Process parameter study for CFRTP
CFRTP（Carbon fiber reinforced thermoplastics ）is one of the discussing topics because of their high cycle molding characteristics. The study regarding process parameter for CFRTP is reported and its summary information is below;
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Hugues Lessarda, Gilbert Lebruna, Abdelhaq Benkaddoura, Xuan-Tan Phamb
Composites Part A: Applied Science and Manufacturing
Volume 70, March 2015, Pages 59–68
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UD prepreg, where the fibers align by one direction, is difficult to control the wrinkle and alignment error by their room to move during the molding process. By contrast, fabric or woven prepreg is easier to keep the fiber's position.
Carbon fibers with the very high heat resistance super engineer plastics, PEEK （polyether ether ketone）, was used in this study and their fiber volume was 59%. Their manufacturer is Tencate. The process parameters were evaluated by molding the shape, which was a quarter sphere at one end, a cylindrical portion in the middle and two flat faces at the other extremity. The parameters were evaluated by the regression analysis and their impact on the molded parts.
Evaluated parameters are;
a. Pre heating temperature （380、420℃）
b. Mold temperature （280、360℃）
c. Transfer time (time to carry pre-heated material into the mold) （10、16 sec）
d. Press load （1.8、3.6 ton）
Preheating temperature was decided by Tencate's recommendation and molding temperature was determined by their previous experiment and the melting temperature of PEEK.
And evaluated items are;
a. Thickness of the molded parts
b. Interlaminar shear strength of the test specimens, cut from the molded parts
Thickness was measured on the flat areas because its difference showed significant on these locations. Interlaminar shear strength was measured by ASTM D2344, using short beam shear (SBB). This coupons were cut from the sphere area, so its strength data are not correct. But it is believed that the evaluation is reasonable if it is the comparative estimations.
Overall, this paper evaluated considering engineering area adding to the academia contents. The regression analysis indicated that molding temperature affected on the molded part thickness and interlaminar shear strength.
Crystallinity and thickness have the relation with interlaminar shear strength as positive and negative, respectively.
You can read the detail result and discussion on the paper.
The point which I would like to say to learn is;
"The process parameter impact on the mechanical and physical properties are evaluated objectively"
The current trend in FRP industries indicated;
– Molding speed
– Low cost
– Good surface condition
are the most important points by the business term's pressure.
By contrast, there are few questions like;
"Why FRPs are necessary to use"
"What the process to let FRPs show their best performance is"
But the questions above show the most important aspect of FRPs.
The study above evaluated the mechanical and physical properties, adding to the thickness objectively. The physical character is often the keyword to apply FRPs. So the logics evaluation from a wide, high and objective view points may be the good reference regarding other engineering evaluation too.
But there are a few of points which need to be modified or added.
The first point is "non-destruction inspection". There is no NDI, like ultrasonic inspection or X-ray, during the study. NDI is one of the most important techniques for FRP parts production to ensure the quality systems.
It is pretty difficult to mold the FRP parts without the inside defects but the threshold of allowable defect should be defined, based on NDI and the mechanical component tests.
Another point is that there is no evaluation including "interaction in the regression analysis". Taguchi method was applied in this study to understand the serious impact factors but interaction by a few of parameters should be also considered. A squared interaction should be enough and you don't have to study more than third derivative interaction. And if the profile simulation, which enable us to understand the best parameters combination, the study would be more profitable for engineering areas.
Such kind of the accumulation of the objective data should lead us to the right strategy direction in the FRP industries.
