Generally, there are two main categories of production systems which are pull systems and push systems. In push systems, before producing the products, manufacturers predict the demand amount of final products and they prepare the production schedule according to these predictions. The product passes the work stations in a sequent. They are manufactured and then, sent to the next work station. They move on the production line in an order of priority.
In push systems, controlling compares the amount of products these are manufactured during the production line and the amount of products which are supposed to be manufactured according to the production schedule which was prepared at the very beginning of the production. Controlling units try to minimize the difference between two of them. In pull systems, there are no production schedules and predictions about demands. The movements of materials are organized according to the real product demands. There are limited stocks and the inventory is dynamic in pull systems.
Production is planned with respect to the predictions of demand in push method, whereas it is planned with respect to the real demands in pull method. There are no schedules in pull method which is different from push method. In case of production mistakes, there are always stocks in push method, since it is hard to define and solve the problems during the production, there are always backups, but in pull method there are not stocks. Both production systems intend to have the required materials at the required place, time, amount and quality in order to manufacture on time.
Push system is perfectly suitable for discontinuous lot production and stock, whereas pull system is suitable for repetitive production. In push systems, production is planned for weeks or months; on the other hand in pull systems there are daily plans. Lot sizes are big in push systems; differently they are small in pull systems. Generally, there are short-term contracts in push system; not similarly long-term contracts are used in pull systems.
http://www. volkanderinbay. com/pull/pull. html