Ellis Developments Limited
Nottingham, United Kingdom
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Ellis Developments Limited Nottingham, United Kingdom
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QUALITY SYSTEMS FOR GARMENT MANUFACTURE ACHIEVING THE RIGHT FINAL PRODUCT ON TIME
The cost of quality Functions of Quality Assurance Commercial advantages form effective control systems Economic aspects of quality assurance The role of quality control Outline of quality control systems requirements Data generated British Standard 5750 Quality control in the sampling/development department From sample to full production The Specification layout Product specification examples Process specification examples Example garment specification Seam specification examples Performance specification examples Fabric and garment dimensions - fabric stability and finished width Fabric inspection - examination of fabric on receipt Basic technology of seams Stitch forming action Quality checks on seams 7.1 Recording Recording systems - making up Supervisors check list Analysis of results 7.2 Tolerances Tolerance limits 7.3 The threshold of faults Training quality standards and faults analysis 7.4 Sampling techniques Checking levels of faults and seconds 7.5 Technology if Inspection Garment examination Seeing colour and the effect of type of illuminant on the apparent shade of a sample Effects of intensity, angle of illumination and type on the apparent shade of a sample Effects on shade of other colours in adjacent areas Mounting and displaying for viewing Colour vision 7.6 checking operatives and examiners Assessment of operative effectiveness from records The supervisor and quality control Weather trials 7.7 Auditing Boxed Stock Boxed Stock Quality Audit 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: - 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: 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:
e.g. by how much will the customer guarantee claims be reduced? How large a reduction in scrap can be expected from Room "X"? e.g. what will extra design administration cost? How much will have to be spent on new test gear?
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
Quality engineering, and testing through pre-production stages; material specifications and design tolerance. Training Quality and Production personnel in quality attainment. Preparing test specifications and quality standards. Specifying test and inspection equipment. Advising on specifications of the production facilities needed to maintain quality standards. Testing and calibrating inspection and production facilities. Quality administration. Replacement of hand by machine operations. Replacement of hand operated by automatic machines. Providing mechanical handling facilities. Providing adequate protective packing. Providing adequate protective storage. Providing bins etc. to protect components during process. Vendor and incoming inspections. Inspecting and testing products and facilities. Field testing. Maintaining, re-testing and calibrating inspection and production facilities. 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;
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
Fault level Waste Seconds Losses Delivery weight of yarn and record results
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
e.g. testing incoming materials etc e.g. 1st examination and final examination. e.g. wash tests, yield tests, and appearance checks, any other checks
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
Check on incorrect condition
Product Tests
Shrinkage, and extension recovery where needed - to be within tolerance of specification Abrasion, pilling or snagging - tested where needed. Rating checked against specification
Further Yarn Checks (2nd order priority)
As specified for correct labelling As required On new deliveries and on demand for fault diagnosis. To be within specified tolerance Test and compare to specification When records of finishing loss, yarn utilisation, count, grey weights, or finished weights abnormal, oil content checked; and also if yarn running abnormally. Content figure to be within tolerance of specification. Shade and size checked to be correct (e.g. buttons) Stability (e.g. linings and trims and zip tapes) within tolerance of specification. Extensibility and modulus (e.g. binding and elastic) within tolerance of specification. Items work properly (e.g. zips) Sewing threads, correct shade, ticket number and sews normally Goods in warehouse - sample checked for quality and faults. Goods rejected - check to see if correctly rejected. Ratio of knitting time or goods produced compared with basis if no down-time. Provides measure of machine performance - analysed against knitter, machinist, fabric quality, garment style and 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 achieve the overall objective you will need to establish, document and maintain a system capable of ensuring that products conform in total to standards, specifications and sealed samples. This will be required at every stage of manufacture. Records must be maintained to give objective evidence that the specified requirements have been met. You will need to appoint a management representative preferably independent of other functions to be responsible to oversee the total control system and inspection at each stage of manufacture. The person appointed should have the necessary authority to execute any action related to achieving the desired standard of product. To be effective the system requires planned periodic review by Senior Management to ensure its effectiveness is maintained. This will entail internal audits, which must be positive and not conducted solely as a matter of expediency resulting from a quality problem. These records should identify: -
Records must be kept up to date and be stored for easy access and retrieval and be available for examination.
All inspection, measuring and test equipment requires effective maintenance and calibration. The quality system must be capable of controlling the standards of materials and services supplied by third party suppliers. Your purchasing documents must clearly define any desired standards or specification requirements. All incoming goods from third party suppliers must be inspected and tested as appropriate and records maintained. In-work inspection should be conducted during manufacture on all characteristics, which cannot be left until final inspection to prevent subsequent sub-standard products. This type of inspection to be effective must act as a process control. The supplier must establish satisfactory written standards and representative samples or workmanship which must equate to standards and specifications laid down in Data Sheets, Make-up Specifications and Sealed Samples. These standards must provide an objective base on which decisions are made by skilled personnel.
All finished products must be inspected and tested to ensure conformity against any relevant standard or -specification. The documented procedure established at this stage should ensure that any inspection or tests conducted at an earlier stage have been performed and the data obtained acted upon. Sampling procedures used should be such that any information gained from the sample equally relates to the bulk from which they were taken. There must be an effective system established to deal with non-conforming material to ensure it is clearly identified, segregated and disposed of. Adequate records must be maintained for subsequent review. Any repair or rework activities to correct non-conforming material must be clearly identified and documented. Where you wish to use alternative inspection procedures and equipment valid evidence must be available to ensure they provide equivalent assurance of quality. You must establish and maintain a procedure to clearly identify products at each stage of manufacture e.g. products not inspected; products inspected and passed; and products inspected and rejected.
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
describe type of garment with sketch/photograph weigh garment record seams and stitches for garment assembly
select nearest suitable commercial yarn available and gauge of machine to be used for adaptation to reproduce sample on the basis of (a) calculate stitch length to be used on the basis of (b) calculate the courses and needles required in each structure calculate course lengths required
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: 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/3cm W/3cm 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/5cm 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
As much as 10% of incoming fabric can be considered to be unsatisfactory, but due to inadequate control or commercial pressures less than 5% is returned. The figure of 10% is not surprising. The material cost saved by a 100% inspection may more than save the cost of that inspection. Moreover valuable information can be obtained to aid in production planning through the factory. Where the quality of each piece has been established before it is issued to the cutting room, the cutter can be given clear instructions in the preferred manner in which any faults can be absorbed. Where 100% inspection is not feasible in the first instance
Procedure for Incoming Fabric Check list Piece of Each pattern Or colourways If satisfactory if not satisfactory Check every check every fifth piece piece If satisfactory Continue checking check every every fifth piece piece
For examination to be a success it is vital that the examiner has an examination specification. This should include items along the lines of the following:- Length Width Weight Incorrect colours Incorrect pattern Bow and Skew Number of parts Fault rate Dye listing or tilt Stains and marks
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
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
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
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.
EXAMPLE SINGLE OPERATION CHECK
EXAMPLE REPAIRS RECORD
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 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
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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 |