Diagnostic Instruments Production Test Analysers

LineCHECK™ Production Test Analyser - Applications

Fast & Accurate NDT for the Production Line 

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.


Testing Rotating & Moving Assemblies

Using 'Signature Feature Extraction' (SFX) ™ technology to analyse noise and vibration, currently available quality inspection equipment (such as the LineCHECK™ system from Diagnostic Instruments Ltd) 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.

Traditional Non-Destructive Test (NDT) Techniques

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
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.

The Sintered Metal Process

One method of producing intricate metal parts is by using sintered metal. This involves a process whereby dry metal powder is poured into moulds then heated and compressed to produce a solid metal part.

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 processes, the quality of a sintered part can vary significantly. The integrity of the process is open to such variables as the copper content of the powder, and the lubricant content that is added to aid the powder flow. Indeed, even the atmospheric humidity on the day of manufacture can have an affect, creating areas of localised density within the part.

Detecting Flaws & Cracks Using LineCHECK™

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 LineCHECK™ Production Test Analyser to the problem of detecting defects in sintered metal components.

The first step was to prove the technique under stringent test conditions. LineCHECK™ was applied to the problem and the results were outstanding. 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.


A Fully Automated Test Station

With the trial out of the way, a fully automated pick and place test system was designed for LineCHECK™. This complete system was engineered to integrate fully into a production line. 

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 a tiny hammer to "ping" 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 final system fully met the design criteria. Which brings us to where non-destructive quality testing is today. The system has proved itself fast and efficient - not to mention inexpensive in comparison with existing testing methods - and because the system can check one part every six seconds (with the capability to carry out the same operation in less time if required), it allows for the testing of 100% of components. Moreover, because the system is fully integrated into the production line, there is no need for operator expertise, even when the same system is being used to test a variety of products.

A fast, efficient, cost effective and fully automated 100% quality testing procedure. What more could industry want?