Design for Manufacturing (DFM) approach for Productivity Improvement in Medical Equipment Manufacturing

Transcription

1 Design for Manufacturing (DFM) approach for Productivity Improvement in Medical Equipment Manufacturing Syam Prasad 1, Tom Zacharia 2, J.Babu 3 1,2,3 St.Joseph s College of Engineering & Technology, Palai, Kerala, Abstract The major challenges in Product Development are making products that function well at the same time easy to build. Difficulty in manufacture makes a product expensive and hard to fabricate. If the required geometry is difficult to manufacture, it requires extra care in production. Design for Manufacture and Assembly is the analysis and redesign of a product or concept to make it easier to produce with minimum time, effort and cost. This paper presents DFM approach for the productivity improvement of a medical device. The results revealed that DFM approach can reduce the production time by 75% and production cost by 8%. Keywords Design for Manufacturing (DFM), Productivity, Re-engineering, Electrocardiograph, DFA index. I. INTRODUCTION Product variation, market competition, globalization, product customization, product diversification, etc., are the major challenges facing manufacturing enterprises in the 21st century. They are in a quandary because those issues work at the core of product design along with environmental characteristics. A product after manufacturing in terms of poor performance, emergent behaviour, and high cost tend to company liquidation. Thus, it is essential for manufacturing enterprises to apply innovative techniques in various phases of product to guarantee a sustainable business development [1]. In order to stay competitive in the modern mass production industry, products have to be designed and manufactured with the following opposing goals: decreasing time and cost; improving quality and flexibility. One way to improve product competitiveness is the design for manufacturing (DFM) approach. DFM involves simultaneously considering design goals and manufacturing constraints in order to identify manufacturing problems while parts are being designed; thereby reducing the lead time for product development and improving product quality [2,3]. Curran et al, in the paper titled Costing tools for decision making within integrated aerospace design pointed that the design for manufacture (DFM) principle embodies the concurrent engineering philosophy through advocating the consideration of the downstream impact of decisions being made, in order to inform decision making at the time when the financial commitment and effort is being made [4]. The importance of designing for manufacturing is underlined by the fact that about 70% of manufacturing costs of a product (cost of materials, processing, and assembly) is determined by design decisions, with production decisions (such as process planning or machine tool selection) responsible for only 20% [5]. Any design activity that can increase reliability will be applied, and this again is a benefit of design for manufacture and assembly. The reason for this increase in reliability is basically that if the production process is simplified, then there is less opportunity for outright errors. Finally, design for manufacturing and assembly also generally increases the quality of design; basically for the same reason as why it increases reliability. If a part is easier to produce, less machine capability is required to achieve the same tolerances [6]. From the literatures, it can be concluded that the design stage is very important in product development. Often an otherwise good design is difficult or impossible to produce. Typically a design engineer will create a model or design and send it to manufacturing for review and invite feedback. This process is called as design review. If this process is not followed diligently, the product may fail at manufacturing stage. If the DFM guidelines are not followed, it will result in iterative design, loss of manufacturing time leading to longer time to market. Hence the present work aims to apply the DFM approach for the process and product improvement of medical equipment. 79

2 II. OVERVIEW OF DFM Several DFM/DFA guidelines have been developed to assist the designer. Consequently product competitiveness has been improved by applying these DFM techniques. Nevertheless, the decision- making process and the expertise of the designer continue to be the key aspects to ensure the success of DFM, due in part to the availability of DFM information [6, 7, 10].The DFM method is illustrated in Fig.1. It consists of five steps plus iteration [7]: i. Estimate the manufacturing cost. ii. Reduce the costs of components. iii. Reduce the costs of assembly. iv. Reduce the costs of supporting production. v. Consider the impact of DFM decisions on other factors. As shown in Fig.1, the DFM method begins with the estimation of manufacturing cost of the proposed design. This helps the team to determine at a general level which aspects of design- components, assembly or support- are. III. PRODUCTIVITY IMPROVEMENT OF MEDICAL EQUIPMENT DFM approach was applied for the productivity improvement of one of the Electrocardiograph (ECG) model called as CARDIART 108T DIGI, manufactured by one of the leading medical equipment company in India. The following problems were identified in its production: 1. Low productivity. The model was initially designed by the company for a low volume of production around 50 to 60 units per month. But presently the production volume is insufficient to meet the demand. 2. Obsolete tools and related quality issues. 3. High manufacturing cost. The Fig.2 shows the various causes for low productivity of the model: FIGURE.2. CAUSE AND EFFECT DIAGRAM OF LOW PRODUCTIVITY OF ECG (CARDIART 108T DIGI) FIGURE.1.THE DESIGN FOR MANUFACTURING (DFM) METHOD The average monthly production of the model was around 200 units. The production capacity has to be increased to meet varying demands from 250 to 1000 units per month. So in order to achieve this target, re-engineering of the product is necessary. The major objectives of reengineering are to improve the volume and reduce the cost of production. Various parts in top panel, bottom panel and the final assembly of CARDIART 108T DIGI are shown in figures 3, 4 &5 and the BOM is shown in Table1. 80

3 TABLE I COMPONENTS IN TOP AND BOTTOM PANEL ASSEMBLY Part List in Top Panel Assembly Part List in Bottom Panel Assembly SL No Part Name SL No Part Name 1 Front Panel Assy 1 M3 4 BUT Screw 2 Top Panel Assy 2 Panel Cover Bottom 3 Side Panel Assy 3 M3 10 CSK Screw 4 Panel Cover Top 4 Bottom Casting 5 M3 6 CSK HD Screw 5 Shield Bracket 6 M3 6 CSK HD Screw 6 Cushion Battery 7 M3 4 BUT Screw 7 Battery 8 M3 4 BUT Screw 8 Battery Bracket FIGURE.4. ASSEMBLY OF BOTTOM PANEL CASTING 9 M3 9 BUT Screw 9 Battery Bracket 10 M3 4 BUT Screw 11 M3 4 BUT Screw FIGURE.3. ASSEMBLY OF TOP PANEL CASTING FIGURE.5. FINAL UNIT ASSEMBLY A. Manufacturing Cost Analysis of Present Model Manufacturing cost is a key determinant of the economic success of a product. 81

4 In simple terms, economic success depends on the profit margin earned on each sale of the product and on how many units of the product the firm can sell. The number of units sold and the sales price are to a large degree determined by the overall quality of the product. Economically successful design is therefore about ensuring high product quality while minimizing manufacturing cost. DFM is one method for achieving this goal; effective DFM practice leads to low manufacturing costs without sacrificing product quality. Component Cost The table below shows the list of major mechanical components of the ECG 108T- DIGI along with the Part code, quantity required per unit and their individual rates. TABLE II COMPONENT COST (INCLUDING MATERIAL AND PROCESSING COSTS) SL. No Component Name Qty/set Rate(`) Cost(`) Total cost of all components (including all other electrical and mechanical components) = `8,560 Assembly and Overhead Costs Average production (quarterly) = 558 units Fixed overhead costs = `10,84,259 Variable overhead costs =` 4,33,894 Selling expenses =` 8,30,125 Depreciation = `1,56,595 Finance Charges = `62,387 Total = `25,67,260 = `4,600/unit Total Manufacturing Cost Total Manufacturing Cost = Component costs + Assembly costs & Overhead Costs = = ` 13,160/unit 1 Clamp limb electrode assembly Bottom panel- painted Top panel painted Ball bearing OD5 mm ID 2 mm Handle sub assembly Outer carton User manual Front panel( moulded) painted Decorative sheet Rubber roller ground Rear panel- aluminum painted Key pad Chest electrode assembly Nut handle Chromium plated Poly-ethylene foam cushion bottom Panel cover bottom painted Panel cover top -black painted Accessory bag Side panel-left, painted & printed Side panel-right, painted & printed B. Reducing the Cost of Components and Cost of Assembly The following DFM strategies are followed to modify the design and to reduce the component cost of CARDIART 108T DIGI: 1. Redesign components to eliminate processing steps: A common example of this strategy is net-shape fabrication. A net-shape process is one that produces a part with the final intended geometry in a single manufacturing step. Several steps may be eliminated through substitution of an alternative process step. Hence the top and bottom panel castings of the ECG model are redesigned for simplification of the production process by changing the aluminium casting to plastic moulded (ABS) cabinets. Many processing steps like drilling, cutting, filing etc are eliminated saving labor cost of around 150 rupees per unit and the design is able to create the part that is very close to the final requirement (near net shape) and demands only minor additional processing (painting). 2. Integrate Parts: If a part does not qualify as one of those theoretically necessary, then it is a candidate for physical integration with one or more other parts. The resulting multifunctional component is often very complex as a result of the integration of several geometric features which would otherwise be separate parts. Nevertheless, moulded parts can often incorporate additional features at little or no added cost. Figures 6 and 7 represent the redesigned top and bottom panels of the ECG.

5 The components like metal pillars(2 nos), Unit spacers (3 nos), main PCB spacers (6 nos), Side panels (LH and RH), Rear Panel etc are integrated in to the top and bottom cabinets eliminating the need for separate processing operations for the individual components and several adjustments in assembly. 3. Standardize Components: During the design modification of the ECG- 108T DIGI, several custom made parts are eliminated and some standard, readily available parts like hexagonal nuts, plain washers, M3 split inserts etc are introduced in to the product. 4. Evaluation of Assembly Efficiency: The assembly efficiency of the product is measured as an index which is the ratio of the theoretical minimum assembly time to an estimate of the actual assembly time for the product. This concept is useful in developing an intuition for what drives the cost of assembly. The expression for DFA index is [7]: After modification, DFA Index = = Thus, the DFA Index shows that the assembly efficiency is improved after the design modification of the product. To determine the theoretical minimum number of parts, the following three questions are asked in the assembly for each part. Only parts satisfying one or more of these conditions must theoretically be separate. 1. The part need to move relative to the rest of the assembly. Small motions that can be accomplished using compliance (e.g., elastic hinges or springs) do not count. 2. The part is to be made of a different material from the rest of the assembly for fundamental physical reasons. 3. The part has to be separated from the assembly for assembly access, replacement or repair. The 3 seconds in the numerator reflects the theoretical minimum time required to handle and insert a part that is perfectly suited for assembly. It can be taken as the average time (sustainable over a whole work shift) required toassemble a small part that is easy to grasp, requires no particular orientation, and demands no special insertion effort. Comparing the DFA index before and after the design modification of CARDIART 108T- DIGI, Before modification, DFA Index = = FIGURE.6. DESIGN OF PLASTIC MOULDED TOP CABINET FIGURE.7. DESIGN OF PLASTIC MOULDED BOTTOM CABINET IV. RESULTS A. Manufacturing Cost Reduction Component cost reduction Table III and IV shows the list of deleted and added components respectively along with their quantity and cost per unit. 83

6 Sl. No TABLE.III LIST OF DELETED COMPONENTS IN MODIFIED DESIGN Name of the Components Qty/Set Rate(`) Cost(`) 1 Disc plastic Plain washer ms m M/c screw ph pan head m3x8 Zn M/c. screw PH PAN HD m3x Top panel painted Bottom panel painted Side panel-rhs Side panel-lhs Rear panel-aluminium painted Main PCB spacer Unit spacer-a Unit spacer-b Unit spacer-c Shield battery Spacer rear panel-aluminuim Leg rear panel-aluminium Eyelet 3x0.3x Pillar 342-m Holder insert bottom M/c screw M3x4 Bind head Sl. No Total cost reduced TABLE IV LIST OF ADDED COMPONENTS IN MODIFIED DESIGN Name of the Components Qty/Set Rate (`) Cost 1 Top cover plastic moulded Bottom cover plastic moulded Hex nut M3 Zn-blue Wire-pvc-24/0.2 green-yellow M3 insert (split type) M/c screw m3x10 Bind head (blackened) (`) screw ph CSK M3x10 Zn blue Total component cost savings = = ` /unit Assembly and Overhead Costs Average production (quarterly) = 956 units Fixed overhead costs = `15,82,490 Variable overhead costs = `8,00,251 Selling expenses = `999,375 Depreciation =` 2,50,840 Finance Charges = `91,625 Total = Rs = `3,896/unit Total Manufacturing Cost Total Manufacturing Cost = Component cost + Assembly Cost & overhead cost = = `12,129/unit Tool Amortization Tool cost = ` 600,000 Amortization period = 1year Quantity for 1 year = 6000 units Amortization cost = ` 100/unit. B. Production Time Comparison Before and After Modification Table.7 shows that there was considerable reduction in the time taken for bottleneck processes like casting and machining of top and bottom panels after the design modification. After the modification the major time savings in machining of top panel and bottom panel which is around 96 minutes, which now plastic moulded needs no machining. This reduces major cost and time savings. Integration of the parts further reduced the time in assembly operation. Moulded parts can often incorporate additional features at little or no added cost. The components like metal pillars, Unit spacers, main PCB spacers, Side panels (LH and RH), Rear Panel etc. are integrated in to the top and bottom cabinets eliminating the need for separate processing operations for the individual components and several adjustments in assembly. 8 Plain washer M Total added cost

7 Work Instruction Process TABLE V PRODUCTION TIME COMPARISON Before Modification Time(Seconds) After Modification Cycle time- top panel Cycle time- bottom panel Top panel machining time Bottom panel machining time Motor assembly Gear assembly Print head assembly Battery assembly Lid assembly Top panel assembly Side panel -RH assembly 22 0 Side panel -LH assembly 33 0 Nut handle assembly(2nos) Handle assembly Front panel assembly Bottom panel assembly Rear panel assembly 50 0 Strip assembly Unit assembly Inner connections PCBs 12 0 Total time (Seconds) Total time in minutes V. CONCLUSIONS This paper outlines the DFM approach for product and process improvement of an ECG device (CARDIART 108T DIGI). The results of the case study emphasize the relevance of DFM methodologies in product design and manufacturing. It also gives idea regarding how manufacturing complexity and costs can be reduced in early design stages. The application of DFM principles resulted in improvements in three major areas; Product Quality, Cost and Delivery. With the help of improved design, the company attained the ability to execute mass orders of 1000 to 1500 units per month without any extra investment in assembly line. Also, the return of investment (cost of new die) was possible within a year. The major quality issues like breakages in castings and noise disturbance in ECG due to aluminium components were averted. With this improved design and processes, the production lead time was reduced from 2 weeks to 1 week. The total production cost and time were also reduced considerably. Although further iterations in the DFM process are not presented, it is recommended that the results of the process should then be fed back into the design process to provide further DFM iterations and improvements through modifications that optimize detailed manufacturability issues. REFERENCES [1] A.S.M. Hoque, P.K. Halder, M.S. Parvez, T. Szecsi; 2013; Integrated manufacturing features and Design-for-manufacture guidelines for reducing product cost under CAD/CAM environment ; Computers & Industrial Engineering 66; [2] Olivier Kerbrat, Pascal Mognol, Jean-Yves Hascoet; 2011; A new DFM approach to combine machining and additive manufacturing ; Computers in Industry 62; [3] S.K. Gupta, D. Das, W.C. Regli, et al.;1997; Automated manufacturability analysis: a survey ; Research in Engineering Design 9 (3); [4] Curran. R,Kundu. A, Raghunathan.S, Eakin, D; 2002; Costing tools for decision making within integrated aerospace design ; Journal of Concurrent Engineering Research 9 (4); [5] Tien-Chienchang, Richard A Wysk, and Hsu-Pin Wang; Computer- Aided Manufacturing, Second Edition, Prentice Hall 1998; 596 to 598. [6] Kevin Otto, Kristin Wood; Product Design Techniques in Reverse Engineering and New Product Development ; Pearson Education 2012; 663 to 718. [7] Karl T Ulrich, Steven D Eppinger, Anita Goyal; Product Design & Development, Fourth Edition, Tata McGraw Hill 2009; 210 to 233. [8] R. Curran, G. Gomis, S. Castagne, J. Butterfield, T. Edgar, C. Higgins, C. McKeever; 2007; Integrated digital design for manufacture for reduced life cycle cost ; Int. J. Production Economics 109; 27 to 40. [9] Johan Vallhagen, Julia Madrid, RikardSöderberg, Kristina Wärmefjord; 2013; An approach for producibility and DFMmethodology in aerospace engine component development ; Procedia CIRP 11; 151 to 156. [10] I. Ferrer, J.Rios, J.Ciurana, M.L.Garcia-Romeu; 2010; Methodology for capturing and formalizing DFM Knowledge ; Robotics and Computer-Integrated Manufacturing 26; [11] David Z. Pan, Peng Yu, Minsik Cho, AnandRamalingam, Kiwoon Kim, AnandRajaram, Sean X. Shi; 2008; Design for manufacturing meets advanced process control: A survey ;Journal of Process Control 18;