Design of product layouts
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.
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 work station 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:
1. Specify the sequential relationships among tasks using a precedence diagram.
2. Determine the required workstation cycle time
3. Determine the theoretical minimum number of workstations Nt =
4. Select a primary rule by which tasks are to be assigned to workstations, and a secondary rule to break ties.
5. 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.
6. Evaluate the efficiency of the balance derived
7. If efficiency is unsatisfactory, rebalance using a different decision rule.
Process layout design
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.
1. List and describe each functional work center
2. Obtain a drawing and description of the facility being designed
3. Identify and estimate the amount of material and personnel flow among work centers
4. Use structured analytical methods to obtain a good general layout
5. 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 center. The description should include the primary function of the work center )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.
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.
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.
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 work station 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:
1. Specify the sequential relationships among tasks using a precedence diagram.
2. Determine the required workstation cycle time
3. Determine the theoretical minimum number of workstations Nt =
4. Select a primary rule by which tasks are to be assigned to workstations, and a secondary rule to break ties.
5. 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.
6. Evaluate the efficiency of the balance derived
7. If efficiency is unsatisfactory, rebalance using a different decision rule.
Process layout design
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.
1. List and describe each functional work center
2. Obtain a drawing and description of the facility being designed
3. Identify and estimate the amount of material and personnel flow among work centers
4. Use structured analytical methods to obtain a good general layout
5. 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 center. The description should include the primary function of the work center )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.
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.
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