Machinability of Fiber-Reinforced Thermoplastics in Drilling

Polymer-based composite materials are used in a variety of industry. Recently, thermoplastic polymer suitable for the resinous matrix in carbon fiber-reinforced composites has been introduced for lower material and processing costs, improved damage tolerance and higher moisture resistance. The successful use of this material requires sophisticated production technology, however little reference of machining of thermoplastics composites can be found. The existing published results are almost exclusively for epoxy-based composite materials showing difficulty in avoiding poor finish, serious tool wear and delamination at hole entrance and exit due to the brittle material response to machining. Thermoplastics-based composite materials possesses better machinability. The current work reveals the machinability of an example of carbon fiber-reinforced ABS (Acrylonitrile Butadiene Styrene) in drilling compared to representative metals and thermoset-based composites. The observation of chips reveals that considerable plastic deformation is involved. Compared to the chip formation of thermoset plastics, it contributes to the improved edge quality in drilling. The edge quality is generally fine except in the case of concentrated heat accumulation at tool lips, which is generated by high cutting speed and low feed rate. Plastics tend to be extruded out of the edge rather than neatly cut. The average surface roughness along hole walls in commonly below one micron for all sets of cutting conditions in the experiment, values between 0.3 and 0.6 microns are typical. The high speed steel drill presents only minor tool wear during the tests. Based on these results, one concludes that the carbon fiber-reinforced ABS demonstrates good machinability in drilling.