As many of us know, there are forming processes that are carried out at high temperatures in order to achieve certain microstructure and final properties in the parts. There are many factors at play, including temperature, times, and applied deformations.
With some knowledge of thermography here at bcb , let’s focus on monitoring and controlling temperatures in this article.
Let’s start with one of the biggest challenges in these processes, which is understanding the thermal variation in the part. So far, for many senior metallurgists, measuring the temperature of the part remains a utopia. Why? Well, if we want to resort to the still widely used thermocouple to make this measurement, we will encounter the limitation of wiring it to a moving part. However, for a thermographic camera of 30 Hz or higher, this turns out to be a simple task, offering the ability to even measure more than one part at a time, something useful if we think, for example, of Hot Stamping or Forging.
The movement sequence of the blank on the centering table. The heat loss is considerable and can be measured with thermography.
The level of detail obtained is quite high to the extent of observing the thermal gradient over the entire surface of the part, which gives us information about the homogeneity of heating in the furnace. Many users of thermographic monitoring notice that the center pieces are hotter than those at the ends or that the left side of the oven is cooler than the right side.
The forged piece above shows higher thermal concentration in its left central section, revealing the area of greatest heat concentration in the furnace, which mainly affects the right part of the piece.
Is the camera placed inside the furnace to see this? The answer is NO. An industrial thermographic camera can operate in environments up to 300°C, a temperature that exceeds most of the thermal conditions inside a furnace. However, immediately upon exiting the furnace, we can observe the piece or pieces of interest. Since a position close to the exit becomes more suitable, it is highly exposed to high thermal radiation, so the thermographic camera must be installed in a water-cooled housing.
And what about production setups where more than one piece comes out per cycle? Surely we will think of the times when in an arrangement of 4 pieces, one of them comes out ahead of the others, causing a spatial mismatch that would result in one of the pieces not being fully measured in the thermographic image. Well, for this condition, there is the option to configure independent processes for each piece, which can be set up from our bcbDieScan system. This type of processing also avoids obstructions caused by the robot.
In the first image, we see the raw image acquired by the thermographic camera. The yellow squares are the scanning area and are independent for each piece. They are capable of making up to 50 measurements per second, from which the complete image of each piece is composed regardless of robot obstructions or distance discrepancies. In the second image, we see the result of the scanning processing. In the third image, we see an example of the post-processing capability of the saved thermographies.
Moving on to the dies, monitoring in this part of the forming process is also critical. It is true that zone measurement here presents a lower level, as there are certain areas of the die where a thermocouple can be placed. However, the detail offered by this sensor is too limited when compared to the measurement provided by a thermographic camera.
Both images feature the same die. In the left image, we have the result of using thermocouples, which is limited to providing information only about the points where the thermocouple was placed, represented by the 6 red dots. In the right image, we have 300,000 measurement points on the mold, allowing us to appreciate the thermal distribution in our die with sufficient detail.
The thermographic camera has very low thermal inertia. What does this mean? It means that temperature changes, no matter how small or rapid, can be simultaneously detected by the camera, unlike the measurement performed by a thermocouple. This is how a metallurgist obtains new useful temperature data, such as the condition of the internal cooling channels of the mold, the proper functioning of the resistors, and the spraying of the dies and molds.
Spray sequence on dies: In 1, we see the condition of the die upon removing the piece. In 2, we can see the spraying in action, and in 3, we see the condition of the die after the spraying.
In the case of thermoforming, it is a process with several heating stages. An important temperature control point is the stock of sheets in the thermoformers, as they must retain a certain heat obtained in the lamination process for their plastic transformation to be successful. Something as simple as thermal monitoring allows indicating if one of the sheets is out of range to prevent it from resulting in a defective product at a more advanced point in the production chain, which would negatively impact operating costs.
Finally, we can obtain the thermal condition of the piece once its shaping is completed. Whether cameras are placed in the appropriate monitoring position or the robot presents the piece to the camera for thermal analysis. Multiple measurements can even be taken, which is useful if, after forming, we have water or air quenching. In Hot Stamping, it is quite simple because the same camera that measures the blank upon arrival can measure the blank upon exit. In processes such as forging or thermoforming, quenching takes place at a later point, which would require an additional camera at that point.
On the left, we see the frames just out of the press, a common analysis in Hot Stamping. On the right, top, we see a forged piece just out of Austenitizing, and on the right, bottom, we see the same piece just out of water quenching.
For these plant needs, thermographic solutions arise in conjunction with image processing software, which allows monitoring the entire process and autonomously and continuously locating thermal deviations, generating alarms in different formats that promptly report the incidence. Teledyne FLIR cameras, along with the powerful bcbDieScan software (from the bcbMonitor 4.0 family), provide these solutions for your processes.
Metals, polymers, and ceramics can all benefit from this technology. You are welcome to approach our experts for advice on the most suitable solution for your process.
