2009 The New JIT and Toyota

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Journal of Advanced Manufacturing SystemsVol. 8, No. 1 (2009) 5–26c© World Scientific Publishing Company

THE FOUNDATION FOR ADVANCING THE TOYOTAPRODUCTION SYSTEM UTILIZING NEW JIT

KAKURO AMASAKA

Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara-shiKanagawa-ken, 229-8558 Japan

kakuro [email protected]

The foundation for advancing the Toyota Production System (TPS) is based on efforts toattain simultaneous acheivement of QCD (Quality, Cost and Delivery) through innova-tion of manufacturing technology utilizing New JIT new management technology prin-ciple for manufacturing in the 21st century. This new principle contains hardware andsoftware systems, “TMS, TDS, TPS and Science TQM ” as the next generation tech-nical principles to accelerate the optimization (high-linkage) of business process cyclesof all the divisions. This in turn is accomplished by having cooperation between on-site“white-collar engineers” and “supervisors and workers” with affiliated and non-affiliatedsuppliers. The author believes that effectiveness of advancing TPS has been demon-strated as described based on the author’s experienced at Toyota.

Keywords: New JIT; advancing the Toyota Production System; QCD research; Toyota.

1. Introduction

The top priority issue of the industrial field today is the “new deployment of globalmarketing” needed to for survive the era of “global quality competition” i.e., torealize manufacturing that places top priority on customers with a good QCDand in a rapidly changing technical environment. For solving today’s managementtechnology issues, the author proposed New JIT by using new hardware and soft-ware systems like, Toyota Marketing System (TMS), Toyota Development System(TDS), Toyota Production System (TPS) and Science TQM to establish new man-agement technology principles for sales, R & D, design, engineering, and production,among others. The proposed New JIT does not stop with TPS and TQM, whichare representative of the Japanese production system called JIT (Just in Time).

In the implementation stage, the foundation for advancing the “TPS ” by sup-porting “TMS ” and “TDS ” is based on efforts to attain simultaneous acheivementof QCD through the innovation of manufacturing technology utilizing New JIT.This in turn is accomplished by having cooperation between on-site “white-collarengineers” and “supervisors and workers” with affiliated and non-affiliated suppli-ers. In this example, innovation of the production line of automobile rear axle unitin Toyota’s “Plant Motomachi” will be presented. It will demonstrate an example

5

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of solving a bottleneck manufacturing technology problem that was inhibiting NewJIT Production.

2. Basics of JIT — The Toyota Production System

What is known as the JIT system, a Japanese production system typified by theToyota Production System (TPS), is a manufacturing system that was developed bythe Toyota Motor Corporation.1,2 These are the basic concepts of JIT which aimsto realize “quality and productivity” simultaneously by effectively applying TotalQuality Control (TQC) and Total Quality Management (TQM) to the automobilemanufacturing process. It also pursues maximum efficiency (optimal streamlining,which is called a Lean System) while also being conscious of the principles of costreduction, and thereby improving the overall product quality.1−4

In the JIT implementation stage, it is important to constantly respond tothe customers’ needs, promote flawless production activities, conduct timely QCDresearch, and put it into practice.5 Therefore, Toyota has positioned TPS andTQM as the core management technologies for realizing “reasonable manufactur-ing” and these management technologies are often likened to being the wheels ofan automobile.4,5

In Fig. 1 these management technologies have been placed on the vertical andhorizontal axes. As shown in the figure, the combination of these technologiesreduces large irregularities in manufacturing to the state of “tiny ripples” wherethe average values are consistently improved in the process. This strategy is anapproach used by reasonable corporate management in which the so-called “lean-ing process” is consistently carried out.

As indicated by the vertical and horizontal axes in the figure, when the hardwaretechnology of the Toyota Production System and the software technology of TQM

Use of SQC reduces fluctuations and raisesthe average level of manufacturing quality.

Fig. 1. Relation between TPS and TQM.

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The Foundation for Advancing the Toyota Production System 7

(TQC) are implemented, the statistical quality management method (SQC) is to beeffectively incorporated to scientifically promote QCD research and achieve constantupgrading of the manufacturing quality. Another point that can be understood fromthe figure is that TQM and SQC are the foundations of maintaining and improvingthe manufacturing quality, and both have also historically served as a basis for theadvancement of JIT.6−9 In this way, the basic concept of JIT and the lean systemapproach have reformed the automobile manufacturing process used at Toyota. Asa result, the effectiveness of JIT has been recognized on a worldwide scale and it isnow regarded as the “core concept of manufacturing”.10−14

3. The Basic Principle of Manufacturing via the TPS

3.1. Simultaneous realization of quality and productivity

via a lean system15

The basic principle of manufacturing via the TPS is lean system production. In thissystem, manufacturing is conducted via one-by-one (single part) production and itsaim is to achieve the simultaneous realization of quality and productivity.

The first basic principle of manufacturing is a thorough quality control by meansof a one-by-one production. This system of “one-by-one production” on a manu-facturing line using an assembly conveyor gives the assembly worker the ability toconduct a self-check on each piece. If a defective item comes to their assembly pointfrom the previous process, they can then stop the conveyor and detect the defectwithout fail. Therefore, the assembly workers can provide 100% quality products tothe downstream processes. It is obvious that compared to lot production, this sys-tem can considerably improve the detection of defective parts from a probabilisticviewpoint. In this context, the one-by-one production is sometimes compared to afine, quick, and pure flow of water upstream in a “mountain stream”, while lot pro-duction is likened to the “broad, stagnant and slow water” found downstream. Truly,the Toyota Production System incorporating this one-by-one production deservesto be recognized as Lean System Production.

The second basic principle of manufacturing is the thorough incorporation ofquality into the process via a one-by-one production. The one-by-one production ina machining process shown in Fig. 2. The diagram illustrates an operation where aworker picks up a piece (work) from the parts box, conducts the machining processoperation on it from process #01 to #10 in the order shown, and finally placesthe completed piece into the completed parts box. Since the production operationis conducted according to a predetermined cycle time, the worker can consistentlycarry out the prepared standard operation in a rhythmical manner. Similar to theprevious case of operation on an assembly conveyor, a self-check can be consistentlyperformed and the “incorporation of quality” is ensured so that the “stabilizationof production” can also be promoted.

Even in the case of a production operation that involves multiple types of workpieces, the intelligent application of production engineering and process designing

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Fig. 2. The basic principle of manufacturing via the TPS.

can be used to support a worker and allow them to conduct the standard operationsin a rhythmical manner. A process like this is depicted in Fig. 2(1). In the casewhere a production process is arranged as shown in Fig. 2(2), the zigzag work flowinterferes with the smooth performance of the standard operations each time awork piece changes. This causes the worker to become fatigued and triggers humanerrors, thus lowering quality and productivity.

3.2. Process control and process improvement 5,16

The “high productivity” and “high quality” of today’s Japanese manufacturing isuniversally acknowledged.2 At the manufacturing sites, the “process control andprocess improvement” is mainly promoted by production workers under the super-vision of their supervisors and the “QCD research” conducted by the white-collarengineers are both equally valued in order to ensure the incorporation of “designquality” that is demanded by customers.

3.2.1. Process control and process improvement

Consideration is given here to the method of manufacturing an automobile and theresulting manufacturing cost (initial cost) and profit based on Fig. 3. The mainparts (heavy material parts) that compose an automobile are the skeletal structuremade up of the body and frame, and the parts that control the running functions,such as the engine and axles. These parts are made of steel plates and cast forgedsteel. Automobile manufacturers procure these materials from steel manufacturers.Parts such as tires, engine ignition batteries, brake units, power steering units, anda wide variety of other parts such as windshields, lights, mirrors, seats, and so onare purchased from specialized parts manufacturers.

In order to produce a complete automobile, the manufacturer also purchasesa variety of machining tools for processing parts, welding machines for the bodyand frame, assembling robots for assembling the vehicle, and other equipment fromspecialized machine or equipment manufacturers. Finally, the electric power neededto operate these machines and equipment is bought from power supply companies.Generally speaking, the manufacturing costs listed above that are borne by the

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Fig. 3. Manufacturing methods and costs.

automobile manufacturer do not differ very much from other manufacturers. Thelabor cost (workers’ wages) is also similar among manufacturers. Therefore, themanufacturing cost (initial cost) shown on the left half of the figure for automobilesof a similar design does not vary greatly from manufacturer to manufacturer. Onthe other hand, the right half of the figure shows the manufacturing cost thatresults from the method of manufacturing the vehicle at the production site anda large difference can result depending on how each manufacturer handles theirmanufacturing process control and process improvement.

The following are some poor cases of process control:

(i) Due to the inconvenient process design and production process, the workercannot carry out their operation according to the standard operation sheetand therefore a number of irregularities result in the operation. This in turncauses the assembly line to stop often and therefore the line operating ratebecomes lower.

(ii) Due to inadequate instructions from the supervisor or due to insufficient edu-cation and training provided to new workers regarding manual (skill required)operation or the handling of the machines, quality defects result from operationerrors or improper machine manipulation. This causes pieces with machiningdefects and then entails their disposal or reworking of these pieces.

For these and other reasons, the manufacturing cost can increase beyond theexpected cost, and the profit rate per vehicle that was initially calculated can alsodecline substantially. Cases such as these should not be neglected and the processcontrol at the production site needs to be thoroughly reviewed. Process improve-ment and preventive measures need to be devised and implemented through ingenu-ity and original suggestions obtained via the full participation of all the on-site staff.If improvement does not make good progress through the efforts of the production

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site staff alone, then the cooperation of the engineering staff from related depart-ments should be obtained to thoroughly implement process improvements. Theultimate objective is to reduce the manufacturing costs and improve the profit rate.

The accumulation of a variety of process improvements at the production sitecan also include conservation that results in lower material cost, parts purchasingcost, and energy consumption (items on the left side of Fig. 3). This will all leadin turn to reducing the number of quality defects and improving the line operatingrate. Furthermore, unnecessary labor cost can be eliminated by reducing excessiveovertime work and the manufacturing cost can be further improved. In addition,continuous efforts to improve process control and process improvement at the pro-duction site will enhance the skills and motivation of the production workers andcontribute greatly to the strengthening of the work environment and work cultureat the production site as well.

3.2.2. Daily improvement activities at the production site 15,17

Next, the third basic principle of manufacturing is the daily improvement activitiesat the production site. The basis for the simultaneous realization of quality andproductivity via the TPS is the improvement of the work environment to preventworker’s fatigue, improvement of the work standards to prevent errors, improve-ment of control through visual confirmation, and so on. These improvements aredesigned to help the workers maintain their standard operations in a rhythmicalflow. Concerted efforts are made to make small improvements that do not incur ina large expense, such as safe work procedures, prioritizing quality, quickening thepace of work by one second, and so on.

The main facilitators of these daily improvement activities are the workers them-selves who carry them out through small group activities, mainly in the formof QC circles or through their own voluntary originality and ingenuity. Duringthe implementation stage, activities such as having an improvement team supportthe production site or promoting greater cooperation between the supervisors andproduction staff are put into practice. One characteristic example of such “dailyimprovement activities” is a process improvement that achieves work operationsthat are less tiring. Similarly, another example is a process improvement madeto an inconvenient work operation. As demonstrated by these daily improvementexamples, carrying out process improvements on a daily basis gives the workersthemselves the opportunity to develop more convenient work processes, make theirwork operations safer, and also ensure that quality is being incorporated. At thesame time, redundant work processes can also be removed.

3.2.3. Innovation of the production process — QCD research activities bywhite-collar engineers 5,15

The fourth basic principle of manufacturing that is capable of quickly respondingto the stringent demands of today’s customers is the innovation of the production

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process and advancements in manufacturing that result from the QCD researchactivities conducted by white-collar engineers.

(i) First, the fundamental principle of JIT production is “manufacturing only whatcan be sold, when it can be sold, in the quantity that can be sold”. To accom-plish this it is essential to establish a flexible production system that will “pro-duce and transport only what is needed, when it is needed, in the quantity thatis needed”, as a rational production measure.

(ii) Second, it is imperative to reinforce the capabilities of the production site andto advance JIT production by actively developing new production technolo-gies that will solve the bottleneck technological problems in production andsubstantially improve the quality and productivity of the production site.

Having said the above, the following is an explanation of a small part of a QCDresearch activity that was promoted by the so-called “white-collar engineers” (orengineering staff and managers responsible for manufacturing technology, produc-tion engineering development, process planning, process designing, and productionmanagement) that contributed to the innovation of the production process.

Figure 4 shows an example of a process improvement for a layout that facilitatesthe incorporation of quality by implementing a countermeasure for the “outlyingisland”, so called “Hanare Kojima” layout. Before the improvement — “Kaizen”,as seen in Fig. 4(1) on the left, the six workers at the automatic table conveyorare separated from one another by the five parts feeders that supply the partsto the assembling machines (the five automated machines, marked as A to E)located at each of the preceding processes. This process arrangement is the “HanareKojima” layout and when there is quality trouble or a “small stop” of the assemblingmachines, it is difficult for an expert worker (skilled worker) to provide instruction(assistance) to a newly assigned worker.

In addition, each worker’s standard operation time differs due to the differencein their experience. Therefore, an expert worker is forced to wait for work from anew worker (creating wasted time) since their operation time is shorter than that ofnewly assigned workers. Moreover, in the case of a production line with this outlyingisland layout, the tact time cannot be set according to the fluctuations (increaseand decrease) in production volume because the tact time is fixed according to theoperation time of the workers. Therefore, the tact time cannot be changed in aflexible manner according to the number of workers.

Given this background, the engineering staff (white-collar engineers) reviewedthe production line where the workers’ manual operations and automated machiningprocesses are combined, so that they could reform the production process. As seenin Fig. 4(2), after the improvements-“Kaizen” were made, the automated machiningprocesses were consolidated. In an effort to create a continuous processing operationfrom A to B to C, as well as from D to E, the set positions of the work pieceswere changed and the processing jigs were altered. The parts feeders that supplythe same parts were also integrated so that the number of parts feeders could be

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Fig. 4. Example of a production layout that facilities built-in quality by eliminating isolatedworksites.

reduced from five to three. These improvement measures rearranged the automatictable conveyor into a single line and the old work layout that had separated theworkers was done away with.

The above case is a characteristic example of a process improvement that real-ized flexible production that could react to fluctuations in production volume,resulting in improvements to the line operating rate, and stabilized the productionquality. This all effectively contributes to meeting the QCD requirements. Theseimprovement measures promoted (a) mutual confirmation between the workers onwork progress, (b) mutual assistance in case of any delay in work operation, (c)observance of “simultaneous confirmation of quality”, (d) improvement in the effi-ciency of material transport, (e) the ability to respond to the increase or decrease inthe number of workers according to the changing production volume, (f) the abilityfor supervisors to respond to short stops of the automated processing line outside oftheir own production line, supply parts to the parts feeders, provide work instruc-tions and assistance to line workers, create greater efficiency in the replacementwork between completed work pieces and materials, (g) the improvement made tohelp solve unforced errors such as wrong or missing parts and misassembled pieces,(h) the process improvements that helped solve human errors using an automaticdiagnosis inspection device for a quantitative evaluation of the quality judgmentand fault diagnosis, and so on.

These process improvement examples are the results of QCD research activi-ties carried out through cooperation between the white-collar and production siteworkers or supervisors in an effort to solve the inconvenient work operations fromthe standpoint of human behavioral science.

4. The Foundation for Advancing the TPS UtilizingNew JIT 4−7,22

4.1. The demand for advancement in management technology

The top priority issue of the industrial field today is the “new deployment of globalmarketing” needed to survive the era of “global quality competition”.18 To realize

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manufacturing that places top priority on customers with a good QCD and in arapidly changing technical environment, it is important to develop a new productiontechnology principle and establish new process management principles to enableglobal production.

Furthermore, a new quality management technology principle linked with overallactivities for higher work process quality in all divisions is necessary for an enter-prise to survive.19 The creation of attractive products requires each of the sales,engineering/design, and production departments to be able to carry out manage-ment that forms linkages throughout the whole organization.20 From this point ofview, the reform of Japanese-style management technology is desired once again.In this need for improvements, Toyota is no exception.21

4.2. Need for strategic QCD studies with affiliated and

non-affiliated suppliers

IT development has led to a market environment where customers can promptlyacquire the latest information from around the world with ease. In this age, cus-tomers select products that meet their lifestyle and a sense of value on the basis of avalue standard that justifies the cost. Thus the concept of “Quality” has expandedfrom being product quality — oriented to business quality — and then to corpo-rate management quality-oriented. They are strict in demanding the reliability ofenterprises through the utility values (quality, reliability) of products. Advancedcompanies in countries all over the world, including Japan, are shifting to globalproduction. The purpose of global production is to realize “uniform quality world-wide and production at optimum locations” in order to ensure company survivalamidst fierce competition.

For the manufacturing industry, the key to success in global production is sys-tematizing its management methods when modeling strategic SCM (supply chainmanagement) for its domestic and overseas suppliers. In-depth studies of the TPS,TQM, partnering, and digital engineering will be needed when these methods areimplemented in the future. Above all, manufacturers endeavoring to become globalcompanies are required to collaborate with not only affiliated companies but alsowith non-affiliated companies to achieve harmonious coexistence among them basedon cooperation and competition. In other words, a so-called “federation of compa-nies” is needed.

4.3. Significance of strategic implementation of New JIT

Having said the above, it is the author’s conjecture that it is clearly impossibleto lead the next-generation by merely maintaining the two Toyota managementtechnology principles, TPS and TQM. To overcome this issue, it is essential torenovate not only TPS, which is the core principle of the production process,but also to establish core principles for marketing, design and development,production and other departments. The next-generation management technology

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Fig. 5. New JIT, a new management technology principle.

model, New JIT, which the author has proposed through theoretical and system-atic analyses as shown in Fig. 5, is the Just in Time system for not only manu-facturing, but also for customer relations, sales and marketing, product planning,R&D, design, production engineering, logistics, procurement, administration andmanagement, for enhancing business process innovation and introduction of newconcepts and procedures.

New JIT contains hardware and software systems as the next generation tech-nical principles for accelerating the optimization (high-linkage) of business processcycles of all the divisions (Fig. 6). The first item, the hardware system, consists ofthe “TMS, TDS, and TPS ” (Toyota Marketing System, Toyota Development Sys-tem and Toyota Production System), which are the three core elements required forestablishing new management technology principles for sales, R&D, design, engi-neering, and production, among others.

The expectations and role of the first principle “TMS ” include the following:(i) Market creation through the gathering and use of customer information, (ii)Improvement of product value by understanding the elements essential to raisingmerchandize value, (iii) Establishment of hardware and software marketing systemto form ties with customers and (iv) Realization on the necessary elements foradopting a corporate attitude (behavioral norm) of enhancing customer value anddeveloping customer satisfaction (CS), customer delight (CD) customer retention(CR), and networks. The expectations and role of the second principle “TDS ” arethe systemization of design management method which is capable of clarifying thefollowing: (i) Collection and analysis of updated internal and external informationthat emphasizes the importance of design philosophy, (ii) Development design pro-cess, (iii) Design method that incorporates enhanced design technology for obtain-ing general solutions, and (iv) Design guideline for designer development (theory,

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action and decision-making). The expectations and new role of the third principle“TPS ” comprise the following: (i) Customer-oriented production control systemsthat place the priority on internal and external quality information, (ii) Creationand management of a rational production process organization, (iii) QCD activitiesusing advanced production technology and (iv) Creation of active workshop capableof implementing partnership.

For the second item, the strategic quality management system, the author isproposing a new principle of quality control, “Science TQM ”6,7 called “TQM-S ”(TQM by utilizing Science SQC) in Toyota as a software system for improving the“business process quality” of the 13 departments shown in Fig. 5.

4.4. Cooperation between on-site “white-collar engineers” and

“supervisors & workers” 5,15

The foundation for advancing the “TPS ” by supporting “TMS ” and “TDS ” isbased on efforts to attain simultaneous acheivement of QCD through innovation ofmanufacturing technology utilizing New JIT. This in turn is accomplished by havingon-site engineering staff to carry out innovation at the manufacturing site, as wellas having “white-collar engineers” to lead in the innovation and improvement ofthe manufacturing technology. All this is done to conduct manufacturing with highquality assurance.

Some of the features of the “TPS ” are the improvement of laborious work oper-ations and the creation of a safe, worker-friendly manufacturing site in which thesupervisors and workers take the initiative, while the manufacturing technologystaff members (white-collar engineers) also cooperate. Through such a process, theimprovement of daily management and maintenance can be reinforced, which real-izes rhythmical and smooth work operations, thus enabling reliable manufacturing(ensuring the process capability and machine capability). Secondly, “TPS ” takeson the challenge of simultaneous achievement of QCD through the innovation ofmanufacturing technology. In this case, the initiative is taken by the white-collarengineers, while the supervisors and workers on the manufacturing site cooperate.This effort is expected to drastically improve the manufacturing technology (forthe working environment, production equipment, production management, produc-tion technology, quality management technology, etc.), which has been a bottleneckobstacle of the manufacturing site.

In the implementation stage, the innovations mentioned above are to be carriedout by a “Strategic Total Task Management Team”6 led by the on-site manufac-turing technical staff and production engineering development staff, while productdesigning and research development staff and even suppliers (parts manufactur-ers, production equipment, and machinery manufacturers, etc.) also participate.By means of these activities, wide-ranging business processes from the suppliers tothe vehicle manufacturers can be linked in a highly efficient manner, and thereforemanufacturing can be conducted in an advancing TPS fashion, called “New JIT

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production”.23,24 Below is an example of the simultaneous achievement of QCDthrough the innovation of manufacturing technology.

5. Application to Simultaneous Achievement of QCD through theInnovation of Manucturing Technology5,15 — Innovation of the

Production Line of Automobile Rear Axle Unit for New JIT

Production25

In this example, innovation of the production line producing rear axle unit-relatedparts for automobiles in Toyota’s “Plant Motomachi” will be presented. It willdemonstrate an example of solving a bottleneck manufacturing technology problemthat was inhibiting New JIT Production.

5.1. Outline of the production process of the rear axle unit

A rear axle unit for an automobile underbody is manufactured in a production pro-cess that includes a machining process and assembly process. These are performedin order by means of the Toyota Production System. This process is generallyreferred to as a lean production (production of one piece at a time) system. Afterthe assembly is complete, the assembled rear axle unit is further combined togetherwith various other products via a method called the sequential parts withdrawalsystem and then it is taken to a vehicle assembly plant via the pull system produc-tion method. Figure 7 illustrates the machining and assembling process of a rearaxle unit manufactured by a typical TPS.

The main characteristic of the “TPS ” is to carry out production without keepingany excess parts in stock. Therefore, in this process, it is necessary to conductassembly in an orderly manner according to the assembly sequence from the startof the conveyor driven assembly process (5) to the latter process in the vehicleassembly plant. This is done by utilizing an intra-process instruction “Kaizen” thatclearly indicates the order of the processes in coordination with the downstreampull system processes.

The main component parts of this product, namely the rear axle housing andrear axle tube, come in a wide variety of different types that are delivered fromparts manufacturing suppliers. Both parts are subjected to machining before beingsupplied to the beginning of the assembly process. Similarly, the various types ofrear axle shaft delivered from a designated supplier are subjected to machiningand then supplied to the beginning of the assembly conveyor. For both products,what is required is synchronized production so-called “Douki-ka”, where finishedprocessed parts of the needed types are supplied in a timely, JIT fashion to the headof the assembly conveyor, while minimizing the amount of intra-process parts andthe number of finished products kept in inventory to the greatest extent possible.

Moreover, what makes this synchronized production even more difficult are theconsiderable differences in the operation availability of each of the processes of

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machining and assembly. Generally, the operation availability of the assembly pro-cess is relatively high, but the previous machining process has low operation avail-ability due to bottleneck problems and other reasons stated in 5.2.1. As discussedabove, the production line for the rear axle units is arranged in a one-unit-at-a-timeproduction manner from machining to assembly. Therefore, “Douki-ka” productionis not easy, particularly in the case where in-process inventory is not held in eachprocess or between processes.

5.2. Before process improvement — bottleneck-like manufacturing

technical problems that inhibit JIT

In addition to the above, in each of the processes of machining, and assembly,bottleneck-like manufacturing technical problems that inhibit JIT exist, and thesehave not been solved for a long time.

5.2.1. Bottleneck technology in the machining process for the rear axle shaft

The bottleneck problems in this process are ensuring manufacturing quality andenergy conservation, as well as the technical hindrances that prevent synchronizedproduction.

As Fig. 7 suggests, the upstream process of machining (#010 - #030) and thedownstream process conducted manually by production operators (#070 - #170)are separated by the (2) large-size, automated high frequency quenching equipment(#040) and (3) heat circulating-type tempering equipment (#050), which consumea large amount of power and have a large amount of in-process inventory. Forthis reason, these processes are left like “remote islands” as it were. As a result,the one-operator work operations in the upstream process (#010 - #030) requireassistance from the supervisor in order to accommodate any extra cycle time in thecase where the number of production units per day is increased. On the other hand,the operators are in standby mode when production volume per day is small.

In addition, the operation of manual stress relief equipment (marked as #060)is dependent on the emprical skills and abilities of expert production operators.The long-sized workpieces (rear axle shafts) supplied from the upstream process(quenching and tempering equipment, #040 - #050) have a stress profile of com-plicated spirals after heat treatment. Also, in cases where the required heat stressadjustment is large, the number of adjustment operations (time needed for adjust-ment) becomes larger, resulting in extra cycle time. When a production operator isoverburdened and conducts excessive adjustment operations in order to avoid theabove situation, cracks can be induced inside or on the surface of these long-sizedwork pieces. Moreover, if the operator has not acquired sufficient skills, this canresult in human error and a supply of defective long-sized work pieces that do notsatisfy the standard stress adjustment specifications to the downstream processes(#070 - #170). This will then cause a number of machining process defects.

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As discussed above, many problems such as defective quality, “Hanare Kojima”work area arrangement, wasteful power consumption, extra cycle time, andin-process inventory have not been solved, presenting themselves, bottleneck manu-facturing technical problems. Due to this situation, half-processed or finished prod-ucts are stuck within the processes as inventory and synchronized production incoordination with the downstream assembly process (5) cannot be realized, partic-ularly in the case of the welding process. This bottleneck situation has not yet beensolved and this prevents the realization of simultaneous achievement of QCD.

5.2.2. Bottleneck problems in the assembly process for the rear axle units

The bottleneck problems of this process range from ensuring product quality, toenergy conservation, to production response to the downstream pull system. Themarket requires that the quality of rust proofing of manufactured products beassured. The steel surface of a rear axle housing is flat and smooth. Therefore,the rustproof coating thickness can be ensured with (6) automated coating robots.However, the rustproof quality of the uneven areas on the cast metal surface cannotbe sufficiently ensured as the coating on convex surfaces tends to be thinner dueto the characteristics of the coating being used, as shown in (6) of Fig. 7 (in theupper right corner).

To avoid such uneven coating, extra coating operations are conducted to ensuresufficient thickness, and this results in a higher coating cost. Furthermore, afterthe coating operation indicated by (6) in the figure, the work pieces are passedthrough the (7) electric heater-type drying machine, which requires considerablepower consumption, and are then cooled down to room temperature in the coolingprocess area. After this, the finished products are unloaded to the pull system cart(9). For this reason, excessive inventory remains on the (8) overhead conveyor,and therefore, as in cases of the upstream welding and machining processes, theseprocesses presents a hindrance to the realization of simultaneous achievement ofQCD.

5.3. After process improvement — Simultaneous achievement of

QCD by innovation of manufacturing technology

In order to solve the above mentioned bottleneck problems of this production line,it is necessary to innovate the manufacturing technology. Given this background,the authors25 decided to take a systematic approach to the improvement of thefundamental process by taking into consideration the timing of production of aforthcoming new vehicle model. Before this plan was implemented, the author6,7

formed a “Strategic Total Task Management Team” led by the technical staff onthe manufacturing site, as well as the production engineering development staff.Participation by the product development staff, parts manufacturers (affiliated andnon-affiliated suppliers) and equipment machine manufacturers was also gained,

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and the authors attempted to realize the simultaneous achievement of QCD withrevolutionary approaches such as those introduced below.

5.3.1. Solution to bottleneck problems related to the processing of the rearaxle shaft 26,27

(1) Development of mid-frequency tempering equipmentIn place of the aforementioned, large-scale, hot air circulating oven, panel-heater-type tempering equipment that consumes a lot of electric power (#050), a newlydeveloped mid-frequency, heat induction coil-type, tempering equipment unit wasinstalled. As indicated in the upper section (3) in Fig. 7, tempering is now conductedfor one work piece at a time while concentrating on the high frequency quenchingarea. This meant that power consumption and in-process inventory were drasticallyreduced and the lead time was also substantially shortened.

(2) Development of automated stress relief equipmentIn addition to the above, the aforementioned manual stress relief equipment (#60)that depends on the empirical skills and abilities of an expert operator was replacedwith a newly developed (4) automated stress relief equipment unit. As indicatedin the upper section (4) in Fig. 7, the master skills commonly acquired by expertoperators are simulated in order to conduct stress relief operations in an automaticand intelligent manner. This equipment is capable of properly conducting stressadjustment operations on work pieces with a variety of different shape profiles(lengths and diameters). Even in the case of a sizable spiral adjustment, stressrelief can be done in a cycle time that is comparable to that of skilled operators.Also, by installing a work piece crack detector, stable quality manufacturing wasensured and uneven cycle times were successfully eliminated.

These improvements in the facility equipment made it possible for the flow ofwork pieces from (3) the high frequency quenching equipment, to the mid-frequencytempering equipment, to the automated stress relief equipment (#040 - #050 -#060) as shown in the figure, to be connected in sequence along with automatictransportation of the work pieces. Consequently, these processes could be separatedfrom the manual work processes. Also, by integrating the upstream processes (#010- #030) and downstream processes (#070 - #170) as illustrated in the figure, theproblem of work operations conducted over “remote island” work areas was alsosolved.

These process improvement measures make it possible to flexibly arrange pro-duction operators according to the increase and decrease in production volume perday, and therefore enhance productivity. As a result, manufactured quality wasimproved, the lead time was considerably shortened, the problems associated withenergy conservation, labor force minimization, and skill acquisition were solved,and synchronized production was realized. This substantially contributed to thesimultaneous achievement of QCD.

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22 K. Amasaka

5.3.2. Solution to bottleneck problems related to the assembly process of therear axle unit

(1) Simultaneous achievement of QCD for the corrosion resistance coating28−30

In recent years, in an aim to improve the product value of parts related to an auto-mobile’s suspension and chassis, efforts have been made toward the simultaneouslyachievement of QCD in the area of corrosion-resistant coating technology by dras-tically improving its rust proofing characteristics without raising the coating cost.In order to implement this project, the authors organized a “Total Task Manage-ment Team” through collaboration with the on-site staff, production engineeringstaff, product development and designing staff, and coating material manufacturers(Aisin Chemical Co., Ltd., one of several affiliated coating manufacturers, and alsonon-affiliated manufacturer, Tokyo Paint Co., Ltd.). The manufacturing technicalstaff took the lead in this project.

Figure 8 shows the development procedure (rust proof quality and coating cost)that aimed for the simultaneous achievement of QCD by improving the coatingmaterials, coating equipment, and drying equipment. In addition, the authors alsoaimed to solve the technical problems in order to enhance the product value (VA isindicated by the rust proof quality/cost) of the rear axle units to which the coatingmaterials manufactured by Tokyo Paint are applied (From Improvement (1) to (8)in the figure). The coating cost in the figure indicates not the price of coatingmaterials, but that of the coating operation, which includes the entire cost of thecoating materials, energy consumed, cleaning, and maintenance cost of the coatingequipment per one work piece.

Conventionally, styrene modified alkyd resin solvent coating had been used,but in an effort to prevent initial rusting caused by the spread of antifreeze agent

Before

100(High) ← →Cost index low

2000

150

5

10

15

Improvement the paint quality

Improvement the painting facilities (

Qual

ity

goal

projectactivities

Qu

alit

y(I

nde

x)

(1)

(2) (3)

(5)(4)

(7)

(6)

(8)

(1) – (7)

(4) – (8) )

( )

( ) ( )

Fig. 8. Improvement process of the paint.

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mainly used overseas, improved phenol modified alkyd resin (Improvement (1))was adopted, and this resulted in an increase in the coating cost due to the highmaterial cost.

Given this background, a task team was formed that set development targets inseveral phases, while also anticipating the required quality improvements demandedby the market, which grow higher year after year, and systematically promoted theproject through close monitoring of the process improvement. In the early phasesof improvement, mainly the coating materials were improved (From Improvement(1) to (7)) and in the latter half, improvements in coating and drying equipmentwere promoted in parallel (From Improvement (4) to (8)). More specifically, thefollowing widely varied improvements were implemented:

(i) The target for improving the solvent coating materials was to have bettercorrosion resistance characteristics. Air drying alkyd resin provides drying andcorrosion resistance characteristics and non-polluting rustproof colorant andfilling colorant were then properly mixed with the modified alkyd resin. Thesewere used as the base materials and improvement of the corrosion resistancewas achieved.

(ii) Another target was to improve the quick drying characteristics and cost, cor-rosion resistance, quality of the coating films, storage stability of the coatingmaterials, and safety (prevention of spontaneous ignition by the coating mist).Improved results were obtained by using a lacquer-type phenol alkyd resinwhich is resistant to oxidation polymerization.

(iii) In order to homogenize the coating films and enhance the finished exterior ofthe film surface, stearin acid and organic bentonite were added to the quickdrying materials to improve thixotropy. This resulted in improvement of thefinish quality, cost, and corrosion resistance characteristics.

(iv) To improve the coating efficiency of the airless electrostatic coating, a polarsolvent and non-polar solvent having strong polarity and high permittivitywere optimally composed in such a way as to satisfy the requirements of cost,drying characteristics, solubility, workability, and storage stability. As a result,the electric resistance of the coating materials was optimally adjusted.

(v) The initial material cost was reduced through an optimal choice of the coatingmaterials, filling colorants, thinners, and various compounding ingredients.

(vi) In order to improve the equipment for the coating and drying processes, irreg-ularities in the coating efficiency and films were reduced by adapting “dilutionadjusted coating materials” to seasonal changes, hot sprays, and so forth, sothat the amount of coating materials consumed per unit was reduced by over30%. Moreover, by implementing collection and reuse of over spray coating andoptimal compounding with new agents, the initial cost was further reduced. Inaddition, the adoption of robots to the coating operation realized a reductionin the running cost and improved the finish quality and coating efficiencyin comparison with the conventional fixed multi-unit airless electrostatic guncoating. (From Improvement (7) to (8))

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24 K. Amasaka

As a result, the final improved coating operation conducted ten months latershowed marked improvement. The rustproof characteristics were improved by 14times (index based) and the visual quality was improved by five times (index based)by homogenizing the coating films. Furthermore, the drying facility was abolishedbecause of the development of the quick drying coating materials with room temper-ature drying characteristics. These improvements reduced the in-process inventorywithin the process to one-third and drastically reduced the coating cost by over30% compared to the conventional method. Even in the case of Aisin Chemical,similar improvement approaches have been taken and resulted in the simultaneousachievement of QCD.

(2) Improvement of the bolt tightening tools31

As shown in Fig. 7 (on the right), the finished rear axle unit products are mountedon pull system carts located at the final process of the assembly conveyor. The workhours needed for this operation have been reduced by improving the bolt tighteningtools for the brake units and disc wheel units that are assembled together with therear axle units.

The conventional bolt tightening operations are conducted in three steps: tight-ening with an impact wrench via the empirical feel of the operators, additionaltightening with a torque wrench, and torque checking. These operations have beenvery burdensome and difficult, even for expert production operators, and tight-ening operations were not always uniform in quality. Given this background, theauthors developed a high precision tightening tool with torque control (tighteningtorque detector), that reduced this operation to only a single step, thereby reduc-ing the manual work time and also improving and stabilizing the bolt tighteningquality at the same time. The efforts made through the task team activities of theon-site manufacturing staff and technical engineers introduced in this discussionwere undertaken to realize the simultaneous achievement of QCD and in an aimto attain high quality assurance manufacturing by innovating the manufacturingtechnology.

These activities have been positioned as the basis for the advance-ment of the “TPS ”, along with daily improvement activities at the manufacturingsite.

6. Conclusion

In this study, the author illustrated the foundation and effectiveness of advancingthe TPS utilizing New JIT principle. This is based on effort to attain simultane-ous achievement of QCD through innovative manufacturing technology by havingcooperation between on-site white-collar engineers and supervisors and workerswith affiliated and non-affiliated suppliers. In this example, the author has provedthe effectiveness of advancing the TPS through innovation of the production lineof automobile rear axle unit.

May 12, 2009 14:59 WSPC/180-JAMS 00161


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2009 The New JIT and Toyota