PPU411 1
What is layout? Layout refers to the configuration of departments, work centers and equipment with particular emphasis on movement of work (customers or materials) through the system. The need for layout planning arises in the process of designing new facilities and redesigning existing facilities. Layout decisions: Require substantial investments (money and effort) Involve long-term commitments Impact the cost and efficiency of short-term operations 2
Layout types Layout requirements are determined by the type of operation. Less complexity, less divergence, and more line flows Process Characteristics (1) Customized process, with flexible and unique sequence of tasks (2) Disconnected line flows, moderately complex work (3) Connected line, highly repetitive work (4) Continuous flows (1) (2) (3) (4) Low-volume Multiple products with low Few major High volume, high products, made to moderate volume products, standardization, to customer higher commodity order volume products Job process Less customization and higher volume Small batch process Batch processes Large batch process Line process Continuous process 3
Layout strategy Fixed position (Project) Extremely low volumes (one of a kind), e.g. bridge, airplane. Process oriented (Job shop) Low volumes, high variety, least efficient, e.g. customized products. Product oriented (Line flow/batch production) High volumes, most efficient, e.g. books, furniture. Continuous flow Extremely high volumes, standard products, e.g. paper, milk. Hybrid layouts Warehouses Service layout 4
Production and Inventory Strategies Make-to-Stock Strategy Used by manufacturers that hold items in stock for immediate delivery, thereby minimizing customer delivery times. Assemble-to-Order Strategy Used by manufacturers that produce a wide variety of products from relatively few subassemblies and components after the customer orders are received. Make-to-Order Strategy Used by manufacturers that make products to customer specifications in low volumes. MTS: ATO: MTO: Supply Prognosis Driven (PD) PD DD PD PD DD OP OP OP DD Demand Driven (DD) Demand Consum e Consum e Consum e 5
Layout strategy Job shop process A process with the flexibility to produce a wide variety of products in significant quantities, with considerable complexity and divergence in the steps performed => Resources allocated around the process Line Process A process with high volumes and standardized products => Resources organized around the product Hybrid layout Create flow lines in parts of the workshop to increase efficiency, e.g. One worker multiple machines, Cell/Group technology. 6
Process vs product focus 7
Reasons for redesign Inefficient operations (e.g. bottlenecks) Accidents or safety hazards Changes in the design of products/services Introduction of new products/services Changes in volume (output or mix) Changes in methods or equipment Changes in environmental or other legal requirements Morale problems (e.g. lack of face-to face contact) 8
Designing Process Layouts Layout planning involves decisions about the physical arrangement of economic activity centers within a facility. An economic activity center could be anything that consumes space (e.g. a machine or a cafeteria) The goal is to allow workers and equipment to operate most efficiently. 9
Designing Process Layouts 1. What centers to include? 2. How much space does each center need? 3. How should each center be configurated? 4. Where should each center be located? 10
Designing Process Layouts Gather information Space requirements of each center Available space in the facility Closeness factor indicates which centers need to be located next to each other 1. Develop current block plan (allocates space and indicates placement of each department by trial and error) 2. Develop proposed block plan Closeness Factors Department 1 2 3 4 5 6 1. Administration 3 6 5 6 10 2. Social services 8 1 1 3. Institutions 3 9 4. Accounting 2 5. Education 1 6. Internal audit 3. Compare the two (e.g. using load-distance method) and make choice! 11
EXAMPLE 1 Designing process layouts (Block plan) 12
Salonen machining is a machine shop that produces a variety of small metal products on general-purpose equipment. A full shift of 26 workers and a second shift of 6 workers operate its 32 machines. Three types of information are needed to begin designing a revised layout for Salonen machining: Space requirements for each center, available space and closeness factors. Departments 3 and 4 can not be moved because of constraints in the building design. Space requirements for each center: Salonen machining has grouped its processes into six different departments: burr and grind, NC equipment, shipping and receiving, lathes and drills, tool crib, and inspection. The exact space requirements of each department, in square meters, are listed below. Department Area needed m 2 1. Burr and grind 100 2. NC equipment 95 3. Shipping and receiving 75 4. Lathes and drills 120 5. Tool crib 80 6. Inspection 70 TOTAL: 540 The layout designer must tie space requirements to capacity plans, calculate the specific equipment and space needs for each center, and allow circulation space such as aisles and the like. 13
Available space: A block plan allocates space and indicates placement of each department. When describing a new facility layout, the plan need only provide the facility s dimensions and space allocations. When an existing facility layout is being modified, the current block plan also is needed. Salonen machining s available space is 36 meters by 15 meters, or 540 square meters. The designer could begin the design by dividing the total amount of space into six equal blocks (90 square meters each), even though inspection needs only 70 square meters. The equal space approximation shown in the figure below is good enough until the detailed layout stage, when larger departments (such as lathes and drills) are assigned more block space than smaller departments. Current Block Plan 2 4 3 6 5 1 15m 36m 14
Closeness factors: The layout designer must also know which centers need to be located close to one another. Location is based on the number of trips between centers and qualitative factors. Below is Salonen machining s trip matrix, which gives the number of trips (or some other measure of materials movement) between each pair of departments per day. Trips between departments Department 1. Burr and grind 2. NC equipment 3 Shipping and receiving 4 Lathes and drills 5 Tool crib 6 Inspection 1 2 3 4 5 6-20 20 80-10 75-15 90-70 - - 15
Develop an acceptable block plan for Salonen machining, using trial and error. The goal is to minimize materials handling costs. Solution: A good place to start is with the largest closeness ratings in the trip matrix (say, 70 and above). Beginning with the largest number of trips and working down the list, you might plan to locate the departments as follows: Departments 3 and 6 close together Departments 1 and 6 close together Departments 2 and 5 close together Departments 4 and 5 close together Departments 3 and 4 should remain at their current locations because of the other considerations. If after several attempts you cannot meet all five requirements, drop one or more and try again. If you can meet all five easily, add more (such as for interactions below 70). The block plan in the figure shows a trial-and-error solutoion that satisfies all five requirements. We started by keeping departments 3 and 4 at their current locaitons. As the first requirement is to locate departments 3 and 6 close to each other, we put 6 in the southeast corner of the layout. The second requirement is to have departments 1 and 6 close together, so we place 1 in the space just to the left of 6, and so on. Proposed Block Plan 5 4 3 2 1 6 36m 15m 16
Improvement analysis: The table below includes all department pairs that have some load in between them. The Distance figures are based on recti-linear movements. Department pair Load Distance Current plan Load- Distance Distance Proposed plan Load-Distance 1-2 20 3 60 1 20 1-4 20 2 40 1 20 1-6 80 2 160 1 80 2-3 10 2 20 3 30 2-5 75 2 150 1 75 3-4 15 1 15 1 15 3-6 90 3 270 1 90 4-5 70 1 70 1 70 Tot: 785 400 Proposed Block Plan 5 4 3 2 1 6 36m Current Block Plan 2 4 3 6 5 1 15m 15m 36m 17
Technical considerations Requirements of different tasks If these are quite different, it may not be feasible to place the tasks in the same workstation. If these are incompatible, it may not even be feasible to put the work stations near each other. Human factors When humans are involved, tasks may take different amount of time to complete. Equipment limitations Space limitations 18
Designing Product Layouts Line balancing is the assignment of work elements to stations in a line. The goal is to achieve the desired output rate with the smallest number of workstations. Arranging stations in a sequence (line) for the product to move from one station to the next until its completion at the end of the line. The slowest station sets the output rate, e.g. 500/week. 19
Designing Product Layouts The goal is to match the output rate to the production plan. 1. The work is separated into work elements (the smallest units of work that can be performed independently) 2. A precedence diagram is constructed, which shows which work elements that must be performed before the next can begin. 3. Determine the desired output rate. 4. Calculate the cycle time (the maximum time allowed for work on a unit at each station) = 1/output rate 5. Assign work elements to stations. Balancing the line gives the minimum amount of stations for a determined output rate, still satisfying all precedence requirements Work Element Description Time (sec) Immediate Predecessor(s) A Bolt leg frame to hopper 40 None B Insert impeller shaft 30 A C Attach axle 50 A D Attach agitator 40 B E Attach drive wheel 6 B F Attach free wheel 25 C G Mount lower post 15 C H Attach controls 20 D, E I Mount nameplate 18 F, G A 40 C 50 B 30 F 25 D 40 G 15 Total 244 E 6 H 20 I 18 20
EXAMPLE 2 Designing product layouts (Line balancing) 21
EXAMPLE X.4 Green Grass, Inc., a manufacturer of lawn and garden equipment, is designing an assembly line to produce a new fertilizer spreader, the Big Broadcaster. Using the following information on the production process, construct a precedence diagram for the Big Broadcaster. Work Element Description Time (sec) Immediate Predecessor(s) A Bolt leg frame to hopper 40 None B Insert impeller shaft 30 A C Attach axle 50 A D Attach agitator 40 B E Attach drive wheel 6 B F Attach free wheel 25 C G Mount lower post 15 C H Attach controls 20 D, E I Mount nameplate 18 F, G Total 244 22
SOLUTION The figure shows the complete diagram. We begin with work element A, which has no immediate predecessors. Next, we add elements B and C, for which element A is the only immediate predecessor. After entering time standards and arrows showing precedence, we add elements D and E, and so on. The diagram simplifies interpretation. Work element F, for example, can be done D anywhere on the line after element C is completed. H However, element I must await completion of B 40 elements F and G. E 30 20 A 40 C F 25 6 50 I G 18 15 23
Designing Product Layouts Theoretical minimum no. of stations: TM = t/c [pc] t = total time required to assemble each unit c = cycle time Idle time (total unproductive time for all stations) IT= nc - t [min] n = no. of stations Efficiency (ratio of productive time to total time) E =( t/nc)*100 [%] Balance delay (amount by ) BD = 100 E [%] 24
EXAMPLE 3 Designing product layouts (Line balancing) 25
EXAMPLE X.5 Green Grass s plant manager just received marketing s latest forecasts of Big Broadcaster sales for the next year. She wants its production line to be designed to make 2,400 spreaders per week for at least the next 3 months. The plant will operate 40 hours per week. a. What should be the line s cycle time? b. What is the smallest number of workstations that she could hope for in designing the line for this cycle time? c. Suppose that she finds a solution that requires only five stations. What would be the line s efficiency? 26
SOLUTION a. First convert the desired output rate (2,400 units per week) to an hourly rate by dividing the weekly output rate by 40 hours per week to get units per hour. Then the cycle time is c = 1/r = 1/60 (hr/unit) = 1 minute/unit = 60 seconds/unit b. Now calculate the theoretical minimum for the number of stations by dividing the total time, St, by the cycle time, c = 60 seconds. Assuming perfect balance, we have TM = St 244 seconds = = 4.067 or 5 stations c 60 seconds c. Now calculate the efficiency of a five-station solution, assuming for now that one can be found: St 244 Efficiency = (100) = = 81.3% nc 5(60) 27
Designing Product Layouts How to assign work elements to stations then Ranked Positional Weight Technique (RPWT) The rationale for the RPWT is that the positional weight is a measure of the task s importance. Tasks with a high positional weight imply much subsequent work and tasks depending on them. Also Longest work element first Shortest work element first Etc 28
Designing Product Layouts Ranked Positional Weight Technique (RPWT) 1. Construct a diagram of precedence relationships among the tasks (arrows indicate which tasks must proceed others) 2. For each task, add up the task times for that task and ALL tasks that must follow it directly and indirectly. This value is called positional weight for the task. 3. Select the task with the largest positional weight and assign it to the first work station. 4. Select the task with the next largest positional weight and assign it to the earliest possible work station that exists, as long as: The maximum cycle time is not exceeded All the task s predecessors must be assign to the same or earlier work stations 29
Largest work-element time rule Same procedure as RPWT, but instead of choosing the work-element with the highest RPW, choose the work-element with the largest time (as long as the precedence requirements are fulfilled). 30
EXAMPLE 4 Designing product layouts (Line balancing) 31
Find a line balancing solution for Green Grass Inc. using the RPWT technique Work Element Description Time (sec) Immediate Predecessor(s) A Bolt leg frame to hopper 40 None B Insert impeller shaft 30 A C Attach axle 50 A B 30 D 40 E H 20 D Attach agitator 40 B E Attach drive wheel 6 B F Attach free wheel 25 C G Mount lower post 15 C H Attach controls 20 D, E I Mount nameplate 18 F, G Total 244 A 40 C 50 F 25 G 6 I 18 Theoretical minimum no of stations = 5 Cycle time = 60 sec 15 32
Find a line balancing solution for Green Grass Inc. using the RPWT technique Work Element Description Time (sec) Immediate Predecessor(s) A Bolt leg frame to hopper 40 None B Insert impeller shaft 30 A C Attach axle 50 A D Attach agitator 40 B E Attach drive wheel 6 B F Attach free wheel 25 C G Mount lower post 15 C H Attach controls 20 D, E I Mount nameplate 18 F, G Total 244 A 40 C 50 B 30 F 25 D 40 E 6 H 20 I Theoretical minimum no of stations = 5 Cycle time = 60 sec G 18 15 33
34
Solution: Station Candidates Choice Cumulative time Idle time S1 A A 40 20 S2 B,C C 50 10 S3 B, F, G B 30 30 E, F, G F 55 5 S4 D, E, G D 40 20 E, G G 55 5 S5 E, I I 18 42 E E 24 36 H H 44 16 When implementing this solution, we must observe precedence requirements within each station. For example, the worker at station S5 can do element I at any time but cannot start element H until element E is finnished. 35
B 30 D 40 E H 20 A 40 C 50 F 25 6 I G 18 15 36
37
The manager of a computer assembly line plans to produce 100 assembled computers per 10-hour workday. Work element data for the assembly is shown in the table below. Work element Time (minutes) Immediate predecessors A 2 None B 3 A C 1 B D 5 B E 5 C, D F 4 E G 1 D, E H 2 F I 6 G J 4 H K 2 I, J L 6 K a) Draw a precedence diagram. b) What cycle time (in minutes) results in the desired output rate? c) What is the theoretical minimum number of work stations? d) Using trial and error, balance the line as best as you can. e) What is the efficiency of your solution? 38
C A B E F H J K L D G I 39
C A B E F H J K L D G I Work element Time (minutes) RPW A 2 41 B 3 39 C 1 31 D 5 35 E 5 30 F 4 18 G 1 15 H 2 14 I 6 14 J 4 12 K 2 8 L 6 6 WS Candidates CT 1 A, B, C 6 2 D 5 3 E, G 6 4 F, H 6 5 I 6 6 J, K 6 7 L 6 40
WS1 C WS4 WS6 WS7 A B E F H J K L D WS2 G WS3 I WS5 41
Improving line efficiency 42
Parallel workstations Bottlenecks may be the result of difficult or very long tasks and may disrupt the flow of products down the line. In these situations, parallel workstations increase the work flow and provide flexibility. 43
Mixed model lines Still another approach is to design the line to handle multiple products, often referred to as mixed model lines. This implies that the products have to be similar with similar work elements. This approach offers great flexibility in varying the amount of output of the products. One example is found in the automotive industry where cars are often made on the same platform. 44
Workers Another approach to achieving a balanced line is to cross train workers to be able to perform multiple tasks. This implies that a worker with temporarily increased idle time can assist other workers to maintain the flow of the line, so called dynamic line balancing. 45
Improving job shop efficiency A job shop has the least efficiency Þ Creating a line flow in parts of the job shop will increase efficiency! One worker multiple machines Cell/Group technology These are called hybrid layouts! 46
One worker multiple machines One worker operates several machines simultaneously to achieve line flow (moves from one machine to the next) The machine set-up can be changed to produce different products or parts 47
Cell/Group technology This manufacturing technique groups parts or products with similar characteristics into families and sets aside groups of machines for their production => A line within the job shop. Based on shape, size, manufacturing requirements etc. Goal: efficient production with minimal change-over and set-up times 48
EXAMPLE 5 Cell/Group technology 49
50
Lathing Milling Drilling L L M M D D L L M M D D Grinding L L M M G G L L A Assembly A G G Receiving and shipping A A G G (a) Jumbled flows in a job shop without GT cells 51
L L M D Cell 1 Cell 2 G A Assembly area A Receiving L M G G Cell 3 L M D Shipping (b) Line flows in a job shop with three GT cells 52
Volvo CE, CS-09 Before: After: 53
Storage layouts The design of storage facilities present a different set of factors than the design of factory layouts. Frequency of order is an important consideration: Items that are ordered frequently should be placed near the entrance of the facility Items that are ordered infrequently should be placed in the rear of the facility. The goal is to minimize picking time and transportation (distance of movement and travel time)! 54
Storage layouts If items are ordered/sold together it is beneficial to store them close to each other. Other considerations: Width and length of aisles Height of storage racks Need to periodically make a physical count of stored items Modes of internal transport Level of automation 55
EXAMPLE 6 Storage Layout 56
57
58
Office layouts Office layouts are undergoing transformations as the flow of paperwork is replaced by electronic communications. This implies that there is less need to place office workers in a layout that optimizes a physical flow. However, providing efficient use of space and possibilities for cooperation between colleagues are of course important issues. 59
Relevant book chapters Chapter: Developing a process strategy Layout Chapter: Managing process constraints Chapter: Designing lean systems Designing lean systems layouts 60
Questions? antti.salonen@mdh.se Next lecture on Tuesday 2017-04-25 Aggregate planning 61