Zengxi Stephen Pan

Fabricating superior NiAl bronze components through wire arc additive manufacturing

Cast nickel aluminum bronze (NAB) alloy is widely used for large engineering components in marine applications due to its excellent mechanical properties and corrosion resistance. Casting porosity, as well as coarse microstructure, however, are accompanied by a decrease in mechanical properties of cast NAB components. Although heat treatment, friction stir processing, and fusion welding were implemented to eliminate porosity, improve mechanical properties, and refine the microstructure of as-cast metal, their applications are limited to either surface modification or component repair. Instead of traditional casting techniques, this study focuses on developing NAB components using recently expanded wire arc additive manufacturing (WAAM). Consumable welding wire is melted and deposited layer-by-layer on substrates producing near-net shaped NAB components. Additively-manufactured NAB components without post-processing are fully dense, and exhibit fine microstructure, as well as comparable mechanical properties, to as-cast NAB alloy. The effects of heat input from the welding process and post-weld-heat-treatment (PWHT) are shown to give uniform NAB alloys with superior mechanical properties revealing potential marine applications of the WAAM technique in NAB production.

Adaptive Partial Shortcuts: Path Optimization for Industrial Robotics

The quality of a path generated from an automated motion planning algorithm is of considerable importance, particularly when used in a real world robotic application. In this work a new path optimization algorithm, called the Adaptive Partial Shortcut algorithm, is presented. This algorithm optimizes paths as a post process to motion planning, and is designed specifically for use on industrial manipulators. The algorithm optimizes a robot’s degrees of freedom independently allowing it to produce manipulator paths of particularly high quality. This new algorithm utilizes an adaptive method of selecting the degree of freedom to optimize at each iteration, giving it a high level of efficiency. Tests conducted show the effectiveness of the algorithm; over a range of different test paths, the adaptive algorithm was able to generate solutions with a 60 % reduction in collision checks compared to the original partial shortcut approach.

Inertial sensing for human motor control symmetry in injury rehabilitation

This paper proposes a series of methods for representing changes in human motion during injury rehabilitation using Micro-Electro-Mechanical Systems (MEMS) inertial sensors. Tracking the changes over a recovery period requires methods for evaluating the similarity of movement in an impaired state against a non-impaired state. We investigate the use of motion analyses such as the centre of mass (COM) tipping distance, the variance of joint velocity eigenvalues and the cumulative state changes of Gaussian mixture models (GMM) for monitoring the symmetry between the left and right sides of body during rehabilitation exercises. The methods are tested on an injured athlete over 4 months of recovery from an ankle operation and validated by comparing the observed improvement to the variation among a group of uninjured subjects. The results indicate that gradual changes are detected in the motion symmetry, thus providing quantitative measures to aid clinical decisions.

Recent progress on sampling based dynamic motion planning algorithms

This paper reviews recent developments extending sampling based motion planning algorithms to operate in dynamic environments. Sampling based planners provide an effective approach for solving high degree of freedom robot motion planning problems. The two most common algorithms are the Probabilistic Roadmap Method and Rapidly Exploring Random Trees. These standard techniques are well established, however they assume a fully known environment and generate paths ahead of time. For realistic applications a robot may be required to update its path in real-time as information is gained or obstacles change position. Variants of these standard algorithms designed for dynamic environments are categorically presented and common implementation strategies are explored.

Automatic program generation for welding robots from CAD

Industrial robotic automation is a key tool for manufacturing companies to achieve flexibility and low production costs. However, the cost associated with re-programming limits the economic viability for low production volumes. Automated Offline Programming is an approach that uses software algorithms to generate robot programs with little or no human effort. This contrasts with typical programming methods that require considerable human effort from highly skilled operators. This paper presents an Automated Offline Programming solution developed for a steel fabrication company and details the motion planning algorithms. It also describes a novel technique to decompose the welding path motion planning problem into sequential sub-problems such that greedy search techniques can be employed. The results show that this programming approach is effective for robot welding applications and reduces programming effort to effectively no cost.

Development of safe optimized welding procedures for high strength Q&T steel welded with austenitic consumables

High strength quenched and tempered (Q&T) steels offer obvious economic benefits originating from their advantageous strength to price and weight ratios. These steels are usually welded using ferritic consumables and for this combination the risk of hydrogen assisted cold cracking (HACC) is high. The use of austenitic stainless steel (ASS) consumables has great potential to significantly improve this issue. Yet, there are no guidelines for determination of safe level of preheat for welding ferritic steels with ASS consumables. For this reason manufacturers adopt this parameter from procedures developed for conventional ferritic consumables thus significantly limiting the benefits ASS consumables are capable to deliver. Productivity could be further enhanced by identifying the upper interpass temperature threshold, thus reducing the stand-off times. Aim of this work is to develop safe highly optimised procedures for welding of high strength Q&T steel with ASS consumable.