Total Quality Lean: The Critical Connection Between Lean Manufacturing and World Class QualityBy: Jack Harrison
In addition, Lean attacks many "quality" aspects that go beyond the product specifications, such as responsiveness and delivery performance. And, Lean philosophy, when correctly done, forces an environment of continuous improvement.
Lots of inventory means lots of potential defects.
Long lead times result in a "cold trail" when trying to identify root cause of a defect.
And Lean Techniques specifically impact product quality:
One fundamental tenant of Lean Manufacturing is the reduction of inventory. Inventory hides waste, and is therefore put under constant pressure to be reduced. It is this on-going focus on reducing inventory that results in an environment of continuous improvement.
How does inventory reduction improve quality? Perhaps an example will best explain.
The week after we began working with a large producer of plated steel, a hidden defect was discovered that could only be detected several operations downstream.
The defect resulted in the down-grading of all of the in-process steel, at a total cost of $600,000.
Six months later, as a result of the inventory reductions resulting from strict kanban controls, their total quality risk for a similar defect had been cut by more than 70%!
Perhaps the largest impact that inventory reduction has on quality is in reducing the time lapse between cause and discovery.
You can think of inventory as items standing in line, waiting for their turn. The more items in line, the longer each item must wait.
How does that impact quality?
Well, one of the critical requirements to eliminate quality problems is the ability to identify the root cause of the defect, so that this cause can be corrected.
Inventory delays the discovery, and hence reduces the likelihood of being able to recognize something that changed that might have caused the defect.
The ability to walk a defect back to the operation that caused it, on the same shift, greatly enhances the likelihood of identifying an underlying cause: "Oh yeh, I just changed tooling" or "I just started using the parts from a new vendor" or "I noticed that the machine started to sound a little different" etc.
Inventory reduction is, without a doubt, the single most powerful thing you can do to improve quality!
There are also a host of Lean techniques in the Lean toolbox. Some of these techniques are targeted specifically at quality improvement. Others have multiple objectives, but also result in quality enhancement. Let's look at a few of these.
Sequential Inspection asks each operator to think of him/herself as a "customer." The preceding operation is the "supplier." As a customer I have a right to expect a quality product.
Sequential inspection identifies key attributes that each operation should check prior to performing their own operation. Doing so further minimizes the number of defects that can be produced before discovery. It also provides immediate feedback to the causing area (Stop the Line and Fix the Problem).
Failsafe is the technique of making an operation "incapable of producing a defect."
Once the cause of a defect has been discovered, we attempt to install failsafe devices to make the process robust enough that either it can no longer produce this defect, or that a defective part is immediately discovered for human adjustment / correction.
Common failsafe devices include go/no-go gauges, limit switches, optical sensors, weight checkers, torque wrenches, on-machine gauging, lock-up devices, part re-design, one-way fixtures, parts standardization, etc.
Operation Checklists, and Work Station Organization (5S) are additional mechanisms to minimize the chance of an error creeping into the process.
Just as you wouldn't want your pilot to skip over his pre-flight checklist, a bulletized listing of critical steps/checks help operators bolster their process.
And a thorough workplace organization discipline (5S) keeps tools, parts, and fixtures in pre-determined locations. Clear labeling, color coding, shadow boards, etc. help to minimize the chances of an error.
Vendor Base Reduction provides for improved parts and raw material consistency. I recall a client that had a huge problem created when they bought an electrical component from another supplier. The new parts DID meet all the specs. It turned out, however, that some additional critical parameters had NOT been specified. The parts from the old supplier just happened to work!
I recall another client that had significant machine set-up issues on some of their automatic equipment. Setting the machine to the previous settings did NOT work, primarily, because the raw material came from a variety of suppliers and each had slightly different properties. If the operators did not "tweak" the set-up, un-usable parts would be generated. And, during this adjustment period, scrap was being generated. Note that while the raw material from all sources would work satisfactorily in the end unit, the set-up issues were substantial.
One more key attribute of Lean Quality lies in the broader customer view of supplier quality.
A quality "product" is the minimum requirement.
Customers also expect their suppliers to be responsive (short lead times), flexible (small lot size / minimum order requirements), and 100% reliable (on-time delivery performance).
We have already discussed how inventory reduction shortens lead times. Inventory reduction also forces lot sizes to be reduced.
But how does Lean improve delivery performance?
Let's go back to our analogy of items standing in line waiting for their turn. The longer the line, the longer the lead time.
But what happens when a critical customer calls and demands that his order be delivered in less than our standard lead time?
You're right! We expedite his order by moving it to the front of the line. But what impact does that have on the rest of the orders?
Right again! It makes some of those orders late!
THE MORE EXPEDITING WE DO, THE MORE DIFFICULT IT IS TO BE RELIABLE!
And, in addition to long internal lead times causing more expediting, long lead times also force our customers to "guess" what they're need further out.
The crystal ball gets hazy out there, so the customer places orders, then requests changes, causing even more expediting.
The bottom line is quite simple, and extremely powerful. Lean Manufacturing philosophy and techniques have a huge positive impact on both product quality and on customer perceived total quality.
All the best on your lean journey.
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© Copyright 2007, Jack Harrison
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