Ellis Developments Limited

Nottinghamshire United Kingdom

QUALITY SYSTEMS FOR GARMENT

MANUFACTURE

ACHIEVING THE RIGHT FINAL PRODUCT ON TIME


Control of quality in garment assembly

Example of quality feedback - marks and stains

Action checklist to improve garment cleanliness

economics of cleanliness

Fault cost assessment record

Quality Control Requirements - Order of Priorities

THE COST OF QUALITY

INTRODUCTION

A manufacturer stays in business only as long as his product quality satisfies his customers at the price they are prepared to pay.

Failure to maintain an adequate quality standard can therefore be disastrous. But maintaining an adequate standard of quality also costs effort. From the first investigation to find out what the potential customer for a new product really wants, through the processes of design, specification, controlled manufacture and sale, to the arrangements for aftersales service to the customer, effort is being spent on ensuring that the company's product - and reputation - are good. If it is spent wisely, it can result in savings greater than the increase in costs, and hence in an improvement to profits.

As products become more and more complex, and as customers - both Government Departments and individuals - become more conscious of the effects on their own economics of receiving a proportion of defective items, the effort required must continually increase.

The costs represented by this effort can be a significant proportion of the products sales value (Do you know what the total is in your Company? In some instances the cost of scrap, rework and inspection costs alone has been found to be as high as 20% of turn-over) and any manufacturer should be interested in making sure that he is getting good value for his expenditure. He cannot feel sure unless he has studied what the costs are, how they are incurred and what they ought to be. If they are higher than they should be, he must consider ways in which they can be reduced.

Here we describe the nature of the costs incurred in ring product quality and reliability and shows how costs can be reduced whilst quality and reliability are maintained or improved.

THE NATURE OF QUALITY COSTS

Quality costs fall naturally into three main groups. First there are Costs associated with attaining or setting an adequate quality standard, sometimes called Prevention Costs. They are incurred largely in advance of production, when the quality standard is set. Insufficient money spent at this stage on, for example, design and development may well give rise to unnecessarily high costs later.

The second group is costs associated with maintaining an adequate quality standard, sometimes called Appraisal Costs. These are the costs associated with keeping the work manufacturing and buying functions up to the quality specified in the design.

The third category covers Failure Costs, or the costs associated with putting right any departure from standard. These include the costs of scrap, reprocessing, and guarantee claims. They are the costs, which arise as a result of shortcomings in, or insufficient expenditure on, the other two phases. They may be caused on the one hand by poor design, poor product engineering, poor operative training or, on the other, by bad workmanship, or slipshod inspection at the appraisal stage.

A list of the types of cost connected with quality and reliability will be found in the Appendix. Some difficulty may well be experienced in separating costs associated with quality and reliability from those more directly concerned with achieving the function of the product, for example, design and development. It is more important to recognise the changes deliberately made in these costs as action is taken to bring quality under control.

THE ATTACK ON COSTS

Obviously, the most significant improvements will usually be achieved by concentrating effort on the areas of high cost. For this purpose an analysis of the principal costs is required. Studies have shown that a fairly typical ratio between the three main groups of costs in a manufacturing company is: -

Prevention Costs 5%

Appraisal Costs 30%

Failure Costs - 65%

Failure Costs, because they are typically the largest, will usually give the largest return for the effort involved in reducing them. An effective way of attacking Failure Costs is through a temporary increase in prevention and appraisal costs.

Appraisal Costs - for example, the cost of production and inspection - might be reduced by more attention to Value Engineering, which would to some extent increase prevention costs, and a closer control of the manufacturing process, which would increase appraisal costs.

Appraisal Costs will usually be the next to come under attack. An analysis of all essential quality control operations will often show opportunities for reducing expenditure without reducing effectiveness. For example, statistical sampling techniques may be used as a means of control, indicating trends in performance and assisting to maintain quality. By improving the control of the process, 100 per cent inspection may no longer be necessary.

Total costs will be lowest when design staff are aware of the cost implications of their work. Good design saves cost not only at the design stage itself but throughout production and testing: products become easier to make "right first time". Good design is needed not only when conceiving the product but also when conceiving systems for production and quality control. After failure and appraisal costs have been reduced by attention to the prevention aspect, it may be possible to reduce prevention costs as well.

We have seen that the process of reducing failure costs may well involve increasing expenditure on the design, developing, testing, manufacturing and inspecting processes. However, there must clearly be a point beyond which it would be uneconomic to incur additional expense. Failure costs might possibly be eliminated but at considerable, possibly prohibitive, costs in other areas. There is a point at which the aggregate of all costs is at a minimum for the intended selling price. Achieving this minimum cost will involve reviewing product designs, and improving planning processes, facilities and methods.

When the initial attack on costs has been successful, it will be logical to provide a means for analysing costs and for reporting on them in order to keep a close watch on progress so that, firstly, a worthwhile reduction in the attacked cost is achieved; and secondly, the expected increase in other costs is not exceeded.

SETTING STANDARDS OF COST

This can be done by setting a standard or budget for each cost item affected by the action, and by comparing periodically the actual cost with the standard. Differences between standard and actual cost are then notified to appropriate executives who can modify the tactics of the attack as necessary to ensure that the differences are reduced or eliminated.

Standards may be of two kinds: -


In a company where executives are properly trained and motivated, the first type of standard is likely to be the more effective. Once the initial expectations have been met, further efforts can be planned and new standards set to correspond.

Improvement comes to be regarded as a normal and continuing process.

In companies where executives lack these qualities it may be preferable to adopt the second type of standard, in which a programme for improvement is autocratically imposed. Active follow-up by a strong personality is characteristically necessary in this situation, to see that executives really do all that is needful.

Standards will usually be set under conditions, which assume a certain volume of throughput and a certain level of incoming quality. If either of these factors changes significantly, the level and balance of costs will probably change also, and standards will need to be adjusted to suit the new conditions.

ASCERTAINING QUALITY COSTS

Cost data will have been required when the first study was made to determine the cost items most open to attack. These data will probably have been derived by ad hoc investigation and analysis. The same figures will have been used to derive standards or budgets.

When costs are to be ascertained regularly for comparison with standards, however, a number of steps are involved. First, it is necessary to decide which costs are to be analysed on a regular routine basis, which are to be analysed less frequently, and which will continue to be derived by special cost studies, or sampling cost methods.

The second step is to decide who is to make each analysis. The preference depends largely upon the source of the information. If the details can be made available from the accounting system the Cost Accountant will logically take on the task. However, if the information is of a technical nature or requires to be extracted from the records of Quality Control or other staff, it may be convenient to have it done by these departments.

Next a system of cost coding to simplify analysis must be provided. Where a code system is already in use it may require modifying to enable quality control costs to be collected in the most meaningful form. It is important that the causes of faults should be revealed and this may necessitate identification of the machine, operator or process where the loss arose.

Finally, one must define the procedure to be followed and the responsibilities of all the affected staff.

CONTROLLING COSTS

The only purpose of reporting costs is to provoke action. Without action the money spent on deriving and reporting data is wasted.

Action is required whenever there is a significant difference between an actual cost and the budget set for it. Action is also required to discover the reason for the difference and to eliminate it. If cost reports are to be effective in provoking this type of action they must be: -

- presented  at suitably short intervals

- presented quickly following the period they represent

- presented in simple, direct, intelligible form

- presented to the people who have the authority and knowledge to act effectively.

It is often effective for reports to be sent both to the person who is expected to take action and also to his immediate superior.

It is important to remember that the actual costs revealed by control reports are the result of joint action by quality control staff and by the design or manufacturing functions. Action to correct undesirable trends may therefore have to be taken by all these groups in co-operation. Action by any one group may well be fruitless.

REPORTING COSTS

Effective quality cost control depends upon good cost reporting.

The cost reporting system should:

- identify the areas of expense, which are being reported

- show actual expenditure compared with that planned

- facilitate the comparison of benefits with the price that is being paid for them

- indicate the causes of excessive costs so that further investigations can be made and corrective action taken.

The data from which the Cost Reports are compiled should be so organised that such further investigations into specific excesses can proceed logically and without the need for too much re-analysis of basic documents.

Reports commonly take one of three main forms, corresponding to the main divisions of Quality Costs. The first is the Failure Cost Report. It is not usually difficult to produce adequate regular reports showing the level of failure costs - scrap, repairs, test rejections, after-sales service, customer returns etc. The essential data they should show includes the cause of failure, the value lost, and the department or process responsible (not necessarily the same, of course, as the department or process at which the failure was discovered and reported).

Supporting data for this report may include reporting point, description of product, part etc., and the responsible machine group or operative. Such supporting data is, however, probably best left out of reports for executive action. It may be more valuable in daily, un-costed, reports for information and action at "shop-floor" level.

The second type is the Appraisal Cost Report. This reflects the cost of operating the quality and reliability surveillance, as compared with budgeted expenditure. The division of account headings may sometimes make it difficult to include the cost of quality appraisal costs incurred by production operatives carrying out additional operations such as the inspection, testing, or grading of pieceparts, but such costs can sometimes be derived from a comparison of actual and standard times for the tasks, and included in a separate section of the report.

Finally, a Prevention Cost Report is required. So many functions of the typical business can be interpreted as contributing to Prevention Costs that it is normally wise to restrict reports to those areas which are being deliberately varied as part of the overall cost reduction project. The scope of such ad hoc reports can be enlarged to include data from which changes in Quality tactics can be planned. Such reports might include: an analysis of the effects on profits of changes in the system of setting manufacturing tolerances; the probable cost effects of introducing a Vendor Rating scheme; recommendations on the most economical points for inspection in a sequence of operations; and an investigation into the economics of buying new testing facilities.

Note that in studies involving a choice of methods we are concerned with the change in profit resulting from the decision - that is the difference in the profit-and-loss accounts before and after adopting the change. The costs which we use for studies of this nature are not likely to be the same as those used for normal cost accounting, for which purpose we have become used to the convention of expressing overheads as a percentage of - say - direct labour. This approach is unsuitable for finding the real cost, or change in cost, since in most cases the choice will cause little change in the fixed part of overhead costs, such as establishment and management expenses.

RECOMMENDATIONS

Here are ten steps that can be taken to reduce Quality Costs in your company:




The precise contribution to profit made by the control of the quality costs will naturally vary with the size, type, and technology of each individual company. However, these suggestions can be regarded as the typical requirements for any programme. Because almost all operations of a manufacturing company have some influence on Quality Costs, a full and accurate analysis of costs can become very complex and may itself be costly to produce. Approximations and estimates will often therefore be adequate. Finally it will always be desirable to keep cost calculations and presentations- simple- so that they can be understood readily by those who will be required to take action upon them. -

APPENDIX


Work scrapped: material and labour costs.

Sorting out bad work.

Reprocessing.

Re-inspection and re-testing.

Technical and clerical effort spent investigating faults and complaints.

Warranty claims, and gratuitous after-sales service.

Loss due to sale as second-grade product.

Delay in payment by customer - interest on outstanding money.

Double handling charges.

Double transport charges.

Double packing charges

From: "The Cost of Quality"

Norton, Ward & Elliott

British Institute of Management 1965

THE FUNCTIONS OF QUALITY ASSURANCE AND QUALITY CONTROL

DEFINITIONS OF QUALITY

"Quality" is defined as that combination of design and properties of materials of a product which are needed for the intended end use and level of the market in which it is sold.

"Requisite Quality" is defined as the design and composition of a product, which has been thoroughly proved by adequate development work, in order to establish its reliability under the conditions to which it will be subjected in use and to avoid producing too high a grade of product for the intended market.

AIMS OF QUALITY CONTROL AS THE INSTRUMENT OF QUALITY ASSURANCE OR TOTAL QUALITY CONTROL

"To ensure that the requisite quality of product is achieved"

This ensures customer satisfaction, but it leaves quality control as a necessary but expensive evil

"TO ENSURE, AT MINIMUM PRACTICABLE COST, THAT THE REQUISITE QUALITY OF PRODUCT IS BEING ACHIEVED AT EVERY STAGE OF MANUFACTURE FROM RAW MATERIALS TO BOXED STOCK.

This means six things:


All of these factors increase the possibility of developing further business and the competitiveness of the company, and is therefore to the benefit of the company; Quality control thus becomes a positive -benefit.

A further point stems from one aspect of Q.C: continually monitoring production and deciding whether, in any part of the manufacturing chain, materials, machines or workmanship need attention to effect a reduction in the fault rate. It is very easy to "pass the buck" that is for production personnel to blame materials or to say that it is the responsibility of QC, and so relax any endeavour on their part to avoid faults. In fact, quality cannot be inspected into goods; it is to direct attention and effort towards the most effective areas for avoiding faults and to maintain product consistency.

DEFINITIONS

Quality Assurance

"The establishment and maintenance of ALL activities and functions concerned with the attainment of requisite quality"

Quality Control

"The systems required for programming and co-ordinating the efforts of the various groups in an organisation to maintain the requisite quality" As such Quality Control is seen as the agent of Quality Assurance or Total Quality Control

Specifications

Quality Control requires the establishment of adequate specifications with proper tolerances

Objective

To maximise the production of goods within the specified tolerances correctly the first time.

By considering such information it can be decided what requires to be monitored. Monitoring the process is the essence of quality control.

We now know where we wish to go and what is possible. -

PREPARATION

The next stage after planning is to extract and expand along the guidelines established in the planning stage the technology or the basic know-how for each projected line. These technologies are;

Engineering - fabric, seams, garment

Communications and feedback sequences - without which there can be no control

Parameters - measurements and tolerances

Recording systems

Staffing decisions and the development of job specifications

IMPLEMENTATION

This is the practical control application to the day-to-day running of the factory - and extends from the basic concept of a style right through to the despatch of the correct boxed stock.

INSTALLATION OF THE OVERALL PLAN

The above plan is a continuing procedure in the sense that if starting from scratch one might have to begin with monitoring to get immediate results. This is then followed by a continuing process of refinement along the lines of adding the checking of raw materials and improving feedback routines.

SPECIFICATION

The requisite quality is the standard required to meet the needs of the customer: this must be determined and specified.

The specification must be clear and complete so that everybody from designer to production operative has a clear idea as to what is needed. Individuals within an organisation need only have parts of the specification that relates to their function. -

OBJECTIVE

To achieve a satisfactory design of the fabric or garment in relation to the level of choice in design, styles, colours, suitability of components and fitness of product for the market. This must be viewed in the context of overriding market considerations and production capabilities

APPROACH




CONSISTENCY

Control must be applied to make sure that all goods passed to the customer reach the satisfactory level Planning procedures must be reviewed periodically -

COST

Cost of achieving the required standard of quality must be targeted at all stages -

PRINCIPLES OF QUALITY CONTROL

The essential requirements for producing a reliable product has been stated as follows:-


An important feature to realise in the establishment of these principles is that, whilst tolerances and quality standards for goods going for despatch may often vary rapidly, depending on the urgency of call-off, it is the duty of Quality Control in enacting items 4-7 above, to stabilise the tolerances and quality standards for goods IN PRODUCTION, based on the recognised Requisite Quality and this largely established from the continual experience gained from item 9 above. Only by production personnel knowing exactly what is expected can they respond to the requirements of Quality Control.

ECONOMIC ASPECTS OF QUALITY ASSURANCE

The ideal situation is to keep the cost of conforming to the requisite quality as low as possible, whilst at the same time achieving the highest percentage of acceptable production.

To find if a company is approaching the optimum total cost trials need to be made to establish the costs of quality control and the cost of defectives.

As a first approximation and as a guide, this total cost is usually achieved when prevention costs = failure costs + appraisal costs, as illustrated in the above diagram, and in the diagram below:-

In this firm the total quality costs were approximately 10% of turnover (very low). By increasing appraisal and prevention a saving on total costs of 15% was effected. This is 15% on 10% of turnover, say 1.5% of £2,000,000 i.e. £30,000 saving in cost, improved product, improved delivery times, and improved customer satisfaction.

Additional benefits were

Quality Costs Sources of Cost information

COST OF FAILURE

Losses due to faulty and spoilt work

Examiners records

Mending

Reprocessing


Administrative Costs


Penalties of not meeting delivery dates, e.g. failure to meet export arrangements, shipping. -

COST OF APPRAISAL


COST OF PREVENTION

Preparation and development of specifications

Time of personnel related to salaries

Developing consistency controls, e.g. use of stitch length

Equipment

Operating consistency controls

Costs and salaries of department personnel

Evolving more effective processes

Quality awareness training Wages, account, and training costs

Maintenance of machinery to maintain product quality, e.g. re-needling knitting machines

Production records, wages and equipment costs.

THE BALANCE OF COSTS VERSUS SAVINGS - ASSESSMENT OF INNOVATIONS

The necessity of making conciliation occurs every time an idea or innovation needs to be assessed.

Suppose a new system has been thought up to meet a problem or situation which needs to be improved. The question before getting too involved in detailed planning of such a system, will be does it pay off? This question needs answering before much time, effort and money are spent.


It is wise to seek a trial first, then the idea can justify itself on its own merits, or can easily be dropped if for any reason it proves to be unsuccessful.

THE ROLE OF QUALITY CONTROL


QUALITY CONTROL DATA GENERATED

Data is generated at each QC point. This must be recorded in simple systems to provide visual on-going checks. These records provide the means for personnel accountability and for rapid feedback for management action. -

Raw Materials


Knitting Machine Settings


Fabric Parameters, Fabric or Garment Blank Checks


Sewing Checks


Final Inspection


Recovery Inspection


Yarn Checks


Levelness of yarn (also User levelness).

Product Tests


Performance rating in appropriate test checked against specification. -

Further Yarn Checks (2nd order priority)


As with machine efficiency, checks on process performance.

Analysed against operation section, style, fabric or yarn.

QUALITY CONTROL RECORDS

The above data, immediately on being generated, is automatically entered on records as continuity charts, either in tabular, graphical or computerised form. This action takes very little time, and enables the current data to be compared with previous data and with other related Q. C. data. The visual impact of the presentation is immediate and creates rapid feed-back of vital information to production and other interested management personnel.

BRITISH STANDARD 5750

Introduction

British Standard 5750 Part 2 specifies a quality system, which is designed to provide a comprehensive, concise and logical approach to total Quality Assurance.

It relates to a method of working and not to any specific performance standard of a product. In principle it can therefore be applied to the manufacture of any product.

The essential features of the standard are contained in the following basic requirements:-


To be of value each and every requirement requires individual manufacturer interpretation and implementation relating to the product being produced

This Quality Management Scheme has proven success in many UK industries. At first sight it appears complex and the first reaction is that it will add extra cost to implement. In truth it is a straightforward logical system which gives total control of quality which when implemented will prove fully cost effective.

REQUIREMENTS


To be effective it is essential to establish and maintain clear, complete and current written records of inspection and test procedures for each operation.

These records should identify: -


Records must be kept up to date and be stored for easy access and retrieval and be available for examination.


Documented procedures must be established and maintained to cover: -



Procedures and instruction must be established to: -



All personnel involved with the management of quality must be experienced to receive adequate training to ensure they are competent to perform their required task.

Training must be an ongoing commitment with appropriate records being maintained.

QUALITY CONTROL IN THE DESIGN AND DEVELOPMENT DEPT

If disorganisation in sampling is to be avoided guideline procedure must be established beforehand.

Modifications to the development sample must be noted for inclusion in the final specification.

A handle sample (sealed if necessary) must be established as well as a working sample.

A proper flow diagram must be established with appropriate time factors, and all personnel concerned informed of the duty and timing of their part.

In the following pages, a diagram of typical steps is shown together with details of the duties of Q.C. personnel in this scheme.

In addition, Q.C. can be involved in development at an earlier stage by sampling new yarns. In combination with wearer trials and laboratory tests, assessments of seasonal and other goods can be made, e.g. tests made to ascertain whether fabric is too heavy for spring, is suitable for trousers, drapes correctly for dresses or curtains, or suitable for use in bright sunlight.

QUALITY CONTROL FUNCTION













A SAMPLE GARMENT TO FULL PRODUCTION

(With particular reference to V-bed knitting)

Steps to follow





N.B. if (c) has been correctly carried out machine adjustment should not be required.









THE SPECIFICATION

The specification is the first stage in a quality control scheme to provide precise values of the variables and acceptable working tolerances.

The levels of the quality of design, and the cost related to it have already been determined when the specification is prepared. If this is not correctly determined the company could make a loss on the production, even when the goods are produced correctly to the specification.

Any modifications introduced into the manufacture of a product must be noted, and relevant details appear in the specification

The specification should contain enough information for any competent personnel to produce the required goods at anytime within tolerance.

To assist in preventing a specification becoming unwieldy, simplification can often be made by omitting those details not subject to change from line to line. These are taught to the operative as part of their induction and can be delegated to training.

Much information can be conveyed and a document provided for quick reference if a standard layout is always used. This is shown by the way we use such massive works as a dictionary or telephone directory. An organised and consistent layout minimises errors and time both in compiling and reading.

Different departments within the factory are concerned with different parts of a specification. It is convenient; therefore, If the specification is laid out in several sections, from which concise "see at a glance" details may be provided for each particular department by assembling just the relevant sections on a sheet from a pre-printed, sectionalised Master Specification.

A further method of simplification can be used in those cases where various lines or styles are produced from really the same fabric or knitting, or by using the same seams, apart from, say just one or two small changes.

The basic knitting, garment blank or sewing details can be recorded for each type or fabric, garment blank or seam, and then given a suitable reference number. The actual specification for a particular line will then call up only this reference, together with any appropriate alteration, as noted in the third paragraph above. This idea is, in a way, a development of the sectionalisation of specification.

This idea can be developed further in regard to yarns and seams.

All the various styles are likely to the produced from only a few yarns or seams, even though more than one type of yarn or seam will be required in a garment. Each yarn and each seam used is first stipulated adequately, and this recorded in an appropriate yarn or seam specification with its own reference. The garment of fabric specification will then make reference to the required yarn or seam by quoting just the yarn or seam specification reference. This will probably occur in the first section of the fabric or garment specification, where details of size, customer, order number, licence or trade mark requirements are given.

Each factory will need to prepare forms appropriate to their own requirements and example specifications, divided into sections are available to provide a suggested basis.

YARN SPECIFICATION - EXAMPLE

YARN TYPE - Cotton/Polyester blend, for single jersey knitting

YARN SPECIFICATION NO. DATE

DESCRIPTION **COUNT

*COMPOSITION

FIBRE QUALITY:

**TWIST FACTOR:

ASTM GRADING:

USTER LEVELNESS: CV%

Thins (50% setting) per 1,000m

Thick (setting 3) per 1,000m

Neps (setting 3) per 1,000m

WINDING

COEFFICIENT. OF FRICTION:

TOLERANCES: *In accordance with Statutory Instrument 2124: 1973 - Textile Products (Indications of Fibre Content) Regulations 1973

**Typical value for count delivery acceptance being +12½% of nominal count. Some Trade Associations give rules applicable to their members.

SHADES:

TOLERANCES:

COLOUR FASTNESS:

(Assessed on 1 x 1 rib fabric sample from yarn supplied)

Change in shade staining

Washing: - Rating

Perspiration

Rubbing

Dry Cleaning

Gas fumes

Light

Staining assessed on

PRODUCT SPECIFICATION - Example

COMMERCIAL DATA

GARMENT DESCRIPTION

SPECIFICATION No: - DATE:

STYLE NO:

DESIGN NO:

SIZES:

WT. PER DOZ.

TECHNICAL DATA

YARNS MAIN GROUND

PILE / INLAY

TRIMS

FABRICS MAIN

TRIMS NECK)

CUFFS)

SKIRT)

FINISHING MAIN

DETAILS

TRIMS

LAYING UP & CUTTING

Patterns Drawings

Lay markers

Cut

GARMENT ASSEMBLY

Make-up order and seam spec

Sewing threads

Tapes Zips

AESTHETIC DATA

SHADE AND HANDLE

As sealed patterns

FABRICS

YARNS

REQUIREMENTS

APPEARANCE AND HANG

As sealed garments ref.

CUSTOMER DATA

MEASUREMENTS: Size chart and measuring points as in drawings

LABELLING: Type

Location

Legend

PERFORMANCE

Stability

Colour fastness - BS 1006

Pilling

Extensibility (cuffs and skirts fabric only and in course direction)

Bursting Pressure (on main fabric only)

Seam stretch

Seam security

Needle damage

NON-KNITTING YARN

RAW MATERIALS SPECIFICATION - Examples

SEWING THREADS

SPECIFICATION NO: DATE:

Needle thread for o/lock, cover seams and L/S tabbing and finishing

Fibre

Structure

Designation

Shade

Other requirements

Colour fastness

Bobbin thread for lockstitch

Same as the needle thread

TAPES

SPECIFICATION NO DATE

Location

Width

Structure

Shade

Colour fastness

ZIPS

SPECIFICATION NO

Location

Length

Tapes

Shade

Colour fastness

Stability

Other requirements

PROCESS SPECIFICATION - Example

FABRIC

REFERENCES SPEC NO

FABRIC DESCRIPTION

PRODUCT SPECIFICATION Nos. RELATING

SPECIFICATION NO DATE

MACHINE GAUGE

DIAM FEEDERS

SPEED

WIDTH ROLL LENGTH FINISHED:

MIN. USEABLE ROLL WEIGHT FINISHED:

DOFFING REVS:

DOFFING TIME

TECHNICAL MANUFACTURING REQUIREMENTS

STITCH LENGTH Ground

Inlay

COMPOSITION FABRIC Ground

(off m/c) Inlay

WIDTH (off m/c)

FINISHING REQUIREMENTS

PROCESSES

FINISHED FABRIC PARAMETERS

C/3 cm W/3 cm wt/sq.m

Width overall

PROCESS SPECIFICATION - EXAMPLE

MAKE-UP ORDER

REFERENCES SPEC NO

MAKE-UP ORDER FOR

SPECIFICATION NO

PRODUCT SPECIFICATION NO. RELATING: -

MANUFACTURING REQUIREMENT

Operation Seam Spec. Ref. Extras/seam finish

PROCESS SPECIFICATION - EXAMPLE

SEAM SPECIFICATION

REFERENCES SPEC NO

SPECIFICATION FOR

SPECIFICATION REF. NO: DATE

MAKE-UP ORDER NOS.:

SEWING THREADS

MANUFACTURING REQUIREMENTS

STITCH

BIGHT S/5 cm

RUN-IN

NEEDLE

TENSION

FABRIC STABILITY AND FINISHED WIDTH

Fabrics knitted on circular machines has a set number of wales, determined b y the knitting machine used, - its diameter and gauge (needles per unit length of cylinder circumference). The fabric will be knitted from a certain yarn type and knitted loop length, partly on economic grounds and partly to avoid being too dense or too light a fabric.

There is a commercial incentive to finish fabric as wide and as long as possible. The loop structure of knitted fabrics makes it possible to stretch these fabrics to an appreciable extent. However, in the stretched state the forces on each loop are not balanced, and so the fabric becomes unstable, giving it a tendency to revert to a more natural, relaxed state during which an increase in fabric stitch density will take place, together with a consequent reduction on area, i.e. shrinkage will always occur. It is not possible to set a fabric at what is in effect unrealistic dimensions and at the same time achieves a stable fabric. Therefore, certain diameters of knitting machines are to be used (which is a must unless we are prepared continually to replace existing machinery). Since the fabric will be knitted within fairly narrow ranges of yarn type, count and loop length, then the fabric must be finished as near as practical to its natural width and length and not over stretched, if it is to be without excessive shrinkage in service (e.g. washing). In this state the fabric will have fairly definite width and length dependent on the machine, yarn and loop length used. Efficient lays should be planned on these dimensions, and not on some predetermined ideal.

If shrinkage is not an important consideration, then extra width and length can be considered. The fabric characteristics can be determined by calculations form the fabric geometry and by trials, and the finished dimensions to be stipulated modified accordingly.

Unless these factors are fully understood, a satisfactory fabric specification will not be possible.

EXAMINATION ON RECEIPT OF FABRIC


There is more to examination machine design than meets the eye. It is worth considering a total examination environment which can improve the overall standard of the examination department.

The main action of a fabric examination machine is to unroll, measure and re-roll the fabric, and to contribute to an environment in which it can be inspected by an examiner. This requires the following characteristics:-


There are a number of critical features of fabric examination machines apart from the above, but which can be expected to be incorporated within a machine which is of a standard which conforms to the above requirements. These include angle of slope of the examination table, distance of fabric from examiners position, speed range of fabric movement, light positions. There are a number of training exercises that have been suggested for new examiners to improve the range of the width of the fabric that is studied during examination and to reduce the training period.

Transmitted light - generally for Quality Control faults - e.g. a fluorescent light inside trousers. Reflected light - generally for commercial faults.

BASIC TECHNOLOGY OF SEAMS

THE PURPOSE OF SEAMS

The main function of a seam is to join pieces of fabric unobtrusively in such a way as the preserve as far as possible the basic properties of the fabrics being joined.

There are many seams and stitches, which are described in a comprehensive British Standard B.S 3870: Part 1 - Stitch Types, and Part 2 - Seam Types.

DESIRABLE FEATURES OF A SEAM


TYPES OF SEAMS

In B.S 3870 part 2, seams are divided into 8 classifications, in each of which there are many variations. However, for purposes of clarity, with weft knitted garments, the seams used may be considered under the following four main types.


Within each of these groups there are many variations of the basic theme. Many of the seams may be produced with one or more stitch types.

BRITISH STANDARD CLASSIFICATION OF STITCHES B.S 3870

Stitches are divided into six classes, within each of which are several types of stitch. The characteristics of each class are indicated below, followed by illustrations of commoner stitch types and details of their properties and applications.

Stitch class 100. Chain stitch

This class stitch is formed with one or more needle threads and has for its general characteristics intralooping*. A loop or loops of thread or thread is passed through the material and secured by intralooping with succeeding loop or loops after they are passed through the material to form a stitch.

Stitch class 200 Hand stitch

These stitches, having little application in mass production, are not included in the succeeding sheets.

Stitch class 300 Lock stitch

This class of stitch is formed with two or more groups of threads and has for a general characteristic the interlacing* of the two groups. Loops of the first group are passed through the material where they are secured by the thread or threads of the second group to form a stitch.

Stitch class 400 Multi-thread chain stitch

This class of stitch is formed with two or more groups of threads and has for a general characteristic the interlacing and interlooping * of the loops of the two groups. Loops of the first group of threads are passed through the material and are secured by interlacing and interlooping with loops of the second group to form a stitch.

Stitch class 500 Overlock stitch (overedge or edge seaming)

This class of stitch is formed with one or more groups of threads and has for a general characteristic that loops from at least one group of thread pass around the edge of the material. Loops of one group of thread are passed through the material and are secured by intralooping with themselves before succeeding loops are passed through the material, or secured by interlooping with loops of one or more interlooped groups of threads before succeeding threads of the first group are again passed through he material.

Stitch class 600 Flat seam stitch

This class of stitch is formed with two or more groups of threads and has for a general characteristic that two of the groups cover the raw edges of both surfaces of the material. Loops of the first group of thread are passed through loops of the third group already cast on the surface of the material and then through the material where they are interlooped with loops of the second group of thread on the underside of the material. The one exception to this procedure is Stitch Type 601 where only two groups of thread are used and the function of the third groups is performed by one of the threads in the first group.

*For the sake of precision in description the following terms have been used:

Intralooping

The passing of a loop of thread through another loop formed by the same thread

Interlooping

The passing of a loop of thread through another loop by a different thread

Interlacing

The passing of a thread over or around another thread or loop of another thread

RECORDING SYSTEMS

Reasons for recording

Recording provides


It is essential for any Quality Control System that adequate records should be devised and kept. Such records are required to supply essential information when goods being manufactured are failing to conform to the specification and the standards required. In the making up room records are needed for


Seam Control checks

These checks should be made on a regular basis usually by the quality control staff; to ensure that the seams being produced are meeting the technical specification laid down. An example for a Seam control check card is given below:

RECORD CARD FOR SEAM CONTROL

(DIAGRAM)

Operative quality checks

These checks should be made not less than once a day by each supervisor. These are checks to ensure that each operative is producing seams that appear satisfactory. In most factories one of a supervisor's duties will be the responsibility for the quality of the work produced in that section.

An example for an Operative quality check card is given. This would be kept by the machine.

Entries on the card would only be made if one or more checks under any one day, or item, are substandard.

RECORD CARD FOR WEEKLY CHECK OF OPERATORS' PERFORMANCE

(DIAGRAM)

As each fault is noted it can be entered against the appropriate item no. In the column for the particular day as five-barred-gates, from which the totals, daily and weekly, for each item can be quickly assessed.

Similar card for Supervisor's record

(DIAGRAM)

To obtain the all-important overall picture of operatives over a period, it may well be a time saver in the examination of these weekly reports, to enter the weekly totals on a Trend Chart.

(DIAGRAM)

EXAMPLE SINGLE OPERATION CHECK

(DIAGRAM)

EXAMPLE REPAIRS RECORD

(DIAGRAM)

It is often helpful for a Supervisor to have a checklist for each operation under her control, as a reminder.

SUPERVISOR'S CHECK LIST

(DIAGRAM)

(DIAGRAM OF REVERSE SIDE)

SEAM CHARACTERISTICS

STITCH CLASS 100 - CHAIN STITCH

Stitches within this class have excellent extensibility and a neat appearance but will unravel easily if the thread is broken.

The single thread Class 101 chain stitch is extensively used for basting, i.e. sewing with temporary stitches and, in the knitted sector for linking neck ribs to garment bodies. The linked seam may be identified by the passage of the sewing thread through the loops of the knitted structure rather than a random penetration.

To form the Class 103 stitch (blind stitch) the needle and thread is passed through the top ply and horizontally through portions of the bottom ply without actually penetrating it to the full depth. The stitch is invisible from the outside and this s used extensively for hemming

Class 104 is essentially decorative and is known as saddle stitching.

STITCH CLASS 101 - Chain Stitch

PROPERTIES


APPLICATIONS


STITCH CLASS 103 - CHAIN STITCH (HEMMING)

PROPERTIES

Invisible from the face side of the garment as the needle and thread is passed through the top ply and horizontally through portions of the bottom ply without penetrating it to the full depth.

APPLICATIONS

Turning up hems on trousers, skirts, etc.

STITCH CLASS 301 - LOCKSTITCH

PROPERTIES


APPLICATIONS

The most widely used stitch in the clothing sector. By virtue of 5 above is very suitable for darts and pleats. Can be secured at both ends of seam by back tacking, i.e., reversing machine over two or three stitches. This stitch is also used in the knitted sector for such applications as stitching pockets onto cardigans.

NOTE

Length of sewing between bobbin renewals limited by the small capacity of the bobbin.

STITCH CLASSES 304, 308 - ZIG-ZAG STITCHES

PROPERTIES

As for lockstitch class 301 except: -

The zig-zag configuration gives a significantly higher extensibility than class 301.

Length of sewing, limited as with type 301.

APPLICATIONS

Widely used in foundation garments and in swimwear.

STITCH CLASS 401 MULTI-THREAD OR DOUBLE LOCKED CHAINSTITCH PROPERTIES


APPLICATION


********************************************************************

STITCH CLASS 402 & 406 - MULTI THREAD CHAIN-STITCH (Cover Stitch)

PROPERTIES


APPLICATION


STITCH CLASS 500 - OVEREDGE STITCH

These are more commonly referred to as over-lock stitches although, to the purist, this is a name peculiar to Wilcox and Gibbs machines.

Contained within the class is the very well known Class 504 three-thread overlock, its subtle variant the Class 505 three thread and the not dissimilar two thread stitches. The class also contains a single thread version.

Eight twin needle overlock stitches are listed in the British Standard 3870 ranging from two to four threads. The most widely used is the four threads Class 505 which is frequently referred to as a "mock safety stitch".

STITCH CLASS 504 - THREE THREAD OVERLOCK

PROPERTIES


APPLICATION


STITCH CLASS 503 - MOCK WELT

This type of stitch is formed with two threads: one needle thread, A and one looper thread, B. Loops of thread A are passed through the material and brought to the edge where they are inter looped with thread B. The loops of thread B extend from this inter looping to the point of needle penetration of the next stitch and then inter loop with thread A.

PROPERTIES


APPLICATION

This seam is used for "serging" or binding edges of trouser seams. Is also used for mock welting of which there are two types - inverse and standard - these names refer to the way in which the fabric is folded. One gives a seam, which is a mirror image of the other.

It is used for underwear e.g. vest bottoms.

STITCH CLASS 514 - TWIN NEEDLE OVERLOCK (MOCK SAFETY)

CONSTRUCTION AND APPEARANCE

Requires, in the case of some three-thread overlock machines, no more than the fitting of the second needle together with the thread and a suitable all round tension adjustment.

PROPERTIES

As Type 504 overlock but with the additional security afforded by the larger bight required by the second needle. Is sometimes referred to as a 'mock' safety stitch.

APPLICATION

Any application in which a three-thread Type 504 overlock seam could be used but, by reason of a very open structure in the knitted fabric, an extra bight and the additional security afforded by two needle threads is desirable.

Such applications frequently include the crutch seam of tights. The seam is also used extensively in modern shirt manufacture from fine gauge warp knitted fabrics.

STITCH CLASS 512 - FOUR THREAD TWIN NEEDLE OVERLOCK

CONSTRUCTION AND APPEARANCE

Similar to Type 514 but both loopers carries over both needles.

PROPERTIES

Similar to Type 514 but with both loopers engaging both needles, there is greater security and extensibility.

APPLICATION

As replacing Type 514

STITCH CLASS 600 - FLAT SEAM STITCH

Flat seam stitches were developed to provide the elasticity necessary in seaming knitted fabrics together with the strength to produce a secure butted seam. They range from three to nine thread stitches and have a wide application.

Seams are formed with three groups of threads, the general characteristic being that one group bridges the butted join on the face of the fabric, the second group bridges the butted join on the reverse of the fabric; the two groups are interconnected through the fabric by the third group i.e. the needle threads. The exception is the Class 601 which is comprised of only two groups, the function of the first group being performed by one of the threads of the third group.

Certain Class 600 stitches are referred to as cover stitches but it should be noted that, unlike Class 400 cover stitches, they cover both the top and bottom of the seam. Notable among them is the Class 602 which is identical to the twin needle Class 406 but with the addition of a top cover thread laid on by an auxiliary finger. The Class 605 is a three needle version of the Class 602.

By virtue of their lack of bulk and covered raw edges stitches in this class, principally the well known nine thread Class 606 and the more extensible six thread Class 607, are used for such applications as gusset insertion, reinforced sections in girdles and corsets, side and shoulder seams on vests and on some of the more expensive garments.

STITCH CLASS 602

PROPERTIES


APPLICATION

A widely used stitch in girdles and corsets. Also used for finishing hem of skirt bottoms

STITCH CLASS 605

PROPERTIES

Same as for stitch class 602.

Stronger than 602, but uses more sewing thread.

APPLICATION

This widely used stitch is sometimes referred to as "triple interlock". Typical examples are in the legs of swimwear either with or without elastic insert. There are other applications in lingerie, underwear and corsetry, e.g. gussets in briefs and panty girdles.

STITCH CLASS 606 - NINE THREAD FLAT-LOCK

PROPERTIES


APPLICATION


STITCH CLASS 607 - SIX THREAD FLAT SEAM

PROPERTIES

As Class 606, which seam the Class 607 was designed to supercede by reason of simplicity and improved extensibility.

APPLICATION

As Class 606.

There are machines available which will produce simultaneously stitches from two of the classes mentioned above, for example, a 401 (twin thread chain stitch) in combination with a 504 lockstitch. These are referred to as safety stitches (see mock safety stitch under class 504).

STITCH FORMING ACTION OF THE ROTARY HOOK MACHINE

Rotary hook machines form the Type 301 lockstitch by carrying the needle-thread loop around the bobbin containing the under thread, in the following manner:

Commencing with the needle at the lowest point of its stroke, as the needle starts to rise the needle-thread, being flexible bulges out away from the need to form a loop. (See Diagram 1)

The needle penetrates the fabric with the needle-thread taut to either side of it. The thread is shrouded in the long groove on the feed in side and is thus free from friction as it passes through the fabric.

As the needle commences to rise from the lowest point of its stroke the combination of thread to fabric friction and the upward movement of the needle eye causes the needle thread to bulge out away from the needle to form a loop on the opposite side of the needle to the long groove. (See diagram 1)

DIAGRAM 1

The loop formed in the needle-thread is entered by the point of the sewing hook, as illustrated in diagram 2.

DIAGRAM 2

As the needle continues to rise and the hook progresses in its rotation, the needle-thread take-up arm provides sufficient slack thread to be drawn down through the material to increase the size of the loop.

On its first revolution, the sewing-hook carries the needle-thread loop around the bobbin-case and bobbin, the inside of the loop sliding over the face of the bobbin-case whilst the outside passes around the back (as shown in Diagram 3) to enclose the under thread.

DIAGRAM 3

As the needle-thread take-up starts to rise, the loop is drawn up through the 'cast-off' opening of the sewing-hook before the revolution is complete.

During the second revolution of the sewing-hook the thread take-up completes its upward stroke, drawing the slack thread through the material and setting the stitch. Meanwhile, the feed-dog has moved forward carrying the material with it and drawing the required length of under thread from the bobbin.

The presser-foot guards against slippage by holding the fabric firmly against the teeth of the feed-dog whilst the feed-dog is carrying the fabric across the smooth face of the throat or needle-plate.

The all important timing relationships between the needle-bar, sewing-hook, thread take-up, etc. are established by the fact that all motions are derived from a common shaft.

VARIABLES OR FACTORS AFFECTING SEAM PROPERTIES

The overlock seam can be taken as an example of the inter-relation of seam variables and properties.

DIAGRAMS

Fabric strength

Needle thread strength

Bight

Seam stitches per unit length

Affect strength across seam

Fabric stiffness

Needle thread extensibility

Needle thread tension

Seam stitches per unit length

Affect seam grinning and gaping

Seam stitches per unit length

Needle thread extensibility

Fabric extensibility

Combined thickness of fabric plies

Cover thread thickness

Needle thread tension DIAGRAM

Presser foot pressure

Affect seam extensibility

Stitches per inch

There is a minimum below which a seam will not hold without gaping and grinning, and the stitches will ride prominently on the fabric surfaces.

There is a maximum above which the seam jams with sewing thread, the base fabric is damaged, the seam puckers and is thick and rigid.

Cost increases with increasing stitches per inch. Thus stitches are kept as low as possible for the seam to look right and to perform correctly - i.e. stitches per inch is a matter of experience. However a guide is provided by dividing the mean of the courses and wales of the fabric by 2.

Bight

This is the term given to the distance between the edges of the fabrics being joined in the seam and the line of the needle thread, - i.e. the sewing line.

This can be too big for comfort and aesthetic considerations or too small so allowing slippage to occur. Again, experience, i.e. appearance, feels and stretching across the seam will decide. If narrow bights have to be used, stitches per inch may need to be increased above the first estimate or a stitch with more than one needle thread used.

Extensibility

If this is inadequate the seam is either too tight or cracks.

The required extensibility is achieved by: -


Summary

The inter-reaction of the various factors is shown below:

DIAGRAM

RECORDING SYSTEMS

Reasons for recording

Recording provides


It is essential for any Quality Control System that adequate records should be devised and kept. Such records are required to supply essential information when goods being manufactured are failing to conform to the specification and the standards required. In the making up room records are needed for


Seam Control checks

These checks should be made on a regular basis usually by the quality control staff; to ensure that the seams being produced are meeting the technical specification laid down. An example for a Seam control check card is given below:

RECORD CARD FOR SEAM CONTROL

(DIAGRAM)

Operative quality checks

These checks should be made not less than once a day by each supervisor. These are checks to ensure that each operative is producing seams that appear satisfactory. In most factories one of a supervisor's duties will be the responsibility for the quality of the work produced in that section.

An example for an Operative quality check card is given. This would be kept by the machine.

Entries on the card would only be made if one or more checks under any one day, or item, are substandard.

RECORD CARD FOR WEEKLY CHECK OF OPERATORS' PERFORMANCE

(DIAGRAM)

As each fault is noted it can be entered against the appropriate item no. In the column for the particular day as five-barred-gates, from which the totals, daily and weekly, for each item can be quickly assessed.

Similar card for Supervisor's record

(DIAGRAM)

To obtain the all-important overall picture of operatives over a period, it may well be a time saver in the examination of these weekly reports, to enter the weekly totals on a Trend Chart.

(DIAGRAM)

EXAMPLE SINGLE OPERATION CHECK

(DIAGRAM)

EXAMPLE REPAIRS RECORD

(DIAGRAM)

It is often helpful for a Supervisor to have a check list for each operation under her control, as a reminder.

SUPERVISOR'S CHECK LIST

(DIAGRAM)

(DIAGRAM OF REVERSE SIDE)

ANALYSIS OF RESULTS OF QUALITY CONTROL CHECKS

Compare: -


Courses of action

If the results show that


TOLERANCE LIMITS

Introduction

All products are subject to variations in consistency, caused by variations in raw materials, processes, operatives, conditions, measuring and so on. The likelihood, therefore, of a product being exactly to specification are therefore remote. However, the variations are just as likely to give results that are too high as they are to give results that are too low - the results will vary in a random manner. This law of randomness is fundamental to an understanding of the statistical approach to quality control. -

RANDOM DISTRIBUTION

If repeated measurements of any particular factor are taken as production proceeds, the results will be found to cluster around a figure we call the average, with a spread of results on either side, with diminishing frequency as we move away from the average. A graph of the result, shown horizontally on the graph below, against the number of occurrences of that result, we obtain typically the shape shown. The specified tolerances ought to bear some relation to the peak in the curve.

Tolerances

If we fix limits within which we will accept a product as satisfactory, then clearly the further apart and on each side of the average we set limits, or tolerances, the greater will be the proportion of production that we will accept. If the tolerances are set too close, then we cannot get it all 'right first time' but if they are too wide, then we will get, for example, garments which will not fit even though manufactured to specification.

Conventional statistical approaches suggest that tolerances should be set from knowledge of the standard deviation of the results obtained. This is perhaps rather like setting the cart before the horse, and suggests that there have to be a certain level of rejected items come what may. Thus it is conventional to reject a certain proportion of production set at perhaps 4%. This is of course a nonsense, since what we are striving to do with our 'right first time' approach is to set everything up carefully, and to manufacture the goods to the best of the capabilities of the personnel and equipment. The tolerances should be set so that if they are made on a machine properly all the goods will be within tolerance. It is only when the mean of the results obtained changes, that our monitoring techniques should cause the alarm to be raised. When we get a drift of the mean then the plan of remedial action set out below comes into play.

Standard Deviation

The scatter of results can be measured through the statistical measure of standard deviation - which is the measure of the spread of results. A number of factors stem from the standard deviation, which also have statistical value, but outside the present scope. -

Action derived from Tolerances

Tolerances, once agreed upon, can be used to decide courses of action.

If a machine average drifts, the machine will produce rejects with a noticeable reject rate. Tolerances will indicate when adjustment is needed, and by how much. The right hand curve represents work from a machine whose average has drifted. The work out of tolerance can be seen.

In order to contain and check any drift without the dangers of over-correction, the required action can be summarised as follows: -



This avoids over-correction.



Before making any actual adjustment it is well worth checking that no obvious fault has occurred, say yarn path dislodged, dirt, lint etc. If it has, rectify the situation and then recheck. If still out make the appropriate adjustment.

Although a certain percentage of work will always be outside the tolerances the whole point of a QC scheme is to prevent as far as is practicable, any drift in the average, in other words that the overall average remains exactly the same. -

TRAINING QUALITY STANDARDS AND FAULT ANALYSIS-

Quality is of prime importance in any aspect of business. Customers demand and expect value for money. As producers of apparel there must be a constant endeavour to produce work of good quality.

QUALITY STANDARDS


By a Quality Standard we mean the establishment of the threshold at which level of severity a defect becomes unacceptable, i.e. a fault. It is the equivalent of tolerances applicable to measurable factors.

Systematic training involves the training of a person in: -


Without this last item defective production cannot be prevented.

These standards are established from the Specification and buying sample, etc.

Next step is control of consistency, - i.e. supervision of, and inspection after, each stage of manufacture.

Quality cannot be inspected into a product; it is either there or not. It must be bred into the making of the product by the operative; this is where quality starts. Instructors of trainees are therefore at the controls of quality.

It is vital that all faults and defects that are likely to arise in any job should be taught to all trainees during their instruction. A machinist, knitter or operative of any kind must be able to recognise these faults and take action on them, that is, to report, correct or prevent them!

Quality Standards must be recognised and agreed by all levels of Management. In the absence of such agreement the operative does not know what is expected of him or her, becomes frustrated, and leaves, with the ensuing needlessly high labour-turnover and training costs of new labour.

This recognition and agreement is greatly assisted by reference to a library of faults, each fault being illustrated in the various degrees of severity, - from certainly acceptable to definitely no. This is discussed in item 6 "Fault Analysis" later in this handout. A major difficulty here arises from the fact that quality standards applied to goods going for despatch may often vary rapidly depending on the priorities balance at that moment for urgency of delivery. However, whatever the situation here, it is the duty of Quality Control to stabilise the Quality Standards applied on the production line. The standards will gradually vary in time, and must be agreed by all levels of management, taking into consideration the feedback from Customer Returns and Store Returns.

Cause of Faults and Action to be Taken



Supervision



General faults are, for example, those resulting from machine or operative defects, such as: -


Job faults are those which occur specifically in the job being studied, in overlocking sleeves, for example: -


General faults should be kept with each machine type used in the factory, so that when asked to teach a new job only the actual job faults need to be studied.

Fault Analysis


It is desirable, in order to teach quality standards well, to build up progressively a library of these faults.


The background and implications of each fault should be listed under the FACERAP headings. It is essential to ensure the accuracy of the information, which can be obtained from a number of sources: -


The information is recorded under the following headings to facilitate teaching: -

FAULT - Correct name/agreed name. (Taught so that trainees can report to the Instructor/Supervisor/Mechanic.)

APPEARANCE - Clear description or an example attached. (Trainee cannot take remedial action unless he/she can recognise the appearance or feel of the fault).

CAUSE - All the main causes, for example: - faulty cutting, incorrect machine setting, machine breakdown, mistake by operative or previous operatives.

EFFECT - Result of the fault, cost of the fault, for example: - weak edges likely to break away, scrapped or seconds, loss of incentive pay.

RESPONSIBILITY - Which defects are trainees' own fault and which are the responsibility of others. Do not encourage the passing of blame, similarly, do not blame unfairly.

ACTION - What action is to be carried out on discovery of the fault, for example: -

reject, unpick and re-sew,

report to Instructor/Supervisor/Mechanic.

PREVENTION - Any action which can or should be taken to avoid a recurrence of the fault should be recorded, for example: - check tensions and stitches on every third garment. Ensure edges match before sewing, etc.

An example is given below for a fault in half hose.

FAULT ANALYSIS CARD

FAULT

Split

Stitch on

Linking

APPEARANCE

Half stitch or part

Of stitch

CAUSE

Failure to place whole stitch on point

EFFECT

Weak part in seam which under pressure will break away

RESPONSIBILITY

Operative

ACTION

Remove fabric from points and run on

PREVENTION

Check each stitch is on a constructive point when fabric is run on

SUGGESTED TEACHING METHODS

This should be carried out by means of knowledge lessons and some suggestions regarding time and how to organise the main part of the session, are given below: -


Then compare the trainees completed cards with the master card and discuss.

A range of examples from various sections of the industry is given below: -

LEVELS OF FAULTS AND SECONDS

USE OF SAMPLING TECHNIQUES

In many situations the cost arid expediency considerations force us to judge a state of affairs from the results of sample tests despite the risks of loss of accuracy. In such situations clearly the larger the sample the more accurate the result, but — the more costly the exercise. Statistics can give us guidance on the optimum size of sample to take. This then leaves us to decide on frequency of testing.


This will depend on the volume of production, various cost considerations and the reason why sampling is required. The sample size does not depend on volume of production, but simply requires that the line is a long run. In this connection a line, or rather a category, can be regarded as containing all items carrying substantially the same fault types and fault rates. Often the whole production is sampled on the basis of the overall fault rate.

The frequency of sampling will largely depend on the desired speed of feedback, and decided in the light of experience. Generally a weekly basis is satisfactory, with sub-weekly sampling, when a situation, i.e. fault rate, goes above the agreed level.

Sampling may be carried out in its own right to obtain information otherwise not available at any stage in the manufacturing chat may he carried out as a regular Q.C. check on any 100% testing already in operation, - e.g. final inspection,

INSPECTION AND RECORDING TECHNIQUES

Inspecting for defectives

Make a quality control inspection of a representative sample.

For example - Total number to be inspected in week, 54 doz.

Week ‘s production 400 doz. of A, 200 doz. of B, 100 doz. of C.

Sample for inspection 30 doz. of A, 16 doz. of B, 8 doz. of C.

Make a form with suitable headings and record faults building five-barred gates. See diagram.

Suggested Sub-Headings for the Extension of Columns

Knitting: - Knitter's knots, press-offs, needle marks, dropped stitches, cuts, moles, swarf, dirt,

Columns "Making-Up" and "Dyeing and Finishing" can be extended in a corresponding manner.

Recording Results of Period Checks

The results of each sample inspected will have been obtained on a percentage basis. These then need to be recorded sequentially on a chart for the reasons given.

A recommended method is to plot on a graph the percentage levels obtained in the inspection. See diagram.

Period checks

Reasons for carrying out periodic checks are:

1. To check that the acceptable levels are being maintained.

2. To provide information on which reappraisals may be made.

3. To obtain a more accurate value of the levels of the total population, and modify the sample size accordingly.

SEEING COLOUR AND EFFECT OF THE TYPE OF ILLUMINANT ON THE APPARENT SHADE OF A SAMPLE



The eye sees colour by reason of three sets of receptors (called cones). One set responds from red to blue with a peak response in the orange band (the "red" receptor); one set responds from orange to blue with a peak at green (the "green" receptor); and one set responds between green and violet with a peak at blue-violet, (the blue/violet receptor).

Consider yellow light reflected from a mid-yellow surface. This light stimulates both the green and red receptors, and the brain says "yellow", as if this occurs in the yellow part of the spectrum. In fact, the tones of yellow, whether orange-yellow or green-yellow are determined by the relative amounts by which the red and green receptors are stimulated. In orange-yellow light the red stimulus predominate, in green-yellow he reverse.

It follows then, that green light and red, because they stimulate their respective receptor, could be blended to give these shades of yellow without yellow light being there at all. The eye would still see yellow shades. This applies to all the other colours between violet and green as well as green and red.


Referring back to the mid-yellow surface, it could be obtained by a colour agent or mixture, reflecting both in the green and the red bands, or by colour reflecting across green to red.