One of the first questions that we get asked in regards to 3D weld inspection is...
- How does it work?
- What are the basic principles?
- How does it understand the dynamics of what we're looking for and not looking for?
In this blog, we will discuss the characteristics of 3D weld inspection and provide the necessary information about this process to determine whether or not these systems fit your operation's needs.
3D weld inspection is a process in which a high-speed laser scanning method uses laser triangulation to take thousands of samples a second and build a topography of the weld. It takes the data coming from the sensor and sends it over to the main controller which has a set of parameters loaded for each weld to help discern if it meets the needed requirements. This is all set up during the commissioning of the system/weld cell and can provide information to various sources including a database, lineside PC, and operator repair station for further analysis.
This process is useful for a number of reasons. Through the usage of automated weld inspection, we can define problematic areas in the weld process in relation to missing welds, shape and length, throat thickness, and porosity. Being able to record this data will help streamline this process and help identify weak points in your production process from stamping to assembly.
Areas such as throat thickness can be hard to identify outside of weld inspection. A lot of people ask - "How do we define throat thickness if we cannot see through the weld?" Usually, throat thickness is done with the cut and etch process or a testing method of some sort. The approach behind measurement in an automated approach is taking a pre-scanned joint that has not been welded and overlay the scan of the weld. With these two sets of data, we can estimate, by the volume assessment, the throat thickness three-dimensionally on the weld.
Among the added benefit of understanding your weld on a deeper level and uncovering problematic areas in the weld process, 3D inline weld inspection can be used in an array of welding applications. MIG/MAG, Laser Welding, Laser Brazing, and even down into Friction Stir and Spot Welding. We use this process for almost every single welding variant application there is. Automation weld inspection systems are almost limitless in their possibilities in what you can do.
One of the questions I get asked, being a tried and true robot guy for twenty-seven years, is why the robot has vibration. If you're scanning at a rate of 400 mm/sec and you're on the end of an arm, you will no doubt have vibration in this. Especially if you're using an extended reach arm that has a moment of inertia and center of gravity. We have vibration elimination algorithms built into the software so when the robot is outputting its TCP data, you have the time of the chronological match-up of the scan rate plus the TCP speed - that is how this process is integrated.
Algorithms like these can reduce vibration and distortion lines in the image. With laser seam tracking, a lot of times you will have a slave-master situation. Meaning, the sensor will guide the robot, but in this case the IO communication between the sensor and robot is very minimalistic. To simplify this, the only thing you have is TCP output speed and sensor on/sensor off controls. There is no slave-master relationship because of how simple and seamless the integration is when it comes to the robot.
What does it take to get started?
Knowing the level of support you have from your integrator and manufacturer is one of the most important aspects to research and understand before investing the time, money and manpower into this process. Being in robotic integration my whole working life, this is something I always had in mind as the companies I worked for would pride themselves on service. I often said, "I'd rather have a robot that was mediocre with great service than a robot that was awesome with no service because everything is going to need help at some point in the game."
Over the years, keeping data records has become exceptionally important. As technology advances, so does the ability to show your progress in work. Back in the day, there was no such thing as traceability. You might look up a serial number that was at a particular lot number and they might have saved it for three years. Nowadays, everything is saved and tracked for as long as the equipment is alive.
Having an automated system that can detect, understand, and allocate your data is crucial. Being able to supply data records to the people you work with will legitimize the work you've done and prove that you are able to maintain this process. If there is a failure down the road and fingers start pointing, your records will prove whether or not you're off the hook. The accountability this provides is phenomenal.
Many different sensor types are available depending on the process and speeds you need to run. The strength, resolution, and field of view will also vary. For example, if you require a sensor capable of measuring fine tolerance laser welds, you will likely need a sensor with narrow field of view and a much higher resolution than one for GMAW applications. Each application will be different. These determinations will be made at the time of system design/ specification clarification and confirmed as part of the commissioning process. Sample and prototype parts are used to run analysis on the equipment before anything is set in stone, making sure to tailor the sensor to the specific needs of your facility.
This is a basic overview of the system, as simple as it gets. One, maybe two, sensors will be on a controller depending on your needs. The sensors will obtain the data acquisition by using laser triangulation and reflecting back into the CMOS sensor. The sensor will take a sample of the data and transmit is to the controller.
Your controller is the main brain of the system. This will control the internal PLC, signal allocation for the robot and sensor, and the parameterization setup. Next, you will have two optional panels that are not mandatory, but most people do have them. The first is the Intelligent Visualization Module, or what we call the Visio Module, which is essentially the user interface for the repair station. This could be located where the rework cell is, with a monitor showing a picture of your existing part and the blueprint right in front of the operator allowing for easy repairs and sight of good or bad welds.
The other system is the Statistics Module. You could think of this in relation to it being the right arm of the controller. This allows you to make changes to the line in order to avoid large, costly shutdowns. You can tweak the data and make all the changes in the module, which is then relayed over to the controller real-time so that you are not fumbling and shutting down the entire production.