A pull system is a very controlled way of ensuring that resources are efficiently replaced. Within a pull system, resources are only replaced when they are used. So there is no stockpiling of items, no saving items up for use ‘later’, no buying items at a very low price and using them whenever they are needed.
A pull system is very much in keeping with the Lean philosophy of ensuring that there is no waste created within the production process. In addition, the lack of huge amounts of stock means that there are is no waste in terms of transporting large volumes of stock or indeed in stocking the parts in a warehouse.
Parts are only produced and made to fit the demand and then replacement components are ordered in, as and when. So there are no partly finished items taking up room in warehouses or on the factory floor. The pull system is therefore very efficient in terms of controlling stock and replacement components.
Kanban and Pull Systems
Kanban derives from the Japanese and was first used within the Toyota Plant, before it became popular worldwide. The kanban is a card or visual aid that indicates when goods need to be replenished, because the replacement of the items works backwards; when goods are used, they are replaced, rather than production being scheduled in as a master schedule.
The pull system comes in because the ‘pull’ is when an item or component is used and then needs to be replaced. For example in supermarkets it is common to have operatives going round and replenishing the shelves after the store has closed (or even during opening hours). The operatives fill the shelves to the same level as it was prior to sales, they do not introduce new stock levels.
Obviously within the factory environment, it is not really practical to have people roaming around looking to ‘top up’ stock levels. But what can be very useful is to have a card displaying the need for items to be replenished. The Kanban system can even have a ‘stock low’ card and another card to indicate that stocks need to be replenished as soon as possible.
Supervisors or foremen are then easily alerted to the need for stock to be procured and yet the staff time that has gone into this communication has been negligible, so it is a very cost effective way of communicating. It is also a cost effective way of keeping control of stock and components and is very much geared towards there being no waste within the entire process.
There are various ways in which Kanban systems can be tweaked to suit the particular needs of a company. Sometimes various Kanban cards are used to be placed at different stages of the production line, according to what has been used. There are also times when the cards may be attached to containers, to easily indicate which need to have stock and which are adequately filled.
Limitations Of Pull Systems
Despite the benefits that a pull system can bring, it is simply not feasible for all businesses to implement such a system.
The replenishment of stock only as it is used assumes that stock and parts will be readily available, yet there are some instances where there will undoubtedly be a requirement for parts that may take some time to be delivered, so there will have to be at least some stockpiling of items, to accommodate the time taken to secure new parts.
However, where stock and components can be readily sourced and where there is no need to secure very specialised part, the pull system is a very efficient way of ensuring that stock is controlled.
