Experimental Study of High-Frequency Vibration Assisted Micro/Meso-Scale Forming of Metallic Materials

Micro/meso-scale forming is a promising technology for mass production of miniature metallic parts. However, fabrication of micro/meso-scale features leads to challenges due to the friction increase at the interface and tool wear from highly localized stress. In this study, the use of high-frequency vibration for potential application in the technology of micro/meso-scale forming has been investigated. A versatile experimental setup based on a magnetostrictive (Terfenol-D) actuator was built. Vibration assisted micro/meso-scale upsetting, pin extrusion and cup extrusion were conducted to understand the effects of workpiece size, excitation frequency and the contact condition. Results showed a change in load reduction behavior that was dependent on the excitation frequency and contact condition. The load reduction can be explained by a combination of stress superposition and friction reduction. It was found that a higher excitation frequency and a less complicated die-specimen interface were more likely to result in a friction reduction by high-frequency vibration

Micro Pin Extrusion of Metallic Materials Assisted by Ultrasonic Vibration

Micro extrusion is an economically competitive process to fabricate micro metallic parts. However, fabrication of extremely small geometric features leads to challenges in tool wear due to localized high stress and friction increase at the interface. This study focuses on micro pin extrusion of aluminum with assistance of ultrasonic vibration. Experiments were conducted with and without ultrasound using magnetostrictive actuator. Load-displacement curves from the experiments showed a load reduction when ultrasonic vibration was applied. Experiments of ultrasonic micro pin extrusion with two configurations were performed. The load reduction behaviors at off-resonance and in-resonance conditions were compared. The reduction can be explained by stress superposition of ultrasonic vibration

Broadband measurement of rate-dependent viscoelasticity at nanoscale using scanning probe microscope: Poly(dimethylsiloxane) example

A control approach to achieve nanoscale broadband viscoelasticmeasurement using scanning probe microscope(SPM) is reported. Current SPM-based force measurement is too slow to measure rate-dependent phenomena, and large (temporal) measurement errors can be generated when the sample itself changes rapidly. The recently developed model-less inversion-based iterative control technique is used to eliminate the dynamics and hysteresis effects of the SPM hardware on the measurements, enabling rapid excitation and measurement of rate-dependent material properties. The approach is illustrated by the mechanical characterization of poly(dimethylsiloxane) over a broad frequency range of three orders of magnitude (∼1 Hz to 4.5 KHz).The following article appeared in Applied Physics Letters 93, 133103 (2008); and may be found at, doi:10.1063/1.2990759.</p

High-speed dynamic-mode atomic force microscopy imaging of polymers: an adaptive multiloop-mode approach

Adaptive multiloop-mode (AMLM) imaging to substantially increase (over an order of magnitude) the speed of tapping-mode (TM) imaging is tested and evaluated through imaging three largely different heterogeneous polymer samples in experiments. It has been demonstrated that AMLM imaging, through the combination of a suite of advanced control techniques, is promising to achieve high-speed dynamic-mode atomic force microscopy imaging. The performance, usability, and robustness of the AMLM in various imaging applications, however, is yet to be assessed. In this work, three benchmark polymer samples, including a PS–LDPE sample, an SBS sample, and a Celgard sample, differing in feature size and stiffness of two orders of magnitude, are imaged using the AMLM technique at high-speeds of 25 Hz and 20 Hz, respectively. The comparison of the images obtained to those obtained by using TM imaging at scan rates of 1 Hz and 2 Hz showed that the quality of the 25 Hz and 20 Hz AMLM imaging is at the same level of that of the 1 Hz TM imaging, while the tip–sample interaction force is substantially smaller than that of the 2 Hz TM imaging