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Product category: Non Destructive Testing
News Release from: Diagnostic Instruments | Subject: LineCHECK system
Edited by the Manufacturingtalk Editorial Team on 09 April 2002

Fast and accurate NDT speeds production
lines

The constant demand from customers for 'best quality', combined with the increasingly competitive nature of the marketplace, has accelerated the development of test methods.

The constant demand from customers for 'best quality', combined with the increasingly competitive nature of the marketplace, has accelerated the development of test methods for automotive manufacturing applications The area of Non Destructive Testing (NDT) is a prime example of this

Traditional NDT techniques do not lend themselves to the manufacturing environment.

The combination of test speed, expense and logistics makes 100% product testing using traditional methods impossible.

However, in recent years we have seen the emergence of dedicated 'production test' equipment based on sophisticated noise and vibration analysis techniques.

This equipment is now widely used in the automotive and domestic appliance industries by OEM's and suppliers to identify defects and quality related issues in moving or rotating equipment.

Current developments are now applying similar 'production test' technology to the field of non-destructive testing, enabling manufacturers to quickly and accurately inspect 100% of their throughput.

This translates into considerable cost savings for the manufacturer, and better quality product both for industry customers, and the car buying public.

The sintered metal manufacturing industry is one example, where new technology is overcoming traditional quality inspection problems.

And since many sintered metal components are safety critical, that is surely no bad thing.

Using 'Signature Feature Extraction' (SFX) technology to analyse noise and vibration, currently available quality inspection equipment (such as the LineCHECK system from Diagnostic Instruments) has a wide range of applications.

It can be used to check the quality of moving assemblies; everything from pumps to electric motors, and from gearboxes to wiper mechanisms, engines, air conditioning units and so on.

This powerful technique detects change in a product's unique noise and vibration "signature" and triggers an alarm condition if this change represents a defect, quality or process related issue.

Simplifying things even further, the pass or fail is indicated by a coloured lamp - red for a fail, green for a pass - with no requirements for operators to understand complex frequency spectra, or the technology driving the pass / fail criteria.

DI can also provide in-house training so that technicians can become skilled at setting up the unit, and programming their own tests.

Traditionally, the time constraints, expense and logistics of NDT techniques meant that only small statistically selected batches of manufactured goods were presented for end of line testing.

These 'batches' were representative of the overall production run.

However, as demand pushes quality levels higher, batch testing is often no longer good enough.

There are many existing NDT techniques currently in use, such as: Magnetic Particle Inspection (MPI); Eddy current testing; X-ray; Radiation; Dye Penetrant and Resonance Search.

These vary in complexity, cost, and speed.

Invariably, none of them are cost effective or fast enough to be used on a production line.

For example, a Resonance Search (which involves the use of a shaker to excite the structure) takes 30 seconds.

By far the quickest from the list above, but on a production line where anything from 450 to 1000 units per hour are produced, still too slow.

Complexity is also an issue for most NDT tests, requiring a specialist knowledge of the technique.

This generally means using qualified staff, and omits the possibility of any kind of automation.

In addition, the equipment needed to carry out the tests generally means that test pieces have to be transported to a separate location in the plant - all very time consuming.

One method of producing net shape components is by using sintered metal.

This involves a process whereby metal powder is fed into moulds then compressed to produce a solid metal compact before sintering.

The obvious advantage is that this straightforward process allows the manufacture of complex and sophisticated metal parts that would otherwise prove costly and difficult to manufacture using traditional methods.

These lightweight sintered parts are used in a variety of applications today, though perhaps the largest increase in their use has been in the automotive industry, typically in the vehicle engine.

A typical component presently being manufactured using this method is the vehicle timing pulley, which drives the camshaft.

Failure of this component would, of course, cause irreparable damage to the engine.

By their very nature, such parts have to be highly reliable.

Indeed, they could even be classed as safety critical.

And this is where the problem arises.

Due to the complex processes and numerous variables the quality of a sintered part can vary significantly.

The integrity of the process is open to such variables as the homogenity of the mixed powder, and the lubricant content that is added to aid the ejection cycle.

Indeed, even the atmospheric humidity on the day of manufacture can have an affect, causing poor filling characteristics and subsequent product quality issues.

One symptom of failure in the process is the presence of hairline fractures.

These fractures are difficult to spot with the human eye, but if the flaw is inside the material, human detection is impossible.

Current methods of crack detection include magnetic particle inspection and X-ray.

Whilst these methods are certainly reliable, they are expensive and too time consuming to be used on a 100% inspection basis.

However, there is another method - sound - or, more accurately, the vibration signature in response to an impact excitation.

In other words, hit it, and listen to the sound it makes, then compare that sound with what is known to be a quality example of the product.

Obviously the SFX technique is much more sophisticated than this.

Using the technique applied to moving assemblies, Diagnostic Instruments turned the powerful LineCHECKT Production Test Analyser to the problem of detecting defects in sintered metal components.

GKN Sinter Metals, based in Lichfield (England) are world leaders in the manufacture of sinter metal parts.

The company is a technology leader, and proved an ideal partner to put this new system through its paces.

Andy Lloyd Jones (Director, Process Development) managed the project, keeping a watchful eye on the results.

The first step was to prove the technique under stringent test conditions.

LineCHECK was applied to the problem and the results were positively encouraging.

In a trial during which 5700 parts were tested, 83 parts were identified as faulty, and consequently rejected.

All the rejected parts were then subjected to magnetic particle inspection, and all showed fractures.

A 100% hit rate.

With the trial out of the way, a fully automated pick and place test system was designed for GKN Sinter Metals.

This complete system was engineered to integrate fully into a production line, and has become one of several automated systems installed by the company.

This automated system had to be capable of testing 450 parts per hour, separating good from bad and recording all results.

A total test time of 6 -8 seconds was allocated to each component.

The finished system comprised of a conveyor belt down which the finished parts travel.

A robotic arm then picks up each part in turn, initiates the test, and places the part according to the result, one belt for rejects, the other for passes.

The sintered part is held while a robotic arm uses an acoustic hammer to excite it.

LineCHECK analyses the results, and the conveyor belt carries the tested part away, ready for the next test.

There is no requirement for expensive sound booths, with the system capable of picking out defects in a noisy industrial environment.

The developed automated / integrated system met the design criteria.

Which brings us to where non-destructive quality testing at GKN Sinter Metals is today.

Since the first trials, the company has developed it's use of the LineCHECK system, applying it throughout the Lichfield plant.

As a result, GKN now use 5 portable systems for adhoc testing and development, and have three fully automated crack detection test systems.

The latest automated system (one of 5 that are planned), can detect cracks in three different locations on a number of different parts.

Since its commission, the new system has been consistently processing a minimum of 500 parts per hour, 24 hours a day ! Diagnostic Instruments has successfully completed research and development in the area of 'greens' testing.

By testing the integrity of a part prior to the sinter process (ie in its 'green' state), maximum cost savings can be achieved by the manufacturer - in fact defective parts can in some cases be re- ground for re-use.

Results of this exciting research show success, and the company is looking for manufacturers to take up the challenge once more and provide the opportunity to prove the LineCHECK green testing in a production environment.

So Diagnostic Instruments can now offer manufactures a complete solution - from greens to sintered parts.

And from initial consultancy and feasibility study, to the manufacture and supply of the test instrumentation, creation of dedicated test applications, and manufacture of fully automated and integrated handling systems.

This means that we fully understand every element of the final solution and take full responsibility for each element.

Guaranteeing you peace of mind and the convenience of a 'one stop shop'.

A fast, efficient, cost effective and fully automated 100% quality testing procedure for sinter metal and green parts.

What more could industry want?.

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