ME/ISE 110 Weekly Lecture Notes

 

General Introduction

  1. What is manufacturing?
    1. Relative to product design
    2. Relative to machinery and tooling
    3. Relative to process planning
    4. Relative to materials
    5. Relative to purchasing
    6. Relative to manufacturing
    7. Relative to production control
    8. Relative to support services
    9. Relative to marketing
    10. Relative to sales
    11. Relative to shipping
    12. Relative to customer service
  2. The product design process and concurrent engineering
  3. Design for manufacture, assembly, disassembly, and service
  4. Manufacturing materials:
    1. Types of Materials:

                                                              i.            Metals

                                                            ii.            Ceramics

                                                          iii.            Polymers

                                                           iv.            Wood

  1. Properties of Materials:
    1. Physical
    2. Chemical
    3. Mechanical
    4. Acoustical
    5. Electrical
  2. Selecting materials
    1. Available shapes or forms
    2. Manufacturing properties
    3. Cost and availability
    4. Appearance, service life, and recycling
  3. Manufacturing processes:
    1. Processes defined

                                                              i.            Casting

                                                            ii.            Forming and shaping

                                                          iii.            Machining

                                                           iv.            Joining

                                                             v.            Finishing

                                                           vi.            Nanofabrication

                                                         vii.            Others

    1. Selecting manufacturing processes:
  1. Environmentally conscious design and manufacturing
  2. Computer-integrated manufacturing:
    1. Computer numerical control (CNC)
    2. Industrial robots
    3. Automated handling of materials
    4. Automated and robotic assembly systems
    5. Computer-aided process planning (CAPP)
    6. Group technology (GT)
    7. Just-in-time production (JIT)
    8. Cellular manufacturing (CM)
    9. Flexible manufacturing systems (FMS)
    10. Expert systems (ES)
    11. Artificial intelligence (AI)
  3. Benefits of CIM:
    1. Improved product quality
    2. Improved labor productivity
    3. Improved equipment productivity
    4. Lower cost of products
    5. Increased market share and more profit
  4. Computer-aided Process Planning (CAPP):
    1. Defined as systematic determination of the methods by which a product is to be manufactured, economically and competitively
    2. Process Selection Example(s)
    3. Process Chart (PC)
    4. Operation Process Chart (OPC)
    5. Benefits of CAPP

                                                              i.            Improved productivity

                                                            ii.            Lower cost of products

                                                          iii.            Consistency of process plans

                                                           iv.            Reduction in time required to develop a process plan

                                                             v.            Faster response to changes in the production parameters

                                                           vi.            Less clerical effort and paperwork

  1. Lean production and agile manufacturing
  2. Quality assurance and total quality management:
    1. Relative to a nation’s competitiveness
    2. Relative to a company’s competitiveness
    3. Relative to student projects
  3. Global competitiveness and manufacturing cost
  4. General trends in manufacturing
  5. Manufacturing resources management:
    1. Relative to facilities (labs and plants)
    2. Relative to machines and tools
    3. Relative to cribs, cabinets and storage
    4. Relative to personnel (students)
    5. Relative to general safety
    6. Relative to citizenship requirement

 

Sheet Metal (chapters 13 & 16)

  1. Rolling of metals (chapter 13):
    1. Rolling mills
    2. The flat rolling process can be cold and hot rolling resulting in a range of rolled products including:

                                                              i.            Structural shapes or sections

                                                            ii.            Bloom and billets

                                                          iii.            Plates, sheets and foils

                                                           iv.            Seamless tubes

    1. Other rolling processes include:

                                                              i.            Shape rolling

                                                            ii.            Roll forging

                                                          iii.            Skew rolling, Ring rolling

                                                           iv.            Thread rolling

                                                             v.            Rotary tube piercing

                                                           vi.            Tube rolling

 

2.      Sheet metal forming processes (chapter 16):

a.      Examples of products made of sheet metals

b.      Sheet-metal forming processes include:

                                                        i.            Shearing

                                                      ii.            Punching

                                                    iii.            Blanking

                                                     iv.            Die cutting (perforating, parting, notching and lancing)

                                                       v.            Fine blanking

                                                     vi.            Slitting

                                                   vii.            Steel rules

                                                 viii.            Nibbling

                                                     ix.            Bending, springback and compensation

                                                       x.            Hemming and seaming

                                                     xi.            Stretch forming

                                                   xii.            Deep drawing

                                                 xiii.            Spinning

 

  1. Sheet-metal processing calculations:
    1. Punch force = F = 0.7TL(UTS)
    2. Shearing force = F = K * Q * t * lultimate

                                                            (Q=perimeter; t = thickness; lultimate = ultimate shear strength; K=1.3)

    1. Bending force = P = (UTS)LT2/W
    2. Minimum bend radius = R = T(50/r –1), where r = tensile reduction of the sheet metal
    3. Blank development: L=total length of blank before bending

                        L= l1+l2+...+1/180)R1+2/180)R2 +...

                        (R= radius of neutral axis= +0.4t;  = inner radius of bend; t = thickness of sheet metal)

 

Metal Forming: Forging and Extrusion (chapters 14 & 15)

  1. Forging of metals (chapter 14):

            a) Cold forming versus hot forming

                        i. Recrystallization temperature defined

b) Open-die forging operations

                        i. Upsetting

                        ii. Cogging (drawing out)

                        iii. Piercing operation

                        iv. Cutting off

                        v. Bending

            c) Examples of open-die forged products

                        i. Large motor shaft, flange coupling & rings

            d) Forging machines

i. Hydraulic presses, mechanical presses, screw presses, hammers, drop hammers etc.

            e) Impression-die and closed-die forging

                        i. Workpiece takes the shape of die cavity

ii. Conventional (or flash) die forging

iii. Flashless forging (closed-die forging)

                        iv. Precision forging

                        v. Drop forging

                        vi. Press forging

            f) Fundamentals of closed-die forging design

                        i. Parting line

                        ii. Draft

                        iii. Corner radii

                        iv. Fillet radii

                        v. Pockets and recesses

2. Forging operations

a)     Coining

b)     Cold heading

c)      Piercing

d)     Rotary and tube swaging

3. Forging force calculations

a)   Forging Force for open die forging = F = Yƒπґ2(1 + 2цґ/3h)

(Yƒ = flow stress, ц = coefficient of friction, ґ = radius, h = height)

b)   Forging Force for closed-die forging = F = kYƒA

(k = multiplying factor, Yƒ = flow stress, A = projected area of the forging)

 

4. Extrusion and drawing of metals (chapter 15)

a)     Extrusion processes and equipment

b)     Drawing processes and equipment

 

Machining Processes and Machines (chapters 21, 22 & 23)

Fundamentals of machining (Chapter 21)

1. Mechanics of cutting and chip Formation

2. Cutting Tools:

            a) Basic geometry:

                        i. Side cutting-edge angle

                        ii. End cutting-edge angle

                        iii. Side relief and end relief angles

                        iv. Back and side rake angle

                        v. Nose radius

3. Machinability defined

4. Safety Practices in Machining

Cutting tool materials and cutting fluids (chapter 22)

1. Cutting tool materials:

a)     Plain-carbon steel

b)     Coated tools

c)      High-speed steel

d)     Cast cobalt alloys

e)     Carbides (tungsten, titanium, sintered cemented-carbide tips)

f)        Alumina-based ceramics and silicon-based ceramics

g)     Cubic boron nitride

h)      Diamonds

i)        Whisker-reinforced tool materials

2. Tool wear and tool life

3. Tool cost reconditioning of tools

4. Temperatures in cutting and cutting fluids:

a)     Necessary characteristics

b)     Types of cutting fluids (pure oils, mixed oils, soluble oils, water solutions & synthetic fluids)

c)      Importance and methods of application of cutting fluids

Machining processes used to produce round shapes (chapter 23)

1. The turning process:

            a) Lathe components:

                        i. Lathe bed

                        ii. Headstock

                        iii. Tailstock

                        iv. Carriage

            b) Lathe types:

                        i. Engine lathes

                        ii. Tool room lathes

                        iii. Turret lathes

                        iv. Vertical turning and boring mills

                        v. Automatic lathes

                        vi. Special purpose lathes

            c) Lathe cutting tools:

                        i. Turning tools

                        ii. Facing tools

                        iii. Cutoff tools

                        iv. Thread-cutting tools

                        v. Form tools

vi. Knurling tools

vii. Boring tools

            d) Methods of supporting workpieces in the lathe operations:

                        i. Holding the workpiece between centers

                        ii. Holding the workpiece in a chuck

                        iii. Mounting the workpiece on a faceplate

                        iv. Using a mandrel

                        v. Holding the workpiece in a chuck collet

            e) Lathe operations:

                        i. Cylindrical turning

                        ii. Facing

                        iii. Groove cutting

                        iv. Boring and internal turning

                        v. Taper turning

                        vi. Thread cutting

                        vii. Knurling

            f) Cutting Speeds and feeds:

i.  rpm = SFM/∏ * D

ii.rpm = SFM * 4/D

iii.                SFM = ∏ * D * rpm

Drilling machines and processes

1. Types of drilling machines

a)     Sensitive type (note parts, functions, and terminologies):

b)     Upright

c)      Radial

d)     Microscopic

e)     Deep-hole drill

f)        Turret drill

g)     Gang type

h)      Multi-spindle types

2. Drilling machine safety and rules:

a)     Hold work with clamps

b)     Wear your goggles

c)      Remove chuck key from chuck

d)     Never stop spindle with your hand

e)     Interrupt feed occasionally to break chips

f)        Use a brush to clear chips

g)     Remove burrs from a drilled work piece

3. Types of drill bits:

a)     Two-, three-, and four-flute twist drills (high-helix, low-helix and straight fluted)

b)     Center drills

c)      Step/sub-land drills

d)     Spade and gun drills

e)     Drill materials include: carbon steel, hss, cobalt high speed, and tungsten carbide.

4. Designation of drill:

Drills are measured with a micrometer or drill gage. They come in:

a)     Number size

b)     Letter size

c)      Fractional and decimal sizes

5. Drilling operations:

a)     Bit selection (based on the fact that hole making refers to drilling, reaming, counter-boring, countersinking, spot-facing, and tapping)

b)     Drilling speed and feed:  rpm=cs*4/d

c)      Tool holding (chuck, key, bit, taper drill shank adapters, drift)

d)     Work holding:  vises (standard, angular, & universal), v-blocks, step blocks, parallels, angle plates, strap clamps & t-bolts, drill jigs.

e)     Using the depth stop

f)        Breaking the chip

g)     Use of oil

h)      Breaking the hole

i)        Grinding the bit

j)        Using drill point gage

Machining Processes and Machines Used to Produce Various Shapes: Milling and Sawing (chapter 24)

1. Milling machine features

2. Milling Operations:

a)     Milling methods:

                                                        i.            Up milling (conventional milling)

                                                      ii.            Down milling (climb milling)

b)     Types of milling cutters:

                                                        i.            Plain (peripheral) milling cutter

                                                      ii.            Face milling cutter

                                                    iii.            Plain metal-slitting saw

                                                     iv.            Side milling cutter

                                                       v.            Angle milling cutter

                                                     vi.            T-slot cutter

                                                   vii.            End mill cutter

                                                 viii.            Form milling cutter

c)      Tool holders for milling:

                                                        i.            Arbors

                                                      ii.            Collets

                                                    iii.            Straight and tapered end-mill tool holders

d)     Cutting speeds and feeds in milling

e)     Types of milling machines

i.                    Column-and-knee type machines

ii.                  Bed-type machines

iii.                Planer-type milling machines

iv.                 Rotary-table machines

v.                   Machining centers (CNC)

vi.                 Profile milling machine

f)    Workholding devices and accessories:

                                                        i.            Vises

                                                      ii.            Jigs and fixtures

                                                    iii.            Rotary tables

                                                     iv.            Indexing heads

3. Sawing machines and processes

a) Types of sawing machines

                                                        i.            Hacksaws: Power and hand types (reciprocating saw)

                                                      ii.            Band saws (vertical and horizontal)

                                                    iii.            Circular saws (table saws and radial-arm saws)

                                                     iv.            Universal tilt frame cutoff

                                                       v.            Abrasive cutoff

                                                     vi.            Cold saw cutoff

b)  Vertical band machines:

                                                        i.            General-purpose with fixed worktable

                                                      ii.            Band machines with power-fed worktables

                                                    iii.            High tool velocity band machines

                                                     iv.            Large-capacity band machines

c) Applications of the vertical band machine:

                                                        i.            Conventional and contour sawing

                                                      ii.            Friction sawing

d) Using reciprocating and horizontal band cutoff machines:

                                                              i.      Cutting speeds

                                                            ii.      Saw blades and selection criteria

                                                          iii.      Saw teeth:  material, kerf, width, gage and pitch

                                                           iv.      Tooth forms: raker, straight and wave

                                                             v.      Work holding

e) Preparing to use and using the vertical band machine:

                                                              i.      Selecting a blade/using job selector

                                                            ii.      Welding band saw blades:  shear, grinder, welder/annealer

                                                          iii.      Installing the band

                                                           iv.      Adjusting band tension and tracking

                                                             v.      Setting saw velocity

                                                           vi.      Straight cutting

                                                         vii.      Contour cutting

f) Sawing machine safety:

                                                              i.      Eye protection

                                                            ii.      Hand protection

                                                          iii.      Blade, feed and speed selection

Metal Casting (Chapters 10 & 11)

Fundamentals of metal casting (Chapter 10)

1. Introduction

a)     Definition of the casting process

b)     Casting pure metals and alloys

c)      Effects of cooling rates

d)     Fluid flow and fluidity of molten metal:

                                                              i.            Viscosity

                                                            ii.            Superheating

                                                          iii.            Mold design and gating systems

                                                           iv.            Inclusions

e)     Shrinkage (relative to pattern development)

f)        Defects in metal casting: Metallic projections, cavities or shrinkage porosity, defective surface, incomplete casting, incorrect dimensions/shape, inclusions, deviation of the chemical composition from the desired one.

Metal casting processes (Chapter 11)

1. Classifications of Casting by Mold Material

            a) Permanent and nonpermanent (expendable) mold casting processes defined

            b) Green sand molds

                        i. Mold materials composition (sand, clay and moisture)

                        ii. Mold materials characteristics: permeability, green compression                              strength, moisture content, flowability, & refractoriness.

                        iii. Sand molding tools

                        iv. Patterns for sand molding

                        v. Allowances in patterns (shrinkage, machine finish and draft)

                        vi. Cores and core making

                        vii. Gating systems

                        viii. Sand molding machines

                        ix. Sand conditioning

            c) Dry sand mold casting

            d) Evaporative-pattern casting

            e) Plaster-mold casting

f) Ceramic-mold casting

            g) Shell mold casting

            h) Investment casting

            i) Graphite-mold casting

            j) Permanent-mold casting

            k) Evaporative pattern/full mold

            l) Die casting: hot and cold chamber types

            m) Centrifugal casting: true centrifugal, semi centrifugal & centrifuging

            n) Continuous casting

o) Slush casting

2. Melting furnaces:

a)     Electric arc furnaces

b)     Induction furnaces

c)      Cupola furnaces

d)     Crucible (pot) furnaces

3. Safety Practices in Casting

 

CHAPTER 34: Surface Treatments, Coatings and Cleaning

1.         Introduction

Significance of surfaces relative to manufactured products and reasons for surface treatment:

a.      Relative to resistance to wear, erosion and indentation

b.      Relative to decorative features

c.      Relative to friction control, fatigue resistance etc

d.      Relative to surface buildup and surface texture modification

e.      Relative to resistance to corrosion and oxidation

2.         Mechanical surface treatments:

            a.         Shot peening

            b.         Roller burnishing (surface rolling)

b.                  Explosive hardening (using a layer of explosive sheet)

3.         Mechanical plating and cladding:

            d.         Cladding (clad-bonding)

            e.         Mechanical plating/coating (using spherical glass, ceramic or porcelain beads)

 4.        Surface Hardening by Heat Treatment and Thermal Spraying:

            a.         Case hardening (carburizing, nitriding etc.)

            b.         Hard facing (using welding techniques)

            c.         Thermal spraying (metalizing)

 5.        Vapor Deposition:

            a.         Physical vapor deposition (vacuum evaporation, sputtering & ion plating)

            b.         Chemical vapor deposition

  6.       Electrochemical Plating:

a.                  Electroplating (workpiece is cathode)

            b.         Electroforming

 7.        Electroless Plating:

            a.         Nickel chloride + sodium hypophosphite = nickel + salt

            b.         Involves a reduction of nickel chloride with sodium hypophosphite as the reducing agent

 8.        Conversion Coating (Chemical reaction priming):

a.                  Anodizing (oxygen reacts with part: anodic oxidation). Workpiece (anode) is immersed in an acid bath)

b.                  Phosphate and chromate coatings principles (applications in the auto industry)

 9.        Hot Dipping:

            a.         Galvanization process

            b.         Tinplate and aluminizing

10.       Porcelain Enameling and Ceramic Coating:

            a.         Enameling (fusing coating material on substrate)

            b.         Applications (metals etc.)

            c.         Dipping, spraying & electro deposition of porcelain enamel

            d.         Glazing

11.       Painting:

            a.         Enamels

            b.         Lacquers (solvent evaporation)

            c.         Water-base paints

            d.         Methods of application

12.       Cleaning Surfaces:

            a.         Reasons for cleaning surfaces before surface treatment

            b.         Degrees of cleaning surfaces

            c.         Cleaning processes

I.                     Mechanical (brushing, sanding, blasting, tumbling etc.)

II.                   Electrolytic cleaning

                        II.          Chemical cleaning (solution, saponification, emulsification, dispersion & aggregation)

            d.         Cleaning fluids (alkaline solutions, emulsions, spirit, petroleum solvents, chlorinated hydrocarbons, acids & salts)

 

Rapid PROTOTYPING (Chapter 20)      

Definition: Rapid prototyping uses modern technology to produce a physical prototype from a CAD (Computer Aided Design) file in a matter of hours instead of days or weeks. These techniques shorten the time required for product development. The ability to translate a 3D computer model into a physical model in a very short time enables you to quickly evaluate your products to ensure a basic fit, form and function.

Advantages:
1. Rapid prototyping techniques shorten the time required for product development. The ability to translate a 3D computer model into a physical model in a very short time enables you to evaluate your products to ensure a basic fit, form and function.
2. Sometimes (with suitable materials), the prototypes can be used in subsequent manufacturing operations to produce the final part.
3. The technology can be used to produce actual tooling (rapid tooling).

Applications: Some of the applications of rapid prototyping include, prototyping, rapid tooling, and rapid manufacturing

Two broad Principles of Rapid Prototyping:
1. Subtractive Processes: Include 3-dimensional CAD, CAD/CAM and CNC systems
2. Additive Processes, including the following:

·         Fused Deposition Modeling (FDM)

·         Stereolithography (SLA)

·         Selective Laser Sintering (SLS)

·         Ballistic Particle Manufacturing (BPM) (AKA or related to 3D Printing or 3DP)

·         Laminated Object Manufacturing (LOM)

·         Solid Ground Curing (SGC)

·         Direct Manufacturing (Rapid Manufacturing [RM])

·         Rapid Tooling (RT)

1) Fused Deposition Modeling (FDM) is one method to develop rapid prototypes or models. The FDM machine builds the part by extruding a semi-molten filament through a heated nozzle in a prescribed pattern onto a platform. This RP technology is available from Stratasys, the inventor of Fused Deposition Modeling technology.

2) Stereolithography (SLA) is the most widely used type of rapid prototyping. Stereolithography produces 3D parts by curing successive layers of UV-curable resin. The parts of the resin that the laser cures in each layer are defined by a CAD model of the part. Because of the accuracy and ability to produce highly detailed parts, Stereolithography is excellent for concept models, masters, assemblies, and patterns for investment casting.

3) In Selective Laser Sintering (SLS), thermoplastic powder is spread by a roller over the surface of a build cylinder. The piston in the cylinder moves down one object layer thickness to accommodate the new layer of powder to be sintered. The powder delivery system is similar in function to the build cylinder. Here, a piston moves upward incrementally to supply a measured quantity of powder for each layer. Process is based on sintering principle.

4) Ballistic Particle Manufacturing (BPM). Developed by BPM technology, it sprays

     material (wax) in 0.002" drops at rates of 12,500 drops per sec to build up slices. The elevator drops as slices are formed. Variable slice thickness is set by changing the flow rate. Part material supports are made from water soluble wax (polyethylene glycol) and are removed after completion by placing the model in water.

     3D Printing (3DP) is a low-end version of additive fabrication technology. One variation consists of an inkjet printing system. Layers of a fine powder (either cornstarch or plaster) are selectively bonded by "printing" a water-based adhesive from the inkjet printhead in the shape of each cross-section as determined by a CAD (computer aided design) file. Alternately, these machines feed liquids, such as photopolymer, into individual jets that deposit tiny droplets as they are scanned to form a layer of the model. The liquid hardens after being deposited. Materials available for spraying include glue, wax, and photopolymer. Photopolymer Phase machines employ an ultraviolet (UV) flood lamp mounted in the print head to cure each layer as it is deposited.

5) In Laminated Object Manufacturing (LOM), Profiles of object cross sections are cut from paper or other web material using a laser. The paper is unwound from a feed roll onto the stack and first bonded to the previous layer using a heated roller which melts a plastic coating on the bottom side of the paper. The profiles are then traced by an optics system that is mounted to an X-Y stage.

After cutting of the layer is complete, excess paper is cut away to separate the layer from the web. Waste paper is wound on a take-up roll. The method is self-supporting for overhangs and undercuts. Areas of cross sections which are to be removed in the final object are heavily cross-hatched with the laser to facilitate removal. It can be time consuming to remove extra material for some geometries, however.

A laser beam is then traced over the surface of this tightly compacted powder to selectively melt and bond it to form a layer of the object. The fabrication chamber is maintained at a temperature just below the melting point of the powder so that heat from the laser need only elevate the temperature slightly to cause sintering. This greatly speeds up the process. The process is repeated until the entire object is fabricated.

6) Solid Ground Curing (SGC), is somewhat similar to stereolithography (SLA) in that both use ultraviolet light to selectively harden photosensitive polymers. Unlike SLA, SGC cures an entire layer at a time. Figure 1 depicts solid ground curing, which is also known as the solider process. First, photosensitive resin is sprayed on the build platform. Next, the machine develops a photomask (like a stencil) of the layer to be built. This photomask is printed on a glass plate above the build platform using an electrostatic process similar to that found in photocopiers. The mask is then exposed to UV light, which only passes through the transparent portions of the mask to selectively harden the shape of the current layer.

Figure 1: Schematic diagram of solid ground curing.

 After the layer is cured, the machine vacuums up the excess liquid resin and sprays wax in its place to support the model during the build. The top surface is milled flat, and then the process repeats to build the next layer. When the part is complete, it must be de-waxed by immersing it in a solvent bath.

7. Direct Manufacturing (Rapid Manufacturing [RM]), is application of any of the rapid prototyping techniques in direct production of engineering metal, ceramic, and polymers components or parts.

8. Rapid Tooling (RP), is application of any of the rapid prototyping techniques in direct production of production tooling including molds, patterns etc.

Engineering Metrology & Instrumentation (Chapter 35)

 

1. Engineering metrology defined: Measurement of dimensions such as length, thickness, diameter, taper, angle, flatness, profile etc.

2. Three reasons for dimensional measurement:

            A) to describe a physical object

            b) to construct a physical object

            c) to control the way an object is produced by many individuals.

3. Four machining terms:

            a) resolution

b) precision

            c) tolerance

            d) accuracy

4. Three basic systems of measurement:

            a) British imperial system

            b) decimal inch

            c) metric system

5. Geometric features of parts: Length, diameter, roundness, depth, straightness, flatness, parallelism, perpendicularity, angles and profile.

6. Direct line-graduated (linear measurement) instruments include: Rules, calipers and micrometers.

7. Indirect linear measurement instruments include calipers, dividers and telescoping gages.

8. Angle measurement instruments include bevel protractor, sine bar and surface plates.

9. Comparative length measurement instruments are dial indicators

10. Straightness, flatness, roundness and profiles are also measured with dial indicators.

11. Non-precision measurement instruments:

            a) the scale and the rule

            b) flexible steel tapes

            c) the depth gage

            d) the combination set

            e) transfer instruments

            f) the slide caliper

            g) the surface gage

            h) the surface plate

12. Precision measurement instruments:

a)     micrometers

b)     dial calipers

c)      vernier instruments

d)     dial indicators

e)     gage blocks

f)        comparator instruments

g)     height gage

h)      sine bars

i)        bevel protractors

j)        Go-not-go gages

13. Advanced precision measurement instruments:

            a) the microscope

            b) optical height gage/industrial magnifiers

            c) optical flats

            d) optical comparators

            e) Coordinate measuring machine (CMM)

            f) profilometers

 

Dimensioning and Tolerancing (Chapter 35)

  1. Dimensional tolerance is the permissible or acceptable variation in the dimensions of a part.
  2. Importance of tolerance control:
    1. No two parts are exactly the same dimension wise.
    2. Dimensional tolerances are needed in mass production.
    3. Dimensional tolerances are needed to have standards.
    4. Dimensional tolerances are needed to have interchangeable parts
    5. Dimensional tolerances become important only when a part is to be mated with another.
    6. Dimensional tolerances can increase or lower product cost significantly.
  3. Definitions:
    1. Allowance: Specified difference in dimensions between mating parts.
    2. Basic size: Dimension from which limits of size are derived.
    3. Bilateral tolerance: Deviation (plus or minus) from the basic size.
    4. Clearance: The space between mating parts.
    5. Clearance fit: Fit that allows for rotation or sliding between mating parts.
    6. Fit: The range of looseness or tightness that can result from the application of a specific combination of allowance and tolerance in the design of mating part features.
    7. Geometric tolerancing: Tolerances that involve shape features of the part.
    8. Interference: Negative clearance.
    9. Interference fit: A fit having limits of size so prescribed that an interference always results when mating parts are assembled.
    10. Limit dimensions: The maximum and minimum dimensions of a part.
    11. Nominal size: An approximate dimension that is used for the purpose of general identification.
    12. Positional tolerancing: A system of specifying the true position, size, and form of the features of a part, including allowable variations.
    13. Standard size: Nominal size in integras and common subdivisions of length.
    14. Transition fit: Fit with small clearance or interference that allows for accurate location of mating parts.
    15. Unilateral tolerancing: Deviation in one direction only from the nominal dimension.
    16. Zero line: Reference line along the basic size from which a range of tolerances and deviations are specified.

 

Geometric dimensioning and tolerancing (GD&T)

  1. Geometric dimensioning and tolerancing (GD&T) is a symbolic language used on engineering drawings and computer generated three-dimensional solid models for explicitly describing nominal geometry and its allowable variation.
  2. It is used to define the nominal geometry of parts and assemblies, to define the allowable variation in form and possibly size of individual features, and to define the allowable variation between features.
  3. Dimensioning and tolerancing and geometric dimensioning and tolerancing specifications are used as follows:

a)     Dimensioning specifications define the nominal, as-modeled or as-intended geometry. One example is a Basic Dimension.

b)     Tolerancing specifications define the allowable variation for the form and possibly the size of individual features, and the allowable variation in orientation and location between features. There are several standards available world-wide that describe the symbols and define the rules used in GD&T.

  1. Two such standard are American Society of Mechanical Engineers (ASME) Y14.5M-1994 and the International Organization for Standardization (ISO).

 

Dimensioning and tolerancing philosophy

9. There are some fundamental rules that need to be applied:

a)     All dimensions must have a tolerance. Every feature on every manufactured part is subject to variation, therefore, the limits of allowable variation must be specified. Plus and minus tolerances may be applied directly to dimensions or applied from a general tolerance block or general note. For basic dimensions, geometric tolerances are indirectly applied in a related Feature Control Frame. The only exceptions are for dimensions marked as minimum, maximum, stock or reference.

b)     Dimensioning and tolerancing shall completely define the nominal geometry and allowable variation. Measurement and scaling of the drawing is not allowed except in certain cases.

c)      Engineering drawings define the requirements of finished (complete) parts. Every dimension and tolerance required to define the finished part shall be shown on the drawing. If additional dimensions would be helpful, but are not required, they may be marked as reference.

d)     Dimensions should be applied to features and arranged in such a way as to represent the function of the features.

e)     Descriptions of manufacturing methods should be avoided. The geometry should be described without explicitly defining the method of manufacture.

f)        If certain sizes are required during manufacturing but are not required in the final geometry (due to shrinkage or other causes) they should be marked as non-mandatory.

g)     All dimensioning and tolerancing should be arranged for maximum readability and should be applied to visible lines in true profiles.

h)      When geometry is normally controlled by gage sizes or by code (e.g. stock materials), the dimension(s) shall be included with the gage or code number in parentheses following or below the dimension.

i)        Angles of 90° are assumed when lines (including center lines) are shown at right angles, but no angular dimension is explicitly shown. (This also applies to other orthogonal angles of 0°, 180°, 270°, etc.)

j)        Dimensions and tolerances are valid at 20 °C unless stated otherwise.

k)      Unless explicitly stated, all dimensions and tolerances are valid when the item is in a free state.

l)        Dimensions and tolerances apply to the full length, width, and depth of a feature.

m)   Dimensions and tolerances only apply at the level of the drawing where they are specified. It is not mandatory that they apply at other drawing levels, unless the specifications are repeated on the higher level drawing(s).

 

 

Symbol

Description

Geometry

Image:Gd&t angularity.png

ANGULARITY

ORIENTATION

Image:Gd&t concentricity.png

CONCENTRICITY

LOCATION

Image:Gd&t cylindricity.png

CYLINDRICITY

FORM

Image:Gd&t flatness.png‎

FLATNESS

FORM

Image:Gd&t parallelism.png

PARALLELISM

ORIENTATION

Image:Gd&t perpendicularity.png

PERPENDICULARITY

ORIENTATION

Image:Gd&t position.png‎

POSITION

LOCATION

Image:Gd&t profile.png‎

PROFILE

PROFILE

Image:Gd&t profileline.png

PROFILE OF A LINE

PROFILE

Image:Gd&t circularity.png‎

CIRCULARITY

FORM

Image:Gd&t runout.png

RUNOUT

RUNOUT

Image:Gd&t straightness.png

STRAIGHTNESS

FORM

Image:Gd&t symmetry.png

SYMMETRY

LOCATION

Image:Gd&t totalrunout.png

TOTAL RUNOUT

RUNOUT

 

Symbol

Modifier

Image:Gd&t freestate.png

FREE STATE

Image:Gd&t leastmaterialcondition.png

LEAST MATERIAL CONDITION

Image:Gd&t maximummaterialcondition.png

MAXIMUM MATERIAL CONDITION

Image:Gd&t projectedtolerancezone.png‎

PROJECTED TOLERANCE ZONE

Image:Gd&t regardlessoffeaturesize.png

REGARDLESS OF FEATURE SIZE

Image:Gd&t tangentplane.png

TANGENT PLANE

Image:Gd&t unilateral.png

UNILATERAL

 

Quality and Productivity (Chapter 36)

 

1.      Current Trends in Manufacturing Industry

a.      Current trends have shown that as a society becomes technically                mediated, it not only enters into the world market but also struggles to survive the powerful forces of domestic and global competition.

b.      Consumers want quality products.

c.      Manufacturers strive to provide quality products for their customers.

d.      This struggle results in a survival-of-the-fittest environment, a major reason why many companies go out of business today.

e.      On an international level, it explains the current massive financial investments in research and development by many industrialized nations

 

2.      Quality: By definition, quality is:

  1. Innate excellence of a product or service, or
  2. An acceptable standard which conforms to design specifications of a product.
  3.  It can also mean a degree of excellence, a distinguishing attribute, or a peculiar and essential character of something.
  4.  In industry, the task of deciding a product’s quality rests heavily on its designer. It is his or her responsibility to incorporate whatever the quality of the product is into the blueprint which is released to the manufacturing personnel during production.
  5.  The production personnel build those qualities into the product by following the designer’s specifications and by using the resources available to them.

 

3. Components of Quality: The components of the quality of a product are probably as many as the number of users of that product, because consumers want different things out of same product. Some of these are:

  1. Performance
  2. Reliability
  3. Durability
  4. Aesthetics
  5. Conformance
  6. Serviceability etc.

 

4. Productivity: The term “productivity” means rate of production, or the ratio of output by input which provides an index of efficiency and effectiveness of a company, worker or economy. It also reflects the status of any organizational performance. This suggests that some kind of input, process, machine, environment, knowledge, and personnel must be involved to generate the output, preferably a higher one. When a higher output is generated, it is said that the worker, organization or economy is being productive.

 

5. Components of Productivity: Some components or elements of productivity include those things that a company would use as input to produce some higher output. These may include:

  1. Machines, processes, technical know-how, input, rate, worker etc.
  2. If machines and processes are improved or automated, the output and rate of production of the worker will be affected (increased) and vice versa.
  3. Likewise, if the worker is changed, such as by insufficient training, drug use, tardy or emotionally, productivity will be reduced, and vice versa.
  4. Productivity is, therefore, improved by changing or improving its components.
  5. This improvement can be in the form of automating, retrofitting, teaching, training, mentoring etc..

 

6. Quality Assurance: Defined as all actions necessary to ensure that quality requirements will be satisfied. It is the total effort made by a manufacturer to ensure that its products conform to a detailed set of specifications and standards. It is the responsibility of everyone involved with design and manufacturing.

 

7. Quality Control: Is the set of operational techniques used to fulfill requirements for quality.

 

8. Total Quality Management: Art of managing the whole to achieve excellence.

  1. Emphasizes the idea that quality must be designed and built into a product:
  2. Defect prevention rather than defect detection is the major goal
  3. A systems approach involving both management and worker involvement
  4. Leadership and teamwork are emphasized
  5. Emphasizes continuous improvement of manufacturing operations
  6. Uses the idea of quality circles
  7. Malcolm Baldrige National quality Award recognize companies for outstanding quality management and achievement

 

9. Deming’s 14 Management Principles:

  1. Create constancy of purpose toward improvement of product and services
  2. Adopt the new philosophy.
  3. Cease dependence on mass inspection to achieve quality.
  4. End the practice of awarding business on the basis of price tag.
  5. Improve constantly and forever the system of production and service, to improve quality and productivity, and thus constantly decrease cost.
  6. Institute training on the job.
  7. Institute leadership (as opposed to supervision).
  8. Drive out fear so that everyone can work effectively.
  9. Break down barriers between departments.
  10. Eliminate slogans, exhortations and targets for zero defects and new levels of productivity.
  11. Eliminate quotas and management by numbers, numerical goals. Substitute leadership.
  12. Remove barriers that rob the hourly worker of pride of workmanship.
  13. Institute a vigorous program of education and self-improvement.
  14. Put everyone in the company to work to accomplish the transformation.

 

Statistical Process Control (Chapter 36)

1. The main rationale for statistical process control is based on the fact that process variation is present in every process due to a combination of equipment, materials, environment, and operator.

2.  Statistical process control tools include:

  1. Cause-and-effect diagram (fish bone diagram)
  2. Check sheet
  3. Pareto diagram
  4. Run chart
  5. Scatter diagram
  6. Histogram
  7. Control chart

                     i.            The X-bar control chart is used to monitor the process for any variation

3. Objectives of variable (and attribute) control charts:

  1. For quality improvement
  2. To determine the process capability
  3. For decisions in regard to product specifications
  4. For current decisions in regard to production process
  5. For current decisions in regard to recently produced items

4. Terms used in control chart construction:

  1. Sample size or the number of parts to be inspected
  2. Random sampling
  3. Population or total number of parts from which samples are taken
  4. X-bar (\bar{x} \,) refers to the sample mean; (\bar{x} \,, enunciated "x bar"). Population mean is ų.
  5. Center line and control limits: upper control limit (UCLx) and lower control limit (LCLx)
  6. s refers to sample standard deviation or s = \sqrt{\frac{1}{N-1} \sum_{i=1}^N (x_i - \overline{x})^2}\,,   while the population standard deviation =  \sigma = \sqrt{\frac{(x_1-\mu)^2 + (x_2-\mu)^2 + \cdots + (x_N - \mu)^2}{N}},
  7. Standard scores or z scores are computer as Z = \frac{X - \mu}{\sigma} \!
  8. The normal curve principle shown below is applied in SPC. Note that 99.73%, 95.46% and 68.26& fall within +-3 sigma, 2 sigma and 1 sigma respectively.

wpe256.jpg (14584 bytes)

5. Control chart procedures:

  1. Select the quality characteristics (e.g. length)
  2. Choose the rational subgroup
  3. Collect the data (e.g. 3.9, 4.0; 3.8, 4.1; 4.2, 4.0; 3.7, 4.1; 4.2’ 3.9)
  4. Determine the trial central line (= Mean)
  5. Determine the upper and lower control limits (UCLx & LCLx = Mean +- 3S)
  6. Plot the control chart (see sample below)
  7. Use the control chart (see sample below)

 

File:ControlChart.svg