Do you know how to detect internal cracks in die castings?

1. Ultrasonic flaw detection

Ultrasonic testing and ultrasonic thickness measurement of various metal pipes, plates, castings, forgings and welds. When ultrasonic waves encounter defects such as cracks, voids, segregation, etc. during propagation, the acoustic parameters such as the speed, amplitude, and frequency of ultrasonic waves will change accordingly . According to the measurement of these changes by the instrument, the existence of the defect can be judged and its specific location can be determined.

Ultrasonic pulse (usually 1.5MHz) is shot from the probe to the detected object. If there is a defect inside, there will be an interface between the defect and the material. Then a part of the ultrasonic wave emitted by the person is reflected or refracted at the defect, and it is originally transmitted in one direction. Part of the ultrasonic energy is reflected, and the energy passing through the interface is reduced accordingly. At this time, the reflected wave at the defect can be received in the reflection direction; the ultrasonic energy received in the propagation direction will be less than the normal value. The occurrence of these two conditions can prove the existence of the defect. In flaw detection, the position and size of the defect can also be checked by using the performance of the probe to receive the pulse signal. The former is called the reflection method, and the latter is called the penetration method.

2. Magnetic particle inspection

It is suitable for non-destructive testing of ferromagnetic materials such as cast, forged and other machined parts.

3. Ultraviolet light

Low price, high reliability and simple operation, leak detection of various pipelines, inspection of uniform coating, detection of impurities or stains, semiconductor and biological fields, medical treatment, and stage special artistic effects.

4. Radiographic inspection

Radiographic flaw detection can be divided into three types: X-ray, γ-ray and high-energy ray flaw detection.

X-ray radiographic testing is based on the attenuation law of rays in materials and the actinic and fluorescent effects of certain materials. From the perspective of ray intensity, when the ray intensity is J0 irradiated on the workpiece, the ray passing through the workpiece is weakened to Jc due to the attenuation of the ray by the workpiece material. If there is a defect in the workpiece, the actual thickness of the workpiece through which the radiation passes at that point decreases, and the intensity of the rays passing through Ja, Jb is higher than the intensity of the radiation at the point without defects. From the perspective of the actinic effect of rays on the negative film, the strong part of the rays has a strong actinic effect on the negative film, that is, the amount of light is large. Negatives with larger light-sensitivity become darker after being processed in a darkroom. Therefore, the defects in the workpiece produce black shadows on the negative through the rays, which is the principle of radiographic flaw detection.