Friction drilling is a hole-making process suitable for thin sections of ductile metal. A rotating tool is plunged into the workpiece to form the pilot hole. The hole is then threaded in a follow-up process. A bushing forms on the exit side of the hole, which allows for longer engagement lengths in threaded assemblies. For comparison purposes, four combinations of threaded-hole processes were applied to 1.5mm-section, 6082-T6 aluminium alloy. The processes involved were friction and twist drilling followed by thread forming or cutting. Vickers hardness and microstructural analyses were used to assess the condition of the material. An in-house test method was developed to measure the axial load-deflection response. Progressive failure occurred by thread stripping. Friction drilling followed by thread forming gave peak loads 35% higher than conventionally drilled and tapped holes. Also, hardness increased from 111HV in the parent metal to 125HV (with an increase in hardness to depths of 0.5mm) due to work hardening. Evidence of precipitate dissolution was negligible which suggests that the friction drilling process operated below the solvus temperature. A novel approach for determining reliably-based, thread-stripping Factors of Safety (FoS) is presented. FoS in the range 3.61 to 4.38 gave a reliability of 95% to 99.9% against thread stripping in friction-drilled, thread formed joints.
Bibliographical noteFunding Information:
This research has been supported by the INTERREGVA, UK (Project ID: IVA5055, Project Reference Number: 047). The North West Centre for Advanced Manufacturing (NW CAM) project is supported by the European Union's INTERREG VA Programme, managed by the Special EU Programmes Body (SEUPB). The views and opinions in this document do not necessarily reflect those of the European Commission or the Special EU Programmes Body (SEUPB). If you would like further information about NW CAM please contact the lead partner, Catalyst, for details.
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- Friction drilling
- thread forming
- twist drilling
- thread cutting
- Mechanical properties
- Thread forming
- Twist drilling
- Thread cutting