Production Release Control: Paced, WIP-Based or Demand-Driven? Revisiting the Push/Pull and Make-to-Order/Make-to-Stock Distinctions

Transcription

1 Production Release Control: Paced, WIP-Based or Demand-Driven? Revisiting the Push/Pull and Make-to-Order/Make-to-Stock Distinctions George Liberopoulos Department of Mechanical Engineering University of Thessaly Volos, Greece 1

2 Outline 1. Introduction 2. Production control in the absence of demands 3. Production control in the presence of demands 4. Examples of hybrid push/pull systems 5. Production control with advance demand information or forecasts 6. Conclusions 2

3 1. Introduction 3

4 Push / pull distinction still unclear Definition 1 (e.g., Karmarkar (1989), Nahmias (2009)): Pull: Production is initiated as a reaction to present demand. Push: Production is initiated in anticipation of future demand. Kanban: pull MRP: push Definition 2 (e.g., Vollmann, Berry, Whybark, Jacobs (2005), Zipkin (2000), Liberopoulos, Dallery (2000)): Pull: Production is triggered by demands for finished products. Push: Production is initiated independently of demands. Kanban, MRP, base stock: pull takt-paced production system: push Definition 3: (e.g., Hopp, Spearman (2004), Karrer (2012), Gonzalez-R, Framinan, Pierreval (2012)) Pull: Explicit limit on the amount of WIP that can be in the system. Push: No explicit limit on the amount of WIP that can be in the system. Kanban, CONWIP, PAC, MRP/WIP constraint: pull MRP, base stock, (Q,R): push 6

5 Make-to-stock (MTS) / Make-to-order (MTO) / Make-toforecast (MTF) distinction Definition 4: MTO/MTF: Production releases are initiated to meet specific actual/forecasted customer orders (demand). MTS: Production releases are initiated to replenish inventory as it is being depleted by actual customer orders (demand). MTO: Production follows demand. MTF and MTS: Production precedes demand. (demand is timed at the due date and not the arrival time of a customer order) 7

6 Pull / Push distinction has to do with what triggers production releases pull: Def 1. present demands Def 2. any (present/future) demands Def 3. WIP level (system state) MTS / MTO distinction has to do with when production releases are triggered MTO: after demand MTF: after forecast but before demand MTS: before demand MTS/MTO distinction makes sense only when production releases are triggered by demand 8

7 2. Production Control in the absence of demands 9

8 Production system with infinite-capacity buffers (no WIP control) raw parts arrival process ( pace maker ) raw parts buffer workstation input buffer machine intermediate buffer finished goods buffer Dotted lines: always empty Only control: RP rate (open loop) 10

9 Production system with kanban control at the individual WS level Free kanbans (PA cards) Parts + kanbans Control: RP rate (open loop) WIP control (closed loop): No. of kanbans K i, i=1,4 11

10 Production system with multi-stage serial kanban control (multi-loop CONWIP) Parts + kanbans Control: RP rate (open loop) WIP control (closed loop): No. of PA cards, K 1-2, K

11 Production system with multi-stage echelon kanban control (integral control) Control: RP rate (open loop) WIP control (closed loop): No. of PA cards, K 1-4, K 3-4 Parts + kanbans (stage 1+2) Note: K 1-4 K 3-4 K 1-4 = K 3-4 CONWIP (next) 13

12 Production system with CONWIP control Free PA cards Parts + PA cards Control: RP rate (open loop) WIP control (closed loop): No. of PA cards, K 1-4 Note: original CONWIP: P 0 = (no open loop control) 14

13 Production system with CONWIP control (equivalent representation) Parts + PA cards 15

14 3. Production Control in the presence of demands: Push or pull? 16

15 Production system with: 1) no WIP control 2) demands for finished goods only (takt-paced production system) Only control: RP rate (open loop) Push/pull? Def 1: neither push nor pull, because production is triggered neither by present nor by future demands Def 2: push, because production is not triggered by demands Def 3: push, because there is no WIP control 17

16 Production system with: (Base stock system) 1) no WIP control 2) demands for finished goods generating demands for raw parts Control: RP rate (open loop) Demand response (closed loop) S 4 = base stock level Push/pull? Def 1: pull, because production is triggered by present demands Def 2: pull, because production is triggered by demands Def 3: push, because there is no WIP control 18

17 Production system with: 1) (simple) CONWIP control 2) demands for finished goods generating demands for raw parts Control: RP rate (open loop) coupled WIP control (closed loop) Demand response (closed loop) K 1-4 = WIP limit base stock level carrier of demands Push/pull? Def 1: pull, because production is triggered by present demands Def 2: pull, because production is triggered by demands Def 3: pull, because there is WIP control 19

18 Production system with: 1) extended CONWIP control 2) demands for finished goods generating demands for raw parts Control: RP rate (open loop) uncoupled WIP control (closed loop) Demand response (closed loop) Push/pull? Same as CONWIP, i.e., pull K 1-4 = WIP limit constrained S 4 = base stock level Demands are carried independently Note: K 1-4 S 4 K 1-4 = S 4 CONWIP K 1-4 = Base stock S 4 = 0 MTO 20

19 Production system with: 1) (K, S) control 2) demands for finished goods generating demands for raw parts Control: RP rate (open loop) uncoupled WIP control (closed loop) Demand response (closed loop) Push/pull? Same as extended CONWIP, i.e., pull K 1-4 = WIP limit unconstrained S 4 = base stock level Demands are carried independently Note: K 1-4 S 4 extended CONWIP K 1-4 < S 4 reserve stock CONWIP 21

20 Thus far: WIP control pull system Q: Can a WIP controlled system be push? A: Sure (based on Definition 2) 22

21 Production system with: 1) (K, S) (equiv CONWIP) control 2) demands for finished goods only (takt-paced production system with WIP Control) Control: RP rate (open loop) WIP control (closed loop) K 1-4 = WIP limit Demands are not carried upstream S 4 makes no sense Push/pull? Def 1: neither push nor pull, because production is triggered neither by present nor by future demands Def 2: push, because production not triggered by demands Def 3: pull, because there is WIP control 23

22 4. Examples of hybrid push/pull systems 24

23 McDonald s production system example, where P 0 = refrigerator, WS 1 = cooking, WS 2 = assembly, WS 3 = bagging, WS 4 = checkout Definitions 2 and 3 partially agree and partially disagree 25

24 Example of push/pull interface, where the push part has WIP control but the pull part does not Definitions 2 and 3 completely disagree 26

25 Example of push/pull interface, where the pull part has WIP control and the push part does not Definitions 2 and 3 completely agree 27

26 5. Production control with advance demand information (ADI) or forecasts 28

27 Production system with: (MRP with (K,S) control) 1) (K, S) control and 2) orders with ADI for finished goods generating time-phased production orders for raw parts T = demand lead-time L 1-4 = planned production lead time Push/pull? Def 1: push, because production is triggered by (present orders but) future demands Def 2: pull, because production is triggered by demands Def 3: pull, because there is WIP control 29

28 Production system with: 1) (K, S) control and 2) demands for finished goods generating forecasts for future demands generating time-phased production orders for raw parts T = forecast horizon; FG = Forecast generator Push/pull? Def 1: push, because production is triggered by future demands (forecasts) Def 2: pull, because production is triggered by demands Def 3: pull, because there is WIP control 30

29 Production system with: 1) (K, S) control and 2) demands for finished goods 3) independent forecasts for future demands generating time-phased production orders for raw parts Push/pull? Def 1: push, because production is triggered by future demands (forecasts) Def 2: push, because production is not triggered by demands Def 3: pull, because there is WIP control 31

30 6. Conclusions 32

31 We looked at paced, WIP-based and demand-driven production release control schemes We adopted Def 2 regarding the push/pull distinction MTO/MTS only makes sense for pull systems Def 1 seems to leave out the situation where production is initiated independently of demand Def 3 does not seem to reserve a clear role for the demand The magic of pull arises when we establish a WIP limit (K, S) system is more versatile than other systems (K, S) system with demand-based forecasts would be worth studying 33

32 Acknowledgement This work was supported by grant MIS Odysseus: A holistic approach for managing variability in contemporary global supply chain networks, which was co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program Education and Lifelong Learning of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALES: Reinforcement of the interdisciplinary and/or inter-institutional research and innovation. 34

33 Thank you for your attention 35