Lean and Agile Systems. Rajiv Gupta FORE School of Management October 2013 Session 6

Transcription

1 Lean and Agile Systems Rajiv Gupta FORE School of Management October 2013 Session 6

2 Module 1 Recap of Session 5 Module 2 Pull Production Rules of Kanban Module 3 Small Batch Production Level Production Module 4 Set-up reduction Jidoka Module 5 Summary and wrap up 2

3 Session 6 Begin Module 1 Recap of Session 5 3

4 Recap Machine cell design involves the determination of the number of workers and the assignment of workers to machines in the cell Machine cell design cannot be done unless we prepare for it, i.e., we must ensure the proper systems are in place such as setup reduction, TPM, quality, etc. Lean tools are what people attempt to apply when they think of TPS. Applying one or two tools in isolation without full management commitment has a good chance of failure 4

5 Recap Inventory is a symptom of other problems in the system. We use inventory to cover for inefficiencies and problems. Carrying inventory takes the focus away from solving the problems so that they do not recur Inventory reduction should not be attempted without working on the root causes for carrying inventory. Several failed attempts at the reducing inventory alone can be attributed to this approach. 5

6 Session 6 End of module 1 6

7 Session 6 Begin Module 2 Pull Sceduling Types of Kanban Rules of Kanban 7

8 Pull Production In Push scheduling each work center gets individual schedule based on a forecast Push scheduling is typically found with systems such as MRP/ERP etc. When there are changes in the requirements, the system has no means to self correct The result is confusion, excess inventory and long lead times 8

9 Pull Production In Pull scheduling, only one work center gets scheduled It pulls material from its upstream operation This continues through all upstream operations The normal approach is known as Kan Ban Borrowed from the grocery industry 9

10 Types of Kanban Production Instruction In-process kanban for scheduling flow processes Signal kanban for scheduling batch processes Kanban Parts Withdrawal Interprocess kanban for internal purposes Supplier kanban for external purposes 10

11 Types of Kanban In-process kanban used to convey instruction to produce small quantities (a pitch) to an upstream process Signal kanban used to convey instructions to produce a batch to an upstream process. Used when production is in batches due to high set ups Inter-process kanban used to signal the need to withdraw parts from a storage area and convey them to a downstream workstation in the same facility 11

12 Types of Kanban (contd.) Supplier kanban used to signal the need to withdraw parts from an external supplier to be conveyed to the plant storage or marketplace 12

13 Kanban Rules Rule 1 The downstream process should withdraw the necessary products from the upstream processes in the necessary quantities at the necessary point in time Any withdrawal without a Kanban should be prohibited Any withdrawal which is greater than the number of Kanbans should be prohibited 13

14 Kanban Rules Rule 2 The upstream process should produce its products in the quantities withdrawn by the downstream process Production greater than the number of Kanbans should not be permitted When several parts are to be produced, the production should follow the original sequence in which each Kanban has been delivered. 14

15 Kanban Rules Rule 3 No items are made or transported without a Kanban (Prevent excess production and transportation) Rule 4 Always attach a Kanban to the goods (It serves as a work order Rule 5 Defective products are not sent to subsequent process 15

16 Kanban Rules Rule 6 Reducing the number of Kanbans increases their sensitivity Kanbans should be used to adapt to small fluctuations in demand Reducing Kanbans reveal existing problems 16

17 Two Kinds of Conveyance There are two kinds of conveyance in the kanban system: Fixed time and variable quantity conveyance. Fixed quantity and variable time conveyance. Fixed time conveyance is preferable when processes are disconnected and conveyance distances are long. Easy to follow or "milk run" routes can be readily set up. External suppliers almost always use this form of conveyance. Fixed quantity conveyance is preferable when processes are connected (e.g., an assembly line) and conveyance distances are short, or when lot sizes are large (e.g., stamping). Toyota uses fixed quantity conveyance for stamped parts and for large injection-molded parts such as instrument panels. 17

18 Session 6 End of module 2 18

19 Session 6 Begin Module 3 Small Batch Production Level Production/Heijunka 19

20 Small Batch Production Batch sizes are a result of long set-up times, long handling distances, and a focus on unit costs As long as product variety was not too much, production in larger batches did not affect responsiveness of production, e.g., Henry Ford and his model T However, as product variety proliferated, large batch production led to various problems and inefficiencies in the system 20

21 Small Batch Production There are two types of batches sizes; production and transfer batches A production batch is the quantity that is produced at one time A transfer batch is the quantity that is moved between processes at one time Large batches result in larger inventory Larger batches result in poor quality feedback Larger batches result in less responsiveness to the customer 21

22 Batch Sizes and Inventory 22

23 Batch Sizes and Lead Times Station 1 Station 2 Station 1 Station 2 23

24 Batch Sizes and Flexibility Workcenter Workcenter 24

25 Level Production Tied to Customer Demand Takt time = No. of working seconds in a day/demand per day This establishes a rhythm for the entire supply chain, through the plant and to the suppliers Example: Demand for a product is 600 pieces per day. Assuming a single shift operation, 450 working minutes per shift or secs per shift. Takt time = 27000/600 = 45 seconds i.e., the line should be running at 45 secs/piece 25

26 Level Production Tied to Customer Demand The takt time represents the rate of demand. It is sometimes confused with the machine cycle time. This is incorrect. Producing at the rate of demand ensures no inventory buildup while meeting demand. The suppliers rate of production should also be matched to the takt rate. Then the entire supply chain will run in sync. The actual demand may vary somewhat from day to day, but this is absorbed by some inventory of finished product. 26

27 Level Production Tied to Customer Demand Assume there are 3 products being produced. The demand per week is 500, 200 and 100. There are several ways in which this can be accomplished This is not leveled production. The production varies from day to day. 27

28 Level Production Tied to Customer Demand Another way would be to produce every part every day Now, the production on any day is the same as on any other day. However, the production is not leveled during the day. This process may be expanded until there is more uniformity During the production in the day. What is the factor that limits how far we can do this? 28

29 Level Production Tied to Customer Demand The ultimate schedule would produce the 3 products in sets of 5, 2, 1. This is called the pitch. This method of production leveling is called Heijunka. 29

30 Session 6 End of module 3 30

31 Session 6 Begin Module 4 Setup reduction Autonomation/Jidoka 31

32 Set Up Reduction Traditional inventory models, such as EOQ, assume that the set up cost/time is a fixed quantity. Some large automated lines and presses can take more than a shift to change over from one product to another. With such long set up times, the batch sizes had to be large. Also, it was impractical to do much load leveling. Toyota challenged the assumption of fixed setup times 32

33 Set Up Reduction Setup Time Die retrieval from storage Tools readied Setup person scheduled Material handling equipment scheduled Removal of previous die Installation of new die Adjustment Tryout of new die Moving old die to storage Time elapsed from good piece to good piece 33

34 Set Up Reduction Problems with existing method of setup Scheduling not done in time resulting in long waiting times. Non standard procedures. Insufficient training. Non standard equipment and dies of different sizes and heights. Searching time. Different shut heights require longer adjustment. Tools, nuts, bolts missing. Excessive adjustment. 34

35 Set Up Reduction Steps in set up reduction (SMED) Determine existing setup procedure Divide activities into internal elements and external elements Internal elements are those that require the machine to be stopped External elements can be performed while the machine is running Try to convert internal elements to external elements Try to improve external elements 35

36 Autonomation - Jidoka Jidoka automation with a human touch or intelligent automation Stopping of a process when there is a problem Output buffer full Process out of control Andon chords Solution of the problem before the process is restarted Prevent expensive transmission of errors downstream 36

37 Jidoka The normal approach when a machine breaks down or if there is a quality problem is to find a quick solution so that the line does not stop. This thinking stems from the numbers mentality that pervades the western approach to manufacturing (the R orientation) The focus on keeping production going prevents the problem from being fully recognized and addressed. The result is that the problem will recur in the future 37

38 Jidoka Problems can occur in production due to a variety of reasons: Human error Lack of proper training/instructions Lack of proper tools Quality of incoming parts Poor design of task Machine problems Problems in the material flow 38

39 Jidoka Human error Sometimes the worker on the shop floor can make mistakes as no one is perfect. This may be due to carelessness, fatigue, or may be just a random occurrence Lack of proper training/instructions In several plants, the only real training a worker receives is brief instructions and then he/she is sent to the line to work This leads to variation in the way in which each task is completed. 39

40 Jidoka Lack of proper tools Due to lack of standardization and work structuring, or poor 5s/housekeeping, the right tools are not available at the workplace, which requires the worker to improvise. This can and does lead to mistakes Quality of incoming parts Poor quality of incoming parts can lead to machining and other production problems over which the worker has no control 40

41 Jidoka Poor design of task Due to the result orientation in several western production plants, the focus is to maximize production without the concern for how this is to be achieved. This leads to shortcuts and pressure on the supervisors and workers This results in little effort in the design of tasks to ensure that it can be consistently completed by the worker in the time allotted 41

42 Jidoka Machine problems If a machine breaks down, instead of ensuring that proper maintenance be performed, the focus is to get the machine up and running as fast as possible to minimize the loss in production The lack of focus on maintenance results in subsequent breakdowns in the machine and the same cycle repeats itself 42

43 Jidoka Problems in the material flow When production flow is not smooth, there may be problems due to non-availability of parts at a machine When there is a part shortage, attempts are made to address the problem as fast as possible, without looking at the root cause, which may be in the material flow design The problem will likely recur and the same cycle repeated 43

44 Jidoka The focus in Toyota is first to spend time in the proper design of the system However, in order to ensure that the system is operating as planned, any time there is a system breakdown, instead of taking shortcuts, the problem is analyzed to ensure that it does not recur This may lead to a short term stoppage in work, but eliminates stoppages in the long term 44

45 Why Jidoka Becomes The focus on numbers Necessary One thing that a plant manager or a supervisor does not want is a stoppage in production. The machine loss time is measured by corporate and few manufacturing personnel will risk their career by permitting lines to stop Fear of blame When a problem occurs, the normal tendency is to ask, who is responsible? rather than why did this problem occur? So people try to hide problems to prevent being found out 45

46 Jidoka The Japanese approach is to bring problems to the surface, analyze the problem going to the root cause, applying countermeasures and then monitoring to ensure that the problem does not recur The production capacity in a Japanese plant takes into account a certain number of andon pulls in a shift. If the number of andon pulls is less than planned, the management feels that either people are hiding problems or not pushing the system to its limits 46

47 Session 6 End of module 4 47

48 Session 6 Begin Module 5 Summary and wrap up 48

49 Summary Pull scheduling was developed by Taiichi Ohno to prevent overproduction There are four types of Kanban, each for a different purpose There are 6 rules of Kanban which must be followed for Kanban to succeed Long set-up times have resulted in batch manufacturing. Also, they result in loss of productive capacity. Therefore the focus in TPS is to reduce set-up times 49

50 Summary Set-up times can be reduced drastically. Some of the changes require little or no investments. Others may require changes to the equipment Jidoka requires that we shut down a process when a problem occurs and take corrective action to prevent the problem from recurring If the line stops once and the focus is on countermeasures preventing the problem, then the loss of production is more than offset by the elimination of future stoppages 50

51 End Module 5 Summary and wrap up 51