Push vs. Pull in Manufacturing: Kanban, FIFO and Pacemaker Explained
How does a station know what to make next? The answer determines inventory, lead time and the number of rush orders. There are two basic principles: push, where a schedule pushes parts into production, and pull, where consumption pulls them. The example line in this lesson has both.
Push vs. pull compared
Push means every station gets an order from production control and produces whether or not the next station needs the parts right now. It is based on forecasts. Pull means only what the next station or the customer has actually withdrawn gets replenished. It is based on real consumption.
- Control: push with schedules sent to many stations; pull with signals (kanban card, empty space, full FIFO lane).
- Inventory: with push unplanned and growing; with pull capped and deliberately sized.
- Response to change: with push sluggish, because schedules have to be recalculated; with pull immediate, because only what was taken is replaced.
- Prerequisite: push needs good forecasts; pull needs stable processes and short changeover times.
Why inventory determines lead time
The link between inventory and lead time is simple math, known as Little's Law: at the same throughput, halving the inventory in the system halves the lead time. Pull works exactly here, because it puts a ceiling on the inventory between processes.
Push in practice
On the example line, production control sends Welding 2 a weekly schedule, and the station works it off. Whatever assembly does not need right away ends up in the inventory behind it: 1,600 welded parts, almost two working days of supply. When the customer changes an order, the wrong parts quickly pile up and the right ones are missing. Typical sign of push on a value stream map: a schedule arrow to a single station with a large inventory behind it.
Pull with supermarket and kanban
A supermarket sits between stamping and welding. Welding 1 withdraws stamped parts from it; every container of 50 pcs carries a kanban card. The card goes back to stamping and is the order to replenish exactly what was taken. No schedule is needed; consumption is in control.
Pull alone is no silver bullet, though. The press stamps in batches of 1,000 pcs because a changeover takes an hour, and the supermarket is correspondingly large. Only shorter changeover times allow smaller batches and therefore a smaller supermarket.
The FIFO lane
Between push and supermarket sits the FIFO lane (first in, first out). Between the two welding stations, no more than 50 assemblies may sit. What goes in first is processed first. When the lane is full, the upstream process stops. This keeps inventory capped without cards and without a supermarket. The prerequisite is that the upstream process can run the same sequence as the downstream process.
Rule of thumb: what goes where?
- Where processes can work directly one after another: continuous flow, with no inventory in between.
- Where takt or batch sizes do not match but the sequence stays the same: FIFO lane with a maximum.
- Where a process supplies several customers or variants, or has long changeovers: supermarket with kanban.
- Only one single point gets a schedule from the office: the pacemaker process.
The pacemaker in the future state
In the future state of the example line, only the cell combining welding and assembly gets the daily schedule. It is the pacemaker. Upstream, a supermarket controls replenishment from stamping; downstream, parts flow to shipping. One single schedule replaces the weekly schedules for individual stations, and inventory in the value stream drops from 13,380 to 3,680 parts.
Getting started tomorrow
Do not start with kanban for everything. Find the spot with the biggest push inventory and cap it first with a FIFO lane: a marked area, a fixed maximum and a clear rule for what happens when it is full, for example "The upstream process stops and helps out downstream". It costs almost nothing and immediately shows where flow gets stuck.
Practice in the editor
Compare "Steering bracket (current state)" and "Steering bracket (future state)": where is push, where is a supermarket, where is FIFO, and which process is the pacemaker?
Open the template in the editor Start blankFrequently asked questions
What is the difference between push and pull?
With push, a schedule pushes orders to every station, based on forecasts. With pull, only what the next process or the customer has actually withdrawn gets replenished.
Is pull always better than push?
Not always. Pull needs stable processes, recurring demand and short changeover times. For one-off orders or very rare variants, order-based control with FIFO often makes more sense than a supermarket.
What is a supermarket in manufacturing?
A capped, controlled inventory from which the downstream process withdraws. Every withdrawal triggers replenishment through a kanban card.
When do you use a FIFO lane instead of a supermarket?
When the upstream process can run the same sequence as the downstream process. If it has to produce in batches or in a different sequence, for example because of long changeover times, you need a supermarket.
What is a pacemaker process?
The one process that receives the customer schedule. It sets the pace: upstream, material is replenished by pull; downstream, it flows to shipping.