Assessing Shop Floor Layouts in the Context of Process Plans
Read this article. The paper seeks to compare performance of three layouts. Do you agree or disagree with the findings of the research?
Brief literature survey
Layouts
A layout establishes the physical location of the transforming resources, i.e., the facilities, machines, equipment, operators, etc.. In addition, it establishes how transformed resources (i.e., raw materials, materials, parts, etc.) should flow along operations. According to Silva & Rentes , the physical location has impacts in several aspects on the shop floor, and Khilwani et al. point out that the type of layout should focus on the flow of materials, seeking to increase production efficiency and reduce costs. The provision of transforming resources in a facility directly affects production costs and throughput. An adequate allocation of resources contributes significantly to the increase of efficiency of the operations and reduces transportation costs.
Virtual cells operate virtually as cells from a logical point of view, that is, resources are dedicated to manufacture a family of parts, similarly to traditional cells. At the moment when family of parts is completely manufactured, the virtual cell formation is undone logically, and each individual resource being able to re-group with others constitute a new virtual cell.
Figure 1 shows an example of virtual cell layout, where three virtual cells are temporarily formed to manufacture one production order each, with the geometric figures representing different types of machines present on the shop floor.
Figure 1 An example of a virtual cell layout.
Arkat & Ghahve point out that the temporary virtual arrangement is often adjusted, being changed according to the characteristics of the batches of parts to be manufactured by the production control and available resources.
It is noteworthy that in the literature there are several approaches regarding the layout theme, for which a simplified Systematic Literature Review (SLR) was developed based on the guidelines of Tranfield et al.. Karl et al. cites the importance of systematic literature review as a way to build approaches from a large number of studies, without neglecting relevant research. Table 1 presents the 5 steps that describe the literature review protocol (SLR) from Tranfield et al. and Karl et al..
Table 1 SLR protocol.
| Step | Details |
|---|---|
| Question formulation | - develop review questions to achieve the aim of the study |
| Location studies | - develop search requires; - search on Scopus, ScienceDirect and Scielo databases; Search in 35-year period (Jan/1982 – Dec/2017) |
| Study selection and evaluation | - 1st selection: title; - 2nd selection: abstract and keywords; - 3rd selection introduction, conclusion and searching for the paper’s content. |
| Analysis and synteshis | - carefully read papers; - use Excel spreadsheet to code and organize the content based on what is intended to answer from the research questions; |
| Result presentation | - answer the review questions based on what is known in the literature. |
Given the purpose of the article in comparing the different layouts, two Review Questions (RQs) are stated:
RQ1 - What types of existing and used layouts?
RQ2 - What are the performance comparisons of different layouts?
The first question (RQ1) surrounds all types of layouts that have already been enunciated in the literature since the creation of the concept of virtual cellular layout in 1982. The second question (RQ2) tends to contemplate the possible comparisons of these different layouts and how performance of each layout in these assessments.
In the next step it is necessary to determine the search queries from the two questions proposed. Tests were made before determining the final search. The searches were carried out in the bases ScienceDirect and Scopus, including the Brazilian base Scielo. The choices of the bases were given by the access of the authors. Table 2 lists the keywords used to develop the search queries.
Table 2 Search parameters.
| Constructs | Keywords | Search queries |
|---|---|---|
| Layouts types | Positional; Functional; Jobshop; Process; Cell; Cellular; Virtual cellular; Virtual cellular manufacturing (VCM); Virtual cellular manufacturing system (VCMS) | layout* W/3 (positional OR functional OR job* OR process OR cell* OR virtual cell* OR VCM OR VCMS) |
| Layouts performance evaluation | Analysis; Configuration; Modelling; Model; Performance; simulation | layout* W/3 (analys* OR configur* OR model* OR performance OR simula*) |
| Layouts types and layouts performance evaluation | Positional; Functional; Jobshop; Process; Cell; Cellular; Virtual cellular; Virtual cellular manufacturing (VCM); Virtual cellular manufacturing system (VCMS); Analysis; Configuration; Modelling; Model; Performance; simulation | (layout* W/3 (positional OR functional OR job* OR process OR cell* OR virtual cell* OR VCM OR VCMS)AND layout* W/3 (analys* OR configur* OR model* OR performance OR simula*)) |
In the study selection and evaluation stage, a period of 35 years was considered, considering that the beginning of publications regarding the virtual cellular layout began in 1982. In the first search, 3,584 articles were identified, and 396 articles were selected after evaluating their respective titles, which are related to the term layout, in addition to some reference to performance, modeling, configuration, design or analysis comparison. From these 396 articles, we verified the keywords and the abstracts, which resulted in 31 articles that were read the introductions and conclusions.
According to Thomé et al. , several alternative approaches can be used to systematically analyze and synthesize the literature review. The analysis of these 31 articles was done using MS Excel to tabulate the information, organize and analyze the data.
The final step intends to present succinctly the results found from the systematic literature review (SLR). Table 3 summarizes and aims to answer the two questions raised above (RQ1 and RQ2) about the types of layouts and the forms of performance of these layouts. It is convenient to emphasize that none of these articles compare the three layouts proposed in this study. Most of the studies found focus on cell layouts (13 articles), and jobshop (7 articles). Only 3 articles deal with virtual cellular layout within the stipulated comparative context. Regarding the methods of comparison, it is noteworthy that 12 articles dealt with the comparison of layouts, besides 9 articles that deal with the formation of cells. About the simulation tool, 7 out of 31 articles used it. However, most of the articles used together, mathematical models, Taguchi, genetic algorithm, optimization and multi-criteria.
Table 3 Layout Types.
| Layout types | Layout performance | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Authors | Functional | Job shop | Cellular | Virtual cellular | VCMS | VCM | Distributed layout | Layout | Dynamic cellular | Reconfigurable manufacturing system |
Mathematical model | Optimization | Simulation | Comparison | Genetic algorithm | Layout design | Taguchi method | Multi-criteria | Cell formation | Layout selection |
| Shafer & Charnes (1993) | x | x | x | |||||||||||||||||
| Morris & Tersine (1994) | x | x | x | |||||||||||||||||
| Ertay (1998) | x | x | x | |||||||||||||||||
| Agarwal & Sarkis (2001) | x | x | x | |||||||||||||||||
| Bazargan-Cart & Nahavandi (2001) | x | x | ||||||||||||||||||
| Assad et al (2003) | x | x | x | x | ||||||||||||||||
| Drolet et al. (2008) | x | x | x | x | ||||||||||||||||
| Rezazadeh et al. (2009) | x | x | ||||||||||||||||||
| Jayachitra et al. (2010) | x | x | ||||||||||||||||||
| Jerbi et al. (2010) | x | x | x | |||||||||||||||||
| Kamaruddin et al. (2011) | x | x | x | x | x | |||||||||||||||
| Rajapakshe et al. (2011) | x | x | ||||||||||||||||||
| Jayachitra & Prasad (2011) | x | x | x | x | x | |||||||||||||||
| Mahdavi et al. (2011) | x | x | ||||||||||||||||||
| Khilwani et al. (2011) | x | x | ||||||||||||||||||
| Hamedi et al., 2012a | x | x | ||||||||||||||||||
| Hamedi et al. (2012b) | x | x | x | |||||||||||||||||
| Hamedi et al. (2012c) | x | x | x | |||||||||||||||||
| Khaksar-Haghani et al. (2012) | x | x | ||||||||||||||||||
| Dias et al. (2014) | x | x | ||||||||||||||||||
| Medina-Herrera et al. (2014) | x | x | ||||||||||||||||||
| Ramachandran & Prasad (2014) | x | x | x | x | ||||||||||||||||
| Mar-Ortiz et al. (2015) | x | x | ||||||||||||||||||
| Shafigh et al. (2015) | x | x | ||||||||||||||||||
| Paydar & Saidi-Mehrabad (2014) | x | x | x | x | ||||||||||||||||
| Hamedi & Esmaeilian (2015) | x | x | x | x | ||||||||||||||||
| Gupta et al. (2015) | x | x | ||||||||||||||||||
| Sakhaii et al. (2016) | x | x | ||||||||||||||||||
| Deep & Singh (2016) | x | x | x | |||||||||||||||||
| Paydar & Saidi-Mehrabad (2017) | x | x | x | |||||||||||||||||
| Rabbani et al. (2018) | x | x | ||||||||||||||||||
Among the articles analyzed, some works have brought interesting contributions. Mahdavi et al. (2011) present an approach based on fuzzy programming to solve a multi-objective mathematical model of the cell formation problem and production planning in a dynamic virtual cell manufacturing system. The authors point out that in a dynamic environment the product mix and demand variation directly affect production planning.
Paydar & Saidi-Mehrabad developed a mathematical model of optimization using virtual cells to integrate all stages, from acquisition, planning, production and distribution.
Deep & Singh presented an integrated mathematical model for the design of cellular manufacturing systems including cell formation, routing process and system reconfiguration. The model presents flexibility in planning considering capacity, in addition to using the algorithm based on optimal sequencing. The results showed that the coexistence of multiple resources provides greater flexibility.
In the context of Virtual Cell Manufacturing Systems (VCMS), different techniques have been developed to solve problems of virtual cell formation ( Hamedi et al., 2012a ; Paydar & Saidi-mehrabad, 2017 ).
Table 4 lists some works that deal with the different types of layout, the researches developed and the results achieved. It is observed that the authors listed in table 1 developed mathematical models for the formation of virtual cells, using the most varied techniques. It is worth highlighting the paper by Ramachandran & Prasad (2014) , which performs a comparison of layouts. Among the differences of the Ramachandran & Prasad proposal for the presented research is the design of experiments that aided in the identification of the main control factors that affect the results. In addition, process plans with alternatives were used in the research.
Table 4 Some publications about different layouts and their results.
| Author | Description | Results |
|---|---|---|
| Rezazadeh et al. (2009) | Contains a mixed‐integer programming model to design VMC in a dynamic environment. They incorporated the information about production planning, system reconfiguration and workforce requirement. It attempts to minimize the total sum of the following costs: manufacturing, material handling, subcontracting, inventory holding, internal production and cross‐training for workers over the planning horizon. A particle swarm optimization algorithm was used to solve the problem. | Advantages of their model: simultaneous consideration of dynamic system configuration, operation sequence, alternative process plans for part types, machine and worker capacity, workload balancing, cell size limit and batch splitting. |
| Jayachitra et al. (2010) | Inspired by principles and advantages of group technology (GT), part family formation for a virtual Cell Manufacturing System (VCMS) using fuzzy logic is performed for dynamic and uncertain conditions. A mathematical binary-integer programming model is proposed to minimize the following: fixed machine costs, variable costs of all machines, and the logical group movement costs. | Very good results were obtained when comparing the proposed fuzzy logic method with a simulated annealing algorithm and a rank order clustering algorithm. |
| Khilwani et al. (2011) | Design virtual cells that maximize similarity and minimize lead time. Emphasis on machine sharing. | The benefits of using virtual cells increase with the greater variety of machines required to process a particular part. They point to the need to study virtual cells more deeply. |
| Hamedi et al. (2012a) | Review on virtual cell manufacturing systems (VCMS). Techniques to solve problems of formation of virtual cells. | They use mathematical programming to get the best solutions to the problem of virtual cell formation. |
| Hamedi et al. (2012b) | Virtual cell formation using a nonlinear programming model. | Better performance when compared with traditional cell systems. |
| Hamedi et al. (2012c) | Multiobjective mathematical model based on elements and resources. They validate the model through a numerical example taken from the literature. | Companies can take advantage of virtual cell manufacturing systems. Especially those that work with a very unpredictable production environment. |
| Ramachandran & Prasad (2014) | A comparative study is done between the layouts via simulation. Operational parameters considered were throughput, machine utilization, average work-in-process and average flow time. | In most of the proposed scenarios the virtual cell layout presented better performance. |
| Hamedi & Esmaeilian (2015) | Concept of capacity-based virtual cell manufacturing systems. The effectiveness of the system was evaluated through job shop and distributed layouts. A multiobjective function with a Tabu Search algorithm was used. | The distributed layout was more efficient than the job shop in terms of the distance travelled, but with regard to capacity utilization there is no significant difference between these layouts. |
| Gupta et al. (2015) | A configuration selection problem was considered to determine the optimal configuration with respect to the set of performance criteria. Due to simultaneous consideration of several criteria in the problem, entropy-based analytical hierarchy process (AHP) was adopted for the analysis. To overcome the subjectivity in the decision maker’s judgment, the results were analyzed for sensitivity. | The proposed method provides a system design analytical tool and can be easily adopted by the system designer or industrial engineering. |
| Rabbani et al. (2018) | New multi-objective mathematical model for dynamic cellular manufacturing system (DCMS) is provided with consideration of machine reliability and alternative process routes. Two meta-heuristic algorithms, namely NSGA-II and MOPSO, were proposed for solving the problem. Also, a simple way to code the problem was introduced. To validate the proposed model, a small-sized problem was solved with GAMS software. | As expected, due to the discrete nature of the problem, the results showed that the NSGA-II could discover more Pareto solutions than MOPSO and the solutions obtained by NSGA-II had more diversity than MOPSO. Also, it had more quality than MOPSO on average, but Pareto solution of algorithm MOPSO had more uniformity. |