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the assigment that i have submitted to the techar during my studies of production system design



2. THE HISTORIACAL PROSPECTIVE OF PRODUCTIONIn order to understand the rationale behind the different approaches toproduction system designs, it is useful to examine their historicalprospective. It is possible to trace back to the Industrial revolution some of thethinking which even today is influencing designers of productionsystems. As well as the technological progress (and which will bedescribed later), some notable organizational principle were alsoestablished by writers such as Charles Babbage and Adam Smith.SCIENTIFIC MANAHEMENT AND BEHAVIOURAL SCIENCE:-After the early principle were established, it is widely accepted thatsome of the most influential work organization was carried out duringthe late 1800s and early 1900s under the general heading of scientificmanagement.Most notable among the scientific management school at this timewas Fredrick W. Taylor. While working with a number of Americancompanies. Taylor sought to prove his belief that a scientific approachto planning and the management of work could produce significantbenefits in terms of output and efficiency. The main thesis on which hisprinciple of scientific management is based is that individual workercan be selected and allocated to jobs they perform best. A financialincentive can then be applied in order that the workers best results areachieved to the financial benefit of both the individual and the firm. Taylors approach, therefore, accepts and builds on the ideas of Smithand Babbage, which advocated division of a job of work down into anumber of functional tasks and the promotion of the high degree ofspecialization on the part of each worker. A Tayloristic approach to designing production system can,therefore, be identified. At the micro level ( e.g productive work), thisSubmitted by MUHAMMAD YOUNUS 08IN70Page 2 3. implies breaking a job into a number of short tasks which can beallocated to the most appropriate operators and performed in arepetitive fashion normally with a direct financial incentive. At themacro level, the Tayloristic approach requires that jobs in all parts ofthe organization are performed by functional specialists. So, in mostmanufacturing companies, are found process planners, qualitycontrollers, stock controllers, machine setters, and even separatespecialist for the various function of the maintenance ( i-e. mechanical,electrical, etc ).Taylors arguments for taking the division of labor logic this far isjustified by his example comparing the frontiersman with thesurgeon. The former was generalist being an architect, housebuilder, lumberman, soldier and doctor while the latter has beentaught and trained under close supervision in an almost identical wayto the factory operative working under scientific management principle.It is in making this comparison that Taylor claimed that the functionalspecialization could still have tasks associated with it which could bedeveloping and broadening, there by reducing the risk of producing aworkforce of automatons.Despite Taylors share of critics, and the despite the passing of almosta hundred years, his influence on the design of production systems isstill profoundly significant, For instance, his principle of scientificmanagement was one of the most likely sources of inspiration forHenry Ford when he conceived the manufacture of the Model T usingflow line techniques and even today this form of production system stillhas widespread acceptance when large production quantities arerequired. Even when demand is lower, Taylors principle can still be applied byrouting discrete batches of parts between functionally arrangeddepartments where specific operation can be carried out. Despite indissimilarity of parts, the similarity of process can provide for divisionSubmitted by MUHAMMAD YOUNUS 08IN70Page 3 4. of labor, specialization of skills and the application of direct financialincentives.It would be wrong to assume that the scientific management schoolformed the complete picture as far as the historical perspective ofproduction organization is concerned. As early as the 1920, as a secondand in many ways equally well-founded school began to emerge; this isnow often referred to as the behavioral science school. This school probably originated with the study conducted over a fiveyear period at the Hawthorne Works of the Western ElectricCompanying the USA. Intended originally to be a straight forwardinvestigation into the effect of different lighting levels output, the studydeveloped into series of experiments which increasingly demonstratedthat human behavior was an important factor affecting output andwhich had been grossly under-estimated by the advocates of scientificmanagement.GROUPS AND SOCIO-TECHNICAL SYSTEMS:-One further consideration relating to the way in which productive workmight be organized is the fact that a set of tasks a can be carried outby people working either as individuals of in groups. The scientificmanagement school presumes that wherever possible tasks should beperformed by individuals since only in this way can the division of laborprinciple be adopted and individuals working independently so in thisrespect the organization of work could still be described asTayloristic.The idea of using cohesive groups of workers in high volume industrialproduction is of relatively recent origin, although group work has longbeen a feature of systems where products are made for customer order(i-e job or custom production). However, one application were groupworking is well developed is in the British coal mining industry.Submitted by MUHAMMAD YOUNUS 08IN70Page 4 5. Traditionally the mining of coal took place using pillar and stallworking where the seam was extracted at a number of single placesonly six to eleven yards in length. The groups who worked at one ofthese places comprised about nine persons, selected by their ownmembers, who were completely responsible for coal production.Group members had a wide range of skills and some of the rotation ofjobs was possible.When mechanized long wall mining came widespread use from the1920s, faces of 160 to 200 yards (146-183 m) were introduced and analternative form of work organization was adopted using the factoryapproach of strict division of labor. However, this form of workingproved to be a problem due to the unpredictable nature of the jobcompared with factory work. The associated reduction in skills alsogave rise to diminishing safety levels and absenteeism became morecommon.To tackle these problems an alternative form of working, called thecomposite work organization and wage system, was introduced washad many similarities to the traditional way of working. Skills werewidened and rotation between jobs and shifts was made possible, whilebonuses were paid to the groups rather than to individuals. The resultwas that smoother changes over from one shift to the next becamepossible, as was previously the case using traditionally methods andmore importantly productivity increase.So significant ere the effects of changes to work organization inmining that they gave rise to a massive research program conductedby personnel from the Tavistock Institute of Human Relations inLondon. They referred to their methods as the socio-technical systemsapproach, since the situation they were dealing with was neither purelya technical system nor a social system an, therefore, required acompletely new form of research methodology.Submitted by MUHAMMAD YOUNUS 08IN70 Page 5 6. The coal mining studies, while very important, relate to a ratherunusual form of work compared with which Taylor and the HawthorneResearches were involved. The systems of group working which weredeveloped were obviously appropriate in the mining environment, butthey could not be proved as being appropriate in the context of afactory producing a wide variety of complex products. With this question in mind. the Philips Company in Eindhoven,Holland, conducted a series of experiments during 1960 in theirtelevision receiver factory. Philips, like most other large volumemanufacturers, were using assembly line technique where, in much thefashion conceived by Henry Ford, jobs were divided into short cycletasks which could be quickly learned and enabled unskilled workers toreach a high level of proficiency. The intention was to create a regularflow of production with high output levels being ensured by a wagesystem geared to effort.However, at the time of the experiment, the company was faced witha number of problems for which the techniques used so far did notprovide suitable answers. The problems, which related to output,quality and morale, caused the researches to question the organizationof the unskilled work and the sophisticated wage system. Both thesefactors were being influenced by changing metal attitudes, fullemployment and better basic levels of education which conflicted withthe rigorous division of labor.Firstly, the researches found that waiting times could be reduced and,therefore, output in increased, as the number of workstation on the linewas reduced. In the experiments this was achieved by breaking downthe single line with no buffer stocks into five groups, each of which wasseparated by a buffer as shown in the figure below. In this way lesstime was lost waiting for material and due to balancing and systemloss.Submitted by MUHAMMAD YOUNUS 08IN70 Page 6 7. Secondly, it was found that re-organizing the line had as effect onquality. By placing inspectors at the end of each group rather than atthe end of the long line, earlier feedback of information was achievedoffering charge hands the opportunity of controlling the quality of workin their areas. Statistical analyses of the relationship between qualityand the work rates also showed that the best quality was achieved byworking at a medium, regular speed.This rate of working was best facilitated using shorter lines with bufferstock between adjacent work places. Moreover, the findings relating toboth output and quality were further confirmed when the line was laidout with only half the no. of workers, performing twice their originalcycle, with storage b/w each work place. In this case it was found thatwaiting time was reduced, any delays had less effect, and qualityimproved as a result of the more even rate of production. Finally, concerning morale, where a questionnaires was used to assesthis factor, the line was broken down into groups. In fact, even highermorale was discovered in groups assembling channel selectors, wherethe level of independence was still higher, and where a complete endproduct was being produced.In their final conclusions, the Philips researches stated that they wereconvinced that small groups with buffer stock were most appropriatefor the kind of work studied, despite requiring more space andmaterials. A proviso is added that the group should be able to obtainindependent results, to set their own pace, have separate qualityassessment, and be paid on a group basis. Although the size of thegroup will depend on production engineering factors and the duration ofthe cycle, at Philips it was found that sociological advantages graduallydecreased if the size exceeded ten.The problems of output, quality and morale experienced by Philipswere by no means unusual among industrial companies during theSubmitted by MUHAMMAD YOUNUS 08IN70 Page 7 8. 1960s. They are, however, better documented than most and theexperiment which took place demonstrate a unique approach, thefindings from which greatly influenced the design of more modernproduction systems in Europe particularly, but also elsewhere in theindustrial world.CONTINIOUS PRODUTION SYSTEMContinuous production involves in a continuous or almost continuous physical flow of material. It makes the used full purpose machines, and produces standardized items in large quantities. Chemical processing, cigarette manufacturing and cement manufacturing are some of the industries engaged in continuous production. The continuous system can be divided into the two categories a) Mass and flow line production b) Continuous or process productionMASS PRODUCTIONIt is characterized primarily by an established and stable objectof production. The parts are produce in large quantitiescontinuously, but are depend upon the individual orders. The quantityis usually 100,000 parts per year. However the most chrematisticfeature of mass production is not the quantity of product beingmanufactured, it is an arrangement where by and single specificoperation is continuously performed at most of the working place. Amass production enterprises deals with the standard product of limitedvariety, such as consumer durables, and products for industrial use(automobiles, tractors, bicycles, electric motors, sewing machines,nuts, bolts, screws, washers, pencils, matches, and engine block, etc)Submitted by MUHAMMAD YOUNUS 08IN70Page 8 9. Other features typical of mass production are: an extensive use ofspecialized (usually permanently set-up) and single purpose machinetools and mechanization and automation of production process withstrict compliance of the principle of inter changeability. The lattergreatly reduces the time required for assembly operations. In massproduction type of production semi skilled or even unskilled worker areneeded to operate the machines. This type of production is capitalintensive, but the unit cost of production is low.The most advanced type of mass production is Continuous flowproduction, whose main feature is that the time required for eachoperation of the production line is equal to or a multiple of the standardtime all along the line. This enables work to be done without producingstock piles and strictly definite interval of time. Example includes: oilrefineries and continuous chemical plants.PROCESS PRODUCTION Continuous or process production is useful where the productconsumes (electricity, petrol, chemical, etc.), and has continuousdemand.All products undergo by same process. Raw material enters atone point and leaves as finished product at another. Material hading isautomatic. Plant layout is a per the requirements of production. Bothtypes of workers, i-e, semi-skilled and skilled are employed. Outputsand inputs are, respectively, measured and regulate, usingsophisticated controls. Machinery employed is one built to the needs.Good plant maintenance and effective quality control are the essentialrequirements.Submitted by MUHAMMAD YOUNUS 08IN70Page 9 10. INIDUSTRIAL FLEXIBLE MANUFACTURINGSYSTEMFlexible manufacturing system can be used in a wide variety ofindustrial processes including sheet metal work, cutting, welding,pressing, painting and assembly work. Most progress however, hasbeen made in metal machining, an area where NC was already well-established.In order to illustrate the scope of FMS and a wide variety of sizes andsystem elements a number of example will now be described. Eachrepresents a different configuration of machines and handlingequipment. They also demonstrate the range of complexity andversatility which is embraced by the general heading of flexiblemanufacturing.EXAMPLE # 01MACHINES AND MACHINCES CELLS SERVED BY THEINDUSTRIAL ROBOTThe simplest and most elementary form of FMS is a single machine or acell of two or more machines served by a robot. Such an arrangementoften represent organizations first step towards a full system capableof producing complete range of parts and products.Figure (below) for instance, show CNC machining centre around whichthere are number of pallet stations. A simple robot transfers a pallet,as required, from station to machine, removing completed work andreturning it to an empty pallet station. A wide range of components canbe produced since it is possible for every pallet to contain a differentset of parts.The main constraints on the systems versatility would normally be theno of tools which can be stored in the machines magazine. Yasda ofJapan, however, produce machining centers which are equipped withcapacity for their hindered tools and Sandvick of Sweden hasSubmitted by MUHAMMAD YOUNUS 08IN70 Page 10 11. developed a magazine for turning machines which can carry more thanone handed tool blocks. This unmanned for at least the complete a shifton a range of different components, each having widely differingmachining requirements.A somewhat different arrangement, built around the same idea, is acell of machines served by a more versatile manipulative robot. Hereindividual components, rather than loaded pallets, are picked up by therobots gripper and then transferred from the machine ( as shown infigure above). The agility and range of possible movements makes thecell capable of producing a no. of components requiring differentpositioning and different machine sequences. Robots used in this typeof application are also much faster n operation than pallet robots sincethey are used in conjunction with simpler, short-cycle operations suchas pressing and drilling.EXAMPLE # 02MACHINE CELLS SERVED BY LINEAR MATERIAL TRANSPORTERSThe type of arrangement just described is obviously restricted to a verysmall number of machines, which in practice is determined by the limitof the robots reach. If the idea is to be extended to include a completeworkshop of machines then some further means a automaticallymoving materials will be required.The simplest method of achieving this is by providing some form ofmechanism for transporting pallets or components between stationsfrom where a robot can then load them on or off the machines. Thesystem used could be a linear powered roller conveyor of the typeemployed in early FMS such as system 24 and Cincinnati VariableMission I.This is still a popular approach where smaller parts are involved andwas chosen by the 600 group for their SCAMD (Systematic ComputerSubmitted by MUHAMMAD YOUNUS 08IN70 Page 11 12. Aided Manufacturing Project). This is a system developed forautomatically producing a range of tuned parts.The load carrying capacity of a roller conveyor is rather limited,however, so an alternative type of transporter for linear movement pfheavier parts is a rail guided vehicle. Proprietary transporters of thistype are available which enable cells to be extended at reasonably lowcost (figure above). A large workshop using a rail-guided partstransportation system is in operation at the Yamazaki machine toolplant in Japan. Here eighteen machining centre are arranged in twolines, with each line being served by a robot. One transporter can carry3 tons and travel 60 meters/min, the other has 8 tons capacity andspeed of 40 meters/min. twelve operators are required in thisworkshop compared with the two-hundred- and-fifteen needed usingconventionally equipped machines.EXAMPLE # 03MACHINE CELLS SERVED BY STRACKER CRANE A novel alternative to roller conveyor or rail-guided transporters is theuse of a computer-controlled stacker crane. This was the approachadopted by BT handling systems in Sweden in preference to thealternative arrangement offered by current suppliers. As amanufactured and experience user of sophisticated material handlingequipment, BT could see the merits of using their own products withina FMS. A conventional GT cell had been used for some years in whichracks and a fork lift truck provided work-in-progress storage and partshandling.Extending the idea using computer-controlled material handling andCNC machines become a relatively a simple step achieved at a cost, in1980, of 120000 for the crane, racking and microcomputer system(figure above). Initially the system was set-up with one fully automaticstation. A Yasda YBM 90N machine centre, and fifteen other machineSubmitted by MUHAMMAD YOUNUS 08IN70 Page 12 13. tools also served by the crane but using operators. As the cell has beendeveloped, further Yasda machines and fully automatic CNC latheshave been added, enabling more of the system to run completelyunmanned during nightshift periods.BTS approach to FMS is interesting in that it represent a view thatprogressive development using limited manning can be a more sensiblealternative than the immediate introduction of highly sophisticated,fully automated system. The view has been reinforced by theintroduction of the second cell, also using a stacker crane, for welding.Again the system was set up using largely manual welding stations, butcapable of being enhances later by progressively replacing them withautomatic processes.EXAMPLE # 04MACHINES CELS SERVED BY AGVSThe use of AGVS (automatically guided vehicles) has already beendescribed in connection with material handling for autonomousworking. Theses highly versatile devices, whose used is wellestablished for assembling work and in automated warehouses, arenow becoming an essential feature of manufacturing systems which aretruly flexible. AGVS requires nothing other than a reasonable flat floorand follow a buried wire, so installation costs are minimal. Thedevelopment of radio-controlled and laser guided AGVs could evenremove the need for the second requirement in future.AGVs are therefore not as limited in their application as rollerconveyors, rail-guided transport and cranes. They can literally go anywhere provided there is an adequate road way, so they can visit anumber of machines together with inspection stations, parts washingfacilities, etc. A small FMS cell developed by Cincinnati Milacron,employing one AGV, is as show in figure (below).Submitted by MUHAMMAD YOUNUS 08IN70Page 13 14. As well as providing a highly versatile FMS, the use of AGVS easilyenables a system to be expanded or contracted. Extra AGVs can simplybe added to increase the frequency with which materials are movedand machines can be added or removed with out disruption to the restof the system. An interesting variation on the conventional type of AGV, whichdecrease its versatility still further is the high-lifting type. Developedfrom a fork-lift truck, this AGV was first introduced by BT handlingsystems. It has the ability to lift work from floor level up to 3m so canload and unload machines having different working heights as well asmoving items in and out of high-bay store. An FMS using high liftingAGVS with three machining centers has been installed at SundsvallsVerkstader in Sweden as shown in figure (below)EXAMPLE # 05FULL FMS WITH TOOL AND PART STORAGEIn order for an automated manufacturing system to be fully flexiblethere must be sufficient material, tool and program storage to allowuninterrupted running for long period on the widest range of parts.There must also be a sufficiently sophisticated set of automated servicefunction to prevent the system from periodically stopping due to minorcorrectable deviations from normal running conditions. A large materialstorage capacity can be incorporate into an FMS system well developedin the wholesale and retailing sectors. The automated warehouse is interfaced with the manufacturingsystems by a transfer device which moves parts between the AGVs(which serves the FMS cells) and the stacker crane (which puts theparts into store and picks them out again when required). FMS systemswhich are linked in this way to an automated warehouse have beeninstalled by Murata Machinery and Mori Seiko in Japan.Submitted by MUHAMMAD YOUNUS 08IN70 Page 14 15. Additionally tool storage can be provided in a similar way. Drums ormagazines from machines are made interchangeable and aretransported to and from a tool store by some from of handling device.Cincinnati Milacron, for instance, has developed a technique using anAGV to change complete magazines, while Yamazaki uses a drumloader robot which functions in a manner similar to an over headcrane. Yet another system involves the use of an industrial robotmounted on an AGV which is also equipped with a tool rack. The robotcan there by change individuals tools, when necessary, rather thancomplete magazines. Program storage is less of a problem than the physical storage ofparts and tools. Although the mini and micro computer attached tomachines and cells have limited capacity, they are invariably linked vianetwork to a larger computer. Moreover, the program storage capacitycan be increased further still using a hierarchy of computers which candownload the programs to the system and machine computers whenrequired.The monitoring of quality and process performance is an importantrequirement of any manufacturing system capable of runninguninterrupted for long periods of time. Quality inspection is generallyachieved some form of in-process gauging device which will checkdimensional accuracy, either while a component is being produced orimmediately afterwards. The machine will automatically compensate forany error trend which is occuring my making adjustment to theappropriate settings. More complex parts will be inspected on separate,numerically controlled, co-ordinate measuring machines which a widevariety of different dimension with out delaying the productionprocesses. The other important type of monitoring, i-e fault-detection anddiagnosis, is still is its infancy but when fully developed it will be thekey which will unlock the door to fully unmanned production. DetectionSubmitted by MUHAMMAD YOUNUS 08IN70Page 15 16. and replacement of broken tools is becoming a common feature ofautomated production systems. The idea will doubtless be extend toinclude other machine components and systems, thereby automatingthe traditionally labor intensive maintenance function.EXAMPLE # 06FMS FOR SHEET METAL FABRICATION AND WELDINGMost of the earlier development works into flexible manufacturinginvolved metal-cutting machine tools. In practice, however, the rangeof production processes goes much wider and the need for automatedsystems extends to a number of other areas where numerical control isless well-established. The last two examples are, therefore, different inthat relate to some of the more important of these areas which, if fullyautomated, will open up the benefits of flexible manufacturing to amuch larger population of producers.Recent years have shown a trend towards sheet metal fabrication andwelding as low cost substitutes fore more conventional casting, forgingand machining work. Their use is together with the shorter productioncycles associated with pressing and welding operation. Automation, onthe other hand, has proved difficult due to the problem of handling thelarge sheet of raw material and work in process. Welding has alsotended to be a manual process since it is usually conducted by eyeand requires a certain degree of operator skill.The creation of an FMS system for producing sheet metal fabricationfollows essentially the sane step as for the more convention systemsalready outlined. The forest step is the application of numerical controlto the individual processes. For shearing, punching, and folding,proprietary machines equipped with NC and CNC are becoming morereadily available. For and vision systems removing the need foroperator control.Submitted by MUHAMMAD YOUNUS 08IN70 Page 16 17. The next step is the introduction of automatic loading and unloadingsystems to allow the un-interpreted running of the individualprocesses. This would involve the use of add on device capablesuction cups. The final step is to link together the various processes thematerial transport and transfer devices. For this purpose the limitlessversatility of the peripatetic AGV can again be utilized to advantage,suitably modified, a proprietary AGV is capable of transporting sheets,either singly or in batches, from one process to another where they canbe linked in with the automatic loading and unloading system.EXAMPLE # 07FLAXEBLE ASSEMBLY SYSTEMSAssembly work is a major area of application for FMS technology, aswas the case with component production, automated assembling waslimited to high volume when using conventional technology. Newtechnologies and, in particular, robotics have now changed this andflexible assembly systems are one of the most rapidly growing areas ofproduction.Compared with other manufacturing process, assembly is unique inthat it requires a far higher degree of manipulative and corrective skill.For this reason conventional automation and even early generationrobot were in capable of performing the sophisticated movements thatcould only be carried out by dexterous human operators. Theavailability of robots with sensory perception, however, has meant thatmany of these tasks need no longer be carried out manually since therequirement to feel or see can be fulfilled by the robot itself. A further important aspect of assembly work is that the amount ofpacing is (relatively) quite high especially where line are being used.This enables both automated and manual assembly operation to becarried out on the same product, provided they are separated by asuitable buffer. Full automation can therefore be introduced graduallySubmitted by MUHAMMAD YOUNUS 08IN70Page 17 18. by progressively replacing manual operation with individual robotstations.An example of this approach can be seen at Saab-Scanias plant forthe production of petrol engines. An increased range of engine optionwas being offered by Saab Cars, but conventional hard automation wasnot appropriate for their assembly because of the relatively low volumeand resulting high frequency of changeovers. Scania, there fore optedfor a flexible assembly system which initially consisted of six ASEArobots installed in a line of otherwise manual operations.The robots, which assembled sundry items such as valve springs,collects, timing covers and flywheels, could be changed to produce adifferent engine variant in about 15 minutes. Once this initialinstallation had been proved, Scania then added another three robotsto automate more of the manual operation and move one further steptowards the ultimate goal of completely automated system. A contrasting approach to Saab-Scanias is that of Perkins Engine (asubsidiary of Massey Ferguson) in the UK. Perkins a large diesel enginemanufacturer opted for a complete flexible assembly system costing 1m for the production of its full range of cylinders head, together withan automated component handling system costing a further 2.5 m.The system provided immediate capacity to produce 1000 cylinderheads per day, automatically, in a mix of sizes and types (three, fouror six cylinder). The inclusion of automated inspection equipment alsoensured that defective components were detected before rather thenafter being into a complete engine.The system at Perkins, and even that at Saab-Scania, represents afairly large scale and specialized case of flexible automated assembly.However, a number of relatively inexpensive robots is becoming readilyavailable which are designed specially for assembly work as show infigure (below).Submitted by MUHAMMAD YOUNUS 08IN70 Page 18 19. Submitted by MUHAMMAD YOUNUS 08IN70 Page 19