CHAPTER 1 INTRODUCTION

Transcription

1 1 CHAPTER 1 INTRODUCTION 1.1 FACILITY LAYOUT DESIGN Layout design is nothing but the systematic arrangement of physical facilities such as production machines, equipments, tools, furniture etc. A plant layout is the best placement of physical facilities which provide an efficient operation. The improved layout affects the cost of material handling, time and throughput. Hence it affects the overall productivity and efficiency of the plant (Hassan 1994). An effective and efficient layout design improves the efficiency of material handling system and reduces total manufacturing cost and time. It improves the effectiveness of space utilization of the system and considers the area of layout, area of production equipments, number of columns, number of rows, dimension of pathway, material movements, types of material handling system, volume of the products, operation sequence, product mix and safety of users. Moreover it ensures smooth and steady flow of production, equipment and work force at a low cost. Besides reducing material handling cost, inventory cost and labour cost, it also improves the effective utilization of equipments and other resources and increases the productivity and efficiency of the plant. The key to good facility layout and design is the integration of people, materials and machinery. The facility layout problem, otherwise called block layout, considers the assignment of facilities to locations so that the quantitative/qualitative objective of the problem is minimized or maximized

2 2 as the case may be, under various constraints. There are two types of objectives for facility layout problem (FLP) (Meller & Gau 1996). The first one is the quantitative objective aiming at minimizing the total material handling cost between departments based on a distance function. The second one is the qualitative goal, aimed at maximizing the closeness relationship scores between departments based on the placement of departments that utilize common materials, personnel, or utilities adjacent to one another, while separating departments for reasons of safety, noise, or cleanliness. 1.2 STATIC AND DYNAMIC FACILITY LAYOUT PROBLEMS Facility layout problems are divided into two categories, static facility layout problem (SFLP) and dynamic facility layout problem (DFLP). The static facility layout problem is the determination of the physical arrangement of production equipments within a facility. The static facility layout problem approach is defined as flow of materials between the work centers, demand of the product and product mix are fixed during the planning horizon. When the flows of material between work centers change during the planning horizon, this problem is known as the dynamic facility layout problem. Nowadays researchers are focused on static facility layout problem. To meet out competition in the global market, facility layout must react to the changes in designs, processes, quantities, scheduling, organizations, and management ideas quickly. Once the changes are made, the manufacturing system needs rearrangement of facilities and their structure must be modified. However, SFLP alone cannot meet this change. Based on the market needs, the plant has to adopt a flexible layout which is able to modify and expand easily the original layout. Flexibility can be reached with modular devices, general-purpose devices and material handling devices. In this critical situation, SFLP needs to add flexibility to meet the production requirement.

3 3 Modification and increase in the robustness of the SFLP are the approaches to get flexibility. Gradually, SFLP develops these two approaches to the dynamic facility layout problem (DFLP) and robust layout, respectively. If there is a long-time material handling flow, DFLP or robust layout is suitable. Otherwise, SFLP is better. If rearrangement is easy when the production requirement changes drastically, DFLP is suitable. If not, choose robust layout (Suo & Liu, 2008). 1.3 CHARACTERISTICS IMPACTING THE LAYOUT In the literature different factors are taken in to accounts in order to emphasize the characteristics layout problems. In general, the layout problems addressed in research works differ, depending on characteristics like manufacturing systems, the facility shapes, layout configuration, flow movements, the layout evolution problems like problem formulation, objectives and constraints addressed and the approaches that are the research methodologies used to solve them. The tree illustration of the layout problem is shown in Figure 1.1. This tree illustration shows how thesis research work is organized in accordance with the most important features identified.

4 4 Product layout Process layout Manufacturing Systems Fixed Position Cellular layout Hybrid layout Facility Shapes Layout Config n FMS layout Regular shape Irregular shape Single row Multi row Loop layout Backtracking Fixed Dimension Aspect ratio U-shape Linear Semicircular Facility Layout Problems Bypassing Flow movement Layout Evaluation Mini moment value Mini traveling distance Static Layout Dynamic Layout Objectives Mini handling cost Constraints Maxi layout moment ratio Mini backtracking moves Area Constraints Space allocation Facility location Research Methodologies Metaheuristics Genetic Algorithm Simulated Annealing Artificial Bee Colony Particle Swarm Optim Figure 1.1 Tree illustration of the layout problem The selection of the problem is based on the many factors and design issues like the variety and volume of the production, type of the material handling system, different flows of products, layout configurations,

5 5 shapes of the facility, objective functions and other constraints. These important factors are detailed below: Variety and Volume of Production The layout design generally depends on the products variety and the production volumes. There are six general types of layouts used in any manufacturing organization, namely Product layout, Process layout, Fixed position layout, Cellular layout, Hybrid or Combined layout and Flexible Manufacturing System (FMS) layout Product layout The product layout is also known as Flow line layout, Line layout, Production line layout, Assembly line layout and Layout by product. The production machines or workstations are arranged in a line based on the sequence of operations required for the manufacturing of the product. It is known as product layout. Figure 1.2 depicts a product layout: Raw material Turning Milling Drilling Grinding Assembly Finished product Figure 1.2 Product layout If a product requires a lathe, drilling, milling, shaping, grinding, assembly equipment and finishing equipments in sequence, then the lathe machines, milling machines, shaping machines, grinding machines, assembly equipments and finishing equipments must be arranged one after another in a straight line. If a single or a few items are to be produced in large quantities in a production plant then this system is used.

6 6 The Product layout has the following advantages. There are fewer inventories, minimum material handling time and cost, reduced processing time, less work in process, low unit cost, small working space, less inspection, fewer delays, less skill set, simple, smooth and effective supervision and control. The disadvantages of the product type layout are lack of flexibility, high investment on equipment, machine stoppage stops the line, slowest station and poor machine utilization Product layout The process layout is also known as Functional layout, Job shop layout and Layout by process. In this type, similar machines or workstations are arranged together at one place based on the process they perform. Figure 1.3 shows the arrangement of machines in a process layout. Turning Milling Shaping Drilling Grinding Assembly & Testing Figure 1.3 Process layout Here all types of turning machines are placed together in one unit. All milling machines are placed together in another unit, and so on. It is useful for a manufacturer involved in a variety of products or items in small

7 7 quantities. It is more suitable for batch production of non-standardized or dissimilar products. The advantages of the process layout are: Greater flexibility, good incentives to workers, low investment, better utilization of machinery and multiple product and process designs. The disadvantages of process layout are: reduced productivity, higher material handling costs, long production lines, complexity in planning and control, critical delays and difficult routing and scheduling Fixed position layout In a fixed position layout, the movement of workers to the product site and machines remain stationary. The other names of fixed position layout include Location layout and Static layout. Figure 1.4 shows a typical fixed position layout. Transport Supplier Project site Human resources Power Materials fefwef Figure 1.4 Fixed position layout

8 8 It is preferred only when the manufactured or processed product is bulky and heavy in size. It cannot be easily transported. Examples are shipbuilding and repair, aircraft manufacturing and servicing, construction of locomotives, boilers, generators, wagons, roads, dams, houses, and automobile manufacturing processes. The fixed position layout has the following advantages. They are less prone to damage, have reduced transport cost, small investment on layouts, higher adjustments and greater flexibility and facilitate changes in product design, product mix, and production volume. The disadvantages of the fixed position layout are listed below: minimum utilization of equipments, increased cost of moving equipments, requirement of more space, higher work-in-process, requirement of skilled personnel, close control and coordination in production and personnel scheduling Cellular layout The combination of process and product type layout is known as cellular layout. It is shown in Figure 1.5 and it works on the principle of Group Technology (GT). So it is also known as Group Technology layout. The principle of GT is to divide the manufacturing facility into small groups or cells of machines (Dilworth 1996).

9 9 lathe drill mill drill inspect pack inspect bore grind Figure 1.5 Cellular layout Each of these cells is dedicated to a specific family or set of part types. Cellular manufacturing is the grouping of the production equipments into machine cells where each machine cell specializes in the production of a particular part family. GT is a manufacturing philosophy in which similar parts are identified and grouped together to take the advantage of their similarities in design and production. Similar parts are arranged into part families, where each part family possesses similar design and/or manufacturing attributes. A part family is a collection of parts that are similar either in geometric shape and size or in the processing steps required in their manufacturing (Mikell 2009). Fixed area cellular layout problems are families of design problems involving the placement or allocation of work centre, which are given a fixed area. The work centre is placed optimally with shorter travelling distance of products (Reis & Anderson 1960). This type of the machine layout is affected by a number of factors like the number of machines, availability of floor space, part sequences and the material handling systems (Hassan 1995). The type of material handling equipment plays an important role in the design and operation of a modern manufacturing facility. It determines the travel time and affects the throughput and the flexibility of the Flexible Manufacturing System (FMS).

10 10 The cellular type layout has the following advantages: High utilization of machineries, less travelling distance, smooth flow of materials, benefits of both product and process type of layout and importance of general purpose equipment. The disadvantages of cellular layout are: requirement of more skill, flow balance and the other demerits of product and process type of layout Hybrid layout A combination of any two or more layouts like product layout, process layout, fixed area layout, and cellular layout is called hybrid layout or combined layout. Many companies do not adopt a single type of layout. For example, a company uses a combination of cellular layout in manufacturing sections, process layout in finishing departments, and product layout in assembly shops. Figure 1.6 describes a hybrid layout: Product layout Raw materials LM MM DM GM Finished products Process layout LM VM DM GM HM Figure 1.6 Hybrid layout

11 11 following Table 1.1 The comparison of various types of layouts are given in the Table 1.1 Comparison of various types of layouts Product Layout Suitable for mass production Material handling cost is low Lesser manufacturing time and cost Lesser work-inprogress Optimum use of floor space Lesser labour cost Effective production control Lesser flexibility Large investment Under utilization of machines Lack of supervision Unskilled employees Large production quantity Car assembly plant Process layout Suitable for bath production Material handling cost is high Higher production time and cost Higher work-inprogress Covers more floor space Higher labour cost Difficult in production control Greater flexibility Lower investment Maximum utilization of machines Effective supervision Skilled employee Small production quantity Hospitals Fixed position layout Suitable for heavy machinery industry Saves the transforming costs Higher production period and ost Higher work-inprogress More space required Higher labour cost Moderate control Maximum flexibility Heavy investment Moderate utilization of facilities Required close control Skilled personnel Single product production Heavy machineries industry Cellular layout Suitable for small to medium batch Less material handling Faster processing time and less cost Less work in process inventory Less space required Higher labour cost Effective production control Higher flexibility Lesser investment High utilization of facilities Effective supervision Multi-skilled employee Moderate production quantity Air craft manufacturing

12 LOAD UNLOAD Flexible Manufacturing System (FMS) layout Figure 1.7 shows an FMS layout that consists of a group of processing work stations interconnected by means of an automated material handling and storage system and it is controlled by an integrated computer control system. It has the capability of processing a variety of different parts and quantities of production and producing large volumes of product at a lower cost. But it is very inflexible in terms of the product types that can be produced. dee Computer Control Room M4 M3 Semi-finished products M5 M6 M2 M1 Raw material Finished product Conveyor M7 M8 Raw material Finished product Figure 1.7 Flexible manufacturing system layout

13 13 The advantages of Flexible Manufacturing Systems are: reduced processing time, better utilization of manpower, improved quality, increased productivity, improved efficiency, reduced set up time, production of a variety of parts, serving a variety of vendors at the same time and production of more product with less time Facility Shapes and Dimensions There are two different facility shapes generally used in the manufacturing industry. They are Regular (generally rectangular) shape (Kim & Kim, 2000) and Irregular (generally polygons containing at least a 270 angle) shape (Lee & Kim, 2000). Figures 1.8, 1.9 show the Regular and Irregular shape layouts respectively. Figure 1.8 Regular shape Figure 1.9 Irregular shape Facility dimension is classified into two types: those with fixed length and a fixed width and those defined by the area (Chwif et al, 1998).

14 Material Handling Systems A material handling system is used to handle the material at appropriate locations. It can be belt conveyors, wheel conveyors, roller conveyors, road guided vehicle, automated guided vehicles, robots, etc. Tompkins et al (1996) estimated that 20 50% of the manufacturing costs are due to the handling of parts and so a good arrangement of handling devices might reduce them by 10 30%. There are two problems in selecting the material handling systems. The two dependent design problems are: finding the facility layout and selecting the handling equipment. Based on the type of material handling system, single row layout, multi-rows layout, loop layout and open-field layout are used Single row layout The single row layout includes linear (Figure 1.10), U-Shaped (Figure 1.11) and semi-circular shapes (Figure 1.12). It is commonly used in Group Technology cells, Just-In-Time (JIT) implemented facilities and FMS. Figure 1.10 Linear layout In the linear layout, there may exist bypassing and backtracking. Backtracking is the movement of some parts from a machine to another

15 15 machine that precedes it in the sequence of placed machines in a flow line arrangement. Bypassing occurs when a part skips some machines while it is moving towards the end of a flow line arrangement. M3 M2 M1 M4 M5 M6 M7 Figure 1.11 U-Shaped layout M3 M4 M2 M5 M1 M6 Figure 1.12 Semi circular layout The material flow are moving along the sequence of operations of all the parts; small material handling cost and time, less delays and better control of operations and the ability to use conveyors are the advantages of single row layout Multi-row layout Normally multi-row layouts are suitable for FMS. Adjacent lines share common equipments. Low investment, small space area, and high machine utilization rate are its other advantages. The limitations of this layout

16 16 are complicated process management and coordinating multi-tasking. Figure 1.13 shows a multi-row layout: M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14 M Loop layout Figure 1.13 Multi-row layout Loop layouts are used in FMS. It has high flexibility in material handling system. Figure 1.14 describes a loop layout arrangement. M 3 M 2 M 1 M 5 M 6 M 7 Figure 1.14 Loop layout

17 Flow of Materials In the facilities layout, the decision regarding placement of the machines is typically made. Depending on the application and availability of space, the machines are placed in one of the following pattern (Tompkins 2010). A pictorial representation of the flow patterns is given in Figure Figure 1.15 Flow patterns In the above Figure, lines 1 and 4 show the Straight line pattern. Lines 1, 3 and 4 or 1, 2 and 4 represent the U-Shaped pattern. Lines 1, 5, 6 and 4 depict the S-Shaped pattern. Lines 2, 7, 6 and 3 or 2, 5, 8 and 3 show the W-Shaped pattern 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 a few. Moreover, the shipping and receiving sections are on the opposite sides. Figure 1.16 shows the arrangement of machines in a straight line pattern.

18 18 M1 M2 M3 M U-Shaped pattern Figure 1.16 Straight line pattern U-Shaped patterns are often used when it is necessary to keep the beginning (receiving) and end (shipping) of the line on the same side and the same end of the plant. U-Shaped patterns are also preferred in just-in-time layouts. Workers are generally placed at the centre of the U-Shape. From there they can monitor more than one machine at a time. A typical U-Shaped pattern is shown in Figure M1 M2 M3 M4 M5 M9 M8 M7 M S-Shaped pattern Figure 1.17 U-Shaped pattern S-Shaped patterns are used for long assembly processes that have to fit in the same area and also when it is necessary to keep the receiving and shipping ends on the opposite sides. Figure 1.18 illustrates S-Shaped pattern:

19 19 M3 M2 M1 M6 M5 M W-Shaped pattern Figure 1.18 S-Shaped pattern W-Shaped pattern, like the S-Shaped pattern used for long assembly processes, which to fit in the same area. When it is necessary to keep the receiving and shipping ends on the same side, the W-Shaped pattern is preferred. Figure 1.19 depicts W-Shaped pattern arrangement. M1 M3 M5 M2 M4 Figure 1.19 W-Shaped pattern

20 Backtracking and Bypassing There are two movements namely, backtracking and bypassing (Figure 1.20) that can occur in flow-line layouts, which impact the flow of the products. Backtracking or counter clockwise movement is defined as a part moving from one facility to another preceding it in the sequence of facilities in the flow-line arrangement. The number of backtracking movements has to be minimized. Bypassing occurs when a part skips some facilities during its moving towards the flow line arrangement. Backtracking Bypassing Figure 1.20 Backtracking and bypassing movement 1.4 OBJECTIVE OF THE RESEARCH This research concentrates on the fixed area cellular layout problems in various manufacturing systems by implementing some relatively important factors by using non-traditional optimization techniques. The machine layout problem is defined as the physical arrangement of X number of dissimilar production equipments to Y number of locations in a given layout area. A sensible arrangement of production equipments reduce the total movement of the products and cost of material handling. Also, it increases the productivity and overall efficiency of the plant. C programming language is used for coding.

21 21 The objectives of the research are listed below: To determine an appropriate physical arrangement of equipment within the cell by minimizing the travelling distance of the products. To minimize the material handling cost by reducing backtracking movements. To reduce total moment value for the sequence. To maximize the layout moment ratio for the proposed layout.

22 22 Details about the organisation of the research methodology is shown in Figure 1.21: Figure 1.21 Organization chart of the research methodology

23 THESIS ORGANIZATION This thesis is organized into nine chapters and the chapters are organized as follows. Chapter 1 furnishes an overview of layout design problems, types of layout, features of a good layout, types of flow material and patterns, procedure for layout design, and factors affecting the layout. Also it presents the objectives of the research with an organization chart of research methodologies. Chapter 2 includes a detailed literature survey made in the area of cellular layout design problems during the course of this research work. It explains the research works described by various authors in the domain of layout design on different manufacturing systems with multiple objectives. Chapter 3 contains a detailed discussion of the research works related to layout design problems by using heuristics and meta-heuristic techniques. It also deals with the non-traditional optimization algorithms applied in this research. Chapter 4 presents a fixed area layout design problem with three parts and eight machines. PSO, GA and SA techniques are applied to the above said problem with particular objectives. Findings are tabulated and compared. The analysis and interpretation of results are expressed graphically. Also, it presents the results and conclusion. Chapter 5 offers help in solving a fixed area cellular layout design problem with ten parts and ten machines. PSO, GA, SA and ABC techniques are applied to the problem with another set of objectives. Results are tabulated

24 24 and compared with one another. The investigation and findings are explained with graphical representation and is concluded with remarks. Chapter 6 deals with a fixed area layout design problem with twenty parts and twelve machines. The above said techniques are employed with all objectives. Results are compared and evaluated. The analysis and conclusion of results are explained with graphs. In Chapter 7, the outcome of the research is discussed in detail for all types of problems. The conclusion of the research is declared in this chapter. Also, the researcher recommends a suitable technique for solving fixed area cellular layout design problems. Chapter 8 lists out the limitations of the research work. Chapter 9 includes the scope of the research. Also, the researcher has recommended the scope for further research. the research work. References and the list of publications are presented at the end of