Session 8
- 1. Operations Management Session 8 – JIT and Lean Operations
- 2. Learning Objectives When you complete this chapter you should be able to: Define just-in-time, TPS, and lean operations Define the seven wastes and the 5 Ss Explain JIT partnerships Determine optimal setup time
- 3. Learning Objectives When you complete this chapter you should be able to: Define kanban Compute the required number of kanbans Explain the principles of the Toyota Production System
- 4. Toyota Motor Corporation Largest vehicle manufacturer in the world with annual sales of over 9 million vehicles Success due to two techniques, JIT and TPS Continual problem solving is central to JIT Eliminating excess inventory makes problems immediately evident
- 5. Toyota Motor Corporation Central to TPS is a continuing effort to produce products under ideal conditions Respect for people is fundamental Small building but high levels of production Subassemblies are transferred to the assembly line on a JIT basis High quality and low assembly time per vehicle
- 6. Just-In-Time, TPS, and Lean Operations JIT is a philosophy of continuous and forced problem solving via a focus on throughput and reduced inventory TPS emphasizes continuous improvement, respect for people, and standard work practices Lean production supplies the customer with their exact wants when the customer wants it without waste
- 7. Just-In-Time, TPS, and Lean Operations JIT emphasizes forced problem solving TPS emphasizes employee learning and empowerment in an assembly-line environment Lean operations emphasize understanding the customer
- 8. Eliminate Waste Waste is anything that does not add value from the customer point of view Storage, inspection, delay, waiting in queues, and defective products do not add value and are 100% waste
- 9. Ohno’s Seven Wastes Overproduction Queues Transportation Inventory Motion Overprocessing Defective products
- 10. Eliminate Waste Other resources such as energy, water, and air are often wasted Efficient, ethical, and socially responsible production minimizes inputs, reduces waste Traditional “housekeeping” has been expanded to the 5 Ss
- 11. The 5 Ss Sort/segregate – when in doubt, throw it out Simplify/straighten – methods analysis tools Shine/sweep – clean daily Standardize – remove variations from processes Sustain/self-discipline – review work and recognize progress
- 12. The 5 Ss Sort/segregate – when in doubt, throw it out Simplify/straighten – methods analysis tools Shine/sweep – clean daily Standardize – remove variations from processes Sustain/self-discipline – review work and recognize progress Two additional Ss Safety – build in good practices Support/maintenance – reduce variability and unplanned downtime
- 13. Remove Variability JIT systems require managers to reduce variability caused by both internal and external factors Variability is any deviation from the optimum process Inventory hides variability Less variability results in less waste
- 14. Sources of Variability Incomplete or inaccurate drawings or specifications Poor production processes resulting in incorrect quantities, late, or non-conforming units Unknown customer demands
- 15. Sources of Variability Incomplete or inaccurate drawings or specifications Poor production processes resulting in incorrect quantities, late, or non-conforming units Unknown customer demands Both JIT and inventory reduction are effective tools in identifying causes of variability
- 16. Improve Throughput The time it takes to move an order from receipt to delivery The time between the arrival of raw materials and the shipping of the finished order is called manufacturing cycle time A pull system increases throughput
- 17. Improve Throughput By pulling material in small lots, inventory cushions are removed, exposing problems and emphasizing continual improvement Manufacturing cycle time is reduced Push systems dump orders on the downstream stations regardless of the need
- 18. Just-In-Time (JIT) Powerful strategy for improving operations Materials arrive where they are needed when they are needed Identifying problems and driving out waste reduces costs and variability and improves throughput Requires a meaningful buyer-supplier relationship
- 19. JIT and Competitive Advantage Figure 16.1
- 20. JIT and Competitive Advantage Figure 16.1
- 21. JIT Partnerships JIT partnerships exist when a supplier and purchaser work together to remove waste and drive down costs Four goals of JIT partnerships are: Removal of unnecessary activities Removal of in-plant inventory Removal of in-transit inventory Improved quality and reliability
- 22. JIT Partnerships Figure 16.2
- 23. Concerns of Suppliers Diversification – ties to only one customer increases risk Scheduling – don’t believe customers can create a smooth schedule Changes – short lead times mean engineering or specification changes can create problems Quality – limited by capital budgets, processes, or technology Lot sizes – small lot sizes may transfer costs to suppliers
- 24. JIT Layout Table 16.1 Reduce waste due to movement JIT Layout Tactics Build work cells for families of products Include a large number operations in a small area Minimize distance Design little space for inventory Improve employee communication Use poka-yoke devices Build flexible or movable equipment Cross-train workers to add flexibility
- 25. Distance Reduction Large lots and long production lines with single-purpose machinery are being replaced by smaller flexible cells Often U-shaped for shorter paths and improved communication Often using group technology concepts
- 26. Increased Flexibility Cells designed to be rearranged as volume or designs change Applicable in office environments as well as production settings Facilitates both product and process improvement
- 27. Impact on Employees Employees are cross trained for flexibility and efficiency Improved communications facilitate the passing on of important information about the process With little or no inventory buffer, getting it right the first time is critical
- 28. Reduced Space and Inventory With reduced space, inventory must be in very small lots Units are always moving because there is no storage
- 29. Inventory Inventory is at the minimum level necessary to keep operations running Table 16.2 JIT Inventory Tactics Use a pull system to move inventory Reduce lot sizes Develop just-in-time delivery systems with suppliers Deliver directly to point of use Perform to schedule Reduce setup time Use group technology
- 30. Reduce Variability Inventory level Figure 16.3 Process downtime Scrap Setup time Late deliveries Quality problems
- 31. Reduce Variability Inventory level Scrap Setup time Late deliveries Quality problems Process downtime Figure 16.3
- 32. Reduce Lot Sizes Figure 16.4 200 – 100 – Inventory Time Q 2 When average order size = 100 average inventory is 50 Q 1 When average order size = 200 average inventory is 100
- 33. Reduce Lot Sizes Ideal situation is to have lot sizes of one pulled from one process to the next Often not feasible Can use EOQ analysis to calculate desired setup time Two key changes necessary Improve material handling Reduce setup time
- 34. Lot Size Example D = Annual demand = 400,000 units d = Daily demand = 400,000/250 = 1,600 per day p = Daily production rate = 4,000 units Q = EOQ desired = 400 H = Holding cost = $20 per unit S = Setup cost (to be determined) Setup time = $2.40/($30/hour) = 0.08 hr = 4.8 minutes Q = 2DS H(1 - d/p) Q 2 = 2DS H(1 - d/p) S = = = $2.40 (Q 2 )(H)(1 - d/p) 2D (3,200,000)(0.6) 800,000
- 35. Reduce Setup Costs High setup costs encourage large lot sizes Reducing setup costs reduces lot size and reduces average inventory Setup time can be reduced through preparation prior to shutdown and changeover
- 36. Lower Setup Costs Figure 16.5 Sum of ordering and holding costs Holding cost Setup cost curves (S 1 , S 2 ) T 1 S 1 T 2 S 2 Cost Lot size
- 37. Reduce Setup Times Figure 16.6 Use one-touch system to eliminate adjustments (save 10 minutes) Step 4 Step 5 Training operators and standardizing work procedures (save 2 minutes) Initial Setup Time Step 2 Move material closer and improve material handling (save 20 minutes) Step 1 Separate setup into preparation and actual setup, doing as much as possible while the machine/process is operating (save 30 minutes) Step 3 Standardize and improve tooling (save 15 minutes) 90 min — 60 min — 45 min — 25 min — 15 min — 13 min — — Repeat cycle until subminute setup is achieved Step 6
- 38. JIT Scheduling Schedules must be communicated inside and outside the organization Level schedules Process frequent small batches Freezing the schedule helps stability Kanban Signals used in a pull system
- 39. JIT Scheduling Table 16.3 Better scheduling improves performance JIT Scheduling Tactics Communicate schedules to suppliers Make level schedules Freeze part of the schedule Perform to schedule Seek one-piece-make and one-piece move Eliminate waste Produce in small lots Use kanbans Make each operation produce a perfect part
- 40. Level Schedules Process frequent small batches rather than a few large batches Make and move small lots so the level schedule is economical “ Jelly bean” scheduling Freezing the schedule closest to the due dates can improve performance
- 41. Scheduling Small Lots Figure 16.7 A B C A A A B B B B B C JIT Level Material-Use Approach A C A A A B B B B B C C B B B B A A Large-Lot Approach Time
- 42. Kanban Kanban is the Japanese word for card The card is an authorization for the next container of material to be produced A sequence of kanbans pulls material through the process Many different sorts of signals are used, but the system is still called a kanban
- 43. Kanban User removes a standard sized container Signal is seen by the producing department as authorization to replenish Figure 16.8 Part numbers mark location Signal marker on boxes
- 44. Kanban Figure 16.9 Purchased Parts Supplier Work cell Raw Material Supplier Kanban Sub-assembly Ship Kanban Kanban Kanban Kanban Finished goods Customer order Final assembly Kanban
- 45. More Kanban When the producer and user are not in visual contact, a card can be used When the producer and user are in visual contact, a light or flag or empty spot on the floor may be adequate Since several components may be required, several different kanban techniques may be employed
- 46. More Kanban Usually each card controls a specific quantity or parts Multiple card systems may be used if there are several components or different lot sizes In an MRP system, the schedule can be thought of as a build authorization and the kanban a type of pull system that initiates actual production
- 47. More Kanban Kanban cards provide a direct control and limit on the amount of work-in-process between cells If there is an immediate storage area, a two-card system can be used with one card circulating between the user and storage area and the other between the storage area and the producer
- 48. The Number of Kanban Cards or Containers Need to know the lead time needed to produce a container of parts Need to know the amount of safety stock needed Number of kanbans (containers) Demand during Safety lead time + stock Size of container =
- 49. Number of Kanbans Example Daily demand = 500 cakes Production lead time = 2 days (Wait time + Material handling time + Processing time) Safety stock = 1/2 day Container size = 250 cakes Demand during lead time = 2 days x 500 cakes = 1,000 Number of kanbans = = 5 1,000 + 250 250
- 50. Advantages of Kanban Allow only limited amount of faulty or delayed material Problems are immediately evident Puts downward pressure on bad aspects of inventory Standardized containers reduce weight, disposal costs, wasted space, and labor
- 51. Quality Strong relationship JIT cuts the cost of obtaining good quality because JIT exposes poor quality Because lead times are shorter, quality problems are exposed sooner Better quality means fewer buffers and allows simpler JIT systems to be used
- 52. JIT Quality Tactics Table 16.4 Use statistical process control Empower employees Build fail-safe methods (poka-yoke, checklists, etc.) Expose poor quality with small lot JIT Provide immediate feedback
- 53. Toyota Production System Continuous improvement Build an organizational culture and value system that stresses improvement of all processes Part of everyone’s job Respect for people People are treated as knowledge workers Engage mental and physical capabilities Empower employees
- 54. Toyota Production System Standard work practice Work shall be completely specified as to content, sequence, timing, and outcome Internal and external customer-supplier connection are direct Product and service flows must be simple and direct Any improvement must be made in accordance with the scientific method at the lowest possible level of the organization
- 55. Lean Operations Different from JIT in that it is externally focused on the customer Starts with understanding what the customer wants Optimize the entire process from the customer’s perspective
- 56. Building a Lean Organization Transitioning to a lean system can be difficult Lean systems tend to have the following attributes Use JIT techniques Build systems that help employees produce perfect parts Reduce space requirements
- 57. Building a Lean Organization Develop partnerships with suppliers Educate suppliers Eliminate all but value-added activities Develop employees Make jobs challenging Build worker flexibility
- 58. JIT in Services The JIT techniques used in manufacturing are used in services Suppliers Layouts Inventory Scheduling