SWIP (Standard Work in Process)
SWIP defines the minimum inventory needed within a process to maintain smooth, uninterrupted flow. It prevents both starvation and overproduction between workstations.
Standard Work in Process (SWIP) is the calculated minimum number of parts or items that must be in the process at any time to keep all stations working without waiting. It is a key element of Standard Work and directly impacts flow efficiency.
SWIP depends on the relationship between takt time, cycle times, and the physical layout of the process. If an operator must walk between machines, parts in transit are part of SWIP. If a machine has an automated cycle, the part inside is SWIP.
Too little WIP causes starvation -- operators or machines wait for parts. Too much WIP causes overproduction, longer lead times, and hidden quality problems. SWIP finds the precise balance between these extremes.
Reducing SWIP is a continuous improvement goal. As processes become more reliable and changeovers faster, less buffer inventory is needed. Every reduction in SWIP shortens lead time and exposes the next problem to solve.
Formula
SWIP = Sum of all parts in machines + parts in transit + parts in buffers needed to maintain continuous flow
Practical Example
A three-station cell has cycle times of 55, 48, and 52 seconds with a takt time of 60 seconds. Each machine holds 1 part during processing. One part is needed between stations 1 and 2, and one between 2 and 3. SWIP = 3 (in machines) + 2 (in transit) = 5 parts. Any inventory above 5 is waste.
How Leanshift Helps
Leanshift records cycle times and process sequences that feed directly into SWIP calculations. By tracking actual WIP against the SWIP standard, teams can see overproduction the moment it occurs.
Frequently Asked Questions
What is the difference between SWIP and WIP?
WIP (Work in Process) is the actual inventory in the process at any time. SWIP is the calculated minimum needed for smooth flow. The goal is to bring WIP as close to SWIP as possible.
How do you reduce SWIP?
Reduce cycle time variation (stabilize processes), shorten distances between stations (improve layout), and increase machine reliability. Each improvement allows SWIP to decrease.
Does SWIP apply to service processes?
Yes. In a service context, SWIP might be the number of open tickets, orders in processing, or documents awaiting review needed to keep the team productively engaged without creating backlogs.
Related Terms
Cycle Time
Cycle time measures how long a single process step actually takes -- from start to finished result. It is the foundation of every process analysis.
Lead Time
Lead time measures the total duration from order receipt to delivery -- including all waiting, storage, and transport times. It determines delivery capability.
Standard Work / Standardized Work
Standard Work documents the current best-known way to perform a task. It defines the sequence, timing, and inventory needed to produce consistent results safely and efficiently.