Temperature Controlled Front Face Flow Drilling of Magnesium AlloysWednesday (08.11.2017) 15:40 - 16:00 Part of:
Front face flow drilling represents a new application of the conventional flow drilling process. With this new technique it is possible to form closed holes with diameters, which can exceed the local wall thickness of the profile. By using a subsequent threading operation like thread forming, it is possible to generate solid joints.
In this article investigations regarding the machining of different magnesium alloys (AZ31 and AZ91) are presented. The feasibility of the front face flow drilling application was analysed for the machining of thin profiles with different wall thicknesses. Flow drilling tools with a diameter of dFD = 5.4 mm have been used. The mechanical loads in form of the feed forces as well as torques were measured during the process. Another important aspect is the quality of the generated bores. Almost every bore generated via front face flow drilling is more or less oval-shaped, because the material can be formed differently in radial direction regarding on the amount of surrounding material. In order to quantify the quality of the bores, measurements of the circularity as well as the diameters were carried out. In addition to those measurements, the microstructure of the subsurface zone was analysed as well as the micro hardness. Both aspects can have an influencing effect on the threading operation.
Due to the low formability of magnesium alloys and especially of AZ91, adjustments of the flow drilling process had to be realised. Besides the variation of process parameters such as peripheral speed and feed rate, a pre-heating of the tool was conducted to raise the formability of the workpiece material and to increase the process stability. The pre-heating of the tool was accomplished by using a portable induction system with an integrated temperature control. In order to analyse the strength of the formed threads, static and dynamic pull-out tests were conducted.
As a result of the investigations, suitable process strategies will be recommended regarding a stable front face flow drilling operation of magnesium alloys.
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