Push manufacturing is characterized by manufacturing to forecast, and emphasizes on batch processing and lot sizes.
Each area runs at maximum capacity, and the material is pushed downstream.
Push planning methods include MRP, reorder points, and optimum order quantities.

Pull manufacturing is a visual replenishment of goods, where only is produced what is demanded by the next work center.
It got its start in America in the grocery business. Only products consumed by the customer where replaced on the shelves.
The most important pull planning methods are based on visual signals.

The main difference between push and pull is the direction in which the information flows.
In the push system, information flows in the same direction as production, whereas in the pull system, information flows in the opposite direction.

Benefits of pull manufacturing:

• reduced inventory levels (raw materials, work in process and finished goods)
• reduced floor space
• reduced lead times
• increased productivity
• smoother production flow
• increased customer satisfaction
• reduced total costs
• higher production visibility

Be careful to introduce pull manufacturing where

• the machine setup times are high and changeovers are frequent
• quality variation is high
• demand variation is high
• machine downtimes are high and frequent

Three pull manufacturing control methods exist: Kanban, ConWip and a Hybrid method.

1. Kanban Control Method

Kan means "card" in japanese, and the word "ban" means "signal".

Kanban controls the WIP between work stations using visual signals.

Visual signals can take the form of

• color-coded cards
• empty containers
• empty floor spaces
• electronic signals

When you can't immediately implement continuous flow, supermarkets are built. These are physical storage areas with a predetermined standard inventory buffer. They serve to control and level production.

Kanban and Supermarkets work together to establish a pull from the customer back through the producer to the supplier.

There are 3 main types of Kanban:

• production kanban: a communication to the supplier process to produce parts
• withdrawal kanban: a communication to the supermarket to request a withdrawal of parts
• material kanban: a communication to trigger purchases

Nothing is ever made unless the downstream process asks for it.

2. ConWip (Constant Work In Process) Control Method

ConWip controls and limits the total WIP in a production system, but doesn't control the WIP at the individual workstation levels.

The customer demand information is passed to the first machine in the line, and all machines in the downsteam are allowed to work on any part in their input buffer.

ConWip handles mix of parts with more ease than the Kanban control method, and is easier to implement.

3. Hybrid Control Method.

In this method, the global ConWip control is supplemented with the secondary Kanban controls.

Which Pull Manufacturing Control Method has to be implemented?

Several parameters have to be identified and measured, before the right method can be choosen.

• workload (% of maximum capacity)
• demand variation
• importance of lead time performance
• importance of low WIP

Visit the Lean Manufacturing Coaching Website for more information about Pull Manufacturing and Kanban.