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Implementation of a Pull System – A Case Study of a Polymeric Production System for the Automotive Industry

Implementation of a Pull System – A Case Study of a Polymeric Production System for the... This work, developed as a case study, propose, describe, and evaluates an implementation of a pull system in a SME company producing polymeric components for the automotive industry. The production system of the com- pany was based on the push paradigm, which creates high stock levels and high lead times. The main purpose was to develop a pull production system controlled by Kanbans in the painting line. To achieve this goal, this case study demonstrates the application of relevant lean tools, such as, VSM, SMED, Kanban System, Supermarkets and Leveling. Through the SMED’s application, it was possible to reduce the setup times in 38% and make annual earnings of approximately 83000€. The application of a Kanban System, Leveling and Supermarket enabled the WIP’s reduction between injection and painting in 56% and, also, between painting and expedition in 45%. Also, the lead time decreased and the value-added time increased. Thus, this is an exemplary case study for the imple- mentation of a pull system and can be used both by practitioners and researchers interested in this theme. Key words: Kanban, Leveling, Pull Production, SMED, Supermarket INTRODUCTION has the purpose of reducing its Work-In-Process (WIP) lev- In order to respond to the increasing competition forced els and the non-value-added activities. by the market, companies must improve their ability to After the introduction, the structure of the present article adjust their production systems through the introduction continues with the literature review. Then, a productive of new paradigms. The Pull Production System’s imple- system’s description is made, followed by a critical analy- mentation involves other Lean Production tools applica- sis. The fourth section present the steps developed for im- tion, such as, Single Minute Exchange of Die (SMED), Kan- plementation of the pull system. Finally, the article ends ban Systems, Leveling and Supermarkets [1]. Several with the discussion and conclusions. works [2, 3, 4] were devoted to the analysis of specific ap- proaches to design a pull system, but it is not common to LITERATURE REVIEW find works focusing on different steps that a company Lean Production has the principal purpose of increasing must carry out to create the conditions to implement a the earnings through the costs’ reduction, through the re- pull system. Studying and researching ways that would moval of wastes [6, 7, 8, 9]. This way, Lean production fo- help to overcome this gap is even more important as a pull cus on delivering value with high quality and fewer defects system was found to be one of the supportive elements in comparison to traditional manufacturing systems such of Lean in the world of Industry 4.0 [5]. as mass production systems [10]. Lean success depends This works tries to make a contribution to the literature on recognizing what is considered as ‘of value’ by the cus- demonstrating a set of integrated steps that may support tomers. This, therefore, needs to be established from the a company to be prepared to the implementation of the outset and will guarantee that Small and Medium-Sized pull system. Thus, this work aims proposing, describing Enterprises (SMEs) can direct the Lean process towards a and evaluating an implementation of a pull system in a concise comprehension of what the customer values [11]. polymeric components company for the automotive in- Moreover, and ultimately important to Lean principles is dustry. The company where the project was developed the respect for the human condition of operators [12] and 254 Management Systems in Production Engineering 2021, Volume 29, Issue 4 the recognition of the importance of teams for Lean suc- excess because the super-market stock is based on the cli- cess [4]. ent’s demand [21]. Production leveling is one of the pillars Being the creation of flow in the production system, a fun- of the Toyota Production System [22]. Since timing and damental goal of lean [13], in order to achieve an efficient volume are critical, production processes are arranged to Pull Production System’s implementation, the problems facilitate production of the required quantity at the re- of the current production system must be analyzed. To do quired time, and worker, equipment, and all other factors that, Value Stream Mapping (VSM) tool is the most com- are organized toward that end. mon tool referred in the literature [14]. A Value Stream As discussed by Chiarini [23] many companies strive to encompasses all the activities, both value-added, and balance lot sizes with setup times, to ensure a good per- non-value added, currently required to bring a product formance of a pull production system. Thus, it is necessary through the material and information flows. The process to reduce the setup times, and, for that, the SMED tool of creating the mapping is developed following a prod- makes it possible to respond quickly to fluctuation in de- uct’s production path from costumer to supplier, and mand, and creates the necessary conditions for lead time carefully drawing a visual representation of every process reductions [24]. In summary, the reduction in manufac- in the material and information flow [15]. A VSM allows to turing lead time requires concentrating on understanding visualize the progressive work being developed, aiming at customer needs, introducing pull system, focusing on highlighting some of the main wastes in the production setup time reduction [15]. system. It provides a pictorial view of existing process and provides guides to identify gap areas for improvement METHODOLOGY OF THE RESEARCH through the application of Lean concepts and tools [16]. As this work aims proposing, describing, and evaluating an The mapping should support to create suggestions based implementation of a pull system in a polymeric compo- on economic feasibility and ease of implementation, and nents company for the automotive industry, a case study thus should lead to a feasible future-state VSM [17] that will be developed. A case study allows to understand in a will become the roadmap to achieve a continuous flow deep way a concrete and real research subject. In this system. Such a flow system is achieved by the establish- way, this work will contribute, both for researchers and ment of a Lean-pull production strategy [16]. practitioners, to get a grasp on the steps involved to im- A Pull System allows to create a Just-in-Time (JIT) produc- plement a pull production system in a SME company de- tion system because it creates a system where each sup- veloping polymeric components for the automotive in- plier (internal or external) serves the quantity demanded dustry. by each client (internal or external), reducing stocks and In order to apply the case study methodology, it is im- wastes related to the productive process, as well as reduc- portant to describe in detail the context of the study. The ing the lead times and ensuring the client’s satisfaction. If current state of the relevant part of the company’s pro- a firm is interested in improving productivity, should be duction system is going to be analyzed. focusing on introducing a Pull System [15]. In such a pro- This company produces cars plastic parts. There are three duction system, each process inside the company acts as production sections: injection, painting and assembly. The an internal client, which should receive the product in the relevant production system for this project, manages correct quantity and time [18]. In order to inform all pro- eleven product references, in which seven go through the cesses about necessary timing and quantity of production path Injection – Painting and the remaining four go parts, the pull system uses Kanbans [3]. Since the pull pro- through the path Injection – Painting-Assembly. duction system engages in small-lot production, frequent The injection’s machines have large setup times, which transport, and frequent delivery, therefore, delivery and leads the company to have a “Batch Production” to avoid receiving locations and parts must be written explicitly in the constant changes of the references, that leads to a the Kanban, in order to maintain and coordinate the dis- high level of WIP in the injection’s supermarket. Following cipline in the pull system [6]. Therefore, a Kanban System this, the products go to the Painting machine to be is a visual control system where the orders are automati- painted. After that, part of the items goes to the finished cally transformed in authorizations through a Kanban products’ warehouse to be shipped and other part of the card. These cards must be organized by its priorities and items goes to the assembly section before going to the put in a Production Planning Board [19]. The number of warehouse. Kanbans in a given loop will therefore depend upon de- When the order arrives, the logistics department sends mand and, if demand changes, then the number of Kan- the information to the different production sections and bans can be adjusted accordingly [20]. the production starts in a push environment, where the A supermarket allows a simple management process of production is pushed through the different sections in the parts. This is a major element in the pull production plan- order mentioned before. ning. A supermarket is a storage area that works with pre- defined rules, such as, having a fixed location for every Critical analysis part number, providing easy picking access, allowing vis- The first step of analysis was the calculation of the takt ual management, keeping the FIFO principle and easy time of each product, considering that the amount of handling of small containers/rollers/trolleys [1]. Besides, available time was equal to the shift of production of the a supermarket is a system that allows controlling the stock B. MARTINS et al. – Implementation Of A Pull System… 255 last process. It was necessary to do such an approach be- Single Minute Exchange of Die cause the three production sections have a different num- Currently, the injection machine’s setup times are an ob- ber of shifts. When comparing the takt-time of the prod- stacle to the pull production system’s implementation, ucts with their respective cycle time it was concluded that since they are very high. To overcome this problem, SMED it is very low. Therefore, the company has enough availa- was selected, because it can be applied to any equipment ble capacity considering the usual demand. or workstation that loses time or efficiency when chang- Furthermore, in order to analyze the current production ing from one product to another [1]. In order to apply system, it was developed a Value Stream Mapping (VSM) SMED, a mold’s changeover was observed in one of the considering the product with the higher demand. injection machines. Then, the SMED was applied based on This product was chosen because it has the higher influ- the following steps [1]: ence in the entire production system. This VSM was de- 1. Current State Analysis. The setup’s study started with veloped in the shop floor where all the details were seen the detailed annotation of all activities that were being and evaluated. So, the final result is shown in Figure 1 made and their duration. The total time of all activities where only the most important part of the VSM is shown. was 1 hour, 25 minutes and 51 seconds. 2. Classification of internal versus external activities. In- ternal activities are those that can be done only with the machine stopped. External activities are those that can be done while the machine is operating. 3. Converting internal activities to external. In this step, a detailed analysis of the internal activities was done. Some of these activities were identified as being po- tential candidates to be done externally to the change- Fig. 1 Current State VSM over. The total time of these activities that could be done with the machine working was 19 minutes and Analyzing the current system, it was concluded that the 22 seconds. lead time of the product is very high when comparing it to 4. Internal work’s reduction. After converting internal to the time where value added activities are being held. This external activities, it is necessary to reduce the total is caused by the time that the product waits on the injec- duration of internal activities. To do that, a prece- tion’s supermarket to go to the next operation. So, it was dence network [25] was developed, identifying the concluded that only in 0.78% of the time is being added tasks that can be done in parallel, which could be exe- value to the product. cuted by more than one setup collaborator. This op- It is also possible to see that the machine’s preparation tion was considered practicable since, usually, an op- time is very high, which leads to a batch-based production erator is responsible for more than one machine, this in order to minimize the effect of the time lost on setups. way, when one of them is in preparation mode, his oc- As seen in the picture, this leads to an excessive amount cupancy rate is always less than 100%. of WIP between sections, occupying an exaggerated 5. External activities time reduction. In terms of external amount of space. work, there is the possibility of reducing the time of Summing up, the problems detected on the company the mold’s transport next to the injection machine. were: the large amount of time that products wait on the Currently, some of the mold are stored 73.79 meters supermarket, an over production and a high travel time away from the machine. for each product. Leveling Steps for the implementation of the pull system After the changeover times were lowered, it was relevant According to Total Flow Management methodology the to level the production. The product demand is very sta- main steps for pull production implementation are reduc- ble, so it was possible to have an idea of the weekly de- ing changeover times, production leveling, Kanban system mand for each product. Then, it is important to note that implementation and finally the implementation of super- the company has deliveries on Tuesday and on Friday, markets [1]. So, it was decided that the first step would be where they have to hand out 40% of the week’s demand reducing changeover times using Single Minute Exchange and 60% of the week’s demand, respectively. In order to of Die (SMED) in order to be able to level the production level the production, and in this way allowing the produc- in smaller cycles decreasing the production batch. Then, it tion line to have more flexibility, it was decided in accord- was possible to develop a production leveling proposal, ance with the company to define two different production followed by a Kanban system and supermarkets to ensure cycles, one starting on Tuesday and ending on Thursday that this system works properly. and the other one starting on Friday and ending on Mon- day. Thus, the company would produce 60% of its demand RESULTS OF RESEARCH on each cycle (20% more than its weekly demand) to pre- This section describes the main results of the developed vent stock breaks and respond to little demand variations case study, regarding the implementation of a pull sys- with an additional stock. tem. 256 Management Systems in Production Engineering 2021, Volume 29, Issue 4 As the injection process takes some time to reach a cer- not used to operate in such a system. Finally, the con- tain stability, it was decided to define one cycle of produc- tainer’s capacity is equal to the capacity of the respective tion for each part of the week, avoiding to change over a box that is used currently for storing the product by the machine more times per week. So, in each cycle, firstly the company. It is important to note that each type of product class A products should be produced, then the class B has its box and its own capacity. products and lastly the class C products. So, the expression that was used is represented below (1) and it is adapted from Sugimori’s equation for the number Kanban System of Kanbans calculation [12]. 𝑎𝑛𝑑𝐷𝑚𝑒 ×𝐿𝑎𝑑𝑒 𝑒𝑇𝑖𝑚 ×(1+𝑢𝑟𝑖𝑡𝑆𝑒𝑐𝑦 𝐹𝑡𝑎𝑜𝑐𝑟 ) The company already stores the products in boxes 𝑎𝑛𝑠𝑎𝑛𝑏𝐾 𝑁𝑟 = (1) 𝐶𝑜𝑛𝑡𝑟𝑎𝑖𝑛𝑒 𝐶𝑎𝑖𝑡𝑝𝑎𝑦𝑐 throughout their production system. As this box can store By using this expression, and the demand provided by the multiple products and are easily transported it was de- company the number of Kanbans was obtained for each cided that this box would represent the Kanban container. production cycle, and for each product. On the first pro- This system will allow the company to produce only when duction cycle (2.33 days) it was calculated 140 Kanbans for its necessary. For each production cycle it is pre-estab- the injection section and 144 Kanbans for the painting lished the number of Kanbans based on the clients’ de- process. On the second production cycle (3 days) it was mand. Thus, it is possible to avoid over-production, lead- calculated 179 Kanbans for the injection section and 183 ing to the decrease of WIP, the major problem in the com- Kanbans for the painting section. pany’s production system. Firstly, the cards will start in the final workstation (Paint- The Kanban-card method involves the use of a Kanban- ing) and move in materials’ opposite direction. This way it card containing information of an individual work item to is possible to pull the production according to the cus- travel together with the inventory [26]. That card will de- tomer’s will, using two Kanban’s cycles: scribe the product transported in the box, with infor- − One cycle between the warehouse and the painting mation about his name, the quantity, the lead-time, workstation. among others, as shown in Figure 2. − Another cycle between the painting workstation and the injection section. This way, each section receives empty boxes with the cor- responding Kanban card, giving the authorization to pro- duce the quantity mentioned in the card. As mentioned, the cards have to move backwards in the production sys- tem, so this empty boxes always come from the forward workstation. For example, the Painting workstation will receive empty boxes that come from the final warehouse. The attachment of cards to the WIP inventory is vital, be- ing the three options for card attachments to be attached (1) to the panels, inserted as (2) part of the job card, or on (3) material transfer [3]. When the empty box arrives in the right workstation, the attached card is moved to a board, allowing the workers to have visual control of what is needed to produce in order to fill the box. After producing what is needed, the Kanban card is moved Fig. 2 Kanban card again and attached to the box, indicating the product that it carries. This full box is ready to be moved forward. For This card is important to secure the boxes flow designed example, the products that come out of the injection on the proposed system and to know the location of a workstations have to be moved to the injection’s super- product in the company. market to fuel the painting machine. In this transition phase (push-pull), it was considered the According to this, the Kanban Flow in each section is rep- time that the company had between the moment they resented in Figure 3. start producing until the moment they have to deliver their products, which is referred as lead-time. As men- tioned before, it was defined that there would be two pro- duction cycles where in each cycle, it is produced 60% of the demand. So, it was obtained a lead-time of 2.33 days, once the company starts producing on Friday and has to deliver on Tuesday, and a lead-time of 3 days once the company starts producing on Tuesday and has to deliver on Friday. As for the security-factor it was defined that it Fig. 3 Kanban Flow in every workstation should be 10% on an initial phase because the company is B. MARTINS et al. – Implementation Of A Pull System… 257 Once calculated the number of Kanbans per section, it is was considered a racks’ depth of 3200 mm, corresponding fundamental to verify if the company has capacity to pro- the space needed for eight boxes. duce what was defined. So, it was developed a Capacity Analysis Chart based on the total available production time of each machine, and the time needed to produce the quantity purposed. As shown in Figure 4 the company has capacity to produce the number of Kanbans calculated previously. With or- ange color it is represented the total available production time for the 1st cycle and in blue the time needed to pro- duce the quantity ordered. With green is represented the available production time for the second cycle and with yellow the time needed to produce the quantity ordered to the 2nd cycle. Fig. 5 Supermarkets’ racks representation After dimensioning the supermarket, it was necessary to define the location of each product. It is important to re- fer that the products will have a fixed location and the products whose number of Kanbans is higher will be lo- cated closest to the next workstation while those with lower number of Kanbans will be further away. In each su- permarket’s rack, there will be a label identifying the product to be placed on that location and the label color will differ according to the product. Fig. 4 Capacity Analysis Figure 6 represents the locations of the products in the supermarket between injection and painting, as well as Supermarkets the different colors for each product. The pull system of this project includes intermediate product supermarkets, whose size was calculated consid- ering a maximum and minimum heights of the racks re- specting ergonomic conditions to the logistic operators’ health and wellbeing. In a pull system, the system aims for a minimum inventory while maintaining an effective man- Fig. 6 Representation of products' locations in a supermarket agement of materials flow [26], so the intermediate prod- between injection and painting workplaces ucts supermarkets are important to support such an ef- fective flow of materials. DISCUSSION The storage system chosen for the supermarkets pro- In this section, the results obtained are analyzed and com- posed was the flow rack, which allows the rotation of pared to the initial state. The SMED’s implementation was boxes by FIFO rule and an easier access to them, with one very efficient in terms of mold changeover time reduction. side of the rack for loading boxes and the other one for This way, it was possible to obtain a reduction comparing unloading. to its initial time of around 38%, so the setup decreased To respect the ergonomic conditions mentioned above, to 52 minutes and 58 seconds. This leads to an increase of the boxes must be handled between the height of the the machines’ working time to 32 minutes and 53 seconds knees and the shoulders, so the maximum height of the by shift, just by planning the tasks and using two opera- racks is 1022 mm and the minimum height is 336 mm tors instead of one. which means that supermarkets can only have two levels In terms of the travelled distance to pick up the new mold, bearing in mind that all the boxes used in this project have it was possible to reduce it around 68% in case the mold’s a dimension of 600·400·280 mm (length·width·height). It storage was in the injection’s section, since there is space was considered that the height of the inclination is available to do that. 100 mm. Figure 5 illustrates the proposed solution for These proposals allowed the company to have annual product supermarkets. earnings of approximately 83000 €. Furthermore, the in- Considering the maximum number of Kanbans per prod- vestment would have its return in the same month that uct, the maximum number of boxes that could be present the SMED is implemented because of the productive time in each supermarket was calculated. For each reference it gained. was considered a capacity gap of 10%. In the supermarket between the injection and the paint- ing, the maximum number of boxes is 179. After this, it 258 Management Systems in Production Engineering 2021, Volume 29, Issue 4 The proposed size for the supermarkets has a satisfactory ACKNOWLEDGMENTS value in terms of the space occupied by the racks versus This work has been supported by FCT – Fundação para a the space available. Ciência e Tecnologia within the R&D Units Project Scope: In order to analyze the obtained results, the future VSM UIDB/00319/2020. was developed based on a simulation in SIMIO software represented in Figure 7. In the VSM were represented the REFERENCES [1] E.A. 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Pereira, "Melhoria dos Processos de Secção de Corte Research, vol. 12, no. 4, pp. 15242-15251, 2017. através da aplicação de ferramentas Lean Production numa Empresa de Componentes para a Indústria Automóvel," 2020. Bruna Martins Tiago Carvalho University of Minho University of Minho School of Engineering, Centro Algoritmi School of Engineering, Centro Algoritmi Department of Production and Systems Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: bruna.alex.martins@hotmail.com e-mail: tiagoandrecarvalho@gmail.com Cláudia Silva Vera Silva University of Minho University of Minho School of Engineering, Centro Algoritmi School of Engineering, Centro Algoritmi Department of Production and Systems Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: claudia2903silva@gmail.com e-mail: vemosilva@hotmail.com Diogo Silva (correspondent autor) Rui M. Lima University of Minho University of Minho School of Engineering, Centro Algoritmi School of Engineering, Centro Algoritmi Department of Production and Systems Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: diogoscb21@gmail.com e-mail: rml@dps.uminho.pt Laura Machado University of Minho School of Engineering, Centro Algoritmi Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: laurapnhmachado@gmail.com Miguel Brás University of Minho School of Engineering, Centro Algoritmi Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: miguel.atf.bras@gmail.com Rui Oliveira University of Minho School of Engineering, Centro Algoritmi Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: rucaalex@hotmail.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Management Systems in Production Engineering de Gruyter

Implementation of a Pull System – A Case Study of a Polymeric Production System for the Automotive Industry

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de Gruyter
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© 2021 Bruna Martins et al., published by Sciendo
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Abstract

This work, developed as a case study, propose, describe, and evaluates an implementation of a pull system in a SME company producing polymeric components for the automotive industry. The production system of the com- pany was based on the push paradigm, which creates high stock levels and high lead times. The main purpose was to develop a pull production system controlled by Kanbans in the painting line. To achieve this goal, this case study demonstrates the application of relevant lean tools, such as, VSM, SMED, Kanban System, Supermarkets and Leveling. Through the SMED’s application, it was possible to reduce the setup times in 38% and make annual earnings of approximately 83000€. The application of a Kanban System, Leveling and Supermarket enabled the WIP’s reduction between injection and painting in 56% and, also, between painting and expedition in 45%. Also, the lead time decreased and the value-added time increased. Thus, this is an exemplary case study for the imple- mentation of a pull system and can be used both by practitioners and researchers interested in this theme. Key words: Kanban, Leveling, Pull Production, SMED, Supermarket INTRODUCTION has the purpose of reducing its Work-In-Process (WIP) lev- In order to respond to the increasing competition forced els and the non-value-added activities. by the market, companies must improve their ability to After the introduction, the structure of the present article adjust their production systems through the introduction continues with the literature review. Then, a productive of new paradigms. The Pull Production System’s imple- system’s description is made, followed by a critical analy- mentation involves other Lean Production tools applica- sis. The fourth section present the steps developed for im- tion, such as, Single Minute Exchange of Die (SMED), Kan- plementation of the pull system. Finally, the article ends ban Systems, Leveling and Supermarkets [1]. Several with the discussion and conclusions. works [2, 3, 4] were devoted to the analysis of specific ap- proaches to design a pull system, but it is not common to LITERATURE REVIEW find works focusing on different steps that a company Lean Production has the principal purpose of increasing must carry out to create the conditions to implement a the earnings through the costs’ reduction, through the re- pull system. Studying and researching ways that would moval of wastes [6, 7, 8, 9]. This way, Lean production fo- help to overcome this gap is even more important as a pull cus on delivering value with high quality and fewer defects system was found to be one of the supportive elements in comparison to traditional manufacturing systems such of Lean in the world of Industry 4.0 [5]. as mass production systems [10]. Lean success depends This works tries to make a contribution to the literature on recognizing what is considered as ‘of value’ by the cus- demonstrating a set of integrated steps that may support tomers. This, therefore, needs to be established from the a company to be prepared to the implementation of the outset and will guarantee that Small and Medium-Sized pull system. Thus, this work aims proposing, describing Enterprises (SMEs) can direct the Lean process towards a and evaluating an implementation of a pull system in a concise comprehension of what the customer values [11]. polymeric components company for the automotive in- Moreover, and ultimately important to Lean principles is dustry. The company where the project was developed the respect for the human condition of operators [12] and 254 Management Systems in Production Engineering 2021, Volume 29, Issue 4 the recognition of the importance of teams for Lean suc- excess because the super-market stock is based on the cli- cess [4]. ent’s demand [21]. Production leveling is one of the pillars Being the creation of flow in the production system, a fun- of the Toyota Production System [22]. Since timing and damental goal of lean [13], in order to achieve an efficient volume are critical, production processes are arranged to Pull Production System’s implementation, the problems facilitate production of the required quantity at the re- of the current production system must be analyzed. To do quired time, and worker, equipment, and all other factors that, Value Stream Mapping (VSM) tool is the most com- are organized toward that end. mon tool referred in the literature [14]. A Value Stream As discussed by Chiarini [23] many companies strive to encompasses all the activities, both value-added, and balance lot sizes with setup times, to ensure a good per- non-value added, currently required to bring a product formance of a pull production system. Thus, it is necessary through the material and information flows. The process to reduce the setup times, and, for that, the SMED tool of creating the mapping is developed following a prod- makes it possible to respond quickly to fluctuation in de- uct’s production path from costumer to supplier, and mand, and creates the necessary conditions for lead time carefully drawing a visual representation of every process reductions [24]. In summary, the reduction in manufac- in the material and information flow [15]. A VSM allows to turing lead time requires concentrating on understanding visualize the progressive work being developed, aiming at customer needs, introducing pull system, focusing on highlighting some of the main wastes in the production setup time reduction [15]. system. It provides a pictorial view of existing process and provides guides to identify gap areas for improvement METHODOLOGY OF THE RESEARCH through the application of Lean concepts and tools [16]. As this work aims proposing, describing, and evaluating an The mapping should support to create suggestions based implementation of a pull system in a polymeric compo- on economic feasibility and ease of implementation, and nents company for the automotive industry, a case study thus should lead to a feasible future-state VSM [17] that will be developed. A case study allows to understand in a will become the roadmap to achieve a continuous flow deep way a concrete and real research subject. In this system. Such a flow system is achieved by the establish- way, this work will contribute, both for researchers and ment of a Lean-pull production strategy [16]. practitioners, to get a grasp on the steps involved to im- A Pull System allows to create a Just-in-Time (JIT) produc- plement a pull production system in a SME company de- tion system because it creates a system where each sup- veloping polymeric components for the automotive in- plier (internal or external) serves the quantity demanded dustry. by each client (internal or external), reducing stocks and In order to apply the case study methodology, it is im- wastes related to the productive process, as well as reduc- portant to describe in detail the context of the study. The ing the lead times and ensuring the client’s satisfaction. If current state of the relevant part of the company’s pro- a firm is interested in improving productivity, should be duction system is going to be analyzed. focusing on introducing a Pull System [15]. In such a pro- This company produces cars plastic parts. There are three duction system, each process inside the company acts as production sections: injection, painting and assembly. The an internal client, which should receive the product in the relevant production system for this project, manages correct quantity and time [18]. In order to inform all pro- eleven product references, in which seven go through the cesses about necessary timing and quantity of production path Injection – Painting and the remaining four go parts, the pull system uses Kanbans [3]. Since the pull pro- through the path Injection – Painting-Assembly. duction system engages in small-lot production, frequent The injection’s machines have large setup times, which transport, and frequent delivery, therefore, delivery and leads the company to have a “Batch Production” to avoid receiving locations and parts must be written explicitly in the constant changes of the references, that leads to a the Kanban, in order to maintain and coordinate the dis- high level of WIP in the injection’s supermarket. Following cipline in the pull system [6]. Therefore, a Kanban System this, the products go to the Painting machine to be is a visual control system where the orders are automati- painted. After that, part of the items goes to the finished cally transformed in authorizations through a Kanban products’ warehouse to be shipped and other part of the card. These cards must be organized by its priorities and items goes to the assembly section before going to the put in a Production Planning Board [19]. The number of warehouse. Kanbans in a given loop will therefore depend upon de- When the order arrives, the logistics department sends mand and, if demand changes, then the number of Kan- the information to the different production sections and bans can be adjusted accordingly [20]. the production starts in a push environment, where the A supermarket allows a simple management process of production is pushed through the different sections in the parts. This is a major element in the pull production plan- order mentioned before. ning. A supermarket is a storage area that works with pre- defined rules, such as, having a fixed location for every Critical analysis part number, providing easy picking access, allowing vis- The first step of analysis was the calculation of the takt ual management, keeping the FIFO principle and easy time of each product, considering that the amount of handling of small containers/rollers/trolleys [1]. Besides, available time was equal to the shift of production of the a supermarket is a system that allows controlling the stock B. MARTINS et al. – Implementation Of A Pull System… 255 last process. It was necessary to do such an approach be- Single Minute Exchange of Die cause the three production sections have a different num- Currently, the injection machine’s setup times are an ob- ber of shifts. When comparing the takt-time of the prod- stacle to the pull production system’s implementation, ucts with their respective cycle time it was concluded that since they are very high. To overcome this problem, SMED it is very low. Therefore, the company has enough availa- was selected, because it can be applied to any equipment ble capacity considering the usual demand. or workstation that loses time or efficiency when chang- Furthermore, in order to analyze the current production ing from one product to another [1]. In order to apply system, it was developed a Value Stream Mapping (VSM) SMED, a mold’s changeover was observed in one of the considering the product with the higher demand. injection machines. Then, the SMED was applied based on This product was chosen because it has the higher influ- the following steps [1]: ence in the entire production system. This VSM was de- 1. Current State Analysis. The setup’s study started with veloped in the shop floor where all the details were seen the detailed annotation of all activities that were being and evaluated. So, the final result is shown in Figure 1 made and their duration. The total time of all activities where only the most important part of the VSM is shown. was 1 hour, 25 minutes and 51 seconds. 2. Classification of internal versus external activities. In- ternal activities are those that can be done only with the machine stopped. External activities are those that can be done while the machine is operating. 3. Converting internal activities to external. In this step, a detailed analysis of the internal activities was done. Some of these activities were identified as being po- tential candidates to be done externally to the change- Fig. 1 Current State VSM over. The total time of these activities that could be done with the machine working was 19 minutes and Analyzing the current system, it was concluded that the 22 seconds. lead time of the product is very high when comparing it to 4. Internal work’s reduction. After converting internal to the time where value added activities are being held. This external activities, it is necessary to reduce the total is caused by the time that the product waits on the injec- duration of internal activities. To do that, a prece- tion’s supermarket to go to the next operation. So, it was dence network [25] was developed, identifying the concluded that only in 0.78% of the time is being added tasks that can be done in parallel, which could be exe- value to the product. cuted by more than one setup collaborator. This op- It is also possible to see that the machine’s preparation tion was considered practicable since, usually, an op- time is very high, which leads to a batch-based production erator is responsible for more than one machine, this in order to minimize the effect of the time lost on setups. way, when one of them is in preparation mode, his oc- As seen in the picture, this leads to an excessive amount cupancy rate is always less than 100%. of WIP between sections, occupying an exaggerated 5. External activities time reduction. In terms of external amount of space. work, there is the possibility of reducing the time of Summing up, the problems detected on the company the mold’s transport next to the injection machine. were: the large amount of time that products wait on the Currently, some of the mold are stored 73.79 meters supermarket, an over production and a high travel time away from the machine. for each product. Leveling Steps for the implementation of the pull system After the changeover times were lowered, it was relevant According to Total Flow Management methodology the to level the production. The product demand is very sta- main steps for pull production implementation are reduc- ble, so it was possible to have an idea of the weekly de- ing changeover times, production leveling, Kanban system mand for each product. Then, it is important to note that implementation and finally the implementation of super- the company has deliveries on Tuesday and on Friday, markets [1]. So, it was decided that the first step would be where they have to hand out 40% of the week’s demand reducing changeover times using Single Minute Exchange and 60% of the week’s demand, respectively. In order to of Die (SMED) in order to be able to level the production level the production, and in this way allowing the produc- in smaller cycles decreasing the production batch. Then, it tion line to have more flexibility, it was decided in accord- was possible to develop a production leveling proposal, ance with the company to define two different production followed by a Kanban system and supermarkets to ensure cycles, one starting on Tuesday and ending on Thursday that this system works properly. and the other one starting on Friday and ending on Mon- day. Thus, the company would produce 60% of its demand RESULTS OF RESEARCH on each cycle (20% more than its weekly demand) to pre- This section describes the main results of the developed vent stock breaks and respond to little demand variations case study, regarding the implementation of a pull sys- with an additional stock. tem. 256 Management Systems in Production Engineering 2021, Volume 29, Issue 4 As the injection process takes some time to reach a cer- not used to operate in such a system. Finally, the con- tain stability, it was decided to define one cycle of produc- tainer’s capacity is equal to the capacity of the respective tion for each part of the week, avoiding to change over a box that is used currently for storing the product by the machine more times per week. So, in each cycle, firstly the company. It is important to note that each type of product class A products should be produced, then the class B has its box and its own capacity. products and lastly the class C products. So, the expression that was used is represented below (1) and it is adapted from Sugimori’s equation for the number Kanban System of Kanbans calculation [12]. 𝑎𝑛𝑑𝐷𝑚𝑒 ×𝐿𝑎𝑑𝑒 𝑒𝑇𝑖𝑚 ×(1+𝑢𝑟𝑖𝑡𝑆𝑒𝑐𝑦 𝐹𝑡𝑎𝑜𝑐𝑟 ) The company already stores the products in boxes 𝑎𝑛𝑠𝑎𝑛𝑏𝐾 𝑁𝑟 = (1) 𝐶𝑜𝑛𝑡𝑟𝑎𝑖𝑛𝑒 𝐶𝑎𝑖𝑡𝑝𝑎𝑦𝑐 throughout their production system. As this box can store By using this expression, and the demand provided by the multiple products and are easily transported it was de- company the number of Kanbans was obtained for each cided that this box would represent the Kanban container. production cycle, and for each product. On the first pro- This system will allow the company to produce only when duction cycle (2.33 days) it was calculated 140 Kanbans for its necessary. For each production cycle it is pre-estab- the injection section and 144 Kanbans for the painting lished the number of Kanbans based on the clients’ de- process. On the second production cycle (3 days) it was mand. Thus, it is possible to avoid over-production, lead- calculated 179 Kanbans for the injection section and 183 ing to the decrease of WIP, the major problem in the com- Kanbans for the painting section. pany’s production system. Firstly, the cards will start in the final workstation (Paint- The Kanban-card method involves the use of a Kanban- ing) and move in materials’ opposite direction. This way it card containing information of an individual work item to is possible to pull the production according to the cus- travel together with the inventory [26]. That card will de- tomer’s will, using two Kanban’s cycles: scribe the product transported in the box, with infor- − One cycle between the warehouse and the painting mation about his name, the quantity, the lead-time, workstation. among others, as shown in Figure 2. − Another cycle between the painting workstation and the injection section. This way, each section receives empty boxes with the cor- responding Kanban card, giving the authorization to pro- duce the quantity mentioned in the card. As mentioned, the cards have to move backwards in the production sys- tem, so this empty boxes always come from the forward workstation. For example, the Painting workstation will receive empty boxes that come from the final warehouse. The attachment of cards to the WIP inventory is vital, be- ing the three options for card attachments to be attached (1) to the panels, inserted as (2) part of the job card, or on (3) material transfer [3]. When the empty box arrives in the right workstation, the attached card is moved to a board, allowing the workers to have visual control of what is needed to produce in order to fill the box. After producing what is needed, the Kanban card is moved Fig. 2 Kanban card again and attached to the box, indicating the product that it carries. This full box is ready to be moved forward. For This card is important to secure the boxes flow designed example, the products that come out of the injection on the proposed system and to know the location of a workstations have to be moved to the injection’s super- product in the company. market to fuel the painting machine. In this transition phase (push-pull), it was considered the According to this, the Kanban Flow in each section is rep- time that the company had between the moment they resented in Figure 3. start producing until the moment they have to deliver their products, which is referred as lead-time. As men- tioned before, it was defined that there would be two pro- duction cycles where in each cycle, it is produced 60% of the demand. So, it was obtained a lead-time of 2.33 days, once the company starts producing on Friday and has to deliver on Tuesday, and a lead-time of 3 days once the company starts producing on Tuesday and has to deliver on Friday. As for the security-factor it was defined that it Fig. 3 Kanban Flow in every workstation should be 10% on an initial phase because the company is B. MARTINS et al. – Implementation Of A Pull System… 257 Once calculated the number of Kanbans per section, it is was considered a racks’ depth of 3200 mm, corresponding fundamental to verify if the company has capacity to pro- the space needed for eight boxes. duce what was defined. So, it was developed a Capacity Analysis Chart based on the total available production time of each machine, and the time needed to produce the quantity purposed. As shown in Figure 4 the company has capacity to produce the number of Kanbans calculated previously. With or- ange color it is represented the total available production time for the 1st cycle and in blue the time needed to pro- duce the quantity ordered. With green is represented the available production time for the second cycle and with yellow the time needed to produce the quantity ordered to the 2nd cycle. Fig. 5 Supermarkets’ racks representation After dimensioning the supermarket, it was necessary to define the location of each product. It is important to re- fer that the products will have a fixed location and the products whose number of Kanbans is higher will be lo- cated closest to the next workstation while those with lower number of Kanbans will be further away. In each su- permarket’s rack, there will be a label identifying the product to be placed on that location and the label color will differ according to the product. Fig. 4 Capacity Analysis Figure 6 represents the locations of the products in the supermarket between injection and painting, as well as Supermarkets the different colors for each product. The pull system of this project includes intermediate product supermarkets, whose size was calculated consid- ering a maximum and minimum heights of the racks re- specting ergonomic conditions to the logistic operators’ health and wellbeing. In a pull system, the system aims for a minimum inventory while maintaining an effective man- Fig. 6 Representation of products' locations in a supermarket agement of materials flow [26], so the intermediate prod- between injection and painting workplaces ucts supermarkets are important to support such an ef- fective flow of materials. DISCUSSION The storage system chosen for the supermarkets pro- In this section, the results obtained are analyzed and com- posed was the flow rack, which allows the rotation of pared to the initial state. The SMED’s implementation was boxes by FIFO rule and an easier access to them, with one very efficient in terms of mold changeover time reduction. side of the rack for loading boxes and the other one for This way, it was possible to obtain a reduction comparing unloading. to its initial time of around 38%, so the setup decreased To respect the ergonomic conditions mentioned above, to 52 minutes and 58 seconds. This leads to an increase of the boxes must be handled between the height of the the machines’ working time to 32 minutes and 53 seconds knees and the shoulders, so the maximum height of the by shift, just by planning the tasks and using two opera- racks is 1022 mm and the minimum height is 336 mm tors instead of one. which means that supermarkets can only have two levels In terms of the travelled distance to pick up the new mold, bearing in mind that all the boxes used in this project have it was possible to reduce it around 68% in case the mold’s a dimension of 600·400·280 mm (length·width·height). It storage was in the injection’s section, since there is space was considered that the height of the inclination is available to do that. 100 mm. Figure 5 illustrates the proposed solution for These proposals allowed the company to have annual product supermarkets. earnings of approximately 83000 €. Furthermore, the in- Considering the maximum number of Kanbans per prod- vestment would have its return in the same month that uct, the maximum number of boxes that could be present the SMED is implemented because of the productive time in each supermarket was calculated. For each reference it gained. was considered a capacity gap of 10%. In the supermarket between the injection and the paint- ing, the maximum number of boxes is 179. After this, it 258 Management Systems in Production Engineering 2021, Volume 29, Issue 4 The proposed size for the supermarkets has a satisfactory ACKNOWLEDGMENTS value in terms of the space occupied by the racks versus This work has been supported by FCT – Fundação para a the space available. Ciência e Tecnologia within the R&D Units Project Scope: In order to analyze the obtained results, the future VSM UIDB/00319/2020. was developed based on a simulation in SIMIO software represented in Figure 7. In the VSM were represented the REFERENCES [1] E.A. 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Bruna Martins Tiago Carvalho University of Minho University of Minho School of Engineering, Centro Algoritmi School of Engineering, Centro Algoritmi Department of Production and Systems Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: bruna.alex.martins@hotmail.com e-mail: tiagoandrecarvalho@gmail.com Cláudia Silva Vera Silva University of Minho University of Minho School of Engineering, Centro Algoritmi School of Engineering, Centro Algoritmi Department of Production and Systems Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: claudia2903silva@gmail.com e-mail: vemosilva@hotmail.com Diogo Silva (correspondent autor) Rui M. Lima University of Minho University of Minho School of Engineering, Centro Algoritmi School of Engineering, Centro Algoritmi Department of Production and Systems Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: diogoscb21@gmail.com e-mail: rml@dps.uminho.pt Laura Machado University of Minho School of Engineering, Centro Algoritmi Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: laurapnhmachado@gmail.com Miguel Brás University of Minho School of Engineering, Centro Algoritmi Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: miguel.atf.bras@gmail.com Rui Oliveira University of Minho School of Engineering, Centro Algoritmi Department of Production and Systems Campus Azurem, 4800-058 Guimaraes, Portugal e-mail: rucaalex@hotmail.com

Journal

Management Systems in Production Engineering – de Gruyter

Published: Dec 1, 2021

Keywords: Kanban; Leveling; Pull Production; SMED; Supermarket

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