SUST Journal of Science and Technology, Vol. 19, No. 5, 2012; P:60-70 Redesigning Cycle Rickshaw Wheel using QFD Technique to Minimize Accident Probability and Severity (Submitted: June 10, 2012; Accepted for Publication: November 29, 2012) K. Nahar 1, *M. M. Hossain 2, K. M. A. Haque 3, M. A. Islam 4, K. S. Hossain 5 and M. A. Khan 6 1-5 Department of Industrial & Production Engineering, Rajshahi University of Engineering & Technology, Rajshahi, Bangladesh 6 Akij Cement Company Ltd., Kadam Rasul, Narayongonj, Bangladesh *E-mail: mosharraf80@yahoo.com Abstract This paper reviews the possible problem areas of non-motorized means of travel in Rajshahi city, particularly cycle rickshaw, with respect to the view of rickshaw pullers and passengers; and severity analysis. Accidents are more frequent now a day mainly caused by lack of rickshaw pullers adequate training and design of rear wheels; according to market analysis and reviews. Violent accidents are occurred while the rickshaws drive beside one another and it is observed that they made collisions and ultimately accident causes human injuries as well as cut off several spokes of the wheel. Additionally spokes are generally broken down frequently during riding on the rough roads. Redesigning of the wheel has been done on the basis of measured maximum load. The dimension of the new model was decided after studying the carried load of each spoke of the wheel. As five spokes were being used instead of forty two spokes, the reliability of the wheel is being increased considerably due to increased rigidity of the spokes. Hub was designed in such a manner that the extension portion of the wheel is no longer responsible to make frequent accidents. As a result of changing design the problems are being solved. This paper is also analyzing the cost factors of rickshaw as the customers are of very diminutive income. A cost comparison with regular one is made. 1. Introduction Cycle rickshaw is an important & major means of travel, particularly in small cities and amongst the urban areas (For short journey lengths) in Bangladesh. These are light weighted environment friendly vehicle. The people of certain class have these vehicles with affordable price as a principal income source. The mechanism of cycle rickshaw is served as a technical platform that encapsulates fundamental of problems in mechanics, vehicle dynamics, stability, motive power, etc. However in Bangladesh most rickshaws are assembled based on the general ideas without investigating the loads and the load bearing capacities. This causes frequent technical failure of rickshaws and due to lack of knowledge the rickshaw pullers are also involved in enhancing the accident probability. There are not many researches related to rickshaw. Chowdhury et al (1996), Vikhashu (2007) and Nahar et al (2010) addressed some technical problems related to rickshaw. However those are not adequate. This paper examines the mechanics of the cycle rickshaw by considering the possible factors. Major problem area is identified as the wheel of the cycle rickshaw. All dimensions and specifications of new model are then developed with computation of mechanics. 2. Problem Selection Market research is conducted to understand the present condition. To meet customer needs for the product survey is done. During the survey some basic questions (See Appendix A) are asked to the rickshaw pullers and as well as passengers. Based on the survey, problem related to wheels are identified as major problems and minor problems and shown in table 1. Customer needs and their priority are provided in table 2.
Redesigning Cycle Rickshaw Wheel Using QFD Technique to Minimize Accident Probability and Severity 61 Table 1: Major (A) and Minor (B) problems A Rear Wheel Axle rim spoke Seat Chain-sprocket B Light hood Driver seat packing Foot rest Table 2: Customer needs and their priority Customer Needs No. of Customer Priority Light Weight 11 3 Economy Cost 16 1 High Endurance Limit 9 4 Longevity 13 2 Reliability 7 6 Aesthetic 5 7 Comfort 8 5 Through this analysis it is identified that the major problem area is wheel with hub, spoke and ball bearing. 2.2 Process Analysis The Another type of analysis is Cause Effect Diagram (CE Diagram) that depicts defects, errors, or problems which has been identified and begins to analyze potential causes of this undesirable effect. Among the types of CE diagram the followings are being used to identify the problem region with their respectable causes i.e. Process Analysis. This diagram provides the information of the process of making the wheel from idea generation to final product development. Fig. 1: Requirements for rim design 3. QFD (Quality Deployment Function) The customers requirements must be translated into measurable design targets to identified critical parameter. Relation among customers requirements and engineering specifications and relation within the engineering specifications are represented in matrix form as quality function deployment (QFD). Correlation legend Strong relationship Medium relationship Weak relationship
62 K. Nahar, M. M. Hossain, K. M. A. Haque, M. A. Islam, K. S. Hossain and M. A. Khan Fig. 2: QFD Matrix Depending upon functional relationship with quality requirement- further design analysis is conducted. 4. Design Analysis and Selection To redesign the existing product, the cycle rickshaw wheel, for reducing accident severity & probability, the initial need is expressed in semantic language as a verbal request or requirement of the customers, in this case the rickshaw pullers & the passengers. Through graphical and analytical analyses; a physical model is being established. Some drawings are initially constructed considering possible problems & resolving techniques. Material selection is done on the basis of some design criteria such as yield strength, ultimate strength, elongation, density, modulus of elasticity, cost etc. Through mechanical analysis the design specifications are developed & correction over the layout is made. Measurements for mechanical property analysis consist of different dimensions of lengths, weight of different parts and rickshaw self weight. Then the reaction/supporting loads at both rear and front wheels are determined according to the law of mechanics. By using the reaction loads at each of the rear wheel s the dimensions of the spokes are being calculated, i.e., the length and width of each spoke. Length of each spoke is found from the dimension of outer diameter of the hub. Outer diameter of the hub is determined by calculating the thickness of the hub according to the law of mechanics as the inner diameter is known from selected bearing s outer diameter. 4.1 Developing Ideas with Drawing Initially several rough drawings are made to figure out the ideas of resolving problems of cycle rickshaw wheel.
Redesigning Cycle Rickshaw Wheel Using QFD Technique to Minimize Accident Probability and Severity 63 Fig. 3: Initial drawing of wheel The drawing shown in fig. 3 is done by only considering the ideas of defined problems of extended portion of axle that causes the distortion of spokes of the wheels of other rickshaws. In that case the hub is designed in such a way (in fig. 3) that the axle extension is no longer visible. After that the spokes are replaced by five equally spaced spokes that are more reliable than spoke and are little subject to distortion. But after developing this primary idea in the drawing the mechanical properties such as the material selection, static and dynamic load carrying capacities, bearing life etc. are being considered to compute the specifications of the spokes used in wheel and the hub s required dimensions as well. The calculations show that the hub is not properly designed shown in the fig. 3, because it uses only one bearing that reduces the bearing life much less than the existing one and also caused by the increased bending moment with spokes at one end of the hub and only one bearing at another end of the hub. Fig. 4: Redesigned wheel Redrawing of the wheel is prepared by taking into account the mechanics for rickshaw wheels and finalized the drawing with specifications to generate physical model of wheels at fig. 4. The specifications of the modified model are developed by calculating different force calculations according to the laws of mechanics. The area of each spoke is calculated for the selected material from load applied to each wheel. The outer diameter of the hub is determined by computing the thickness of the hub assuming the inner diameter as the outer of the bearings used with hub. By getting two of the bearings in the hub which retains the bearing life more than the existing one and the maximum bending moment for the eccentric placement of the spokes the thickness of the hub is being calculated. 4.2 Material Selection After that the material selection is done considering some significant properties of different possible materials. Possible materials those are nearly suitable for the wheel manufacturing purpose are selected and then prioritized them according to the required material property for rim. Priorities are given under score of 20 for each materials property. Over total priority of each material i.e. 200 score the % of priority is calculated. Amongst three competitive materials Aluminium Alloy with certain composition, which is conventionally used for rim manufacturing, is being selected in cycle rickshaw wheel manufacturing. Properties of selected materials are provided in Appendix B in detail. 4.3 Mathematical Calculation 4.3.1 Design of Spoke The testing result from universal testing machine for yield and failure of existing wheel shows that it can sustain about 14000 N loads. On behalf of this capacity the new design of wheel is made.
64 K. Nahar, M. M. Hossain, K. M. A. Haque, M. A. Islam, K. S. Hossain and M. A. Khan Fig. 5: Sketch of load on each spoke The wheel is designed with five equally spaced spokes because more than five bars it causes reduction of cross-section area of each; thus the reliability of each spoke. And for less than that number the cross-section area is increased and thus the weight is also increased. At equilibrium, + F y =0 so F' =3908.79 N Now, F' = σa = σbt, thus bt=15.39 mm 2. Where, A=area of the wheel bar & σ=254 N/mm 2 If the breadth of each spoke, b=25.4 mm than the thickness of each spoke, t= 1.82 mm. Having FS=3 for mild sh4ock of ductile material and with trial & error basis the breadth of each spoke is determined as, b=25.4 mm and the thickness of each spoke, t= 1.82 mm. 4.3.2 Hub Design Fig. 6: Redesigned hub As the bearing is of the same number 6204, the designed wheel s hub diameter (inner) is known. The designed wheel s hub diameter (inner) is known from bearing number. The minimum length of hub is determined by required spaces for two bearings, one nut and clearance between two bearings. To determine the thickness of hub it is required to calculate the forces on different point of the hub (Fig. 7), applied forces are F 1 and F 2 and supporting loads are R 1 and R 2. Where the distances are AB=0.014m, BC=0.007m, CD=0.027m, DE=0.007m. Fig. 7: Forces on hub Fig. 8: Reaction forces on hub By determining the value of R 1 from the figure of right most corner (Fig. 8), the unknown loads over the hub i.e. F 1 & F 2 are calculated. Formulating with laws of mechanics, R 1 =6015 N, F 1 =5503.7N, F 2 =8694.29N.
Redesigning Cycle Rickshaw Wheel Using QFD Technique to Minimize Accident Probability and Severity 65 By using those values the thickness of hub is being determined with the established formula of maximum bending moment. In the Figure 9 the lower portion of the hub is considered as simply supported beam with breadth as same as the spokes breadth. Having maximum moment and with the known values of material strength and breadth the part thickness of the hub is being determined. The formula is- Maximum bending moment, M= σi /C= σbh 2 /6. By putting the known values, the unknown value i.e thickness of the hub, h, is determined as 7.2mm. Fig. 9: Shear & Moment diagram for hub 4.3.3 Impact of the loads Bearing life is calculated on basis of the loads that are practically applied to the wheel, that is, the load those are calculated in earlier section. In this case existing bearings of number 6204 ball bearing are used. Where, Applied forces on each wheel bearings, F=194.32 kg Sprocket weight, W=0.5 kg Rickshaw puller s pulling force, P=465kg Distances, d 1 =d 2= 0.5715 Vertical reaction forces on bearings are, R V1 & R V2 Horizontal reaction forces on bearings are, R H1 & R H2 Fig. 10: Forces on Bearing According to law of mechanics, over vertical & horizontal forces we get R V1 =194.32 kg, R V2 =194.57 kg, R H1 =232.5 kg & R H2 =232.5 kg. At point B of the Fig. 10 there are two bearings so that the forces on the bearing are needed to calculate with respect to practically applied load. Practically applied loads are computed for each bar i.e. F =620.3N & spoke support R 1 =954.54 N. In the Fig. 10, F=F 1 +F 2 and F 1 & F 2 are the loads applied through the bearings at point C and D. again from laws mechanics we get F 1 =948.555N & F 1 =955.780N, where F= 194.32 kg is a calculated value of applied load on bearings.
66 K. Nahar, M. M. Hossain, K. M. A. Haque, M. A. Islam, K. S. Hossain and M. A. Khan Fig. 11: Forces on Bearing By using the forces on bearings the reaction forces of bearings are computed to determine the radial load of the bearings. Fig. 12: Forces on Bearing Here the calculated values are R v1 =953.87N, R v2 =952.90N, R h1 = 1689.05N & R h2 =589.4N. Now, Reaction at bearing D, R d = (R h1 2 +R V1 2 )=1788.93N Reaction at bearing C, R c = (R h2 2 +R V2 2 )=1120.45N Basic load rating for 6204 ball bearing, C= 12700N, C o =6200N With no axial thrust, X=1 & Y=0 and F rd= F ad = R d =1788.93N The equivalent dynamic load, P = XF rd +YF ad = 1788.93N Bearing life at C, L d = (C/1.5P) 3 = 106.01 million rev and L hd = L*10 6 /60*60= 40.9 months With no axial thrust, X=1 & Y=0, F rc= F ac = R c =1120.45N The equivalent dynamic load, P = XF rc +YF a = 1120.45N Bearing life at D, L c = (C/1.5P) 3 = 431.5 million rev and L hc = L*10 6 /60*60= 166.6 months. The life of the bearings is 40.9 months and 166.6 months at points D and C respectively. 5 Cost Comparisons By considering monthly production 2,400 Pc, all fixed costs and variable costs per product is calculated, thus the total cost is calculated. First set of cost calculation is for existing product and next set shows the cost for redesigned product. Fixed cost: Design: Cost of design: TK 10,000/15 year Cost per unit production: TK 0.023 Table 3: Machineries cost But welding Polishing Office Type of M/C: Rim M/C Drill machine Roller machine machine machine Furniture Cost of buying: Tk 170,000/15 yr Tk 80,000/12yr Tk 90,000/12yr Tk 300,000/15yr Tk 15,000/5yr Tk 150,000/15yr No of machine: 1 2 1 1 2 Total cost: Tk 170,000 Tk 160,000 Tk 90,000 Tk 300,000 Tk 300,000 Salvage value: Tk 25,000 Tk 10,000/12 yr Tk 10,000/12 yr Tk 60,000 Tk 1,000 Total depreciation: Tk 9,666/yr Tk 972/yr Tk 6,666/yr Tk 16,000/yr Tk 5,600/yr Per unit cost: Tk 0.34 Tk 0.40 Tk 0.23 Tk 0.55 Tk 0.194 Tk 0.35
Redesigning Cycle Rickshaw Wheel Using QFD Technique to Minimize Accident Probability and Severity 67 Total Fixed cost: TK 1.737 per unit Variable cost: Fixed cost: Table 4: Cost of Raw Material Raw Material Buying cost per kg Per unit required material Total cost Mild Steel Tk 70/kg 1.5kg Tk 105 Nickel Tk 70/kg 100gm Tk 7 Design Cost: Cost of design: TK 40,000/15 year Cost per unit production: TK0.0926 Type of M/C: Lathe machine Table 5: Other Variable Cost Worker Administration Tax & Unit Transport Electricity Total Rent Cost Outsourced Materials Hub Spoke Set 80000 100000 50000 50000 12000 292000 121.66 Tk 70 Tk 60 Total cost of existing product: TK 365.75 per unit. Table 6: Machineries cost High pressure metallic molding machine But welding machine Polishing machine Office Furniture Cost of buying: Tk 300,000/15yr Tk 500,000/10yr Tk 300,000/15yr Tk 15,000/5yr Tk 150,000/15yr No of machine: 2 1 1 2 Total cost: Tk 600,000 Tk 500,000 Tk 300,000 Tk 300,000 Salvage value: Tk 40000 Tk 80,000 Tk 60,000 Tk 1,000 Total Tk 34666/yr Tk 42000/yr Tk 16,000/yr Tk 5,600/yr depreciation: Per unit cost: Tk 1.2 Tk 1.458 Tk 0.55 Tk 0.194 Tk 0.35 Total fixed cost of the designing product: TK 3.844 Variable cost: Table 7: Cost of Raw Material Raw Material Buying cost per kg Per unit required material Total cost Mild Steel Tk 70/kg 3.5kg Tk 245 Nickel Tk 70/kg 200gm Tk 14 Table 8: Other Variable Cost Worker Administration Tax & Unit Outsourced Transport Electricity Total Rent Cost Materials Hub Spoke Set 50000 85000 50000 45000 12000 242000 100.83 Tk 70 Tk 60 Total cost of redesigned product: TK 363.67 per unit.
68 K. Nahar, M. M. Hossain, K. M. A. Haque, M. A. Islam, K. S. Hossain and M. A. Khan 6. Results The redesigned wheel is shown in Fig. 4. Specifications of the wheel, hub, bearings are as: number of spokes, 5; thickness of each spoke, 1.82 mm; breadth of each spoke, 25.4 mm; rim is same as the existing one; hub diameter (inner) is same as 6204 ball bearing s outer diameter; hub thickness, 7.2 mm, the expected life of the bearings are 40.9 months and 166.6 months. Costs of existing and redesigned model are around Tk 366 and Tk 364 respectively. 7. Discussion and Conclusion Redesigned wheels are constructed at the university lab. Although unit cost does not decrease significantly comparative with existing model it satisfies customer requirement with desired quality. It is tested for functionality. At the initial stage it is found that the wheels are performing well with comfort to the rickshaw puller. This hub design does not have any extended portion as the existing extension of rear axle. This will prevent the collision with the other rickshaws while overtaking each other. It is beyond this study to investigate the reliability, longevity, product life cycle and accident probability due to long cycle time or product life cycle. However it is believed that due considering the engineering design criteria, this redesigned wheel will serve the following purposes: Redesigned wheel will reduce the accident severity. This will minimize the problem of spoke distortion and axle position. Wheel longevity will be comparatively high. Wheel cost is reasonable. Outlook is good enough. Overall it can be said that the redesigned wheel with accessories are good enough to prevent the accident severity and the maintenance cost will be reduced. References [1] Ullman D. G., The Mechanical Design Process, Second Edition, PP 293-308, McGraw-Hill, Inc. [2] Beer F. P. and Johnston E. R. Jr., Vector Mechanics For Engineers (Statics &Dynamics), third Edition, Tata McGraw-Hill, Inc. [3] Chowdhury A. R., Prahan, C. K. and Mukherjee A. K., (1996), Evaluation of occupational health problem of cycle rickshaw pullers and redesign of cycle rickshaw on economical principles, Redesign of cycle rickshaw. [4] Vikhashu S., Cycle Rickshaw Project Research and Finding Product design Department,, Srishti School of Art Design and Technology, [2007] [5] Edwards, K. S. Jr. and Mckee R. B., Fundamentals of Mechanical Component Design, [1991] EWD., McGraw-Hill, Inc. [6] Nahar K., Khan M. A. and Hossain K. S., (2010), Redesigning Cycle Rickshaw Wheel to Minimize Accident Probability and Severity, Unpublished B.Sc. Engg. Thesis, Rajshahi University of Engineering & Technology, Rajshahi. [7] Pytel A. and Singer F. L., Strength of Materials, Fourth Edition, Harper & row. [8] Hasin M. A. A., Quality Control and Management, pp 40-48, 84-86, 102-112, Bangladesh Business Solutions. [9] Montgomery D. T., Introduction to Statistical Quality Control, Third Edition, pp 154-156, John Wiley & Sons. [10] Allen J. S., Kirskna D. and Wilson D. G., Human Power, Technical Journal of the IHPVA, Number 53, Spring [2002]. [11] Mondal B. N., Green Solution to the Urban Transport System, Research planning & business Dept), Central Mechanical Research Institute India. [12] Gadepalli S, (2006), Rickshaw in the new millennium, daily star june 30, 2006 [13] http://www.nariphaltan.virtualave.net/mapra.pdf (17/10/2010) [14] http://www.alibaba.com/showroom/cycle-rickshaw.html (17/10/2010) [15] http://www.injuryjournal.com/article/s0020-1383(05)00516-4 (17/10/2010)
Redesigning Cycle Rickshaw Wheel Using QFD Technique to Minimize Accident Probability and Severity 69 [16] http://www.cmse.ed.ac.uk/mse3/topics/mse3-nonferrous.pdf (17/10/2010) [17] Error! Hyperlink reference not valid. [18] http://www.rickshaw/bicycle%20components,bicycle%20saddles [19] http://www.rickshaw/pedicab%20rickshaws.mht [20] http://www.rickshaw/rickshaw%20manufacturing.mht [21] http://catalog.indiamart.com/cat_ifmare.htm [22] http://www.tntech.edu/me/courses/zhang/me30103110/chap11pt4.ppt
70 K. Nahar, M. M. Hossain, K. M. A. Haque, M. A. Islam, K. S. Hossain and M. A. Khan Appendix A (Questionnaire) To identify the problems related to cycle rickshaw, some basic questions were asked to the rickshaw puller, passengers and vendors. The questions are provided here. 1. What are the major problems that you face with your rickshaw? 2. How longer the rickshaw give service? 3. How much reliable it is? 4. What about the failure rate? 5. How much load you can carry? 6. Do you feel that the maintenance cost is ok with you? 7. Do you think rickshaw need improvement? 8. What parts should be modify and why? Many other effective questions are done to clarify exact needs during market research. Appendix B (Priority to Materials) SI Materials Property Stainless steel Given priority 1 Tensile strength, MPa 500 12 2 Yield strength, MPa 200 5 3 Endurance limit, GPa 280 14 4 Elongation, % Not found 0 5 Modulus of elasticity, 200 GPa 15 GPa 6 Density, g/cc 7.5-8.5 12 7 Melting temp., ºC 2500 5 8 Cost per lb 0.8-2.5 12 9 Hardness, BHN 52 2 10 Corrosion 10 Total priority 101 % over total priority 40.5 SI Materials Property Al Alloy (Conv.) Given priority 1 Tensile strength, MPa 373 8 2 Yield strength, MPa 254 12 3 Endurance limit, GPa 200 10 4 Elongation, % 39.9% 5 5 Modulus of elasticity, 200 GPa 14 GPa 6 Density, g/cc 7-8 11 7 Melting temp., ºC 550 14 8 Cost per lb.2-.5 15 9 Hardness, BHN 150 16 10 Corrosion 7 Total priority 111 % over total priority 55.5 SI Materials Property Al Alloy Given priority 1 Tensile strength, MPa 200 5 2 Yield strength, MPa 300 8 3 Endurance limit, GPa 100 7 4 Elongation, % 15-25% 8 5 Modulus of elasticity, 90 GPa 10 GPa 6 Density, g/cc 3 5 7 Melting temp., ºC 700 10 8 Cost per lb 3-4 7 9 Hardness, BHN 52-100 12 10 Corrosion 14 Total priority 86 % over total priority 43
Redesigning Cycle Rickshaw Wheel Using QFD Technique to Minimize Accident Probability and Severity 71