Many characteristics of a weld can be evaluated during welding inspection, some relating to the welds size, and others relating to the presence of weld discontinuities. The size of a weld can be extremely important, as it can often relate directly to the weld's strength and associated performance, undersized weld's may not withstand stresses applied during service. Weld discontinuities can also be important. These are imperfections within or adjacent to the weld, which may or may not, dependent on their size and/or location, prevent the weld from meeting its intended performance. Typically these discontinuities, when of unacceptable size or location, are referred to as welding defects, and can sometimes cause premature weld failure through reduction of the weld strength or through producing stress concentrations within the welded component.
The inspection of welds can be conducted for a number of reasons. Perhaps the most fundamental reason is to determine whether the weld is of suitable quality for its intended application. In order to evaluate a weld's quality, we must first have some form of measuring block with which to compare its characteristics. It is impractical to attempt to evaluate a weld's quality without some form of specified acceptance criteria.
Weld quality acceptance criteria can originate from a number of sources. The welding fabrication drawing/blue print will typically provide weld sizes and possibly other welding dimensional information, such as length and location of welds. These dimensional requirements will usually have been established through design calculations or taken from proven designs that are known to meet the performance requirements of the welded connection.
Acceptable and unacceptable levels or amounts of weld discontinuities for welding inspection are usually obtained from welding codes and standards. Welding codes and standards have been developed for many types of welding fabrication applications. It is important to choose a welding standard that is intended for use within the particular industry or application in which you are involved.
Welding inspection can often require a wide variety of knowledge on the part of the welding inspector: the understanding of welding drawings, welding symbols, weld joint design, welding procedures, code and standard requirements and inspection and testing techniques, to name a few. For this reason many welding codes and standards require that the welding inspector be formally qualified or have the necessary knowledge and experience to conduct the inspection services. There are a number of welding inspection training courses available and a number of welding inspector certification programs internationally. The most popular program used in the USA is administered by the American Welding Society (AWS). This is the Certified Welding Inspector (CWI) program. Certification as a welding inspector: will typically require demonstration of an individual's knowledge of welding inspection through passing examination.
In order to further appreciate the extent of welding inspection we will need to examine specific areas of inspection techniques and welding inspection applications. I have chosen the following topics to provide this welding inspection overview:
Inspection and Testing for Welding Procedure Qualification – Types of inspection used for these requirements and how they can be an essential part of the overall welding quality system.
Visual Inspection – Often the easiest, least expensive, and probably, if performed correctly, the most effective method of welding inspection for many applications.
Surface Crack Detection – Methods such as Liquid Penetrant Inspection and Magnetic Particle Inspection – How they are used and what they will find.
Radiographic and Ultrasonic Weld Inspection – Methods known as Non Destructive Testing (NDT) and used typically to examine the internal structure of the weld in order to establish the weld's integrity without destroying the welded component.
Destructive Weld Testing – Methods used to establish weld integrity or performance, typically through sectioning and/or breaking the welded component and evaluating various mechanical and or physical characteristics.
One of the main ingredients of a successful welding quality system is the establishment, introduction and control of a sound welding inspection program. Only after the full evaluation of the weld quality requirements/acceptance criteria, the full appreciation of the inspection and testing methods to be used, and the availability of suitably qualified and/or experienced welding inspectors can such a program be established.
» Read More...
RF welding is a basic technology, and the basic devices necessary to affect such a weld have not changed since the inception of the process. Today, as in 1942, we need a generator to provide RF, a transmission line to transfer power, a press to apply force and an electrode in the desired geometric pattern to be welded.
The terms "Radio Frequency (RF) Welding or Sealing" are often used interchangeably with "High Frequency (HF) or dielectric welding or sealing." When matter is brought into contact with an electromagnetic field, some portion of the electromagnetic field will go through a change of energy state. As a result, it will be converted to heat and dissipated within the contacted matter. The degree to which this con-version will occur, or the efficiency of this conversion of energy state is dependent on the atomic and molecular structure of the matter, the frequency of the electromagnetic field, and the field potential (Volt-age/cm). The term dielectric heating correctly describes this phenomenon at any frequency while RF or HF heating describes the process over the lim-ited frequency range from 1 to 200 megacycles/sec (megahertz/sec).
The area where most of the technological changes have taken place is in the components from which the individual devices are constructed. Solid state components have replaced mercury vapor rectifier tubes. Digital timers have replaced industrial timers. Programmable Logic Controllers (PLC) have replaced relay logic.
When a PLC is used with linear and optical encodes, precise control can be achieved over the various functions that determine the specific characteristics of the weld. Using these types of devices it is possible to monitor and control functions of time, pressure, current and voltage and their profiles.
When modern material handling systems are used in conjunction with these devices, high speed automatic production systems can be built. Many hundreds of such systems are in use throughout the U.S. These systems manufacture a wide variety of products for the automotive, stationary products, and medical industries.
The continuing stream of new RF responsive materials being brought to the market further impact the industry. In addition, additives and RF responsive adhesives are continually being developed for specialized applications. It is now possible to bond materials that in the past were considered unsuitable for the RF process. These changes are opening up a new range of products that can now be manufactured by this time proven technology. This will have a great effect in the medical industry, as it tries to eliminate the use of vinyl.
Both electron beam and laser welding, when initially discovered, were thought to be possible replacement technologies. However, these technologies have been found to be more applicable for spot or seam welding of metals or other rigid materials where welding times are measured in minutes and hours. In RF welded products, welding times are measured in seconds or fractions thereof. Guideline believes the likelihood of these becoming competing technologies is very low. In Guideline's opinion there is nothing on the horizon that will replace RF welding in the next 5 to 10 years. Its place will be as secure as it is today, not only as the economically preferred way to weld certain materials, but in many cases the only feasible method.
» Read More...
RF welding is a basic technology, and the basic devices necessary to affect such a weld have not changed since the inception of the process. Today, as in 1942, we need a generator to provide RF, a transmission line to transfer power, a press to apply force and an electrode in the desired geometric pattern to be welded.
The terms "Radio Frequency (RF) Welding or Sealing" are often used interchangeably with "High Frequency (HF) or dielectric welding or sealing." When matter is brought into contact with an electromagnetic field, some portion of the electromagnetic field will go through a change of energy state. As a result, it will be converted to heat and dissipated within the contacted matter. The degree to which this con-version will occur, or the efficiency of this conversion of energy state is dependent on the atomic and molecular structure of the matter, the frequency of the electromagnetic field, and the field potential (Volt-age/cm). The term dielectric heating correctly describes this phenomenon at any frequency while RF or HF heating describes the process over the lim-ited frequency range from 1 to 200 megacycles/sec (megahertz/sec).
The area where most of the technological changes have taken place is in the components from which the individual devices are constructed. Solid state components have replaced mercury vapor rectifier tubes. Digital timers have replaced industrial timers. Programmable Logic Controllers (PLC) have replaced relay logic.
When a PLC is used with linear and optical encodes, precise control can be achieved over the various functions that determine the specific characteristics of the weld. Using these types of devices it is possible to monitor and control functions of time, pressure, current and voltage and their profiles.
When modern material handling systems are used in conjunction with these devices, high speed automatic production systems can be built. Many hundreds of such systems are in use throughout the U.S. These systems manufacture a wide variety of products for the automotive, stationary products, and medical industries.
The continuing stream of new RF responsive materials being brought to the market further impact the industry. In addition, additives and RF responsive adhesives are continually being developed for specialized applications. It is now possible to bond materials that in the past were considered unsuitable for the RF process. These changes are opening up a new range of products that can now be manufactured by this time proven technology. This will have a great effect in the medical industry, as it tries to eliminate the use of vinyl.
Both electron beam and laser welding, when initially discovered, were thought to be possible replacement technologies. However, these technologies have been found to be more applicable for spot or seam welding of metals or other rigid materials where welding times are measured in minutes and hours. In RF welded products, welding times are measured in seconds or fractions thereof. Guideline believes the likelihood of these becoming competing technologies is very low. In Guideline's opinion there is nothing on the horizon that will replace RF welding in the next 5 to 10 years. Its place will be as secure as it is today, not only as the economically preferred way to weld certain materials, but in many cases the only feasible method.
» Read More...
Posts
