1785_氣門(mén)搖臂軸支座的機(jī)械加工工藝及夾具設(shè)計(jì),氣門(mén),搖臂,支座,機(jī)械,加工,工藝,夾具,設(shè)計(jì) Int J Adv Manuf Technol (2005) 25: 551–559DOI 10.1007/s00170-003-1843-3ORIGINAL ARTICLES.H. Masood · B. Abbas · E. Shayan · A. KaraAn investigation into design and manufacturing of mechanical conveyors systemsfor food processingReceived: 29 March 2003 / Accepted: 21 June 2003 / Published online: 23 June 2004? Springer-Verlag London Limited 2004Abstract This paper presents the results of a research investi-gation undertaken to develop methodologies and techniques thatwill reduce the cost and time of the design, manufacturing andassembly of mechanical conveyor systems used in the food andbeverage industry. The improved methodology for design andproduction of conveyor components is based on the minimisa-tion of materials, parts and costs, using the rules of design formanufacture and design for assembly. Results obtained on a testconveyor system verify the bene?ts of using the improved tech-niques. The overall material cost was reduced by 19% and theoverall assembly cost was reduced by 20% compared to conven-tional methods.Keywords Assembly · Cost reduction · Design · DFA · DFM ·Mechanical conveyor1 IntroductionConveyor systems used in the food and beverage industry arehighly automated custom made structures consisting of a largenumber of parts and designed to carry products such as foodcartons, drink bottles and cans in fast production and assemblylines. Most of the processing and packaging of food and drink in-volve continuous operations where cartons, bottles or cans are re-quired to move at a controlled speed for ?lling or assembly oper-ations. Their operations require highly ef?cient and reliable me-chanical conveyors, which range from overhead types to ?oor-mounted types of chain, roller or belt driven conveyor systems.In recent years, immense pressure from clients for low costbut ef?cient mechanical conveyor systems has pushed con-veyor manufacturers to review their current design and assemblymethods and look at an alternative means to manufacture moreeconomical and reliable conveyors for their clients. At present,S.H. Masood (u) · B. Abbas · E. Shayan · A. KaraIndustrial Research Institute Swinburne,Swinburne University of Technology,Hawthorn, Melbourne 3122, AustraliaE-mail: smasood@swin.edu.aumost material handling devices, both hardware and software, arehighly specialised, in?exible and costly to con?gure, install andmaintain [1]. Conveyors are ?xed in terms of their locations andthe conveyor belts according to their synchronised speeds, mak-ing any changeover of the conveyor system very dif?cult and ex-pensive. In today’s radically changing industrial markets, there isa need to implement a new manufacturing strategy, a new systemoperational concept and a new system control software and hard-ware development concept, that can be applied to the design ofa new generation of open, ?exible material handling systems [2].Ho and Ranky [3] proposed a new modular and recon?gurable2D and 3D conveyor system, which encompasses an open re-con?gurable software architecture based on the CIM-OSA (opensystem architecture) model. It is noted that the research in thearea of improvement of conveyor systems used in beverage in-dustry is very limited. Most of the published research is directedtowards improving the operations of conveyor systems and inte-gration of system to highly sophisticated software and hardware.This paper presents a research investigation aimed at im-proving the current techniques and practices used in the de-sign, manufacturing and assembly of ?oor mounted type chaindriven mechanical conveyors in order to reduce the manufactur-ing lead time and cost for such conveyors. Applying the con-cept of concurrent engineering and the principles of design formanufacturing and design for assembly [4, 5], several criticalconveyor parts were investigated for their functionality, materialsuitability, strength criterion, cost and ease of assembly in theoverall conveyor system. The critical parts were modi?ed andredesigned with new shape and geometry, and some with newmaterials. The improved design methods and the functionality ofnew conveyor parts were veri?ed and tested on a new test con-veyor system designed, manufactured and assembled using thenew improved parts.2 Design for manufacturing and assembly (DFMA)In recent years, research in the area of design for manufacturingand assembly has become very useful for industries that are con-552sidering improving their facilities and manufacturing methodol-ogy. However, there has not been enough work done in the areaof design for conveyor components, especially related to the is-sue of increasing numbers of drawing data and re-engineeringof the process of conveyor design based on traditional methods.·····Emphasise standardisationUse the simplest possible operationsUse operations of known capabilityMinimise setups and interventionsUndertake engineering changes in batchesA vast amount of papers have been published that have investi-gated issues related to DFMA and applied to various methodolo-gies to achieve results that proved economical, ef?cient and costeffective for the companies under investigation.The main classi?cations of DFMA knowledge can be iden-ti?ed as (1) General guidelines, (2) Company-speci?c best prac-tice or (3) Process and or resource-speci?c constraints. Generalguidelines refer to generally applicable rules-of-thumb, relat-ing to a manufacturing domain of which the designer shouldbe aware. The following list has been compiled for DFMguidelines [6].These design guidelines should be thought of as “optimalsuggestions”. They typically will result in a high-quality, low-cost, and manufacturable design. Occasionally compromisesmust be made, of course. In these cases, if a guideline goesagainst a marketing or performance requirement, the next bestalternative should be selected [7].Company-speci?c best practice refers to the in-house designrules a company develops, usually over a long period of time, andwhich the designer is expected to adhere to. These design rulesare identi?ed by the company as contributing to improved qualityand ef?ciency by recognising the overall relationships between·················Design for a minimum number of partsDevelop a modular designMinimise part variationsDesign parts to be multifunctionalDesign parts for multiuseDesign parts for ease of fabricationAvoid separate fastenersMaximise compliance: design for ease of assemblyMinimise handling: design for handling presentationEvaluate assembly methodsEliminate adjustmentsAvoid ?exible components: they are dif?cult to handleUse parts of known capabilityAllow for maximum intolerance of partsUse known and proven vendors and suppliersUse parts at derated values with no marginal overstressMinimise subassembliesparticular processes and design decisions. Companies use suchguidelines as part of the training given to designers of productsrequiring signi?cant amounts of manual assembly or mainte-nance. Note that most of the methodologies are good at eitherbeing quick and easy to start or being more formal and quanti-tative. For example, guidelines by Boothroyd and Dewhurst [8]on DFA are considered as being quantitative and systematic.Whereas the DFM guidelines, which are merely rules of thumbderived from experienced professionals, are more qualitative andless formal [9].3 Conventional conveyor system designDesign and manufacturing of conveyor systems is a very com-plex and time-consuming process. As every conveyor system isa custom-made product, each project varies from every otherproject in terms of size, product and layout. The system designFig. 1. Layout of conveyor sys-tem for labelling plasic bottles553is based on client requirements and product speci?cations. More-over, the system layout has to ?t in the space provided by thecompany. The process of designing a layout for a conveyor sys-tem involve revisions and could take from days to months or insome instances years. One with the minimum cost and maximumclient suitability is most likely to get approval.Figure 1 shows a schematic layout of a typical conveyorsystem installed in a production line used for labelling ofplastic bottles. Different sections of the conveyor system areidenti?ed by speci?c technical names, which are commonlyused in similar industrial application. The “singlizer” sec-tion enables the product to form into one lane from multiplelanes. The “slowdown table” reduces the speed of productonce it exits from ?ller, labeller, etc. The “mass ?ow” sec-tion is used to keep up with high-speed process, e.g., ?ller,labeller, etc. The “transfer table” transfers the direction of prod-uct ?ow. The purpose of these different conveyor sections isthus to control the product ?ow through different processingmachines.A typical mechanical conveyor system used in food and bev-erage applications consists of over two hundred mechanical andelectrical parts depending on the size of the system. Some ofthe common but essential components that could be standard-ised and accumulated into families of the conveyor system areside frames, spacer bars, end plates, cover plates, inside bendplates, outside bend plates, bend tracks and shafts (drive, tail andslave). The size and quantity of these parts vary according to thelength of conveyor sections and number of tracks correspond-ing to the width and types of chains required. The problems andshortcomings in the current design, manufacturing and assemblyof mechanical conveyors are varied, but include:4 Areas of improvementIn order to identify the areas of cost reduction in material andlabour, a cost analysis of all main conveyor parts was conductedto estimate the percentage of cost of each part in relation to thetotal cost of all such parts. The purpose of this analysis was toidentify the critical parts, which are mainly responsible for in-creasing the cost of the conveyor and thereby investigate meansfor reducing the cost of such parts.Table 1 shows the cost analysis of a 50-section conveyor sys-tem. The analysis reveals that 12 out of 15 parts constitute 79%of the total material cost of the conveyor system, where furtherimprovements in design to reduce the cost is possible. Out ofthese, seven parts were identi?ed as critical parts (shown by anasterisk in Table 1) constituting maximum number of compo-nents in quantity and comprising over 71% of overall materialcost. Among these, three components (leg set, side frame andsupport channel) were found to account for 50% of the totalconveyor material cost. A detailed analysis of each of these 12parts was carried out considering the principles of concurrent en-gineering, design for manufacture and design for assembly, anda new improved design was developed for each case [10]. De-tails of design improvement of some selected major componentare presented below.5 Redesign of leg set assemblyIn a conveyor system, the legs are mounted on the side frame tokeep the entire conveyor system off the ?oor. The existing designof conveyor legs work, but they are costly to manufacture, they····Over design of some partsHigh cost of some componentsLong hours involved in assembly/maintenanceUse of non-standard partshave stability problems, and cause delays in deliveries. The delayis usually caused by some of the parts not arriving from over-seas suppliers on time. The most critical speci?cations requiredfor the conveyor legs are:Table 1. Conveyor critical parts based on parts cost analysisProduct descriptionLeg set?Side frame?Support channel?Bend tracksRt. roller shaft?Tail shaftSpacer bar?Support wear strip?Support side wear strip?End plateCover plateBend platesTorque arm bracketSlot coverInside bend plateQty68804008139391354001323939818978Material usedPlastic leg + SS tube2.5 mm SSC channel SSPlastic20 dia. SS shaft35 dia. Stainless steel50X50X6 SS40 × 10 mm plasticPlastic2.5 mm/SS1.6 mm S/S2.5 mm/SS6 mm S/S plateStainless steel2.5 mm/SSCost (%)20.2216.0715.0014.366.706.275.435.363.011.881.571.291.210.970.66Improvement possible (Yes/No)YesYesYesNoYesNoYesYesYesYesNoYesYesYesYesTotal?Critical parts100.00554····Strength to carry conveyor loadStabilityEase of assemblyEase of ?exibility (for adjusting height)1 and part 3 in Fig. 2) was not rigid enough. The connectionsfor these parts are only a single 6 mm bolt. At times, when theconveyor system was carrying full product loads, it was observedthat the conveyor legs were unstable and caused mechanical vi-bration. One of the main reasons for this was due to a single boltFigure 2 indicates all the parts for the existing design ofthe conveyor leg. The indicated numbers are the part numbersdescribed in Table 2, which also shows a breakdown of cost an-alysis complete with the labour time required to assemble a com-plete set of legs. The existing leg setup consists of plastic legbrackets ordered from overseas, stainless steel leg tubes, whichare cut into speci?ed sizes, leg tube plastic adjustments, whichare clipped onto the leg tube at the bottom as shown in Fig. 2.Lugs, which are cut in square sizes, drilled and welded to the legtube to bolt the angle cross bracing and backing plate to supportleg brackets bolts. The # of parts in Table 2 signi?es the numberof components in each part number and the quantity is the con-sumption of each part in the leg design. Companies have usedthis design for many years but one of the common complaintsreported by the clients was of the instability of legs.From an initial investigation, it became clear that the connec-tion between the stainless steel tube and plastic legs bracket (partFig. 2. Existing leg design assembly with partnames shown in Table 1Table 2. Cost analysis for old leg design assemblyconnection at each end of the lugs in part 3 and part 7. The sta-bility of the conveyor is considered critical matter and requiresrecti?cation immediately to satisfy customer expectations.Considering the problems of the existing conveyor leg de-sign and the client’s preferences, a new design for the conveyorleg was developed. Generally the stability and the strength ofthe legs were considered as the primary criteria for improve-ment in the new design proposal but other considerations werethe simplicity of design, minimisation of overseas parts and easeof assembly at the point of commissioning. Figure 3 shows, thenew design of the conveyor’s leg assembly, and Table 3 gives adescription and the cost of each part.Figure 3 shows that the new design consists of only ?ve mainparts for the conveyor’s leg compared to eight main parts in theold design. In the old design, the plastic leg bracket, the legtube plastic adjustment and the leg tube were the most expensiveitems accounting for 72% of the cost of leg assembly. In the newPart no.15, 647238Part descriptionPlastic leg bracketLeg tube plastic adjustmentLugAngle cross bracingBacking plateLeg tubeBolts# of parts2421226Qty2221226Cost$ 30.00$ 28.00$ 4.00$ 5.00$ 4.00$ 25.00$ 3.00SourceOverseasOverseasIn-houseIn-houseIn-houseIn-houseIn-houseTotal assembly cost (welding) $ 15.00 In-houseTotal 19 17 $ 114.00555Fig. 3. New design for leg assembly with partnames in Table 3Table 3. Cost analysis for new design leg assemblyPart no.13452Part descriptionStainless steel angle (50 × 50 × 3 mm)Leg plastic adjustmentCross brassingBoltsBacking plate# of parts22182Qty22142Cost$ 24.00$ 10.00$ 7.00$ 4.00$ 4.00SourceIn-houseOverseasIn-houseIn-houseIn-houseTotal assembly cost $ 10.00 In-houseTotaldesign, those parts have been replaced by a stainless steel angleand a new plastic leg adjustment reducing the cost of leg assem-bly by almost 50%. Thus the total numbers of parts in the leghave been reduced from 19 to 15 and the total cost per leg setup15····11Size of side frame (depth)Strength of the materialEase for assemblyEase for manufacturing$ 59.00has been reduced by $ 55 in the new design.The new conveyor leg design, when tested, was found to bemore secure and stable than the old design. The elimination ofpart number 1 and 5 from old conveyor design has made the newdesign more stable and rigid. In addition, the width of the crossbracing has also been increased with two bolts mount instead ofone in old design. This has provided the entire conveyor leg setupan additional strength.6 Redesign of the side framesThe side frame is the primary support of a conveyor systemthat provides physical strength to conveyors and almost all theparts are mounted on it. The side frame is also expected to havea rigid strength to provide support to all the loads carried onthe conveyor. It also accommodates all the associated conveyorcomponents for the assembly. The critical considerations of sideframe design are:Figure 4 shows the side frame dimension and parameters.The side frame used in existing design appears to be of rea-sonable depth in size (dimension H in Fig. 4). From the initialinvestigation, it was found that the distance between spacer barholes and return shaft (dimensions G and F in Fig. 4) could bereduced, as there was some unnecessary gap between those twocomponents. The important point to check before rede?ning thedesign parameters was to make sure that after bringing those twocloser, the return chains would not catch the spacer bar while theconveyor is running. The model of the new side frame design wasdrawn on CAD to ensure all the speci?cations are sound and theparts are placed in the position to check the clearances and the?ts. Using the principle of design for manufacturing the new sideframe design was made symmetrical so that it applies to all typesof side frames. This change is expected to reduce the size of sideframe signi?cantly for all sizes of chains.Table 4 shows a comparison of dimensions in the old designand the new design of side frames for the same chain type. It556Fig. 4. Side frame dimensionsTable 4. New and old side frame dimension parametersOld designChain type3.25 LF/SS STR/LBP/MAGA31B92C71D196E65F105G211H241I136J58K85L196TAB 22 83 62 187 56 96 202 232 127New designChain type3.25 LF/SS STR/LBP/MAG/TABA31B100C73D173E67F107G167H199I92J58K85L152is noted that the overall size (depth) of the conveyor has beenreduced from 241 mm to 199 mm (dimension H), which givesa saving of 42 mm of stainless steel on every side frame manu-factured. Thus, from a stainless steel sheet 1500 × 3000 mm, theold design parameters allowed only six 3 m long side frames butwith the new design parameter now it was possible to produceseven side frames of 3 m long from the same sheet size.The amount of material used for side frames was also re-viewed for further investigation. It is estimated that about 55%of the total cost of the conveyor system is spent on materials.The current material used for side frames is 2.5 mm thick stain-less steel food grade 304. Currently, there are other materialsavailable in the market with alternative thickness that could beconsidered as an option. For this, a de?ection analysis has beenconducted to estimate if there was any other type of material suit-able to replace the existing material so that it does not fail itsstrength criteria.6.1 De?ection analysis for side framesFigure 5 shows the experimental setup to determine the de?ec-tion of new side frame in X and Y direction under differentloading conditions. With the new design parameters a set ofside frames were manufactured to investigate the de?ection on1.6 mm thick stainless steel side frames. A section of side framebolted with spacer bar and return shaft was assembled for test-ing with the experiment. The results for de?ection were obtainedby applying variable loads on a section of the side frame viaa hydraulic press. As shown in Fig. 5, the de?ection gaugesare placed on vertical (Y ) and horizontal (X ) axes to measureany reading observed on the side frames. The loads are appliedon side frame via the hydraulic press in downward direction.The side frames are supported by stands from the same positionwhere the legs are mounted on the side frames.Three sets of experiments are conducted on four, six andei