Research and Testing of an Electromechanical solution for Vibration Assisted Drilling of Aerospace Materials

Abstract: This thesis considers vibration drilling in aerospace materials. The tolerances of the drilled holes in aerospace industry are very low since hole quality is an important factor. Conventional methods of drilling create long ribbon formed chips that increases the heat formation and decreases the hole quality. The solution is to introduce low frequency axial vibrations at the drill to break the chips. Smaller chips are easier to evacuate and leads to less heat formation and increased hole quality. Mechanical solutions to create the axial vibrations are commonly used in so called Advanced Drilling Units (ADUs). These drilling machines mounts on the surface to be drilled, actuates the drill with a feeding motion and drills the hole automatically. The ADU PFD1100 from Atlas Copco uses a mechanical chip breaking module called the ChipLet. The ChipLet has fixed amplitude and frequency hence the ChipLet module needs to be replaced to change vibration parameters. This thesis proposes the idea to instead use an electromechanical solution to create the vibration with an electric motor. This would make the possibility to change vibration parameters on the fly. A motor has been coupled to the feeding mechanism of the PFD1100 using a created prototype. The motor modifies the feeding motion of the spindle by doing a superposition of the constant feeding with a sinusoidal motion hence creating vibrations on the spindle. To compare the prototype to the current ChipLet, force and torque data have been gathered and analysed with spectral signal processing using the power spectral density estimate (PSDE). Conventional drilling with both the prototype and the ChipLet have been tested and analysed to use as a baseline and reference. The prototype shows that electronic control of the vibration parameters is possible. The prototype is also capable of breaking the chips although at lower frequency and amplitude than the ChipLet. The PSDE shows that conventional drilling reference frequencies are present in the vibration drilling data sets. The PSDE also shows that both the prototype and the ChipLet have several overtones in addition to the main harmonic.