Define: Just In Time (JIT)

Workers in manufacturing plant

Just In Time (JIT) is an inventory strategy implemented to improve the return on investment of a business by reducing in-process inventory and cycle time. The process is driven by a series of signals, or Kanban, that tell production processes to make the next part. When implemented correctly, JIT can lead to dramatic improvements in a manufacturing organization’s return on investment, quality, and efficiency.

First used by the Ford Motor Company as part of “dock to factory floor” in which incoming materials are not even stored or warehoused before going into production.  Subsequently adopted by Toyota as part of its Toyota Production System (TPS).  Japanese corporations cannot afford large amounts of land to warehouse finished products and parts. Before the 1950s, this was thought to be a disadvantage because it reduced the economic lot size.

It was realized that another method was possible. The factory could be made more flexible, reducing the overhead costs of retooling and reducing the economic lot size to the available warehouse space.  Toyota engineers redesigned car models for commonality of tooling.

Toyota engineers then determined that the remaining critical bottleneck in the retooling process was the time required to change the stamping dies used for body parts.  Toyota implemented a strategy called Single Minute Exchange of Die (SMED).  Almost immediately, die change times fell to about half an hour.  Procedural changes (such as moving the new die in place with the line in operation) and dedicated tool-racks reduced the die-change times to as little as 40 seconds.

After SMED, economic lot sizes fell to as little as one vehicle in some Toyota plants.  This made it possible to store as little as one part in each assembly station. When a part disappeared, that was used as a signal to produce or order a replacement.

Components and Implementation

  • Pull vs. Push Scheduling
  • The Problem of Inventory
  • Just In Time
  • Principles
  • Benefits and Limitations
  • Implementing JIT
  • Kanban
  • Pull Systems
  • Quality
  • One Piece Flow
  • Continuous Flow
  • Takt Time
  • JIT and Suppliers

Lean manufacturing is really about minimizing the need for overhead which is about concentrating precisely on only what is necessary which is about linking interdependent supply system decisions, and actions which needs to be visual, responsive and simple to manage

Push Scheduling

  • traditional approach
  • “move the job on when finished”
  • problems – creates excessive inventory

Pull scheduling

  • coordinated production
  • driven by demand (pulled through system)
  • extensive use of visual triggers (production/withdrawal kanbans)

Management philosophy of continuous and forced problem solving (forced by driving inventory out of the production system).  Supplies and components are ‘pulled’ through system to arrive where they are needed when they are needed.  Goal: Achieve the minimal level of resources required to add the necessary value in the production system.

The Philosophy of JIT

  • JIT means getting the right quantity of goods at the right place and the right time
  • Often termed “Lean Systems”
  • All waste must be eliminated- non value items
  • Broad view that entire organization must focus on serving customers
  • JIT is built on simplicity- the simpler the better
  • Focuses on improving every operation- Kaizen
  • Install simple visible control systems
  • Flexibility to produce different models/features

JIT Manufacturing is a philosophy of value-added manufacturing, Achieved by

  • Inventory reduction – exposes problems
  • Kanbans & pull production systems
  • Small lots & quick setups
  • Uniform plant loading
  • Flexible resources
  • Efficient facility layouts

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