Aircraft manufacturing is a complex process involving many links, from parts production to part assembly and then to final assembly, any problem in any link may affect the product quality and flight safety of the aircraft, therefore, quality inspection in the aircraft manufacturing process is particularly important.

When we feel unwell, the first thing we do is to seek the help of a doctor, who will give us a series of examinations to find out the problem and then treat it, so that we can recover our health. As an essential part of our daily life, do you know how airplanes are "checked"?

Non-destructive testing

In fact, just like a person needs a doctor to check his body at birth, an airplane also needs a doctor to conduct a comprehensive and very detailed "inspection" from the very beginning of manufacturing. This is what "aviation doctors" call non-destructive testing.

Non-destructive testing technology refers to the use of sound, light, electromagnetic and other principle techniques to detect and evaluate materials, parts, equipment defects and stresses, and other factors without damaging or affecting the performance of the object being tested.

In our daily life "non-destructive testing" is actually very common! Don't be surprised, have you ever picked a watermelon? Hold the watermelon in your hands, and then take a hand to gently pat the watermelon, the sound is crisp and clear that is raw melon eggs, muddy just right, muffled is "overcooked". There is a scientific basis for doing so, different degrees of maturity of the watermelon, the internal flesh of the different densities, when patted, the frequency of the resulting sound is not the same, this method in the "non-destructive testing" community, called the "acoustic vibration method" detection.

With the development and progress of science and technology, NDT technology is widely used in various fields, especially in aviation equipment. NDT technology plays a vital role as a technical means of quality control in the preparation and manufacturing process of aviation products and their materials. Therefore, in the modern aviation industry, NDT has been regarded as one of the core supporting technologies and an effective element of the industry chain and technology chain of the aviation industry.

Modern non-destructive testing technology throughout the entire life cycle of the aircraft at all stages and processes, from aircraft design, materials research and preparation, process research and optimization, manufacturing and assembly of structural components, the whole aircraft service and structural repair, etc. are inseparable from the support of non-destructive testing technology.

Non-destructive testing "weapons"

So, what are the NDT "weapons" in the hands of "aviation doctors"? In hospitals for medical examinations, there are many types of tests, including X-ray, ultrasound, CT and so on. These "tricks" are also the "aviation doctor" to see the skills.

X-rays, for example, are taken in hospitals for chest X-rays, where an invisible beam of light passes through your body and imprints your little heart and soul on the negative.

In fact, the "aviation doctor" use X-ray inspection method is also the principle, so that X-ray penetration to test the aircraft parts, the internal structure of the parts are all displayed in the negative, so that the "aviation doctor" will be able to find whether there is a problem inside the parts. Sometimes, you feel that the hospital film can not see, can not read, to tell you the truth, doctors also have this feeling, wide-eyed or can not see the details, then the doctor will recommend doing CT again.

"Industrial CT imaging technology uses X-rays to scan a certain thickness of the part to be inspected, and the detector receives X-rays through that level, and the information obtained from the scan is calculated to obtain the X-ray attenuation coefficient or absorption coefficient for each voxel. The information obtained from the scan is calculated to obtain the X-ray attenuation coefficient or absorption coefficient of each voxel and then arranged into a matrix, which is processed by an imaging algorithm to form a CT image.       

CT is good, but it has radiation! So is there a test without radiation hazards?

There is a hospital physical examination called ultrasound, especially for mothers and fathers with small children at home, this test should be more impressive. When the baby's mother goes to the hospital for this test, the doctor takes a detector and puts it on the belly of the mother carrying the baby, and then the parents-to-be can see the baby's lovely appearance! Isn't it amazing?

A similar technique is called "ultrasonic phased array technology" in the field of non-destructive testing. It uses a specified sequence of line or surface arrays of array elements in a certain time sequence to excite ultrasonic pulse signals to control the focus and sweep of the acoustic beam in the structure.

For the material and structure of different aircraft parts and other characteristics, "aviation doctor" will set up different inspection algorithms and process parameters to detect and image the interior. In this way, defects and flaws in aircraft parts are nowhere to be seen! 

The entire manufacturing process of an aircraft, from the material level to the part level after processing and manufacturing, and then to the whole process of assembling the parts into a whole aircraft, requires many "aviation doctors" to carry out a lot of non-destructive testing work, and with the development of science and technology, more and more new technologies emerge and are used in the industrial field. The "doctors" in the aviation industry have been working on the latest non-destructive testing technology to achieve quality assessment of aircraft parts to ensure that our aircraft can deliver everyone safely to their destinations.

The history of aircraft "medical examination" equipment development

Broadly speaking, quality inspection during aircraft manufacturing has gone through three stages of development:

First, the visual inspection stage. In the early stages of aviation development, the overall structure of the aircraft is relatively simple, the number of on-board equipment is small, the on-board maneuvering system is mostly composed of rigid tie rods or steel cables, pulleys, with which the inspection and maintenance means are also relatively simple. During this period, there is almost no special equipment for the inspection of aircraft load-bearing structural parts or components, mainly visual inspection, the accuracy and reliability of the test results rely heavily on the skills and experience of the inspectors themselves.

Second, the stage of simulation-type equipment. During this period, the structure of the aircraft and the on-board equipment have developed greatly compared to the initial stage, and the complexity has increased significantly, and the inspection technology has also been developed accordingly. Engineers began to explore new testing methods and developed some professional testing equipment and instruments, such as magnetic particle flaw detector, pulse ultrasonic detector and eddy current flaw detector. Most of these testing equipment and instruments are based on analog circuits, in the detection of precision and accuracy is still lacking, but compared to visual inspection has been a great improvement.

Third, the stage of digital equipment. With the increasing technological content of aircraft, as well as in the aircraft manufacturing process began to use digital technology, some advanced digital inspection equipment gradually put into use, such as intelligent ultrasonic flaw detector and aviation magnetic particle flaw detector. These equipment and instruments are generally based on digital circuitry, the application of microcontroller or industrial control computer technology, the various types of aircraft damage detection process programming, curing in the instrument, the use of microcontroller or industrial control computer to complete the damage detection in the detection parameters set and the analysis of the results of processing, reducing the labor intensity of the inspectors, but also reduce the detection errors and errors caused by human factors, so that the detection results of The accuracy and reliability of the test results are greatly improved.

Aircraft "medical examination" project

Surface class features inspection: In the process of aircraft assembly, the main surface class features include gap, order difference, corrugation and aerodynamic shape. At present, the international advanced surface class features inspection mainly adopts optical non-contact inspection technology, the inspection method is mainly photogrammetry and white light measurement.

Internal structural features detection: internal structural features include frame position, intersection holes, process holes, key flight sensor brackets, etc. As the above features are located inside the body, the visibility is poor, and it is difficult for conventional optical inspection instruments to function. In the actual inspection, large-range measurement tools such as laser tracker or LIDAR are mainly used.

Large component assembly quality inspection: large component docking of the aircraft is usually measured in combination, and the mainstream combination schemes include indoor GPS combined with laser tracker, indoor GPS combined with LIDAR, etc.

Moving parts inspection: Moving parts include aircraft rudder surfaces, moving hatches, landing gear, etc., and usually use dynamic monitoring technology. Dynamic monitoring requires the installation of multiple cameras. In the measurement process, the camera is fixed at the workstation, multiple cameras together to form a complete dynamic monitoring system.

Aircraft "medical examination" technology trends

At present, the most widely used technology in the field of aircraft manufacturing is digital inspection technology. As an important part of aircraft digital manufacturing, digital inspection technology integrates modern computer, communication, precision instrumentation, automatic control and management technologies, which is of great significance for the rapid and high-quality delivery of aircraft products.

Digital inspection system uses advanced digital measurement equipment to provide strong support for the realization of accurate, fast and automated measurement. After years of development, digital inspection has gradually gotten rid of the past fixed offline inspection method and shifted to portable online inspection where the inspection process is more integrated with the manufacturing process.

Source: Aviation industry, large aircraft