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Optimal parts quality through online thermography
WITTMANN BATTENFELD at K 2010
Mold tempering is one of the critical key parameters in injection molding. The temperature distribution in the mold has a decisive influence on warpage and consequently the quality of plastic parts. Therefore a consistent high quality of complex parts requires even tempering of different mold segments.
Online thermography enables the detection of quality fluctuations at every shot, combined with immediate temperature regulation whenever tolerance margins are exceeded. This "quality assurance while the part is hot" has been made possible by "photography" of the molded part's surface temperatures with an IR camera directly after demolding. The data set is subsequently analyzed with a special software. For this purpose, the part is presented to the camera in different positions by a linear robot immediately following demolding. The evaluation is shown on a monitor, any deviations from the release status are visualized and calculated for individual segments for the WITTMANN FLOWCON water flow control unit connected with it. Any temperature adjustments that may be necessary are thus implemented in real time.
A considerable advantage of this process is the external temperature measurement on the demolded part. This does not require any alterations or supplementary equipment on the mold used in each case.
By contrast to conventional temperature measurement with thermal sensors inside the mold, thermographic measurement on the molded part offers a number of significant advantages:
The camera systems used are considerably more accurate and robust than thermal sensors. Due to its high resolution, an IR camera is able to scan large areas and detect critical points, such as hot spots. In case of failure, the camera can be replaced within a minimum of time and without having to dismount the mold.
Consistent tempering enables permanently optimized cycle times. This process also leads to an improvement in production start-up and a reduction in start-up scrap. The even temperature distribution ensures sustainable quality improvement. Rejects due to tempering errors are detected immediately, which reduces rejection and complaint costs. One advantage inherent in statistical process monitoring is the ability to have mold servicing carried out in good time and thus prevent unscheduled repairs. And last but not least, the traceable "thermal fingerprint" (thermal image) is an important process parameter.
At the K, the performance of online thermography will be demonstrated on an EcoPower 240/750. An ABS component will be produced and presented to a thermal camera by a W821 WITTMANN robot. The robot is equipped with a rotary axis, so that a "thermal fingerprint" can be taken of the part from five different angles. The analyzed thermal images serve as documentation for quality assurance, and the values are used for mold temperature adjustment as well. After the thermal images have been taken, the robot transports the parts to a laser printing station.
In this process, the handling system plays a vital part. Only with high-precision, repeatable positioning can the thermal images be taken with accuracy and compared to the target state by the SKZ software. Servo technology controlled by WITTMANN R8 software enables the necessary highly accurate and repeatable movements.
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