Mechanical Engineering 101

Transcription

1 Mechanical Engineering 101 University of California, Berkeley Lecture #19 1

2 Today s lecture Pull systems Kanban Variations, Scheduling, Assumptions CONWIP (constant work in process) choosing N backlog lists 2

3 Kanban systems one card system kanban squares empty spot triggers production signal kanbans two card system 3

4 Signal kanbans signal authorizes production of entire EMQ signal kanban signal kanban signal kanban Part A Part B Part C 4

5 Signal kanbans signal authorizes production of entire EMQ possibly preceded by material order authorization material kanban signal kanban material kanban material kanban signal kanban signal kanban Part A Part B Part C 5

6 Oatmeal kanban ME 101 lecture 18 6

7 Oatmeal kanban ME 101 lecture 18 7

8 Oatmeal kanban ME 101 lecture 18 8

9 Kanban systems one card system kanban squares empty spot triggers production signal kanbans two card system producer makes parts in response to arrival of kanban card inventory stored in buffers between stages at user 9

10 Kanban systems two card system both input (user) and output (producer) buffers maintained Useful with multiple work centers using same part parts already waiting in output buffer when withdrawal kanban arrives from user producer makes parts in response to production kanban posted when a previous order was filled could have been triggered by any work center using part 10

11 2 card kanban example withdrawal kanban (aka transport) kanban production kanban products M,V,W,X,Y,Z PM 2 WM M 2 M PV 1 WV 1 V PW 1 WW 1 W PX 1 WX 1 X PY 1 WY 1 Y PZ 1 WZ 1 Z Inter-process inventory 11

12 Steady state i input buffer WM 2 M WV 1 V WW 1 W WX PM 2 WM 2 M M M M 1 X M X WY 1 Y WZ 1 Z process i i output buffer PV 1 V PW 1 W PX 1 PY 1 Y PZ 1 Z transit i+1 input buffer WV 1 V WW 1 W WX 1 X WY 1 Y WZ 1 Z 12

13 Kanban scheduling rules several choices FCFS first come first served SPT shortest processing time families often FCFS between families EMQ wait until EMQ orders accumulated 13

14 Kanban scheduling rules yet more choices cyclical production fixed, repeating sequence (most efficient sequence) continuous time production quantity set to total number outstanding authorizations» but often have a min and a max periodic review do one full sequence per production period» based on outstanding orders at start of period variation: signal kanbans send signal kanban at reorder point with earlier material kanban signals 14

15 Assumptions needed for efficient use of kanbans demand and demand mix approximately constant otherwise need to adjust # kanbans short setup times allows rapid response to actual demand or you ll need large buffers (lots of inventory) disciplined workforce proper transfer of kanbans produce only if kanban available, flexible capacity cross-trained workers maintenance 15

16 Today s lecture Pull systems Kanban Variations, Scheduling, Assumptions CONWIP (constant work in process) choosing N backlog lists 16

17 Conventional kanban parts in production & output buffer inventory part of WIP for each part type, a constant level of WIP Raw mat ls Buffers controlled by item type i-1 i i+1 Mat l flow Info flow Finished products Work center Buffers control max WIP level 17

18 CONWIP Raw mat ls Multi-item buffers i-1 i i+1 Finished products Forecasts, order or backlog list parts in production & output buffers = WIP aggregate part types maintain constant level of N jobs in system release new jobs to production as items removed based on prioritized backlog list 18

19 Selecting target WIP level N capacity Average Demand Rate WIP vs. Production Tradeoff (practice) WIP vs. Production (theory) N WIP Goal is N where average production rate matches average demand 19

20 Selecting target WIP level N if demand is near capacity, want enough WIP to avoid starving bottleneck gradually increase N until bottleneck input queue rarely empty 20

21 CONWIP variations simplest is measuring WIP in jobs when work per job similar or jobs to workstations ratio N:M low variation: measure WIP in hours (work-hours in final product) variation: bottlenecks measure WIP headed toward bottleneck keep bottleneck busy 21

22 Today s lecture Pull systems Kanban Scheduling, Variations, Assumptions CONWIP (constant work in process) choosing N backlog lists A. Target inventory level method B. Demand forecasting method 22

23 Backlog list example A CONWIP w/ N=150 hours Target inventory level approach to get some demand feedback 24

24 Backlog list example A CONWIP w/ N=150 hours Target inventory level approach Based on historical lead-time demand part batch target current current production no. size inventory inventory in process hrs/batch 1A B C D E F G H

25 .Backlog list example A check production hrs in target inventory 2* * *2.2 = hrs part batch target current current production no. size inventory inventory in process hrs/batch 1A B C D E F G H

26 .Backlog list example A production hours in current inventory (95/50)*3.5 + (240/50)*8.4 + = hrs part batch target current current production no. size inventory inventory in process hrs/batch 1A B C D E F G H

27 .Backlog list example A WIP in process = 23.1 hrs part batch target current current production no. size inventory inventory in process hrs/batch 1A B C D E F G H

28 Backlog list example A Are we ready to release more parts to production? 1. Yes 2. No CONWIP w/ N=150 hours production hours in current inventory (95/50)*3.5 + (240/50)*8.4 + = hrs WIP in process = 23.1 hrs 32

29 .Backlog list example A What s currently in backlog? 3C,5E,6F,7G part batch target current current production no. size inventory inventory in process hrs/batch 1A B C D E F G H

30 Today s lecture Pull systems Kanban Scheduling, Variations, Assumptions CONWIP (constant work in process) choosing N backlog lists A. Target inventory level method B. Demand forecasting method 36

31 Priority backlog list example B assign due dates based on sales or forecasts target release date = due date - expected flow time prioritize by earliest target release date 37

32 Priority backlog list example B Release date = due date - expected flow time Measured throughput 2 days center B, 5 days center D, 1 day all others What is first job on prioritized backlog list? PN work centers due expected date flow time 1 C,D,A 10 2 B,E,F,C 6 3 C,D,A 8 4 A,C,E 7 5 A,C,G,D,E 12 6 A,C,E 4 7 A,B,C,G,D 7 target release 38

33 Homework 8 Askin reading: pp Assume only fixed cost ($275K), no variable cost for conveyor What info is missing in problem? State the assumptions you use in the absence of this information In line three, when it says demand is 50 units/day and growing by 5 units per day each week they mean daily demand is growing by 5 units each week E.g. 50 units/day week1, 55 units/day week2, etc. The remaining problems reference the films shown in lecture 43

34 Homework 8 (continued) The remaining problems reference the films shown in lecture: Referencing the film 1924 On the Line: Compare and contrast the British and American factories (as portrayed in the film) after both had converted to mass production on moving assembly lines. Do you think the assembly line workers at Mazda as portrayed in the second film (Mazda Miracles) had better work lives than the workers portrayed in the first film (1924 On the Line)? Why or why not? For both of these problems, your answer should be in paragraph form, written in complete sentences, with a topic sentence, etc. 44