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The microstructure of parts produced by sective laser melting of Ti-6Al-4V is typically martensite in elongated prior β grains, which leads to anisotropic mechanical properties. A heat treatment can reduce this anisotropy by making these grains more equiaxed. In this work, simulations are performed wherein the evolution of the microstructure during a heat treatment is modelled using a cellular automata method. The results obtained from this simulation are compared to experimentally obtained micrographs. The simulated microstructure shows a similar evolution of the prior β grains from columnar to equiaxed, although the average diameter of the grains is slightly smaller in the simulations.

Structured surfaces involved in a tribological test are quantified using an automated contact area measurement method. The method involves an image segmentation algorithm based on local image gradient extrema. The gradients are then used to accurately determine band-edge segmentation in order to measure the line thickness of the structured surfaces. The traceability of the method was established through an optical standard from NPL in the line-thickness range 10 -100 μm achieving expanded uncertainties in the range 0.5-1.9 μm. The specimen line thickness of different combinations of asperity angle and deformation load, were subject to 10 repeated automatic measurements. The combination of the parameters produce different contact areas, which are interesting for the tribological properties of the surfaces.

Injection moulding using inserts from vat polymerization, an additive manufacturing technology, has been investigated for pilot production and rapid prototyping purposes throughout the past years. Experiments have used a standard mould is equipped with additively manufactured inserts in a rectangular shape of (20 x 20 x 2.7) mm3 produced with vat photo polymerisation. While the lifetime compared to conventional materials such as brass, steel, and aluminium, is reduced, the prototyping and design phase can be shortened significantly by using flexible and cost-effective additive manufacturing technologies. While crack propagation has been significantly reduced, further developments become possible, such as multi-scale injection moulding inserts with dimensions of (80 x 60 x 10) mm3 where an insert with larger outside dimensions and micro features on the surface is used during the manufacturing process. Higher manufacturing volume still exceed the capability of additively manufactured inserts, which are overruled by the stronger performance of less-flexible but stronger materials. This contribution discusses the heat transportation within the inserts made from a thermoset material, brass, steel, and ceramic material. It therefore elaborates on the possibilities of injection moulding as well as the thermal challenges connected with the use of polymer inserts. They are an essential part for further calibrations of the injection moulding process.

Using additive manufacturing (AM) processes for direct fabrication of complex three-dimensional objects in a fewer time incomparison to the subtractive method is the advancement of this technology. This study connecting the AM with injection moulding (IM) process. AM inserts are directly manufactured by photopolymer material and used in IM process. Different combinations of IM parameters are used in order to find out the influence of various settings on the fabrication of the parts with soft inserts. The effects of injection moulding parameters are investigated by the use of a design of experiment (DOE) and optical metrology. DOE analysis concludes that the IM speed and cooling time are significant factors, for the geometry of the features. The height of bricks and knobsare also measured on the IM parts for assessment of different batches before any cracks appear on the inserts.

Industries seek to anticipate product dimensional measurements to quickly control the process and ensure production conformity. The anticipation of the dimensional measurement is often prevented due to dimensional instabilities of the produced parts. In the case of injection moulded polymer components, one of the main instabilities is represented by expansion due to temperature changes. This work proposes a methodology consisting in the prediction of the dimensions at reference temperature conditions using information from measurements performed within few minutes from the moulding process. An industrial component consisting of a thin wall tubular part made of POM (polyoxymethylene) has been selected for the investigation. The measuring equipment included an inductive probe, two thermocouples for concurrent measurements of length and temperature. The dimension at reference temperature conditions is estimated using the information from the transitory cooling period subsequent to the moulding process and through the definition of an apparent coefficient of thermal expansion. Further development of themethodology must be introduced to tackle other dimensional instabilities, such as hygroscopic swelling, stress relaxation and recrystallization.

Application of process monitoring solutions to micro polishing is affected by the low intensity of the measured signals, which influences the capability to extract useful information. This work explores the applicability of acoustic emission monitoring for detection of process completion through End Point Detection (EPD) in micro polishing. Several polishing tests have been conducted by gradually reducing the contact area and the acoustic emission signal generated by the process is acquired and analysed. The work shows that the monitoring solutions applied in conventional polishing can potentially be applied to the micro process.

In this paper, a transient 3-dimensional thermal model for the selective laser melting process, based on the finite volume method, has been developed, which takes into account the phase change and powder to bulk material transition. A parametric study has been performed for the temperature field as well as the melt pool dimensions, and the results show the impact on melt pool size. Also, in this paper, a straightforward metallurgical model has been coupled to a thermal model, which uses the temperature gradient and the cooling rate on the melt pool borders at the onset of solidification to determine whether the grains have columnar or equiaxed morphology. Furthermore, the effect of process parameters on the size of grains and subsequently the yield stress has been studiedvia empirical equations. The results show that low speed along with high laser power (higher laser energy density) will cause low cooling rates and prompt the formation of large grain. This would consequently give rise to lower tensile strength, as compared tolower laser energy density where smaller grains are formed due to higher cooling rates.

The shape of the printed strand in extrusion-based additive manufacturing is an important factor that affects the surface roughness and the geometrical accuracy of the 3D printing fabrication. We used Computational Fluid Dynamics simulations to investigate the effect of the geometry of the extrusion nozzle on the cross-section of the printed strand. The extrusion of a single thread on a planar surface was modelled as an isothermal incompressible Newtonian fluid flow. The deposition of the strand is a creeping flow that solely depends on the geometry of the nozzle, the gap and the ratio of the extrusion speed to the printing speed. We considered three different nozzle geometries: a cylindrical nozzle, a square nozzle, and a cylindrical nozzle with a side plate extension retaining side flows. The numerical simulations provided the cross-section of the deposited strand as well as the printing force applied by the extruded material on the substrate. The side plate improved the compactness of the strand cross-section, while the square nozzle did not present any advantage as compared to the cylindrical nozzle, in the printed configuration that we considered.

The optical principle of structural colouration provides to a surface unnatural and iridescent colouring properties. Surface topographycombined with lighting characteristics are the physical driver of the phenomenon. Structural colouring arises from the presence on the specimen of nanoscale features distanced by a length comparable to the near visible light spectrum (300‐1000 nm). The microstructures behave as a bandpass filter for certain light wavelengths, enabling an unnatural colouring effect. Elliptical Vibration Texturing (EVT) is an on development technology for fast texturing of gratings on metal inserts for structural colouration purposes.To identify the accuracy of EVT, in this study, two different microscopes assess an EVT grating with a 1000 nm nominal pitch on asteel flat surface. On first, optical‐based metrology is selected adopting a Laser Scanning Confocal Microscope (SCM) with a 405 nm blue source to tackle the measuring purpose. Secondly, an Atomic Force Microscope (AFM) in Intermittent contact mode (IC‐AFM) isadopted. Considering the differences in set‐up time and scanning range, the objective of this research is to identify the mostfavourable measuring technique.On the sample images, five average profiles on different locations provide consistent information about the process repeatability.Pitch estimation comes by means of FFT algorithm on the extracted profiles. The average result for SCM measures is 1002 ± 31 nmwhile for AFM is 972 ± 15 nm. At last, from these results, the estimation of EVT accuracy is presented.

In recent years, direct rapid soft tooling based on inserts manufactured additively by light reactive photopolymer curing has become a solid alternative to classic tooling based on subtractive machining of metals for prototyping and pilot production of polymer parts by injection moulding. Reported numbers of injection-moulded parts per insert are in the low to medium three-digit range. This, however, is based on using additive manufacturing for the production of both mould halves. It was found that combining a soft tooling insert on one mould half and a metal insert on the other half can increase insert lifetime to more than 10 000 parts in acrylonitrile butadiene styrene (ABS) with a negligible influence of insert wear on the dimensional stability of the injection-moulded parts. Photopolymers are known for their very low heat conductivity compared to metals and their sensitivity to elevated temperatures leading to degradation and negative effects on their mechanical properties. Considering heat transfer laws, it can be assumed that most thermal energy brought into the cavity during the plastic injection is conducted away through the steel half of the mould, thus leading to a significant reduction of the thermal ageing of the photopolymer insert. This research supports the quantification of the influence of thermal ageing on insert lifetime by performing experiments with photopolymer samples aged thermally after exposure to different elevated temperature levels for different time spans.

This paper focuses on a new methodology for conducting a comprehensive benchmarking of Additive Manufacturing (AM) technologies. The quality of the built products using AM strongly depends on the machine capabilities, and it is thus essential to develop a proper benchmarking design that would allow their comparative evaluation. The benchmarking presented has been designed with the purpose of conducting a comparison between different AM machines, with a particular focus on metal powder-bed AM. The main scope is to make an extensive evaluation of the technologies from multiple points of view, covering: accuracy and precision of the machine, residual stresses on the parts (particularly important in the case of metal AM), homogeneity (in terms of density and residual porosity), build speed, mechanical properties, surface finish and corrosion resistance. For each evaluation criteria, a specific analysis method is employed. The aim of this work is to analyse the current technology capabilities and limitations, in order to assess what different AM machines can deliver in a net-shape process chain scenario. The benchmark is employed for a statistically designed series of experiments to study in detail the AM machine´s real limitations and their working process windows. The design also includes features that represent a challenge for the AM machine, and sometimes exceed the machine´s actual capabilities. Furthermore, the benchmark has been developed to be used as a periodic quality control-job for the operational performance of the AM machines.

Functional nanostructures applied on various consumer products has attracted increasing attention in the industry. Examples of functional nanostructures are well known from nature, where organisms and plants possess optical, adhesive, and self-cleaning capabilities. The aim of the present work is to produce injection moulding tool inserts with the nanostructured functional surfaces as mentioned above. In order to manufacture these structures on the double-curved surfaces of the injection moulding tool inserts, a technology called nanoimprint lithography (NIL) with flexible stamps is applied. However, the resolution limit due to distortion of the stamp when applying the pressure, and complications regarding deformations of the flexible stamp, is a major concern for precise replication of the nanostructures whose functionality might change dramatically with just a few nanometres of distortion. Here, the application of modelling tools is essential in order to predict how the flexible stamp will deform during the transferring process. However, such models are quit complicated since the overall behaviour is non-linear. A review of different manufacturing and simulation cases will be presented and gives an overview of today’s methodologies for transfer of nanostructures to curved surfaces.

The growing demands for quality and flexibility and at the same time production speed challenges conventional metrology. The future tendency is that metrology is an integrated part of the production line and thus is placed in a production environment. This is a challenge since dimensional metrology in a production environment might lead to higher uncertainties due to dynamic variations both in the conditions of the environment and in the conditions produced parts, with all the influencing factors such as temperature, vibrations, forces and humidity etc. that lies outside the requirements from todays standards referring to 20oC and 0 N (zero forces acting on the part). However, many of these effects can be treated as systematic errors if the physical phenomena leading to the deviations can be described. Today, it is very common to compensate for the variations in temperature in a classical 1D manner where a measurand is compensated via the coefficient of thermal expansion (CTE) and the difference from the reference temperature. However, when temperature gradients and very complex part geometries exist the deformation pattern might not at all follow a linear path. Instead, more advanced three-dimensional thermomechanical numerical models should be used for predicting the deformation of the parts due to the thermal effects taking the inherent build-up of residual stresses and warpage into account. The same goes for other effects that might change the dimensions over time such as hygroscopic swelling (for polymer parts), which can be taken into account by considering numerical modelling. In the present work, different academic and industrial parts will be used as cases in order to show the advantages of using numerical simulation tools for compensation of the dynamic changes and further also highlight and discuss where the classical 1D approaches might be sufficient for a desired uncertainty.

Electro-sinter-forging (ESF) is a sintering process based on the resistance heating principle, which makes it faster than conventional sintering. The process is investigated as a function of the main process parameters, namely compacting pressure, electrical current density and sintering time. The present work is focused on analysing the influence of these process parameters on the final density of a disc sample made from commercially pure titanium powder. Applying the design of experiments (DoE) approach, the electrical current was seen to be of largest influence. The maximum obtained density was 94% of the bulk density of pure titanium. Density measurements were carried out by measuring the mass and volume separately. The volume was estimated applying two methods, namely the Archimedes’ suspension method and 3D scanning to build and measure the volume mesh of the sample. The density calculations proved to be compatible.

This research investigates the effect of injection moulding process parameters on photopolymer mould inserts produced with the Digital Light Processing (DLP) additive manufacturing (AM) method. The main motivation of applying AM to produce mould inserts, is the potential of reducing lead time and manufacturing cost, as well as achieving a more flexible manufacturing method in case of non-mass produced products such as prototypes. In this research moulds inserts of 20 x 20 x 2.7 mm with mould cavities as small as 5 x 4 mm in dimensions are tested. The parts are analyzed and evaluated by the measurements of different features and the influence of the IM process.

In micro-manufacturing, the accurate prediction of defects affecting the part quality by means of process simulations is of paramount importance. With this purpose, micro-injection moulding process simulations can be fundamental with the aim of strongly reducing experimental and quality assurance efforts. In this study, the usage of process simulations for the prediction of the size of the flash affecting an ultra-small three-dimensional polyoxymethylene (POM) micro component is discussed. A three-dimensional multi-scale mesh was used to discretize a geometry comprising the part and the feed system of the one-cavity micro mould. The venting channel was included into the model in order to simulate the flash formation as a virtual short-shot. Simulation were run with Autodesk Moldflow Insight 2017® and results validated by comparing numerical results with experimental observation of the flash size. A state-of-the-art 3D focus variation measurement instrument was used for characterizing the flash on moulded parts. Four injection moulding process parameters were tested using a Design of Experiment (DoE) approach in both real experiments and simulations in order to validate the numerical outputs with respect to process variations. The results showed that flash size was generally overestimated by simulations. However, both real parts measurements and numerical results agreed on the signs and magnitudes of the effects of the investigated process parameters, demonstrating that simulations are an useful tool for process/product optimization.

The importance of Additive Manufacturing (AM) in the field of micro manufacturing is increasing. Vat Polymerization Methods are one of the lead AM technologies to produce polymer micro parts. In the Technical University of Denmark (DTU), a vat photopolymerization AM machine able to print features in a micro scale was developed, build and validated. The work here presented analyses the capability of the machine in terms of geometry, when printing features of different sizes and geometries. For this study, two test parts have been designed, a circular stepped pyramid and a square stepped pyramid, both having micro size steps at the top of the pyramids. Five batches of each test part have been printed to evaluate the variability of the results in a single and in various prints.

This paper investigates the influence of shear-rate dependent viscosity on the strand deposition flow during Extrusion-Based Additive Manufacturing. Extrusion-Based Additive Manufacturing, also known as Fused Deposition Modeling (FDM), is a manufacturing method in which material is joined layer by layer into a 3D object. A solid filament is heated above the melting point and extruded through a nozzle to form a strand. The process is modelled within the paradigm of Computational Fluid Dynamics as an isothermal Generalized Newtonian fluid flow. The power law is used as the constitutive relation between the shear-rate and the viscosity. A sensitivity study of the model’s input parameters (power-law index and consistency index) is made. The simulations are performed varying two process parameters: the vertical distance between the substrate and nozzle exit as well as the relative horizontal velocity between the substrate and nozzle. The model is used to investigate the cross-sectional shape of the strand after the deposition and the force exerted on the substrate by the material extruded from the nozzle (the printing force). Under the tested conditions, we find a neglible change in the cross-sectional shape and the printing force behaviour when varying the power-law index and the consistency index. Thus, it is concluded that the Newtonian fluid model provides a sufficient approximation to simulate the deposition flow under the given assumptions.