PLANT LAYOUT AND MATERIAL HANDLING

Transcription

1 LECTURE NOTES ON PLANT LAYOUT AND MATERIAL HANDLING COURSE CODE A80365 IV B.TECH. II SEM JNTUH Prepared By Mr. G. S. Vivek, Assistant Professor Mr. A. Venu Prasad, Assistant Professor Department of Mechanical Engineering INSTITUTE OF AERONAUTICAL ENGINEERING (AUTON0MOUS) DUNDIGAL, HYDERABAD

2 UNIT-I 1.1. Classification of Layout, Advantages and Limitations of different layouts i. Process layout ii. Product layout iii. Combination layout iv. Fixed position layout v. Group layout Process Layout : Process layout is recommended for batch production. All machines performing similar type of operations are grouped at one location in the process layout e.g., all lathes, milling machines, etc. are grouped in the shop will be clustered in like groups. Thus, in process layout the arrangement of facilities are grouped together according to their functions. A typical process layout is shown in the following figure. The flow paths of material through the facilities from one functional area to another vary from product to product. Usually the paths are long and there will be possibility of backtracking. Process layout is normally used when the production volume is not sufficient to justify a product layout. Typically, job shops employ process layouts due to the variety of products manufactured and their low production volumes Process layout Advantages In process layout machines are better utilized and fewer machines are required. Flexibility of equipment and personnel is possible in process layout. Lower investment on account of comparatively less number of machines and lower cost of general purpose machines. Higher utilization of production facilities. A high degree of flexibility with regards to work distribution to machineries and workers. The diversity of tasks and variety of job makes the job challenging and interesting. Supervisors will become highly knowledgeable about the functions under their department. Limitations: Backtracking and long movements may occur in the handling of materials thus, reducing material handling efficiency. Material handling cannot be mechanized which adds to cost. Process time is prolonged which reduce the inventory turnover and increases the in- process inventory. Lowered productivity due to number of set-ups. Throughput (time gap between in and out in the process) time is longer. Space and capital are tied up by work-in-process Product Layout: In this type of layout, machines and auxiliary services are located according to the processing

3 sequence of the product. If the volume of production of one or more products is large, the facilities can be arranged to achieve efficient flow of materials and lower cost per unit. Special purpose machines are used which perform the required function quickly and reliably. The product layout is selected when the volume of production of a product is high such that a separate production line to manufacture it can be justified. In a strict product layout, machines are not shared by different products. Therefore, the production volume must be sufficient to achieve satisfactory utilization of the equipment. A typical product layout is shown in the following figure. Product layout Advantages: The flow of product will be smooth and logical in flow lines. In-process inventory is less. Throughput time is less. Minimum material handling cost. Simplified production, planning and control systems are possible. Less space is occupied by work transit and for temporary storage. Reduced material handling cost due to mechanised handling systems and straight flow. Perfect line balancing which eliminates bottlenecks and idle capacity. Manufacturing cycle is short due to uninterrupted flow of materials. Small amount of work-in-process inventory. Unskilled workers can learn and manage the production. Limitations A breakdown of one machine in a product line may cause stoppages of machines in the downstream of the line. A change in product design may require major alterations in the layout. The line output is decided by the bottleneck machine. Comparatively high investment in equipments is required. Lack of flexibility. A change in product may require the facility modification Combination Layout: A combination of process and product layouts combines the advantages of both types of layouts. A combination layout is possible where an item is being made in different types and sizes. Here machinery is arranged in a process layout but the process grouping is then arranged in a sequence to manufacture various types and sizes of products. It is to be noted that the sequence of operations remains same with the variety of products and sizes. The following figure shows a combination type of layout for manufacturing different sized gears. Combination layout for making different types and sizes of gears

4 Fixed Position Layout: This is also called the project type of layout. In this type of layout, the material, or major components remain in a fixed location and tools, machinery, men and other materials are brought to this location. This type of layout is suitable when one or a few pieces of identical heavy products are to be manufactured and when the assembly consists of large number of heavy parts, the cost of transportation of these parts is very high. Advantages The major advantages of this type of layout are: Helps in job enlargement and upgrades the skills of the operators. The workers identify themselves with a product in which they take interest and pride in doing the job. Greater flexibility with this type of layout. Layout capital investment is lower. Group Layout (or Cellular Layout) There is a trend now to bring an element of flexibility into manufacturing system as regards to variation in batch sizes and sequence of operations. A grouping of equipment for performing a sequence of operations on family of similar components or products has become all the important. Group technology (GT) is the analysis and comparisons of items to group them into families with similar characteristics. GT can be used to develop a hybrid between pure process layout and pure flow line (product) layout. This technique is very useful for companies that produce variety of parts in small batches to enable them to take advantage and economics of flow line layout. The application of group technology involves two basic steps; first step is to determine component families or groups. The second step in applying group technology is to arrange the plants equipment used to process a particular family of components. This represents small plants within the plants. The group technology reduces production planning time for jobs. It reduces the set-up time. Thus group layout is a combination of the product layout and process layout. It combines the advantages of both layout systems. If there are m-machines and n-components, in a group layout (Group-Technology Layout), the M -machines and n -components will be divided into number of machine-component cells (group) such that all the components assigned to a cell are almost processed within that cell itself. Here, the objective is to minimize the intercell movements. The basic aim of a group technology layout is to identify families of components that require similar of satisfying all the requirements of the machines are grouped into cells. Each cell is capable of satisfying all the requirements of the component family assigned to it. The layout design process considers mostly a single objective while designing layouts. In process layout, the objective is to minimize the total cost of materials handling. Because of the nature of the layout, the cost of equipments will be the minimum in this type of layout. In product layout, the cost of materials handling will be at the absolute minimum. But the cost of equipments would not be at the minimum if

5 the equipments are not fully utilized. In-group technology layout, the objective is to minimize the sum of the cost of transportation and the cost of equipments. So, this is called as multi-objective layout. A typical process layout is shown. Advantages of Group Technology Layout Group Technology layout can increase Component standardization and rationalization. Reliability of estimates. Effective machine operation and productivity. Customer service. It can decrease the Paper work and overall production time. Work-inprogress and work movement. Overall cost. Limitations of Group Technology Layout This type of layout may not be feasible for all situations. If the product mix is completely dissimilar, then we may not have meaningful cell formation DESIGN OF PRODUCT LAYOUT In product layout, equipment or departments are dedicated to a particular product line, duplicate equipment is employed to avoid backtracking, and a straight-line flow of material movement is achievable. Adopting a product layout makes sense when the batch size of a given product or part is large relative to the number of different products or parts produced. Assembly lines are a special case of product layout. In a general sense, the term assembly line refers to progressive assembly linked by some material-handling device. The usual assumption is that some form of pacing is present and the allowable processing time is equivalent for all workstations. Within this broad definition, there are important differences among line types. A few of these are material handling devices (belt or roller conveyor, overhead crane); line configuration (U-shape, straight, branching); pacing (mechanical, human); product mix (one product or multiple products); workstation characteristics (workers may sit, stand, walk with the line, or ride the line); and length of the line (few or many workers). The range of products partially or completely assembled on lines includes toys, appliances, autos, clothing and a wide variety of electronic components. In fact, virtually any product that has multiple parts and is produced in large volume uses assembly lines to some degree. A more-challenging problem is the determination of the optimum configuration of operators and buffers in a production flow process. A major design consideration in production lines is the assignment of operation so that all stages are more or less equally loaded. Consider the case of traditional assembly lines illustrated in the following figure. Traditional assembly line In this example, parts move along a conveyor at a rate of one part per minute to three groups of workstations. The first operation requires 3 minutes per unit; the second operation requires 1 minute per unit; and the third requires 2 minutes per unit. The first workstation consists of three operators; the second, one operator; and the third, two operators. An operator removes a part from the conveyor and performs some assembly task at his or her workstation. The completed part is returned to the conveyor and transported to the next operation. The number of operators at each workstation was chosen so that the line is balanced. Since three operators work simultaneously at the first workstation, on the average

6 one part will be completed each minute. This is also true for other two stations. Since the parts arrive at a rate of one per minute, parts are also completed at this rate. Assembly-line systems work well when there is a low variance in the times required to perform the individual subassemblies. If the tasks are somewhat complex, thus resulting in a higher assembly-time variance, operators down the line may not be able to keep up with the flow of parts from the preceding workstation or may experience excessive idle time. An alternative to a conveyor-paced assembly-line is a sequence of workstations linked by gravity conveyors, which act as buffers between successive operations. LINE BALANCING Assembly-line balancing often has implications for layout. This would occur when, for balance purposes, workstation size or the number used would have to be physically modified. The most common assembly-line is a moving conveyor that passes a series of workstations in a uniform time interval called the workstation cycle time (which is also the time between successive units coming off the end of the line). At each workstation, work is performed on a product either by adding parts or by completing assembly operations. The work performed at each station is made up of many bits of work, termed tasks, elements, and work units. Such tasks are described by motion-time analysis. Generally, they are grouping that cannot be subdivided on the assembly-line without paying a penalty in extra motions. The total work to be performed at a workstation is equal to the sum of the tasks assigned to that workstation. The line-balancing problem is one of assigning all tasks to a series of workstations so that each workstation has no more than can be done in the workstation cycle time, and so that the unassigned (idle) time across all workstations is minimized. The problem is complicated by the relationships among tasks imposed by product design and process technologies. This is called the precedence relationship, which specifies the order in which tasks must be performed in the assembly process. The steps in balancing an assembly line are: Specify the sequential relationships among tasks using a precedence diagram. Determine the required workstation cycle time C, using the formula C=Production time per day Required output per day (in units) Determine the theoretical minimum number of workstations (Nt) required to satisfy the workstation cycle time constraint using the formula Nt= Sum of task times (T)Cycle time (C) Select a primary rule by which tasks are to be assigned to workstations, and a secondary rule to break ties. Assign tasks, one at a time, to the first workstation until the sum of the task times is equal to the workstation cycle time, or no other tasks are feasible because of time or sequence restrictions. Repeat the process for workstation 2, workstation 3, and so on until all tasks are assigned. Evaluate the efficiency of the balance derived using the formula Efficiency=Sum of task times (T)Actual number of workstations (Na) Workstations cycle time (C). If efficiency is unsatisfactory, rebalance using a different decision rule. ILLUSTRATION 7:The MS 800 car is to be assembled on a conveyor belt. Five hundred cars are required per day. Production time per day is 420 minutes, and the assembly steps and times for the wagon are given below. Find the balance that minimizes the number of workstations, subject to cycle time and precedence constraints.

7 SOLUTION: Draw a precedence diagram as follows: Determine workstation cycle time. Here we have to convert production time to seconds because our task times are in seconds C=Production time per day Required output per day (in units) Determine the theoretical minimum number of workstations required (the actual number may be greater) Nt=Production time per day Required output per day (in units) =TC =195 seconds50.4 seconds =3.87 = 4(rounded up) Select assignment rules. Prioritize tasks in order of the largest number of following tasks: Our secondary rule, to be invoked where ties exist from our primary rule, is (b) Prioritize tasks in order of longest task time. Note that D should be assigned before B, and E assigned before C due to this tiebreaking rule.

8 Make task assignments to form workstation 1, workstation 2 and so forth until all tasks are assigned. It is important to meet precedence and cycle time requirements as the assignments are made. Calculate the efficiency. Efficiency= TNaC=1955*50.4=.77 or 77% Evaluate the solution. An efficiency of 77 per cent indicates an imbalance or idle time of 23 per cent (1.0.77) across the entire line. In addition to balancing a line for a given cycle time, managers must also consider four other options: pacing, behavioral factors, number of models produced, and cycle times. Pacing is the movement of product from one station to the next after the cycle time has elapsed. Paced lines have no buffer inventory. Unpaced lines require inventory storage areas to be placed between stations. BEHAVIOURAL FACTORS The most controversial aspect of product layout is behavioral response. Studies have shown that paced production and high specialization lower job satisfaction. One study has shown that productivity increased on unpaced lines. Many companies are exploring job enlargement and rotation to increase job variety and reduce excessive specialization. For example, New York Life has redesigned the jobs of workers who process and evaluate claims applications. Instead of using a production line approach with several workers doing specialized tasks, New York Life has made each worker solely responsible for an entire application. This approach increased worker responsibility and raised morale. In manufacturing, at its plant in Kohda, Japan, Sony Corporation dismantled the conveyor belts on which as many as 50 people assembled camcorders. It set up tables for workers to assemble an entire camera themselves, doing everything from soldering to testing. Output per worker is up 10 per cent, because the approach frees efficient assemblers to make more products instead of limiting them to conveyor belt s speed. And if something goes wrong, only a small section of the plant is affected. This approach also allows the line to match actual demand better and avoid frequent shutdown because of inventory buildups. NUMBER OF MODELS PRODUCED A mixed-model line produces several items belonging to the same family. A single-model line produces one model with no variations. Mixed model production enables a plant to achieve both high-volume production and product variety. However, it complicates scheduling and increases the need for good communication about the specific parts to be produced at each station.

9 CYCLE TIMES A line s cycle time depends on the desired output rate (or sometimes on the maximum number of workstations allowed). In turn, the maximum line efficiency varies considerably with the cycle time selected. Thus, exploring a range of cycle times makes sense. A manager might go with a particularly efficient solution even if it does not match the output rate. The manager can compensate for the mismatch by varying the number of hours the line operates through overtime, extending shifts, or adding shifts. Multiple lines might even be the answer. The analysis involved in the design of production lines and assembly lines relates primarily to timing, coordination, and balance among individual stages in the process. For process layouts, the relative arrangement of departments and machines is the critical factor because of the large amount of transportation and handling involved. PROCEDURE FOR DESIGNING PROCESS LAYOUTS Process layout design determines the best relative locations of functional work centers. Work centers that interact frequently, with movement of material or people, should be located close together, whereas those that have little interaction can be spatially separated. One approach of designing an efficient functional layout is described below. List and describe each functional work centre. Obtain a drawing and description of the facility being designed. Identify and estimate the amount of material and personnel flow among work centers Use structured analytical methods to obtain a good general layout. Evaluate and modify the layout, incorporating details such as machine orientation, storage area location, and equipment access. The first step in the layout process is to identify and describe each work centre. The description should include the primary function of the work centre; drilling, new accounts, or cashier; its major components, including equipment and number of personnel; and the space required. The description should also include any special access needs (such as access to running water or an elevator) or restrictions (it must be in a clean area or away from heat). For a new facility, the spatial configuration of the work centers and the size and shape of the facility are determined simultaneously. Determining the locations of special structures and fixtures such as elevators, loading docks, and bathrooms becomes part of the layout process. However, in many cases the facility and its characteristics are a given. In these situations, it is necessary to obtain a drawing of the facility being designed, including shape and dimensions, locations of fixed structures, and restrictions on activities, such as weight limits on certain parts of a floor or foundation. Relationship flow diagram

10 To minimize transport times and material-handling costs, we would like to place close together those work centers that have the greatest flow of materials and people between them. To estimate the flows between work centers, it is helpful to begin by drawing relationship diagram as shown in the above figure. For manufacturing systems, material flows and transporting costs can be estimated reasonably well using historical routings for products or through work sampling techniques applied to workers or jobs. The flow of people, especially in a service system such as a business office or a university administration building, may be difficult to estimate precisely, although work sampling can be used to obtain rough estimates. The amounts and/or costs of flows among work centers are usually presented using a flow matrix, a flow-cost matrix, or a proximity chart. Flow Matrix A flow matrix is a matrix of the estimated amounts of flow between each pair of work centers. The flow may be materials (expressed as the number of loads transported) or people who move between centers. Each work centre corresponds to one row and one column, and the element fij designates the amount of flow from work centre (row) I to work centre (column) Normally, the direction of flow between work centers is not important, only the total amount, so fij and fji can be combined and the flows represented using only the upper right half of a matrix. Flow Matrix Table Flow-cost Matrix A basic assumption of facility layout is that the cost of moving materials or people between work centers is a function of distance travelled. Although more complicated cost functions can be accommodated, often we assume that the per unit cost of material and personnel flows between work centers is proportional to the distance between the centers. So for each type of flow between each pair of departments, i and j, we estimate the cost per unit per unit distance,

11 Flow-cost Matrix Table Proximity Chart Proximity charts (relationship charts) are distinguished from flow and flow-cost matrices by the fact that they describe qualitatively the desirability or need for work centers to be close together, rather than providing quantitative measures of flow and cost. These charts are used when it is difficult to measure or estimate precise amounts or costs of flow among work centers. This is common when the primary flows involve people and do not have a direct cost but rather an indirect cost, such as when employees in a corporate headquarters move among departments (payroll, printing, information systems) to carry out their work Overview : The ability to design and operate manufacturing facilities that can quickly and effectively adapt to changing technological and market requirements is becoming increasingly important to the success of any manufacturing organization. In the face of shorter product life cycles, higher product variety, increasingly unpredictable demand, and shorter delivery times, manufacturing facilities dedicated to a single product line cannot be cost effective any longer. Investment efficiency now requires that manufacturing facilities be able to shift quickly from one product line to another without major retooling, resource reconfiguration, or replacement of equipment. Investment efficiency also requires that manufacturing facilities be able to simultaneously make several products so that smaller volume products can be combined in a single facility and that fluctuations in product mixes and volumes can be more easily accommodated. In short, manufacturing facilities must be able to exhibit high levels of flexibility and robustness despite significant changes in their operating requirements. In industry sectors, it is important to manufacture the products which have good quality and meet customers demand. This action could be conducted under existing resources such as employees, machines and other facilities. However, plant layout improvement, could be one of the tools to response to increasing industrial productivity. Plant layout design has become a fundamental basis of today s industrial plants which can influence parts of work efficiency. It is needed to appropriately plan and position employees, materials, machines, equipment, and other manufacturing supports and facilities to create the most effective plant layout.

12 1.4.Process layout & Product layout: Selection, specification. Implementation and follow up Product Layout The product layout approach involves setting up the production facilities around the steps involved in manufacturing the product. The product goes from one step to another as it is manufactured. This is the typical assembly line approach. For example, in the manufacturing process of a car, the car body goes from one stage of production to the next. Employees at each stage work on the car and then pass it on to the next stage. Process Layout In a process layout, management groups together machines that perform similar functions. For example, it may put all of the lathes together in one part of the factory. The part that is being manufactured goes from one process area to another process area as it is manufactured. Hospitals typically follow a process layout. For example, the maternity ward is in an area where the hospital attends to all aspects of the maternity process. Similarly, the cardiac unit attends to all aspects of cardiac care. Suitability Businesses producing a variety of different products that have to go through a similar manufacturing process find it more convenient to adopt a process layout. For instance, if a business makes different types of wood-based products, it might adopt a process layout. On the other hand, a business that manufactures primarily one product, such as shoes, would benefit from a product layout that flows the product through the production process most efficiently. Workflow The workflow through a process layout system is variable. A variety of products flow through the system and the shop floor personnel have to move around the material that goes into the products. This happens as the products move from one process to another. With a product layout, the shop floor workers don t have to move around the materials and the workflow is more uniform. The factory locates the materials for each stage of production at the place where the workers use them. This makes for more efficiency.

13 Comparison of product and process layout:

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37 2.4. Quadratic Assignment Problem (QAP): The more common Mathematical. Formulation for intra- company location problems (especially in case of job shop production) is the Quadratic Assignment Problem (QAP). For the QAP the cost of an assignment is determined by the distances and the material flows between all given entities. While, in case of (Linear assignment problem) LAP the costs for assigning a machine to a location do not depend on the location chosen for any other machine we now want to take distances of locations and material flow between entities into account as well. In fact, we are now going to minimize the total transportation costs occurring due to the chosen assignment whereas for the LAP we minimize isolated locationoriented costs. An Activity Relationship Charts are useful graphical means of representing the desirability of locating pairs of machines/operations near to each other. The following letter codes have been suggested in literature for determining a closeness rating. A Absolutely necessary. Because two machines/operations use the same equipment or facilities, they must be located near each other. E Especially important. The facilities may require to the same personnel or records. I Important. The activities may be located in sequence in the normal work flow. O Ordinary importance. It would be convenient to have the facilities near each other, but it is not essential. U Unimportant. It does not matter whether the facilities are located near each other or not. X Undesirable. Locating a wedding department near one that uses flammable liquids would be an example of this category. Example: Met Me, Inc., is a franchised chain of fast-food hamburger restaurants. A new restaurant is being located in a growing suburban community near Reston, Virginia. Each restaurant has the following departments: 1. Cooking burgers 2. Cooking fries 3. Packing and storing burgers 4. Drink dispensers 5. Counter servers 6. Drive-up server The burgers are cooked on a large grill, and the fries are deep fried in hot oil. For safety reasons the company requires that these cooking areas not be located near each

38 other. All hamburgers are individually wrapped after cooking and stored near the counter. The service counter can accommodate six servers, and the site has an area reserved for a drive-up window. An activity relationship chart for this facility appears in the following. In the chart, each pair of activities is given one of the letter designations A, E, I, O, U, or X. Once a final layout is determined, the proximity of the various departments can be compared to the closeness ratings in the chart. Figure 2-1 illustrates the activity relationship chart for Met me Inc. In the original conception of the QAP a number giving the reason for each closeness rating is needed as well. In case of closeness rating X a negative value would be used to indicate the undesirability of closeness for the according machines/operations. 2.5 Branch and Bound model Branch and Bound method for exact solution The method used for arriving at an optimal solution to the problem of quadratic assignment is Branch and Bound. Example: To locate four machines, four feasible locations are available. The wij, the cost per unit distance of material movement between machines i and j is given in the flow matrix (Table 1). Table 1. Flow matrix Location Machine The distance between locations i and j is given in Table 2 Table 2. Distance matrix Location Location

39 How should the machines be assigned to available locations so as to minimize the total cost of material handling? Solution Lower bond to the problem The total cost will contain the sum of six elements. Each element being the product of one of the elements of the flow matrix W and the distance matrix D. suppose the elements of the flow matrix are arranged in descending order. The array can be written as A = { } Similarly, suppose the elements of the distance matrix are written in ascending order. The array can be written as B = { } The dot product of vectors A and B gives the value 21. A little thought will reveal that the cost for the layout cannot be less than this figure. The cost for the optimal layout will be 21 or more. This is known as a lower-bound to the problem. Branching from the starting node Suppose machine 1 is assigned to location 1. What will be the cost of material handing? The elements of the flow matrix which represent material movement associated with machine 1 are w12, w13, and w14 (5, 0, 1). Let these be designated by set p1 given by P1 = {5, 0, 1} Distances from machine 1 to the other available locations are d12, d13, and d14 (1, 2 or 6). Let these be designated by set Q1 given by Q1 = {1, 2, 6} When machine 1 is assigned to location 1, the other machines 2, 3 and 4 can be assigned to locations 2, 3 and 4. The flow associated with these machines designated as set R is given by R= {w23, w24, w34} = {3, 0, 2} The distance associated with locations 2, 3 and 4, designated as set S is given by S= {d23, d24, d34} = {3, 5, 4} The cost layout will consist of six elements; the first three will be obtained by multiplying each element of set P1 with some set of Q1. The last three will be obtained by the product of each element of set R with some element of set S. thus we can get a lower-bond by the flowing steps: Step 1 Create vectors by arranging set P1 in descending order and Q1 n ascending order. Find their dot product. Call this C1 Step 2 Create vectors by arranging set R in descending order and S in ascending order. Find their dot product. Call this C2. Step 3 Find the lower bound by adding C1 and C2. For the present case, the lower- bound is given by LB= (5, 1, 0). (1, 2, 6)+ (3, 2, 0). (3, 4, 5) = 5x1+1x2+0x6+3x3+2x4+0x 5 = = 24

40 Similarly, the lower bound when facility 1 is assigned to location 2, 3 or 4can be evaluated. The results are given in Table 3 Table 3 Lower-bound when facility 1 is assigned to locations 1, 2, 3 or 4 Facility 1 is assigned to Lower-bound Location 1 24 Location 2 22 Location 3 26 Location 4 32 Facility 2 can be assigned in only four feasible ways. Therefore, the options can be pictorially represented in Fig. 2 (1) 0 LB 21 LB 24 (2) (4) (3) 1 LB 22 LB 32 2 LB Fig. 2 Lower-bound for all feasible assignments of facility 1 Branching from the node with the lowest-bound The lowest LB is 22 for node 2. We will expand the tree from here. Node 2 is for assignment of machine 1 to location 2. When machine 1 has been assigned to location 2, machine 2 can be assigned in three feasible ways. Suppose machine 2 is assigned to location 1. The flow and distance matrices can be written as shown in Table 4 and 5 respectively. Table 1. Flow matrix Location Machine

41 Table 2. Distance matrix Location Location Pair of machines 1 and 2 will be assigned to locations 2 and 1. The LB will be obtained by the following steps. 1. Define sets P1, Q1, P2, Q2, R and S. Where P1: Set of all elements of flow matrix W associated with machine 1 and unasigned machines 3 and 4 = {0, 1} P2: Set of all elements of flow matrix W associated with machine 2 and unasigned machines 3 and 4 = {3, 0} Q1: Set of all elements of distance matrix D associated with machine 1 and unasigned locations 3 and 4 = {3, 5} Q2: Set of all elements of distance matrix D associated with machine 2 and unasigned locations 3 and 4 = {2, 6} R: Set of all elements of flow matrix W associated with unasigned machines 3 and 4 = {2} S: Set of all elements of distance matrix D associated with unasigned locations 3 and 4 = {4} To find a LB proceed as follows: 1. Define vectors by arranging P1 in descending order, Q1 in descending order. Find their dot product. Call this C1. C1= {1, 0}.{3,5} = 3 2. Define vectors by arranging P2 in descending order, Q2 in descending order. Find their dot product. Call this C2. C2= {3, 0}. {2, 6} = 6 3. Define vectors by arranging R in descending order, S in descending order. Find their dot product. Call this C3. C3= {2}. {4} = 8 4. Find the cost of material movement between all facilities that have been assigned. Call this C4. Thus, C4= w12 x d21 = 5x1= 5 5. The LB is given by LB= C1+C2+C3+C4= = 22

42 Similarly, the LB when machine 2 is assigned to locations 3 and 4, respectively, are 34 and 42. These options may be added as nodes to the tree in Fig. 3. Figure 4 shows the expanded tree with LBs for all feasible assignments of facility 2 (with facility 1 already assigned to location 2) Plant Layout and Material Handling 1 (1) 0 LB 21 LB 24 (2) (4) (3) LB 32 LB 22 LB 26 2 (2, 1) (2, (2, LB 22 LB 42 LB 34 Fig. 3 LBs by branching from node 52 of Fig. 2 7 Now we can branch from node 5. There are two 6 feasible layouts. Machine 3 can be assigned to location 3 and machine 4 to location or machine 3 to location 4 and machine 4 to location 3. Each gives a complete layout. The costs for these layouts are 24 and 28, respectively. The expanded tree with these nodes added to the tree is shown in Fig (1) 0 LB 21 LB 24 (2) (4) (3) 1 LB 32 (2, 1) LB 22 2 (2, 4) LB 26 LB 22 (2, 3) LB 42 LB (2, 1, 3, 4) (2, 1, 4, 3) B =24 LB = Fig. 4 Further branching from node 5 of Fig. 3

43 Upper Bound to the Problem The nodes at 8 and 9 give the complete assignments to the problem. For the node 8 the machines 1, 2, 3 and 4 assigned to respective locations 2, 1, 3 and 4 yield the total cost to be 24. For node 9 the machines are assigned to respective locations 2, 1, 4 and 3 and for which the total cost is 28. As yet we do not know what the optimal solution to the problem. However, it is certain that the optimal layout will never have a cost more than 24, why? We have a layout with a total cost of 24. The optimal layout cannot be worse than this. That is why this cost may be considered as an upper bound to the problem. In general, if the total costs for a set of feasible solutions are known and TC* is the minimum total cost of this set, the total cost for the optimal layout will be TC*, or more. Therefore, TC* may be considered as an upper-bound to the problem. For the current problem, the upper bound is 24. The pruning of branches from the tree The problem will never have solution in which the cost is more than 24. If you reach node 3 by assigning machine 1 to machine 3, the cost will never be less than 26. Since we have got a solution at cost 24, which is less than the lower-bound at node 3, machine 1 will never be assigned to location 3. The same is the case with nodes 4, 6 and 7. These nodes need not be considered at any future time. We can delete them from the diagram. Even if we assign machine 1 to location 1 (node 1), we will arrive at a final solution for which the cost will be 24, or more. Since we have already got a solution with a total cost of 24, we need not assign machine 1 to location 1. Hence the optimal layout for the current problem is to assign machines 1, 2, 3, and 4 to respective locations 2, 1, 3 and 4. The total cost for the optimal layout is 24.

44 3.1 Introduction to Material handling system: Unit - III Haynes defines Material handling covers the basic operations in connection with the movement of bulk, packaged and individual products in a semi-solid or solid state by means of gravity manually or power-actuated equipment and within the limits of individual producing, fabricating, processing or service establishment. Material handling does not add any value to the product but adds to the cost of the product and hence it will cost the customer more. So the handling should be kept at minimum. Material handling in Indian industries accounts for nearly 40% of the cost of production. Out of the total time spent for manufacturing a product, 20% of the time is utilized for actual processing on them while the remaining 80% of the time is spent in moving from one place to another, waiting for the processing. Materials handling can be also defined as the function dealing with the preparation, placing and positioning of materials to facilitate their movement or storage. Material handling is the art and science involving the movement, handling and storage of materials during different stages of manufacturing. Thus the function includes every consideration of the product except the actual processing operation Objectives of Material Handling: 1. Minimize cost of material handling. 2. Minimize delays and interruptions by making available the materials at the point of use at right quantity and at right time. 3. Increase the productive capacity of the production facilities by effective utilization of capacity and enhancing productivity. 4. Safety in material handling through improvement in working condition. 5. Maximum utilization of material handling equipment. 6. Prevention of damages to materials. 7. Lower investment in process inventory. 3.2 Principles of Material Handling: Following are the principles of material handling:

45 1. Planning principle: All handling activities should be planned. 2. Systems principle: Plan a system integrating as many handling activities as possible and coordinating the full scope of operations (receiving, storage, production, inspection, packing, warehousing, supply and transportation). 3. Space utilization principle: Make optimum use of cubic space. 4. Unit load principle: Increase quantity, size, weight of load handled. 5. Gravity principle: Utilize gravity to move a material wherever practicable. 6. Material flow principle: Plan an operation sequence and equipment arrangement to optimize material flow. 7. Simplification principle: Reduce combine or eliminate unnecessary movement and/or equipment. 8. Safety principle: Provide for safe handling methods and equipment. 9. Mechanization principle: Use mechanical or automated material handling equipment. 10. Standardization principle: Standardize method, types, size of material handling equipment. 11. Flexibility principle: Use methods and equipment that can perform a variety of task and applications. 12. Equipment selection principle: Consider all aspect of material, move and method to be utilized. 13. Dead weight principle: Reduce the ratio of dead weight to pay load in mobile equipment. 14. Motion principle: Equipment designed to transport material should be kept in motion. 15. Idle time principle: Reduce idle time/unproductive time of both MH equipment and man power. 16. Maintenance principle: Plan for preventive maintenance or scheduled repair of all handling equipment. 17. Obsolescence principle: Replace obsolete handling methods/equipment when more efficient method/equipment will improve operation. 18. Capacity principle: Use handling equipment to help achieve its full capacity.

46 19. Control principle: Use material handling equipment to improve production control, inventory control and other handling. 20. Performance principle: Determine efficiency of handling performance in terms of cost per unit handled which is the primary criterion. 3.3 Material Handing Equipments: Broadly material handling equipment s can be classified into two categories, namely: (a) Fixed path equipments, and (b) Variable path equipments. (a) Fixed path equipments which move in a fixed path. Conveyors, monorail devices, chutes and pulley drive equipments belong to this category. A slight variation in this category is provided by the overhead crane, which though restricted, can move materials in any manner within a restricted area by virtue of its design. Overhead cranes have a very good range in terms of hauling tonnage and are used for handling bulky raw materials, stacking and at times palletizing. (b) Variable path equipments have no restrictions in the direction of movement although their size is a factor to be given due consideration trucks, forklifts mobile cranes and industrial tractors belong to this category. Forklifts are available in many ranges, they are maneuverable and various attachments are provided to increase their versatility Material Handing Equipments may be classified in five major categories. Conveyors: Conveyors are useful for moving material between two fixed workstations, either continuously or intermittently. They are mainly used for continuous or mass production operations indeed, they are suitable for most operations where the flow is more or less steady. Conveyors may be of various types, with rollers, wheels or belts to help move the material along: these may be powerdriven or may roll freely. The decision to provide with care, since they are usually costly to install; moreover, they are less flexible and, where two or more converge, it is necessary to coordinate the speeds at which the two conveyors move. Industrial Trucks Industrial trucks are more flexible in use than conveyors since they can move between various points and are not permanently fixed in one place. They are, therefore, most suitable for intermittent production and for handling various sizes and shapes of material. There are many types of truck petrol- driven, electric, hand-powered, and so on. Their greatest advantage lies in the wide range of attachments available; these increase the trucks ability to handle various types and shapes of material.

47 Cranes and Hoists The major advantage of cranes and hoists is that they can move heavy materials through overhead space. However, they can usually serve only a limited area. Here again, there are several types of crane and hoist, and within each type there are various loading capacities. Cranes and hoists may be used both for intermittent and for continuous production. Containers These are either dead containers (e.g. Cartons, barrels, skids, pallets) which hold the material to be transported but do not move themselves, or live containers (e.g. wagons, wheelbarrows or computer self-driven containers). Handling equipments of this kind can both contain and move the material, and is usually operated manually. Robots Many types of robot exist. They vary in size, and in function and maneuverability. While many robots are used for handling and transporting material, others are used to perform operations such as welding or spray painting. An advantage of robots is that they can perform in a hostile environment such as unhealthy conditions or carry on arduous tasks such as the repetitive movement of heavy materials. The choice of material-handling equipment among the various possibilities that exist is not easy. In several cases the same material may be handled by various types of equipments, and the great diversity of equipment and attachments available does not make the problem any easier. In several cases, however, the nature of the material to be handled narrows the choice. Some of the materials handling equipment are shown in Figs. 5.1 to Wheel conveyor 3.2 Screw conveyor 3.3 Belt conveyor 3.4 Roller conveyor

48 3.5 Jib crane 3.6 Bridge crane 3.7 Platform truck..8 Fork truck 3.9 Chain hoist 3.10 Electric hoist

49 3.11 Spiral chute 3.12 Industrial tractor 3.13 Electrical hoist 3.4 Relationship between Plant Layout and Material Handling: The production efficiency of a manufacturing unit depends on how well various machines, flow paths, storage facilities, and employee amenities are located in the plant. A systematically designed plant can ensure the smooth and rapid movement of material, from the raw material stage to the end product stage. Plant layout encompasses new layout as well as improvement in the existing layout. In modern manufacturing facilities, efficient layout is complemented by world class material handling equipment to drive the overall efficiency. Some of the issues that warrant careful layout planning and utilizing material handling equipments are improper material flow paths resulting in production idle time, production bottlenecks due to improper facility layout and planning, increased material handling costs due to increased number of "touches" across different operations, inability to scale up operations due to poorly designed infrastructure and material flow patterns, and reduced employee morale due to non availability of adequate amenities across the facility.

50 There is a close relationship between plant layout and material handling. A good layout ensures minimum material handling and eliminates rehandling in the following ways: 1. Material movement does not add any value to the product so, the material handling should be kept at minimum though not avoid it. This is possible only through the systematic plant layout. Thus a good layout minimizes handling. 2. The productive time of workers will go without production if they are required to travel long distance to get the material tools, etc. Thus a good layout ensures minimum travel for workman thus enhancing the production time and eliminating the hunting time and travelling time. 3. Space is an important criterion. Plant layout integrates all the movements of men, material through a well designed layout with material handling system. 4. Good plant layout helps in building efficient material handling system. It helps to keep material handling shorter, faster and economical. A good layout reduces the material backtracking, unnecessary workmen movement ensuring effectiveness in manufacturing. Thus a good layout always ensures minimum material handling.

51 UNIT IV 4.1 Selection of Material Handling Equipment: Selection of Material Handling equipment is an important decision as it affects both cost and efficiency of handling system. The following factors are to be taken into account while selecting material handling equipment Properties of the Material Whether it is solid, liquid or gas, and in what size, shape and weight it is to be transported are the main factors to be taken into consideration and can lead to a preliminary elimination from the range of available equipment under review. If a material is fragile, corrosive or toxic this will imply that certain handling methods and containers will be preferable to others Layout and characteristics of the building Another limiting factor is the convenience of space for handling. Low-level ceiling may exclude the use of hoists or cranes, and the presence of supporting columns in difficult places can restrict the size of the material-handling equipment. If the building is multi-storied, chutes or ramps for industrial trucks may be used. Layout itself will indicate the type of production operation (continuous, intermittent, fixed position or group) and can suggest some items of equipment that will be more proper than others. Floor capacity also aids in selecting the best material handling equipment Production Flow If the flow is properly constant between two immovable positions, fixed equipment such as conveyors or chutes can be effectively used. If, the flow is not continuous and the direction changes rarely from one point to another because several products are being produced simultaneously, moving equipment such as trucks would be desirable Cost considerations The previous factors can help to limit the range of suitable equipment, while costing can help in taking a final decision. Several cost features need to be taken into consideration, when the comparisons are made between several items of equipment that are capable of handling the same load. Initial investment and operating and maintenance costs are the major cost to be measured. By comparing the total cost for each of the items of equipment, a more rational decision can be made on the most appropriate choice Nature of Operations Equipment Selection also depends on mode of operations like whether handling is temporary or