Best Forging Inspection Methods
Inspection is a crucial step in the forging process. By testing, you can assess the chemical and physical properties of a forged metal part. Forging inspection methods range from simply hitting the metal to test the resonant sound to advanced techniques like radiographic testing and ultrasonic inspection. In this article, we’ll take you through the inspection of forged metal and how to decide which method is best for you.
Why inspect forged metal?
Forging inspection methods are essential to the forging process because they provide quality control and ensure that finished pieces fit customer requirements. Many issues can arise in forging processes, including internal and external cracking, flaking and unwanted seams. Especially when using steel forgings for manufacturing processes, spotting flaws earlier rather than later can save you both time and money.
Why does stainless steel rust slowly?
Chromium is stainless steel’s weapon against rust. When exposed to the surrounding oxygen, the chromium within stainless steel creates a thin layer of chromium oxide surrounding the metal piece. Unlike iron oxide, which forms flaky and corrosive rust, chromium oxide clings to the steel and acts as a barrier. This barrier separates the steel’s iron content from water and oxygen in the air. This reaction gives stainless steel components resistance in corrosive environments, the passive layer giving them a huge advantage over normal steel.
Non-destructive testing is a group of forging inspection methods covering any technique that maintains the integrity of the forged materials, leaving them ready for use in manufacturing processes or other applications. Different non-destructive testing techniques can detect surface and internal flaws in metal pieces, ensuring quality control while avoiding waste.
The most basic nondestructive inspection method is visual testing. Visual testing can locate surface anomalies and subsurface issues. Trained eyes can often detect surface imperfections later confirmed by macro photography, magnification devices and other tools.
Magnetic particle inspection
Magnetic particle inspection is another nondestructive technique. This approach can find internal and external imperfections in steel forgings and other ferromagnetic materials. By applying a magnetic field or ultraviolet light to the test piece, different flaws can be revealed by the subsequent behaviour of magnetic particles, showing issues that are too small to be picked up by the naked eye. In general, this test is employed after a certain value is added to the parts in question, such as forging or welding.
Ultrasonic testing is a popular inspection technique that can uncover the internal quality of forged materials. Ultrasonic inspection pinpoints the size, location and distribution of internal flaws. Ultrasonic testing has a series of clear advantages, including cost-effective, portable equipment and highly accurate findings, making the technique a common choice in product testing. This testing is usually employed to the raw material to determine that value is added after passing this test.
Liquid penetrant testing
A final nondestructive technique is liquid penetrant testing. This versatile process works for ferromagnetic materials and other types of forged materials. In particular, liquid penetrant testing is exceptionally good at detecting external discontinuities and surface imperfections too small for human eyes.
Destructive testing is the second major category of forging inspection methods, covering tests that apply force to a forged piece until it fractures. Destructive testing requires a test piece, which will be unusable after testing is complete. Despite this damage, destructive tests can provide more information about forged products than nondestructive counterparts. In fact, the results of such tests provide valuable information as to the expected field performance of the forgings.
Tensile testing is one of the simplest destructive inspection methods. A tensile test measures how well a piece can withstand tension, pulling the metal object in two directions to accurately measure its strength and strain capacity. Due to its useful results and simplicity, tensile testing is one of the most common destructive inspection methods.
Stress rupture testing
Stress rupture testing is similar to tensile testing and tests the metal piece by applying force until it creates a break. In particular, this technique can be used to test how forged pieces will cope with high temperatures, leaving stress rupture testing an important option for industrial applications.
Another type of destructive testing is hardness testing. In this technique, machines press loads against the part for a set period of time. This pressure creates a deformation, indentation, or scratching that experts can use to calculate the exact hardness of the forged material. In turn, this information is used to predict the wear resistance of a metal component.
Charpy impact testing
Finally, there is Charpy impact testing, which precisely records the energy required to fracture forged metal pieces. Charpy impact inspection is a popular option for testing forged products, as results are a measure of the toughness of the final product.
Finding the best technique
The forging industry offers a range of forging inspection methods that ensure the quality and utility of forged materials. Given the variety of techniques available, it can be bewildering to figure out which approach will deliver for you. By considering a series of factors, you can isolate the technique which best suits your needs.
Firstly, the type of metal you’re testing is significant. Are you looking at stainless steel or a different metal? While techniques like ultrasonic testing work for most metals, others only function with electromagnetic materials.
Secondly, what structural issues are you checking for? If it’s an external flaw, then visual inspection or liquid penetrant testing will suit you better than techniques like ultrasonic inspection, which assesses a piece’s internal quality.
Finally, it’s worth considering costs and production. Destructive testing will leave metal pieces unusable, meaning it’s an expensive choice when you’re testing large, complex pieces in small production runs. A practical way to deal with such issues is to agree with a customer, based on their requirements, or utilise statistical techniques that provide measurable confidence levels of the final products. Once agreed, representative batch or lot samples are identified for destructive testing at an independent and certified laboratory, and results are reported against national or international standards.
Our testing expertise
All of our testing is performed by NATA-endorsed (National Association of Testing Authorities) laboratories to ensure full traceability and transparency of the final products. Greg Sewell Forgings is the partner you can trust for conducting quality assurance tests and inspections. We are an accredited team constantly adopting the latest quality control and product testing innovations. Alongside our services like forged steel threaded fittings, CNC machining, and custom stainless steel fabrication, we ensure that our work reaches customers with an iron-clad quality guarantee.