Various input parameters will affect the results of the traditional strip stacking process. The quality of the materials used is important, but it is also important to ensure that the specified strip width is accurate and reliable. Sensor technology and intelligent software concepts are expected to significantly improve product quality during strip stacking. In some areas, production lines programmed with advanced software solutions have been able to optimize processes autonomously.To achieve better results in the future, the tape stacking line must generate other information that can be directly used to control the progress of the process. Therefore, the sensing capabilities of the production line will become a key factor in determining the coverage of the thermoplastic composite market. In the future, production lines need to be able to select relevant information about a specific stacking process from various sensor data. Camera technology will play a key role here. The image data provides information, and then the modified software solution is incorporated into the process control settings. It can also be executed separately for each component. Higher structural performance Thermoplastic composites in the form of organic plates are already on a large scale. They contain fabrics made of glass fibers or carbon fibers embedded in a thermoplastic matrix of PP, PA, PC or PEEK. Tape is another form of this composite material. The advantage of these unidirectional reinforcing materials is that there are no fiber fluctuations, that is, ripples-which usually appear on the fabric. The fibers in the component have been optimally stretched to provide higher structural performance. The use of tape also eliminates the need for the weaving step. Glass fiber or carbon fiber roving is directly embedded into the thermoplastic matrix material by a continuous method. In addition, materials can be processed in a way that minimizes waste. The strip can withstand the expected load after a special arrangement, and different thicknesses can coexist in one part. Therefore, in general, thermoplastic composites based on tape have a bright future. Stacking accuracy determines quality In many applications, a single strip cannot provide the required mechanical properties. Therefore, it is necessary to combine several strips together to form a stack, and form a so-called blank after the stack is consolidated. The strip thickness range is usually between 0.14 and 0.3 mm. For example, a wall thickness of 1.5 mm requires five to ten layers of tape. In addition, each tape layer is usually composed of multiple pre-cut tapes because a single tape cannot cover the required width, and combining multiple pre-cut tapes together helps to minimize waste. The pre-cut strips are spot welded together during stacking. Then, the strip stack is compacted into a strong panel. It is done by carefully melting the entire structure to fuse the entire surface of the various strip layers and then solidify into a blank when cooled. Finally, by heating the resulting semi-finished product in an infrared oven and placing it in a mold for molding and, if necessary, functionalizing it by injection molding to produce actual parts. The quality of the finished product depends on the accuracy of the pre-cut strip stacking. Because once positioned, the strips cannot be rearranged. Therefore, strip stacking is the only opportunity for improvement. Any gaps that exist between the strips will form channels, the matrix material will accumulate in these channels during the consolidation process and the fibers can move sideways. In the worst case, a needle-like cavity may be created during the consolidation process. Moreover, if two strips overlap where they meet, the fibers will move during the consolidation process. The consequence of cavity and overlap is to create weak points in the part. The stack of strips needs to be highly accurate to achieve the ideal state where the edges are as flush as possible. Technical specifications usually allow a gap or overlap of ±1.0mm, and some applications are only ±0.5mm. In order to ensure stacking accuracy, the process of using equal-width sliced strips must strictly comply with the nominal strip width. The change of strip width will automatically change the accuracy of the stacking process. Then, the challenge becomes how to overcome this dependency with software solutions. This is where the sorting method comes in. Pay attention to the correction value of each stacking position The first step in stacking strips by sorting is to choose the largest pre-cut strip on the wide roll as much as possible. Simple shapes can be cut directly from the roll. Complicated shapes require punching. The two main management principles are to minimize waste and maximize production line output. In an ideal situation, the strip stack should be designed in this way during the component design stage-that is, make full use of the belt rolls and process the material into a stack with fewer stacking operations. The traditional sorting process requires highly accurate pre-cut strips and precise guide rails in the silo, as well as additional alignment and centering modules. Optical metrology brings new possibilities because it enables the production line to meet the accuracy requirements and make the arrangement controllable. The end-of-manipulator tool (EOAT) is used to pick up the pre-cut strip-the accuracy of the strip and its position on the EOAT are not important here. The position of the pre-cut strip relative to the reference mark on the EOAT can only be determined after the camera has arrived. When the robot stacks pre-cut strips on the worktable, this information can be used to influence the position of the robot's positioning. The transition from the strip to the background is determined at multiple locations along the edge area of the strip-25 such locations are shown in the example  These points are connected together to produce a line of best fit, which is projected outside the search window. Do the same for the second edge. The projection of the last two straight lines forms a corner point . Compared with direct optical measurement, this corner point can be more accurately determined by the pre-cut edge, because punching or cutting usually cannot produce precise and sharp corner points. The position and angle information of the strip on the EOAT can be used to position the strip placed on the workbench. The point along the edge of the strip can be determined within three pixels. After several measurements, the laying accuracy of the laboratory production line has reached ±0.5mm and below. In other words, the gap or overlap is less than 0.5mm. However, the achievable laying accuracy also depends on the straightness of the cutting or punching edge. Other factors that affect the determination of the edge are the color of the strip and the contrast with the background. Strip stacking accuracy is the metric for optimization of the entire process. However, the concept behind this high laying accuracy is the key. By using camera technology, information can be collected to support software-based active adjustments to optimize stacking accuracy. The software has been working to produce the best results, that is, to maximize stacking accuracy. Real-time high performance In the medium term, software-based or software-led process technology will outperform traditional solutions in many areas. The latter can achieve corresponding quality through precise testing, adjustment and verification, but they are always highly dependent on the quality of mechanical components and raw materials. This method is close to the natural limit. A more effective method is to enable the production line to identify and evaluate the performance of surrounding materials and take appropriate measures. In addition, additional value can be gained by using sensor technology to check the strip for cracks, uneven fiber runs or missing corners, which can detect deviations that are much more subtle than the careful line operators can detect. The preferred design of the strip stacking unit includes two robots and a camera table. The first strip is fixed on the stacking table with a vacuum device. All subsequent layers are spot welded to the next layer. The pre-cut strips are separated in the stacking bin and placed on the picking table to be fixed in place. Then, the robot can approach the worktable at high speed . EOAT is equipped with vacuum grippers for grabbing pre-cut strips. This configuration enables each process step to have a highly dynamic stacking process. After several tests, through the alternate operation of the robot, the stacking time of each strip blank on the test production line is 3.4s. In order to help the optical measurement system to easily identify the strip on the EOAT, the entire receiving surface is illuminated with an electroluminescent film, and then the EOAT and the strip are pressed on the glass plate. After detecting the edge, determine the corner point of the pre-cut strip and compare the result with the EOAT tool center point. This information will then be transmitted to the robot controller so that it can correct the position and angle of the strip. Therefore, the strip can be placed accurately and flush with existing edges. When the strip enters the stacking station, the algorithm used to determine the exact stacking position is applied to the digital image material. Therefore, this method requires high real-time performance of the production line. Sorting of mixed stacks By using the sorting type strip stacking device, the strip stacking can be completed with high precision in a short time. In order to increase the laying speed and provide the required correction data in time, only selected edges and corners are measured during the optical measurement process. However, the camera data can be saved for subsequent evaluation and analysis of stacking quality. Which files are automatically saved together with the process data is determined by the product specifications. If it is a safety-critical part, all image data will be saved; in other cases, it is best to save only those images related to process errors and scrap. A big advantage of the sorting concept is the ability to produce mixed stacks. Since the stacked silo can not only place tapes, but also organic composite materials composed of multiple fabric layers, as well as consolidated tape blanks with a constant wall thickness and other thermoplastic semi-finished products, inexpensive multilayer semi-finished products can be used as substrates And only partially enhance it. Suitable for glass fiber and carbon fiber with different load ranges Strip stacking is a key technology for cost-effective and lightweight design. By locally strengthening the component according to the load path, the nominal wall thickness can usually be reduced. Therefore, the mixed material structure can not only reduce the weight, but also generally can significantly reduce the cost. Therefore, as the nominal wall thickness of the component decreases, more expensive carbon fiber can be considered for mass production settings. The area of the component that bears light load can be reinforced with low-cost glass fiber, and the area that must bear the heavy load is reinforced with carbon fiber. *This article is translated from KUNSTSTOFFEINTERNATIONAL magazine

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