D.J. de Beer

IMPLEMENTING THE SOUTH AFRICAN ADDITIVE MANUFACTURING TECHNOLOGY ROADMAP – THE ROLE OF AN ADDITIVE MANUFACTURING CENTRE OF COMPETENCE

The Rapid Product Development Association of South Africa (RAPDASA) expressed the need for a national Additive Manufacturing Roadmap. Consequentially, the South African Department of Science and Technology commissioned the development of a South African Additive Manufacturing Technology Roadmap. This was intended to guide role-players in identifying business opportunities, addressing technology gaps, focusing development programmes, and informing investment decisions that would enable local companies and industry sectors to become global leaders in selected areas of additive manufacturing. The challenge remains now for South Africa to decide on an implementation approach that will maximize the impact in the shortest possible time. This article introduces the concept of a national Additive Manufacturing Centre of Competence (AMCoC) as a primary implementation vehicle for the roadmap. The support of the current leading players in additive manufacturing in South Africa for such a centre of competence is shared and their key roles are indicated. A summary of the investments that the leading players have already made in the focus areas of the AMCoC over the past two decades is given as confirmation of their commitment towards the advancement of the additive manufacturing technology. An exposition is given of how the AMCoC could indeed become the primary initiative for achieving the agreed national goals on additive manufacturing. The conclusion is that investment by public and private institutions in an AMCoC would be the next step towards ensuring South Africa’s continued progress in the field.

SUITABILITY OF A SOUTH AFRICAN SILICA SAND FOR THREE-DIMENSIONAL PRINTING OF FOUNDRY MOULDS AND CORES

Applications of three-dimensional printing (3DP) to metal casting include, among other things, the direct manufacturing of foundry moulds and cores in refractory materials such as silica sand. The main properties of silica sand that are essentially related to the traditional moulding and core-making processes are: size distribution, clay content, pH, acid demand, and refractoriness. The silica sand used for 3DP must also be appropriately selected for the layer-based manufacturing process involved in 3DP. Properties such as grain size distribution, grain surface morphology, angularity, flowability, and recoating abilities have a particular importance when determining sand suitability. Because of these extra requirements, only a limited range of available foundry silica sands can be used for 3DP processes. The latter situation explains the scarcity and high cost of suitable silica sands, thus contributing to the relatively high operational costs of the 3DP processes for the production of sand moulds and cores. This research paper investigates the suitability of a locally-available silica sand for use in a Voxeljet VX1000 3DP machine. The local silica sand was assessed and compared with an imported silica sand recommended by the manufacturer of 3DP equipment in terms of foundry characteristics and recoating behaviour. The study shows that, despite the differences between the characteristics of the two silica sands, the local sand could be considered a suitable alternative to imported sand for rapid sand casting applications.

Emotional load and social support as indicators of bullying at work

This study sought to ascertain whether elevated emotional load and a lack of social support could be indicative of bullying at work. Participants totalled 1442 employees from the manufacturing industry in South Africa. Data on emotional load, social support, and bullying were gathered using a self-report survey. Structural equation modelling methods were implemented to establish the variance explained in bullying by colleagues and bullying by supervisors, as outcomes, with emotional load and social support as predictor variables. Additionally, multi-group analyses were performed to investigate how the explained variances might differ based on gender and race. Results revealed that the models fitted the data well and that emotional load and a lack of social support explained a substantial amount of variance in bullying by superiors and bullying by colleagues. With regard to the multi-group analysis more variance was explained for females than for males, but the values were quite similar in all groups which give strength to the generalisability of the findings. The findings of this study therefore indicate that elevated emotional load and a lack of social support are indicators of bullying behaviour at work.

Non-destructive, high-resolution X-ray micro-CT of a Hairy Stalagmite: investigating the structural details of a biogenic speleothem

Three-dimensional X-ray micro-computed tomography permits to investigate the internal structure of objects at a high resolution without altering its original form. It also facilitates the rendering and visualization of a virtual replica, which can be subjected to rigorous and complex analyses. In the present study, micro-computed tomography was used to investigate a unique and fragile speleothem (cave formation) named a “Hairy Stalagmite”. Non-destructive analyses have revealed the calcareous internal structure of this speleothem, which consists of hollow, interconnected tubes. Rendered two-dimensional cross-sections also clearly revealed the outline of a once dense root nest that formed part of the speleothem’s biogenic origin. The internal structure was further visualized using an image sequence of two-dimensional cross-sections to create a video that “brings the speleothem to life”, also illustrating its complexity and variability. Statistical analyses revealed structural variability in void fraction, which is likely related to changing environmental conditions. In addition, the micro-computed tomography data were used as input for additive manufacturing (three-dimensional printing) in order to produce an enlarged replica of the Hairy Stalagmite sample, which made physical inspection possible. This combined approach represents the first of its kind and provides much benefit for future studies.

Direct metal laser sintering, using conformal cooling, for high volume production tooling

Existing techniques to manufacture conventional tool steel inserts for the plastic injection moulding process are expensive and time-consuming. Complex mould inserts, difficult to manufacture with conventional processes, can be produced using Direct Metal Laser Sintering (DMLS) with Maraging tool steel (MS1). MS1 is an additive manufacturing (AM) material made available by Electro Optical Systems (EOS) GmbH. Contrary to material removal processes, DMLS can produce MS1 tool steel inserts directly from Computer-Aided Design (CAD) files suitable for high volume plastic injection moulding. Through DMLS it is possible to create conformal cooling channels inside the MS1 inserts that have advantages in reducing heat rapidly and evenly. This can result in a reduction of cycle times, cost per product as well as improving part quality by eliminating defects such as warpage and heat sinks. This paper will present a comparison between Finite Element Analysis (FEA) simulations of the injection mould inserts with actual mould trails of AM and conventional manufactured inserts. It also includes the design and manufacturing of conventional and DMLS inserts and compares the manufacturing costs and lead times. Using FEA simulations, the design of conformal cooling channels is optimised by comparing the mould temperature of different cooling channel layouts.