Some manufacturing businesses make for stock, others make to order, and a number do a little of both. The first two are considered “push” and “pull” manufacturing respectively, while the third is a hybrid approach. This blog compares push vs. pull systems, considers the benefits of going hybrid and discusses the implications for machine maintenance.
Understanding push systems
In push manufacturing, work is scheduled through the factory based on forecast demand. Typically, the ERP system looks at required delivery dates and determines when each order should be released to production. The material then travels through the factory from machine to machine or process to process.
In many cases material travels as a batch, with the batch size determined by some form of economic batch quantity formula. A characteristic of batch production is that the batch can’t move on to the next operation until all units have been processed through the preceding step. Batches create buffers of inventory between successive process steps.
Push systems are generally used to replenish finished goods inventory in a warehouse or distribution center. Production is therefore detached from customer purchasing patterns.
Packaged foods are a class of products manufactured in push systems, with produce arriving at the factory when harvested and being packaged to a schedule based on forecast demand.
Understanding pull systems
In pull manufacturing, production is initiated by demand from a customer. Through the factory, each process step or operation is a “customer” of the previous step. A customer order sends requests upstream to be satisfied by material flowing downstream. Pull systems often use simple visual signals to request production from an upstream operation.
Pull is one of the fundamental principles of lean manufacturing. It prevents overproduction and the creation of work-in-progress (WiP) inventory. It is used in make-to-order environments where a “takt time” or drumbeat is established that forms the required production rate. A perceived advantage of pull is that it supports process optimization in manufacturing by eliminating buffers.
Fast food restaurants provide an example of pull manufacturing. While the ingredients are all available in advance, assembly is only undertaken when the customer places an order.
Considering push vs. pull systems
All businesses are different, and while pull makes sense in some, for others a push system will prove to be a more effective means of meeting customer demand and operational goals. In comparing push vs. pull production, it will be helpful to consider the following:
- Inventory: Push systems operate with higher levels of inventory. This also tends to mean longer manufacturing lead times.
- Production initiation: In push manufacturing, orders are released as determined by the ERP system in order to meet shipment/completion dates. In pull, a customer order starts the sequence of processing steps.
- Maintenance impact: The inventory buffers present in a push environment increase tolerance to unplanned downtime. In contrast, in a pull system, machine breakdowns are extremely disruptive placing greater emphasis on running an effective preventive maintenance system.
- Customer expectations: Push systems satisfy customer orders from finished goods inventory, so response is faster than in a true make-to-order operation. Customer acceptance of the time needed to fulfill an order is one of the biggest factors in whether a pull system can be made to work.
- Waste: If customer demand changes suddenly, in a push system this can result in obsolete products and a lot of waste. There is less waste in a pull system where goods are only produced when a customer wants them.
Some manufacturers have developed ways to adopt elements of both push and pull manufacturing. In these so-called hybrid systems orders are released based on a demand forecast. However, the rate at which customers place orders is used as a signal that more production is needed.
Benefits of using a hybrid push-pull system
When businesses adopt a hybrid model in pursuit of higher levels of operational efficiency in manufacturing, they see benefits including:
- Flexibility: By using push processes for predictable aspects and pull processes where variability is higher, they can manage variable demand more efficiently.
- Efficiency: A hybrid system tolerates inventory and some overproduction waste as the tradeoff for ensuring product is available when the customer wants it.
- Responsiveness: There is an enhanced ability to respond quickly to changes in customer demand without carrying significant inventory.
- Cost-effectiveness: It’s easier to optimize resource allocation in a hybrid model as people can be moved to where they are needed most when they are needed, potentially lowering overall operational costs.
- Scalability: Lasting changes in demand are met through adjustments to the production schedule while the pull system handles short-term fluctuations.
Help with maintenance in every manufacturing system
While pull systems offer many perceived benefits for manufacturers, they are not the right solution in every case. Particularly where lead times are long and customers expect immediate satisfaction, a push system with its associated inventory may prove more effective.
Some manufacturers have sought a “best-of-both-worlds” approach to manufacturing, using a hybrid system combining both pull and push production. While this runs counter to “lean” thinking, it often provides an optimal solution in terms of inventory, waste and the ability to satisfy customer demand.
Unplanned machine downtime is disruptive in every production environment. Arguably though, it is more costly in a pull system where low inventory levels remove the buffers that allow other operations to keep running.
Maintenance specialists at ATS are experienced in working in a range of production environments and understand the different challenges of pull vs. push systems. We can help implement and operate maintenance strategies to improve operational performance in pull, push and hybrid factories. Contact us to learn more.
