Carwyn Ward

Development of the manufacture of complex composite panels

Composite reinforcements can be difficult to form manually over complex geometries due to difficulties arising from the types of drape mechanisms available. Often more than one can be found in action, and different geometrical features require specific formability characteristics. This is true when manufacturing composite sandwich panels and particularly so if the structure includes cut–outs as these features are very difficult to form. Forming complexities can also be found in automated methodologies, particularly when relatively complex parts are manufactured, as the techniques attempt to minimise manual operations. Development towards automated manufacturing therefore requires: 1) reappraisal of the most appropriate deformation properties in reinforcements; 2) methods to achieve them reliably. This paper examines those requirements and presents simple examples that aim to enhance formability. It also presents novel concepts of tow steering and pin–bed preforming that take an alternative approach to drape by reorganising the material according to the panel design offline. The details of both concepts are explored and examples show their potential for use in complex geometry manufacture. The paper concludes that both concepts are suitable processes for future development to enable automated lay–up.

Draping processes for composites manufacture

Abstract This chapter focuses on the deformation properties of uncured composite reinforcements and their impact on the manufacturing of composite structures. It examines how the understanding of those deformation properties has matured over time, and the development of the ability to incorporate that understanding into models in support of manufacturing. It also looks at the practical manufacturing implications of the way in which reinforcements are matched to tool geometries, and how that impacts the potential for automation. Lastly, this chapter considers future research directions.

Reusing automotive composites production waste

Research continues to improve prospects for the increased reuse of automotive composites production waste. J.P. Snudden, C. Ward, and K. Potter of the Advanced Composites Centre for Innovation and Science (ACCIS) at the University of Bristol in the UK discuss this possible high value solution.

Hand layup: understanding the manual process

The hand layup of pre-impregnated woven materials is still a large part of the composite manufacturing industry, requiring the skills and experience of a human workforce to form flat plies into complex shapes. It is capable of producing high performance and complex parts, but can be an expensive and variable process. Despite its importance, there appears to have been very little research into the actual methods and techniques used by workers to manipulate flat sheets of composite material into shape during layup. This work presents the first known detailed study of the approach and techniques used by laminators. Four participants laid up onto 15 different shaped molds that replicated features commonly found on composite components. The actions used in layup were grouped into eight distinct techniques. Use of these techniques across tasks of different geometry, ramp angles, radii and drape path was identified using video analysis techniques from the ergonomics field. This revealed strong links between specific features and techniques, revealing a systematic approach to layup. This has enabled the first step toward producing a design for manufacture knowledge base surrounding hand layup. This could then be used to inform the development of the layup process, improve training methods and assist in the design of future automated solutions. Graphical Abstract

The manufacture of honeycomb cores using Fused Deposition Modeling

Abstract Sandwich panels are used in many industries for the advantageous properties of high stiffness, good strength to weight ratio, and impact resistance. This paper investigates properties of thin-walled cores manufactured through Fused Deposition Modeling (FDM); a process which, through a wider design space, could improve the functionality of sandwich panels. The bond strength between the layers of thin walls manufactured through FDM was evaluated through tensile testing. To measure the effect of modified manufacturing speeds, wall thicknesses were varied through the flow rate and nozzle speed. Honeycomb cores using FDM were produced with different toolpaths, and compared with an example of an industry standard Nomex honeycomb core. During tensile testing, thick-walled FDM components exhibited a more ductile failure with a lower yield point when compared to thinner specimens. The ultimate tensile stress remained constant across samples within each of the tested ABS and PLA polymers used. Honeycomb cores produced using FDM were found to have a higher compressive failure force than Nomex honeycomb, and a lower specific strength. The force–displacement curves of compressive failure show a ductile response for thick specimens, consistent with the previous result. These results, combined with the increased flexibility of additive manufacture technologies, could provide a method of manufacturing high strength cores with complex geometry.

Stabilizing textile preforms by means of liquid resin print: a feasibility study

Abstract This study demonstrates the feasibility of creating stable, preconsolidated, yet permeable preforms for liquid resin infusion (RIFT) manufacture of composite materials. While being one of the cheapest and simplest methods of composites manufacture, RIFT with flexible tooling is known for high risk of dimensional and internal defects due to insufficient consolidation of textile preforms. Achieving the quality of a rigid mold solution, at the cost and simplicity of a flexible mold process, is the principal challenge of the RIFT. The approach presented suggests stabilizing a compliant preform through pointwise and highly controlled integration of a binder, and its consolidation prior to liquid molding. The printed resin creates a stiff skeleton, securing material for resin infusion and curing. This study explores the feasibility and efficiency of novel binding techniques, and the effects it may have on preform properties. Successful implementation of the concept for a multiply woven preform is demonstrated and the concept potential is discussed.

On the evolution of the distribution of entrapped air at the tool/first ply interf‘ace during lay-up and debulk

Abstract Air entrapped during the material deposition stage of prepreg layup can contribute to voidage in the cured laminate, which is a major factor in determining the quality of the resulting laminates and components. Removal of this entrapped air is therefore a priority to achieve maximum part performance. To date, there does not appear to have been any consistent study of the processes by which voids can be entrapped. This paper seeks to address this by presenting direct observations of the contact between a glass tool surface and the first ply of carbon fiber prepreg laid down onto it. The entrapment of air between the tool and ply is investigated, in terms of its distribution and evolution during debulk under vacuum at room temperature. A counterintuitive inverse relationship between initial area of contact and the final level of entrapped air was observed, with higher levels of initial contact leading to higher final levels of entrapped air. An initial examination was also carried out to review the effects of ply terminations and bagging practices on air entrapment.

The Application of a Lean Philosophy During Manufacture of Advanced Airframe Structures in a New Product Introduction (NPI) Environment

The manufacture of primary structural wing components from high-performance composite materials is a relatively new technique. GKN Aerospace faces the challenge of manufacturing complex large-scale aero-structures by the ‘Automated Fibre Placement’ (AFP) process whilst transitioning from the ‘new product introduction environment’ to meet contractual production rates. This paper reports on the adoption of the Lean philosophy within a ‘value stream’ by capturing staff perceptions to gain an understanding of the success levels and areas of concern. The research is of particular importance since the ‘barriers of resistance’ in manufacturing environments can be high if Lean is not introduced in a fashion production staff can relate to. Therefore, the research conducted offers GKN the opportunity to focus on the specific areas to realise continuous improvement through the adoption of Lean. The research investigation consisted of a questionnaire employed to gauge staff perceptions from the end of operations at Year 1. At the end of Year 2, the questionnaire was repeated to broaden the cross-sectional study over a longitudinal time horizon. The results were subject to statistical significance testing which showed the differences in staff perceptions were evident. These differences were attributed to the overall level of Lean understanding and appreciation within the facility. The novelty of this research is manifested in how well Lean practice has been adopted in a large-scale aerospace manufacturing facility transitioning from the NPI environment to serial production. Other Lean practitioners and academics will be able to apply the approach in their work, especially those looking to incorporate a Lean philosophy in a NPI environment.

Exploring the discrete tools used by laminators in composites manufacturing: application of novel concept

Abstract This research investigates the handheld and often personally owned tools used by laminators to form advanced composites into components for aerospace, defense, and autosport; and reports on the application of a novel concept. The lack of formal knowledge that surrounds the existence and use of these tools presents an opportunity to explore what significance they have for process standardization and composites’ design and manufacture. The paper presents results from layup trials that were performed to test a prototyped tool, designed with user-centered and geometry-driven research in mind. The trials showed tool use is aligned with the laminator’s goals for the layup task; and suggest that it is also used as the laminator’s method for reporting quality feedback. The trials also raised questions about why the laminators habitually use their tools and the necessity of supporting a laminator through the decision processes involved in a layup task. This suggests the development of a prototyped tool can be of significant benefit in the realm of skills and training. Graphical abstract

Studying effects of preshearing on hand layup

Abstract Advanced composites are used extensively in many high performance applications. As they are taken up in a wider range of applications, the volume of demand is pushing manufacturing methods, especially hand layup of woven prepreg cloth, to their limits. An alternative approach to hand layup over complex geometries is proposed. The regular method of layup involves generating shear using grasps and pressures in the prepreg as and when it is needed during layup, leading to a sometimes complex and time consuming process. In the method proposed, all the shear deformation is created in the ply prior to any contact between the prepreg and the mold surface. Guidelines were drawn onto the prepreg surface to enable the correct shear distribution to be ‘presheared’ by hand. These were created by processing the outputs from a simple kinematic drape simulation within MATLAB. Once preshearing was completed, the ply is laid up onto the mold using regular hand layup techniques. The process was tested alongside regular manual lamination across three example parts and using video analysis effects of the process were investigated via a variety of metrics. This revealed that significant time savings and reduced likelihood of manufacturing variations are possible with this approach. There was also a significant simplification of the layup process, leading participants to comment that a previously ‘difficult’ layup had become ‘easy’. An improved bespoke system for communicating the required preshearing was subsequently developed, and successfully trialed on a fourth example part. Preshearing has the potential to make hand layup more economically viable for years to come. As well as the productivity and cost benefits, preshearing shows promise as a training aid, especially for beginner laminators. Concepts for integrating preshearing into existing industrial practice and its further potential in the field of automation are also discussed.