Every step in metal casting, from creating the pattern to heat treating, is carefully controlled to prevent various issues; even when castings are made with great care, they should still go through inspection for quality control. Small issues can sometimes occur unexpectedly, and hidden defects can affect the mechanical strength of the casting and casting quality control. Inspection helps the foundry and the client ensure they have a high-quality product.
Casting inspection methods are crucial to catching any hidden defects during production. Common casting defects include surface flaws, inclusions, and cooling problems.
In this blog, we will explore the common issues that can occur during casting quality control and what preventive methods can be done to maintain the quality of the components.
Why Casting Quality Control Matters?
Testing products for quality control and assurance is crucial to prevent defects from reaching your customers. If done right, it protects your brand’s reputation and saves you from costly refunds or replacements. Defective products can seriously damage your business, leading to lost revenue and customers. To avoid these risks, it’s essential to partner with an experienced service provider who has a robust casting quality control system. They will identify and fix any issues before your products are shipped, ensuring that only high-quality products reach your customers.
What are Common Casting Failures?
As casting is a manufacturing process where molten metal is poured into a die to create components, there is a margin for a few common failures, too. Even if you are using advanced techniques or high-quality material, the result might not be as expected. Let’s discover some of the possible failures while casting quality control your components:
1. Porosity
Porosity happens when gas gets trapped in the molten metal during casting quality control. This can occur for several reasons, such as poor mold venting due to bad design, impurities in the metal, or using the wrong melting temperature. When gas bubbles get trapped, they create small holes in the metal. These holes can weaken the die cast product, making it more likely to fail.
2. Cold Shuts and Hot Tears
Cold shuts and hot tears are two common issues in die-casting. Cold shuts occur when molten metal doesn’t flow smoothly into the mold, leading to visible lines or seams on the final product. Hot tears happen when the metal cools and solidifies too quickly, causing cracks or tears in the casting.
3. Leaking Casting
Castings can leak due to various factors, such as worn-out dies or porosity in the material. To check for leaks, parts are placed underwater in a dunk tank at a set time and pressure. If air bubbles appear in a particular spot, it shows that there’s a leak. This method is commonly used as a non-destructive way to detect leaks in castings.
4. Dimension Issues
Sometimes, parts may not match the expected dimensions due to issues like die wear, poor die design, or improper metal filling. The quality assurance team plays a crucial role in checking that the casting quality control meets the exact dimensions to achieve precise shapes. Ensuring this helps to avoid defects and maintain high-quality standards.
5. Trimming Issues
Excess material on die-cast parts can signal poor die-cast maintenance. You can usually spot trimming issues by eye if there’s extra material. For parts where trimming problems aren’t obvious, a coordinate measuring machine is needed to check if the dimensions are accurate.
What Should Be Considered While Casting Quality Control?
While casting inspection covers five main areas. These areas are critical to maintain the quality and durability of the components. Here are these five areas to be considered while casting quality control:
Casting Finish
The surface finish of casting is affected by several factors. These factors include the type of pattern or molding, coating, and cleaning process. Currently, measuring surface roughness through instruments hasn’t been very effective. Instead, it’s often done by visually comparing the casting with test panels that show different levels of surface roughness.
Dimensional Accuracy
Dimensional variations in castings can occur due to mold cavity expansion caused by the heat and pressure of molten metal, as well as the metal’s contraction during cooling and heat treatment. Patternmakers account for these changes by adjusting the pattern’s design. For large-scale casting production, facilities frequently check critical dimensions to monitor for potential drift, particularly due to pattern wear. When tight tolerances are essential for a part’s application, the customer should specify these tolerances.
Mechanical Properties
When checking the mechanical properties of castings, several factors need to be considered to ensure the material meets the necessary standards. These properties include hardness, which affects how easily the material can be machined and how resistant it is to wear. The tensile strength of the material is also important, as it determines how much stress the casting quality control can withstand before breaking. Additionally, the material’s ductility, or its ability to deform without breaking, is a key factor in assessing the overall strength and durability of the casting.
Chemical Composition
The chemical composition of an alloy significantly impacts the performance of the material. Minor alloying elements can further influence the material’s properties. Casting alloys are usually specified according to ASTM, SAE, or AMS standards. Depending on the alloy’s sensitivity to chemical variation, chemical analysis might be required to ensure the correct composition for achieving the desired properties.
Casting Soundness
Internal and surface flaws that cannot be seen with the human eye can impact the performance of metal components. Several non-destructive testing procedures can be utilized to identify these “invisible” faults. These methods determine casting integrity without causing physical damage, allowing the casting to be used if it passes the tests. Below is a detailed list of non-destructive testing methods.
What are Casting Quality Control Methods?
There various methods exist to measure mechanical properties. A combination of all the methods is often used to document casting quality. Here are the most common methods:
Visual Inspection
This easy method employs the human eye to detect surface flaws, poor filling, and molding problems. Sand holes, uneven surfaces, surface shrinkage, blowholes, misruns, cold shuts, and surface slag are some of the most commonly identified faults.
Dimensional Inspection
To ensure that parts meet dimensional requirements, casting facilities may use manual measurements or a coordinate measuring machine (CMM). Dimensional accuracy checks help avoid costly post-production machining. CMMs have improved the speed and precision of measuring casting dimensions, with computerization allowing for repetitive use and statistical analysis.
Dye Penetrant and Fluorescent Powder Testing
This method detects tiny surface cracks and pores that are hard to see. A dye solution, suspended in penetrating oil, is applied to the casting surface. The dye seeps into defects and becomes visible when a special developer is applied. A similar technique uses fluorescent powder that glows under ultraviolet light, revealing surface cracks. While effective and economical, this method only detects surface flaws and cannot identify internal defects.
Magnetic Particle Inspection
Used on ferrous alloys, this quick and inexpensive method detects small surface cracks. A high-amperage, low-voltage current creates a magnetic field in the casting. Cracks and defects disrupt this field, and magnetic particles highlight these disruptions, indicating the crack’s shape and position.
Ultrasonic Testing
This method uses high-frequency sound waves to detect internal defects, wall thickness, and other properties. The sound waves travel through the casting until they hit an interface or defect, which reflects the energy to a receiver. The reflected energy pattern helps determine the defect’s location and size. However, accurate interpretation of results requires significant expertise, making this method more expensive.
Radiographic Inspection
Considered the best non-destructive method for detecting internal defects like shrinkage and inclusions, radiographic inspection involves exposing the casting quality control to X-rays. Dense areas absorb more radiation, appearing lighter on the film, while less dense areas appear darker. Any crack or inclusion shows up as a dark spot. Radiographic inspection also offers a permanent record of casting quality that multiple people can review. However, the method is limited by casting thickness and density.
Eddy Current Inspection
This method detects small surface cracks in electrically conductive materials. An alternating current passes through a coil, inducing an eddy current in nearby metal. The current reaction to the coil pinpoints small cracks or defects. Accurate interpretation requires considerable knowledge, which adds to the cost of this method.
Pressure Leak Testing
Pressure testing is used for castings that must be leak-proof. The casting is sealed and pressurized with air, gas, or water. Leaks are detected by watching for water seepage or air bubbles when the casting is submerged in clear water.
Conclusion
When selecting a die-casting service provider, quality control is a crucial factor to consider. At Frigate, we place a strong emphasis on quality assurance. Our process begins with a thorough inspection of raw materials and continues with rigorous testing of the finished products. We also conduct regular audits of our facilities and processes to maintain high standards. This meticulous approach ensures that our customers receive top-quality products. Contact us today to learn more about our die-casting process and other manufacturing capabilities.
