PNNL

Abstract

In this paper, we present the first demonstration of single-step gear manufacturing via an innovative in-situ friction stir forging approach. This near-net-shape process is robust and viable for a wide range of materials. This novel process is a natural extension to the friction stir processing technique and relies on shear and normal stresses to form the complex shapes. In this process friction stir welding pin tool with shoulder is plunged at high revolutions per minute (rpm) into the sample to heat it to the desired temperature and enable plastic flow. Then, the tool is forged at high plunge rate to form the desired structurally-sound and defect free complex shapes. In this work we demonstrate forming spur gears made out of lightweight structural materials and also demonstrate a complex gear made out of MMC. To better visualize the process the experiments are complemented by a 3D, thermomechanically coupled, smoothed particle hydrodynamics (SPH) model to understand the material flow pattern both radially and through thickness in the gear teeth, plastic strain distribution, and temperature profile. Electron backscatter diffraction analysis of the forged gears exhibited a directional material flow pattern due to the normal forging action and formation of dynamically recrystallized grains across the radial, through-thickness direction and is in good agreement with the corresponding SPH simulation results. Scanning electron microscopy/energy dispersive X-ray spectroscopy analysis exhibits uniform distribution of fine and fragmented second phase particles in the MMC gear.