1、Just-In-Time Systems (Lean Production),Origins of JIT and Lean Production,Pioneered by Toyota Adopted by other Japanese manufacturers Discovered much later by Western manufacturers Known by many names: Toyota Production System Just In Time Lean production Flow production,Lean Production Benefits,Dou
2、ble labour productivity 90% reduction in throughput times 90% reduction in inventory Improved quality Reduced time to market,How Long does it Take?,Womack and Jones document many cases where major improvements are achieved in a matter of days,How Much does it Cost?,The cost is usually very low In ma
3、ny cases, companies replace expensive equipment with much simpler and cheaper equipment Lean production does not emphasize technology or automation,Hewlett Packards Cupertino California plant,1982 (before JIT),1986 (after JIT),15 days,11.3 hours,$670,000,$20,000,200,2,The Lean Transformation at Lant
4、ech,From: Womack and Jones, Lean Thinking, p.121,Relative Performance in Auto Industry,1993-94, from Womack and Jones, Lean Thinking,Relative Performance in Auto Industry,1993-94, from Womack and Jones, Lean Thinking,Porsches Lean Transition,Source: Womack and Jones, Lean Thinking,Porsches Lean Tran
5、sition,Source: Womack and Jones, Lean Thinking,What is JIT/Lean Production ?,Producing only what is needed, when it is needed A philosophy An integrated management system JITs mandate: Eliminate all waste,Examples of Waste,Watching a machine run Waiting for parts Counting parts Producing parts that
6、arent needed Moving parts over long distances Storing inventory Looking for tools or parts Machine breakdown Rework and scrap Products that dont meet the needs of customers,Lean Principles,Specify value defined by the customer Identify value stream eliminate all activities that dont add value Flow p
7、roducts should flow along value stream,Lean Principles,Pull let the customer pull products they want, rather than pushing products they may not want Perfection strive for perfection through continuous improvement,Targets for Eliminating Waste,Zero defects Zero setup time Zero inventories Zero part h
8、andling Zero breakdowns Zero lead time Lot size of one Match products to customer needs,Zero Defects,The traditional assumption is that a certain level of defects is unavoidable Traditional manufacturing measures defect rates and compares them to acceptable quality levels acceptance sampling average
9、 outgoing quality JIT strives to eliminate once and for all the causes of defects,Zero Inventories,In traditional manufacturing, inventories are seen as assets Inventories provide a safety buffer, and result from maximizing machine utilization JIT views inventory as waste Inventory is evidence of po
10、or design, poor coordination, and poor operation of a manufacturing system,Inventory Hides Problems,PoorQuality,Unreliable Supplier,Machine Breakdown,Inefficient Layout,Bad Design,Lengthy Setups,Lower Levels Of Inventory To Expose Problems,PoorQuality,Unreliable Supplier,Machine Breakdown,Inefficien
11、t Layout,Bad Design,Lengthy Setups,Zero Setup Time,Traditional thinking considers the setup time to be given and irreducible Traditional Economic Order Quantity and Economic Production Lot formulas find a tradeoff between setup cost and inventory cost JIT thinking recognizes the importance of reduci
12、ng the setup time If the setup time is zero, the optimal lot size is one,Zero Lead Time,Short setups and small lots lead naturally to short lead times The planning horizon can be closer, and the forecasts more accurate The system can change quickly in response to changing demand The flexibility is t
13、hus improved,Zero Parts Handling,JIT considers all part handling to be a waste, since it does not add value Part handling includes component feeding component handling parts inspection shipping and transportation,Zero Parts Handling,Unnecessary handling can be eliminated by careful design of the pro
14、duct and the process design for assembly design for manufacturability cellular manufacturing JIT deliveries to point-of-use,Zero Breakdowns,Maintain equipment in top condition Implement Total Productive Maintenance Dont wait for problems to occur The old saying “If it aint broke, dont fix it” is wro
15、ng!,Zero Leadtimes, Lot Size of One,If setup times are zero, lot size of one is feasible Lot size of one allows continuous flow instead of batch-and-queue WIP and lead times will be slashed as a result,Matching Product Design to Market Demand,Concurrent engineering reduces the design cycle Greater p
16、roduct variety is achieved through modular design Reduced number of parts and components is achieved through good design, and through standardization and reuse of common items.,Mass Customization,Provide every customer with an individualized product Make to order (customer pull) Maximize value,Keys
17、to Mass Customization,Define value (QFD) Design modular product architectures Standardize components, minimize unnecessary variety Configure individual products from standard modules,Basic Elements of JIT,1. Flexible resources2. Cellular layouts3. Pull production system4. Kanban production control5.
18、 Small-lot production6. Quick setups7. Uniform (mixed model) production8. Quality at the source9. Total productive maintenance10. Supplier networks,Flexible Resources,Flexible labour multifunction, adaptable operators the number of operators can be changed to change capacity Flexible equipment a var
19、iety of products are produced on the same equipment this requires multifunctional machines Achievable with basic technology!,Product Families,Group Technology (GT) is commonly used to identify product families based on similarities in design or processing GT helps reduce unnecessary duplication in p
20、roduct design GT identifies product families with similar processing requirements These families can be manufactured in well-defined manufacturing cells,Cellular Manufacturing,Group dissimilar machines in manufacturing cell to produce family of parts Work flows in one direction through cell One work
21、er tends several machines Cycle time adjusted by changing number of workers,Manufacturing Cell With Worker Routes,Enter,Worker 1,Worker 2,Worker 3,Exit,Key:,Product route Worker route,Machines,Flow Based Production,Cellular manufacturing achieves the benefits of flow based manufacturing This simplif
22、ies material flow compared to a traditional process layout Ownership and responsibility for a product rests with the operators of the cell,The Traditional Push System,In traditional manufacturing, an item is released for production at a specified time, with an associated due date The item moves thro
23、ugh a sequence of operations,The Traditional Push System,When one operation is finished, the item is “pushed” to the next operation Finally, the product is pushed to inventory, to meet forecast demand This is classical push-type production, as incorporated in the MRP approach,The Pull System,The pul
24、l system focuses on the output of the system rather than the input Finished products are “pulled” from the final operation in response to firm customer orders,The Pull System,This leads to a chain reaction, with each station pulling material from its preceding station JIT uses the “Kanban” system to
25、 control the flow of material with very little work-in-process inventory,The Kanban System,The Kanban system uses simple cards to strictly control production The basic idea is that no station is permitted to produce more than is immediately required by the succeeding station This simple idea prevent
26、s the buildup of inventory No computer is required!,Kanban Production Control System,Kanban card indicates standard quantity of production Derived from two-bin inventory system Kanban maintains discipline of pull production Production kanban authorizes production Withdrawal kanban authorizes movemen
27、t of goods,A Sample Kanban,Machining M-2,Assembly A-4,Part no.: 7412 Description: Slip rings,From :,To:,Box capacity 25Box Type AIssue No. 3/5,The Origin Of Kanban,Q = order quantity R = reorder point= demand during lead time,Bin 1,Bin 2,Q - R,Reorder Card,Kanban,a. Two-bin inventory system b. Kanba
28、n Inventory System,Dual Kanbans,P,W,Container with withdrawal kanban,Container with production kanban,X X X,X,X,Flow of work,Flow of kanban,Kanban Squares,X,X,X,X,Flow of work,Flow of information,Types Of Kanbans,Kanban Square marked area designed to hold items Signal Kanban triangular kanban used t
29、o signal production at the previous workstation Material Kanban used to order material in advance of a process Supplier Kanbans rotate between the factory and suppliers,Determining Number Of Kanbans,where N = number of kanbans or containers d = average demand over some time period L = lead time to p
30、roduce parts S = safety stock C = container size,Kanban Calculation Example,Problem statement: d = 150 bottles per hour L = 30 minutes = 0.5 hours dL = (150)(0.5) = 75 S = 10% dL = 10% x 75 = 7.5 C = 25 bottlesSolution:Round up to 4 (allow some slack) or down to 3 (force improvement),Small-Lot Produ
31、ction,The pull system reduces inventory by minimizing the number of kanbans This results in frequent material movement or production, in small lots Small-lot production has many advantages,Small-Lot Production,Reduces inventory Requires less space & capital investment Moves processes closer together
32、 Makes quality problems easier to detect Makes processes more dependent on each other,Setup Time Reduction,Small lots require short setups! Setup times can be reduced from hours to minutes Shingo developed Single Minute Exchange of Dies (SMED) system die change under 10 minutes,SMED Principles,1. Se
33、parate internal setup from external setup 2. Convert internal setup to external setup 3. Streamline all aspects of setup 4. Perform setup activities in parallel or eliminate them entirely,Setup Reduction Techniques,Preset desired settings Use quick fasteners Use locator pins Prevent misalignments El
34、iminate tools Make movements easier,Mixed Model Production,JIT permits the manufacture or assembly of a range of products simultaneously, using the same production equipment This is known as mixed model production The result is repetitive flow production versus traditional batch production Mixed mod
35、el production requires small batches and short setups,Example of mixed model scheduling,Traditional Batch Schedule,JIT Schedule,JIT Production Schedule,Mixed model production of six different products repeats on a 48 minute cycle.,Advantages of Level Scheduling,Batch production becomes repetitive Lo
36、w inventories Flexible and responsive Simple to control - computers are not needed!,Quality At The Source,Jidoka is authority to stop production line Andon lights signal quality problems Undercapacity scheduling allows for planning, problem solving & maintenance Visual control makes problems visible
37、 Poka-yoke prevents defects,Visual Control,Library shelf,Work station,Visual kanbans,Tool board,Machine controls,Better,Good,Best,30-50,How to,sensor,Kaizen,Continuous improvement Requires total employment involvement Essence of JIT is willingness of workers to spot quality problems halt production
38、when necessary generate ideas for improvement analyze problems perform different functions,Total Productive Maintenance (TPM),Breakdown maintenance repairs to make failed machine operational Preventive maintenance system of periodic inspection & maintenance to keep machines operating TPM combines pr
39、eventive maintenance & total quality concepts,TPM Requires Management To,Design products that can be easily produced on existing machines Design machines for easier operations, changeover, maintenance Train & retrain workers to operate machines Purchase machines that maximize productive potential De
40、sign preventive maintenance plan spanning life of machine,The Relationship with Suppliers,Traditional relationship with suppliers is adversarial Relationships are short term, based solely on cost Large number of suppliers are played against one another,The Relationship with Suppliers,JIT views the s
41、upplier relationship as critical Fewer suppliers The relationships are long-term, based on cooperation Suppliers must strive to continuously improve To achieve frequent deliveries of small lots, just in time, suppliers must adopt JIT methods as well,Trends In Supplier Policies,1. Locate near to the
42、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 an
43、d accept payment at regular intervals rather than upon delivery,Benefits Of JIT,1. Reduced inventory2. Improved quality3. Lower costs4. Reduced space requirements5. Shorter lead time6. 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,
