Every step is taken in a careful manner in die casting to get quality outputs, which do not have issues with the surface finish, soundness, mechanical properties, as well as final dimensions. Yet, even components cast with diligence have to undergo inspection, as part of the quality control measures. Small issues could arise, and several die cast parts have mechanical requisites that might just be undermined by a not-easily-visible defect. With inspection, die casters and their clients get to feel more confident about the quality of the end product.
Types of Testing
There are many methods to test and detect issues inside the casting. These techniques help to make sure that it does not fail under load. The two main types of internal inspection methods are destructive as well as non-destructive testing.
As the name implies, the destructive method involves opening up a casting, to check its metal properties closely. The inspecting person would look for porosity, inclusions and shrinkage. In contrast, the other method does not involve cutting the cast object to check its external and internal soundness. It is done by workers of a foundry, clients of die casters, as well as NDT technicians.
Of course, non-destructive testing includes visual inspection. There are other, more advanced testing methods too, that do not involve damaging the casting.
Non-Destructive Testing Methods
Dimensional Inspection
It is undertaken to make sure a die cast part meets dimensional tolerances/requirements. This can be performed manually or using a CMM (coordinate measuring machine). These are the two main ways to perform the dimensional inspection. The equipment uses probes to obtain extremely precise measurements. Other tools are also used to do it. The accuracy of the measuring tools also contributes to the manufactured part’s dimensional consistency and quality.
Liquid Dye Penetrant Testing
Also known as LPI (Liquid Penetrate Inspection), this method finds small cracks, pores, or other flaws on the surface of a casting that would be difficult to detect with the naked eye. The tester initially cleans the component to get rid of any particles of dust or grit, which may keep the liquid dye from entering cracks on the metal part. After it is clean and dry, they bathe the die cast component using a penetrant solution.
Different kinds of LPI use distinct solutions, including a brightly dyed oil having low viscosity and high capillary, meaning the liquid dye will run freely to cracks on the component. The liquid dye is left to be in the same position so that the dye can work its way to any invisible cracks.
Once enough time is passed to let it do what it is meant to, excess liquid is cleared from the surface of the part. This is usually performed by gently wiping the excess amount of liquid using a damp cloth, ensuring not to flood the part as that may possibly remove the dye in its cracks. Then, the tester applies a special developer on the casting, and its flaws become able to be seen clearly.
Magnetic Particle Inspection
MPI is also used to find small holes and cracks on the surface of a casting, or in its shallow subsurface, and the process is similar to the above-mentioned one in that sense. However, it can only be used to test components made of ferromagnetic metals, which can create magnetic fields, such as cobalt, nickel, iron as well as some alloys. The die cast part is magnetized, typically with electromagnets, to begin the trial.
A magnetic field in metal is stronger than in air. When discontinuities such as holes or cracks exist on the casting, or at the subsurface of it, the induced magnetic field will be disrupted.
In order to find the disruptions, foundry workers spray the casting with a liquid or dust having iron oxide particles or other substance that react in the field. The sprayed particulate then clusters close to the edges of the distortions, outlining areas with low magnetic flux. As a result, magnetic powder and magnets can be used in order to show distortions where the air is more than metal, above any holes or in any cracks.
Radiographic Inspection or X-Ray Testing
It creates images such as those in a medical facility that show broken bone. This method is used to find out the areas where there are defects. These X-rays help a metalworker determine if the mechanical properties of the casting are compromised by inclusions, holes, or shrinkage, and whether it is possible to fix them before the product is shipped.
After the tests are finished in the foundry, the accepted die cast component is at times used as it is. Normal surface discontinuities or irregularities may not matter much, to the use of a sound product. Die casters take several measures, such as surface finishing or other treatments, to make it of top quality.