed (f)
Secondary Motion
Basics of Turning
Single point tool, Rotating cylindrical part, tool fed parallel to access of rotation, Lathe = Tool
Description - Forming
Specially designed tools are moved radially inward to machine the part. Generally used for specialty products, with unique surface characteristics, quickly and easily
Water Jet Machining
Spray water directly at workpiece to cut it -Uses Pump, Accumulator, Control, Hydraulic Unit attached to an Intensifier
Mold Features for Injection Molding
Spruce, Main Runner, Branch Runner, Part
Polymer Defintion
Substance that has a molecular structure consisting chiefly or entirely of a large number of similar units bonded together, e.g., many synthetic organic materials used as plastics and resins.
Column-and-Knee Type Mills - Function of Knee
Supports the saddle and gives the table vertical movement
Traverse grinding
Table reciprocates longitudinally and is fed laterally in the direction of the spindle axis
FRIABILITY
The ability of abrasive grains to breakdown/fracture into smaller pieces. This enables self-sharpening characteristics in these tools -Why the cracks work as a means to sharpen in bonded abrasives
SURFACE FINISH
The amount of roughness left on the surface of a part after processing
Chisel-point Drill
The function of the pair of margins is to provide a bearing surface for the drill against walls of the hole as it penetrates. Drills with four margins (double-margin) are available for improved drill guidance and accuracy. Drills with chip-breaker features also are available.
DEBURRING
The process of removing burrs from the edge of material that has been cut.
Increase in Machining and Finishing Cost as a Function of Surface Finish Required
This is the main reason that the surface finish specified on parts should not be any finer than necessary for the part to function properly.
Components of Lathe - Ways
Tracks which guide the carriage
PARISON
Tube like shape made of plastic material prepared for use in blow moulding -Raw Material for Blow Molding
Lathe Cutting Operation - Single point tools
Turning (or straight turning), Facing, Taper turning, Contour turning, Chamfering, Boring, Threading
Thermoplastics Raw Material
Typically pellets or powders
4-axis Machining - What is the 4th-axis?
Typically rotation about either the x-axis or the y-axis
Components of Lathe - Lead screw
Used for cutting of threads
Chemical Mechanical Polishing (CMP) Process
Used widely in the manufacture of silicon wafers and integrated circuits and also is known as chemical-mechanical planarization. For other materials, more carriers and more disks per carrier are possible.
Plunge grinding
Wheel is moved radially into the workpiece as it is when grinding a groove
Horizontal boring mill
Workpiece is stationary; cutting tool is mounted on a spindle and can move vertically and longitudinally
HEAT AFFECTED ZONE (HAZ)
Workpiece properties have changed & have gone through a head treatment process - likely creates brittleness (cracks/breakage likely) -Associated with Electronic Discharge Machining (EDM)
Vertical boring mill
Workpiece rotates about a vertical axis, as the cutting tool is fed into the work piece
Can drilling be done on a lathe?
Yes, drilling can also be done on a lathe with a rotating workpiece and a drill mounted in tailstock
BLIND HOLE
a hole that is reamed, drilled, or milled to a specified depth without breaking through to the other side of the workpiece
Components of Lathe - Headstock
contains the drive mechanism (motor and spindle)
Column-and-Knee Type Mills - Head
contains the spindle and cutter holders
Super abrasives
cubic boron nitride (CBN) or diamond
Mixed Model Line
multiple models are intermixed rather than produced in batches (negligible changeover)
MACHINE TOOL
power operated, non-portable and valuable machine that can perform multiple machining operations by remove excess material from a pre-formed blank with the help of a suitable cutting tool.
Single model line
produces only one model and there is no model variation
FEED
rate at which the cutting tool crosses the workpiece; it's the rate at which metal is removed in the direction of that tool's travel
Column-and-Knee Type Mills - Over Arm
used on horizontal machines to adjust arbor lengths
MATERIAL REMOVAL RATE (MRR)
volume of material removed per unit time
Dimension - w
width of cut
Boring option - Boring bar rotated
workpiece fed past tool
Importance of Polymers
•Can be molded into intricate geometries; net shape processing •Attractive material properties -Low density, good strength-to-weight ratios, high corrosion resistance, low electrical & thermal conductivity •Cost competitive with metals •Generally require less energy for processing
Process Description - Broaching
•A cutting operation where accurate sizing and finishing of a surface or shape is achieved by a single pass of a multi-point cutter (broach) •Machined surfaces are parallel to the axis of tool motion •Generally used to machine internal and external surfaces (holes, keyways, gear teeth) •Cutting fluids are recommended •Often faster than milling •Produces tight tolerances and good surface finishes
Barrel Tumbling
•A finishing process wherein abrasive media, the workpieces, water and a cleaning compound are rotated in a drum -For the purpose of cleaning, descaling, deburring and burnishing -Tumbling creates relative movement between the workpieces and abrasive media -May use a wide range of synthetic, metallic or natural finishing media -Typically requires a cleaning or rust inhibitive compound
Honing - Process Description
•A low velocity abrasive machining process in which a bonded abrasive stone removes small amounts of material by simultaneous rotating and reciprocating motion between the tool and the workpiece. The workpiece generally rotates and the tool reciprocates.
Grinding Process
•A material removal process that abrades or wears away a workpiece through the use of friction, generally through the use of an abrasive wheel •Material removal is minimal; this is generally a secondary operation •Frequently used for metals but allows material removal from nonmetallic workpieces
Extrusion
•A plastic shaping process in which a continuous workpiece is produced by forcing molten thermoplastic material through a shaped die •A continuous high volume process used to make sheets, tubes & bars •The hot workpiece is carried along a conveyor, cooled and cut or coiled •For thermoplastics, the molded material is injected through a cooler extrusion die, for thermosets, the material is injected through a die followed by an in-line curing oven
Centerless Grinding
•A process that relies on the relative rotation of a grinding wheel and a regulating wheel to rotate the workpiece. •Process is most efficient for through-feed grinding situations. Workpiece does not require chucking, mounting or locating between centers
Cylindrical Grinding
•A process that removes material from the exterior of a cylindrical workpiece •Grinding wheel and workpiece rotate in opposite directions while in contact •Workpiece is mounted between centers and is rotated by a workpiece holder (Abrasive wheels of various sizes for straight, tapered or formed workpieces) •Between centers=two small tapered items holding •Usually requires a coolant Cylindrical grinding can also form shapes like plunge or form grinding
Production Line Operation
•A series of workstations arranged so the product moves from one station to the next; at each location a portion of the total work is performed -Production rate of the line is determined by its slowest station (called the bottleneck station)
A Perspective on FMS Adoption p1
•Although FMSs were popular at first, these systems failed to live up to their expectations and have not been the solution to the "productivity crisis" •Proposed benefits of FMS... -Flexibility (both in number of parts and volume) -Graceful degradation in face of failures -Higher utilization of capital equipment -Increased productivity, lower WIP, shorter lead times •Instead... -High capital investment posed high risks -Inadequate experience to ensure smooth installations -Many unanticipated problems in comparison to stand alone machines -No appreciation of need for performance analysis: interconnection between tooling, fixtures, AGVs, mix of parts, failures... FMS production rate would be only 30% of planned rate!!!
Typical Parts Abrasive Machining and Finishing
•Any part requiring high dimensional accuracy and surface finish such as ball and roller bearings, piston rings, valves, cams, gears, tools and dies
The Line Balancing Problem
•Assign tasks to workers so that all workers have an equal amount of work •Total work to be accomplished on the line = the total work content •Total work content can be divided into minimum rational work elements -Each element is concerned with some small portion of the total work content Minimum rational work elements must be grouped into logical tasks and assigned to workers at stations
Process Description - Peripheral (Plain) Milling
•Axis of cutter rotation parallel to the workpiece surface •Cutters may have straight or helical teeth, helical teeth are preferred
Description - Thermoplastics
•Can be reheated, melted multiple times -But, distinction made between virgin material and regrind (material that has experienced thermal cycling) •Thermal aging -Slow, chemical deterioration when subjected to continuous, elevated temperatures below Tm
Elastomers
•Capable of large elastic deformation when subjected to low stresses
Process Description - Electrical Discharge Machining (EDM) - Part 2
•Creates a heat affected zone •Can use a new electrode for finishing and an old one for roughing •Wire EDM replaces the electrode with a continuous wire •Creates heat affected zone where workpiece properties have changed & have gone through a head treatment process - likely creates brittleness (cracks/breakage likely)
Face Milling
•Cutter mounted on a spindle with axis of rotation perpendicular to the workpiece •Leaves feed marks on surface
Why Are Station Task Times Different?
•Different work elements require different times •When grouped together and assigned to workers, the service times will not be equal due to the variable nature of element times •Precedence constraints = restrictions on order in which work elements can be performed •These and other limitations make it virtually impossible to achieve perfect balancing Some workers will end up with more work, while other workers will have less
Process Description - Electrochemical Machining
•Direct electric current is used to speed up the rate at which the material dissolves using a chemical etchant
Additives - List
•Fillers •Plasticizers - Keeps material soft •Colorants •Lubricants •Flame retardants •Cross-linking agents •UV light absorbers •Antioxidants
Laser Beam Machining (LBM)
•Generally referred to as laser cutting •A high energy cutting process in which the work material is melted, vaporized and/or combusted by a narrowbeam of coherent light supported by a coaxial supply of cutting gas -Produces small precision cuts or holes -Usually produces rough metal surfaces, however, composite fabrics are cleanly cut -Has good repeatability -Leaves a narrow heat affected zone, and in some cases heat treatment results
Internal Grinding - General Uses & Requirements
•Generally used for finishing bearings and bushings (components that reduce friction between moving parts in a mechanical product) -Requires a coolant and provides a high degree of surface finish
Blow Molding - Facts
•High production rates, low costs •Used for thin walled hollow parts like plastic milk and soft drink bottles •Detailed features like screw threads can be produced •Molds are expensive •Parting lines are present, flash is minimal if trimming process works well
Overview of Production Lines
•Important class of manufacturing system for large quantities of identical or similar products •Total work divided into small tasks, and workers or machines perform these tasks with great efficiency •Examples: -Assembled products (e.g., automobiles and appliances) Mass produced machined parts (e.g., engine blocks and transmission housings)
FMS Potential Benefits
•Increased machine utilization •Fewer machines required •Reduction in floor space •Greater responsiveness to change •Reduced inventory •Lower manufacturing lead times •Reduced direct labor requirements & higher labor productivity •Opportunity for unattended production
Limitations of Polymers
•Low strength relative to metals & ceramics •Low modulus of elasticity (stiffness) •Limited service temperatures •Some polymers degrade when exposed to sunlight or other radiation (UV Radiation) •Viscoelastic properties limit load bearing capabilities -If you apply a stress to a plastic, there is a delay in it returning to normal shape
FMS Applications
•Machining - most common application •Assembly •Inspection •Sheet metal processing (punching, shearing, bending, and forming) •Forging
Chemical Milling / Machining - Description
•Metal is dissolved with a chemical etchant. Parts of the surface can be protected by using a mask or tape or wax. -Etchants: sodium hydroxide, solutions of hydrochloric or nitric acid
Process Description - Electrical Discharge Machining (EDM) - Part 1
•Metal removed by intense heat of sparks (no chemicals used) •Workpiece and tool are submerged in a dielectric fluid (a mineral oil) •At low voltages, the fluid acts as an insulator •As voltage increases, a spark passes through the gap between the tool and the workpiece •The spark vaporizes some of both the workpiece and the tool
Applicability of FMS
•Might make sense if- -Parts currently produced in batches or in a manned GT cell -1 or more part families can be created -Parts have moderate volume (~5,000 - 75,000 parts/year) -Parts have moderate variety
Process Description - Injection Molding
•Molten polymer is injected into a mold cavity and held under pressure until cured or cooled •Utilizes a ram or screw type plunger to force molten plastic material into a mold cavity •Produces a solid or open ended shape conforming to the shape of the mold cavity •Ejector pins in the mold eject the part when finished •Creates a parting line, and leaves marks from the sprue and gate removal and by ejector pins •Mold is vented to allow air to escape (prevent trapped gas)
Automated Production Lines
•Multiple automated workstations connected by a parts transfer system that is coordinated with the station service time •Ideally, no human workers are on the line, except to perform auxiliary functions such as -Tool changing -Parts loading and unloading -Repair and maintenance
Assembly Line Design
•N distinct tasks that must be completed on each item. •Time to complete a task is a known constant, ti. •Goal is to organize tasks into groups, where each group of tasks is performed at a single workstation. In most cases, maximum time allocated to each work station is determined by the desired rate of production
Computer Functions in an FMS
•NC part programming: development of NC programs for new parts introduced to the system •Production control: product mix, machine scheduling, other planning functions •NC program download: part programs must be downloaded to individual stations •Machine control: individual workstations require controls, usually CNC •Work piece control: monitor status of each work piece, pallet fixtures, loading/unloading instructions •Transport control: control of work handling system •Tool management: Tool inventory, tool status diagnostics, tool transport -System management:compile management reports on performance (utilization, piece counts, production rates, etc.)
Applicability of Blow Molding
•Only used with thermoplastics •Makes thin-walled hollow parts -Bottles & similar containers •Typically very high production volumes
Applicability of Thermoforming
•Only used with thermoplastics •Produces trays, drawers, bathtubs, refrigerator door liners, blister packs, computer cases, cookie & candy trays, etc. •Medium to high production volumes
Group Technology
•Parts that are similar in geometry, function, and/or manufacturing processes are grouped together -Manufacturing done in one location (e.g. in a cell or FMS) -Part designers can use groupings to organize and standardize their work
Climb or Down Milling
•Piece is fed with the rotation of the tool (cutting forces hold the piece down) •Has a high initial cutting force •Better surface quality is produced •Should not be used when workpiece has a surface scale •Can be dangerous on a manual mill due to gear backlash
Tapping
•Produces uniform, internal, helical threads in existing holes -Requires an appropriate sized hole prior to the hole being tapped -Produces small chips, requires cutting fluids and frequent removal of tap from hole for chip removal
FMS Design Guidelines
•Production rate of system determined by bottleneck station •Number of parts in FMS à about 2 parts per server; make sure there are enough not to starve the bottleneck station -If WIP too low, production rate suffers; if WIP too high, lead time suffers
Cross-linking of Thermosets
•Referred to as 'curing' or 'setting' -NOT Drying. Drying is removing liquid. Curing has more going on
Chemical Milling / Machining - Process
•Residual stresses from prior processing are first relieved, surfaces are degreased and cleaned thoroughly, masking material is applied, exposed material is machined by etchants, parts are rinsed, masking is removed
Potential Injection Molding Defects
•Short shots •Flashing •Sink marks and voids •Weld lines
Chemical Blanking
•Similar to blanking of sheet metal, but material is removed by chemical dissolution rather than shearing -Used in burr free etching of printed circuit boards, decorative panels and thin sheet metal stampings
Description - Fillers
•Solid materials, powders or fibers •Possible reasons -Alter mechanical properties -Reduce cost -Improve dimensional stability -Improve thermal stability
FILLER
•Solid materials, powders or fibers •Possible reasons -Alter mechanical properties -Reduce cost -Improve dimensional stability -Improve thermal stability
Description - Thermosets
•Typical material properties compared to thermoplastics -More rigid -More brittle -Less soluble -Capable of higher service temperatures -Not capable of being melted (can degrade/burn)
Parts Made with Milling Processes
•Typical product features: slots, grooves, pockets, holes, gear teeth, and surface contours •Major types of milling: peripheral milling, face milling, end milling
5-axis Machining - What is the 5th-axis?
•Typically has table rotation about x & y •May have a rotating spindle head instead
FMS Capabilities
•Typically- -Mixed model production -Multiple automated workstations -Variable routings among stations
Trepanning
•Used for larger diameter through holes when machine power is limited •Machines a ring around the periphery, leaving a core in the middle
Internal Grinding - Description
•Uses a grinding wheel to produce formed surfaces on the interior of the workpiece -The workpiece is generally held on a rotating chuck as in a lathe and the tool rotates at high speeds (30,000 rpm)
End Milling
•Versatile capability to produce, pockets, angles, profiles and curved surfaces •Cutter (end mill) has a straight or tapered shank •Cutter rotates on an axis perpendicular to the workpiece surface •On some machines, it can be tilted to conform to machine tapered or curved surfaces
Applicability of Injection Molding
•Widely used for thermoplastics •Also used for thermosets & elastomers •Produces many components (for toys, electronics, cars, packaging, etc.). •Part size from a few ounces ® 50 lbs. •Economical only for large production quantities (because molds are expensive)
Applicability of Extrusion
•Widely used for thermoplastics and elastomers •Rarely used for thermosets •Produces tubing, pipes, hose, sheet, film, filaments, coated wire & cable, etc.
Applicability of Transfer Molding
•Widely used for thermosets & elastomers (rarely for thermoplastics) •Parts more intricate than compression molding, less intricate than injection molding •Works well for insert molding -Metal or ceramic insert placed into the mold cavity before the material is transferred
