Just in time (JIT), Push/Pull production systems, Elements of JIT Manufacturing, Small Lot Sizes & Quick Setups, Implementation of JIT

Just in time (JIT)

To have only the right materials, parts & products in the right place at the right time

• Only what is needed, nothing more
• Continual improvement & a pull system

- Smaller inventories & Improved quality
- Shorter lead times & Lower production costs

- Reduced space requirements
- Increased productivity
- Greater flexibility

Misconceptions

• Only an inventory control system
• A method to “Push” inventory back to the supplier
• A quality control program

Elements of JIT Manufacturing

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

Role of Inventory Reduction

• Inventory = Lead Time (less is better).
• Inventory hides problems.
• Reducing the level of inventory (water) allows management (the ship) to see the problems in the operation (the rocks) & work to reduce them.

Push/Pull production systems

Push Systems

Schedule work releases based on demand (make to stock)

• Production oriented
• Inherently due-date driven
• Control release rate, observe WIP level

Pull Systems

Authorize work releases based on system status (make to order)

• Customer oriented
• Inherently rate driven
• Control WIP level, observe throughput

Push/pull interface

• Make-to-stock & make-to-order can be used in same system
• Dividing point is called the inventory-order interface or push-pull interface
• Eliminate entire portion of cycle time seen by customers by building to stock

Advantages of Pull Systems

• Low Unit Cost (low inventory, reduced space, little rework)
• High External Quality (high internal quality, pressure for good quality, promotion of good quality)
• Good Customer Service (short cycle times, steady & predictable output stream)
• Flexibility (avoids committing jobs too early, encourages floating capacity)

Implementing Pull

• Pull is Rigid (replenishing stocks quickly (just in time) requires level mix, volume, sequence)
• Support Rigidity (production smoothing/mix stabilization)
• Mitigate Rigidity in Production System (capacity buffers, setup reduction, flexible labor, facility layout, product design)
• Mitigate Rigidity in Organization (TQM, vendor management)

Small Lot Sizes & Quick Setups

• Small lots mean less average inventory & shorten manufacturing lead time
• Small lots with shorter setup time increase flexibility to respond to demand change
• Strive for single digit setups < 10 minutes (SMED)
• Ultimate goal is single unit lot sizes

Flexible Resources

• Movable, general purpose equipment

• Portable equipment with plug in power/air

• Capable of being setup to do many different things with minimal setup time

• Multi-functional workers

• Workers assume considerable responsibility 

• Cross-trained to perform several different duties 

• Trained to also be problem solvers

Effective Facility Layouts

• Workstations in close physical proximity to reduce transport & movement
• Streamlined flow of material
• Often use 

• Cellular Manufacturing or ‘U’ shaped lines

Implementing JIT

• Starts with a company shared vision of where it is & where it wants to go
• Management needs to create the right atmosphere & designated “Champion”
• Implement the sequence of following steps

• Make quality improvements, Reorganize workplace & Reduce setup times

• Reduce lot sizes & lead times 
• Implement layout changes 
• Switch to pull production
• Develop relationship with suppliers