As different as the industries are which focus on the processing of light metals, so different are the requirements for the properties of the components used. While flawless surfacesin the packaging industry ensure a perfect appearance, an intact structure of the interior is indispensable for safety in the automotive industry, for example. In order to guarantee a high quality of the metal components, various quality control methods have been established.
What are the Differences in Quality Assurance?
A fundamental difference in the quality assurance of metal is destructive testing and non-destructive testing. In destructive testing, random samples of castings that have already been produced are cut open and analysed for possible defects. In order to provide information about the quality of the production process, quality inspectors search specifically for inclusions, porosity and shrinkage.
Non Destructive Testing Methods
While destructive quality assurance provides for the destruction of the casting under investigation, non destructive testing methods offer the possibility of testing intact castings with regard to their internal and external properties. This does not impair the functionality of the tested components. The inspection procedures range from superficial inspection with the naked eye to radiographic inspection (X-Ray).
Visual inspection: Cast parts are inspected by eye. In this way, surface defects, inclusions of slag or sand, cracks, cold shuts, gas evolution, molding flaws or mis-runs can be detected at first glance.
Dimensional inspection: Coordinate measuring machines (CMM) are used to use probes to check whether a casting meets dimensional requirements/tolerances. Manual measurement is also possible.
Radiographic Inspection (X-Ray): The castings to be inspected are exposed to X-rays or gamma rays in order to make fractures, cracks or pinhole dots of porosity visible. The X-ray film is released by the radiation, which is not absorbed by the casting. While thicker areas of the casting absorb less radiation, lower seal components absorb more radiation, resulting in higher film exposure. This makes it easy to see dark areas that indicate defects such as gaps or cracks. A major advantage of this process is the low demands placed on the surface quality of a wide variety of materials.
Liquid Penetrant Inspection (LPI): First, the castings must be thoroughly cleaned and freed from any sealants such as paint or varnish. They are then placed in a colored penetrating solution with high capillary action and low viscosity, so that it can flow freely through the cracks of the components under investigation. After a certain exposure time, the penetrating agent is wiped off the surface with a damp cloth. In the next step, another liquid is applied, which is called a developer. The agent reacts with the remaining penetrating agent, making defects on the surface of the casting visible. Alternatively, cracks can be made visible with a fluorescent penetrant that glows under UV radiation. LPI is therefore a cost-effective and efficient process which is used in the automotive, aerospace and mechanical engineering sectors, for example.
Ultrasonic Testing (UT): After thorough cleaning of paint and loose scale, castings are examined with the aid of high-frequency acoustic energy. Sound waves pass through the components until they hit the opposite surface, an interface or a defect. At this point the sound waves are reflected and bounced back. In this way, a pattern is created which can provide information about the position and size of a defect. The wall thickness of a pipe can also be determined with this method. A major advantage over other methods is that even small defects deep inside the casting can be reliably detected.
Magnetic Particle Inspection (MPI): This technique is suitable for testing ferromagnetic metal castings. These include iron, nickel, cobalt and some of their alloys.
Quality Control within the Manufacturing Process
Quality control does not only have to be carried out in the aftermath, but can also be carried out during production. In September 2019, Gerfetec presented a new machine version of the ARC 405 and the process head ARC QM Head. Quality assurance is carried out with the aid of a melt pool control, which enables monitoring, recording and documentation of the welding process. During the production of aluminum die cast parts, inductive displacement sensors based on eddy also offer gap monitoring without gaps at several measuring points. The system can be integrated into existing machines and is insensitive to high temperatures, dust, dirt or pressure. Thus, eddyNCDT 3005 ensures high product quality, improves tool life and reduces rework.
