LESSON 24: JUST-IN-TIME

Transcription

1 LESSON 24: JUST-IN-TIME Outline Just-in-Time (JIT) Examples of Waste Some Elements of JIT 1 Just-in-time Producing only what is needed and when it is needed A philosophy An integrated management system 2

2 Just-in-time Theme: eliminate all waste including the ones caused by: inventory management supplier selection defective parts scheduling of production and delivery information system 3 Examples Of Waste Watching a machine run Waiting for parts Counting parts Overproduction Moving parts over long distances Storing inventory Looking for tools Machine breakdown Rework 4

3 Some Elements Of JIT 1. Focused factory networks 2. Grouped Technology: Cellular layouts 3. Quality at the source 4. Flexible resources 5. Pull production system 6. Kanban production control 7. Small-lot production and purchase 8. Quick setups 9. Supplier networks 5 Cellular Layouts Group dissimilar machines in a cell to produce a family of parts Reduce setup time and transit time Send work in one direction through the cell (resembling a small assembly line) Adjust cycle time by changing worker paths 6

4 Cellular Layouts Enter Machines Worker 1 Worker 2 Worker 3 Exit Key: Product route Worker route 7 Original Process Layout Assembly A B C Raw materials 8

5 Part Routing Matrix Machines Parts A x x x x x B x x x x C x x x D x x x x x E x x x F x x x G x x x x H x x x 9 Part Routing Matrix - Reordered Machines Parts A x x x x x B x x x x C x x x D x x x x x E x x x F x x x G x x x x H x x x 10

6 Part Routing Matrix - Reordered Machines Parts A x x x x x D x x x x x B x x x x C x x x E x x x F x x x G x x x x H x x x 11 Part Routing Matrix - Reordered Machines Parts A x x x x x D x x x x x B x x x x C x x x E x x x F x x x G x x x x H x x x 12

7 Part Routing Matrix - Reordered Machines Parts A x x x x x D x x x x x F x x x B x x x x C x x x E x x x G x x x x H x x x 13 Part Routing Matrix - Reordered Machines Parts A x x x x x D x x x x x F x x x B x x x x C x x x E x x x G x x x x H x x x 14

8 Part Routing Matrix - Reordered Machines Parts A x x x x x D x x x x x F x x x C x x x G x x x x B x x x x E x x x H x x x 15 Cellular Layout Solution Assembly Cell1 Cell 2 6 Cell Raw materials A C B 16

9 Advantages of Cellular Layouts Reduced material handling and transit time Reduced setup time Reduced work-in-process inventory Better use of human resources Easier to control Easier to automate 17 Disadvantages of Cellular Layouts Inadequate part families Poorly balanced cells Expanded training and scheduling of workers Increased capital investment 18

10 Quality At The Source Jidoka is the authority to stop a production line Andon lights signal quality problems Undercapacity scheduling allows for planning, problem solving & maintenance Visual control makes problems visible Poka-yoke prevents defects 19 Kaizen Continuous improvement Requires total employment involvement The essence of JIT is the willingness of workers to spot quality problems, halt production when necessary, generate ideas for improvement, analyze problems, and perform different functions 20

11 Flexible Resources Multifunctional workers General purpose machines Study operators & improve operations 21 Flexible Resources 22

12 Flexible Resources Cell 1 Cell 2 Worker 1 Worker 2 Worker 3 Cell 3 Cell 4 Cell 5 23 Pull Production System In a push system, a schedule is prepared in advance and as soon as one process completes its work, its products are sent to the next process. In a pull system, workers take the parts or materials from the preceding stations as needed.workers at the preceding stations may produce the next unit only after their outputs are taken by the workers in the subsequent processes. Although the concept of pull production seems simple, it can be difficult to implement. Kanbans are introduced to implement the pull system. 24

13 KanbanProduction Control Part no.: 7412 Description: Slip rings Box capacity 25 From : Machining M-2 Box Type A Issue No. 3/5 To: Assembly A-4 A kanban is a card that indicates quantity of production Kanbans maintain the discipline of pull production - A production kanban authorizes production - A withdrawal kanban authorizes the movement of goods 25 The Origin Of Kanban a. Two-bin inventory system b. Kanban Inventory System Reorder Card Bin 1 Bin 2 Q - R R Q = order quantity R = reorder point = demand during lead time Kanban 26

14 A Single-Kanban System 27 A Single-CardKanban System Consider the fabrication cell that feeds two assembly lines. 1. As an assembly line needs more parts, the kanban card for those parts is taken to the receiving post and a full container of parts is removed from the storage area. 2. The receiving post accumulates cards for both assembly lines and sequences the production of replenishment parts. 28

15 A Dual Kanban System 29 A Two-Card System 1. When the number of tickets on the withdrawal kanban reaches a predetermined level, a worker takes these tickets to the store location. 2. The workers compares the part number on the production ordering kanban at the store with the part number on the withdrawal kanban. 3. The worker removes the production ordering kanban from the containers, places them on the production ordering kanban post, and places the withdrawal kanbans in the containers. 4. When a specified number of production ordering kanbans have accumulated, work center 1 proceeds with production. 30

16 5. The worker transports parts picked up at the store to work center 2 and places them in a holding area until they are required for production. 6. When the parts enter production at work center 2, the worker removes the withdrawal kanbans and places them on the withdrawal kanban post. 31 Kanban Squares X X X X X X Flow of work Flow of information

17 Kanban Racks Signal Kanban

18 KanbanPost Office Types Of Kanbans Kanban Square marked area designed to hold items Signal Kanban triangular kanban used to signal production at the previous workstation Material Kanban used to order material in advance of a process Supplier Kanban rotates between the factory and supplier

19 Determining Number Of Kanbans avg.demand during lead time + safety stock No. ofkanbans = container size DL + w y = a where y = number of kanbans or containers D = average demand over some time period L = lead time to produce parts w = safety stock, usually 10% of the demand during lead time a = container size Kanban Calculation Example Problem statement: D = 150 bottles per hour L = 30 minutes = 0.5 hours DL = (150)(0.5) = 75 w = 10% of DL a = 25 bottles Solution: y = DL + w 75+ ( 0. 1)( 75) = a 25 = 3. 3 Kanban containers Round up to 4 (allow some slack) or down to 3 (force improvement)

20 Small-Lot Production Requires less space & capital investment Moves processes closer together Makes quality problems easier to detect Makes processes more dependent on each other 39 Small-lot Production and Purchase 40

21 Reducing Setup Time Preset desired settings Use quick fasteners Use locator pins Prevent misalignments Eliminate tools Make movements easier 41 Trends In Supplier Policies 1. Locate near to the customer 2. Use small, side loaded trucks and ship mixed loads 3. Consider establishing small warehouses near to the customer or consolidating warehouses with other suppliers 4. Use standardized containers and make deliveries according to a precise delivery schedule 5. Become a certified supplier and accept payment at regular intervals rather than upon delivery 42

22 Benefits Of JIT 1. Reduced inventory 2. Improved quality 3. Lower costs 4. Reduced space requirements 5. Shorter lead time 6. Increased productivity 7. Greater flexibility 8. Better relations with suppliers 9. Simplified scheduling and control activities 10. Increased capacity 11. Better use of human resources 12. More product variety 43 READING AND EXERCISES Lesson 24 Reading: Section 7.6 pp (4 th Ed.) pp (5 th Ed.) Exercise: 37 p. 395 (4 th Ed.), p. 384 (5 th Ed.) 44