Fused Layer Modeling Research Articles

Adhesion Studies during Generative Hybridization of Textile-Reinforced Thermoplastic Composites via Additive Manufacturing.

Generative hybridization enables the efficient production of lightweight structures by combining classic manufacturing processes with additive manufacturing technologies. This type of functionalization process allows components with high geometric complexity and high mechanical properties to be produced efficiently in small series without the need for additional molds. In this study, hybrid specimens were generated by additively depositing PA6 (polyamide 6) via fused layer modeling (FLM) onto continuous woven fiber GF/PA6 (glass fiber/polyamide 6) flat preforms. Specifically, the effects of surface pre-treatment and process-induced surface interactions were investigated using optical microscopy for contact angle measurements as well as laser profilometry and thermal analytics. The bonding characteristic at the interface was evaluated via quasi-static tensile pull-off tests. Results indicate that both the bond strength and corresponding failure type vary with pre-treatment settings and process parameters during generative hybridization. It is shown that both the base substrate temperature and the FLM nozzle distance have a significant influence on the adhesive tensile strength. In particular, it can be seen that surface activation by plasma can significantly improve the specific adhesion in generative hybridization.

Systematic development of load-path dependent FLM-FRP lightweight structures

Abstract Additive manufacturing offers a high degree of design freedom. When Design for Additive Manufacturing is conducted properly, lightweight potential can be exploited. This contribution introduces a novel design approach for the widespread fused layer modelling (FLM) technology when using orthotropic Fibre Reinforced Polymer filament. Its objective is to obtain stiff and strong load-path optimized FLM structures in a structured and algorithmic way. The approach therefore encompasses (1) build orientation optimization to consider weaker bonding between layers than intralayer; (2) topology optimization with orthotropic material properties to obtain favourable overall geometry and inner structure; (3) direct build path generation from optimized material orientation and alternatives to the direct generation and (4) simulation. The approach is demonstrated using a lift arm under multiple load cases and further demonstrator parts to show its general applicability. Lightweight potential of individual optimization steps and the influence of modifications contrasting general non-FLM-specific optimization are studied and discussed.

Investigation of Process Control Influence on Tribological Properties of FLM-Manufactured Components

In recent years, additive manufacturing methods such as Fused Layer Modeling have been continuously improved by industry and research institutions. In many cases, the influence of process control on the mechanical component properties is being investigated. Influencing parameters include the infill and its orientation as well as patterns. Extrusion parameters such as the volume flow, which can be influenced by the speed, the line width, and the layer thickness, and the temperatures, which determine the interlaminar bonding between the lines and layers, are relevant as well. In this contribution, the influence of process control on the tribological properties of cylindrical tribo-test specimens made of polybutylene terephthalate is investigated. Using a reciprocating pin-on-plate tribo-tester, the static and dynamic friction forces as well as the linear wear is determined. The results show a significant influence of the orientation and density of the infill on the tribological properties. Due to the process-specific large degrees of freedom, the advantage of a load-compatible individualisation and consequently the optimisation of tribologically exposed components is given compared to conventional manufacturing processes.

Comparing mechanical properties of impact modified polypropylene-copolymer (IMPP) from injection molding (IM) and fused layer modeling (FLM) processes

Purpose The purpose of this study was to produce dimensionally accurate and reliable fused layer modeling (FLM) feedstock composed of an impact modified polypropylene matrix, compounded with a cellulose nanofiber (CNF) reinforcement and coupled by a maleic anhydride coupling agent to produce comparable mechanical properties in comparison to the industry-standard method of injection molding (IM). Design/methodology/approach A spray dried CNF (SDCNF) was compounded with the polymer matrix using a masterbatch method. The composite was diluted with neat polymer and extruded into a filament and then printed into standardized mechanical testing samples. For comparison, the filament was chopped and standardized samples were produced with IM. Findings A loss in mechanical properties of up to 30% was observed in FLM samples. If normalized to reflect improved density from a part consolidation method, losses are reduced to 15% or show improvements in the neat polymer matrix. Originality/value Limited research has been done on producing FLM feedstock, reporting mechanical property results based on standardized testing and comparing the same material with IM.

Additive Manufacturing of Steel and Copper Using Fused Layer Modelling: Material and Process Development

AbstractFused Layer Modelling (FLM) is one out of several material extrusion (ME) additive manufacturing (AM) methods. FLM usually deals with processing of polymeric materials but can also be used to process metal-filled polymeric systems to produce metallic parts. Using FLM for this purpose helps to save costs since the FLM hardware is cheap compared to e.g. direct metal laser processing hardware, and FLM offers an alternative route to the production of metallic components.To produce metallic parts by FLM, the methodology is different from direct metal processing technologies, and several processing steps are required: First, filaments consisting of a special polymer-metal composition are produced. The filament is then transformed into shaped parts by using FLM process technology. Subsequently the polymeric binder is removed (”debinding”) and finally the metallic powder body is sintered. Depending on the metal powder used, the binder composition, the FLM production parameters and also the debinding and sintering processes must be carefully adapted and optimized.The focal points of this study are as following:1. To confirm that metallic parts can be produced by using FLM plus debinding and sintering as an alternative route to direct metal additive manufacturing.2. Determination of process parameters, depending on the used metal powders (steel and copper) and optimization of each process step.3. Comparison of the production paths for the different metal powders and their debinding and sintering behavior as well as the final properties of the produced parts.The results showed that both materials were printable after adjusting the FLM parameters, metallic parts being produced for both metal powder systems. The production method and the sintering process worked out well for both powders. However there are specific challenges in the sintering process that have to be overcome to produce high quality metal parts. This study serves as a fundamental basis for understanding when it comes to the processing of steel and copper powder into metallic parts using FLM processing technology.

Analysing the influence of raster angle, layer thickness and infill rate on the compressive behaviour of EVA through CNC-assisted fused layer modelling process

The current study analyses the compressive behaviour of ethylene vinyl acetate specimens processed through extrusion-based additive manufacturing. The compression specimens have been fabricated using an in-house developed fused layer modelling process. Response surface methodology technique has been adopted to generate the experimental runs by selecting raster angle, layer thickness and infill percentage as input process parameters. Further, analysis of variance has been used to analyze the obtained compression data. The infill percentage is found to be the most significant parameter for compressive strength; however, raster angle has shown an insignificant effect. The empirical relation has been established between the selected input process parameters and compressive strength. The predicated and experimental results have also been compared to validate the derived empirical model. Results showed good conformity.

Effects of the infill pattern on mechanical properties of fused layer modeling (FLM) 3D printed wood/polylactic acid (PLA) composites

In this paper, possible influences of various infill orientations (deposition angles) on specific material characteristics—such as tensile strength, compressive strength, charpy impact strength and heat deflection temperature (HDT)—of fused layer modeling (FLM) processed test specimens were evaluated. Two specially made wood filaments, made of the same polylactic acid (PLA) polymer but two different wood fiber contents, were used for sample manufacturing and evaluated as a function of fiber content as well as infill orientation. In the context of the wood fiber content, formulations containing 15 wt. % as well as 25 wt. % of fibers were examined. In connection with infill orientation, the influence factor of seven FLM 3D printing infill orientations (deposition angles)—in particular 0°, 15° crossed, 30° crossed, 45° crossed, 60° crossed, 75° crossed and 90°—on several material properties was investigated. It could be proven that there is a direct interaction between the infill orientation (deposition angle) and the resulting mechanical performance of the test specimens. This is not exclusively a direct correlation, but there is a mutual dependency. Apart from that, the analysis showed that the higher the fiber content in the filament, the higher the resulting mechanical properties.

Active thermography for quality assurance of 3D-printed polymer structures

ABSTRACT Additively manufactured test specimens made of polyamide 12 (PA 12) by Laser Sintering as well as of acrylonitrile butadiene styrene (ABS) by Fused Layer Modelling, were characterised with active thermography directly after manufacturing and after artificial weathering. For this, two different excitation methods (flash and pulse heating) were used and compared, regarding their suitability for the detection of constructed and imprinted defects inside the test specimens. To increase the quality of the thermograms, data processing methods like thermal signal reconstruction (TSR) and Fourier Transformation after TSR were applied. To further investigate the long-term stability of the additively manufactured test specimens towards environmental stress, like UV radiation, heat, humidity, water contact and frost with active thermography, an artificial weathering test over 2000 hours (~3 months) was applied to the specimens. The monitoring of the changes in the optical properties of the weathered plastics was supplemented by spectral reflectance and UV/VIS spectroscopy.

Single-step Laser Plastic Deposition (LPD) using a near-infrared Thulium fiber-laser

Additive Manufacturing of thermoplastic polymers is typically carried out using techniques such as Selective Laser Sintering (SLS) or Fused Layer Modeling (FLM), both of which require the use of support structures that have to be removed after the production process. The laser welding of thermoplastic polymers using laser sources with a wavelength of around 1 μm and thus also Direct Selective Laser Melting (SLM) in the same wavelength spectrum requires the admixing of additives such as carbon black in order to improve the absorption of laser light within the polymer and hence poses an additional process step that has to be performed. Laser sources like Thulium fiber-lasers with a wavelength of around 2 μm enable the absorber-free welding of thermoplastic polymers and therefore promise to be a new source for the SLM of thermoplastic polymers as well as a possible adaption of the known Laser Metal Deposition (LMD) to plastics, the so called „Laser Plastic Deposition“ (LPD).In the present paper, the feasibility of a single-step LPD process using irradiation of a 1,94 μm Thulium fiber-laser is investigated through the manual deposition of unfilled and absorber-free polyamide-12 powder on polyamide-6 substrates. Powder material and the created structures are characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). In addition to that, optical microscopy and computer tomography analysis (CT) are carried out and discussed for the created LPD structures. From the experiments, it is to be concluded that a single-step LPD process can be carried out using a 2 μm Thulium fiber-laser.

“Improving the impact strength of PLA and its blends with PHA in fused layer modelling ”

Abstract Poly-(lactic acid) (PLA) is one of the most popular thermoplastics for fused layer modelling (FLM). Due to its semi-crystalline nature, the influences of printing parameters on the properties of the printed part are more complicated than with amorphous thermoplastics like acrylonitrile-butadiene-styrene (ABS). In present study, the influence of the process parameters, such as temperature of the plate as well as printing angle used for the three-dimensional printing process was studied in the case of virgin PLA. In addition, PLA was mixed with an amorphous polyhydroxyalkanoate (PHA) copolymer with the aim to improve its impact properties. Mechanical performance of virgin PLA and its PLA/PHA blend prepared by 3D printing method was compared with the mechanical performance of the parts produced by injection moulding. Small and wide angle X-ray measurements were performed in order to study the influence of the crystal morphology on the mechanics of PLA and PLA/PHA 3D printed as well as injection moulded parts. The PLA/PHA parts produced by 3D printing showed higher impact strength and notched impact strength values than injection moulded parts.

Generating Permanent and Temporary Material Compounds in FLM Processes

Like all additive manufactured parts, FLM (fused-layer-modeling) components are characterized by a large number of joints between the similar and different materials. These joints can be divided into five categories:- Permanent cohesive bonds between single layers of the same thermoplastic material,- Permanent adhesive bonds between single layers of different thermoplastic materials- Temporary adhesive bonds between single layers of different thermoplastic materials,- Permanent adhesive bonds between a single layer of thermoplastic material and a non-thermoplastic base material,- Temporary adhesive bonds between a single layer of thermoplastic material and a non-thermoplastic base material.The first three types of bonds describe the binding process when parts are manufactured of base material, a second permanently bonded component or a support material that has good release properties. The last two types of connection describe the permanent connection between the printing part and a non-FLM-component or the temporary joint between the printed part and the build platform during the printing process. The resulting compounds can be characterized as material compounds.Since the FLM process is mainly used for design and hobby applications, the fundamentals of the bonding processes and their influence on the internal structure of the material are hardly described. Some information can be taken from the literature for welding plastics and the production of hybrid parts by injection molding. Due to the different pressure and temperature conditions as well as the very large surface-volume-ratio of the discharged strand occur significant differences in the following factors: melt flow, solidification time, formation of surface layers and wetting of the surfaces.The investigation and characterization of these effects as a function of external process parameters is an important constituent for the further development of the FLM process into an industrially suitable manufacturing process for thermoplastic components with very high lightweight and complex geometry in small series etc.

Influence of High, Disperse API Load on Properties along the Fused-Layer Modeling Process Chain of Solid Dosage Forms.

In order to cope with the increasing number of multimorbid patients due to demographic changes, individualized polypill solutions must be developed. One promising tool is fused layer modeling (FLM) of dosage forms with patient-specific dose combinations and release individualization. As there are few approaches reported that systematically investigate the influence of high disperse active pharmaceutical ingredient (API) loads in filaments needed for FLM, this was the focus for the present study. Different filaments based on polyethylene oxide and hypromellose (HPMC) with different loads of theophylline as model API (up to 50 wt.%) were extruded with a twin-screw extruder and printed to dosage forms. Along the process chain, the following parameters were investigated: particle size and shape of theophylline; mechanical properties, microstructure, mass and content uniformity of filaments as well as dosage forms and the theophylline release from selected dosage forms. Especially for HPMC, increasing theophylline load enhanced the flexural strength of filaments whilst the FLM accuracy decreased inducing defects in microstructure. Theophylline load had no significant effect on the dissolution profile of HPMC-based dosage forms. Therefore, a thorough analysis of particle-induced effects is necessary to correlate mechanical properties of filaments, printability, and the dosage-and-release profile adjustment.

PREDICTION OF THE SHAPE ACCURACY OF PARTS FABRICATED BY MEANS OF FLM PROCESS USING FEM SIMULATIONS

The prediction of component properties from the Additive manufacturing (AM) process poses a challenge. Therefore, this paper presents the development of a novel machine data (G-Code) based procedure as well as its programming implementation of a process simulation in ANSYS Mechanical for the fused layer modelling (FLM) process. For this purpose, an investigation of additively produced components with varying parameters made of polylactic acid (PLA) is carried out and simulated by means of the developed method. Application of the developed method makes it possible to predict the thermally induced distortion of PLA-Parts based on the machine data from the FLM process before production.

Investigation of FLM materials for application in high-temperature and high-vibration automotive environments

Currently, long-term application of additively manufactured parts in automotive environments is hindered by insufficient data on their behavior under harsh temperature and vibration conditions. Providing additional knowledge on the material behavior, new possible applications can be investigated. To gain this information, tests at increasing temperatures for tensile specimens of various FLM (Fused Layer Modeling) materials in three manufacturing orientations have been conducted. Furthermore, the long-term fatigue behavior of an exemplary material has been investigated. With the results a first indication for the material selection, manufacturing- and mounting-orientation of FLM parts for application in high-temperature and high-vibration environments is provided.

Investigation on the effects of process parameters in CNC assisted pellet based fused layer modeling process

A new CNC assisted pellet-based fused layer modeling (FLM) process has been presented. It allows the fabrication of highly flexible parts which is not easily possible through the fused filament fabrication (FFF) process as buckling occurs when the flexible filament is fed into liquefier head. Instead of the filament, the presented FLM process utilizes the material in pellet form. The FLM process is different from the other extrusion based AM processes and has its own characteristics. Therefore, the current paper presents a parametric investigation in the developed FLM process by considering the ethylene vinyl acetate (EVA) material. Experiments have been conducted using the ‘one factor at a time’ (OFAT) approach. The effects of barrel temperature, bed temperature, screw speed, deposition speed, standoff distance between nozzle and bed surface have been studied on the melt flow rate, layer thickness and road width. The obtained results showed that the melt flow rate of EVA is increased with the increase in the screw speed and barrel temperature. A significant variation of approximately 27% was observed in the layer thickness with the change in the deposition speed and standoff distance. A decrease of 42.42% was observed in the road width when the standoff distance was reduced from 2 to 0.8 mm. Based on the investigation, a set of suitable process parameters was obtained to fabricate the flexible parts of the EVA material. The outcomes of the current study showed that the developed FLM process has the capabilities of fabricating parts utilizing a set of suitable process parameters.

Additive manufacturing of flexible electrically conductive polymer composites via CNC-assisted fused layer modeling process

The applications of electrically flexible conductive polymer composites are rapidly growing over the time due to their widespread use in fabrication of health monitoring devices, sensors, and flexible displays fabrication, etc. Various techniques have been explored to develop electrically conductive polymer composites. In the recent past, fused deposition modeling (FDM) process has been gained tremendous attention to fabricate electrically conductive parts considering rigid polymers along with conductive filler particles. This allows to avail all advantages and benefits of additive manufacturing in the fabrication of complex electrically conductive parts. However, FDM process faces challenges of filament buckling while fabricating flexible parts. Hence, there is need to develop an economically viable and simplified process to fabricate the flexible electrically conductive polymer composite objects. In the present study, fabrication of flexible electrically conductive polymer composite objects has been attempted by developing a novel CNC assisted fused layer modeling process. The developed process uses the material in pellet form instead of a filament, which eliminates the issues of filament buckling and allows flexible object fabrication. The ethylene vinyl acetate (EVA) and graphite (Gr) particles have been used as the polymer matrix and conductive filler material respectively. Solvent and melt blending techniques have been employed to develop EVA/Gr composites. Three-dimensional flexible electrically conductive objects have been fabricated successfully. The experimental result shows the remarkable improvements in electrical conductivity of EVA polymer by incorporation of graphite particles. The outcome of the presented approach may help to fabricate flexible electrically conductive complex structures for soft robotics and electronics applications.

Effect of fused layer modeling (FLM) processing parameters on impact strength of cellular polypropylene

Fused layer modeling (FLM) or fused deposition modeling (FDM) can be used to produce polymer components with a cellular structure. The existence of cells (voids) in FLM parts degrades mechanical properties. This study was done to understand the influence of two printing parameters, layer height (0.1 mm and 0.3 mm) and extrusion temperature (200 °C and 250 °C), on the Izod impact strength of polypropylene (PP). Morphological analysis showed that smaller layer height and higher extrusion temperature generally resulted in smaller cell size but larger cell density. Printed PP components were lighter than injection molded PP parts. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses confirmed that both α and β type crystals existed in printed PP. PP printed at 250 °C had lower impact strength while components printed at 200 °C had similar impact strength to injection molded PP.

FEM based evaluation of Fused Layer Modelling monolayers in tensile testing

In a previous work, dumbbell specimens were shown to be inadequate for the tensile testing of Additive Manufacturing monolayers. Finite Element Method (FEM) has been used in this contribution for comparing tensile-stress distributions in both conventional and rectangular samples. Different extrusion paths for the manufacturing via Fused Layer Modelling (FLM) were taken into account. The calculations showed stress concentrations in the dumbbell type specimens in the zone of variable width away from the gauge length. The results were used for explaining the differences between mechanical behavior of dumbbell and rectangular specimens made with FLM from Poly-Lactic Acid (PLA). The mechanical behavior in the experiments closely matches the FEM results. At least 20 % of the tested dumbbell specimens fractured away from the gauge length, compromising the resulting tensile strength data. Rectangular tensile test specimens are proposed as a better alternative.

Investigation of a New Approach for Additively Manufactured Continuous Fiber-reinforced Polymers

First additive manufacturing processes (AM) for the production of fiber reinforced plastics (FRP) have been developed, which use Fused Layer Modelling (FLM) processes by implementing the fibers into the matrix material prior to extruding or within the nozzle. A method for implementing the fibers outside of the printing nozzle and outside of the thermoplastic filaments directly into the part while it is being manufactured has not yet been analyzed properly. This study shows the gain in tensile strength and Young's modulus for different implementation methods of glass and carbon fibers on the building platform.

An Architecture for Hybrid Manufacturing Combining 3D Printing and CNC Machining

Additive manufacturing is one of the key technologies of the 21st century. Additive manufacturing processes are often combined with subtractive manufacturing processes to create hybrid manufacturing because it is useful for manufacturing complex parts, for example, 3D printed sensor systems. Currently, several CNC machines are required for hybrid manufacturing: one machine is required for additive manufacturing and one is required for subtractive manufacturing. Disadvantages of conventional hybrid manufacturing methods are presented. Hybrid manufacturing with one CNC machine offers many advantages. It enables manufacturing of parts with higher accuracy, less production time, and lower costs. Using the example of fused layer modeling (FLM), we present a general approach for the integration of additive manufacturing processes into a numerical control for machine tools. The resulting CNC architecture is presented and its functionality is demonstrated. Its application is beyond the scope of this paper.