Weld quality assurance involves the use of technological methods and actions to test and ensure the quality of welds, and secondarily to confirm their presence, location, and coverage. In manufacturing, welds are used to join two or more metal surfaces. Because these connections may encounter loads and fatigue during product lifetime, there is a chance they may fail if not created to proper specification.
Weld testing and analysis Methods of weld testing and analysis are used to assure the quality and correctness of the weld after it is completed. This term generally refers to testing and analysis focused on the quality and strength of the weld but may refer to technological actions to check for the presence, position, and extent of welds. These are divided into destructive and non-destructive methods. A few examples of destructive testing include macro etch testing, fillet-weld break tests, transverse tension tests, and guided bend tests. Other destructive methods include acid etch testing, back bend testing, tensile strength break testing, nick break testing, and free bend testing. Non-destructive methods include fluorescent penetrate tests, magnaflux tests, eddy current (electromagnetic) tests, hydrostatic testing, tests using magnetic particles, X-rays and gamma ray-based methods, and acoustic emission techniques. Other methods include ferrite and hardness testing.
Imaging-based methods
Industrial Radiography X-ray-based weld inspection may be manual, performed by an inspector on X-ray-based images or video, or automated using machine vision. Gamma Rays can also be used
Visible light imaging Inspection may be manual, conducted by an inspector using imaging equipment, or automated using machine vision. Since the similarity of materials between weld and workpiece, and between good and defective areas, provides little inherent contrast, the latter usually requires methods other than simple imaging. One (destructive) method involves the microscopic analysis of a weld cross-section.
Ultrasonic- and acoustic-based methods Ultrasonic testing uses the principle that a gap in the weld changes the propagation of ultrasonic sound through the metal. One common method uses single-probe ultrasonic testing involving operator interpretation of an oscilloscope-type screen. Another senses using a 2D array of ultrasonic sensors. Conventional, phased array and time of flight diffraction (TOFD) methods can be combined into the same piece of test equipment. Acoustic emission methods monitor for the sound created by the loading or flexing of the weld.
Peel testing of spot welds This method includes tearing the weld apart and measuring the size of the remaining weld.
Weld monitoring Weld monitoring methods ensure the weld's quality and correctness during welding. The term is generally applied to automated monitoring for weld-quality purposes and secondarily for process-control purposes such as vision-based robot guidance. Visual weld monitoring is also performed during the welding process. On vehicular applications, weld monitoring aims to enable improvements in the quality, durability, and safety of vehicles – with cost savings in the avoidance of recalls to fix the large proportion of systemic quality problems that arise from suboptimal welding. Quality monitoring of automatic welding can save production downtime and reduce the need for product reworking and recall. Industrial monitoring systems encourage high production rates and reduce scrap costs.
Inline coherent imaging Inline coherent imaging (ICI) is a recently developed interferometric technique based on optical coherence tomography that is used for quality assurance of keyhole laser beam welding, a welding method that is gaining popularity in a variety of industries. ICI aims a low-powered broadband light source through the same optical path as the primary welding laser. The beam enters the keyhole of the weld and is reflected back into the head optics by the bottom of the keyhole. An interference pattern is produced by combining the reflected light with a separate beam that has traveled through a path of a known distance. This interference pattern is then analyzed to obtain a precise measurement of the depth of the keyhole. Because these measurements are acquired in real-time, ICI can also be used to control the laser penetration depth by using the depth measurement in a feedback loop that modulates the laser's output power.
Transient thermal analysis method Transient thermal analysis is used for range of weld optimization tasks.
Signature image processing method
Signature image processing (SIP) is a technology for analyzing electrical data collected from welding processes. Acceptable welding requires exact conditions; variations in conditions can render a weld unacceptable. SIP allows the identification of welding faults in real time, measures the stability of welding processes, and enables the optimization of welding processes.
Development The idea of using electrical data analyzed by algorithms to assess the quality of the welds produced in robotic manufacturing emerged in 1995 from research by Associate Professor Stephen Simpson at the University of Sydney on the complex physical phenomena that occur in welding arcs. Simpson realized that a way of determining the quality of a weld could be developed without a definitive understanding of those phenomena. The development involved:
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