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Purpose Over the past few years, the number of related research to additive manufacturing (AM) has risen. The selective composite formation (SCF) can also be found among the new technologies that were developed. This technology was first introduced in 2013, and because of its innovative character, there are still many challenges to be overcome. Therefore, the main aim of this study is to present a finite element method which allows to investigate the processing of the material during the selective formation of a composite material based on cellulose and acrylic. Design/methodology/approach In the beginning, we introduced a brand new finite element method approach which is based on light transmittance network and photopolymerisation in transient state. This method is mainly characterised by internal light absorption, transversal reflectance, light transmittance coefficient and photopolymerisation kinetics. The authors defined experimentally the main model coefficients besides investigating the formation of composite material in six case studies. The main variables evaluated in those studies were the number of layers and the number of lines. By the end, the degree of polymer conversion and the preliminary evaluation of adherence between layers were identified in addition to the formation profile of composite material. Findings The presented method evidence that the SCF resulted in a profile of polymerisation which is different from profiles found in vat polymerisation processes. It was shown that the light diffraction increases polymerisation area to outside of laser limits and reduces the penetration depth. It was also exposed that the selective formation of composite material on the top layer interferes with the polymerisation of previous layers and might increase the polymerised area in about 25 per cent per layer. By the end, adherence between layers was evidenced because of a high-pass filter that limited polymer conversion to over 60 per cent. In this case, the adherence between the top layers was provided by the interface between layers, while the deeper layers resulted in a solid formed by composite. Originality/value This paper presents research results related to a very new AM technology and also proposes a new method to characterise this concept. Because of this new analytic approach, the process planning can be simulated and optimised, in addition to being a useful tool for other researches related to photocurable polymers and AM technologies.

Purpose– The purpose of this study is to present a novel additive manufacturing (AM) technology which is based on selective formation of cellulose-acrylate composite. Besides proposing a process that combines the benefits of fibres and photopolymers, this paper reports the development of material, characterisation of a straight line composite formation, adherence between layers and functional feasibility of the proposed concept.Design/methodology/approach– For the preliminary evaluation of the proposed process, a composite material based on cellulose-photopolymer was developed, while a multi-objective optimisation study indicated the formulation which results in the maximum values of layer adherence, tensile strength of composite and the effect of the water on the mechanical strength of material. For the characterisation of the process, three main subjects were analysed: the characterisation of straight line composite formation, the effect of composite formation process on previous layers and the functional feasibility of technology.Findings– In the material development, the tensile strength of dry composite was identified between 20 and 30 MPa, while the tensile strength of wet composite was between 5 and 12 MPa. It is important to note that the dry and wet cellulose presented tensile strength, respectively, equal to 15 and 1 MPa, indicating the possibility of residual material removal only with the use of water or other soft solvent. The values of adherence between layers (peeling test) were found to be between 0.12 and 0.15 kgf, and the photopolymer formulation which resulted in the maximum adherence has monomer/oligomer ratio equal to 1.5 and 2 per cent wt of photoinitiator percentual. As result of the optimisation study, the material formulation was compounded by monomer – 10 ml, oligomer – 4.5 ml and photoinitiator – 2 per cent, being found suitable to characterise and evaluate the proposed process. The study of composite formation along a straight line showed values of line width between 1,400 and 3,500 μm in accordance with light power, laser velocity and laser beam diameter. On the other hand, the number of previous layers affected by the composite formation varied from 0 to 4, indicating a potential process limit. In the functional feasibility study, a feasible process window which resulted in the maximum dimensional deviation equal to 0.5 mm was identified. In addition, the mean mechanical tensile strength was found to be around 30 MPa for longitudinal laser trajectory (90°) and 15 MPa for transversal laser trajectory (0°), highlighting the anisotropic behaviour of final parts according to the manufacturing strategy.Originality/value– This paper proposed a novel AM technology and also described studies related to the characterisation of this concept. This work might also be useful to the development of other AM processes and applications.

PurposeOver the last several years, the range of applications of photopolymerization process has been steadily increasing, especially in areas such as rapid prototyping, UV inks, UV coats and orthodontic applications. In spite of this, there are still several challenges to be overcome when the application concerns materials with thick layers. In this context, the main goal of this work is to outline a scheme to optimize the process of photopolymerizarion for thick layers, identifying its differences in relation to those applicable for thin layers.Design/methodology/approachFor this research, the authors have applied multivariable analysis methods which allow the identification of principal conclusions, based on analytical and experimental results. For analytical analysis, the authors applied numerical optimization for multivariables, while experimental analysis was done based on design of experiments. Both the analyses were based on methyl methacrylate as monomer and Omnirad 2500 as photoinitiator, with the adjustable variables being initiator concentration; power of light source; light wave length; and thickness of layer. The range of values chosen for initiator concentration was between 1 and 10 per cent, while for light power, the range was 5‐9 W. For light wave length, the authors selected 325 and 400 nm as limits for their study and 0.12 and 4 mm as the range for thickness of layers. For the analytical approach of their study, it was possible to identify optimum conditions for curing thick layers, besides looking at optimum condition at each step along the varying thickness. On the other hand, in the experimental approach, the authors just considered the initiator concentration and thickness as variables, applying gravimetric and photometric analysis to determine the conversion curve of material.FindingsIn conclusion based on these studies, it was possible to identify the influence of thickness and initiator concentration as function of penetration depth, polymerization rate and homogeneity of material, in addition to determining the effect of light power and light wave length over the process. As a result of these studies, it was possible to identify situations wherein the material will possibly undergo a high degree shrinkage in addition to showing consequences of high quantity of initiator. On the other hand, low concentration of initiator is shown to provide more homogeneous solution besides being more suitable for deep layers. It was also possible to compare analytical and experimental results, making it possible to predict the behaviour of material for other conditions.Originality/valueThe main value of this work is to show the possibility of optimizing photopolymerizable systems through an analytical approach. In addition, it emphasized the viability of the application of UV curable material for producing moulded parts.

PurposeAs a result of the increased number of applications for additive manufacturing technologies and in addition to the demand for parts produced with high accuracy and better quality, the need for the improvement of positioning and precision equipment in manufacturing has become evident. To address this needed improvement, the main goal of this work is to provide a systematic approach for designing additive manufacturing machines, allowing the identification of the relationship between estimated errors and the cost of equipment. In the same way, this study also intends to indicate a suitable configuration of a machine as a function of final accuracy and total equipment cost.Design/methodology/approachTo identify the suitable elements of the machine, a numerical model that estimates the final error and relative cost of equipment as a function of cost and tolerance of the machine elements was constructed and evaluated. After evaluating this model by comparing it with first‐generation fused deposition modelling (FDM) machines, an optimisation study was performed that focused on the minimisation of both the total cost and final equipment error. The optimisation problem was defined in accordance with the goal attainment method, which allowed identification of the Pareto optimum of the study. The optimisation results were then compared with current equipment concepts, and possible improvements and restrictions of the optimised concept were described.FindingsWith regard to the evaluation of the numerical model of final error, the general error in the x‐ and y‐direction was observed to have a deviation of 2 μm, while the numerical error in the z‐direction was found to be inferior to that of currently used equipment. The optimisation study also allowed the identification of the machine elements that provide the minimal error and cost for the equipment, identifying an optimal Pareto of the system. In such an optimal case, the average of the final errors for the balanced solution (in which the objective functions have equal importance) was found to be 141 μm. In addition, the cost of this solution was 1.57 times higher than the cheapest solution found. Finally, a comparison between the configuration of commercial FDM machines and the optimum values was found, highlighting the main points that would possibly provide an improvement to the current concepts and an increase in equipment profitability.Originality/valueDespite the growth of additive manufacturing development, there are still several challenges to overcome to increase the accuracy of the final parts, such as the reduction of mechanical errors. However, in addition to the complexity of this subject, the cost of equipment restricts the development of new solutions. As a result, a systematic approach to identify a suitable configuration of each machine in accordance with the optimal accuracy and cost of equipment is needed.