Mass production, traditionally, has not been a Lean strategy for manufacturing. Instead, Lean manufacturing heavily relies on a pull system (just-in-time) rather than a push system (mass production). The difference between these two methods lie in the scheduling of production. In mass production systems, customer demand is predicted based off data, shopping trends, etc., and production is scheduled to meet that forecasted demand. However, just-in-time production schedules production when, and only when, there is an actual demand to meet.
The Lean philosophy actually aims to directly reduce the most common wastes (named the Seven Wastes of Lean) associated with manufacturing. Examples os wastes resulting from mass production and pull systems include:
- Inventory: Possibly the most notorious and costly waste of manufacturing is the waste of excess inventory. The unpredictability of push systems and possibility of sudden changes in demand can often leave facilities with piles of unsold inventory taking up valuable storage space.
- Overproduction: When production is not leveled or properly planned, it can place a burden on equipment and machines. Additionally, overproduction is the catalyst for several of wastes and can hide the need for improvement.
- Defects: Defective products are often passed down the line before the issue is caught and may even stay hidden within the large batch until it is shipped out for delivery.
The other four wastes identified in Lean manufacturing are transportation, motion, waiting, and over-processing.
A key advantage for JIT production and Lean manufacturing is the flexibility of the production system. For whatever reason recalls, change in opinion, new product features, etc., can require you to make some major changes. It may also leave you with outdated inventory that no longer can be sold. Because products are only made on demand and equipment was designed to reduce changeover, any changes to the production line will result in minimal loss.