Bringing inspection into the light

AMJuly18Features - ITL1
AMJuly18Features - ITL1

Inspection Technologies’ technical director, Dr Geoff Diamond explains how to fully-automate cast part inspection in daylight conditions - with no human inspector intervention - for a truly 100% quality-assured compliance.

High-tolerance investment castings are often critical components in the aerospace industry which cannot afford to have manufacturing defects go unnoticed. Currently, the dark-room conditions and enclosed inspection cells required for dye-penetrant inspection of cast components increases manpower, reduces floorspace and is the cause of severe production bottlenecks and low throughput rates at inline inspection points. Moreover, reliance on human inspection, attention span and skill levels are approaching their limit. The variation between human inspectors often results in quality standard inconsistencies and the failure to detect defects altogether.

A new system, the ML-2000, developed and patented by UK company, Inspection Technologies not only removes the production bottleneck problem by enabling inspection of aerospace castings to be performed under bright light conditions, but also eliminates the need for a human inspector altogether with a fully-automated software solution that can scan a part at least 10 times faster than a human inspector and can find every defect on millions of inspected components to provide full 100% quality audit. All captured images (‘pass’ or ‘fail’) are permanently stored for traceability of parts even after they have entered service.

‘Mixed light’ inspection is the term given to this new technique. Apart from its ability of being able to detect low-level fluorescent dye-pen indications whilst working under strong daylight conditions, the system comes with its own proprietary software that rapidly identifies regions of interest for the operator and provides false-colour overlays on top of visual images of the inspected part. Moreover, the mixed light technology is fully-compatible with ASTM 2297 and the E 165 and E 1417 standards.

Illuminate to innovate

The mixed light, ML-2000 comprises a specialised scanner and a self-contained LED UV (365nm) light source. The system can inspect small fast-moving components, large, slow-moving components or even fixed plant in-situ. The system’s software can be adapted to automatically detect and report any class of surface or process defect that fall both inside and outside of the range of user-defined acceptance criteria. Inspection therefore, takes a very small fraction of the time required by a human inspector.

Permanent record keeping for 100% QA and process control Left: example of a ‘pass’. Right: example of a ‘fail’

If required, a false-colour rendition of the defect can be simultaneously overlain in real-time on a regular image of the part to assist an inspector locate the defect and also for location for QA and process control purposes.

For full 100% QA, permanent records of all inspections (‘pass’ or ‘fail’) can be kept with relevant details such as part/batch number, operator time and date of inspection, etc.

Apart from the cost-savings, reducing production bottlenecks by speeding up inspection and increasing overall production throughput, other advantages include: no limitations on metal composition or heat-treated condition; no limitations that are imposed on the size or shape of parts which can be inspected; liquid penetrant inspection can now be performed at any stage of manufacture, irrespective of background light conditions.

The system also overcomes the ever-increasing problem of the shortage of qualified inspectors rising from the ranks and emerging from the training system. Because the ML-2000 is an expert system, it means that technician-grade staff can be used in lieu of a more fully-trained inspector, and/or the productivity of a qualified inspector can be increased dramatically, if they were able to inspect remotely via telemetry by supervising or reviewing the work of technicians on the ground in multiple geographically separated sites.

In terms of inspection cycle times, if an inspected item satisfies the user-defined acceptance criteria, it proceeds to packing and shipping. However, if the inspected part is defective in any way, the part is either rejected and/or appropriate alerts are delivered to operators and management. The entire test cycle typically takes just seconds.

Depending on the size and complexity of the part, the use of automated handling equipment can enable the inspection throughput rate time for relatively small parts to be as high as hundreds of parts per hour.

Consistency and reliability

The ML-2000 system has been specifically designed to eliminate the false acceptance of defective parts due to human error. This addresses a very real customer need as it is a generally accepted estimate that a typical operator for example, detects only about 80% of the defective parts.

Additional benefits are that plant scrap rate will also be reduced because parts with superficial marks, scratches, thin flaps or overlaps of metal that do not extend structurally into the forging, and other surface blemishes, are saved because these defects do not alter the structural integrity of the part.

Aerospace standards for sizing accuracy: small defects which are even too small to be readily detected under dark-room conditions are very suitable candidates for the mixed light technology.

There are also other collateral benefits: quality control in a factory could reject large numbers of cast parts without any significant financial consequences. However, if a casting breaks whilst in service, then the damage and associated cost will be considerably larger. For example, if a turbine were to fail, then the entire vehicle would have to be taken out of service.

Hence, quality control during manufacturing of all classes of cast parts is of paramount importance and the ML-2000, apart from reducing labour costs, overhead, increasing production throughput rates etc., also adds considerable value to both manufacturer and end-user by delivering a superior level of quality assurance.

https://inspectiontechnologies.co.uk

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