Fused deposition modelling using direct extrusion

In the present work, a process based on the principle of polymer extrusion is developed: the extruder deposition process (EDP). This system uses a screw extruder to deposit the material on a computer-controlled positioning system to build components. Experiments (Box-Behnken technique is used for experimental design) are carried out to study the influence of three process variables: nozzle temperature, chamber temperature and road gap on bond strength (inter-road and interlayer) and surface finish. Surface roughness and ultimate tensile strength values are measured for test specimens. Analysis of variance (ANOVA) is used to determine the significance of process variables. It is concluded that the developed EDP eliminates many of the shortcomings of the systems developed based on the principles of extrusion and produces components having higher bond strength than that achieved in commercial fused deposition modelling (FDM) systems.     

Experimental investigations on fused deposition modelling of polymer-layered silicate nanocomposite

Polymer-layered silicate (PLS) nanocomposites exhibit enhanced mechanical and thermal properties when compared with pristine polymers and macrocomposites. Utilizing the benefits of PLS nanocomposite in the fused deposition modelling (FDM) process is of great significance. It could assist to overcome the limitations imposed by availability of materials in the FDM process; the need to widen the range of materials is critical in order to fabricate parts with improved mechanical properties. Experimental investigations were carried out on the development and processing of PLS nanocomposite for the FDM process. Organically modified montmorillonite and polymer pellets were used to develop the nanocomposite. The mechanical properties and mesostructure were investigated experimentally. The nanocomposite was utilised to produce filament and was found to be suitable for use in FDM. Significant improvements in mechanical properties, reduced porosity and better neck formation were observed for the developed nanocomposite which marks the material as a promising candidate for the FDM process. The developed nanocomposite may reduce the gap for availability of materials for FDM in terms of improved mechanical properties. The work will assist to promote low-cost FDM processed parts for direct applications.     

Parametric appraisal of mechanical property of fused deposition modelling processed parts

Fused deposition modelling (FDM) is a fast growing rapid prototyping (RP) technology due to its ability to build functional parts having complex geometrical shape in reasonable time period. The quality of built parts depends on many process variables. In this study, five important process parameters such as layer thickness, orientation, raster angle, raster width and air gap are considered. Their influence on three responses such as tensile, flexural and impact strength of test specimen is studied. Experiments are conducted based on central composite design (CCD) in order to reduce experimental runs. Empirical models relating response and process parameters are developed. The validity of the models is tested using analysis of variance (ANOVA). Response surface plots for each response is analysed and optimal parameter setting for each response is determined. The major reason for weak strength may be attributed to distortion within or between the layers. Finally, concept of desirability function is used for maximizing all responses simultaneously.     

Analysis of mechanical error in a fused deposition process using a stochastic approach

A stochastic model has been developed for studying the mechanical error in different rapid prototyping (RP) processes. Tolerances and clearances, which cause mechanical error, have been assumed to be random variables. The coordinates of a point on the work surface traced by the laser beam or the tip of the extruder head is expressed as a function of the random variables involved in the process. Using a unified approach for the RP processes, the mechanical error in the fused deposition process is analysed. In a numerical example, the mechanical error has been found for a grid of points traced by the nozzle tip. The three-sigma bands of the error in tracing example curves are plotted. This is the band in which the nozzle tips of 99.73% of machines, produced on a mass scale, lie for the given tolerances and clearances. Stringent values of tolerances and clearances reduce the error at the nozzle tip, but the cost of manufacturing and assembling the machines may become prohibitive.     

Fused glass deposition modelling for applications in the built environment

For the built environment and for engineers, glass is an indispensable material with unique properties. Recent developments have shown that there is a potential market for additive manufacturing technology in the building industry, based on the production with a relatively small amount of repetitions and the tendency of applying technological innovations for advanced buildings. This paper focusses on the potential of fusing glass filaments on a glass base plate in order to develop a scientific base to create a process that is able to print 3D glass on glass plates for applications in the building industry. These fused components could eliminate boreholes for joints in glass panes including related disadvantages. Also, the fused deposition glass components can be a potential reinforcement of flat glass. Therefore, the fusing of soda lime silicate glass and borosilicate glass has been investigated. Based on these experiences, samples with different glass thicknesses are manufactured and the fused components are tested for their bending strength. The manufactured samples are analysed with polarized images, 3D computer tomography, microscopy and energy dispersive X‐ray spectroscopy. This paper describes, presents and discusses the results of the investigations, and demonstrates that load transfer via fused glass joints is possible in principle.     

Modelling and estimation of tensile behaviour of polylactic acid parts manufactured by fused deposition modelling using finite element analysis and knowledge-based library

With the rise of the Fused Deposition Modelling (FDM) industry, a better understanding of the relationship between FDM process parameters and mechanical behaviour —especially tensile behaviour —of designed parts is needed to enable development of industry specifications. To optimise and control the deposition process, modelling and predicting the mechanical behaviour of a manufactured part under various process parameters is required. Existing numerical modelling approaches either require input of extensive experimental data or lack cross-validation. In this paper, the mechanical behaviour of polylactic acid manufactured parts under tensile conditions was studied both experimentally and numerically, and the effects of printing pattern and infill density on ultimate tensile strength (UTS)-weight ratio and the modulus of elasticity were evaluated. The experimental results revealed that minimising air gaps and using a triangular infill pattern are beneficial for obtaining a good UTS/weight ratio. Of all the specimens considered, the 20% triangular pattern had the highest UTS/weight ratio. The numerical investigation revealed that the meso-structure approach described in this paper can be used to predict the modulus of elasticity and the breaking point, and does not require input from the unidirectional specimen stress-strain curves. Finally, the meso-structure numerical model and artificial neural network were used to construct a knowledge-based library that can predict the modulus of elasticity of FDM manufactured polylactic acid with three infill patterns and any infill density with an average prediction error of 14.80%.     

Fused deposition modeling with polypropylene

This paper addresses the potential of polypropylene (PP) as a candidate for fused deposition modeling (FDM)-based 3D printing technique. The entire filament production chain is evaluated, starting with the PP pellets, filament production by extrusion and test samples printing. This strategy enables a true comparison between parts printed with parts manufactured by compression molding, using the same grade of raw material. Printed samples were mechanically characterized and the influence of filament orientation, layer thickness, infill degree and material was assessed. Regarding the latter, two grades of PP were evaluated: a glass-fiber reinforced and a neat, non-reinforced, one. The results showed the potential of the FDM to compete with conventional techniques, especially for the production of small series of parts/components; also, it was showed that this technique allows the production of parts with adequate mechanical performance and, therefore, does not need to be restricted to the production of mockups and prototypes.     

A review on composite materials and process parameters optimisation for the fused deposition modelling process

Fused deposition modelling is the most significant technique in additive manufacturing (AM) that refers to the process where successive layers of material are deposited in a computer-controlled environment to create a three-dimensional object. The main limitations of using fused deposition modelling (FDM) process in the industrial applications are the narrow range of available materials and parts fabricated by FDM are used only as demonstration or conceptual parts rather than as functional parts. Recently, researchers have studied many ways in order to increase the range of materials available for the FDM process which resulted in the increase in the scope of FDM in various manufacturing sectors. Most of the research are focussed on the composite materials such as metal matrix composites, ceramic composites, natural fibre-reinforced composites and polymer matrix composites. This article intends to review the research carried out so far in developing samples using different composite materials and optimising their process parameters for FDM in order to improve different mechanical properties and other desired properties of the FDM components.     

STEP-based approach for direct slicing of CAD models for layered manufacturing

Direct slicing can generate precise slice contours from original CAD models and obviates the error-detection and repairing process of STL files. At present, most direct slicing approaches are restricted to some CSG solids or particular CAD packages. In this paper, an approach for direct slicing of CAD models based on STEP for layered manufacturing is presented. The original CAD model is first transferred from CAD systems to the slicing system by neutral STEP files. Using OpenGL graphics libraries, the solid model is then displayed, and the user is prompted to specify the layer thickness. Finally, the CAD model is sliced directly, and the sliced model is exported by SSL (Stratasys Layer interface files) file format which can be sent to many kinds of layered manufacturing systems for direct fabrication. The approach of STEP-based direct slicing is more flexible and does not rely on any specific CAD system; in addition, the STEP files are much smaller than the STL files. Implementation details and results are also presented.     

Anisotropy in tensile properties and fracture behaviour of 316L stainless steel parts manufactured by fused deposition modelling and sintering

Fused deposition modelling and sintering (FDMS) is a potential metal additive manufacturing technology due to its low cost and high efficiency. The mixture of metal powder and binder goes through heating, extrusion, debinding and sintering processes to produce the compact finished part. However, it is generally believed that parts produced by FDMS possess poor and anisotropic tensile properties, which always attributes to the weak interlayer combination. The current work aimed to enhance tensile properties and better understand the anisotropic fracture behavior of the 316L stainless steel prepared by FDMS. By process optimization, the yield strength and ultimate tensile strength obtained in this work are increased by 26.1% and 15.2%, based on the highest performance reported in previous studies. According to the ultimate tensile strength, the performance difference between the horizontal and vertical directions has been reduced to 27%. Furthermore, the experimental results indicated that the clustered irregular shape holes evolved from primitive voids prefer to distribute in the build direction, resulting in anisotropic tensile performance. It is suggested that the mechanical properties could be improved by applying a smaller extrusion diameter and rolling-assisted printing. In addition, the current FDMS parts show qualified performance for producing the customized and small batch components.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00402-4     

Dynamic behaviour of high strength steel parts developed through laser assisted direct metal deposition

High strength steel alloys are good candidates for many engineering applications particularly those involving high strains and impact loads. Such applications in energy absorption devices require materials that can sustain dynamic loading and remain strong under demanding conditions. But the processing cost of these alloys has been a prohibitive factor, thus re-enforcing the research on porous and cellular structures made of stainless steels. Direct metal deposition (DMD) is a process which employs the power of a CO₂ laser to melt and deposit metallic powders onto steel substrates. Such structures offer advantages of creating novel configurations only by computer control of laser “tool path”. This research investigates the mechanical behaviour of solid and porous parts with prismatic cavities under quasi-static and dynamic compressive loading. Apart from two main deficiencies of relatively large variations of properties among the test specimen and sufficiently low modulus of elasticity, the stress strain behaviour is very close to the commercial grades of stainless steel produced by rolling and forming. The energy absorption behaviour of porous specimen is also very encouraging and renders DMD as a suitable process for manufacturing of customized sandwich and graded structures that can be used as a substitution for many engineering applications such as monolithic compression plates and explosion shields.     

Effect of chemical treatment on tensile strength and surface roughness of 3D-printed ABS using the FDM process

Fused deposition modelling (FDM) is one of the most commonly used additive manufacturing processes because of its environment-friendly nature and cost-effectiveness. However, it suffers badly from low surface quality due to a larger layer resolution. The surface finish of FDM parts can be enhanced by post chemical treatment using various solvents. The chemical treatment reduces the surface roughness by dissolving the external surfaces of 3D-printed samples. Chemical treatment is an easy, fast and economical technique. In the present investigation, the effect of chemical treatment on surface roughness and tensile strength of acrylonitrile butadiene styrene (ABS) parts made using the FDM process is investigated using two chemicals, namely acetone and 1, 2 dichloroethane. The post chemical treatment dramatically improves the surface finish and dimensional accuracy of ABS specimens. But chemical treatment results in the reduction of the tensile strength. Better tensile strength is obtained while using acetone solvent and a better surface finish is obtained using dichloroethane.     

Optimization of process parameters in fused deposition modelling of thermoplastics: A review

Among the several techniques for additive manufacturing (AM), fused deposition modelling (FDM) is widely used. Fused deposition modelling process uses a thermoplastic material, which is melted and then extruded layer by layer through a nozzle, in order to create a three-dimensional object. As a result of the default setting of process parameters provided by the manufacturers, produced parts normally have a poor surface finish, low mechanical properties, low dimensional accuracy, and increased residual stresses compared to the parts produced using conventional manufacturing processes like molding (casting). Qualities of fused deposition modelled (FDMed) parts are generally affected by process parameters including the layer thickness, extrusion temperature, build orientation, printing speed, raster angle, infill density, raster width, nozzle diameter, and air gap. Increasing infill density, printing temperature, and decreasing print speed and layer thickness lead to increase mechanical strength and improve the surface finish of the printed parts. The optimal process parameters are preferred to achieve superior properties of the parts. This paper reviews the optimal fused deposition modelling process parameters on part qualities for making the stability of used deposition modelled parts for use. Various process parameters are identified in order to obtain desirable qualities in the manufactured parts. Areas for future research are proposed.     

In-process thermal treatment of polylactic acid in fused deposition modelling

Polylactic acid (PLA) is one of the most widely used open source fused filament fabrication materials due to its ease of extrusion, biodegradability, and mechanical strength. The mechanical strength of PLA largely depends on the proper growth of its semi-crystalline structure, which can be severely impaired by a low rate of crystallization, particularly in open source printers. This can be further aggravated by the non-uniform thermal distribution of heat that causes improper curing among the extruded beads of the printing material. As a result, PLA printed on open source printers does not achieve the best mechanical properties. This research, for the first time, proposes an additive-free solution implemented through a detailed set of experimentation to improve the curing rate through in-process temperature variations to cure the joints among the beads. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy is used to confirm the improvements in the bead joints. This work is conducted in two phases of experiments. In the first phase, a full factorial ANOVA is used to investigate various process parameters and the important variables are used in the second phase to print test specimens in four different sets.     

Experimental and numerical investigation of the thermal behaviour of polylactic acid during the fused deposition process

Fused deposition modelling (FDM) has become the most popular additive manufacturing process worldwide since the early 2000s. However, limited understanding of its deposition process greatly hinders the future growth of the technology. In order to optimise and control the deposition process, modelling and predicting the thermal behaviour change of the material during such a process is required. In this paper, the thermal behaviour of FDM process was studied both experimentally and numerically; effects of nozzle temperature, platform temperature, extrusion speed, and layer thickness on effective diffusion time, maximum vertical distortion, and maximum thermal stress were evaluated. It is shown that the developed simulation model could predict the effective diffusion time with the error of less than 13% in 6 out of 9 experimental conditions, relatively lower than the existing simulation and theoretical prediction models. Both the experimental and numerical results suggested that polylactic acid would have the longest diffusion time at high nozzle temperature, high platform temperature, low printing speed, and high layer thickness. And the numerical model revealed that reducing extrusion temperature, slowing printing speed, decreasing layer thickness are beneficial of reducing the vertical distortion and residual thermal stress.     

Estimation of reliability and validity of agility constructs using structural equation modelling

The main objective of this study was to create an agile manufacturing (AM) model and to validate the model using structural equation modelling (SEM). AM concentrates on turbulent market changes and the responsive actions of the manufacturing firm, in terms of process, tooling, material and trained experts. The AM model consists of five major drivers of agility, namely the workforce, manufacturing management, manufacturing strategy, manufacturing technology and organisational structure. After development of the AM model, a questionnaire was prepared and data collected from 30 automotive organisations located in Tamil Nadu, India. After data collection, the SEM approach was used to conduct a statistical validation. The results indicate the validity and reliability of AM constructs.     

On direct laser deposited Hastelloy X: dimension,surface finish,microstructure and mechanical properties

Abstract

For the first time, the influence of laser power, scan speed, scan spacing and nominal laser power density on the tensile properties, dimensional accuracy, surface roughness, number of cracks and top surface concavity of samples of Hastelloy X manufactured using a laser powder bed facility, has been assessed systematically on three-dimensional samples. It has been found that the nominal laser power density is the dominant factor, but the influence of scan spacing and scan speed can sometimes be significant. Density of >99·5% can be obtained using most conditions. Cracks are observed at corners of the samples. An optimised process window can be derived from the above systematic analysis under which the component can be built smoothly, with good surface finish and dimensional accuracy, consistent mechanical properties and the properties are comparable with those of forged products.     

Effects of direct metal deposition combined with intermediate and final milling on part distortion

ABSTRACT

Combining direct metal deposition and milling in one machine promises the additive fabrication of complex parts with a high surface quality and dimensional accuracy. However, residual stress induced by the additive process can impair the final part shape after finishing. Undercuts and inaccessible areas are particularly prone to distortion since they require intermediate milling steps during buildup. Herein, strategies to reduce residual stress by process optimisation are discussed and demonstrated. The effects of intermediate and final milling on dimensional accuracy are analysed for the fabrication of a distortion-critical beam from stainless steel. 3D scans reveal that additive buildup on a semi-finished part causes local warpage of milled surfaces, resulting in deviations in length that are by factor 10 higher than the milling accuracy. Global distortion of the substrate plate is significant, but the milling sequence itself has finally no considerable influence.     

Energy and material flow modelling of additive manufacturing processes

Additive manufacturing (AM) processes allow fabrication of three-dimensional complex parts. Due to the exact amount of material used during the manufacturing step, these new manufacturing processes offer great opportunities for sustainable manufacturing. However, existing studies on these processes focus mainly on energy consumption and information about resources consumptions and waste flows are still lacking. This study aims to quantify with accuracy inventory data of AM processes during the manufacturing step of the life cycle of products. In order to accurately assess the environmental impact of a product, a generic method for acquisitions and characterisation of inventory data for parts made by AM processes is proposed. This methodology focuses not only on the electrical energy consumption but also on material consumption. This paper also describes the development of a parametric process model, which provides to an operator, an accurate estimation of the environmental performances of the fused deposition modelling process.     

Effect of substrate cooling on the epitaxial growth of Ni-based single-crystal superalloy fabricated by direct energy deposition

The columnar-to-equiaxed transition(CET)or the formation of stray grains in the laser melting deposition is the least desirable for the repair of single-crystal blades.In this work,the forced water-cooling was conducted on a single-crystal Rene N5 substrate during the direct energy deposition(DED).The single track remelting,one-layer,two-layer,and eight-layer depositions were investigated to explore the grain growth mechanism.The solidification conditions of the DED process,including temperature field,temperature gradient,and solidification speed,were numerically analyzed by a finite element model.The single-track remelting results showed that the fraction of columnar crystal regions increases from55.81%in the air-cooled sample to 77.14%in the water-cooled one.The single-track deposits of one-and two-layer have the same trend,where the proportion of columnar crystal height was higher under the forced water-cooled condition.The electron backscattered diffraction(EBSD)grain-structure maps of an eight-layer deposit show that the epitaxial growth height increases from 1 mm in the air-cooling sample to 1.5 mm in the water-cooling one.The numerical results showed that the tempe rature gradient in[0011 direction was significantly increased by using forced water-cooling.In conclusion,the in-situ substrate cooling can become a potential method to promote epitaxial growth during DED via the influence on CET occurrence.