In casting process, first few castings will be inspected dimensionally and the pattern is qualified afterwards, only few random inspection will be done. Every casting must be inspected to find out the defects in casting process.
Different methods of inspection to find out defects in casting process are discussed below
- Radiographic Examination
- Ultrasonic inspection
- Visual Inspection
- Hydrostatic Pressure Test
- Magnetic Particle Inspection
- Dye Penetrant Inspection
- Coin Testing
Radiographic Examination
Radiographic examination is another inspection method used to identify defects in a casting. This method is expensive as it needs the proper equipment and only some die casting companies use it. A radiographic examination involves the use of both X-rays and γ-rays for detecting any sort of defects in the casting.
A film placed behind the casting can register the flow of rays through the casting in the form of variations in exposure that will help to identify any defects. An advantage of radiographic examination is that it can detect most of the defects such as cracks, void, tears, nonmetallic inclusions and porosity in the castings.
Ultrasonic Inspection
Ultrasonic inspection can detect any sort of cracks or other abnormalities within the casting, with a very high accuracy. Most die cast companies used ultrasonic testing to check the quality of the casted components. In this process, an ultrasonic signal is sent through the casting and the return signal monitored to find errors in the casting.
If the casting has any defect in its interior, it can change the wavelength of signal that is reflected back to the detector thereby helping to identify any defects. Moreover, the time interval between the transmitted and received signal can help to ascertain the exact location of the defect inside the casting.
Visual Inspection
Carrying out a detailed visual inspection is the most commonly used method to identify any defects in castings. A visual inspection can reveal some of the commonly occurring defects on casted components such as surface cracks, roughness, missing cores, and shifts. Special instruments such as an articulating fiberscope are used to carry out detail examinations of the surface of the castings. Moreover, other method like hitting the cast with a mallet and checking the tone is also used to identify any cracks in the casting surface.
Hydrostatic Pressure Test
The Hydrostatic pressure test is conducted on a casting to be used as a pressure vessel.
In this test, first all the flanges and ports are blocked.
Then the casting is filled with water, oil or compressed air, Thereafter, the casting is submerged in a soap solution when any leak will be evident by the bubbles that come out.
Magnetic Particle Inspection
The Magnetic particle test is conducted to check for very small voids and cracks at or just below the surface of a ferromagnetic material. The test involves inducing a magnetic field through the section inspection. this done, the powdered ferromagnetic material is spread out onto the surface. The presence of voids or cracks in the section results in an abrupt change in the permeability of the surface; this, in turn, causes a
leakage in the magnetic field. The powdered particles accumulate on the disrupted magnetic field, outlining the boundary of a discontinuity.
Dye Penetrant Inspection (DPI)
The dye penetrant inspection method is used to detect invisible surface defects in a nonmagnetic casting. The casting is brushed with, sprayed with, or dipped into a dye containing a fluorescent material. The surface to be inspected is the wiped, dried and viewed in darkness. The discontinuous in the surface will then be readily discernible.
Coin Testing
By hitting with coin on to the component and by hearing the sound coming from the casing, the presence of defect can be estimated.
