Lean Manufacturing Principles and Their Benefits

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Lean Manufacturing Principles and Their Benefits

The Toyota Production System (TPS) or Lean Manufacturing System focused on lead-time reduction, in order to fulfill the new requirements imposed by the market, a set of improvement tools was developed.

Lean Manufacturing is often associated with a focus on cost reduction. However, through the implementation of lean manufacturing processes, many injection molders also realize reduced lead times, improved on-time delivery scores, and an increase in overall customer satisfaction.

With those types of added benefits, it’s easy to see what many shops are adopting lean principles.

One of the key principles in lean manufacturing is to view things from the customers perspective. Getting and using feedback from customers about your product line will ensure you make products that satisfies their needs.

What’s more, customer feedback ensures resources are not wasted on making a product that has features that they are not interested in and not willing to pay for.


How Can Lean Manufacturing Principles Benefit Injection Molding?

Many people initially believe that lean techniques are mostly about cost reductions. In fact, they provide the one feasible way to cut costs while also shortening lead times and times to market, improving quality, and providing customers with exactly what they want precisely when they want it.[1]

One of the principles used to achieve these benefits is to eliminate all waste in a manufacturing process. Waste is any action that does not add value to the end customer.


In injection molding, the most obvious example of waste is making defect parts. This is frequently due to poor mold design. Mold design must be right from the beginning which will not only save you years of frustration of having to deal with quality issues and disgrunted employees but will also improve cycle times.

Consider the same injection moulding machine producing a food containers with a cycle time of 9.1 seconds. If the cycle time is reduced by 5% then the cycle becomes 8.6 seconds which means some part of the cycle needs to be reduced by 0.5 seconds. In the injection moulding process there are typically 6 phases that occur during each cycle.

The 6 phases:

  1. Mould closing
  2. Injection of plastic into the mould
  3. Holding of plastic in the mould to allow proper formation of the container
  4. Cooling of the container so that it is rigid enough to eject from the mould
  5. Opening stroke of the mould
  6. Ejection time; the container can be physically ejected off the mould

The following is a real life example performed on an injection molding machine in Melbourne, Australia running a 2 cavity mould.

The 9.1 second cycle time had the following breakdown:

Phase (seconds)

  1. Closing 1.3
  2. Injection 1.2
  3. Hold 2.0
  4. Cooling 2.1
  5. Opening 1.5
  6. Ejection 1.0

Total 9.1

In order to reduce the cycle time by 0.5 seconds, the first thing considered was the phase that would have the smallest effect on part quality. This was the ejection time.

In this example the ejection was started 0.2 seconds earlier while the mould was still in the opening stroke. There was no need to wait for the moving side to completely stop before starting the ejection stroke. Therefore, the ejection time was reduced to 0.8.

Additionally, the opening and closing times were reduced by 0.1 each saving another 0.2 seconds by reducing the opening stroke.

Another 0.1 was subtracted from the cooling time which achieved our target of 0.5 seconds. Although the part shrinkage was slightly more it was still within the quality limits and made no difference to the end user.

Here is a summary of the changes:

  1. Closing 1.3 reduced to 1.2
  2. Injection 1.2 unchanged
  3. Hold 2.0 unchanged
  4. Cooling 2.1 reduced to 2.0
  5. Opening 1.5 reduced to 1.4
  6. Ejection 1.0 reduced to 0.8

Total cycle changed from 9.1 to 8.6 seconds without effecting quality

This is why molders need to identify areas of waste, and this is why COPAR chose to execute the Lean Manufacturing.


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