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Transcript of Introduction Lecture 1 · PDF file Mech 311 Lecture 1 1 Lecture 1 Introduction Credits: 3.75...

  • Mech 311 Lecture 1 1

    Lecture 1

    Introduction

    Credits: 3.75 Session: Fall

    Time: _ _ W _ F 13:15 - 14:30

    MECH 311 Manufacturing Processes

    –Section X

    Instructor: Sivakumar Narayanswamy

  • Objective of the course

    To provide the basic understanding of

    • Measurements,

    • Tolerancing and

    • Design and understanding of different manufacturing methods ( Conventional and non-conventional).

    • Feel for manufacturing:

    – What machine at what situation?

    – What is possible by existing manufacturing methods?

    – Cost effective routes!

    – Feel for numbers!

  • How to Ensure?

    what we produce is what we want.

    Inspection

  • Manufacturing Processes

    Measurement: Fundamental exercise of inspection; Act of measuring or being

    measured.

    Why measure? Manufactured parts correspond to the specs of the product:

    (QA) Confirm functionality, performance, reliability, process capability, etc.

    How to measure? Attributes ( Qualitative, go or not-go, Gaging, decisions)

    Variables (quantitative, dimensions, useful for analysis and decision)

    What to measure? Size/geometry of tools

    Size/geometry of a part from a machine tool

    Benefits Determines capability of a process.

    Indicates the need of maintenance.

    Feedback of manufacturing.

  • Attribute Vs Dimensional

    • Qualitative

    • Fast and economical

    • Pass or fail

    • Mostly for standard and

    less severe applications

    (Automobile)

    • Useful after process

    development

    • Large production volume

    • Quantitative

    • Slow and expensive

    • Exact dimension is needed

    • Useful for highly reliable

    applications (Aircrafts)

    • Needed for development

    • Small production volume

  • Standard Measurements:

  • Issues Units are different => Conversion scales

    Linear Standards

    Metric Systems ANSI System

    1in ~ 41,929.399 wavelengths related to human body

    sizes Of orange-red light Kr86

  • Standard set of rectangular gage blocks with ±0.000050-in.

    Wrung-together gage blocks

    in a special holder, used with

    a dial gage to form an

    accurate comparator.

    Screw gage blocks wrung together to build

    up a desired dimension.

    Length Standards: Gage blocks or slip gages (Alloy

    steel with Rc65)

  • Standard gages of meter – exist in any workshop ( standard blocks); need to calibrate

    every specific period ( various precision).

    Calibrated at 20°C

  • Accuracy Vs. Precision

    Accuracy: ability to reach the aimed size

    Precision: repeatability of accuracy

    (Left):Accuracy versus precision. Dots in targets represent location of shots.

    Cross (X) represents the location of the average position of all shots.

  • Allowance and Tolerance:

    Allowance: intentional desired difference between the dimensions of 2 mating parts

    Tolerance: undesirable but permissible deviation from a desired dimension.

    Most manufacturing processes products with dimensions distributed normally

    ( clustering around the average)

    n

    x x

    i

    n

    i 1

       

    n

    xxi

    n

    i

    2

    1

      

  • The manner in which the distributions of the

    two mating parts interact determines the fit.

    UNTL upper natural tolerance limit =  3 LNTL, lower natural tolerance limit =   3

    When mating parts are designed,

    each shaft must be smaller than

    each hole of a clearance fit.

    Wear or lack of process control  shifting

  • Clearance?

    Range of Fit?

    MMC?

    LMC?

    Bilateral?

    Unilateral?

    Limits

  • How to Specify Tolerances?

    ANSI – 8 classes of fits

    •Class 1. Loose fit: large allowance. Accuracy is not essential.

    •Class 2. Free fit: Liberal allowance. For running fits where speeds are above 600 rpm and

    pressures are 600 psi ( 4.1 MPa) or above

    •Class 3. Medium Fit: Medium allowance. For running fits below 600 rpm and pressure below

    600 psi ( 4.1 MPa) and for sliding fits.

    •Class 4. Snug Fit: Zero allowance. No movement under load is intended, and no shaking is

    wanted. This is the tightest fit that can be assembled by hand

    •Class 5. Wringing fit: zero to negative allowance. Assemblies are selective and not

    interchangeable.

    •Class 6. Tight fit: slight negative allowance. An interface fit for parts that must not come

    apart in service and are not to be disassembled or are to be disassembled only seldom. Light

    pressure is required for assembly. Not to be used to with stand other than very light loads.

    •Class 7. Medium force fit: an interference fit requiring considerable pressure to assemble;

    ordinarily assembled by heating the external member or cooling the internal member to provide

    expansion or shrinkage. Used for fastening wheels, crank disks, and the like to shafting. The

    tightest fit that should be used on cast iron external members.

    •Class8. Heavy force and Shrink fits: considerable negative allowance. Used for permanent shrink on steel members.

  • ISO System of Limits and Fits • Clearance fits

    • Transition fits/ Location fits/ Assembly fits

    • Interference fits

    Shaft-basis and hole-basis system for specifying fits in the ISO system

    What is Hole based or Shaft based system?

    WHY?

  • Geometric Tolerances: Permitted tolerance on shape/geometry/form/position

    (Left) Geometric tolerancing symbols; (Right Up) Feature control symbols for

    part drawings; (Right Down) Example of use of geometric tolerancing

    (tolerancing for flatness)

    MMC – Parts are made with the largest amount of material possible

    LMC - Parts are made with the least amount of material possible

    RFS – Regardless of feature size

    Datums- Concept/Feature common for design, manufacturing and inspection

  • Inspection methods for measurement

    Metrology: measurement laboratory selected according to certain criteria:

    • Gage capability ( rule of 10)

    Measuring device has to be 10times more precise than the tolerance measured:

    Eg. +/-0.001  +/-0.0001  +/-0.00001

    •Linearity

    Linear working range (Input Vs Output)

    •Repeat accuracy

    Repeatability of the measurement

    •Stability

    Retaining calibration over time, no-drift

    •Magnification

    Amplification of the output portion of the device, bigger dials.

    •Resolution

    Sensitivity; smallest input value that can be detected or measured

  • Measurement instruments ( linear)

    * Ruler (0.5mm) * Combination set

    * Vernier Caliper(0.01mm) * Micrometer caliper

    * Optical Comparators (0.001mm) * Laser/ interferometers(0.0001mm)

    Combination set.

  • Three styles of calipers in common use today

    Internal and external

    Digital Micrometer for measurements

    from 0 to 1in., in 0.0001-in.

    graduations.

  • Vision Systems of measurement

    Optical Comparator,

    measuring the contour on a

    workpiece. Digital indicators

    with in/.mm conversions add

    to the utility of optical

    comparators.

    Coordinate measuring

    machine with inset showing

    probe and a part being

    measured.

    Coordinate Measuring Machines

    (CMM)

  • Interference bands can be used to measure the size of objects to great accuracy

    a a)(bottom left) Calibrating the X-axis linear table displacement of a vertical

    spindle milling machine; b) ( top right) Schematic of optical setup ; c) ( bottom

    right) Schematic of components of a two frequency laser interferometer. Resolution ~ 10nm

  • The principle of the optical flat

  • Angle Measurement

    • Sine Bar: 1sec of arc

    Setup to measure an angle on a part using a

    sine bar. The dial indicator is used to

    determine when the part surface X is parallel

    to the surface plate

  • (Top) Plain plug gage having go member

    on one end and not-go member on other

    other; (Bottom) Ring gage with stepped go

    and not-go member

    Go and not-go ring gages for checking a

    shaft.

    Gages for Attributes ( mass production):

  • Ring Gage

    GO

    Ring gage

    No GO

    100+/- 0.1

    Shaft

    100.1 99.9

    Plug gage

    GO

    Plug gage

    NO GO

    100+/- 0.1

    Hole

    99.9 100.1

  • Top) Microtopographer, a stylus profile device used to measure

    and depict surface roughness and character (surface profile);

    Bottom) Typical surface-roughness profiles.

    Schematic of surface profile as produced

    by stylus device showing some typical y