輕型立式薯類去皮機結(jié)構(gòu)設(shè)計,輕型立式薯類去皮機結(jié)構(gòu)設(shè)計,輕型,立式,薯類,去皮,結(jié)構(gòu)設(shè)計 DOI 10.1007/s00170-003-1843-3 ORIGINAL ARTICLE Int J Adv Manuf Technol (2005) 25: 551559 S.H. Masood B. Abbas E. Shayan A. Kara An investigation into design and manufacturing of mechanical conveyors systems for food processing Received: 29 March 2003 / Accepted: 21 June 2003 / Published online: 23 June 2004 Springer-Verlag London Limited 2004 Abstract This paper presents the results of a research investi- gation undertaken to develop methodologies and techniques that will reduce the cost and time of the design, manufacturing and assembly of mechanical conveyor systems used in the food and beverage industry. The improved methodology for design and production of conveyor components is based on the minimisa- tion of materials, parts and costs, using the rules of design for manufacture and design for assembly. Results obtained on a test conveyor system verify the benefits of using the improved tech- niques. The overall material cost was reduced by 19% and the overall assembly cost was reduced by 20% compared to conven- tional methods. Keywords Assembly Cost reduction Design DFA DFM Mechanical conveyor 1 Introduction Conveyor systems used in the food and beverage industry are highly automated custom made structures consisting of a large number of parts and designed to carry products such as food cartons, drink bottles and cans in fast production and assembly lines. 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 filling or assembly oper- ations. Their operations require highly efficient and reliable me- chanical conveyors, which range from overhead types to floor- mounted types of chain, roller or belt driven conveyor systems. In recent years, immense pressure from clients for low cost but efficient mechanical conveyor systems has pushed con- veyor manufacturers to review their current design and assembly methods and look at an alternative means to manufacture more economical and reliable conveyors for their clients. At present, S.H. Masood (a117) B. Abbas E. Shayan A. Kara Industrial Research Institute Swinburne, Swinburne University of Technology, Hawthorn, Melbourne 3122, Australia E-mail: smasoodswin.edu.au most material handling devices, both hardware and software, are highly specialised, inflexible and costly to configure, install and maintain 1. Conveyors are fixed in terms of their locations and the conveyor belts according to their synchronised speeds, mak- ing any changeover of the conveyor system very difficult and ex- pensive. In todays radically changing industrial markets, there is a need to implement a new manufacturing strategy, a new system operational concept and a new system control software and hard- ware development concept, that can be applied to the design of a new generation of open, flexible material handling systems 2. Ho and Ranky 3 proposed a new modular and reconfigurable 2D and 3D conveyor system, which encompasses an open re- configurable software architecture based on the CIM-OSA (open system architecture) model. It is noted that the research in the area of improvement of conveyor systems used in beverage in- dustry is very limited. Most of the published research is directed towards 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 floor mounted type chain driven 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 for manufacturing and design for assembly 4, 5, several critical conveyor parts were investigated for their functionality, material suitability, strength criterion, cost and ease of assembly in the overall conveyor system. The critical parts were modified and redesigned with new shape and geometry, and some with new materials. The improved design methods and the functionality of new conveyor parts were verified and tested on a new test con- veyor system designed, manufactured and assembled using the new improved parts. 2 Design for manufacturing and assembly (DFMA) In recent years, research in the area of design for manufacturing and assembly has become very useful for industries that are con- 552 sidering improving their facilities and manufacturing methodol- ogy. However, there has not been enough work done in the area of design for conveyor components, especially related to the is- sue of increasing numbers of drawing data and re-engineering of the process of conveyor design based on traditional methods. A 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, efficient and cost effective for the companies under investigation. The main classifications of DFMA knowledge can be iden- tified as (1) General guidelines, (2) Company-specific best prac- tice or (3) Process and or resource-specific constraints. General guidelines refer to generally applicable rules-of-thumb, relat- ing to a manufacturing domain of which the designer should be aware. The following list has been compiled for DFM guidelines 6. Design for a minimum number of parts Develop a modular design Minimise part variations Design parts to be multifunctional Design parts for multiuse Design parts for ease of fabrication Avoid separate fasteners Maximise compliance: design for ease of assembly Minimise handling: design for handling presentation Evaluate assembly methods Eliminate adjustments Avoid flexible components: they are difficult to handle Use parts of known capability Allow for maximum intolerance of parts Use known and proven vendors and suppliers Use parts at derated values with no marginal overstress Minimise subassemblies Fig.1. Layout of conveyor sys- tem for labelling plasic bottles Emphasise standardisation Use the simplest possible operations Use operations of known capability Minimise setups and interventions Undertake engineering changes in batches These design guidelines should be thought of as “optimal suggestions”. They typically will result in a high-quality, low- cost, and manufacturable design. Occasionally compromises must be made, of course. In these cases, if a guideline goes against a marketing or performance requirement, the next best alternative should be selected 7. Company-specific best practice refers to the in-house design rules a company develops, usually over a long period of time, and which the designer is expected to adhere to. These design rules are identified by the company as contributing to improved quality and efficiency by recognising the overall relationships between particular processes and design decisions. Companies use such guidelines as part of the training given to designers of products requiring significant amounts of manual assembly or mainte- nance. Note that most of the methodologies are good at either being 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 thumb derived from experienced professionals, are more qualitative and less formal 9. 3 Conventional conveyor system design Design and manufacturing of conveyor systems is a very com- plex and time-consuming process. As every conveyor system is a custom-made product, each project varies from every other project in terms of size, product and layout. The system design 553 is based on client requirements and product specifications. More- over, the system layout has to fit in the space provided by the company. The process of designing a layout for a conveyor sys- tem involve revisions and could take from days to months or in some instances years. One with the minimum cost and maximum client suitability is most likely to get approval. Figure 1 shows a schematic layout of a typical conveyor system installed in a production line used for labelling of plastic bottles. Different sections of the conveyor system are identified by specific technical names, which are commonly used in similar industrial application. The “singlizer” sec- tion enables the product to form into one lane from multiple lanes. The “slowdown table” reduces the speed of product once it exits from filler, labeller, etc. The “mass flow” sec- tion is used to keep up with high-speed process, e.g., filler, labeller, etc. The “transfer table” transfers the direction of prod- uct flow. The purpose of these different conveyor sections is thus to control the product flow through different processing machines. A typical mechanical conveyor system used in food and bev- erage applications consists of over two hundred mechanical and electrical parts depending on the size of the system. Some of the common but essential components that could be standard- ised and accumulated into families of the conveyor system are side frames, spacer bars, end plates, cover plates, inside bend plates, outside bend plates, bend tracks and shafts (drive, tail and slave). The size and quantity of these parts vary according to the length of conveyor sections and number of tracks correspond- ing to the width and types of chains required. The problems and shortcomings in the current design, manufacturing and assembly of mechanical conveyors are varied, but include: Over design of some parts High cost of some components Long hours involved in assembly/maintenance Use of non-standard parts Table 1. Conveyor critical parts based on parts cost analysis Product description Qty Material used Cost (%) Improvement possible (Yes/No) Leg set 68 Plastic leg + SS tube 20.22 Yes Side frame 80 2.5 mm SS 16.07 Yes Support channel 400 C channel SS 15.00 Yes Bend tracks 8 Plastic 14.36 No Rt. roller shaft 139 20 dia. SS shaft 6.70 Yes Tail shaft 39 35 dia. Stainless steel 6.27 No Spacer bar 135 50X50X6 SS 5.43 Yes Support wear strip 400 40 10 mm plastic 5.36 Yes Support side wear strip 132 Plastic 3.01 Yes End plate 39 2.5mm/SS 1.88 Yes Cover plate 39 1.6 mm S/S 1.57 No Bend plates 8 2.5mm/SS 1.29 Yes Torque arm bracket 18 6 mm S/S plate 1.21 Yes Slot cover 97 Stainless steel 0.97 Yes Inside bend plate 8 2.5mm/SS 0.66 Yes Total 100.00 Critical parts 4 Areas of improvement In order to identify the areas of cost reduction in material and labour, a cost analysis of all main conveyor parts was conducted to estimate the percentage of cost of each part in relation to the total cost of all such parts. The purpose of this analysis was to identify the critical parts, which are mainly responsible for in- creasing the cost of the conveyor and thereby investigate means for 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 further improvements in design to reduce the cost is possible. Out of these, seven parts were identified as critical parts (shown by an asterisk in Table 1) constituting maximum number of compo- nents in quantity and comprising over 71% of overall material cost. Among these, three components (leg set, side frame and support channel) were found to account for 50% of the total conveyor material cost. A detailed analysis of each of these 12 parts was carried out considering the principles of concurrent en- gineering, design for manufacture and design for assembly, and a new improved design was developed for each case 10. De- tails of design improvement of some selected major component are presented below. 5 Redesign of leg set assembly In a conveyor system, the legs are mounted on the side frame to keep the entire conveyor system off the floor. The existing design of conveyor legs work, but they are costly to manufacture, they have stability problems, and cause delays in deliveries. The delay is usually caused by some of the parts not arriving from over- seas suppliers on time. The most critical specifications required for the conveyor legs are: 554 Strength to carry conveyor load Stability Ease of assembly Ease of flexibility (for adjusting height) Figure 2 indicates all the parts for the existing design of the conveyor leg. The indicated numbers are the part numbers described 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 leg brackets ordered from overseas, stainless steel leg tubes, which are cut into specified sizes, leg tube plastic adjustments, which are 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 leg tube to bolt the angle cross bracing and backing plate to support leg brackets bolts. The # of parts in Table 2 signifies the number of components in each part number and the quantity is the con- sumption of each part in the leg design. Companies have used this design for many years but one of the common complaints reported 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 (part Fig.2. Existing leg design assembly with part names shown in Table 1 Table 2. Cost analysis for old leg design assembly Part no. Part description # of parts Qty Cost Source 1 Plastic leg bracket 2 2 $ 30.00 Overseas 5, 6 Leg tube plastic adjustment 4 2 $ 28.00 Overseas 4 Lug 2 2 $ 4.00 In-house 7 Angle cross bracing 1 1 $ 5.00 In-house 2 Backing plate 2 2 $ 4.00 In-house 3 Leg tube 2 2 $ 25.00 In-house 8 Bolts 6 6 $ 3.00 In-house Total assembly cost (welding) $ 15.00 In-house Total 19 17 $ 114.00 1 and part 3 in Fig. 2) was not rigid enough. The connections for these parts are only a single 6 mm bolt. At times, when the conveyor system was carrying full product loads, it was observed that the conveyor legs were unstable and caused mechanical vi- bration. One of the main reasons for this was due to a single bolt connection at each end of the lugs in part 3 and part 7. The sta- bility of the conveyor is considered critical matter and requires rectification immediately to satisfy customer expectations. Considering the problems of the existing conveyor leg de- sign and the clients preferences, a new design for the conveyor leg was developed. Generally the stability and the strength of the legs were considered as the primary criteria for improve- ment in the new design proposal but other considerations were the simplicity of design, minimisation of overseas parts and ease of assembly at the point of commissioning. Figure 3 shows, the new design of the conveyors leg assembly, and Table 3 gives a description and the cost of each part. Figure 3 shows that the new design consists of only five main parts for the conveyors leg compared to eight main parts in the old design. In the old design, the plastic leg bracket, the leg tube plastic adjustment and the leg tube were the most expensive items accounting for 72% of the cost of leg assembly. In the new 555 Fig.3. New design for leg assembly with part names in Table 3 Table 3. Cost analysis for new design leg assembly Part no. Part description # of parts Qty Cost Source 1 Stainless steel angle (50503 mm) 2 2 $ 24.00 In-house 3 Leg plastic adjustment 2 2 $ 10.00 Overseas 4 Cross brassing 1 1 $ 7.00 In-house 5 Bolts 8 4 $ 4.00 In-house 2 Backing plate 2 2 $ 4.00 In-house Total assembly cost $ 10.00 In-house Total 15 11 $ 59.00 design, those parts have been replaced by a stainless steel angle and a new plastic leg adjustment reducing the cost of leg assem- bly by almost 50%. Thus the total numbers of parts in the leg have been reduced from 19 to 15 and the total cost per leg setup has been reduced by $ 55 in the new design. The new conveyor leg design, when tested, was found to be more secure and stable than the old design. The elimination of part number 1 and 5 from old conveyor design has made the new design more stable and rigid. In addition, the width of the cross bracing has also been increased with two bolts mount instead of one in old design. This has provided the entire conveyor leg setup an additional strength. 6 Redesign of the side frames The side frame is the primary support of a conveyor system that provides physical strength to conveyors and almost all the parts are mounted on it. The side frame is also expected to have a rigid strength to provide support to all the loads carried on the conveyor. It also accommodates all the associated conveyor components for the assembly. The critical considerations of side frame design are: Size of side frame (depth) Strength of the material Ease for assembly Ease for manufacturing 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 initial investigation, it was found that the distance between spacer bar holes and return shaft (dimensions G and F in Fig. 4) could be reduced, as there was some unnecessary gap between those two components. The important point to check before redefining the design parameters was to make sure that after bringing those two closer, the return chains would not catch the spacer bar while the conveyor is running. The model of the new side frame design was drawn on CAD to ensure all the specifications are sound and the parts are placed in the position to check the clearances and the fits. Using the principle of design for manufacturing the new side frame design was made symmetrical so that it applies to all types of side frames. This change is expected to reduce the size of side frame significantly for all sizes of chains. Table 4 shows a comparison of dimensions in the old design and the new design of side frames for the same chain type. It 556 Fig.4. Side frame dimensions Table 4. New and old side frame dimension parameters Old design Chain type A B C D E F G H I J K L 3.25 primeprime LF/SS STR/LBP/MAG 31 92 71 196 65 105 211 241 136 58 85 196 TAB 22 83 62 187 56 96 202 232 127 New design Chain type A B C D E F G H I J K L 3.25 primeprime LF/SS STR/LBP/MAG/TAB 31 100 73 173 67 107 167 199 92 58 85 152 is noted that the overall size (depth) of the conveyor has been reduced from 241 mm to 199 mm (dimension H), which gives a saving of 42 mm of stainless steel on every side frame manu- factured. Thus, from a stainless steel sheet 1500 3000 mm, the old design parameters allowed only six 3 m long side frames but with the new design parameter now it was possible to produce seven 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 materials available in the market with alternative thickness that could be considered as an option. For this, a deflection analysis has been conducted to estimate if there was any other type of material suit- able to replace the existing material so that it does not fail its strength criteria. 6.1 Deflection analysis for side frames Figure 5 shows the experimental setup to determine the deflec- tion of new side frame in X and Y direction under different loading conditions. With the new design parameters a set of side frames were manufactured to investigate the deflection on 1.6 mm thick stainless steel side frames. A section of side frame bolted with spacer bar and return shaft was assembled for test- ing with the experiment. The