Quality Control

QUALITY ASSURANCE (QA)

• 1. The operational techniques and activities that sustain the product or service quality to specified requirements.

• 2. The use of such techniques and activities.

• .

QUALITY ASSURANCE (QA)

• 3. Operations intended for the assessment of the quality of products at any stage of processing or distribution .

• 4. Part of quality assurance intended to verify that components and systems correspond to predetermined requirements.

QUALITY CONTROL (QC)

• Quality control, focuses on the end result, such as testing a sample of items from a batch after production.

• Inspection takes place at all stages of the process from design to dispatch

•

QUALITY CONTROL (QC)

•Basically quality control tests that the standards laid out by the quality assurance standards have been met

QUALITY INSPECTION

• Inspection takes place at stages

• Goods inward

• During production

• Final inspection

QUALITY ASSURANCE VS. QUALITY CONTROL

Quality Assurance

An overallmanagement plan to guarantee theintegrity of data(The “system”)

Quality Control

A series of analytical measurements usedto assess thequality of the analytical data(The “tools”)

TRUE VALUE VS. MEASURED VALUE

True Value

The known, accepted value of a quantifiable property

Measured Value

The result of an individual’s measurement of a quantifiable property

REPRODUCABILITY

The ability of a system to achieve the same results

when using different operators and

different measuring equipment

ACCURACY VS. PRECISION

AccuracyHow well a measurement agrees with an accepted value

PrecisionHow well a series of measurements agree with each other

ACCURACY VS. PRECISION

ISO 9000

• Is an international standard that many companies use to ensure that their quality assurance system is in place and effective. Conformance to ISO 9000 is said to guarantee that a company delivers quality products and services.

ISO 9001

• ISO 9001 is for all organisations large or small and covers all

sectors, including charities and the voluntary sector. It will help you to be more structured and

organised.   it is a process standard, not a service or product

standard.

ISO 9001

• ISO 9001 gives the requirements for what the organisation must do

to manage processes affecting quality of its products and services. It does this through the creation of a Quality Management System.

ISO 9001

• The standard requires you to have certain documented

procedures. They must meet the requirements as described in the following 6 clauses as mentioned

in the standard:

ISO 9001

• (clause 4.2.3) Control of documents

• (clause 4.2.4) Control of records

• (clause 8.2.2) Internal audit

• (clause 8.3) Control of nonconforming product

• (clause 8.5.2) Corrective action

• (clause 8.5.3) Preventative action

BENEFITS OF ISO 9001

BENEFITS OF ISO 9001

• Improved consistency of service and product performance

• Higher customer satisfaction levels.

• Improved customer perception

• Improved productivity and efficiency

• Cost reductions

• Improved communications, morale and job satisfaction

• Competitive advantage and increased marketing and sales

• opportunities.

BENEFITS of ISO 9001

STANDARD FOR QUALITY MANAGEMENT SYSTEMS

• Products should conform to standards of quality assurance and demonstrate

conformity to product requirements. Action should be taken to eliminate non conformity.

Action should be taken prevent the use of non conforming products. (without

waiting for the customer to complain)

MEASURING INSTRUMENTS

•Micrometers•Vernier Calipers•Dial Indicators•Telescopic Gauges•Small Hole Gauges•Thickness Gauges•Straight Edge

MICROMETERS

OUTSIDE MICROMETER

Instrument for making precise linear measurements of dimensions such as diameters, thicknesses, and

lengths of solid bodies.It consists of a C-shaped frame with a movable jaw

operated by a screw. The accuracy of the measurements depends on the accuracy of the

screw-nut combination.

IMPERIAL AND METRIC

INSIDE MICROMETER

DEPTH MICROMETER

DIGITAL MICROMETERS

COMBINATION DIGITAL

Metric or Imperialat the push of a button

PARTS OF A MICROMETER

READING THE SLEEVE AND THIMBLE

Imperial Micrometer

31

2

Number on Sleeve

Graduation on Sleeve

Number on Thimble

Thimble numbers go from 0 to 20

SAMPLE READING

First numberis the size of the Mic

0.000

Example using a 0-1” Outside Micrometer

Second number is the first number

on Sleeve.000

Third numberis .025 graduations

you see on Sleeve.025 x 2 = .050

Fourth numberis read on the

Thimble.016

RECORDING MEASUREMENT FROM SAMPLE READING

First reading – Range of Mic.

0 – 1” so the first number would be 0.000 Second reading – number on Sleeve

Number you see is Zero so it would be .000

Third reading – graduation on SleeveTwo graduations exposed so number is .050

Final number is number on the Thimble

Final number is .016

TOTAL READINGSFirst reading – Range of Mic. 0.000

Second reading – number on Sleeve 0.000

Third reading – graduation on Sleeve 0.050 Final number is number on the Thimble 0.016 ______

Total is ? 0.066

Reading an Imperial Micrometer

READING AN IMPERIAL MICROMETER

EXERCISE 1 (2-3” MIC)

Answer : 2.550

READING AN IMPERIAL MICROMETER

EXERCISE 2 (0-1” MIC)

Answer: 0.802

READING AN IMPERIAL MICROMETER

EXERCISE 3 (1-2” MIC)

Answer: 1.645

CALIPERS

INTRODUCTION

• Calipers can be direct reading or measuring transferring tools.

• Direct reading calipers are capable of a wider measurement range than micrometer calipers.

• Six (6), eighteen (18) and twenty four (24) inch are popular.

INTRODUCTION

• Three common designs of direct reading calipers;

• Vernier

• Dial

• Digital

VERNIER CALIPER

• Vernier calipers are an old tool that has been mostly replaced by dial and digital calipers.

• They are manufactured with decimal scales, metric scales and fractional scales.

• The Vernier scale is still used on many mechanical measuring tools.

VERNIER SCALE

• The reference point is the 0 on the vernier scale.

• To read a Vernier, the line of coincidence must be located.

• The line of coincidence (LOC) is the line on the Vernier that coincides with a line on the main scale.

• Illustration LOC = 19

• In theory only one LOC is possible, but usually when reading the vernier it appears several exist. When this occurs pick the middle line.

• A Vernier is a mechanical means of magnifying the last segment on the main scale so addition subdivisions can be made.

VERNIER CALIPER-PRACTICE

• Smallest whole unit 1.000

• Tenths of an inch 0.200

• Twenty five thousands 0.000

• Vernier scale 0.011

Sum (measurement) 1.211

LOC

Read the Vernier caliper in the illustration.

DIAL CALIPER

A dial replaces the Vernier.

This makes the caliper easier to read.

The reader must still determine the units and graduations.

READING A VERNIER CALIPER # 12.641

READING A VERNIER CALIPER # 2

1.581

READING A VERNIER CALIPER # 2

0.508

MEASUREMENT TRANSFERRING

TOOLS

INTRODUCTION

•Measurement transferring tools are tools that collect a measurement, but do not have a scale to read the measurement.

INTRODUCTION

• .

• Common tools are:

• Spring calipers

• Dividers

• Telescoping gauges

• Ball gauges

SPRING CALIPERS

• Spring calipers are used to transfer measurements.

• Three types of spring calipers

• Outside

• Inside

• Hermaphrodite

DIVIDERS

• Dividers are very useful for laying out several equal distances or transferring a distance measurement when other measuring devices cannot be used.

TELESCOPING GAGES

• Telescoping gages are used to measure inside diameters.

• One or both ends are spring loaded so they can be retracted and inserted into the hole being measured.

• The measurement is made with a caliper or micrometer.

BALL GAUGES

• Ball gauges are use to transfer measurements that are too small for telescoping gauges.

• The ball is split and a tapered wedge is used to increase and decrease the diameter of the ball halves.

MEASURING STRAIGHTNESS

Measuring straightness manually with (a) a knife-edge rule and (b) a dial indicator.

MEASURING FLATNESS

(a)Interferometry method for measuring flatness using an optical flat.

(b) Fringes on a flat, inclined surface. An optical flat resting on a perfectly flat workpiece surface will not split the light beam, and no fringes will be present.

(c) Fringes on a surface with two inclinations. Note: the greater the incline, the closer together are the fringes.

(d) Curved fringe patterns indicate curvatures on the workpiece surface.

MEASURING ROUNDNESS

(a) Schematic illustration of out-of-roundess (exaggerated). Measuring roundess using (b) a V-block and dial indicator, (c) a round part supported on centers and rotated, and (d) circular tracing.

MEASURING GEAR-TOOTH THICKNESS AND PROFILE

Figure 35.8 Measuring gear-tooth thickness and profile with (a) a gear-tooth caliper and (b) pins or balls and a micrometer.

OPTICAL CONTOUR PROJECTOR

A bench-model horizontal-beam contour projector with a 16-in. diameter screen with 150-W tungsten halogen illumination.

FIXED GAUGES

Figure 35.10 (a) Plug gage for holes with GO and NOT GO on opposite ends. (b) Plug gage with GO and NOT GO on one end. (c) Plain ring gages for gaging round rods. Note the difference in knurled surfaces to identify the two gages. (d) Snap gage with adjustable anvils.

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

ELECTRONIC GAGE

Figure 35.12 An electronic gage for measuring bore diameter. The measuring head is equipped with three carbide-tipped steel pins for wear resistance. The LED display reads 29.158 mm. Source: Courtesy of TESA SA.

ELECTRONIC GAGE MEASURING VERTICAL LENGTH

Figure 35.13 An electronic vertical-length measuring instrument with a resolution of 1 μm

LASER MICROMETERS

Figure 35.14 (a) and (b) Two types of measurements made with a laser scan micrometer. (c) Two types of laser micrometers. Note that the instrument in the front scans the part (placed in the opening) in one dimension; the larger instrument scans the part in two dimensions.

COORDINATE-MEASURING MACHINE

(a) Schematic illustration of a coordinate-measuring machine. (b) A touch signal probe. (c) Examples of laser probes. (d) A coordinate-measuring machine with a complex part being measured.

(b) (c) (d)

COORDINATE-MEASURING MACHINE FOR CAR BODIES

Figure 35.16 A large coordinate-measuring machine with two heads measuring various dimensions on a car body.

TOLERANCE CONTROL

Tolerance is the range of sizes in within which a component is

acceptable

METHODS OF ASSIGNING TOLERANCES

Various methods of assigning dimensions and tolerances on a shaft:

(a) bilateral tolerance, (b) unilateral tolerance, and (c) limit

GO AND NO GO GAUGES

GAUGES

SIMPLE PLATE GAUGE

Flatness Gauge

FEELER GAUGES

SNAP GAUGE

EXTERNAL THREAD GAUGE

RING THREAD GAUGE

PLUG GAUGES

THREAD PLUG GAUGE

THREAD PROFILE GAUGE

'GO' LIMIT • 'go' limit is the one between the two size limits which

corresponds to the maximum material limit

• the upper limit of a shaft and the lower limit of a hole

• 'GO' gauge can check one feature of the component in one pass

'NO GO' LIMIT

• 'no go' limit is the one between the two size limits which corresponds to the minimum material condition

• the lower limit of a shaft and the upper limit of a hole.

5.2.1 LIMIT PLUG GAUGE

• Limit plug gauges are fixed gauges usually made to check the accuracy of a hole with the highly finished ends of different diameters

• If the hole size is correct within the tolerable limits, the small end (marked “go”) will enter the hole, while the large end (“not go”) will not.

PLUG GAUGE EXAMPLE

• Dimension on part to gauge

• The nominal hole size on part to gauge is 1.0000”;

• Tolerance of the hole is +0.002”/-0.000” ;

• This means the hole must be manufactured somewhere between 1.0000” and 1.0020” in size;

5.2.2 LIMIT RING GAUGE

• Limit plug gauges are fixed gauges usually made to check the accuracy of a shaft with highly finished ends of different diameters is used

• If the shaft size is correct within the tolerable limits, the large end (marked “go”) will go through the shaft, while the small end (“not go”) will not.

RING GAUGE EXAMPLE

• Dimension on part to gauge:

• Post on part to gauge is 1.0000”;

• Tolerance of post on part is +0.002”/-0.000”;

• This means the post will be somewhere between 1.0000” and 1.0020” in size;

STANDARD DEVIATION

Find the mean and the standard deviation for the values 78.2, 90.5,

98.1, 93.7, 94.5.

The mean is 91, and the standard deviation is about 6.8.

234.045

= 6.8

= = 91   Find the mean.(78.2 + 90.5 + 98.1 +93.7 +94.5)5

x

= Find the standard deviation.

(x – x)2

n

Organize the nextsteps in a table.78.2 91 –12.8 163.84

90.5 91 –0.5 .2598.1 91 7.1 50.4193.7 91 2.7 7.2994.5 91 3.5 12.25

x

x

x – x

(x – x)2

One standard deviation away from the mean (μ) in either direction on the horizontal axis accounts for around 68 percent of the data. Two standard deviations away from the mean accounts for roughly 95 percent of the data with three standard deviations representing about 99.7 percent of the data.

SIX SIGMAone to six sigma conversion table

'Long Term Yield' (basically the percentage of successful outputs or operations)

Defects Per Million Opportunities (DPMO)

'Processs Sigma'

%99.99966 3.4 6

99.98 233 599.4 6,210 493.3 66,807 369.1 308,538 230.9 691,462 1

• A six sigma process is one in which 99.9999966% of the products manufactured are statistically expected to be free of defects (3.4 defects per million),

SIX SIGMA

• Six Sigma team leaders (Black Belts) work with their teams (team members will normally be people trained up to 'Green Belt' accreditation) to analyse and measure the performance of the identified critical processes. Measurement is typically focused on highly technical interpretations of percentage

DOCUMENT CONTROL

• There must be evidence of the existence of a system

• A record of the correct operation must be kept

• This is important to trace evidence of inspection in case of future complaints or problems

MTBF

• Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a system during operation

• MTBF can be calculated as the (average) time between failures of a system