Technology review of thermal forming techniques for use in composite component manufacture

There is a growing demand for composites to be utilised in the production of large-scale components within the aerospace industry. In particular the demand to increase production rates indicates that traditional manual methods are no longer sufficient, and automated solutions must be sought. This typically leads to automated forming processes where there are a limited number of effective options. The need for forming typically arises from the inability of layup methods to produce complex geometries of structural components. This paper reviews the current state of the art in automated forming processes, their limitations and variables that affect performance in the production of large scale components. In particular the paper will focus on the application of force and heat within secondary forming processes. It will then review the effects of these variables against the structure of the required composite component and identify viability of the technology. Through this, an understanding of the key criteria involved in the forming of composite aerospace components can be utilised to better inform improved manufacturing processes and capabilities

Development of in-situ monitoring systems for the thermoforming of pre-preg composite laminates

Recent developments in automated composite manufacturing technologies, such as Automated Fibre Placement, AFP, and Automated Tape Layup, ATL, have enabled larger components to be produced efficiently, leading to an increased use of prepreg composites in aerospace. These processes are limited in the geometry that may be produced and therefore secondary forming processes are commonly required for implementation. There is, therefore, a need to improve reliability and increase forming capability using these processes, whilst ensuring that defects in the laminate are limited. Thermoforming of composite and polymer materials is a well-known forming method for use with polymers and polymer based materials. This paper will discuss the monitoring methods and results used in a typical thermoforming process based on experimental results from a composite material during Thermal Roll Forming (TRF). The focus of this testing is to characterise the effect of temperature and dynamic contact forces on the composite against the real-time development of defects such as wrinkles during TRF forming

Closed Loop Force Control of In-Situ Machining Robots using Audible Sound Features

Detecting, measuring and controlling the forces between cutting tools and machined components is essential in circumstances where direct position control (e.g. depth of cut, feed speed, etc.) is inaccurate and/or impossible. This paper explores the use of airborne sound signals that result from the machining process to control the cutting force in closed loop for generating accurate machined features when performing in-situ robotic repair of complex installations. The sound signals during indentation at various cutting forces are analysed and used to calibrate a remotely mounted microphone sensor and signal processing control system. The power spectral density of the audible sound is used to estimate tool cutting force and the sound intensity used in turn to estimate the resulting process energy. The described controller uses intensity of sound to mitigate the e_ects of resonance with workpiece natural frequencies while controlling the spindle velocity of the tool based on the dominant audible frequency. The performance of the controller is validated using a representative test rig and demonstrated using a robotic arm to machine thin Ni-Cr-Co alloy cantilever beams with a miniature air-driven grinding tool. Results from the test rig show that such a sound-based control approach can achieve consistent cutting forces with an accuracy of 0.08 N. The robot arm is shown to be capable of grinding features of consistent depth (to within 0.05 mm) on beams with surface defects of unde_ned shape using only the sound of the process for closed loop force control

Evaluation of control methods for thermal roll forming of aerospace composite materials

With increased demand for composite materials in the aerospace sector there is a requirement for the development of manufacturing processes that enable larger and more complex geometries, whilst ensuring that the functionality and specific properties of the component are maintained. To achieve this, methods such as thermal roll forming are being considered. This method is relatively new to composite forming in the aerospace field, and as such there are currently issues with the formation of part defects during manufacture. Previous work has shown that precise control of the force applied to the composite surface during forming has the potential to prevent the formation of wrinkle defects. In this paper the development of various control strategies that can robustly adapt to different complex geometries are presented and compared within simulated and small scale experimental environments, on varying surface profiles. Results have found that traditional PID control can be utilized, although its robustness under varying conditions reduces performance in situations that are far from the tuned scenario. This causes the PID controller to struggle with geometries containing surfaces with high frequency surface variations. To enable more robust control an H∞ based controller was therefore developed for the thermal roll forming process. Simulated results show that while the individual implementation of both controllers were successful in achieving the desired response, the H∞ based controller was able to perform better across a wider range of desired surface profiles

Embodiment design of soft continuum robots

This article presents the results of a multidisciplinary project where mechatronic engineers worked alongside biologists to develop a soft robotic arm that captures key features of octopus anatomy and neurophysiology. The concept of embodiment (the dynamic coupling between sensory-motor control, anatomy, materials and environment that allows for the animal to achieve adaptive behaviours) is used as a starting point for the design process but tempered by current engineering technologies and approaches. In this article, the embodied design requirements are first discussed from a robotic viewpoint by taking into account real-life engineering limitations; then, the motor control schemes inspired by octopus nervous system are investigated. Finally, the mechanical and control design of a prototype is presented that appropriately blends bio-inspiration and engineering limitations. Simulated and experimental results show that the developed continuum robotic arm is able to reproduce octopus-like motions for bending, reaching and grasping

Dynamics for variable length multisection continuum arms

Variable length multisection continuum arms are a class of continuum robotic manipulators that generate motion by structural mechanical deformation. Unlike most continuum robots, the sections of these arms do not have (central) supporting flexible backbone, and are actuated by multiple variable length actuators. Because of the constraining nature of actuators, the continuum sections can bend and/or elongate (compress) depending on the elongation/contraction characteristics of the actuators being used. Continuum arms have a number of distinctive differences with respect to traditional rigid arms namely: smooth bending, high inherent compliance, and adaptive whole arm grasping. However, due to numerical instability and the complexity of curve parametric models, there are no spatial dynamic models for multisection continuum arms. This paper introduces novel spatial dynamics and applies these to variable length multisection continuum arms with any number of sections. An efficient recursive computational scheme for deriving the equations of motion is presented. This is applied in a general form based on structurally accurate and numerically well-posed modal kinematics that assumes circular arc deformation of continuum sections without torsion. It is shown that the proposed modal dynamics are highly scalable, producing efficient and accurate numerical results. The spatial dynamic simulation results are experimentally validated using a pneumatic muscle actuated multisection prototype continuum arm. For the first time this enables investigation of spatial dynamic effects in this class of continuum arms