Layup Speed Research Articles

Effect of Flashlamp Heating System Parameters on the Wedge Peel Strength of Thermoplastic Carbon Fiber Tape in the Automated Tape Placement Process

Laser-assisted automated tape placement systems are currently the state of the art regarding thermoplastic tape placement. Flashlamp heating systems are rather new in this field of application and offer high energy density with low safety requirements and moderate costs compared to laser-assisted automated tape placement systems. In this study, the effect of processing parameters on interlaminar bonding of carbon fiber-reinforced polyamide 6 tapes is investigated using a flashlamp heating system. The temperature during placement is monitored using an infrared camera, and the bonding strength is characterized by a wedge peel test. The bonding quality of the tapes placed between 210 °C and 330 °C at a lay-up speed of 50 mm/s is investigated. Thermogravimetric analysis, differential scanning calorimetry, and micrographs are used to investigate the material properties and effects of the processing conditions on the thermophysical properties and geometric properties of the tape. No significant changes in the thermophysical or geometric properties were found. Moisture within the tapes and staining of the quartz guides of the flashlamp system have significant influence on the bonding strength. The highest wedge peel strength of dried tapes was found at around 330 °C.

Experimental Investigation on Comparing Mechanical Properties in 3D Printed Polymers by Varying Process Parameter

The Desktop 3D printing is a quickly emergent additive manufacturing process due to its capacity to build complex geometry functional parts. Polymer filaments are used as a raw material for building various functional parts. 3D printing process parameters influence the mechanical properties of a built part. The present study investigate the effect of process parameters like layer thickness and layup speed on the mechanical properties of PLA, Bronze filled PLA and ABS samples manufactured with a low cost 3D printer. Tensile and flexural tests based on ASTM D638 and ASTM D760 standards were performed, respectively to determine the mechanical response of the printed specimens. With respect to the layup speed and layer thickness, it is found PLA has better tensile and flexural properties compared to ABS and Bronze filled PLA.

The effects of processing parameters on the wedge peel strength of CF/PEEK laminates manufactured using a laser tape placement process

Manufacturing thermoplastic composites (TPCs) with excellent mechanical properties require advanced methods with reduced costs and better overall efficiencies. In this study, fiber-reinforced thermoplastic polymer composite laminates were manufactured using an automated fiber placement (AFP) manufacturing technology. The effects of processing temperature (from 320 to 500 ℃), lay-up speed (from 20 to 260 mm/s), consolidation force (from 100 to 600 N), and prepreg tape tension (from 0 to 9 N) on the quality of the resulting laminates manufactured using the laser AFP system were investigated. The interlayer bond strength was characterized using wedge peel tests on samples prepared with different process parameters. The studies were complemented by measurements of the thermal properties of the composites using differential scanning calorimetry. The optimized process parameter windows were determined to be 360 to 400 ℃ for the irradiation temperature, 140 to 160 mm/s for the lay-up speed, 100 N for the consolidation force, and 3 to 5 N for the prepreg tape tension, respectively. The microscopic analysis of the sample cross-sections and peel-damaged surfaces revealed that the different distributions of the resin matrix resulting from the different processing parameters affected the interlayer strength. These results may provide an important reference for manufacturing TPC used in aerospace, defense, and automotive applications.

As-built FE thermal analysis for complex curved structures in automated fiber placement

This research aims to predict and manage material temperatures on complex curved surface structures during automated fiber placement (AFP). A thermal analysis model is developed by incorporating the information of path points as well as the heating time into the radiative heat transfer model. In it, the heating time is determined by the layup speed which is formulated using the S-shaped speed forward planning method. Finally, the thermal analysis algorithm is integrated into a three-dimensional (3D) finite element (FE) model to predict and regulate material temperatures on complex curved structures. In this paper, the thermal analysis method is exemplarily applied to a C-beam. The predicted material temperature under the condition of the constant power is validated by the AFP experiments. A good agreement between the temperature-predicted value and the experimental results is observed. Moreover, the power design method based on laying temperature analysis is proposed to manage the material temperatures within the optimal laying specification.

Effect of process parameters on mode-II interlaminar fracture toughness and fractographic features of automated fibre placement prepreg laminates

The present study concerns the quantitive assessment of the influence of process parameters on the interlaminar properties of carbon fiber reinforced epoxy composites. Mode II interlaminar fracture toughness is evaluated based on the ENF test. Scanning electron microscopy images are used to evaluate the change in microstructures. The results indicate that the process parameters have a direct influence on the microstructural features and fracture toughness of laminates. Specifically, the elevation of layup speed leads to the increase of interlaminar porosity which results in a decline of fracture toughness. The moderate pressure could sufficiently evacuate air bubbles during the deposition which to a certain extent decreases the porosity; however, the excessive pressure squeezes resin out from the interlaminar region, which decreases the fracture toughness. Furthermore, the excessive temperature could both increase porosity and result in a thinner resin layer due to the change in resin flowability. In which case, the fracture toughness would be significantly decreased.

Experimental investigation of prepreg tackiness in automated fiber placement

Automated fiber placement (AFP) is widely used to manufacture composite lightweight structures in different industries, including aerospace. Prepreg tackiness plays an important role in the AFP process. This study aims to measure the prepreg tackiness at different AFP processing conditions and predict the optimum parameters for high tackiness levels. Two in-house setups were developed for layup and to measure tackiness. The first setup was designed to simulate the AFP process and precisely control layup speed, compaction force, and temperature. It is used to layup the prepreg under different conditions and with different rollers. The second setup performs a peel-off test to measure the sample’s tackiness. The Taguchi method is applied to optimize the layup process parameters and find the optimal combination for high resultant tackiness. It is also applied to study the effect of the placing roller. Analysis of results shows that prepreg tack is affected by the interaction among the process parameters rather than the individual effect of these parameters. The study shows that the Taguchi method is suitable to solve the stated problem with a minimum number of trials as its results are experimentally validated.

An investigation of in-situ AFP process parameters using CF/LM-PAEK

In recent years the use of thermoplastics has become popular in aerospace applications, with a primary focus on fiber-reinforced composites. Displaying greatly improved mechanical properties, new components using these materials still need to be characterized and their suitability for aviation applications demonstrated. A common restriction to the implementation of fiber-reinforced thermoplastic parts is the almost default autoclave manufacturing, which is both time consuming and expensive. Aiming for a more economical final product, this study utilizes a one-step in-situ Automated Fiber Placement (AFP) process to produce samples for mechanical and thermal characterization. The recently developed and highly popular material CF/LM-PAEK was used within this study, with the four major AFP processing parameters varied to assess material sensitivity. Test samples were manufactured using Design of Experiment (DoE). Subsequently, single lap shear (SLS) and differential scanning calorimetry (DSC) tests were performed to assess consolidation quality. With rising tooling temperature, both SLS strength and crystallinity increase up to 31 MPa and 25%, respectively. A post-manufacturing tempering process improved crystallinity of the tested CF/LM-PAEK specimens up to 29% and SLS strength up to 38 MPa. Within the tested parameter range, CF/LM-PAEK appeared to be unaffected by increasing layup speed, which is a promising aspect with regard to faster industrial production.

Postprocessing method-induced mechanical properties of carbon fiber-reinforced thermoplastic composites

Promising carbon fiber-reinforced thermoplastic (CF/polyetherketoneketone (PEKK)) composites were fabricated by the state-of-the-art technology known as “Automated Fiber Placement.” The mechanical properties of CF/PEKK were evaluated for four different postprocessing methods: in situ consolidation, annealing, vacuum bag only (VBO), and hot press (HP). The evaluation was performed by narrowing down the relevant processing parameters (temperature and layup speed). Furthermore, the void content and crystallinity of CF/PEKK were measured to determine the effect of these postprocessing processes. The HP process resulted in the best quality with the highest interlaminar shear strength, highest crystallinity degree, and lowest void content. The second most effective method was VBO, and annealing also realized an improvement compared with in situ consolidation. The correlation between the postprocessing method and the void content and crystallinity degree was also discussed.

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.

Experimental investigation on fabrication of thermoset prepreg composites using automated fibre placement process and 3D printed substrate

Robot-based Automated fibre placement (AFP) techniques are continuously progressing towards maturity. However, as AFP becomes mainstream, the manufacturing of tooling used in AFP requires additional attention for large and complex-geometry composite structures. Based on this requirement, fused deposition modeling (FDM) has been identified as the most suitable technology of choice for rapid production of high-temperature, low volume, composite lay-up and repair tools, also for moderate temperature production tooling. In this current research, 3D printing and AFP technology are combined to manufacture the composite parts with high complexity. Also, the curing process of prepreg material, which is most important for manufacturing process, has been monitored. The cure behavior was first characterized using differential scanning calorimetry (DSC) using isothermal condition. Then, the 3D printed substrates were fabricated and AFP prepreg lay-up experiments were conducted. Prepreg lay-up can undergo deformation and slip between each layer over a 3D printed substrate. As a result, the final product quality gets affected, with defects such as delamination, overlaps and gaps. Therefore, experimental investigations were done with an in-house robot-based AFP system by varying process parameters like bed temperature, compaction force and lay-up speed. In addition, the fibre placement was done over different 3D printed polymer material substrates and tested for oven curing capabilities. The fabricated samples were tested to determine their mechanical properties.

Influence of manufacturing parameters on the strength of PLA parts using Layered Manufacturing technique: A statistical approach

A 3D printing was successfully used to fabricate samples of Polylactic Acid (PLA). Processing parameters such as Lay-up speed, Lay-up thickness, and printing nozzle were varied. All samples were tested for flexural strength using three point load test. A statistical mathematical model was developed to correlate the processing parameters with flexural strength. The result clearly demonstrated that the lay-up thickness and nozzle diameter influenced flexural strength significantly, whereas lay-up speed hardly influenced the flexural strength.

Heater power control for multi-material, variable speed Automated Fibre Placement

Automated Fibre Placement requires accurate control of the heater power to deposit the material at appropriate temperatures throughout the process. This paper presents a simple semi-empirical thermal model of the process which correlates the heater power and the layup speed with the substrate surface temperature. The deposition temperature was measured over a range of heater powers and layup speeds. The experimental data is used to define and validate a semi-empirical thermal model for two classes of materials used in conjunction with a diode laser: carbon fibre reinforced thermoplastics and bindered dry fibres. This enables open-loop, speed dependent heater power control, based on defining and programming the speed dependent heater power function in the machine controls.

Processing and characterization of the thermoplastic composites manufactured by ultrasonic vibration–assisted automated fiber placement

To obtain the autoclave-level mechanical properties using in situ consolidation of thermoplastic composites by automated fiber placement (AFP) with high efficiency is the focus of recent research. Different heat resources were utilized to pursue improved mechanical properties and deposition rates but yet not very satisfactory. In this article, E-glass fiber/polypropylene laminates, manufactured by ultrasonic vibration–assisted AFP (UAFP) and autoclave, were compared by means of mechanical properties and crystallization. The interfacial bonding mechanism was analyzed theoretically based on the principle of ultrasonic heating and the autohesion. The orthogonal tests were designed to study the effect of the process parameters on the interlaminar shear strength (ILSS), including the ultrasonic amplitude, layup speed, and pressure, to optimize the manufacturing process of specimens. The mechanical tests and differential scanning calorimetry (DSC) were utilized to evaluate the ILSS, mode I interlaminar fracture toughness GIC, impact toughness, and degree of crystalline of laminates from hot-press and UAFP. The experimental results indicate that the ILSS of the specimens from UAFP can match with the hot-press specimens. The GIC and the impact toughness of the UAFP specimens are 59.9% and 20.1% lower than the hot-press ones, respectively, which are due to the lower degree of crystalline caused by the higher cooling rate during the UAFP process. The results of DSC show that the crystallinity of specimens made from UAFP is only 38.5%, whereas the 49.2% crystallinity is tested for the hot-press.

Influence of AFP Process Parameters on the Temperature Distribution Used for Thermal in-process Monitoring

Automated Fiber Placement is an important manufacturing process when it comes to aerospace part generation. To minimize the machine downtime, an online monitoring system is necessary to prevent time consuming visual inspection. Therefore, a new thermal in-process monitoring system is integrated. Herewith spotted temperature difference enable the localization of placed tows and detection of defects. The thermal contrast between subsurface and tows depends on different process parameters such as lay-up speed, tooling temperature and compaction pressure. This influence is analyzed and discussed within lay-up studies to gain further knowledge about the different effects to increase the reliability of in-process monitoring as well as AFP processes.

Modeling and experimental investigation of out-of-plane deformation on mechanical performance of composites manufactured by ATL

The change of mold normal curvature along the trajectory may result in out-of-plane waviness during the automated laying process, on which the layup speed and temperature would have an effect. A new parameter, deformation rate, was defined by combining the effect of mold curvature change rate and layup speed. A predicting model was proposed based on the fiber waviness and interlaminar sliding model to calculate the relationship between stiffness retention and the layup process parameters, including deformation rate and temperature. An experimental study on the effect of different deformation parameters on the tensile performance of composites was carried out based on a new manufacturing method of plated specimens with different levels of waviness by means of a four-point bending fixture. The experimental results showed that when the deformation temperature increases from 20℃ to 80℃, the tensile strength increases first and then decreases while the tensile module keeps increasing. While the deformation rate decreases from 0.40 to 0.04 mm−1/s, both tensile strength and module showed an increasing trend. The predicting model being validated by experimental results can be utilized to optimize the layup process parameter to satisfy the quality and efficiency requirements.

Investigation of peel resistance during the fibre placement process

In this study, the influence of compaction load, layup speed and temperature on the adhesive properties of automated fibre placement grade towpreg has been investigated on the ply-tool interface where higher peel forces are required to permit the deposition of subsequent plies. The automated layup process was simulated on a CNC milling machine, using a roller assembly and the adhesion properties of the towpreg were determined using a floating roller peel test. The processing window for the towpreg was determined using a dynamic mechanical analyser and a two-level, full factorial design of experiments was developed for the three factors, to understand their effects on the peeling force, both individually and synergistically. The design of experiments analysis indicates a strong temperature effect, with the towpregs requiring a higher layup temperature to accommodate higher layup speeds. A strong load-temperature interaction was detected, with a negative temperature effect at lower loads and a strong positive temperature effect at higher loads. The predicted factor settings to achieve a peeling force of 246 N/m are, 1 kN compaction load, 65℃ layup temperature, and a layup speed of 120 mm/min. Experimental tests, carried out at the predicted factor settings, agree well with the analysis, yielding a peel force of 256 N/m with a standard deviation of 25 N/m.

Laser-powered tape placement process – simulation and optimization

The laser-assisted thermoplastic tape placement process for unidirectional carbon fiber reinforced polyetheretherketon (CF PEEK) tapes was investigated. In this process, tapes are melted, laid-up on a tool, and consolidated under a roller. As an out of autoclave process, thermoplastic tape placement has high potential for aerospace manufacturing industry. To optimize laser settings for high efficiency and reproducibility, a thermal simulation was created. Process windows are calculated based on critical process temperatures. A parameter study was conducted to investigate the influence of lay-up speed and laser settings, especially laser beam height and angle of impact, on the process. For different lay-up speeds, optimum values and limits of laser settings are found to gain autoclave quality with high material output and high reproducibility. Peel specimens have been produced to verify simulated optimum parameters, which showed good agreement. Economical potential of thermoplastic tape placement was shown in a direct comparison to thermoset tape placement.

Impact of layup rate on the quality of fiber steering/cut-restart in automated fiber placement processes

AbstractDeveloping reliable processes is one of the key elements in producing high-quality composite components using an automated fiber placement (AFP) process. In this study, both simulation and experimental studies were carried out to investigate fiber steering and cut/restart under different processing parameters, such as layup rate and compaction pressure, during the AFP process. First, fiber paths were designed using curved fiber axes with different radii. Fiber placement trials were then conducted to investigate the quality of the steered fiber paths. Furthermore, a series of sinusoidal fiber paths were fiber placed and investigated. Moreover, a six-ply laminate with cut-outs in it was manufactured in the cut/restart trials. The accuracy of the fiber cut/restart was compared at different layup rates for both one- and bi-directional layups. Experimental results show that it was possible to layup steered fiber paths with small radii of curvature (minimum 114 mm) designed for this study when the proper process condition was used. It was observed from the cut/restart trials that the quality of tow cut was independent of layup speed; however, the accuracy of tow restart was related to the layup speed. The faster the layup speed, the less accurate was the tow restart.

The Mechanics of Prepreg Conformance

Experiments are reported and mathematical models are developed to describe the me chanics of prepreg conformance to a substrate. Two distinctly different behaviors are identi fied for graphite epoxy prepregs, called: 1) pressure driven lay-up behavior, and 2) surface tension driven lay-up behavior. In the first case it is shown that there is a force-velocity superposition principle that applies to the lay-up parameters. In the second case, the ap plied force is unimportant. For both cases an upper bound on the lay-up speed is observed and mathematical models are developed to describe the phenomena. Reasons for the dif ferent behavior, and applications to lay-up of prepregs in machine tools are discussed.