Automated Fiber Placement Machine Research Articles

Automatic process control of an automated fibre placement machine

Automatic process control of an automated fibre placement machine

Kinematic modeling and error parameter identification of automated fiber placement machine based on measured data

This paper presents a novel kinematic modeling and error parameter identification method for a six-axis gantry automated fiber placement (AFP) machine. Multi-body system theory is used to model the kinematics of the AFP machine, and then use the homogeneous transformation matrix to represent the transfer relationship of the coordinate system. Based on 54 geometric errors of the AFP machine, a volumetric error transfer model is established. To eliminate the training bias caused by sampling randomness, 10-fold cross-validation combined with the Levenberg–Marquardt method is used to train the kinematic model of the AFP machine. Based on the coordinates of random points in space measured by a laser tracker, all the position-dependent geometric errors and position-independent geometric errors of the linear and rotary axes can be identified simultaneously. After the error parameters are identified, the average error of the random points in the X-direction is reduced from 0.72 to 0.08 mm, a drop of 88.9%. Corresponding experiments are carried out on the body diagonals and the winglet placement path. The experimental results show that the volumetric error transfer model and error parameter identification method proposed in the article can accurately predict the volumetric errors of the AFP machine, and can also meet the requirements of the AFP machine placement accuracy.

V.I.E.T.N.A.M. by 4D printing of composites

This paper presents an application of 4D printing of composites (4DPC) to make composite structures of complex geometries without the need for complex moulds. This application is illustrated through the formations of the letters V, i, e, t, n, a, and m, which form the word Vietnam. In the procedure, laminates made of carbon/epoxy prepregs are laid on a flat mould. The deposition of the prepregs on the flat mould is done using an automated fibre placement machine (AFP), which can be considered as a large size 3D printer. For a smaller structure, the prepreg deposition can be accomplished using an AFP machine or by hand lay-up. Upon curing and cooling to room temperature, the laminate transforms itself from a flat configuration to the shape of the intended letter, except for the letter V. The mechanism that enables this transformation relies on the anisotropy of the laminate. This method has many potential applications, particularly in the delivery of bulky three-dimensional structures to remote locations.

Dynamic modeling and parameter identification for a gantry-type automated fiber placement machine combined with hydraulic balance system and nonlinear friction

A dynamic model considering hydraulic balance system and nonlinear friction is established for a gantry-type automated fiber placement (AFP) machine. To facilitate a comprehensive understanding, the AFP machine is introduced firstly. Due to the vertical movement of large masses, the AFP machine is equipped with a hydraulic balance system, thus a hydraulic model is secondly proposed to reveal the relationship between hydraulic pressure and the movement of the vertical axis. Then, a dynamic equation of the AFP machine is built by the Newton-Euler method, which is subsequently converted into the form of linearized minimum inertia parameters. In addition, the problems of nonlinear friction are also studied, and a segmented friction model is developed. To identify the parameters, issues regarding excitation trajectory, filtering, and identification algorithm are discussed. Corresponding experiments are performed, and the experimental results suggest that the prediction of the dynamic model is highly coincident with measurement data, and their relative error rates are less than 5%, proving the effectiveness of the established model and the identified parameters. Further analysis indicates that the proposed friction model is more in line with the actual situation, and can provide guidance for other friction research.

Measurement, identification, and compensation of pose errors for six-axis gantry automated fiber placement machine

Measurement, identification, and compensation of pose errors for six-axis gantry automated fiber placement machine

Dynamic modeling and parameter identification for a gantry-type automated fiber placement machine

Dynamic models play a critical role in the design of model-based controllers, which has a significant effect on the dynamic characteristics of motion equipment. This paper mainly focuses on the dynamic modeling and parameter identification for a gantry-type automated fiber placement (AFP) machine. First, a dynamic modeling process combining prismatic axes and revolute axes is conducted by Newton-Euler method, in which the effects of friction and hydraulic balance system are also considered. Then, as the convenience for parameter identification and the application in linearity control, the methods of dynamic model linearization and determination of minimum inertial parameters based on the multi-body system (MBS) theory are proposed, with which a dynamic model in the form of linearized minimum inertial parameters is consequently established. To identify the parameters in the model, key issues regarding excitation trajectory, filtering, and identification algorithm are discussed in detail. Finally, corresponding experiments are performed on the AFP machine, and experimental results show that there is a good agreement between the prediction of the model and the measurement in actuality. Data analysis shows that except for Z-axis, the relative error rates of the others are not greater than 5%, which proves the effectiveness of the established dynamic model and the identified parameters.

Buckling Optimization of Variable Stiffness Composite Panels for Curvilinear Fibers and Grid Stiffeners

Automated Fiber Placement (AFP) machines can manufacture composite panels with curvilinear fibers. In this article, the critical buckling load of grid-stiffened curvilinear fiber composite panels is maximized using a genetic algorithm. The skin is composed of layers in which the fiber orientation varies along one spatial direction. The design variables are the fiber orientation of the panel for each layer and the stiffener layout. Manufacturing constraints in terms of maximum curvature allowable by the AFP machine are imposed for both skin and stiffener fibers. The effect of manufacturing-induced gaps in the laminates is also incorporated. The finite element method is used to perform the buckling analyses. The panels are subjected to in-plane compressive and shear loads under several boundary conditions. Optimization results show that the percentage difference in the buckling load between curvilinear and straight fiber panels depends on the load case and boundary conditions.

Experimental investigation of the effect of half gap/half overlap defects on the strength of composite structures fabricated using automated fibre placement (AFP)

The Automated Fibre Placement (AFP) process has gained traction as an efficient manufacturing method for large and complex composite structures. An AFP machine uses a computer-controlled arm with a head at the end capable of constant placement of uncured pre-impregnated carbon fibre tows grouped together to form bands. While AFP offers benefits through automation, certain defects inherent to the manufacturing method are induced. Primary defects observed by the aerospace industry are misaligned tows, often the result of trying to steer the tows. This defect occurs when a tow deviates from the intended path causing a combination of both side-to-side gaps and overlaps. In this first of a two-part paper, we experimentally investigate the effects of steered tow defects on the mechanical performance of carbon-epoxy composite structures made with AFP. The orientation, size and number of steered tow defects embedded in the laminates are varied, and their mechanical effects are examined by static tension, static compression and fatigue tests. The major experimental result is that compression is more critical than tension with the largest strength reductions reaching 25% and 10%, respectively. The configuration of the defects has a significant effect on the results. For example, the greater the number of defects, the lower the compressive strength for 45° oriented defects but the opposite is observed for 90° oriented defects. An increased defect width leads to a higher compressive strength in 45° configurations while it is the opposite for tensile tests. The experiments give insight into the behaviour of AFP panels and help to understand their failure modes.

Off-Part Motion Optimization for an Automated Fiber Placement Machine using Travelling Salesman Problem

Computer-Aided Design and Applications is an international journal on the applications of CAD and CAM. It publishes papers in the general domain of CAD plus in emerging fields like bio-CAD, nano-CAD, soft-CAD, garment-CAD, PLM, PDM, CAD data mining, CAD and the internet, CAD education, genetic algorithms and CAD engines. The journal is aimed at all developers and users of CAD technology to ptovide CAD solutions for various stages of design and manufacturing. The journal publishes all about Computer-Aided Design and Computer-Aided technologies.

Modeling and compensation of volumetric errors for a six-axis automated fiber placement machine based on screw theory

This paper presents a novel modeling and compensation method for the volumetric errors of a six-axis gantry automated fiber placement (AFP) machine. Based on the screw theory, the forward and inverse kinematics models of the AFP machine are established. In order to improve the accuracy of the inverse kinematics solution, the Paden-Kahan sub-problem method is used to perform the inverse kinematics solution for the simplified topology of the rotary axes. Using error motion twist to establish a volumetric error transfer model for 54 geometric errors. According to the measurement data of a laser tracker and the Levenberg-Marquardt method to identify the geometric error parameters. The explicit formula of the inverse kinematics solution is used to obtain the error compensation of each motion axis, and the G code of the laying path is modified by the iterative method to realize the compensation of the volumetric errors. By comparing the positions of the tool center point before and after the error compensation, the practicability of the volumetric error modeling and iterative compensation methods are verified, and the geometric accuracy of the AFP machine can be effectively improved.

Fiber Layup Generation on Curved Composite Structures

We present a new two-step process for defining optimal composite fiber paths for use in automated fiber placement machines and finite element analysis models. Building upon work done previously in the area of discrete geodesic path generation, we present a method for predicting minimum strain energy paths initialized by fast approximate geodesic paths on triangular meshes. We compare the effectiveness of this process with those already discussed in the literature and show how this process is fast, accurate, and ready to use in commercial applications. This study also shows how this process effectively finds optimal fiber paths on complex, non-developable surfaces, which will improve finite element analysis models and provide composite manufacturers with the ability to create components with complex geometry. We have also implemented our proposed method on the GPU, which speeds up the process for large surface mesh sizes by computing geodesic paths in parallel. The algorithms developed in this study are available freely online and have been successfully integrated into an automated finite-element model-building software called De-La-Mo (https://idealab-isu.github.io/autofiber/).

Placement suitability analysis of automated fiber placement on curved surfaces considering the influence of prepreg tow, roller and AFP machine

Automated fiber placement (AFP) is an important process used for fabrication of composite structures. Path planning is one of the important steps in the process of AFP. The rationality of the path is directly related to the quality of the composites component. However, the generation of the placement path is constrained by a variety of factors, including geometry characteristics of curved surface, prepreg tow deformation performance, compaction roller deformation characteristics and capabilities of AFP machine. Unreasonable planning parameters selection will lead to local placement path failure or even entire path planning failure. Thus, this paper deals with making some necessary analysis about the placement suitability before path planning and then selecting the appropriate parameters, including the tow width series, compaction roller specifications and AFP machine type. The selection of suitable planning parameters can reduce the unreasonable risk of path planning and then improve the efficiency of path planning.

Tensile strength of CFRP with curvilinearly arranged carbon fiber along the principal stress direction fabricated by the electrodeposition resin molding

To strengthen carbon fiber reinforced plastics (CFRPs), fiber placement along the principal stress directions have been studied as a promising approach. However, a method to sufficiently impregnate a resin between the curved carbon fibers has not established thus far, although arbitrary arrangement of carbon fibers is feasible using the automated fiber placement (AFP) machine. Previously, the authors had developed an electrodeposition resin molding method based on electrophoresis. In this method, the carbon fiber preforms sewn by the AFP machine is immersed in the electrodeposition solution containing polymers with epoxy groups, and optimal current is applied to impregnate resin between carbon fibers. In this study, we showed that a CFRP specimen could be fabricated with arranging the carbon fibers along the principal stress direction, resulting in approximately 10% higher tensile strength than that of the specimen with unidirectional carbon fibers.

Kinematic modeling and parameter identification for a heavy gantry-type automated fiber placement machine considering gravity deformation

Automated fiber placement machine is the key equipment for low-cost and automated manufacturing of high-performance carbon composite materials. In order to meet the required position accuracy of fiber placement, this paper focuses on the kinematic modeling and parameter identification of the automated fiber placement machine. A kinematic model taking account of geometric deviations is established firstly. Since joint interfaces are the main origin of gravity deformation in a machine tool, an elastic beam deformation model is introduced to represent the joint interface, and then the former kinematic model is modified by analytical expressions of the gravity deformation for each joint interface. Based on the measurement data and the Levenberg-Marquardt optimization method, the parameter identification of the kinematic model is realized, and main issues such as measurement data selection, objective function definition are discussed. Finally, a kinematic calibration experiment is performed, and the experimental results verify the feasibility and validity of the modeling method. The position errors in Z direction of the automated fiber placement machine are effectively reduced by over 80%, which suggests that the proposed method reduces the effect of the gravity deformation and improves the accuracy of the automated fiber placement machine.

Influence of fiber misalignments on buckling performance of variable stiffness composites using layerwise models and random fields

Additive manufacturing brought to the emergence of a new class of fiber-reinforced materials; namely, the Variable Angle Tow (VAT) composites. Automated fiber placement machines allow the fibers to be relaxed along curvilinear paths within the lamina. In theory, the designer can conceive VAT structures with unexplored capabilities and tailor materials with optimized stiffness-to-weight ratios. In practise, steering brittle fibers, generally made of glass or carbon, is not trivial and highly affected from the printer signature. This paper wants to explore the effect of fiber misalignment on the buckling response of laminated VAT composites. For doing so, we use the Carrera Unified Formulation (CUF), which allows to develop layerwise models with unprecedented accuracy in a straightforward and systematic manner. Variation patterns are generated at the layer scale by means of random fields through a Monte Carlo analysis. The stochastic variation (defects) is propagated through the scales and correlated with the global buckling response of VAT panels. The results show that layerwise models outperform equivalent single layer theories, since the former are able to foresee eventual switching between buckling modes, and thus making them fundamental in uncertainty analysis.

Mechanical behavior of thick composite tubes under four-point bending

This paper presents the behavior of thick thermoplastic composite tubes made by an automated fiber placement machine, and subjected to four-point bending load. The mechanical behavior includes flexural stiffness, and strains. Methods for the determination of these behaviors include strength of material, analytical solution, finite element method and experimental measurement. The correlation between the different methods provides validation of some methods and indication of the degree of accuracy of some other methods. The accuracy of some calculating methods provides the ability to predict the performance of other thick composite tubes subjected to similar loading and support conditions.

Curvature-controlled trajectory planning for variable stiffness composite laminates

Variable-stiffness laminates can redistribute the applied load and increase critical buckling loads compared to traditional straight fiber laminates. To take full advantage of fiber reinforced composite materials, a practical trajectory planning method is generated based on the maximum principle stress vector field. A reference path is represented as a blend curve of a sequence of uniform cubic B-spline segments passing through some given maxi-stress points. Based on the local-support property of each B-spline segment, subsequent paths within single lamina can be easily obtained by shifting the reference path along a specific direction. A fast localized curvature-correction algorithm is proposed to control the curvatures of the reference path and strictly constrain the void gap or overlap in a variable stiffness lamina. This trajectory planning method takes the requirement of automated fiber placement machines into account, and improves the mechanical properties of the variable stiffness composite laminates by decreasing the occurrence of gap-errors, such as buckling and wrinkling between adjacent paths. A practical case of variable stiffness trajectory planning is provided to demonstrate the feasibility and efficiency of the proposed method. In this practical case, the gap-error rate has decreased from 45.8% to 4.2%.

FUNCTIONAL DEPENDENCE OF LASER POWER AND LAYUP SPEED FOR AUTOMATIC FIBRE PLACEMENT TEMPERATURE CONTROL

Automated Fiber Placement (AFP) is a relatively new technology that has revolutionized the production of composite structures in the aerospace and space industries for more than two decades and is nowadays increasingly used in new industries such as the wind energy. Generally, the AFP machine consists of an automatic manipulator (robot) on which a layup head is fixed for laying multiple individual composite strips at once (certainly not excluding the possibility of laying a single wider tape when it comes to Automatic Tape Placement). The layup process is performed on a mandrel or tool with a certain geometric shape. The laying head should at least include a feeder, a cutting mechanism, a compaction mechanism (usually roller) and a certain type of heater (depending on the material type). Conventionally, three types of composite materials are used in combination with AFP technology: continuous fibers reinforced with thermoset resin (usually epoxy resin), same continuous fibers reinforced with thermoplastic resin as well as bonded continuous carbon fibers. Depending on the type of material this technology uses various types of heat sources in order to achieve a good adhesion to the individual fibers that are deposited in the laying process and the pre-laid composite layers. Thermoplastic pre-impregnated material requires high temperature to reach degree of melting of the resin used to achieve complete 'welding' with the previous layers. The melting temperature varies for different materials and ranges from 130°C to 200°C for low melting thermoplastics (such as Polyamide PA and Polypropylene PP), 280°C to 350°C for Polypropylene Sulfide (PPS) up to 400°C - 450oC for Polyether Ether Ketone (PEEK). For more than two decades, hot gas torches have been used for thermoplastic layup - not a very expensive system but very difficult to control. One of the newer sources of heat close to infrared radiation (λ = 0.9-1.1 μm) is diode laser heating. This research presents a simple thermal model of the process which correlates the heater power and the layup speed with the temperature of the heating area. The deposition temperature was measured over a range of heater powers and layup speeds. The experimental data is used to define and validate a thermal model for thermoplastic material used in conjunction with a diode laser: carbon fibre reinforced thermoplastics PEEK. This enables open-loop, speed dependent heater power control, based on defining and programming the speed dependent heater power function in the machine controls. Obtained functional dependency was implemented in the AFP machine control system and tested for production of several plates with different layup angles. The achieved temperature during layup process is monitored on the thermal camera and through several pyrometers.

Manufacturing procedure to make flat thermoplastic composite laminates by automated fibre placement and their mechanical properties

Automated fibre placement (AFP) is a relatively new process for the manufacturing of composite structures. Among many attractive features, it provides high-speed of material deposition, more repeatability in terms of quality of the part, less labour intensive (as compared with traditional methods of manufacturing such as Hand Lay-Up), less waste and the ability to transition more seamlessly from design to manufacturing. AFP can be used to process both thermoset composites and thermoplastic composites. Thermoplastic composites processing holds many potential benefits. This is because if the process is done right in producing parts with good quality, it is fast since it does not require a second process such as curing in an autoclave or oven. For the purpose of comparison of performance and for design, it is necessary to determine the mechanical properties of laminates made using this process. However, there are challenges in making flat coupons for the purpose of testing for mechanical properties. This article presents these challenges and the procedure developed to make flat laminates using a simple AFP machine. Mechanical properties of these laminates are also determined and compared with those obtained from laminates made using conventional autoclave moulding.

An online detection method for composite fibre tow placement accuracy

Fibre composite is widely used in the field of aerospace because of its excellent performance. However, during the process of fibre placement using an automated fibre placement machine, it is difficult to guarantee accurate fibre placement. To solve the problem, this study established an online detection method for fibre tow placement accuracy. It captures the image of the detection region using an industrial charge-coupled device camera, identifies those regions with gaps in the image using computer vision methods and then acquires the gap widths which are the fibre placement accuracy of each fibre tows. When the angle between upper and lower fibre tows was small, to find the position of edges in the images accurately, we presented an improved image enhancement method based on histogram stretching. The experimental results showed that this online detection method was applicable and can quickly and effectively identify the position and width of the gaps in the detection region. Furthermore, it had high resolution, which can meet the requirements of practical engineering.