An overview to push pull systems By Tiruvannamalai

An overview to push & pull systems By: Tiruvannamalai R. S. Date: 11/16/2001

Agenda • Objective • Definitions • Comparison of push & pull systems • AHP for push & pull system • POLCA - A case study • Hybrid push/pull systems • Conclusion • References

Objective To provide an overview to • Push production systems • Pull production systems • POLCA • Hybrid push/pull systems

Definitions Push: Production is triggered based on due dates of customer FORECAST orders or desired restocking to inventory levels. Pull: Production is triggered only in response to actual DEMAND consumption of inventory. 3

Comparison between pull and push systems Push System: Information Flow Forecast ? Cell 1 Cell 2 WIP Cell 3 WIP Cell 4 WIP Material Flow MRP schedule triggers production Pull System: Custome Information Flow r Withdrawals trigger production demand Cell 1 Cell 2 WIP Cell 3 WIP Material Flow Cell 4 WIP 2

Characteristics of push and pull systems Parameters Planning information Flow of information Manufacturing technique Inventory level affected by Push Pull Historical data Customer demand Same as material flow Opposite to material flow Make to stock Make to order Forecasting errors Fluctuation in customer demand 2, 3, & 4

Comparison between push and pull systems Parameters Push Pull Suitable Not suitable Product introduction Faster Slower Demand fluctuation Suitable Not suitable Repetitive Customized Lead Time Manufacturing cost Inventory, WIP level Customer service Throughput Changing product mix and variety Machine utilization Manufacturing environment 1, 3, 4, 5, & 6

Methodology for selection of push & pull systems

Methodology for selection Analytic Hierarchy Process(AHP) approach: A simple decision-making tool • To deal with complex, unstructured and multi-attribute problems • To classify push, pull and hybrid push-pull systems in production planning • To analyze push-pull systems using quantitative and qualitative criteria • To devise a 3 D state-space model • To simulate multiple environments 8

Three-dimensional state-space model (AHP model) 1 & 5 - Uses pull systems High 2, 4, 6, 7 & 8 - Uses push systems 7 Unreliable 3 8 3 - Employs push/pull systems 4 Low suppliers & lead time 5 6 Serviceability, Commitment, & Costs Low 1 Low 2 Demand Fluctuation High 8

POLCA

POLCA • Paired-cell Overlapping Loops of Cards with Authorization • “Novel material control strategy used in QRM, which combines the best of push and pull methods to limit congestion while at the same time providing a high degree of flexibility. ” 9

POLCA (contd. ) Where does POLCA work? • High level material requirement planning system (HL/MRP) • Cellular organization • Flat BOM’s 9

POLCA (contd. ) Key features: features • To release authorizations by HL/MRP • To control card based on material control methods • To produce control cards (POLCA cards) • To use POLCA cards for each pair of cells 9

Case study- CFP corporation • Products- Customized faceplates & nameplates • Features- Printing, holes, notches, bends • Strength- Small batches for specialized markets • Uses cell concept to satisfy highly varied markets 9

Applying POLCA-CFP Corporation (contd. ) Printing cells Fabrication cells Assembly cells Shipping cell A 3/S 1 Loop F 1 A 1 P 1/F 2 Loop F 2/A 3 Loop P 1 A 2 F 2 S 1 P 2 F 3 A 3 9

Applying POLCA-CFP Corporation (contd. ) P 1/F 2 F 2/A 3 P 1/F 2 Loop P 1/F 2 F 2/A 3 F 2/A 4 Loop F 2 9

Advantages of POLCA over push-pull systems • Assures that each cell only works on jobs that are destined for downstream cells • Uses of HL/MRP authorization to prevent buildup of unnecessary inventory • Flows in longer flexible loops • Overlapping loops gives greater degree of flexibility 9

Hybrid push/pull Issues – 1. When to push ? 2. When to pull? Hybrid push-pull: • Pushes through certain manufacturing stages and pulls else where based on the characteristics and value addition in stages • Draws a demarcation for determining stages in production that needs to work in push and those in pull

Hybrid push/pull Delayed differentiation strategy: A method to combine push and pull systems within a production line Customer demand Forecast Push-pull boundary Push strategy Pull strategy 7

Hybrid push/pull (contd. ) Advantages: • Allows to realize advantages of both push & pull approaches • Helps to improve economies of scale • Helps to reduce FGI • Caters to a wide range of customer demands • Provides better shop floor control 7

Hybrid push/pull (contd. ) Area of research: • Locating the push-pull boundary • Looking for more than one possible differentiation point Work done so far: • Literature review • Determined the various stages in a multi stage production line

Hybrid push/pull (contd. ) Work planned ahead: • Model a multi stage production line with hybrid push/pull system • Determining the push pull boundary line

Summary • Comparisons between push & pull systems • Methodology for selecting push & pull systems • POLCA • Hybrid push pull • Area of research • Future work

References 1) APICS International Conference & Exposition-Oct 28 -31, 2001. 2) Black, JT. (1991). The design of the factory with a future. New York: Mc. Graw Hill, Inc. 3) Bonney, M. C. , Zhang, Z. , Head, M. A. , Tien, C. C. , & Barson, R. J. (1999). Are push and pull systems really so different? International Journal of Production Economics, 59, 53 -64. 4) Grosfeld-Nir, A. , Magazine, M. , & Vanberkel, A. (2000). Push and pull strategies for controlling multistage production systems. International Journal of Production Research, 38, 11, 2361 -2375. 5) Huang, C. C. , & Kusiak, A. (1998). Manufacturing control with a push-pull approach. International Journal of Production Research, 36, 1, 251 -275. 6) Krishnamurthy, A. , & Suri, R. Push can perform better than pull for flexible manufacturing systems with multiple products. Center for Quick Response Manufacturing. 7) Levi, D. S. , Kaminsky, P. , & Levi, E. S. (2000). Designing and managing the supply chain. New York: Mc. Graw Hill, Inc. 8) Razmi, J. , Rahnejat, H. , & Khan, M. K. (1998). Use of analytic hierarchy process approach in classification of push, pull and hybrid push-pull systems for production planning. International Journal of Operations & Production Management, 1134 -1151. 9) Suri, R. (1998). Quick response manufacturing. Portland, Oregon: Productivity press.