Laser-assisted Tape Placement Research Articles

From virtual to actual assisted tape placement − application of the Frenet frame to robotic steering trajectories

A novel computational tool is presented that integrates the design and manufacturing of variable-angle tow composites for automated tape placement, facilitating the creation of tow-steered trajectories for cut-outs. Steering movements of the robot are planned and executed within a MATLAB virtual environment via short paths and linear commands. Leveraging piecewise-continuous clothoid splines and the Frenet frame, the tool furnishes crucial details on trajectory vectors, steering angles, and curvatures. Via four integrated modules, the user can define input parameters such as the robot’s actuators and structural geometry, allowing for the subsequent visualisation of the steered trajectories as well as the generation of the manufacturing code. Finally, to assess the potential and limitations of this methodology, the file containing all details is integrated into the Kuka KR L240-2 robot model to continuously steer a carbon fibre/PEEK tape around an elliptical cut-out in a composite panel using laser-assisted tape placement, representative of an access hole in an aircraft wing.

Recycling CF/PEEK offcut waste from laser assisted tape placement: Influence of overlaps and gaps

A recycling method for waste CF/PEEK prepreg tapes is proposed that uses offcuts from laser assisted tape placement (LATP) processing, without shredding, grinding or further cutting. Laminates (using the prepreg waste) representing different configurations were manufactured considering overlaps and gaps reflecting observed defects in LATP. Interlaminar shear strengths (ILSS) with 0° fibre (Parallel) and bending strength for 90° fibre (Normal) directions were measured. The parallel samples with 3 mm overlap had the highest ILSS (100.3 MPa) while the 2 mm gapped samples had the lowest ILSS (58.7 MPa). The Normal samples failed at the surface due to matrix-dominated failure providing bending strengths between 44.0 MPa and 82.1 MPa. Failure mechanisms were identified similar to that of non-recycled composites reported in the literature (50–120 MPa), indicating that the recycled prepreg tapes retained approximately 84 % of the ILSS of the highest reported values.

The effect of laser assisted tape placement processing conditions on microstructural evolution, residual stress and interlaminar shear strength of carbon fibre/PEEK laminates

In the present study, both experiments and thermo-mechanical coupled simulations were conducted to characterise the diverse crystallisation behaviours and the processing parameter-microstructure-mechanical property relationships occurring in laser-assisted tape placement (LATP) manufacturing of carbon fibre (CF)/Polyetheretherketone (PEEK) laminates. Specifically, at various processing temperatures (350 °C or 400 oC), increasing the compaction pressure from 2 to 4 bar causes distinct defect distribution behaviours. However, variations in processing parameters show minimal effect on the morphology and size of crystallised spherulites, which were consistently around 2–3 μm in size, resulting in a final crystallinity of manufactured laminates within 30%–35%. It was found that the cold crystallisation processes occurring in PEEK during LATP play an important role in determining the final degree of crystallinity. Experimental measurements and simulations indicate that changes in processing parameters have a negligible effect on residual stress levels, especially regarding interlaminar residual stresses. A processing temperature of 400 °C was found to generate a diffuse, yet coherent, interphase spanning the fibre/matrix interface with a thickness approximately 70 nm. In contrast, at a processing temperature of 350 °C, a distinct, incoherent interface was confirmed between fibre and matrix. The formation of the interphase, coupled with fewer defects, leading to a relatively high interlaminar shear strength (78 MPa) of manufactured laminates under appropriate processing conditions. Therefore, it is suggested that regulating the degree of cold crystallisation in polymer matrices while ensuring a strong fibre/matrix interfacial bond by the optimisation of processing temperature, will enable the tailoring of microstructure and design of composites to meet specific strength property requirements.

A numerical and experimental identification of crystallinity gradients in carbon fiber reinforced thermoplastic composites obtained by laser assisted filament winding

The presence of temperature and crystallinity gradients in carbon fiber–reinforced PolyEtherEtherKetone (PEEK) composite laminates, produced via laser-assisted tape placement, is investigated in this paper. The manufacturing process takes place with high deposition speed and using localized laser source for heating, therefore enhancing the formation of temperature and crystallinity gradients through the laminate thickness. A previously validated thermal model coupled with a non-isothermal crystallinity model and a fusion model are used to simulate the temperature and crystallinity distributions through the laminate thickness. The results from the model are correlated with Dynamic Mechanical Analysis (DMA) tests and Differential Scanning Calorimetry (DSC) tests since a crystallinity gradient is difficult to monitor experimentally. The simulated gradients suggested the presence of an amorphous layer between two consecutive plies and an increase in the crystallinity through the material’s thickness. This observation is correlated with the behavior reported for the semi-crystalline laminates during the DMA test, where the modulus drops abruptly during the glass transition, a typical behavior for an amorphous material.

Experimental quality assessment of thermoplastic composite corner regions manufactured using laser-assisted tape placement

Over the past 25 years, interest in thermoplastic composites in aircraft has steadily increased. Combining winding and laser-assisted tape placement is a promising method to manufacture thermoplastic structures using in-situ consolidation, as shown recently by manufacturing a variable stiffness, unitized, integrated-stiffener thermoplastic wingbox at the University of Limerick. The corner regions are a critical point of the structure and require in-depth characterization studies, for example by unfolding L-shaped samples in a 4-point bend test. In this work, samples with radii varying from 2 to 10 mm were manufactured and tested. Two manufacturing parameters were varied: the rotational speed and acceleration of the tool. Test data show that decreasing the radius increases the corner strength, but an optimum radius exists to withstand a maximum unfolding force/moment. In addition, the slowest deposition rate with least acceleration of the head used during manufacturing lead to the highest corner strength for the same radius.

Ultra-fast Consolidator Machine Development – Individualized Mass Production of Thermoplastic Tailored Blanks based on Laser-assisted Tape Placement with in-situ Consolidation

The new UItra-Fast Consolidator Machine development offers both high flexibility and mass production of tailored thermoplastic laminates with reduced scrap. The machine system can be configurated to achieve fully consolidated multi-layer laminates with different fiber directions and minimized scrap (thermoplastic tailored blanks) produced in cycle times below 5 seconds. This individualized mass production is accomplished by a combination of laser-assisted tape placement with in-situ consolidation and a piece-flow principle, which is state of the art in the printing industry but has not been used in such a way within composite production. The achievable productivity is enhanced to more than 500 kg/hour by this piece-flow principle with carriers moved through multiple application stations which are equipped with multiple tape placement applicators. The new machine is scalable: multiple application stations can be added, e.g. for each layer one station for mass production or for each fiber direction one station with a carrier-conveyor carousel: here the carriers are moved multiple times through the application stations.
 This innovative machine system is a result of an 18-months AZL Joint Partner Project, conducted in 2017-2018 by the research partners AZL Aachen and Fraunhofer IPT Aachen, in cooperation with 12 industrial partner companies including Conbility, Covestro, Engel, Evonik, Fagor Arrasate, Faurecia SE, Laserline, Mitsui Chemicals, Mubea Carbo Tech, Philips Photonics, SSDT and Toyota (in alphabetical order). The system won the international JEC Innovation AWARD 2019 in the category “Industry & Equipment”.

Optimization of thermal model and prediction of crystallinity during the laser-assisted tape winding process

Laser-assisted tape placement and tape winding represent the most advanced automated manufacturing technologies for thermoplastic composites. It is important to accurately predict the complete thermal history of the manufacturing process, on which many properties of the product are strongly dependent, such as interlaminar bonding strength and crystallization. In this article, a nonlinear two-dimensional transient heat transfer model was established in ANSYS APDL, and a new temperature closed-loop controlled near-infrared laser heat source was described. Most importantly, the thermal contact pairs were introduced following the activation of elements, and the value of interlaminar thermal contact resistance was obtained by fitting an independent experiment and finite element analysis, which greatly optimized the heat transfer process in the direction of thickness. The thermal model was verified by infrared cameras and an online temperature measuring system based on thermocouples. The results of thermal history are in good agreement with the experiment, which were input into the crystallization kinetics model to predict the evolution and distribution of crystallinity in the laser-assisted tape winding process. The calculated results are coincident with the differential scanning calorimeter test very well, and the crystallinity was about 17% higher than that before manufacturing.

Modeling and Numerical Simulation of Laminated Thermoplastic Composites Manufactured by Laser-Assisted Automatic Tape Placement

Abstract A comprehensive numerical model is developed for the simulation of the laser-assisted automated tape placement process of carbon fiber/thermoplastic composites. After being heated with a laser, the thermoplastic is welded with the help of a consolidation roller onto a substrate made up of layers of tapes bonded onto one another. Under the pressure applied by the roller, the thermoplastic flows and the tape reaches its final thickness. The numerical model is developed in three sequential steps that can be used to identify the required pressure and temperature distribution to achieve a good bond. Firstly, a heat transfer simulation is performed to determine the temperature distribution into the incoming tape under the consolidation roller. Secondly, a rheological model is developed to examine the polymer flow under the roller and to obtain the pressure field. Finally, the consolidation level between the substrate and the tape is investigated through the degree of intimate contact, which is related to the processing parameters such as the roller velocity, the laser power density and the compaction force.

Morphology of ply drops in thermoplastic composite materials manufactured using laser-assisted tape placement

Mechanical properties of composite laminates can be tuned by either tailoring ply orientations or by using ply drops to change thickness profiles. The latter cause resin-rich pockets to form in thermoset composites that are autoclave cured after lay-down. This paper focuses on the morphology of ply drop regions with carbon fibre thermoplastic composites manufactured using in-situ consolidation with laser-assisted tape placement. Our work shows that when laying a 0° ply (parallel to the ply drop) over a ply drop then the ply readily conforms to the shape of the ply drop, eliminating voids. However, when a 90° ply covers a ply drop, the processing direction affects behaviour. When the ply ascends a ply drop, a void is created. On the other hand, when the ply descends a ply drop, the substrate changes its shape due to combined laser heat and roller pressure, leading to significantly smaller voids.

3D Numerical Modeling of Laser Assisted Tape Winding Process of Composite Pressure Vessels and Pipes-Effect of Winding Angle, Mandrel Curvature and Tape Width.

Advanced thermoplastic composites manufacturing using laser assisted tape placement or winding (LATP/LATW) is a challenging task as monitoring and predicting nip point (bonding) temperature are difficult especially on curved surfaces. A comprehensive numerical analysis of the heat flux and temperature distribution near the nip point is carried out in this paper for helical winding of fiber reinforced thermoplastic tapes on a cylindrically shaped mandrel. An optical ray-tracing technique is coupled with a numerical heat transfer model in the process simulation tool. The developed optical-thermal model predictions were compared with experimental data available in literature to validate its effectiveness. The influences of winding/placement angle, mandrel curvature and tape width on the incident angles, the laser absorbed intensity, and the process temperature distribution are studied extensively using the validated model. Winding/placement angle has a considerable effect on the temperature distribution. Increase in winding angle results in a higher temperature for tape due to more reflections coming from the substrate. On the other hand, substrate temperature decreases as the winding angle increases due to a decrease in the laser incident angles based on the local surface curvature. An increase in mandrel curvature results in higher nip point temperatures for substrate and lower one for tape. Different mandrel sizes for 90 placement path do not have a strong effect on the substrate process temperature as for other winding angles because of less curvature change of the corresponding irradiated area. Tape width causes local temperature variations at the edges of the tape/substrate. In order to obtain the desired process temeprature during LATW or LATP processes, the laser intensity distribution on the tape and substrate surfaces should be regulated.

A comparative study for shear testing of thermoplastic-based composites and metal-composite hybrids

This study presents the novel application of the compression shear test (CST) for characterising bonding strength of metal-composite hybrids made of steel and carbon fibre/polyamide 6 (CF/PA 6). An automated laser-assisted tape placement (ATP) process was used to lay-up the CF/PA 6 tapes on laser textured steel substrates. CST is of interest due to the ease of sample manufacturing as a relatively small test specimen is required. The results were compared with standardised single lap shear tests (ASTM D3165), which requires manufacturing of a double-notched test specimen. For benchmarking purposes, the compression shear test was also used to characterise the interlaminar shear strength of a plain CF/PA 6 composite. The results showed equivalent shear strength and similar failure modes for both tests of the metal-composite hybrid specimens. Grooved texturing of the steel substrate in the hybrid specimens promoted a mixed-mode (cohesive and adhesive) failure and a higher shear strength than for the composite-only specimens. Overall, the results showed that the compression shear test is a valid and efficient method to characterise the bonding strength of metal-composite hybrids and composites.

Properties of a thermoplastic composite skin-stiffener interface in a stiffened structure manufactured by laser-assisted tape placement with in situ consolidation

A critically important consideration of stiffened structural panels is the interfacial properties between skin and stiffener. In the present study a novel implementation of laser-assisted tape placement (LATP) was used to produce a representative skin-stiffener of a wingbox from carbon fibre reinforced PEEK. First, a stiffener is manufactured using this method and subsequently the skin is attached using the same method without need for a secondary bonding process. The interfacial properties between the skin and stiffener have been characterised in terms of interlaminar shear strength (ILSS) and fracture toughness (Mode-I and Mode-II) properties. LATP laydown direction and laser power was found to influence the skin-stiffener interface Mode-I fracture toughness, but not affect the Mode-II fracture toughness. The values of ILSS and fracture toughness compare favourably with those results reported in the literature, in particular for those reported for equivalent aerospace certified CF/PEEK material (APC-2).

Concurrent design and manufacture of a thermoplastic composite stiffener

Fibre reinforced composite materials are finding increasing application in aerospace structures due to their superior specific properties. Aerospace structures make widespread use of stiffening elements, such as stringers, for example in wingboxes and fuselage structures. Sizing of stiffeners to fulfil strength, stiffness and manufacturing considerations is a significant challenge. Herein, a novel manufacturing approach using winding in combination with laser-assisted tape placement is used to manufacture an omega-shaped stiffener made from carbon fibre thermoplastic material. This paper discusses the integrated approach taken by considering material choice, manufacturing constraints and structural design on the performance of a closed-section omega stiffener. The sizing is based on the buckling response of the wingbox, with manufacturing constraints taken into consideration. In the collapsible mould, a low-melt aluminium alloy is used as a spacer, which can be removed post-process by exposing the mould to the alloy melt temperature, which is below the glass transition temperature of the thermoplastic composite material. Manufacturing tests show that repeatable stiffeners of the appropriate dimensions are manufactured. Characterisation tests show that both the bond strength, measured using an interlaminar shear strength test, and the corner strength, assessed using a four-point bend test, are satisfactory.

Adaptive tape placement process control at geometrically changing substrates

The laser-assisted tape placement process faces thermal challenges at geometrically changing substrates. Due to changing optical conditions and thereby varying local energy absorption, local differences of the process temperature occur. These temperature inhomogeneities become even more pronounced due to restrictions with regard to machine dynamics. In particular, strong directional changes, which are necessary e.g. for small machining radii, result in the relative speed between workpiece and laser beam not being constant. The use of vertical-cavity surface-emitting lasers (short: VCSEL) as adaptive heat sources could improve the temperature control especially by use of application adapted intensity distributions that can be calculated through inverse simulations.In this work, the optical and thermal effects during tape placement on geometrically changing substrates are described and analyzed. A possible solution to the described challenges is shown by using application adapted intensity distributions, which aim at a suitable, constant process temperature. The simulations will consider the three-dimensional part geometry, specific intensity distributions of the VCSEL as well as machine dynamics. By the use of tape placement equipment of the Fraunhofer IPT the occurring local temperature changes and the resulting degree of process optimization are experimentally validated.

The Double Drum Peel (DDP) test: A new concept to evaluate the delamination fracture toughness of cylindrical laminates

Standard delamination tests of monolithic composites prescribe configurations where the crack is a symmetry plane for both overall geometry and stacking sequence, ensuring a controlled mode ratio. These normalized configurations do not enable testing of curved specimens, like those manufactured by filament winding. Here, we propose a new concept for the delamination testing of cylindrical laminates, the Double Drum Peel, related to the peel tests used for adhesives or thin-films debonding. A global energy analysis, including all sources of energy release and dissipation, provides the expression of the critical strain energy release rate. As in the classical peel test, the energy dissipated by mechanisms other than delamination should be accounted for to determine intrinsic interface properties. The local mode mixity is evaluated based on analytical results on the classical peel test. Tests using carbon-peek rings manufactured by laser assisted tape placement are presented to illustrate the potential of the DDP.

Sensitivity thermal analysis in the laser-assisted tape placement process

Nowadays, the production of large pieces made of thermoplastic composites is an industrial challenging issue as there are yet several difficulties associated to their processing. The laser-assisted tape placement (LATP) process is an automated manufacturing technique to produce long-fiber reinforced thermoplastic matrix composites. In this process, a tape is placed and progressively welded on the substrate. The main aim of the present work is to solve an almost state of the art thermal model by using an efficient numerical technique, the so-called Proper Generalized Decomposition (PGD) that considers parameters (geometrical and material) as model extra-coordinates. Within the PGD rationale the parametric temperature field is expressed in a separated form, as a finite sum of functional products, where each term depends on a single coordinate (space, time or each one of the parameters considered as extra-coordinates). Such a separated representation allows the explicit expression of the sensitivity fields, from the temperature derivative with respect to each parameter. These sensitivity fields represent a very valuable methodology to analyze and establish the influence of the critical input parameters on the thermal response, and therefore, for performing process optimization and control, as well as for evaluating the effect of parameters variability on the thermal response.

Rotational moulding of PEEK polymer liners with carbon fibre/PEEK over tape-placement for space cryogenic fuel tanks

PEEK polymers are investigated as replacement materials for metallic liners in composite overwrapped pressure vessels (COPVs) for fuel tank applications in space. A novel, integrally heated, rotational moulding tool has been developed to produce PEEK polymer liners, samples of which have then been overwrapped using CF/PEEK in a laser assisted tape-placement (LATP) process to produce demonstrator samples of a polymer lined COPV. Helium permeability testing has shown that the designs are capable of resisting leakage to acceptable levels for fuel storage, while X-ray CT scanning and cryogenic cycling have shown that the current design is capable of resisting crack growth over multiple cycles. Nano-indentation testing has shown that the LATP process has created a region of reduced modulus in the PEEK polymer at the surface of the liner where the CF/PEEK has been tape-laid. This laser-affected zone of reduced polymer modulus in the composite interface region has enabled an enhanced resistance to crack growth formations from thermal residual stresses in comparison to hot plate moulded test samples.

Joining of Thermoplastic Tapes with Metal Alloys Utilizing Novel Laser Sources and Enhanced Process Control in a Tape Placement Process

Automated laser assisted tape placement is an additive manufacturing technology for the production of composite parts. Composite parts are common in various markets. Especially the automotive sector has a demand for lighter and stronger materials. The combination of standard sheet metal materials and fiber reinforced plastics promises to deliver enhanced properties and performances over the separate materials themselves. This multi-material combination is classically done with mechanical connections. This paper addresses a direct in-situ approach of putting carbon fiber reinforced thermoplastic tapes directly onto pre-structured sheet metal parts and shows the prerequisites needed for achieving a consolidation between both materials.

Selective high-speed tape placement using cut-on-the-fly for local reinforcement of GMT substrates towards a waste-reducing production of multi-material components

Cost-efficient production technologies for lightweight composite components are the key enabler for a broad range of application. Manufacturing technologies like laser-assisted tape placement offer the opportunity to produce thermoplastic multi-material composite parts with optimum reinforcement, weight and cost profile. By the selective tape placement and in-situ consolidation of continuous unidirectional fibre-reinforced thermoplastic tapes in predetermined locations of existing composite structures, composite parts can be efficiently and economically manufactured. Enhanced by the new manufacturing process route, the weight of components can be significantly reduced by the combination of different reinforcement fibres in one single structure. This allows the achievement of an optimised relation between performance and weight. As a key enabler for drastically reducing the waste as well as the production times during in-situ selective tape placement the findings presented in this paper focus on the system and process technology to make an add-&-cut-on-the-fly process possible. Further findings focus on the increase in the process velocity and the influence of the lay-up pattern when using selective laser-assisted tape placement for the local reinforcement of a high-volume-suited polyamide 6-based glass mat thermoplastic substrate material.

Increasing Cost and Eco Efficiency for Selective Tape Placement and Forming by Adaptive Process Design

The automated placement of continuous fiber-reinforced polymer prepregs (pre-impregnated) is a generative manufacturing technology for composites. Particularly laser-assisted tape placement of unidirectional continuous fiber-reinforced tapes provides potentials for highly flexible composite manufacturing. Whereas the single process of tape placement to generatively build up load carrying structures was already optimized in several research activities and projects, an integrated process chain approach promises further increases in cost and eco efficiency. An adaptive process design considering interdependencies between selective tape placement and a subsequent forming improves the entire process chain. Due to the knowledge of process interdependencies, the advantages of high speed placement on predetermined load carrying areas can be fully exploited. The system and process design for this adaptive manufacturing approach, the underlying assessment methodology as well as its application on a manufacturing process chain for structural composite parts are presented in this paper.