Study on Form Rolling Method of High Strength FRP Screw Thread Using Ultrasonic Vibration

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The bolt, that is fastening threaded parts, has been produced of fiber reinforced thermoplastics (FRTP) which have been applied in many field. However, FRTP screw threads produced by the injection molding or the form rolling have some problems concerning form accuracy and mechanical strength. If the ultrasonic vibration is utilized for the form rolling of FRTP threads, the thread blank is heated from its inside and is apt to deform. Therefore the improvement of form accuracy and mechanical strength is expected.Firstly, the form rolling machine in order to roll annular multi-V-grooves are designed and produced on trial, and then the relationship between the rolling condition, such as vibration amplitude, rolling force and so on, and the form accuracy of annular multi-V-grooves was evaluated. As a result, the height of V-groove was not enough in comparison with that of tool indentation, though the effect of ultrasonic vibration was confirmed. As a reason, it is guessed that the amount of indentation couldn't be sufficiently controlled because the stiffness of rolling mechanism was not enough and the rolling force was given by a lever with dead weights.Therefore, a new indentation device which has high stiffness and can control the amount and the speed of tool indentation, was designed and produced on trial, and the experiment was carried out, varying the rolling condition, and the V-groove section was observed by SEM.The obtained main result are followings ;(1) The condition of form rolling in order to make the annular multi V-groove with high accuracy was clarified.(2) The fiber flow at the section of V-groove is improved by the form rolling in the new machine using ultrasonic vibration.