Physical flow is the rate of movement or elapsed time from start to completion of the manufacturing process.
In Velocity Scheduling System we are focused on physical flow in manufacturing. In Velocity Pricing System we focus on the flow of money. For this article we are referring to physical flow.
Flow or Velocity as we call it in Velocity Scheduling System is the time it takes from the time we start on a job until we complete the job. This is also often referred to as leadtime. The fewer the disruptions to flow, the faster it will move through the shop, the shorter the leadtime and the faster the Velocity.
We also look at the rate of flow by taking into account the job size. Smaller jobs should flow faster than larger jobs.
In Theory of Constraints you’ll hear “Balance flow not capacity”. And this is an extremely important, often overlooked, aspect to improving operations. Flow was one of the main concepts in The Goal. However, most people read The Goal and focused on the concept of finding and eliminating the constraint. But for complex job shops where the constraint can move week to week or even day to day, the FLOW concept is much more powerful.
Flow Based Scheduling or Flow Manufacturing is simple. Improvement in physical flow occurs when queues are reduced. And to reduce queues you must reduce work in process (WIP). We have previously discussed Little’s Law, how and why the reduction of WIP is so important in these articles:
- Job Shop Scheduling – The Secret To Getting On Time & Reducing Lead Times
- Scheduling Job Shops: Flow is KEY!
As discussed in these articles there are many benefits to reducing WIP, including:
- Queue time reduces
- Lead time reduces
- Lead time predictability increases
- On time delivery increases
- Quality increases
- Cash flow increases
Plossl’s Law: All benefits will be directly related to the speed of flow of materials and information
In complex job shops, flow based scheduling (like Velocity Scheduling System) is the only solution that works! Traditional scheduling solutions where you try to schedule every job on every machine and even “off the self” Drum Buffer Rope, don’t work in complex job shops and machine shops.