2 - design mrp2 systems

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Journal of Quality in Maintena

Engineering, Vol. 6 No. 3, 20

pp. 177-191. # MCB Univer

Press, 1355-2

Design of maintenance systemin MRPII

W.H. Ip, C.K. KwongHong Kong Polytechnic University, Hong Kong and

R. FungCity University of Hong Kong, Hong Kong

Keywords Maintenance, Design, MRPII

Abstract Very limited research has attempted to consider maintenance strategies in thedesign of MRPII. The manufacturers who need to optimise the return of their assets and

facilities using systematic maintenance management will find that the MRPII system is unable to provide them with the solution. Proper design and integration of maintenance management

into MRPII enable the manufacturers not only to manage their production planning andscheduling activities but also to analyse their maintenance history, carry out cost analysis and study the failure trends to determine how the available labour and materials in maintenancecan be used effectively. In order to overcome the weakness of the MRPII system in themanagement of maintenance activities, this paper describes some research work that has beencarried out using the integrated definition method (IDEF) model to systematically integratemaintenance into MRPII. Moreover, in order to illustrate the methodology, a lampmanufacturing company with a lot of highly automated equipment and facilities which dependson modern maintenance strategies as well as MRPII-type production planning and control isdescribed.

1. IntroductionModern maintenance strategies employ many techniques such as corrective

maintenance (Blanchard et al., 1995), fixed-time maintenance (Jardine, 1987),condition-based maintenance (Neale, 1985) and improvement maintenance(Harrington, 1995) for the assessment of availability, reliability andmaintenance characteristics (Priel, 1974). Priel defined the principles ofmaintenance management as the effective use and co-ordination of informationand resources to achieve the following objectives:

. ensure equipment availability to meet short term and long termutilisation targets;

. preserve equipment performance to meet output targets; and

.

balance the levels of preventive and corrective work to achieve the bestpossible trade-off between direct and indirect maintenance costs.

The techniques mentioned above can help engineers to predict the momentwhen the equipment will fail and plan the maintenance (Willmott, 1994). Senju(1992) defined maintenance as a simpler form:

. utilising plant capability to its fullest extent to reduce equipmentstoppages (both line stoppages and stoppages for reworking);

. to quantitatively and qualitatively enhance equipment capability; and

The current issue and full text archive of this journal is available at

http://www.emerald-library.com


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. to improve safety, health and environmental factors in the expectation thatsuch improvements will contribute to better quality and higher profits.

It is based on teamwork and provides a method for the achievement of world

class levels of overall equipment effectiveness through people and not onlythrough technology or systems alone. In real life, the inputs of the abovemethods are mainly based on historical data and the companies who wish toimplement the maintenance strategies must therefore consider computerisedmanagement systems. On the other hand, many companies world-wide haveinstalled and implemented computer systems to automate their productionplanning and control activities using MRPII (Wight, 1981). Many of them arenow using MRPII with various levels of satisfaction. However, very oftenMRPII appears to be isolated from maintenance management activities. Theresearch into the integration of these two computerisation areas into logisticsmanagement is necessary in order to take the advantages of both modern

maintenance strategy and production planning strategy. Integration strategy isconsidered an absolute requirement if a company is to remain competitive.Gerelle and Stark (1988) stated that, ``Those manufacturing enterprises thatintend to survive into the twenty-first century will have to come to terms withthe techniques of integrated manufacturing.''

In this paper, a brief background of the case study and maintenance processof the company is given in Section 2. Section 3 describes the MRPII system andIDEF model that is used to achieve the integration. Section 4 describes thedetail maintenance system in the MRPII. Finally, recommendations andconclusions are given in the last section.

2. Maintenance managementThe main product of this company is lighting products (Burgin, 1984) which canbe classified by the shape and technology of the light bulb produced. Varioustypes and shapes of bulbs such as pear shaped, round or conical shaped andtube shaped are produced by this manufacturer. The basic raw materials usedare boron lead wire, glass rods, glass tubing, electrical wiring and cap. Morethan 100 models are produced by this manufacturer, some of which are:

. bicycle lamps;

. energy-saving lamps;

. radio panel lamps;

. toy lamps;

. pen torch lamps;

. flashing lamps;

. pre-focusing radio panel lamps, etc.

They are all produced according to different customer specifications, such aslamp power and safety standard. Each type of product has highly automatedspecialised machines consisting of three major processes:


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(1) glass bulb forming;

(2) core assembling; and

(3) body assembling.

The bulb-forming process forms the size and shape of glass bulb, and controlsthe amount of chemical required to blow the bulb and the time and temperatureof flame. The core fabricating process forms the mounting and produces therequired cycle of filament. The body assembly process assembles the bulbsusing the high-speed fixture, feeder and clamping devices, it also controls theamount of gas injected into the glass bulb. The production rate of the machinesranges from 2,000 to 3,000 pieces per hour and there are over 50 machines in thefactory. It is essential to minimise breakdown times of the machines to increasethe productivity of this production system. One of the major competitiveadvantages of this industry is hence the effective utilisation of its very

expensive specialised machine and equipment. The majority of these machinesare designed and manufactured by the company and hence very strongemphasis is placed on the maintenance planning and control. Figure 1illustrates the maintenance process of this company. The objective is to obtainthe maintenance data, perform analysis of the production system and providemanagement with detailed knowledge about the failure behaviour of themachines as well as to plan the maintenance activities. However, this processwas mainly performed manually and the planning and control activities suchas searching and accessing maintenance information were impossible, makingmaintenance management ineffective.

Maintenance management is an important activity in this company toensure that the loss due to machine failure could be minimised. In order tomonitor the progress of corrective and preventive maintenance activities sothat timely decisions can be made on the available resources, the actual man-hours spent and the man-hours of planned work achieved should coincide witheach other and it should be ensured that they are evenly distributed throughoutthe entire maintenance time period. However, in reality, man-hours spentseldom follows the plan, this is due to the different natures of routine and non-routine maintenance work, their data collection and interpretation and theirsubsequent measurement and control would be treated separately. As we cansee from Figure 1, the ways of collecting routine maintenance work data consist

of the following steps:(1) Routine work card return by serial number. A work card is said to be

completed when all items of the work card content are carried out,signed by a supervisor and subsequently certified by an approvalengineer.

(2) Routine work cards return by card count. Work cards returned by cardcount are also recorded. This is done simply by counting what has beenrecorded as mentioned in (1).


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(3) Routine work cards work in progress. Some work cards contain morethan several items of work in which some items may be carried out and

certified and some may not. These incomplete work cards usually

remain on the card board and will not be returned until all items are

certified.

(4) Reports of routine man-hours. Statistical reports containing up-to-dateman-hours by maintenance activities.

With the data collected for routine work as mentioned in (1) to (4), different

productivity curves can then be plotted, they can be classified into three types:

(1) Routine-work planned man-hours curve.

(2) Planned man-hours of routine cards return. It measures project progressby jobs completed and signed. It has a major drawback that a job is

often completed but the paper work is not signed resulting in a serious

time lag in revealing true project progress.

Figure 1.

Maintenance process ofthe lamp manufacturer


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(3) Average planned man-hours of routine cards returned curve. This curveappears to be a better fit to the actual planned man-hours and has lesstime lag as compared to the other curves. However, this method has the

disadvantage that the work cards were returned at the early stages ofthe project. Therefore it carried less man-hours than the work cards

returned at the later stages of the project which have been averagedout in the calculations.

3. MRPII systemManufacturing resource planning (MRPII) is recognised as being one of the

important elements in logistics management. Descriptions of MRPII in logisticscan be found in Dobler and Burt (1996), Martin (1992) and Blanchard (1986).

MRPII has an excellent planning and scheduling capability that can offerincreases in customer service and reduction in inventory and material costs.

Owing to these benefits, the MRPII system has become one of the most rapidlygrowing computerisation areas in the manufacturing sectors and much related

software has appeared in recent years. Early research on MRPII can be found in

Orlicky (1975) and Wight (1981), recent research on MRPII detail design suchas scheduling and implementation are available from Burns (1991), Plossl

(1994) and Ang (1994). However, the research of integrating maintenancestrategy into MRPII is limited. This is particularly important with the

increasing complexity of modern machine tools and production systems, forexample, in the case of this lamp manufacturing company where there is

expensive and highly automated equipment.

In the design of the maintenance management system for the MRPII, IDEFwas selected. IDEF, derived from the US Air Force (Winosky, 1987) is a

structured analysis and design method based on graphic and text descriptionsof functions, information and data. Earlier examples of using IDEF in

manufacturing industry can be seen in Coloquhoun et al. (1989) who providedan IDEF model for process planning, Hargove (1995) further applied the same

approach to the design and planning of machine fixtures. The IDEF method iswidely understood and well documented (Benjamin et al., 1993; Hill, 1995) andthe method includes guidance for modelling, together with rules for modelsyntax, diagram and model format and text presentation, as well as structured

model validation, document control procedures and interview techniques.The first step in IDEF modelling is thus concerned with establishing the

objectives of the modelling effort from which a context and viewpoint canevolve. Moreover, this is a top-down method which starts from general

applications and moves on to more specific issues, from a single page thatrepresents an entire system to more detailed pages that explain how the

subsections of the system work. It includes both procedure and a language forconstructing a model of the decisions, actions and activities in an organisation.

``DESIGN/IDEF'' (Design/IDEF, 1998) software package was selected to be the


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modelling tool to build the model. Based on this methodology, a set ofprocedures was generated and the required documents and forms were alsoproduced to match these procedures.

In adapting the techniques provided by IDEF, all the activities involved inthe design of the system for this manufacturer are modelled firstly by definingthe most important input, output, control functions and required mechanisms.Figure 2 shows the top diagram A0 of the model. Figure 3 illustrates the nodetree of this model generated by IDEF.

Figure 4 shows the detailed design of the model, this is generated by theDesign/IDEF software and demonstrates the node tree decomposition of themodel, giving the relevant titles and page numbers. Moreover, based on the toplevel A0 of the model, it is split into several levels:

(1) planning system;

(2) engineering system;(3) production system;

(4) maintenance system;

(5) marketing system; and

(6) financial system.

Due to space limitations, only three major designs related to MRPII; designplanning system, design engineering system and design production system aredescribed in this section. The design of the maintenance system in the MRPIIsystem is described in the next section.

Figure 2.Node A0 of theenhanced MRPII model


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From Figures 3 and 4 we can seen that one of the major components in MRPII isthe engineering system, which includes three sub-systems; product data control

system, lot/serial number control system and engineering change system. Theimportance of this system and its interrelationship with other MRPIIcomponents are illustrated using this system. The product data control systemis used to maintain and control all product information, including thegeneration of the bill of material (BOM), routings, and work centre related datarequired to manufacture the lamps. Figure 5 shows the output elements of thissub-system part number, BOM, product structure and routing. The controlelements are customer specification, safety standard and part numberingspecification. The generation of BOM of the product (C211) bicycle lamp is

Figure Node tree of t

enhanced MRPII mod


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illustrated in Table I. The data fields included in the BOM are part number,part name, description, source, quantity per assembly, unit of measurement(UOM), lead time, standard cost, lot size, price and vendor, etc. The partnumber is controlled according to the part numbering specifications andassigned to each component according to the classification of the type of

Figure 4.A331 design detailMRPII functions

Figure 5.Product data controlsystem


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product, type of material and the assembly level. The planning system (A3311)uses the master production schedule to determine the gross requirements, it isthen exploded using the BOM, subtract the corresponding inventory fromgross requirements. The net requirements are then allocated to differentperiods to reflect vendor lead times and the purchasing and manufacturingactions during the manufacturing process when the assembly and materialswill be required. The detail production in the lamp manufacturing is supportedby the production system (A3313) which issues production orders, work

instructions and management for the material issue and transactions in theproduction process.

4. The integrationThe design of the maintenance system is part of the MRPII model functioningunder the level A3313. The purpose of this system is to integrate themaintenance activities described in Section 2 into the MRPII. It is used toprovide the information and analysis in order to minimise breakdown times,

Part no. Part name SourceQuantity

per lot UOMLead time

(days)Standard

cost

C211 Bicycle

(1.2V 0.30A)

F 10,000 EA 2 2,000

C21-01-03 Glass bulb(C21-series)

F 10,000 EA 1 50

C21-03-12 Tungsten wire(Mod# C211)

B 10,000 EA 14 200

C21-05-12 Core Assembly(Mod# C211)

F 10,000 EA 4 200

C21-05-13 Lamp BodyAssembly(Mod# C211)

F 10,000 EA 2 300

G00-01-02 Glass rod B 0.333 KG 30 0.7G00-01-04 Glass bead P 10,000 EA 0 0.5G00-01-11 Glass tube B 40 KG 30 164

G00-02-11 E10 screw base B 10,000 EA 30 2,000G00-03-01 Copper alloy wire

(18mm long)P 20,000 EA 0 0.5

G00-03-02 Roll of copperalloy wire

B 0.4 ROLL 60 50

G00-04-01 Paste B 115.5 LB 14 1,650G00-04-02 Tin/lead

alloy 55/45B 10.5 KG 14 120

G00-04-03 Flux B 0.05 L 14 1.5G00-05-01 Bead wire

assembly (18mm)F 10,000 EA 2 300

Notes: F, B and P in the ``source'' field represent fabricate, buying and phantom items,

respectively

TableBOM of a typic

bicycle lam


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find out weak points in the maintenance process and diagnose the technical andorganisational problems for improving maintenance strategy. Specifically, it isaimed at the following:

.

a total system of maintenance equipment and manpower managementcovering the whole life of the equipment;

. the system is run in all departments including, the production andmaterial planning department, the equipment planning department, theequipment operational department, the engineering department as wellas the personnel department; and

. promoting preventive maintenance to achieve zero breakdownmaintenance.

Emphasis is placed on the belief that maintenance activities should not beviewed in isolation from the MRPII functions described earlier. The technical and

operational staff need to maintain the equipment, design and implement visualinspection aids, keep machine checklist records, make inspections according tocalculated schedules and report serious problems, they should become routine

jobs for the maintenance team. The key to success of this integrated system restson the timely information collection and analysis which can improve themaintenance process of this lamp manufacturer illustrated in Figure 1.

In the design of the maintenance system, two major components areintroduced; manpower productivity analysis and maintenance productivityanalysis. Analytical estimating technique is used to build up from theestimation of all the elements of different jobs together with agreed allowancesto arrive at a standard time for a particular job. Allowance is important becauseof the non-routine jobs that are generated as a result of regular inspection. Non-routine work requirements are subjected to inspection findings and aretherefore not known until they are raised after the commencement of amaintenance project. The allowances are also dependent on the age of theequipment, the geographic region and the type of its operations such as longoverhaul or short overhaul. Manpower capacity is measured by taking thecount of each maintenance activity multiplied by the number of working hoursless sick leave, annual leave, lunch and tea breaks and training hours. Theavailable man-hours are then multiplied by a weighting factor in accordancewith the grade of labour to arrive at a total effective manpower capacity. Thus,

the experience and skill level of each individual is taken into account. Theeffective man-hours of supervisors and senior supervisors are less than that ofa skilled mechanic and their weighting factor is less than one. Engineers are notincluded in the manpower capacity calculation as they are performingsupervisory tasks for most of the time. In order to support these analyses,detailed information must be available and can be accessed quickly. The MRPIIsystem hence is improved to include all the above requirements. Figure 6illustrates the detailed input, output, control and mechanisms that are used toachieve the maintenance activities.


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Before the enhancement of the MRPII system, maintenance work done on theequipment was recorded manually; the retrieval of information of various typesof maintenance performance was difficult and time-consuming. The integrateddesign now provides accurate and up-to-date information to cater for themaintenance activities. From Figure 7, it can be seen that the MRPII systemincorporates a data capture sub-system (A33141) to collect maintenanceinformation.

This sub-system is used to capture staff attendance and maintenance jobrecords. The staff attendance records and job records are inputted into thesystem automatically through a bar coding system. These data are transferred

Figure A3314 maintenanmanagement syste

Figure A33141 data captu

syste


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into the database and the staff attendance and maintenance job records andfiles are updated in the MRPII system. The work card system mentioned inSection 2 is also managed by this system. It provides a means for maintainingwork cards of the maintenance projects. This system creates maintenance

schedules and distributes them to the shop order. From these shop orders, thework cards for the maintenance works can be generated and stored into workcard data files. Figure 8 illustrates the work card system.

The other two major elements in the maintenance systems are themaintenance planning and the job progress in A33143 and A33144 respectively(see Figures 9 and 10). The maintenance planning sub-system consists of awork card data bank of work specifications that include job type, jobdescription details, estimated man-hours, job turn round time, spare parts andmaterial requirements, and tooling requirements. Together with the staffattendance and job records files, maintenance planning as well as the work carddata files generated earlier, the work card databank is created and updated.

The job progress system provides the facilities for the creation ofmaintenance projects and jobs, printing of work cards, printing of a work cardtally list, inquiry and updating of the job status, recording of man-hoursbooked against the projects and jobs, and generation of miscellaneous projectsand job progress reports. From the work specification generated in themaintenance planning sub-system, the various projects/jobs can then becreated. These projects or jobs undergo the job commencement module and the

job-tracking module. The job status is reported regularly and the informationcollected can be used to construct the maintenance productivity analysisdescribed in Section 2.

Furthermore, the maintenance management system is also interfaced withother basic MRPII sub-systems, specifically, they are the customers order andrecords; purchasing/stock control for spare parts and materials; documentation

Figure 8.A33142 work cardsystem


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location management; cost analysis and control; equipment and engineering

detail records. Hence, the MRPII system not only consists of production

planning and control functions but also the management of maintenance

activities and productivity analysis. The system is now used to create

maintenance projects and jobs for each piece of equipment or module stripped

Figure Block A33143

maintenance plannisyste

Figure 1Job progress syste


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from the machines. Live maintenance project records are available for thesupervisors for searching, selection, modification and deletion. The system canbe used to produce different types of reports:

.

project progress reports;. job stage tracking reports;

. project backlog reports; and

. project productivity reports.

Most of the above mentioned reports can be displayed on the users' terminalsnext to the machines. The estimated man-hours can be calculated usinghistorical records and analytical estimating. A complete maintenance projectactivity list and the job list are available; the critical path of the maintenanceproject can be identified. The maintenance man-hours are now processed daily

by the MRPII system so that job costs on the maintenance projects can becompiled automatically. In addition, with the information on maintenance jobbooking hours, the system will highlight attendance patterns and produceexception reports that can be used to generate the productivity analysis as wellas to forecast future maintenance requirements. As the maintenance project isin progress, it also provides work summary reports for the project so thatinformation such as the number of man-hours and materials that are spent oneach maintenance job are available. The maintenance productivity analysis canbe displayed and updated accordingly, significant variations between estimateand actual man-hours can be identified.

4. ConclusionIn this paper, an enhanced MRPII system that incorporates maintenancemanagement has been designed and implemented with the use of IDEFmethodology. The lamp manufacturer has successfully applied thismethodology to achieve the integration of maintenance management intoMRPII; to manage their production planning and scheduling as well as themaintenance activities. The company is now able to plan and control themaintenance activities, analyse the maintenance history and carry out failuretrends investigations. Overall maintenance performance of the highlyautomated and expensive equipment employed by this manufacturer has been

shown to improve by 30 per cent; downtime decreased by 20 per cent. Modernmaintenance strategies such as corrective and preventive maintenance can nowbe practised through the effective use and co-ordination of information in theMRPII system. The result of this study demonstrates that MRPII should not beviewed in isolation from maintenance management in the system design andimplementation, their integration using appropriate system design methodssuch as IDEF is invaluable. Further research could be done using this approachto enhance the MRPII system and improve logistics management as well asphysical distribution functions of any organisation.


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Burgin, R. (1984), ` The development of tungsten filament lamps'', Lighting Research &Technology, Vol. 16 No. 21984, pp. 61-72.

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