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Improve Welding Quality-Profile scanning

15-09-2020
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in 

Metal fabrication is a manufacturing process that utilises a variety of techniques to shape or join sheet metals into assembly parts, goods or end-user products such as cans, pipes, metal windows, automotive parts, bolts, screws and much more.

It is used to manufacture components for application in industries such as aerospace, agricultural, automotive, construction, medical, military and defence as well as OEM.

Welding is one of the most common techniques used for joining metal sheets during fabrication. It’s also one of the most used methods in the metal fabrication process.

Advanced growth in technology has enabled the development of welding robots for calculating welding processes in advance before they are carried out. This enables the manufacturer to fully automate their welding process while maintaining the quality of the welded seam.

High precision sensors and scanning technology have been used and integrated in the welding robot for optimising the weld quality. However, these systems are costly, which prompts manufacturers to question their need for that optimisation.

The weld quality quantifies a welded joint’s ability to perform the functional requirements of the weld during the service life of the welded product. It can be durability, corrosion resistance, appearance and other mechanical functions.

Numerous research studies have shown a correlation between fatigue strength and weld quality.

Substandard weld quality significantly increases the risk of failures at the early stage and should be avoided.

On the other hand, excessive welding increases fabrication cost and does not add customer value to the product.

Laser Profile Scanner as a welding quality inspection system

Inspection of welding quality should be done on both the insides and outsides of the welds. The ideal inspection system primarily requires sensors that are able to detect the height and width of the welded seam as well as interruption and residue clinging on to the seam.

The sensors should also be capable of performing inline measurement in the production line.

Non-contact laser profile scanners are popular for factory automation applications due to their high-speed, high accuracy scanning even when used in-line. The laser profile scanners detect the shape deviations and fault locations on the welded seam. It can also detect foreign contaminants such as welding wire residue left during the welding process.

The laser profile scanner works based on the laser triangulation principle by projecting a laser line into the target. The diffusely reflected light is registered onto the CMOS array in the camera optical system while the controller computes the profile data.

The controller also uses this camera image to calculate the position along the laser line in x-axis and distance in z-axis. These values are output in a two-dimensional coordinate system that is fixed with respect to the sensor.

The profile scanners can also be moved back and forth or used for performing measurement on traversing objects to generate 3D profiles.

The inspection is carried out after the welding process while the parts are still hot. This is done as the products can be passed on for rework if errors are detected at this early stage.

The tolerance limit is defined and saved in the system. The pass/fail assessment is conducted based on this saved limit. This high-speed inspection system can measure with 10kHz sampling rate to inspect 100 per cent of the parts.

Scanner integration in welding robots

Robots have been widely used to automate the welding process. To achieve optimum quality of the welded seam, robots scan the seam and calculate the optimum welding path to optimise the amount of materials used. To be technically feasible, this requires a high precision profile scanning system.

The design of the laser profile scanners is also compact to enable installation into hard-to-access areas and, for high-volume OEM applications, integration into robots or machinery as well.

The scanner can be easily fixed into welding robots to detect the geometry of the seam to be welded before the actual welding process begins.

Once the scanning starts, the robot can calculate the number of welding passes, the position of the weld seams, the weld speed and the oscillation width. Then it automatically performs the welding process and finds the optimum welding path based on the calculated results.

Some profile scanning systems are available with smart and integrated controllers in the sensor head to enable calculation of profile properties such as width, edge angle, groove, gap etc. This smart feature is essential for measurement and inspection during production of longitudinally welded pipes.

Manufacturers are required to know the exact edge position based on the sheet edge length and ensure that the sheet edges are aligned perfectly. The laser profile scanner also offers a non-contact, wear-free and fast measurement of these parameters to ensure they are perfectly aligned before welding starts.

Other potential industrial welding applications

Industries such as mining or applications such as pipeline maintenance may also benefit from utilising laser profile scanning systems for inspection of welded seams.

Mining machineries such as excavators incur high capital cost, making it more economical to repair worn parts than replacing them with brand new ones. The steel parts on an excavator chain link wear out after approximately four years of continuous operation in harsh environments 

The eroded parts should be welded to restore the chain links to working order.

The surface of the defective area can be scanned with the profile scanner to obtain the 3D profile and calculate optimum welding line. Surface pre-treatment is not required prior to welding due to the high quality of the scanning and high resolution of the data.

In industrial applications, pipeline maintenance is essential to ensure continuous supply of utilities and continuous operation of the process plant and machinery. Laser profile scanners can be used to automate the inspection process of the external welded seams. These are installed directly above the seam for real-time monitoring 

The deviation of the welded seam position from the ideal central position can be communicated to the inspection unit via analogue signal.

Ultimately, laser profile scanning is a simple-to-operate yet high-end measurement system that offers high versatility and superior resistance to moisture, dirt and corrosion. Operated via PC, it has a wide range of measurement applications in industrial and factory automation.

The scanners measure with high precision and accuracy with fast response times and can easily be adapted to achieve sharp, reliable measurement on various surfaces including oily, metallic and reflective bases.

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