Split-Plot I-Optimal Design Optimisation of Combined Oil-Based and Friction Stir Rotation-Assisted Heating in SPIF of Ti-6Al-4V Titanium Alloy Sheet under Variable Oil Pressure

Abstract

The aim of this paper is to determine the optimal input parameters for the process in order to ensure the maximum formable wall angle is obtained in a conical frustum with a varying wall angle fabricated using Single Point Incremental Forming (SPIF). The test material was 0.8-mm-thick Ti-6Al-4V titanium alloy sheets, and the test used a tungsten carbide tool with a rounded tip with a radius of 4 mm. Complete workpieces were heated using hot oil with a temperature of about 200 °C, and in addition, the high rotation speed of the forming tool generated an amount of friction heat. The input parameters were tool rotational speed, feed rate, step size, and tool rotation direction. Various oil pressures were used to improve both the accuracy of the components formed and the friction heating process. On the basis of calculations performed by means of the response surface methodology, split-plot I-optimal design responses were obtained by means of polynomial regression models. Models were fitted using REstricted Maximum Likelihood (REML), and p-values are derived using the Kenward–Roger approximation. Observation of the fracture surface of Ti-6Al-4V drawpieces showed that the destruction is as a result of ductile fracture mode. Tool rotational speed and step size are the most significant factors that affect the axial force, followed by feed rate. It was also found that step size is the most significant factor that affects the in-plane SPIF force.

Advances in Friction, Lubrication, Wear and Oxidation in Metals Manufacturing

“…Trzepiecinski et al [19] focused on the sheet manufacturing of a Ti6Al4V alloy, in terms of a single-point incremental forming (SPIF) experiment and using a grease-free dry anti-friction spray of MoS 2 as the lubricant. They determined the optimal input processing parameters during warm SPIF of a Ti6Al4V sheet with an initial thickness of 0.8 mm based on a split-plot I-optimal design to ensure the maximum formable wall angle.…”

Advanced FEM Insights into Pressure-Assisted Warm Single-Point Incremental Forming of Ti-6Al-4V Titanium Alloy Sheet Metal

“…The long processing time compared to conventional forming makes incremental forming methods suitable for small batch sheet metal forming operations [21]. SPIF can be performed under cold and hot conditions using heat blowers [22], frictional heat generated by tool rotation [23] and liquid heating [24].…”

“…An established numerical model has not been found in the literature to the best of our knowledge. A finite element-based numerical model build in Abaqus/Explicit took into account the experimental parameters presented in the authors' previous article [24]. This article focuses on the numerical analysis of deformations and forming forces for the optimal set of SPIF process parameters experimentally obtained in [24].…”

Investigation of Surface Roughness in Incremental Sheet Forming of Conical Drawpieces from Pure Titanium Sheets

“…A review of the literature [2] on SPIF of titanium and titanium alloy sheets showed that there are insufficient investigations into the synergistic effect of rotational speed and tool rotation direction on the surface roughness of SPIFed drawpieces. In another previous paper, [43], the authors applied a split-plot I-optimal design to optimise combined oil-based and friction stir rotation-assisted heating in SPIF of Ti-6Al-4V sheets. It was concluded that step size is the most significant factor that affects the in-plane forming force.…”