Resistance seam welding of carbon fiber semi-finished products

Abstract

The DLR preforming process for non-crimped-fabrics (ncf) as part of the RTM-Process chain consists of automated draping, a new binder activation process through electrical resistance heating, consolidation inside a membrane press and trimming of the preform to net shape. On the ncf a powder binder is applied. During the process of binder activation the binder powder is heated under pressure until it melts and then cooled down. As a result plies can be fixed to each other respectivly consolidated.

Consolidation with the help of a membrane press is energy inefficient and time consuming, since membrane and tool are heated as well. In this paper it is investigated whether a roll electrode has the ability to replace a conventional consolidation press. Since a roll electrode applies heat and pressure at the same time a consolidation is possible. In this process the carbon fibers are heated by an electric current. In contrast to state of the art electrical resistance heating, the voltage is applied in through-thickness direction.

In order to have a homogeneous temperature distribution the parameters pressure, roll width, number of fiber layers and activation speed was varied in a full-factorial experimental plan. Ultrasonic fine-trimming of roll-electrode consolidated preforms was investigated. Also the fiber volume content of the preform was measured with the help of a laser light sheet sensor and compared to specimen of a consolidation press.