7 Types of Waste in Injection Molding – “TIMWOOD”


As a trainer and consultant in lean manufacturing. I stumbled upon the 7 types of wastes – TIMWOOD. This kindled my curiosity to consider the different sorts of waste inside a typical Injection Molding process and classify them in to these 7 kinds of waste.

7 Types of Waste

Naturally, Injection Molding is really a complex procedure that involves coordination among various departments. There’s great potential for reducing waste in the Molding Process.

1. “T” for Transportation – The unnecessary movement of people or parts between processes.


  • Moving molds from storage to the press and vice versa
  • The movement of resin from warehouse to the press
  • The movement of tools and auxiliary device
  • The unnecessary movement of finished goods or semi-finished goods before they are shipped

Address transportation issues by

  • If possible, placing the process nearby, using material that shifts from tactics to process without significant delays
  • Expansion of production route
  • Acquiring multiple storage locations
  • Not creating extended or complicated material handling system


2. “I” for Inventory – Holding unnecessary material or parts when not needed


  • Extra resin inventory – Stocking more resin than necessary
  • Surplus parts inventory – Producing parts more than necessary
  • Extra machine spare/expendable items/tools

To avoid getting over stock, you can

  • Adjust the development process to achieve smooth flow
  • Work with a small batch size
  • Adhere to the first-in-first-out principle of stagnant material.
  • Reduce switching time


3. “M” for Motion – Unnecessary Motion that contributes no value


  • Opening and closing the security gates for removing parts from the mold/tool without using sprue robots
  • Manual de-gating and extra secondary operation
  • Reaching too far over for handling parts
  • Walking around for searching tools

Reducing motion waste by

  • Improving workstation layouts to avoid excessive walking or bending
  • Organizing techniques to allow parts to transfer easily from one hand to another
  • Redesigning work layout to reduce change in direction of material
  • Reduction of batch size


4. “W” for Waiting – People or parts that wait for a work cycle to be completed


  • Waiting for Machine – Barrel heating, mold heating/cooling, hot runner manifold, machine failure, machine maintenance
  • Waiting for Material – Preheating
  • Waiting for Men – Paper making for quality inspection/approval, missing schedule
  • Waiting for Mold – Tool repairing, tool adjustments under out-of-tolerance conditions

The key to eliminating waiting waste is

  • Procedures
  • Following checklists for activities where available
  • Keeping the work area to specified standard


5. “O” for Over-processing – Using equipments that are not necessary for the work


  • Making parts which are of tighter tolerance than is needed by Customer
  • Over rejecting/over inspecting parts beyond customer needs
  • Using bigger press/greater tonnage press that is needed for that mold
  • Produce parts with more cycle time
  • Running multi-cavity tool with cavities off leading to more cycle time/part produced

Reduce over-processing by:

  • Standardizing best approaches for workers to follow along with
  • Setting obvious specifications and quality acceptance standards


6. “O” for Over-production – Generating parts than precisely what it takes


  • Producing more parts than customers need
  • Making more parts in anticipation of more orders
  • Making many parts due to schedule problems
  • Running a mold when only one part is required from multiple cavities

Avoid over-production by:

  • Dealing with smaller sized batch sizes
  • Making more reliable processes
  • Creating stable schedules
  • Balancing cells or departments
  • Using accurate forecast information which reflects the particular demand


7. “D” for Defects – Rework, Scrap, Incorrect documentation


  • Making wrong parts – wrong specifications/color/wrong Rev
  • Wrong set up – secondary operations
  • Parts with missing documents/documents with errors
  • Packaging parts with incorrect/wrong box labels
  • Mixing two various parts while shipping

To reduce the regularity of defects, attempt to

  • Institute sufficient training to enhance workers’ skills
  • Improve processes
  • Source capable suppliers
  • Reduce operator error
  • Lower the surplus stock
  • Improve transportation plans


There’s also another kind of waste – Skills wastage which is recognized as the eighth kind of waste


  • Allowing untrained/under-trained Labor or Operator to function specialized equipment
  • Insufficient specialized training sources for that molding operations personnel
  • Underutilizing human sources for doing rudimentary tasks


Identifying these kinds of wastes and classifying them in to the 7/8 kinds of waste could be useful in creating a Lean Molding Shop. As more shops around the world adjust to Lean culture, this exercise could be interesting for that Injection Molding Business.


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