- Email: [email protected]
Plant layout
Chapter 18
Plant layout Chapter takeaways After completion of this chapter the reader would be able to 1. Appreciate the influence of plant layout on the successful performance of the production planning and control department and the rules and guidelines for a successful layout. 2. Understand the types and modalities of the layout to choose the one that best suits the production line. 3. Understand the different flow patterns that can be adapted to production lines to suit your existing building parameters and the space required for your production. 4. Appreciate the benefits of group layout and cellular layout to plan for the production where needed and possible.
18.1 Introduction Plant layout, also known as facilities planning and layout, deals with the orderly and proper arrangement of manufacturing facilities and the use of available resources, including men, money, machines, tools, materials, and methods of production inside the factory. In effect, plant layout is the allocation of space and the arrangement of equipment in such a manner that overall operational cost can be minimized. A well-designed plant layout is concerned with maximum and effective utilization of available resources at minimum operating costs. Smooth and quick material flow is the essence an ideal manufacturing facility. A systematic planning of the layout allows integration of all movements in a logical overall pattern. There are four categories of facilities planning and layout discussed in detail in this chapter: 1. 2. 3. 4.
New facility construction New design in an existing facility Redesign of a restricted or limited area Adding a machine in an existing facility
Production Planning and Control. DOI: https://doi.org/10.1016/B978-0-12-818364-9.00018-4 Copyright © 2019 BSP Books Pvt. Ltd. Published by Elsevier Inc. All rights reserved.
261
262
Production Planning and Control
18.2 Factors contributing to the necessity for layout changes 1. Due to design and market changes a. Changes in the design of the product b. Addition of new products or deletion of old models or methods c. Changes in the volume of market, generally resulting in expansion of all departments d. Adding new departments like centralizing of drilling machines, which were earlier distributed over several production sections e. Moving a department either within the site or to a new geographical location f. Replacing obsolete equipment g. Changes in market location 2. Due to increased production problems and/or bottlenecks a. Frequent failure to meet the delivery commitments or production schedules b. Frequent production bottlenecks due to nonreceipt of work in progress from the previous shops c. High idle time and low machine utilization d. Frequent accidents e. Increased rejections and scrap f. Insufficient storage area leading to congestion in stores and aisles g. Unsuitability of the existing layout for required material handling equipment h. Shortage of material handling equipment, leading to the necessity of readjusting the layout to suit the available equipment. i. Increased maintenance activities on the buildings and equipment. j. Cost reduction studies initiated either by suggestion schemes or other industrial engineering studies k. Utilization of available vertical space 3. Labor relation oriented changes a. Frequent complaints on working conditions b. Frequent requests for additional equipment c. Provision of additional employee facilities d. Sudden increase in absenteeism and high labor turnover e. Increased difficulty in finding suitable employees
18.3 Definitions on plant layout Plant layout is a mechanism which involves knowledge of the space requirements for the facilities and also involves their proper arrangement so that continuous and steady movement of the production cycle takes place. http://www.mbaofficial.com
Plant layout Chapter | 18
263
A plant layout study is an engineering study used to analyze different physical configurations for a manufacturing plant. https://en.wikipedia.org Plant layout embraces the physical arrangement of industrial facilities. This arrangement, either installed or in plan, includes the space needed for material movement, storage, indirect labour and all other supporting activities or services, as well as for office equipment and personnel. Richard Muther Plant layout is the arrangement of machines, work areas and service areas within a factory. George R. Terry Plant layout involves the development of physical relationship among building, equipment and production operations, which will enable the manufacturing process to be carried on efficiently. Morris E. Hurley Plant layout is an arrangement of machines and facilities is layout. F.G. Moore. Plant layout can be defined as a technique of locating machines, processes and plant services within the factory so as to achieve the greatest possible output of high quality at the lowest possible total cost of manufacturing. Spreigel and Lansburgh Plant layout ideally involves the planning and integrating the paths of the component parts of a product to achieve the most effective and economic interrelationships between the operating equipment and personnel, the material movement, storage facilities, service functions and auxiliary equipment. J. Lundy
18.4 Objectives of plant layout 1. To achieve economies in handling of raw materials, work-in-progress, and finished goods. 2. To reduce the quantum of work-in-progress. 3. To have the most effective and optimum utilization of available floor space. 4. To minimize bottlenecks and obstacles in various production processes, thereby avoiding the accumulation of work at important points. 5. To introduce a system of production control.
264
6. 7. 8. 9. 10. 11. 12.
Production Planning and Control
To To To To To To To
ensure means of safety and provision of amenities to the workers. provide better quality products at lesser costs to the consumers. ensure loyalty of workers and improve their morale. minimize the possibility of accidents. provide for adequate storage and packing facilities. work out possibilities of future expansion of the plant. provide such a layout that permits meeting of competitive costs.
18.5 General rules and objectives of successful plant layout 1. Arrange the layout to enable a smooth and efficient production process. 2. Make the arrangement sufficiently flexible to allow production and equipment changes to be made with minimal disruption. 3. Allow adequate but not too much space for the plant and equipment with efficient utilization of the space. 4. Provide for the efficient utilization of the vertical space with easily accessible racks. Plan for effective handling of equipment in the stores. 5. Plan for prompt movement of the work-in-progress, thereby reducing the production time, shop inventories, with better utilization of the capital. 6. Aim for a high level of equipment utilization, especially in new layouts. 7. Utilize the manpower efficiently by reducing the walking distances and eliminating uneconomical manual handling operations. 8. Provide for safe working conditions in equipment operation. 9. Integrate the new facilities with the existing plant as closely as possible. 10. Ensure efficient supervision to achieve all the these objectives.
18.6 Richard Muther’s guidelines for successful systematic layout planning Richard Muther, the father of systematic layout planning, developed a systematic procedure as elaborated in detail in his book Systematic Layout Planning. This is illustrated in detail in this chapter.
18.7 Influence of plant layout 18.7.1 Production planning and control Samuel Eilon, in his book Elements of Production Planning and Control, specifies the following effects of plant layout on various aspects of production planning and control (PP&C): 1. The layout determines the location of departments and production centers, and their proximity to each other and to other services. It enables efficient utilization of the available space.
Plant layout Chapter | 18
265
2. It outlines the nature of flow in the plant and affects the distance traveled by materials and personnel, and thereby the time, effort, and costs spent on material movement. 3. It affects the types of handling systems, their integration in the overall production program, and the costs of their installation. 4. It specifies the location, accessibility, and size of the stores and also the space and location of temporary storage space for work in progress. 5. It affects the amount of work in progress and work awaiting further processing, thereby involving the total time and the capital tied up in work in progress. 6. Machine utilization is partly decided by the layout. This is reflected in the output per machine hour, the total required machine capacity, and in the capital tied up in equipment. 7. Operator’s span of activities, responsibilities, auxiliary tasks, walking time, fatigue, and efficiency may be dictated by the layout considerations. 8. Maintenance procedures, schedules, and costs as well as policy of repairs, reserves, and replacements may be affected. 9. The amount of supervision required and the degree of specialization necessary in supervision are sometimes dependent on the layout. 10. PP&C may be greatly affected, particularly the complexity of routing, machine loading, scheduling, expediting, and the paperwork involved in control mechanisms. 11. The effect on time lag between inspection and corrective actions is to be studied, and this may be reflected in the amount of rejected work.
18.8 Symptoms of poor plant layout 1. 2. 3. 4. 5. 6.
Excessive handling cost. Excessive work-in-progress inventories. Excessive idle time for men and equipment. Excessive downtime and maintenance cost. Increase in the frequency of accidents. Excessive damages due to mishandling.
18.9 Benefits of plant layout The benefits of optimal plant layout are achievement of the preceding objectives, which can be summarized as congestion reduction. 1. 2. 3. 4.
Elimination of unnecessary occupied areas. Reduction of administrative and indirect work. Improvement on control and supervision. Better adjustment to changing conditions.
266
5. 6. 7. 8. 9. 10.
Production Planning and Control
Better utilization of the workforce, equipment, and services. Reduction of material handling activities and stock in process. Reduction on parts and quality risks. Reduction on health risks and increase on workers safety. Morale and workers’ satisfaction increase. Reduction of delays and manufacturing time, as well as increase in production capacity.
Once the departments are laid out as detailed here and by systematic layout planning as detailed in this chapter, the next phase would be to arrange the machinery inside each designation area.
18.10 Types of plant layout There can be four possible types of arrangement of machinery: 1. 2. 3. 4.
Fixed-position layout Process layout Product layout Combination type layout
18.11 Fixed-position layout Fixed-position layout is adapted only in case of large products like boilers, power plant generators, atomic reactors, airplanes, and ships. The major component remains in a fixed location while other materials, parts, tools, machinery, manpower, and other supporting equipment are brought to this location. It follows the principle that it is economical and convenient to bring the necessary tools and equipment to the workplace along with the manpower because the product is too heavy or too big, as in shipbuilding or airplane assembly. Sometimes the major component or body of a final product, like the shell of a train coach, is manufactured in a fixed location, as at the Chennai Integral Coach Factory.
18.11.1 Advantages of fixed-position layout 1. Material movement is reduced. 2. Capital investment is minimized. 3. Continuity of operations is ensured because operators perform their tasks independent of others. 4. This facilitates effective planning and loading since each production center is independent of each other. When two ships are simultaneously produced, each is located at its own fixed position. 5. Thus total production cost will be reduced. 6. It offers greater flexibility and allows change in product design, product mix, and production volume.
Plant layout Chapter | 18
267
18.11.2 Disadvantages of fixed-position layout 1. Highly skilled manpower is required. 2. Movement of machines and other equipment to production center may be time consuming. 3. Complicated fixtures may be required for positioning of jobs and tools. This may increase the cost of production.
18.12 Process or functional layout In process layout, the production facilities are grouped according to their types by the nature or type of operations they can perform, like the machine shop, the press shop, painting shop, welding shop, etc., regardless of which products each workstation is working on. This layout is adapted for low volume and/or nonrepetitive production of standard products and components. Even in a machine shop, all the lathes can be grouped together and the drilling machines can be grouped together, etc. (Fig. 18.1).
18.12.1 Advantages of process layout 1. The total investment on equipment purchase is less because the same machine can work on different products and so the duplication of machines will be less. 2. It enables better and more efficient supervision through specialization on specific machinery at various levels. 3. There is greater flexibility in equipment and manpower and thus load distribution is easily controlled. 4. Better utilization of equipment allows individual processes to function more efficiently by pooling resources. 5. Breakdown of equipment can be easily handled by transferring work to another machine/workstation. 6. There will be better control of complicated or precision processes, especially where much inspection is required.
FIGURE 18.1 Process layout.
268
Production Planning and Control
18.12.2 Disadvantage of process layout 1. There are long material flow lines and hence expensive handling is required. 2. Total production cycle time is increased, owing to long distances and waiting at various points. 3. Since more work is in queue and waiting for further operation, bottlenecks occur. 4. Generally, more floor area is required. 5. Since work does not flow through definite lines, counting and scheduling are tedious. 6. Specialization creates monotony, and it will be difficult for laid-off workers to find job in other industries.
18.13 Product or line layout The product layout groups different workstations together according to the operation sequence of the products they work on. This layout is adapted for high volume, highly standardized, and repetitive production of products and components. The raw material is supplied at one end of the line and goes from one operation to the next quite rapidly with a minimum work-inprocess, storage, and material handling. Generally, only one product of one type of products is produced in the line at a time.
18.13.1 Advantages of product layout 1. 2. 3. 4.
Lower total material handling cost. Less work in processes. Better utilization of men and machines. Less floor area occupied by material in transit and for temporary storages. 5. Greater simplicity of production control. 6. Total production time is also minimized.
18.13.2 Disadvantages of product layout 1. No flexibility, which is generally required, is obtained in this layout. 2. The manufacturing cost increases with a fall in production volume. 3. If one or two lines are running light, there is a considerable machine idleness. 4. A single machine breakdown may shut down the whole production line. 5. Specialized and strict supervision is essential. 6. Product layouts require more space than process layouts, since tools and equipment cannot be shared as easily between workers performing the same tasks on different products (Fig. 18.2).
Plant layout Chapter | 18
269
FIGURE 18.2 Product layout.
18.14 Comparison between product and process layout See Table 18.1.
TABLE 18.1 Comparison between product and process layout. S. no.
Criterion
Product layout
Process layout
1
Investment
Heavy investment needed
Low investment needed
2
Duration of production
Less manufacturing times as the flow is well set and planned
Frequent changes of men and material increases production time
3
Floor space
Use of special purpose machines can reduce the space
Requires more space
4
Material handling
Less amount of material handling
Involves greater handling of material requiring more time, money, and efforts
5
Effect of breakdowns
Breakdown of any unit/ component immobilizes the whole system
If one machine breaks down, other similar machines can be used
6
Quality control
Specialized and expertise control is possible
Comparatively lesser efforts on control
7
Flexibility
Inflexible as each machine can perform predesigned operation only
Flexible as the operation can be performed elsewhere
8
Demand and supply relationship
Better balancing between demand and as these are made to stock
Balancing between demand and supply is difficult as these are made to order
270
Production Planning and Control
18.15 Combination layout A majority of medium-scale industries work on the production of several products that need a process layout, though some of them are produced in large volume, for which the product layout is preferable. In such cases, a combination layout is adapted. The majority of the machines are laid out per the process layout, but some special purpose machines are positioned along the product flow as a compromise of the previously mentioned layouts, taking the benefits of each of them.
18.16 Group technology Wikipedia defines group technology as a manufacturing technique in which parts having similarities in geometry, manufacturing process, and/or functions are manufactured in one location using a small number of machines or processes. Nancy L. Hyer and Urban Wemmerlo¨v in their article “Group Technology and Productivity” in the July 1984 edition of Hayward Business Review have elaborated the benefits of group technology and how it has revolutionized productivity improvement practices. This concept involves machining components that have similar dimensional parameters and characteristics. A factory unit may be producing several models of similar products in which the components (such as axles) would look similar but vary slightly in the dimensional parameters, like the outside diameters or bores or other turning requirements in which operations can be done on the same machine but with slightly different tool settings. Such components are grouped together, and the equipment layout is planned in such a way that all these components can be operated on these machines with slight changes in tool settings, thereby eliminating the traditional schedule changeovers. Fig. 18.3 illustrates machined components that are
FIGURE 18.3 Components for group technology.
Plant layout Chapter | 18
271
FIGURE 18.4 Group layout. Source: HBR Journal of 1984.
dimensionally different and used in entirely different sets of products manufactured by the company. This technique is called group technology, and the type of layout to accommodate such machinery is called the group layout (Fig. 18.4).
18.16.1 Advantages of group layout 1. Increased throughput as the components are completely machined in one group where the machines are grouped together and under the control of a single supervisor 2. Reduced handling 3. Reduced inventories and reduced investment 4. Reduced scrap and improved quality 5. More reliable delivery time 6. Reduced investment in equipment, since more than one component flows through the product layout. 7. Reduced tool setting cost and thereby improving machine unitization. 8. Reduced direct and indirect labour 9. Increased job satisfaction 10. It results on reduction of component varieties, since this gives more opportunities for standardization.
18.17 Cellular layout Cellular manufacturing is based on the principles of group technology proposed by Flanders in 1925 and integrates just-in-time manufacturing and lean manufacturing techniques. Business Dictionary defines cellular manufacturing as a lean method of producing similar products using cells, or groups of team members, workstations, or equipment to facilitate operations by eliminating setup and unneeded costs among operations. A work cell is a work unit larger than an individual machine or workstation but smaller than the usual department. Typically, it has 3 12 people and 5 15 workstations in a compact arrangement.
272
Production Planning and Control
Cells might be designed for a specific process, part, or a complete product. They are favorable for single-piece and one-touch production methods and in the office or the factory. Because of increased speed and the minimal handling of materials, cells can result in great cost and time savings and reduced inventory. Cellular design often uses group technology, which studies a large number of components and separates them into groups with like characteristics, sometimes with a computer’s help, and which require the coding of classifications of parts and operations. Period batch control (PBC) is a production planning system that has been proposed for application within cellular manufacturing by grouping it into a certain number of stages and giving each stage the same amount of time to complete the required operations. Integration of the PBC system with cellular manufacturing would result in shorter and more reliable throughput times and lower inventory costs.
18.17.1 Advantages of cellular layout G G G G G
G
G G
Reduced material handling and transit time Reduced setup time Reduced work-in-process inventory Better use of human resources Self-managed team, in most cases more satisfied with the work that they do Flexible resource. Workers in each cell are multifunctional and can be assigned to different routes within a cell or between cells as demand. volume changes. Easier to control Easier to automate
18.17.2 Disadvantages of cellular layout G
G
G
Inadequate part families G Part families identified for design purposes may not be appropriate for manufacturing purposes. Poorly balanced cells G It is more difficult to balance the workflow through a cell than a single-product assembly line because items may follow different sequences through the cell that require different machines or processing times. Expanded training and scheduling of workers G Training workers to do different tasks is expensive and time consuming and requires the workers’ consent.
Plant layout Chapter | 18
273
FIGURE 18.5 Cellular layout. G
Increased capital investment G Existing equipment may be too large to fit into cells or may be underutilized when placed in a single cell. G Additional machines of the same type may have to be purchased for different cells. G The cost and downtime required to move machines can also be high (Fig. 18.5).
18.18 Flow pattern The manner in which the materials move in the production process inside a workshop is called the flow pattern, and it has an impact to a great extent in planning for the equipment location inside the department.
18.18.1 Straight line pattern The straight line pattern is normally used when products are produced in large quantities and the number of steps required for their production is few. Moreover, the shipping and receiving sections are on the opposite sides.
274
Production Planning and Control
18.18.2 U-shaped pattern U-shaped patterns are often used when it is necessary to keep the beginning (receiving) and end (shipping) of the line at the same side and same end of the plant. U-shaped patterns are also preferred in just-in-time layouts. Workers are generally placed in the center of the U. From there, they can monitor more than one machine at a time.
18.18.3 S-shaped pattern S-shaped patterns are used for long assembly processes that have to fit in the same area as well as when it is necessary to keep the receiving and shipping ends on the opposite sides.
18.18.4 W-shaped pattern W-shaped patterns, like the S-shaped pattern, are also used for long assembly processes, which have to fit in the same area. When it is also necessary to keep the receiving and shipping ends on the same side, the W-shaped pattern is preferred.
18.18.5 L-shaped pattern When the building shape is restricted to an L shape or if one portion of the department is restricted for some other use, then the flow of the material would be L-shaped, necessitating the machinery to be located as illustrated.
18.18.6 O-typed pattern When several assembly operations are to be performed on a rotary table, the material flow and consequently the work table layout would be circular. Sometimes even small machining operations like drilling on small components shall be done on a rotary table, as illustrated.
18.18.7 Vertical flow pattern When the production is done in two or more floors, it is called a vertical flow pattern as illustrated. In process industries, the flow is generally downward. However, in the case of light engineering industries like switchgear manufacturer, which is located in multistorey buildings for space economy and where the raw material is far heavier than the final product, the flow can also be upward, as is the case of L&T Swichgear Unit at Powai, Bombay. In some cases of production of nonstandard items on a smaller scale, the flow can also be zigzag.
276
Production Planning and Control
18.19 Roof shapes for industrial buildings The shape of roofs is mainly influenced by required strength, waterproof level, insulation, fire resistance, cost, durability, the climate, the materials available for roof structure, and low maintenance charges. Illustrated below are some of the roof types normally provided for industrial buildings.
18.19.1 Gable roof Gabled roof is a normal type of industrial roof with two sloping sides that come together at a ridge at the top, called a gable, creating end walls with a triangular extension. In view of the simplicity, they are the most common roofs for small and medium-sized industrial buildings, providing columnless width up to 80 ft.
18.19.2 V roof These are shed type buildings with simple roof structures on open frames. These buildings are used for workshop, warehouses, etc. These building provide large and clear areas unobstructed by the columns. When required, the industrial buildings are constructed with adequate headroom for the use of an overhead traveling crane.
18.19.3 Flat roof Flat roofs are found in traditional buildings in regions with low rainfall and snowfall. They are simple and most economical but unsuitable for a majority
Plant layout Chapter | 18
277
of regions with excessive rainfall or snowfall. In some cases, the flat roof is made up of two layers to provide skylights along the walls.
18.19.4 Inverted V roof Inverted V roof, also called butterfly roof, is not widely used even though it provides plenty of light and ventilation because is not effective when it comes to water drainage. They are also not ideal for areas with high winds because they easily can catch the wind, much as a sail would.
18.19.5 Sawtooth roof Saw-tooth roof is the most common roof, comprising a series of ridges with dual pitches on either side. The steeper surfaces are glazed and face away from the equator to shield workers and machinery from direct sunlight but at the same time they admit natural light.
18.19.6 Mono-pitched roof Mono-pitched roof is a saw-tooth roof with a single sawtooth, suitable for smaller factory buildings to get the advantage of good sunlight.
278
Production Planning and Control
18.20 Conclusion The successful performance of the PP&C department depends very much on the layout type adapted for the workplace, whether process layout or product layout. It is hence essential for us to appreciate fully the need to adapt the layout as per the size of the undertaking and the type of production situation, whether batch or mass production. While the flow patterns affect the PP&C function directly, the roof types are affected indirectly by the lighting factor.
Further reading 1. Eilon, S., 1962. Elements of Production Planning and Control. 2. Muther, R., 1984. Systematic Layout Planning, Cahners Books. 3. Muther, R., 2001. In: Maynard, H.B. (Ed.). Plant Layout in Section 8 of Industrial Engineering Handbook. 4. Spreigel, W., Landsburgh, R.H., 1947. Industrial Management. 5. Wild, R., 1995. Production and Operations Management. 6. Hyer, N.L., Wemmerlo¨v, U., 1984. Group technology and productivity. Hayward Bus. Rev. 7. https://en.wikipedia.org 8. https://en.wikipedia.org/wiki/Plant_layout_study 9. www.yourarticlelibrary.com 10. www.mbaofficial.com 11. www.1.coe.neu.edu 12. www.managementguru.net Criteria questions (The figures in the bracket provide a clue to the answer.) 1. What is the difference between plant location and plant layout? (18.1) 2. What factors contribute to the need for change of a layout? (18.2) 3. What is the influence of plant layout on PP&C? (18.7) 4. Distinguish between product and process layouts. (18.12) 5. What is group technology? How does it help PP&C? (18.16) 6. What is cellular layout? How does it differ from product layout? (18.17) 7. Illustrate some of the flow patterns normally found in a plant. (18.18) 8. Distinguish between gabled roof and sawtooth roof. (18.19)
Plant layout Chapter takeaways After completion of this chapter the reader would be able to 1. Appreciate the influence of plant layout on the successful performance of the production planning and control department and the rules and guidelines for a successful layout. 2. Understand the types and modalities of the layout to choose the one that best suits the production line. 3. Understand the different flow patterns that can be adapted to production lines to suit your existing building parameters and the space required for your production. 4. Appreciate the benefits of group layout and cellular layout to plan for the production where needed and possible.
18.1 Introduction Plant layout, also known as facilities planning and layout, deals with the orderly and proper arrangement of manufacturing facilities and the use of available resources, including men, money, machines, tools, materials, and methods of production inside the factory. In effect, plant layout is the allocation of space and the arrangement of equipment in such a manner that overall operational cost can be minimized. A well-designed plant layout is concerned with maximum and effective utilization of available resources at minimum operating costs. Smooth and quick material flow is the essence an ideal manufacturing facility. A systematic planning of the layout allows integration of all movements in a logical overall pattern. There are four categories of facilities planning and layout discussed in detail in this chapter: 1. 2. 3. 4.
New facility construction New design in an existing facility Redesign of a restricted or limited area Adding a machine in an existing facility
Production Planning and Control. DOI: https://doi.org/10.1016/B978-0-12-818364-9.00018-4 Copyright © 2019 BSP Books Pvt. Ltd. Published by Elsevier Inc. All rights reserved.
261
262
Production Planning and Control
18.2 Factors contributing to the necessity for layout changes 1. Due to design and market changes a. Changes in the design of the product b. Addition of new products or deletion of old models or methods c. Changes in the volume of market, generally resulting in expansion of all departments d. Adding new departments like centralizing of drilling machines, which were earlier distributed over several production sections e. Moving a department either within the site or to a new geographical location f. Replacing obsolete equipment g. Changes in market location 2. Due to increased production problems and/or bottlenecks a. Frequent failure to meet the delivery commitments or production schedules b. Frequent production bottlenecks due to nonreceipt of work in progress from the previous shops c. High idle time and low machine utilization d. Frequent accidents e. Increased rejections and scrap f. Insufficient storage area leading to congestion in stores and aisles g. Unsuitability of the existing layout for required material handling equipment h. Shortage of material handling equipment, leading to the necessity of readjusting the layout to suit the available equipment. i. Increased maintenance activities on the buildings and equipment. j. Cost reduction studies initiated either by suggestion schemes or other industrial engineering studies k. Utilization of available vertical space 3. Labor relation oriented changes a. Frequent complaints on working conditions b. Frequent requests for additional equipment c. Provision of additional employee facilities d. Sudden increase in absenteeism and high labor turnover e. Increased difficulty in finding suitable employees
18.3 Definitions on plant layout Plant layout is a mechanism which involves knowledge of the space requirements for the facilities and also involves their proper arrangement so that continuous and steady movement of the production cycle takes place. http://www.mbaofficial.com
Plant layout Chapter | 18
263
A plant layout study is an engineering study used to analyze different physical configurations for a manufacturing plant. https://en.wikipedia.org Plant layout embraces the physical arrangement of industrial facilities. This arrangement, either installed or in plan, includes the space needed for material movement, storage, indirect labour and all other supporting activities or services, as well as for office equipment and personnel. Richard Muther Plant layout is the arrangement of machines, work areas and service areas within a factory. George R. Terry Plant layout involves the development of physical relationship among building, equipment and production operations, which will enable the manufacturing process to be carried on efficiently. Morris E. Hurley Plant layout is an arrangement of machines and facilities is layout. F.G. Moore. Plant layout can be defined as a technique of locating machines, processes and plant services within the factory so as to achieve the greatest possible output of high quality at the lowest possible total cost of manufacturing. Spreigel and Lansburgh Plant layout ideally involves the planning and integrating the paths of the component parts of a product to achieve the most effective and economic interrelationships between the operating equipment and personnel, the material movement, storage facilities, service functions and auxiliary equipment. J. Lundy
18.4 Objectives of plant layout 1. To achieve economies in handling of raw materials, work-in-progress, and finished goods. 2. To reduce the quantum of work-in-progress. 3. To have the most effective and optimum utilization of available floor space. 4. To minimize bottlenecks and obstacles in various production processes, thereby avoiding the accumulation of work at important points. 5. To introduce a system of production control.
264
6. 7. 8. 9. 10. 11. 12.
Production Planning and Control
To To To To To To To
ensure means of safety and provision of amenities to the workers. provide better quality products at lesser costs to the consumers. ensure loyalty of workers and improve their morale. minimize the possibility of accidents. provide for adequate storage and packing facilities. work out possibilities of future expansion of the plant. provide such a layout that permits meeting of competitive costs.
18.5 General rules and objectives of successful plant layout 1. Arrange the layout to enable a smooth and efficient production process. 2. Make the arrangement sufficiently flexible to allow production and equipment changes to be made with minimal disruption. 3. Allow adequate but not too much space for the plant and equipment with efficient utilization of the space. 4. Provide for the efficient utilization of the vertical space with easily accessible racks. Plan for effective handling of equipment in the stores. 5. Plan for prompt movement of the work-in-progress, thereby reducing the production time, shop inventories, with better utilization of the capital. 6. Aim for a high level of equipment utilization, especially in new layouts. 7. Utilize the manpower efficiently by reducing the walking distances and eliminating uneconomical manual handling operations. 8. Provide for safe working conditions in equipment operation. 9. Integrate the new facilities with the existing plant as closely as possible. 10. Ensure efficient supervision to achieve all the these objectives.
18.6 Richard Muther’s guidelines for successful systematic layout planning Richard Muther, the father of systematic layout planning, developed a systematic procedure as elaborated in detail in his book Systematic Layout Planning. This is illustrated in detail in this chapter.
18.7 Influence of plant layout 18.7.1 Production planning and control Samuel Eilon, in his book Elements of Production Planning and Control, specifies the following effects of plant layout on various aspects of production planning and control (PP&C): 1. The layout determines the location of departments and production centers, and their proximity to each other and to other services. It enables efficient utilization of the available space.
Plant layout Chapter | 18
265
2. It outlines the nature of flow in the plant and affects the distance traveled by materials and personnel, and thereby the time, effort, and costs spent on material movement. 3. It affects the types of handling systems, their integration in the overall production program, and the costs of their installation. 4. It specifies the location, accessibility, and size of the stores and also the space and location of temporary storage space for work in progress. 5. It affects the amount of work in progress and work awaiting further processing, thereby involving the total time and the capital tied up in work in progress. 6. Machine utilization is partly decided by the layout. This is reflected in the output per machine hour, the total required machine capacity, and in the capital tied up in equipment. 7. Operator’s span of activities, responsibilities, auxiliary tasks, walking time, fatigue, and efficiency may be dictated by the layout considerations. 8. Maintenance procedures, schedules, and costs as well as policy of repairs, reserves, and replacements may be affected. 9. The amount of supervision required and the degree of specialization necessary in supervision are sometimes dependent on the layout. 10. PP&C may be greatly affected, particularly the complexity of routing, machine loading, scheduling, expediting, and the paperwork involved in control mechanisms. 11. The effect on time lag between inspection and corrective actions is to be studied, and this may be reflected in the amount of rejected work.
18.8 Symptoms of poor plant layout 1. 2. 3. 4. 5. 6.
Excessive handling cost. Excessive work-in-progress inventories. Excessive idle time for men and equipment. Excessive downtime and maintenance cost. Increase in the frequency of accidents. Excessive damages due to mishandling.
18.9 Benefits of plant layout The benefits of optimal plant layout are achievement of the preceding objectives, which can be summarized as congestion reduction. 1. 2. 3. 4.
Elimination of unnecessary occupied areas. Reduction of administrative and indirect work. Improvement on control and supervision. Better adjustment to changing conditions.
266
5. 6. 7. 8. 9. 10.
Production Planning and Control
Better utilization of the workforce, equipment, and services. Reduction of material handling activities and stock in process. Reduction on parts and quality risks. Reduction on health risks and increase on workers safety. Morale and workers’ satisfaction increase. Reduction of delays and manufacturing time, as well as increase in production capacity.
Once the departments are laid out as detailed here and by systematic layout planning as detailed in this chapter, the next phase would be to arrange the machinery inside each designation area.
18.10 Types of plant layout There can be four possible types of arrangement of machinery: 1. 2. 3. 4.
Fixed-position layout Process layout Product layout Combination type layout
18.11 Fixed-position layout Fixed-position layout is adapted only in case of large products like boilers, power plant generators, atomic reactors, airplanes, and ships. The major component remains in a fixed location while other materials, parts, tools, machinery, manpower, and other supporting equipment are brought to this location. It follows the principle that it is economical and convenient to bring the necessary tools and equipment to the workplace along with the manpower because the product is too heavy or too big, as in shipbuilding or airplane assembly. Sometimes the major component or body of a final product, like the shell of a train coach, is manufactured in a fixed location, as at the Chennai Integral Coach Factory.
18.11.1 Advantages of fixed-position layout 1. Material movement is reduced. 2. Capital investment is minimized. 3. Continuity of operations is ensured because operators perform their tasks independent of others. 4. This facilitates effective planning and loading since each production center is independent of each other. When two ships are simultaneously produced, each is located at its own fixed position. 5. Thus total production cost will be reduced. 6. It offers greater flexibility and allows change in product design, product mix, and production volume.
Plant layout Chapter | 18
267
18.11.2 Disadvantages of fixed-position layout 1. Highly skilled manpower is required. 2. Movement of machines and other equipment to production center may be time consuming. 3. Complicated fixtures may be required for positioning of jobs and tools. This may increase the cost of production.
18.12 Process or functional layout In process layout, the production facilities are grouped according to their types by the nature or type of operations they can perform, like the machine shop, the press shop, painting shop, welding shop, etc., regardless of which products each workstation is working on. This layout is adapted for low volume and/or nonrepetitive production of standard products and components. Even in a machine shop, all the lathes can be grouped together and the drilling machines can be grouped together, etc. (Fig. 18.1).
18.12.1 Advantages of process layout 1. The total investment on equipment purchase is less because the same machine can work on different products and so the duplication of machines will be less. 2. It enables better and more efficient supervision through specialization on specific machinery at various levels. 3. There is greater flexibility in equipment and manpower and thus load distribution is easily controlled. 4. Better utilization of equipment allows individual processes to function more efficiently by pooling resources. 5. Breakdown of equipment can be easily handled by transferring work to another machine/workstation. 6. There will be better control of complicated or precision processes, especially where much inspection is required.
FIGURE 18.1 Process layout.
268
Production Planning and Control
18.12.2 Disadvantage of process layout 1. There are long material flow lines and hence expensive handling is required. 2. Total production cycle time is increased, owing to long distances and waiting at various points. 3. Since more work is in queue and waiting for further operation, bottlenecks occur. 4. Generally, more floor area is required. 5. Since work does not flow through definite lines, counting and scheduling are tedious. 6. Specialization creates monotony, and it will be difficult for laid-off workers to find job in other industries.
18.13 Product or line layout The product layout groups different workstations together according to the operation sequence of the products they work on. This layout is adapted for high volume, highly standardized, and repetitive production of products and components. The raw material is supplied at one end of the line and goes from one operation to the next quite rapidly with a minimum work-inprocess, storage, and material handling. Generally, only one product of one type of products is produced in the line at a time.
18.13.1 Advantages of product layout 1. 2. 3. 4.
Lower total material handling cost. Less work in processes. Better utilization of men and machines. Less floor area occupied by material in transit and for temporary storages. 5. Greater simplicity of production control. 6. Total production time is also minimized.
18.13.2 Disadvantages of product layout 1. No flexibility, which is generally required, is obtained in this layout. 2. The manufacturing cost increases with a fall in production volume. 3. If one or two lines are running light, there is a considerable machine idleness. 4. A single machine breakdown may shut down the whole production line. 5. Specialized and strict supervision is essential. 6. Product layouts require more space than process layouts, since tools and equipment cannot be shared as easily between workers performing the same tasks on different products (Fig. 18.2).
Plant layout Chapter | 18
269
FIGURE 18.2 Product layout.
18.14 Comparison between product and process layout See Table 18.1.
TABLE 18.1 Comparison between product and process layout. S. no.
Criterion
Product layout
Process layout
1
Investment
Heavy investment needed
Low investment needed
2
Duration of production
Less manufacturing times as the flow is well set and planned
Frequent changes of men and material increases production time
3
Floor space
Use of special purpose machines can reduce the space
Requires more space
4
Material handling
Less amount of material handling
Involves greater handling of material requiring more time, money, and efforts
5
Effect of breakdowns
Breakdown of any unit/ component immobilizes the whole system
If one machine breaks down, other similar machines can be used
6
Quality control
Specialized and expertise control is possible
Comparatively lesser efforts on control
7
Flexibility
Inflexible as each machine can perform predesigned operation only
Flexible as the operation can be performed elsewhere
8
Demand and supply relationship
Better balancing between demand and as these are made to stock
Balancing between demand and supply is difficult as these are made to order
270
Production Planning and Control
18.15 Combination layout A majority of medium-scale industries work on the production of several products that need a process layout, though some of them are produced in large volume, for which the product layout is preferable. In such cases, a combination layout is adapted. The majority of the machines are laid out per the process layout, but some special purpose machines are positioned along the product flow as a compromise of the previously mentioned layouts, taking the benefits of each of them.
18.16 Group technology Wikipedia defines group technology as a manufacturing technique in which parts having similarities in geometry, manufacturing process, and/or functions are manufactured in one location using a small number of machines or processes. Nancy L. Hyer and Urban Wemmerlo¨v in their article “Group Technology and Productivity” in the July 1984 edition of Hayward Business Review have elaborated the benefits of group technology and how it has revolutionized productivity improvement practices. This concept involves machining components that have similar dimensional parameters and characteristics. A factory unit may be producing several models of similar products in which the components (such as axles) would look similar but vary slightly in the dimensional parameters, like the outside diameters or bores or other turning requirements in which operations can be done on the same machine but with slightly different tool settings. Such components are grouped together, and the equipment layout is planned in such a way that all these components can be operated on these machines with slight changes in tool settings, thereby eliminating the traditional schedule changeovers. Fig. 18.3 illustrates machined components that are
FIGURE 18.3 Components for group technology.
Plant layout Chapter | 18
271
FIGURE 18.4 Group layout. Source: HBR Journal of 1984.
dimensionally different and used in entirely different sets of products manufactured by the company. This technique is called group technology, and the type of layout to accommodate such machinery is called the group layout (Fig. 18.4).
18.16.1 Advantages of group layout 1. Increased throughput as the components are completely machined in one group where the machines are grouped together and under the control of a single supervisor 2. Reduced handling 3. Reduced inventories and reduced investment 4. Reduced scrap and improved quality 5. More reliable delivery time 6. Reduced investment in equipment, since more than one component flows through the product layout. 7. Reduced tool setting cost and thereby improving machine unitization. 8. Reduced direct and indirect labour 9. Increased job satisfaction 10. It results on reduction of component varieties, since this gives more opportunities for standardization.
18.17 Cellular layout Cellular manufacturing is based on the principles of group technology proposed by Flanders in 1925 and integrates just-in-time manufacturing and lean manufacturing techniques. Business Dictionary defines cellular manufacturing as a lean method of producing similar products using cells, or groups of team members, workstations, or equipment to facilitate operations by eliminating setup and unneeded costs among operations. A work cell is a work unit larger than an individual machine or workstation but smaller than the usual department. Typically, it has 3 12 people and 5 15 workstations in a compact arrangement.
272
Production Planning and Control
Cells might be designed for a specific process, part, or a complete product. They are favorable for single-piece and one-touch production methods and in the office or the factory. Because of increased speed and the minimal handling of materials, cells can result in great cost and time savings and reduced inventory. Cellular design often uses group technology, which studies a large number of components and separates them into groups with like characteristics, sometimes with a computer’s help, and which require the coding of classifications of parts and operations. Period batch control (PBC) is a production planning system that has been proposed for application within cellular manufacturing by grouping it into a certain number of stages and giving each stage the same amount of time to complete the required operations. Integration of the PBC system with cellular manufacturing would result in shorter and more reliable throughput times and lower inventory costs.
18.17.1 Advantages of cellular layout G G G G G
G
G G
Reduced material handling and transit time Reduced setup time Reduced work-in-process inventory Better use of human resources Self-managed team, in most cases more satisfied with the work that they do Flexible resource. Workers in each cell are multifunctional and can be assigned to different routes within a cell or between cells as demand. volume changes. Easier to control Easier to automate
18.17.2 Disadvantages of cellular layout G
G
G
Inadequate part families G Part families identified for design purposes may not be appropriate for manufacturing purposes. Poorly balanced cells G It is more difficult to balance the workflow through a cell than a single-product assembly line because items may follow different sequences through the cell that require different machines or processing times. Expanded training and scheduling of workers G Training workers to do different tasks is expensive and time consuming and requires the workers’ consent.
Plant layout Chapter | 18
273
FIGURE 18.5 Cellular layout. G
Increased capital investment G Existing equipment may be too large to fit into cells or may be underutilized when placed in a single cell. G Additional machines of the same type may have to be purchased for different cells. G The cost and downtime required to move machines can also be high (Fig. 18.5).
18.18 Flow pattern The manner in which the materials move in the production process inside a workshop is called the flow pattern, and it has an impact to a great extent in planning for the equipment location inside the department.
18.18.1 Straight line pattern The straight line pattern is normally used when products are produced in large quantities and the number of steps required for their production is few. Moreover, the shipping and receiving sections are on the opposite sides.
274
Production Planning and Control
18.18.2 U-shaped pattern U-shaped patterns are often used when it is necessary to keep the beginning (receiving) and end (shipping) of the line at the same side and same end of the plant. U-shaped patterns are also preferred in just-in-time layouts. Workers are generally placed in the center of the U. From there, they can monitor more than one machine at a time.
18.18.3 S-shaped pattern S-shaped patterns are used for long assembly processes that have to fit in the same area as well as when it is necessary to keep the receiving and shipping ends on the opposite sides.
18.18.4 W-shaped pattern W-shaped patterns, like the S-shaped pattern, are also used for long assembly processes, which have to fit in the same area. When it is also necessary to keep the receiving and shipping ends on the same side, the W-shaped pattern is preferred.
18.18.5 L-shaped pattern When the building shape is restricted to an L shape or if one portion of the department is restricted for some other use, then the flow of the material would be L-shaped, necessitating the machinery to be located as illustrated.
18.18.6 O-typed pattern When several assembly operations are to be performed on a rotary table, the material flow and consequently the work table layout would be circular. Sometimes even small machining operations like drilling on small components shall be done on a rotary table, as illustrated.
18.18.7 Vertical flow pattern When the production is done in two or more floors, it is called a vertical flow pattern as illustrated. In process industries, the flow is generally downward. However, in the case of light engineering industries like switchgear manufacturer, which is located in multistorey buildings for space economy and where the raw material is far heavier than the final product, the flow can also be upward, as is the case of L&T Swichgear Unit at Powai, Bombay. In some cases of production of nonstandard items on a smaller scale, the flow can also be zigzag.
276
Production Planning and Control
18.19 Roof shapes for industrial buildings The shape of roofs is mainly influenced by required strength, waterproof level, insulation, fire resistance, cost, durability, the climate, the materials available for roof structure, and low maintenance charges. Illustrated below are some of the roof types normally provided for industrial buildings.
18.19.1 Gable roof Gabled roof is a normal type of industrial roof with two sloping sides that come together at a ridge at the top, called a gable, creating end walls with a triangular extension. In view of the simplicity, they are the most common roofs for small and medium-sized industrial buildings, providing columnless width up to 80 ft.
18.19.2 V roof These are shed type buildings with simple roof structures on open frames. These buildings are used for workshop, warehouses, etc. These building provide large and clear areas unobstructed by the columns. When required, the industrial buildings are constructed with adequate headroom for the use of an overhead traveling crane.
18.19.3 Flat roof Flat roofs are found in traditional buildings in regions with low rainfall and snowfall. They are simple and most economical but unsuitable for a majority
Plant layout Chapter | 18
277
of regions with excessive rainfall or snowfall. In some cases, the flat roof is made up of two layers to provide skylights along the walls.
18.19.4 Inverted V roof Inverted V roof, also called butterfly roof, is not widely used even though it provides plenty of light and ventilation because is not effective when it comes to water drainage. They are also not ideal for areas with high winds because they easily can catch the wind, much as a sail would.
18.19.5 Sawtooth roof Saw-tooth roof is the most common roof, comprising a series of ridges with dual pitches on either side. The steeper surfaces are glazed and face away from the equator to shield workers and machinery from direct sunlight but at the same time they admit natural light.
18.19.6 Mono-pitched roof Mono-pitched roof is a saw-tooth roof with a single sawtooth, suitable for smaller factory buildings to get the advantage of good sunlight.
278
Production Planning and Control
18.20 Conclusion The successful performance of the PP&C department depends very much on the layout type adapted for the workplace, whether process layout or product layout. It is hence essential for us to appreciate fully the need to adapt the layout as per the size of the undertaking and the type of production situation, whether batch or mass production. While the flow patterns affect the PP&C function directly, the roof types are affected indirectly by the lighting factor.
Further reading 1. Eilon, S., 1962. Elements of Production Planning and Control. 2. Muther, R., 1984. Systematic Layout Planning, Cahners Books. 3. Muther, R., 2001. In: Maynard, H.B. (Ed.). Plant Layout in Section 8 of Industrial Engineering Handbook. 4. Spreigel, W., Landsburgh, R.H., 1947. Industrial Management. 5. Wild, R., 1995. Production and Operations Management. 6. Hyer, N.L., Wemmerlo¨v, U., 1984. Group technology and productivity. Hayward Bus. Rev. 7. https://en.wikipedia.org 8. https://en.wikipedia.org/wiki/Plant_layout_study 9. www.yourarticlelibrary.com 10. www.mbaofficial.com 11. www.1.coe.neu.edu 12. www.managementguru.net Criteria questions (The figures in the bracket provide a clue to the answer.) 1. What is the difference between plant location and plant layout? (18.1) 2. What factors contribute to the need for change of a layout? (18.2) 3. What is the influence of plant layout on PP&C? (18.7) 4. Distinguish between product and process layouts. (18.12) 5. What is group technology? How does it help PP&C? (18.16) 6. What is cellular layout? How does it differ from product layout? (18.17) 7. Illustrate some of the flow patterns normally found in a plant. (18.18) 8. Distinguish between gabled roof and sawtooth roof. (18.19)