SELECTIVE LASER MELTING OF Al-Cu12 IN-SITU ALLOYING DEVELOPMENT FOR ANCHOR-LESS PROCESSING

The feedstock used within the additive manufacturing process Selective Laser Melting (SLM) is generally deposited and laser processed in a pre-alloyed state. The full melting and rapid solidification of feedstock leads to the creation of components with mechanical properties comparable and sometime exceeding those of traditionally cast. For high performance applications within aerospace and automotive, pure elemental powdered blends for use within SLM are generally not used due to poor powder distribution and difficulty in controlling composition across the component. In-situ elemental blending of feedstock represents a route for testing the feasibility of different elemental mixtures, creating alloys in-situ in a cost-efficient way, however the resultant properties of component made using such a feedstock are not fully understood. This research aims to develop an in-situ aluminium hardenable alloy using a novel Semi-Solid Processing (SSP) method known as, Anchorless Selective Laser Melting (ASLM). This method requires two or more separate materials within the feedstock to be in-situ alloyed under the action of the laser to form into various combinations of eutectic/hypo/hyper eutectic alloys in a stress reduced state. The ASLM method results in the elimination of supports required during manufacture due to maintaining the processed material in a semi-solid state. In this investigation, Selective Laser Melting (SLM) was applied to an identified suitable candidate materials for ASLM processing requiring elemental blending and developed optimum processing parameters for the in-situ fabrication of an Al-Cu12 alloy from pure elemental blends of aluminium and copper powders. Design of Experiments (DOE) were applied for parameter optimisation in order to minimise internal defects and studying the influence of SLM parameters such as layer thickness, laser power, scan strategy, scan speed and hatch spacing concluding that 67o meander scanning strategy and a combination of high power source and reduced scanning velocities leads to a higher densification. Findings shows that the use of elevated pre-heat temperatures created a coarser cellular-dendritic microstructure consisting of supersaturated Al-rich matrix with a uniform globular microstructure with finer Al2Cu phase compared to as-fabricated samples at room temperature. It was found that Al-Cu12 in-situ processed samples achieved maximum tensile strength values comparable to cast AlCu12 alloy. Processing at elevated pre-heat temperatures created components with higher ultimate tensile strength and ductility and minimised warping distortion compared to standard room temperature built samples due to it assisting a more complete melting of Al and Cu particles. An in-situ age hardening resulted of the prolonged high temperature processing and slower cool down, producing an equilibrium α + θ microstructure

Defect Probability Estimation for Hardness-Optimised Parts by Selective Laser Melting

The development of reliable additive manufacturing (AM) technologies to process metallic materials, e.g. selective laser melting (SLM), has allowed their adoption for manufacturing fnal components. To date, ensuring part quality and process control for low-volume AM productions is still critical because traditional statistical techniques are often not suitable. To this aim, extensive research has been carried out on the optimisation of material properties of SLM parts to prevent defects and guarantee part quality. Amongst all material properties, defects in surface hardness are of particular concern as they may result in an inadequate tribological and wear resistance behaviour. Despite this general interest, a major void still concerns the quantifcation of their extent in terms of probability of defects occurring during the process, although it is optimised. Considering these issues, this paper proposes a novel approach to quantify the probability of occurrence of defects in hardness-optimised parts by SLM. First, three process variables, i.e. laser power, scan speed and hatching distance, are studied considering their efect on hardness. Design of Experiments and Response Surface Methodology are exploited to achieve hardness optimisation by controlling process variables. Then, hardness defect probability is estimated by composing the uncertainty afecting both process variables and their relationship with the hardness. The overall procedure is applied to AlSi10Mg alloy, which is relevant for both aerospace and automotive applications. The approach this study proposes may be of assistance to inspection designers to efectively and efciently set up quality inspections in early design phases of inspection planning

DIRECT METAL LASER SINTERING OF TI-6AL-4V ALLOY: PROCESS-PROPERTY-GEOMETRY EMPIRICAL MODELING AND OPTIMIZATION

DIRECT METAL LASER SINTERING OF TI-6AL-4V ALLOY: PROCESS-PROPERTY-GEOMETRY EMPIRICAL MODELING AND OPTIMIZATIO

Laser powder bed fusion of cemented tungsten carbide cutting tools

Thesis (PhD)--Stellenbosch University, 2022.ENGLISH ABSTRACT: Cemented carbides are extremely hard, wear resistant materials, and one of the most widely used tool materials in numerous manufacturing industries. Metal cutting tools are commonly manufactured from cemented carbides using standard powder metallurgy processes such as the press and sinter process. The tooling market is highly competitive and the companies with the best research and development departments have the competitive advantage when it comes to cutting edge technology. However, historically, the development process for a new cutting tool or production technology is a lengthy and costly venture. The use of laser powder bed fusion (L-PBF) for research, development, and small-batch production of cemented tungsten carbide cutting tools has not been extensively reported, and commercialisation does not seem apparent as yet. While the usage of L-PBF to produce cutting tools may be beneficial to advancing cutting tool technology, the process has many inherent drawbacks that affect part quality. However, there are many changes to the current L-PBF process that can be investigated to improve the final quality of L-PBF-produced tools before post-processing. The successful application of L PBF technology could help develop and manufacture cutting tools at an improved rate. The aim of this study was to determine and manage the influences of certain factors encountered during L-PBF of tungsten carbide cobalt (WC-Co) and their effects on specific cutting tool properties and cutting performance to produce L-PBF cutting tools that could be comparable to a conventionally produced tool. To accomplish this, three powders were analysed and investigated for their use in the L-PBF process. Then, characterisation of an existing cutting tool was performed to be used as a quality benchmark for L-PBF cutting tools. After a reasonable understanding of powders and conventional cutting tools was obtained, single track scans were performed on a tool steel base plate to understand adhesion and the feasibility of using a conventional base plate. The next stage of the study involved understanding the effects of different laser parameters and scanning strategies on the track morphology, density, hardness, and cobalt content of L-PBF produced WC-12wt%Co samples. Various parameter optimisation methods and strategies were tested and L-PBF-produced cutting tools were utilised in preliminary cutting tests to determine their cutting ability and to deduce which factors had the greatest effects on cutting contact time. The L-PBF scanning strategy was observed to be the most significant factor for successful cutting operations. A diagonal raster strategy with an 80-degree alternating rotation produced the best cutting inserts for the specific insert geometry and grade. Verification WC-12wt%Co inserts were produced with L-PBF for final cutting tests. These inserts were comparable to conventionally produced tungsten carbide inserts with respect to cutting performance indicators such as contact time and workpiece surface roughness. On average, after roughly 16M30S contact time, the L-PBF cutting tools exhibited 0.7 mm maximum flank wear versus 0.4 mm for similar conventional inserts. These results suggest that L-PBF could, one day, be a viable solution for research, developments, and small-batch production of WC-Co cutting tools.AFRIKAANSE OPSOMMING: Sinterkarbiede is uiters hard, slytasiebestand en een van die gereedskapsmateriale wat die algemeenste in talle vervaardigingsbedrywe gebruik word. Metaalsnygereedskap word gewoonlik met behulp van standaard poeiermetallurgieprosesse, soos die pers- en sinterproses, uit sinterkarbiede vervaardig. Die werktuigmark is baie mededingend en ondernemings met die beste navorsingen ontwikkelingsdepartemente, het die mededingende voordeel as dit by die nuutste tegnologie kom. Histories is die ontwikkelingsproses vir ʼn nuwe snybeitel of produksietegnologie egter ʼn lang en duur proses. Die gebruik van laser- poeierbedsamesmelting (L-PBF) vir navorsing, ontwikkeling en kleinskaalproduksie van gesementeerde-wolframkarbiedsnygereedskap is nog nie wyd gerapporteer of gekommersialiseer nie. Hoewel die gebruik van L-PBF voordelig vir die bevordering van snygereedskaptegnologie kan wees, het die proses baie inherente nadele wat die gehalte van die onderdele beïnvloed. Daar is egter baie veranderinge aan die huidige L-PBF-proses wat ondersoek kan word om die finale gehalte van L-PBF-vervaardigde gereedskap voor ná-vervaardiging te verbeter. Die suksesvolle toepassing van L-PBF-tegnologie kan help om snygereedskap vinniger te ontwikkel en te vervaardig. Die doel van hierdie studie was om die invloed van sekere faktore tydens die L-PBF van wolframkarbied-kobalt (WC-Co), en die uitwerking daarvan op spesifieke snygereedskapseienskappe en -snyprestasie te bepaal en te bestuur, om uiteindelik L-PBF-snygereedskap te vervaardig wat met ʼn konvensioneel vervaardigde werktuig vergelykbaar is. Om dit te bewerkstellig, is drie poeiers vir gebruik in die L-PBF-proses ontleed en ondersoek. Vervolgens is karakterisering van ʼn bestaande snybeitel uitgevoer om as ʼn gehaltenorm vir L-PBF-snygereedskap te dien. Nadat ʼn redelike begrip van poeiers en konvensionele snygereedskap verkry is, is enkelbaanskanderings op ʼn basisplaat van gereedskapstaal uitgevoer om die aanklewing en dus die haalbaarheid van die gebruik van ʼn konvensionele staalbasisplaat te ondersoek. Die volgende fase van die werk het die bestudering van die effekte van verskillende laserparameters en skanderingstrategieë op die baanmorfologie, digtheid, hardheid en kobaltinhoud van L-PBF geproduseerde WC-12wt%Co-monsters behels. Verskeie parameter-optimaliseringsmetodes en - strategieë is getoets en L-PBF-vervaardigde snygereedskap is in voorlopige snytoetse gebruik om hulle snyvermoë te bepaal en af te lei watter faktore die grootste effek op die snykontaktyd het. Waarneming het aangedui dat die L-PBF-skanderingstrategie die belangrikste faktor vir suksesvolle snywerk is. ʼn Diagonale rasterstrategie met ʼn wisselrotasie van 80 grade het die beste snyinvoegstukke opgelewer vir die spesifieke invoegstukgeometrie en -graad wat bestudeer is. Verdere WC-12wt%Co-snyinvoegstukke is ter bevestiging vir finale snytoetse met behulp van L PBF vervaardig. Hierdie invoegstukke was met betrekking tot snyprestasie, soos kontaktyd en oppervlakruheid van die werkstuk, met konvensioneel vervaardigde wolframkarbied-invoegstukke vergelykbaar. Na ongeveer 16M30S se kontaktyd vertoon die L-PBF-snybeitel ʼn gemiddelde flankslytasie van 0.7 mm teenoor 0.4 mm vir soortgelyke konvensionele invoegstukke. Hierdie resultate dui daarop dat L-PBF in die toekoms wel ʼn lewensvatbare oplossing vir die navorsing, ontwikkeling en kleinskaalproduksie van WC-Co-snygereedskap kan wees.Doctora

Harnessing Artificial Intelligence for the Next Generation of 3D Printed Medicines

Artificial intelligence (AI) is redefining how we exist in the world. In almost every sector of society, AI is performing tasks with super-human speed and intellect; from the prediction of stock market trends to driverless vehicles, diagnosis of disease, and robotic surgery. Despite this growing success, the pharmaceutical field is yet to truly harness AI. Development and manufacture of medicines remains largely in a ‘one size fits all’ paradigm, in which mass-produced, identical formulations are expected to meet individual patient needs. Recently, 3D printing (3DP) has illuminated a path for on-demand production of fully customisable medicines. Due to its flexibility, pharmaceutical 3DP presents innumerable options during formulation development that generally require expert navigation. Leveraging AI within pharmaceutical 3DP removes the need for human expertise, as optimal process parameters can be accurately predicted by machine learning. AI can also be incorporated into a pharmaceutical 3DP ‘Internet of Things’, moving the personalised production of medicines into an intelligent, streamlined, and autonomous pipeline. Supportive infrastructure, such as The Cloud and blockchain, will also play a vital role. Crucially, these technologies will expedite the use of pharmaceutical 3DP in clinical settings and drive the global movement towards personalised medicine and Industry 4.0

Chemical machining of advanced ceramics

Not until recently did we see an enormous surge of interest in the study of machining of advanced ceramics. This has resulted in significant advances lately in their development and usage. Machinable glass ceramics, boron nitride and silicon carbide are commonly used in the industry and their major features of attraction are their inherent properties. Previous studies on machining of these materials were mainly performed by other machining methods, such as electrode discharge machining, laser beam machining and abrasive jet machining. Although chemical machining is one of the oldest machining methods employed, the literature survey reveals a lack of knowledge in this particular aspect. Further understanding is required on the chemical machining characteristics of advanced ceramics as well as their performance and relationship between the variables and parameters involved in the process. Therefore, the aim of our study is to examine and establish the relationship between etching rate, surface roughness and dimensional accuracy with the relevant variables involved and at the same time to develop the predictive models for all outputs that we believe are beneficial to the manufacturing industries.A comprehensive review was written and published recently in a Journal on the current advanced ceramics machining techniques [1]. The chemical machining process was successfully conducted in this study with a variety of selected etchants. Using the RSM methodology the first and second order models were developed to study the chemical machining process and relationship between the outputs (etching rate, surface roughness and dimensional accuracy) with the selected variables, namely, etching temperature, etching duration, etchant and etchant’s concentration. A number of predictive models were developed followed by optimisation studies of chemical machining to obtain the best performance of chemical machining of advanced ceramics. Artificial neural network was also used as the analytical tool to evaluate the experimental data and validate the results generated by response surface roughness, and both results were found to be in good agreement with each other. Artificial neural network was performed by software of NeuroSolution 5.From the chemical etching studies both the etching temperature and etchant used have significant influence on the etch rate. Generally, the higher the etching temperature the greater the etch rates was observed for the substrates. The best etch rate was found in HBr etchant for MGC and BN, and the highest etch rate performance for SiC was found in H3PO4 etchant. For surface roughness, different substrates were found to be influenced by different variables. For MGC and BN, these substrates were affected by etching temperature and the best surface roughness occurred at high etching temperature of 90oC. Etching duration was also found to be critical in determining the quality of SiC surface roughness during chemical machining.Experimental data revealed that etching rate was closely correlated to surface roughness as well as the etching ratio. However, using the best etching rate it failed to yield the quality surface roughness, but produced the best etching ratio. Each variable presented different level of significance for each output of chemical machining. The results of etch rate and etch ratio also showed that etching temperature and etching duration imparted significant impact on the chemical machining of all substrates. In the analysis of surface roughness, etching temperature was found to be the critical variable in chemical machining of machinable glass ceramics. Etching temperature and etchant influenced the surface roughness of boron nitride whereas surface roughness of silicon carbide was more dependent on etching duration and etchant used.Predictive models were developed using DE 7 once the analysis of data was completed. A total of 27 predictive models were developed for each substrate and each output. This predictive model can be used directly in the industry with the selected substrate and etchant. Optimisation of chemical machining was also performed. For machinable glass ceramic, the optimum of chemical machining happened at 100oC in 10.5 molarity HCl etchant for 30 minutes. Results of chemical machining of machinable glass ceramics were obtained with optimal etching rate of 0.0008g/min, surface roughness improvement of 81.818nm (48% improvement) and etching ratio of 3.403. In chemical etching of boron nitride, the best result occurred at 40oC in 6 molarity HBr for 62 minutes. The etching rate obtained for BN is 0.00025g/min, with surface roughness improvement of 0.01nm (16% improvement) and etching ratio of 3.153. For the chemical etching of silicon carbide, the best performance occurred at 75oC in 8.5 molarity of HBr for 240 minutes. The optimal value of etching rate for silicon carbide is 0.0009g/min, with surface roughness improvement of 128.71um (35% improvement) and etching ratio of 10.004

Investigation of the "orange peel" phenomenon

Selective Laser Sintering (SLS) or Laser Sintering (LS) allows functional parts to be produced in a wide range of powdered materials using a dedicated machine, and is thus gaining popularity within the field of rapid prototyping. Two current manufacturers of LS equipment and materials are EOS GmbH and 3D Systems. The PA2200 semi-crystalline polyamide powder studied here was developed by EOS and was processed using the 3D Systems Sinterstation 2500 HiQ LS machine. One of the advantages of employing LS is that the loose powder of the building chamber can be recycled. However, the properties of some recycled powders such as polyamide 12 (PA 12) deteriorate by comparison to those of fresh powder. Fabricating parts using only new powder, although providing the best quality, is considerably more expensive than using recycled powder. On the other hand, using recycled powder creates the problem of the coarse, rough, and uneven surface texture. This thesis examines LS fabricated parts which are affected by the "orange peel" phenomenon due to the usage of recycled PA 12 powder. This problem must be addressed before the technology can be widely accepted. This thesis presents the problematic areas and proposes solutions to manage and utilise the recycled powder. Further, the thesis discusses experimental work on the deterioration or ageing of PA 12 powder properties in the LS process, the microstructure of "orange peel" texture and the improvement of part surface finish to avoid the "orange peel" problem.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Investigation of the "orange peel" phenomenon

Selective Laser Sintering (SLS) or Laser Sintering (LS) allows functional parts to be produced in a wide range of powdered materials using a dedicated machine, and is thus gaining popularity within the field of rapid prototyping. Two current manufacturers of LS equipment and materials are EOS GmbH and 3D Systems. The PA2200 semi-crystalline polyamide powder studied here was developed by EOS and was processed using the 3D Systems Sinterstation 2500 HiQ LS machine. One of the advantages of employing LS is that the loose powder of the building chamber can be recycled. However, the properties of some recycled powders such as polyamide 12 (PA 12) deteriorate by comparison to those of fresh powder. Fabricating parts using only new powder, although providing the best quality, is considerably more expensive than using recycled powder. On the other hand, using recycled powder creates the problem of the coarse, rough, and uneven surface texture. This thesis examines LS fabricated parts which are affected by the "orange peel" phenomenon due to the usage of recycled PA 12 powder. This problem must be addressed before the technology can be widely accepted. This thesis presents the problematic areas and proposes solutions to manage and utilise the recycled powder. Further, the thesis discusses experimental work on the deterioration or ageing of PA 12 powder properties in the LS process, the microstructure of "orange peel" texture and the improvement of part surface finish to avoid the "orange peel" problem