Este trabalho descreve a importância e a conveniência dos procedimentos multivariados de otimização experimental, destacando as vantagens e aplicações dos sistemas de planejamento fatorial que permitem avaliar simultaneamente o efeito de um grande número de variáveis, a partir de um reduzido número de experimentos. Por meio de um exemplo prático é apresentada uma discussão do efeito da interação entre as variáveis e o estabelecimento de ótimos verdadeiros na otimização de parâmetros experimentais envolvidos na fotopolimerização do metacrilato de metila (MMA) comercial, na forma de oligômero, denominado "cola BERKEL", por radiação UV. Aspectos relativos ao desenho experimental e à interpretação de resultados também são apresentados. PALAVRAS-CHAVE: Planejamento fatorial; análise multivariada; fotopolimerização; metacrilato de metila (MMA). ABSTRACT:This paper describes both the value and the role of multivariated methods of experimental procedure in scientific research. It is highlighted the advantages of factorial design systems which let simulate simultaneously several variables concerned a studied system, reducing the number of experiments of the research. The impact of these variables on the photopolymerization system is discussed upon the photocure of oligo(methyl methacrylate) (MMA), commercially called Berkel glue B 20, initiated by an UV light source. As feedback of the system it was measured the quantity of oligomer converted to polymer (in weight), finding the polymerization rate (in percent). Aspects related to the experimental design and the interpretations of results are also presented. KEY-WORDS: Factorial design; multivariate analysis; photopolymerization; methyl methacrylate (MMA).

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.

Purpose The additive manufacturing technologies have been facing an extraordinary growth along the past years. This phenomenon might be correlated with rise of low-cost FDM technologies into the non-professional market segment. In contrast with that, among the main disadvantages found in this sort of equipment are the final object finishing and low mechanical strength. For that reason, the purpose of this paper is to present and characterise a surface treatment which is based on solvent vapour attack and that is also known as smoothing process. In addition, a concise overview about the theory beneath this process is presented besides an experimental study that evaluates the main effects on the mechanical properties of object. Design/methodology/approach To analyse the benefits of this process, the authors preliminarily investigated the working mechanism that supports such surface treatment. It allowed them to identify and select a proper solvent for each material. The authors have also established that the exposure time repetition numbers (passes) were the main variables, whereas temperature, solvent type, drying time, object direction and object shape were constants. The main object dimensions, surface roughness, absorbed solvent mass and mechanical strength were the main study responses. Findings As a result of this work, the peak-peak roughness was reduced in 71 per cent, indicating the potential benefit of this process. On the other hand, excessive solvent exposure implied on relevant dimensional distortions and internal disruptures. It was also possible to see that the vapourised solvent penetrate into the object surface and fused layers and filaments. As consequence, the mechanical strength was also improved. Originality/value Despite the growth that additive manufacturing market segment has seen along the past years, the finishing and mechanical strength of low-cost equipment still lack for improvements. For that reason, applications like solvent vapour attack or smoothing process new perspectives for this non-professional segment, whereas roughness and mechanical strength are improved after its treatment. As a consequence, it is possible to consider a final object to be obtained directly from low-cost FDM in combination with smoothing process.

As a consequence of the growth in additive manufacturing applications, research on the improvement of these processes has gained relevance. One such process, the Fused Deposition Modelling (FDM)-process, deposits a support material to build negative surface features such as snap-fits. The purpose of this work is to determine the parameters that enable the fabrication of these types of features without a support material. We applied a design-ofexperiments method to identify the quality of the non-supported deposition and the adherence between layers. As to control factors, we defined the deposition temperature and the extrusion and deposition velocities, while the nozzle diameter and the deposition height were held constant. For response factors, we defined the distance, the non-supported deposition quality, and the ultimate tensile stress. Additionally, an optimisation study was performed to maximise the mechanical strength and the non-supported distance, thereby making it possible to determine the suitable range of parameters for implementation of the process.