Using Portable Laser Vision to Improve Weld Quality
The benefits of incorporating portable laser vision inspection into a weld quality system are discussed.
The benefits of incorporating portable laser vision inspection into a weld quality system are discussed.
Walt Bylsma, Certified Welding Inspector (CWI) at Crown Equipment Corp., New Bremen, Ohio, knows a thing or two about quality. Crown, a manufacturer of powered industrial lift trucks for 75 years, has become well known for the quality and longe-vity of its products. The company is always looking for the latest technologies that will enable it to continue to raise the bar in terms of the value it delivers to its customers.
Bylsma, having spent 20 years as a welder and then another 20 years as a welding inspector using both destructive and nondestructive methods, knows that creating a strong structural foundation is key to producing a robust and capable forklift. After utilizing manual welding gauges to inspect tens of thousands of welds over the years, he believes the new technology Crown uses for visual inspection of welds is another significant step toward providing the best quality product for the company’s customers.
“During my time of inspecting welds pre-laser scanning, I always hoped, and held out belief, that someday the technology of visual weld inspection would, ‘catch up’, to the significant advancements made, and continually being made, in the welding industry as a whole,” said Bylsma. “At the time, I didn’t know what that might look like, but I believe that laser scanning is one of those advancements.”
Inspection of welds has always been a crucial part of the welding quality management process, but utilizing traditional manual gauges can be subjective and time-consuming. Manual gauges also cannot be connected to the digital world (Figure 1). Laser scanning technology is now available in a portable format for weld examination that can inspect welds quickly, consistently, and accurately (Figure 2). With this state-of-the-art technology, laser inspection devices allow for remote collaboration, real-time data diagnostics, and measurement of features that are nearly impossible to measure with gauges (i.e., toe reentrant angle, overwelding, and theoretical throat, among others). Other advantages include being noncontact (supporting inspector safety) and achieving more repeatable and reproducible results. Laser vision inspection can also contribute to achieving Sigma Six welding quality, which is defined as having a defect rate less than the acceptable industry level of 3 parts per million. Additionally, being digital allows for easier and seamless sharing, meeting the needs of Internet of things (IoT) and Industry 4.0 standards.
Figure 1: Traditional gauge (shown for reference only, not correct positioning).
Figure 2: WiKi-SCAN™ welding inspection system from Servo-Robot Corp.
Typical weld quality control has relied mostly on postweld inspection, but the versatility of laser vision monitoring allows for the welding process to be monitored before, during, and after the weld is made. The pre-weld joint information can be correlated to the in-process welding to reduce postproduction and time-consuming inspection requirements. This added information provides useful data to help improve both the welding and upstream material preparation processes. Laser vision systems can also be automated to further extend the capability for in-process monitoring.
Comparison of Laser Scanning vs. Manual Gauging for Weld Inspection
Standard visual weld inspection utilizing manual welding gauges depends on an inspector’s visual acuity and their ability to use the go/no-go gauges properly. However, there are inherent challenges with this methodology. The following issues can all be addressed satisfactorily with laser scanning.
Subjective Go/No-Go Inspection
Manual weld inspection provides only an estimation of measurement values. This would limit the usefulness in the digital world if numbers were assigned and then manually entered into spreadsheets. Also, weld profile features such as convexity, reinforcement, and theoretical throat present even further subjectivity. Issues compound with the inherent difference between welding inspectors: visual acuity, attitude, knowledge, and skill sets. These elements contribute adversely to this variation, which, when combined, result in low repeatability and reproducibility. All these variables result in a high level of subjectivity, and laser scanning can address all these issues.
Unconventional Weld Types
A skewed T-joint is a good example of a weld joint configuration that is increasingly common in many industries; however, it can be difficult to measure with available manual gauges (Figure 3). The challenges and time-consuming activities involved include measuring the actual angles and then calculating the required weld leg lengths and theoretical throat values by utilizing a manual slide ruler, such as the skew-t fillet weld calculator. Only then can the skew-t fillet weld gauge be used to measure the weld acute or obtuse sides. This takes several minutes, whereas a laser scanner completes this in mere seconds due to the incorporated algorithms.
Figure 3: Skewed fillet weld where measurement of an obtuse angle is done.
Full Weld-Length Measurement
Traditional visual inspection is generally accomplished by viewing an overall weld length and then gauging it at specific, incremental locations. This is time-consuming and leaves open the possibility of missing defects where gauging was not performed. Laser scanning accomplishes this for 100% of the weld length for all dimensions and defects and reports the locations and lengths for any out-of-tolerance conditions.
Although most traditional manual weld gauges are small, there are cases where accessibility is an issue (Figure 4). To be appropriately utilized, the gauge must be positioned on the base material and over the weld and be seen clearly from all angles to interpret results correctly. Sometimes, due to joint design or location issues, or both, it is not always possible to utilize a traditional welding gauge. For laser scanning, “line of sight” within a 4 in. depth field-of-view is the only requirement.
Figure 4: Access challenges with manual gauges.
Non-Contact Inspection of Hot Parts
For safety considerations, inspecting with traditional weld gauges typically needs to be performed after a part has been allowed to cool to the touch to avoid the possibility of burns. Since laser scanning is noncontact and performed several inches off the part, the inspection can begin within seconds after terminating a weld. In the case of time-sensitive inspections needing to be performed, this is beneficial (Figure 5). Additionally, the possibility of receiving scrapes or cuts on material that may have dross or burrs is minimized.
Figure 5: Immediate inspection can be performed as soon as welding is completed.
Other Difficult-to-Quantify Features
There are certain features of weld profiles that are difficult to measure or quantify using traditional methods, including weld toe reentrant angles, undercut, and the ratio of weld height and width. All of these contribute to the crucial determinations of fatigue life of welded structures. Let’s look at each one in more detail.
The reentrant angle is formed on a fillet or groove weld between the weld toe and the adjacent base material. This angle generally defines the difference between an acceptable transition between weld and base material and a critical defect defined as overlap (nonstandard term is cold lap). A value of fewer than 90 deg indicates overlap. In contrast, a value of 90 deg or greater indicates a smoother transition, reducing the notch effect and increasing fatigue life. Some companies specify a value of more than 150 deg to attain the required fatigue life for products such as mining shovels and wind towers. Traditional gauges, such as a protractor, are difficult to ascertain the weld toe or base plate area visually and are, therefore, challenging to achieve any degree of accuracy. A laser scanner automatically measures these with precision. A few welding standards, including American Welding Society (AWS) D14.4, Specification for the Design of Welded Joints in Machinery and Equipment, now specify a requirement for reentrant angles between weld passes (weld to weld), in addition to weld toes. This measurement can be performed manually utilizing the laser scanner digital caliper.
A variety of methods have been utilized to check undercut, ranging from the use of one’s fingernails to V-WAC, Bridge Cam, and various other depth gauges. Any of these methods lack the necessary accuracy and repeatability, especially when specifications from some codes, such as AWS D14.4, require values to 0.010 in. In addition, many people inadvertently measure features such as a weld bead edge scallop or roughness as undercut, when, in fact, they are not. Laser scanning correctly measures undercut as a notch right outside the weld toe, which descends into the base material.
Many codes, including AWS D1.1, Structural Welding Code — Steel, require a height-to-width ratio of less than 10% for fatigue life considerations. Doing this manually requires multiple gauges and measurements, followed by calculations. Laser scanning performs this instantly and accurately.
Every inspection record includes all digital results for dimensions, geometry, and defects combined with pictures and additional notes shown in an Excel spreadsheet (Figure 6). This information is stored in the scanner database and is downloadable using Wi-Fi or a flash drive. This information can then be customized and analyzed to determine problem areas and trends and report internally in the company or to a customer or supplier.
Figure 6: A WiKi-SCAN report spreadsheet showing recorded inspections.
Continuous Process Improvement
Possessing actual measurement values for all weld features rather than just go/no-go results can further support a continuous improvement process plan. Trends can easily be detected and corrective actions initiated. Specific welds, welders, robots, shifts, and processes, for example, could be identified as potentially problematic, requiring process or other changes to ensure conformance to standards. For example, suppose one consistently sees the leg lengths on a T-fillet weld to be excessively unequal. This could indicate a robot is not targeting the wire properly into the joint, indicating a higher probability of lack of proper root penetration and sidewall fusion. Laser-scanning activities actionable to continuous improvement include the following:
Robotic welding process validation
Verification of new products and processes
Certification of incoming supplier product
Process capability studies.
The operation of the laser scanner can be monitored remotely via a Wi-Fi connection. For example, the scanner can be utilized within a confined space and manually or automatically manipulated with results viewable on an outside monitor. Another example is the inspector could be onsite inspecting pipeline welds while the quality control inspector is in the home office viewing the inspection and results in real time.
Training and Education
The objective results obtained from the report can also be utilized as a supplemental tool for the training of new inspectors, welders, or various other weld shop personnel for general educational purposes. Onboard graphics displaying the weld’s cross-sectional profile are an invaluable visual tool for illustration and the clarification of the theoretical throats of welds. For training, as an example, a score could be assigned to each weld produced and then appraised to signal areas or techniques, or both, that might need improvement. With overall results providing crisp and clear pictures of the weld surface, cross-sectional profiles, and all measurement data, the weld quality as a function of welding parameters and technique can be easily assessed for functional and practicable training.
In our fast-paced world, the need for quality to keep up with production while emphasizing and maintaining safety is crucial. The quality of welds in virtually any product must meet or exceed engineering specifications regardless of the industry.
An efficient and cost-effective weld quality program should also embrace the accuracy and speed of data collection. Laser scanning of welds can help address all of these issues while building a database of actionable data that allows for clearly established performance benchmarks further enhanced by continuous improvement.
Jeff Noruk, president of Servo-Robot Corp., Wauwatosa, Wis., believes that laser scanning is one of the most significant and singular advancements in the world of visual weld inspection to date. Noruk is excited when other companies like Crown embrace new technology not only to advance their production processes but also to improve the products they are delivering to their customers. Successes like these continue to encourage change that moves the industry forward, so long as we remain open to the opportunities. As an anonymous writer once noted, “When it comes to technology, the last thing you want to do is be resistant to change, because that’s when you get left behind.”
This article was written by Walt Bylsma (Level III Inspector at Crown Equipment Corp., New Bremen, Ohio) and Jeff Noruk (president of Servo-Robot Corp., Wauwatosa, Wis.) for the American Welding Society.