Lo #4 manufacturing technology (jan 2016)

Manufacturing Technology 1

Manufacturing TechnologyManufacturing Technology

LO #4 Part 1 - Measurement & Inspection

- Reference e-textbook (Chapter #6, P. 131 ~ 153)

2Manufacturing Technology

Interchangeability

One of the important aspects of parts manufacturing is interchangeability of the produced parts.

Interchangeable parts are parts that should be identical. They are made to the specifications of the designer that ensure they are all nearly identical and they can fit in any assembly of the same type.

These parts can freely replace another, without any further custom fitting such are filing or machining.

This interchangeability allows easy assembly of new devices, and easier repair of existing devices, while minimizing both the time and skill required of the person doing the assembly or repair.

The concept of interchangeability was crucial to the introduction of the assembly line at the beginning of the 20th century, and has become a universal element of modern manufacturing.

Examples of Interchangeable parts

• Started in mass production assembly, the Ford Model T auto parts.

Interchangeability & Dimensional Tolerance

Interchangeability is determined by the dimensional tolerances of the parts.

Dimensional tolerances is the permissible variation in the dimensions of a part.

Tolerances are important because of their impact od the proper functioning of a product, part interchangeability, and manufacturing costs.

The smaller the tolerances, the higher the production cost.

But if the tolerances are higher than permitted this will lead to poor product quality and functionality.

Measurement & Inspection

A procedure in which an unknown quantity is compared with a known standard, using an accepted and consistent system of units.

- U.S. Customary system (U.S.C.S.)- International System of Units (SI, metric system)

Measurement provides a numerical value of the quantity of interest within certain limits of accuracy and precision.

Measurement

Measurement & Inspection

Inspection is a procedure in which a part or product characteristic, such as dimension is examined to determine whether it conforms to the design specification.

Many inspection methods rely on measurement techniques, while others use gauging method.

Gauging (=Gaging) is faster than measurement, but provides scant(=inadequate) information about the actual value of the characteristic.

In inspection part passes or fails.

Inspection

Quality - InspectionQuality - Inspection

- Coordinate metrology is concerned with the measurement of the actual shape and dimensions of an object and comparing these with the desired shape and dimensions.

- In this connection, coordinate metrology consists of the evaluation of the location, orientation, dimensions, and geometry of the part or object.

- A Coordinate Measuring Machine (CMM) is an electromechanical system designed to perform coordinate metrology.

Coordinate Measuring Machine (CMM)

QualityQualityCoordinate Measuring Machine (CMM)

CMM quality depends on four(4) characteristics;

-Resolution : it specifies the CMM’s finest incremental reading.

-Repeatability : it also called precision, is that CMM’s ability to duplicate a measurement. It is a function of machine stiffness.

-Accuracy : the lack of error in measurement, the difference between what the CMM measures and what a perfect CMM would have measured.

-Linearity : the least effective measure of CMM quality. It checks the machine for its movement along the three linear directions X, Y, and Z.

Manufacturing Technology

QualityQualityCoordinate Measuring Machine (CMM)

CMM quality : Accuracy - Precision

Manufacturing Technology

Dimensional ToleranceDimensional Tolerance

It is defined as the permissible or acceptable variation in the dimensions (height, width, depth, diameter, and angles ) of a part.

Tolerances are unavoidable, because it is impossible and unnecessary to manufacture two parts that have exactly the same dimensions.

Dimensional tolerances become important only when a part is to be assembled or mated with another part.

Dimensional ToleranceDimensional Tolerance

Engineering Golden Rule

Dimensional Tolerance - Dimensional Tolerance - MethodsMethods

Allowances : the specified difference in dimensions between the mating parts.

Basic size : Dimension from which limits of size are derived with the use of tolerances and allowances.

Bilateral tolerance : The variation is permitted in both positive and negative directions from the nominal dimensions.

Unilateral tolerance : The variation from the specified dimensions is permitted in only one direction, either positive or negative.

Limit dimensions : Alternative method to specify the permissible variation in a part feature size. They consists of the maximum and minimum dimensions allowed.

Zero line : Reference line along with the basic size from which a range of tolerances and deviations are specified.

Feature : A physically identified portion of a part, such as hole, slot, pin, or chamfer.

Dimensional Tolerance - Dimensional Tolerance - MethodsMethods

Bilateral tolerance Unilateral tolerance Limit dimensions

Dimensional Tolerance – Dimensional Tolerance – Shaft & holeShaft & hole

PH –

PS –

LPH : Largest Possible HoleSPH : Smallest Possible HoleLPS : Largest Possible ShaftSPS : Smallest Possible Shaft

Dimensional Dimensional Tolerance – Tolerance – Shaft & holeShaft & hole

Dimensional Tolerance – Dimensional Tolerance – ISO 286 ; 1988ISO 286 ; 1988- - ANSI B4.2 :1978ANSI B4.2 :1978- EN 20286 : 1993- EN 20286 : 1993

Deviation : Difference between the size and the corresponding basic size. The basic size is assigned as limits of deviation. it is same for both parts of their fits.

Lower Deviation : Difference between the min limit of part's size and corresponding basic size. It is designated "EI" for Hole, "ei" for shaft.

Upper Deviation : Difference between the max limit of part's size and the corresponding basic size. It is designated "ES" for hole," es" for shaft.

Fundamental Deviation : One of the deviations closest to the basic size.

Tolerance : The algebraic difference between the max and min limits on the part.

Measurement InstrumentsMeasurement Instruments

Surface Plate

A large solid block whose top surface is finished to a flat plane.

Most surface plates today are made of granite. Granite has the advantage of being hard, non-rusting, non magnetic, long wearing, thermally stable, and easy to maintain.

Graduated & Non-graduated measuring devices

Graduated measuring devices include a set of markings (called graduations) on a linear or angular scale to which the object’s feature of interest can be compared for measurement.

Non-graduated measuring devices posses no such scale and are used to make comparison between dimensions or to transfer a dimension for measurement by a graduated devices.

Steel Rule

The most basic of the graduated measuring device. It used to measure linear dimensions. Rules are available in various length.

Calipers

It is available in either non-graduated or graduated styles.

Outside caliper & Inside caliper.

Non-graduated : Inside & Outside

Outside - Graduated

Inside - Graduated

Vernier Caliper

Vernier Caliper – a reading example

Micrometer

Micrometer – a reading example

Vernier Height Gauge

A height gauge is a measuring device used either for determining the height of something, or for repetitious marking of items to be worked on.

These measuring tools are used in metalworking or metrology to either set or measure vertical distances; the pointer is sharpened to allow it to act as a scriber and assist in marking out work pieces.

Dial Indicator

It converts and amplifies the linear movement of a contact pointer into rotation of a dial needle.

Dial Indicator – an example in Shaft Alignment Shaft alignment is the process to align two or more shafts with

each other to within a tolerated margin. It is an absolute requirement for machinery before the machinery is put in service.

Types of misalignment

Methods of shaft alignment

Vernier Protractor – Angular Measurements

A vernier protractor is used to obtain a very accurate measurement of angles through the vernier scale.

Surface textureSurface texture

Nominal surface ;

- It representing the intended surface contour of the part, and is defined by lines, ideal circles, round holes, and other edges and surfaces that are geometrically perfect.

Surface texture;

- Surface Texture or Surface Topography is the local deviations of a surface from a perfectly flat plane. The measure of the surface texture is generally determined in terms of its roughness, waviness, lay, and flaws.

Roughness; refers to the small, finely spaced deviations from the nominal surface that are determined by the material characteristics and the process that formed the surface.

Waviness ; is defined as the deviations of much larger spacing; they occur because of work deflection, vibration, heat treatment, and similar factors. Roughness is superimposed on waviness.

Lay ; is the predominant direction or pattern of the surface. It is determined by the manufacturing method used to create the surface, usually from the action of cutting tool.

Flaws ; are irregularities that occur occasionally on the surface; these include cracks, scratches, inclusions, and similar defects in the surface.

LO #4 Measurement & Inspection : Part 2 - SPC (Statistical Process Controls)

- Reference e-textbook (P. 1061 ~ 1064)

Statistical Process Control

Terminology

UCLUCL

LCLLCL

Statistical process control (SPC) involves the use of various statistical methods to assess and analyze variations in a process. SPC methods include simply keeping records of the production data, histograms, process capability analysis, and control charts. Control charts are the most widely used SPC method.

Groover, Mikell P. Fundamentals of Modern Manufacturing: Materials,

Process Capability and Tolerance

In any manufacturing operation, variability exists in the process output. In a machining operation, which is one of the most accurate processes, the machined parts may appear to be identical, but close inspection reveals dimensional differences from one part to the next. Manufacturing variations can be divided into two types ; random and assignable.

Random variations are caused by many factors: human variability within each operation cycle, variations in raw materials, machine vibration, and so on. It is normal statistical distribution. It said to be in Statistical Control.

Process Capability and Tolerance

Assignable variations indicate an exception from normal operating conditions. Something has occurred in the process that is not accounted for by random variations. Reasons for assignable variations include operator mistakes, defective raw materials, tool failures, machine malfunctions, and so on. Assignable variations in manufacturing usually betray themselves by causing the output to deviate from the normal distribution. The process is no longer in statistical control.

TerminologyA control chart is a graphical technique in which statistics computed from measured values of a certain process characteristic are plotted over time to determine if the process remains in statistical control. The general form of the control chart is illustrated in Figure 40.1. The chart consists of three horizontal lines that remain constant over time: a center, a lower control limit (LCL), and an upper control limit (UCL). The center is usually set at the nominal design value. The upper and lower control limits are generally set at +/-3 standard deviations of the sample means.

Basic types of Control Charts Control charts for variables require a measurement of the quality

characteristic of interest. Control charts for attributes simply require a determination of

whether a part is defective or how many defects there are in the sample.

Control Charts for Variables

The x-chart (call it “x bar chart”) is used to plot the average measured value of a certain quality characteristic for each of a series of samples taken from the production process. It indicates how the process mean changes over time.

The R-chart plots the range of each sample, thus monitoring the variability of the process and indicating whether it changes over time.

Process Control Charts – An Example

11 22 33 44 55 66 77 88 99 1010Sample numberSample number

UpperUppercontrolcontrol

limitlimit

ProcessProcessaverageaverage

LowerLowercontrolcontrol

limitlimit

Out of controlOut of control

A process is in control if……

1. … no sample points outside limits2. … most points near process average3. … about equal number of points above and

below centerline4. … points appear randomly distributed

X-bar Chart

X-bar Chart Example

X-bar Chart Example (Cont.)

Statistical Process ControlR - Chart

Statistical Process ControlR – Chart Example

Statistical Process ControlR – Chart Example (cont.)

RkR = = = 0.115 1.15

10UCL = D4R = 2.11(0.115) = 0.243

LCL = D3R = 0(0.115) = 0

Retrieve Factor Values D3 and D4

Statistical Process ControlR – Chart Example (cont.)

UCL = 0.243

LCL = 0

Sample number

R = 0.115

0.28 –

0.24 –

0.20 –

0.16 –

0.12 –

0.08 –

0.04 –

Statistical Process ControlSequence to solve problems

Statistical Process ControlExample

LO #4 Measurement & Inspection : Part 3 – Fit, Limits & GT (Geometric Tolerance) - Reference pages in e-textbook (P. 96 ~ 97 & 834 ~ 837 )

Fit and Limits

Clearance : The space between mating parts.

Fit : The range of looseness or tightness that can result from the application of a specific combination of allowance and tolerance in design of mating-part feature.

Terminology

Clearance fit : Fit that allows for rotation or sliding between mating parts.

Transition fit : A fit with small clearance or interference that allows for accurate location of mating parts.

Interference fit : A fit having limits of size so that interference always results when mating parts assembled.

Fit and LimitsExamples of Fit Clearance fit : Bicycle chain

– Clearance required between pins and bushes.

Transition fit : Crank shaft joints – Crank shaft must run with minimum least clearance to avoid vibration.

Pump shaft & casing assembly by press machine

Fit and LimitsExamples of Fit

Interference fit: Shrink – fittingShrink-fitting is a technique in which an interference fit is achieved by

a relative size change after assembly. This is usually achieved by heating or cooling one component before assembly and allowing it to return to the ambient temperature after assembly, employing the phenomenon of thermal expansion to make a joint

Fit and Limits Examples of Fit

MMC (Maximum Material Conditions) : The point at which a feature contains the most amount of material within its acceptable size limit. The smallest acceptable hole and the largest acceptable shaft are examples of MMC.

LMC (Least Material Conditions) : The point at which a feature contains the least amount of material within its acceptable size limit. The largest acceptable hole and the smallest acceptable shaft are examples of LMC.

Fit and Limits

Maximum Material ConditionLeast Material Condition

Fit and Limits

Examples of FitFit and Limits

Examples of Fit

When the specified size limits of mating part features always result in clearance at assembly, the parts are said to have a clearance fit.

EXAMPLE: In the drawing above, even when the fastener is at its MMC size of .747 and the hole is at its MMC size of .750, there is clearance.

When the specified size limits always produce interference at assembly, mating part features are said to have an interference fit.

EXAMPLE: In the center drawing, even when the fastener is at its LMC size of .5012 and the hole is at its LMC size of .5007, there is interference.

When mating part features do not fit together in their maximum material condition, but do fit at some point as they approach their least material condition, they are said to have a transition fit.

EXAMPLE: In the drawing on the right, when the fastener is at its maximum material condition size of .5003, it will not fit the hole at its MMC size of .5000. However, when both features are manufactured at their least material condition size, they will fit together.

Fit and Limits

Fit and LimitsThe hole-basis Vs Shaft-bases system

Fit and LimitsThe hole-basis system

Fit and Limits

The hole-basis system

Geometric Tolerance & Symbols

A Datum is a reference point, axis, or plane is identified in the engineering drawings, it is used to measure and specify the part features or measurements from.

It is a theoretical exact feature from which dimensions may be taken.

A Datum is generally chosen as an edge or feature which has the greatest influence in a specific measurement.

Terminology

Geometric Tolerance & Symbols

Geometric Dimensioning and Tolerancing (GD & T) : GD & T method is used to control location, form, profile, orientation, and run out on a dimensional feature. Its purpose is to ensure proper assembly and/or operation of parts, and especially useful in quantity production of interchangeable parts.

Terminology

Geometric Tolerance – Symbols & Tolerance Characteristics

Straightness

Flatness

Circularity (Roundness)

Cylindricity

Profile – Line & Face

Parallelism

Angularity

Perpendicularity

Position- Line- Holes

Concentricity

Symmetry

Run-Out

Ex) Bearing Housing

Section dwg.

ISO dwg.

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