iSixSigma

Rework

Definition of Rework:

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Customers typically only care for the product or service they receive, not for how much effort it took you to make it happen, nor how many times you had to change or rework it to get it right. 

Understanding what rework is and — crucially — how to avoid rework activities makes perfect business sense. Let’s explore further.

Overview: What is rework? 

Rework is an action performed upon a non-conforming product or service that, when completed, makes it conform to its requirements. Rework can include activities such as:

  • Disassembly
  • Part replacement / modification
  • Reassembly

Crucially, after the rework activity is complete, the functional specification and requirements are fully met.

In the context of the 8 wastes of lean, if we produce a defective (non-conforming) product or service, we can either rework or we can scrap. If we choose to rework, all of the associated activity required to return the product or service to conformance is non value-added. The customer does not recognise, nor is willing to pay for these rework activities. The associated costs, often termed the costs of non-conformance, are absorbed by the supplier with a negative impact on profitability.

Often the terms rework and repair are used either incorrectly or interchangeably. The key differences between rework and repair are subtle but important to understand:

  • Rework: An action on a non-conforming product or service to make it conform to its requirements

Example: An automotive tire should be inflated to 3 bar pressure and be free from damage leading to deflation. The tire was found to be inflated to 2.7 bar and free from damage, a rework activity inflated the tire to 3 bar pressure, and the tire conformed to its requirements.

  • Repair: An action on a non-conforming product or service to make it acceptable for the intended use

Example: An automotive tire should be inflated to 3 bar pressure and be free from damage leading to deflation. The tire was found to be inflated to 2.2 bar with a nail embedded. A repair activity removed the nail, applied a patch, and inflated the tire to 3 bar pressure. The tire was then acceptable for the intended use.

2 drawbacks and 1 benefit of rework 

Reducing, or even better, eliminating, the need for rework is implicit in a Lean Six Sigma approach. Let’s explore some drawbacks of rework — and even think about a potential benefit.

1. It’s resource-hungry and non value-added

Fixing something to meet its functional requirements that should have been right the first time takes valuable resources and disrupts your process flow. Your downstream customer just wants the right product, process, or service, and every time you rework to meet the requirements adds no value to the output.

2. It’s a sure-fire way to reduce customer satisfaction and loyalty 

Rework before delivery to the customer (sometimes called internal rework) is damaging to your costs and staff motivation. Often even more damaging is rework after delivery to the customer (sometimes called external rework). Here we have both the impact of costs to rework and of reputational damage, with the likely outcomes being reduced customer satisfaction and loyalty. 

3. It’s an opportunity to improve robustness

Is there a positive to be had from rework activity? Yes, but only if we use this as an opportunity to better understand our products and processes. We can redesign or reconfigure to reduce the probability of non-conformance and, therefore, improve our robustness.

Why is rework important to understand? 

Do it once, and do it right. Easy to say, but for complex, real-world products and processes, rework can become unavoidable. Let’s investigate a little deeper.

It tells you something is wrong in your product, process, or service

We should not accept rework as a natural outcome from our product, process, or service. Fundamentally, something is either wrong or not well-optimised, and we need to explore where and why this is occurring so we can implement changes.

It’s bad for your costs and the financial bottom line 

Rework is fixing something that should have been done right the first time. It takes time, it disrupts process flow, and it’s a non-value-add activity. All of this is an unnecessary additional cost that strips out your profit margin.

It demotivates your staff

Do you fancy working on the rework line this week? It can be hugely demotivating processing and reworking products, and this can quickly remove any sense of pride employees have in their job. It’s a far better use of your staff to understand and fix the root cause of your rework activity.

An industry example of rework 

A large, Tier 1 supplier to the rail industry was awarded a new contract for supply of hub bearings. The bearing technology was new but had performed well through durability and functional testing based on prototype test parts. Through prototype production, the final assembly process was developed and optimised, eliminating the need for costly rework activities.

Shortly after full-scale production commenced, there were a number of non-conforming bearings being rejected in the final assembly line. A Six Sigma black belt project was authorised to understand the reasons for the non-conformance and return the line to both capacity and capability. 

Due to the volume of parts required by the customer it was necessary to install a temporary inspection and rework line adjacent to the final assembly line. The costs associated with inspection and rework were significant, but none of the costs could be passed on to the customer.

With careful consideration and investigation into the assembly process and reviewing of the Process FMEA and critical control characteristics, it was possible to determine the root cause for the non-conformance. The assembly line speed was modified allowing for assembly to be completed correctly the first time, every time, and the removal of the temporary inspection and rework line. 

The cost of rework activity was calculated at $250,000 over a two-week period, and all costs were absorbed by the Tier 1 supplier.

3 best practices when thinking about rework 

There are some fundamentals to get right and help us understand how and why rework can creep in. Let’s take a look at some of these.

1. Understand and investigate your processes 

It all starts with a deep understanding of your processes. Make sure you have fully captured your process inputs and outputs and you understand where variation can occur. Revisit your failure mode and effects analysis to ensure all failure modes are captured.

2. Measure, inspect, and control the right things 

We definitely need to avoid unnecessary rework activity. Does your product or service meet its requirements? Are you controlling the correct characteristics to ensure these requirements are met? Time to revisit your control plan and cross-check your key process input and output variables.

3. Learn from mistakes and remove defects

Mistakes happen, and the worst thing we can do is ignore them. If we generate products or services that do not meet requirements, we need to learn how and why this has occurred. Fortunately, we can use well-established methods such as root cause analysis to understand where things have gone wrong and reduce the probability of recurrence.

Frequently Asked Questions (FAQ) about rework

1. Are repair and rework the same thing? 

No, there are subtle but important differences between rework and repair. Rework is an action on a non-conforming product or service to make it conform to the requirements. Repair is an action on a non-conforming product or service to make it acceptable for the intended use.

2. How can I reduce the level of rework in my process? 

You need to fully understand your process steps, carefully evaluate the input and output variables, and control those key input variables that deliver variation in output.

3. Is rework a lean waste?

Yes, when we apply lean principles, we evaluate all of the non-value-added steps in our processes. If we generate defects or need to rework our products or service, these activities are classed as waste.

It’s a wrap on rework

No matter what our product, process, or service, we gain no competitive advantage by introducing and embracing rework activities. Focus on delivering things right the first time and every time, keeping one step ahead of your competition and growing customer satisfaction and loyalty.

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