Hybrid Push vs Pull

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Push and Pull Production Systems
Make-to-Order: You say yes. I say no. You say stop. and I say go, go, go! – The Beatles

What Pull is Not!

• MRP with firm orders on MPS is make-to-order. • But it does not limit WIP and is therefore a push system.

Make-to-Stock:
• Pull systems do replenish inventory voids. • But jobs can be associated with customer orders.

Forecast Free:
• Toyota’s classic system made cars to forecasts. • Use of takt times or production smoothing often involves production without firm orders (and hence forecasts). 1 4
© Wallace J. Hopp, Mark L. Spearman, 1996, 2000

© Wallace J. Hopp, Mark L. Spearman, 1996, 2000

http://www.factory -physics.com

http://www.factory -physics.com

The Key Difference Between Push and Pull
Push Systems: schedule work
releases based on demand. • inherently due-date driven • control release rate, observe WIP level

Push and Pull Examples
Are the following systems essentially push or essentially pull? • Kinko’s copy shop: • Soda vending machine: • “Pure” MRP system: • Doctor’s office: • Supermarket (goods on shelves): • Tandem line with finite interstation buffers: • Runway at O’Hare during peak periods: • Order entry server at Amazon.com:

Pull Systems: authorize work
releases based on system status. • inherently rate driven • control WIP level, observe throughput

2
© Wallace J. Hopp, Mark L. Spearman, 1996, 2000

5
© Wallace J. Hopp, Mark L. Spearman, 1996, 2000

http://www.factory -physics.com

http://www.factory -physics.com

Push vs. Pull Mechanics
PUSH
(Exogenous) Schedule

Push and Pull Line Schematics
Pure Push (MRP)

PULL

Stock Point

...
Pure Pull (Kanban)

Stock Point

(Endogenous) Stock Void

Stock Point

...


Stock Point

Production Process

Production Process

Job

Job

CONWIP
Stock Point

...

Stock Point

Push systems do not limit WIP in the system.
© Wallace J. Hopp, Mark L. Spearman, 1996, 2000

Pull systems deliberately establish a limit on WIP.
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Authorization Signals
© Wallace J. Hopp, Mark L. Spearman, 1996, 2000

Full Containers

6

http://www.factory -physics.com

http://www.factory -physics.com

Pulling with Kanban
Outbound stockpoint
Completed parts with cards enter outbound stockpoint.

Example – Quick Taco Production Line
Outbound stockpoint Make -to-Order I/O Interface Make -to-Stock

Refrigerator

Cooking

Assembly

Packaging

Sales

Production cards

Warming Table

Customer

When stock is removed, place production card in hold box.

Production card authorizes start of work.

Notes : • I/O interface can differ by time of day (or season). • I/O interface can differ by product. 7 10
© Wallace J. Hopp, Mark L. Spearman, 1996, 2000

© Wallace J. Hopp, Mark L. Spearman, 1996, 2000

http://www.factory -physics.com

http://www.factory -physics.com

Inventory/Order Interface
Concept:
• Make-to-stock and make-to-order can be used in same system. • Dividing point is called the inventory/order interface. • This is sometimes called the push/pull interface, but since WIP could be limited or unlimited in both segments, this is not a strictly accurate term.

Example – IBM Panel Plant
Original Line
Treater Prepreg , Copper Lamination Machining Circuitize Drilling Copper Plate Procoat Sizing, Test

I/O Interface

Benefit: eliminate entire portion of cycle time seen by customers by building to stock. Implementation: • kanban • late customization (postponement)

Revised Line
Treater Prepreg , Copper Lamination Machining

process that gives boards “personality”
Core Blanks Copper Plate

Circuitize

Drilling

Procoat

I/O Interface

Sizing,

Test Notes : • Moving I/O interface closer to customer shortens leadtime seen by customer. • Small number of core blanks presents opportunity to make them to stock. 8 11 © Wallace J. Hopp, Mark L. Spearman, 1996, 2000

© Wallace J. Hopp, Mark L. Spearman, 1996, 2000...
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