Industrial CT nondestructive testing helps to improve the production process of castings

Date：2021-09-08 11:32:36Views：1043

Casting inspection is the operation process of inspecting whether the casting is qualified by visual inspection, measuring tools, instruments or other means according to the user's requirements, drawing technical conditions and other relevant agreements. Due to the coarse grain, poor sound permeability and low signal-to-noise ratio of the casting, flaw detection will be more difficult. It uses the sound beam with high-frequency sound energy to reflect when it encounters the internal surface or defects. The reflected sound energy is a function of the directivity and nature of the inner surface or defect and the acoustic impedance of this reflector. Therefore, the sound energy reflected by various defects or inner surfaces can be used to detect the location, wall thickness or depth of defects under the surface.

For the internal defects of castings, the common nondestructive testing methods are radiographic testing and ultrasonic testing. Common internal defects of castings include shrinkage porosity, shrinkage porosity, bubbles and inclusions. According to the radiographic results, the internal defects of castings are classified, and qualified and unqualified are judged.

Among them, the effect of radiographic testing is the best. It can get an intuitive image reflecting the type, shape, size and distribution of internal defects. However, for large castings with large thickness, ultrasonic testing is very effective. It can accurately measure the location, equivalent size and distribution of internal defects.

What are the main contents of casting quality inspection?

(1) Inspection of relevant technical conditions. Including inspection contents such as chemical composition and mechanical properties of castings. The inspection of technical conditions such as mechanical property inspection and metallographic and chemical composition inspection must be carried out in accordance with relevant national standards (omitted here).

(2) Surface quality inspection. The inspection of casting blank by the front-line personnel of machining production in the process is mainly to inspect its appearance casting defects (such as sand holes, sand holes, looseness, insufficient pouring, casting cracks, etc.); And whether the blank machining allowance meets the machining requirements.

(3) Geometric dimension inspection of finished castings. The main one is to use the marking method to check whether the machining allowance of the blank is sufficient. Another method is to use the reference datum of the blank (also known as the process datum) as the relative measurement method of the inspection datum of the blank (it is necessary to measure the size of the relative datum and carry out simple conversion).

However, for castings with complex and irregular shape and internal structure, X-ray radiography (RT) or ultrasonic method (UT) is no longer suitable for internal defect detection. Industrial CT is not affected by the structure and shape of the sample. CT and RT usually provide more defect information. This is because the information in RT overlaps, which reduces the sensitivity, while these factors can be eliminated in CT.

NDT Industrial CT

(1) CT is one of the most accurate and reliable nondestructive evaluation methods at present because of its high resolution in the detection of castings;

(2) Three dimensional imaging detection can observe the spatial shape of internal defects of castings, realize the measurement of arbitrary section density and internal structure size, and solve the limitations of scanning fault direction and fault discontinuity of both. A very important computer-aided evaluation method.

(3) The interface problem with rapid prototyping is solved, which realizes the application in reverse engineering and shortens the design, product development and production cycle of aerospace die.

CT can determine the size and location of looseness, pores, shrinkage cavities and cracks in the specimen. For defect classification and evaluation, in-depth information is very useful. Since all spatial information and defect information of the test piece can be obtained through industrial CT, defects can be judged more accurately, and wrong judgment or wrong judgment can be reduced. Nowadays, castings have been widely used in aviation and aerospace, including aluminum alloy, magnesium alloy, titanium alloy, superalloy and other industries. Compared with casting and blank processing to form workpieces, castings have low cost and can form very complex shapes, which is difficult for processing technology. Most castings have defects, some even seriously affect the performance of the whole casting. Therefore, nondestructive testing must be performed to ensure its quality.