Data-driven process analysis for iron foundries with automatic sand molding process

This paper proposes a methodological framework to develop a data-driven process control using pure industrial production data from a cast iron foundry, despite the limitation of complete casting traceability. The aim is to help sand foundries to produce good castings. A reference foundry, which produces mainly automotive and oven parts with automatic sand molding and pouring machines, was selected. Past data, where only good castings were produced, were extracted from the database to determine parameter control limits (upper and lower control limits) with the aid of statistical approach. To identify critical process parameters associated with casting defects, process data from the zero and high scrap production batches were systematically compared. This method clearly identified unstable parameters without exact synchronization between inline and part quality data. Molding sand moisture, temperature and compactability, liquidus temperature of the melt, phosphorus content, carbon equivalent and pouring temperature were found to be the critical parameters to be stabilized. Finally, a regression model for predicting and controlling of molding sand moisture and liquidus temperature of the melt was created. The determined boundaries and the models were helpful for the foundry in assisting ongoing production control and correction of process inputs to achieve target casting quality

A method for characterising the influence of casting parameters on the metallurgical bonding of copper and steel bimetals

Traditional casting technology offers two mayor drawbacks towards research activities. On the one hand, time and resources needed for every casting are rather high. The mould has to be able to withstand the high temperatures introduced by the melt and provide cooling for the cast part. Preparation and installation of measuring equipment therefore takes time. Additionally, due to the high mass of the mould when compared to the cast part, parameter variations are rather limited in their resulting effect on the temperature-time profile being one of the most prominent factors regarding cast quality. Especially when pouring by hand, variations in casting times and rates superimpose effects created intentionally. Therefore, a different process was advanced and evaluated, allowing to minimise some of the drawbacks mentioned before. The key idea is to drastically reduce casting size to the dimensions of one specimen and to apply a highly automated production route. As such, a mirror furnace was modified as to allow the processing of melt. Due to the specimens size, an adaption of mechanical testing equipment was performed and evaluated. As an example, copper-iron bimetal specimens were examined by light microscopy, micro hardness testing, nanoindentation as well as tensile and torsion testing. As the results were consistent, the newly introduced method can be applied successfully in casting research. This allows for highly reproducible results, reducing the uncertainty of temperature measurements of a specimen due to the distance between them. The possibility of separating influencing variables like maximum temperature and cooling rate allows an analysis of the casting process, which would require different moulds to do so in traditional casting methods. The next steps will be directed at a broader variety of metals processed and at a direct comparison between the new process route and traditional casting technology

Influence of salt support structures on material jetted aluminum parts

Like most additive manufacturing processes for metals, material jetting processes require support structures in order to attain full 3D capability. The support structures have to be removed in subsequent operations, which increases costs and slows down the manufacturing process. One approach to this issue is the use of water-soluble support structures made from salts that allow a fast and economic support removal. In this paper, we analyze the influence of salt support structures on material jetted aluminum parts. The salt is applied in its molten state, and because molten salts are typically corrosive substances, it is important to investigate the interaction between support and build material. Other characteristic properties of salts are high melting temperatures and low thermal conductivity, which could potentially lead to remelting of already printed structures and might influence the microstructure of aluminum that is printed on top of the salt due to low cooling rates. Three different sample geometries have been examined using optical microscopy, confocal laser scanning microscopy, energy-dispersive X-ray spectroscopy and micro-hardness testing. The results indicate that there is no distinct influence on the process with respect to remelting, micro-hardness and chemical reactions. However, a larger dendrite arm spacing is observed in aluminum that is printed on salt

Analysis of salts for use as support structure in metal material jetting

Material jetting (MJT) is a category of additive manufacturing processes where the build material is deposited in the form of individual droplets. MJT has recently been expanded into the field of metal processing due to a potentially high printing speed at low equipment and raw material cost. For full 3D capability, support structures are needed that have to be removed after the print job. We examine water soluble salts and suitable nozzle materials to realise the printing of molten salt in a MJT process. Here, the wetting characteristics of the melt and nozzle are crucial because pronounced wetting is problematic for the ejection of droplets. A sessile-drop contact angle test stand was set up to evaluate the wetting characteristics of three salts or salt mixtures (NaCl, KCl–NaCl and NaCl–Na2CO3) on six different nozzle materials (various ceramics and graphite), i.e. potential nozzle materials. The results indicate a high wetting tendency of most of the examined samples with the exception of KCl-NaCl on graphite. Application of these materials on a MJT test stand confirm the feasibility of our findings

Acoustical and optical determination of mechanical properties of inorganically-bound foundry core materials

Inorganically-bound sand cores are used in many light-metal foundries to form cavities in the cast part, which cannot be realised by the mould itself. To enable FEM simulations with core materials, their mechanical properties have to be measured. In this article, we adapt methods to determine the Young’s and shear modulus, the Poisson ratio and the fracture strain of sand cores. This allows us to fully parametrise an ideal brittle FEM model. We found that the Young’s and shear modulus can be obtained acoustically via the impulse excitation technique. The fracture strain was measured with a high-speed camera and a digital image correlation algorithm

Binder content and storing conditions of inorganically-bound foundry cores determine the intensity and onset time of gas release in metal casting

Organically-bound foundry cores are substituted by inorganically-bound cores increasingly. This trend is due to regulatory efforts, workplace safety issues, and increasing costs for waste deposits. Changing the binder system reduces the emissions to mostly water vapor, solving health and safety issues. Yet, the difference in the behavior of the gas phase, namely, the condensation potential of water, changes the casting process drastically. In contrast with the continuous generation and discharge of combustion products in the case of organic binders, water accumulates within the foundry core. Only once the cold spots of the core reach boiling temperature noteworthy amounts of vapor are created, increasing the chance for gas defects of the cast parts. Countermeasures have to be taken when designing the core’s geometry. We conducted the following research to improve the understanding of core gas release and its interactions with the foundry core’s binder content and storage conditions. Both binder content and relative humidity during storage were varied in three steps. Their influence on the core gas amount, time of gas generation, and gas permeability of the cores were investigated. The experiments were performed in the institute’s Induction Analysis Furnace and an aluminum melt bath. We found a strong dependency of storage humidity, further increased by increasing binder content on the gas amount and time of the gas release

Localization of cavities in cast components via impulse excitation and a finite element analysis

In this work, the acoustic resonance testing method has been extended by a finite element analysis of the examined component to localize cavities within die casting parts. This novel method aims at a fast and efficient quality inspection which allows hidden cavities in cast components to be detected, which is only possible with X-ray technology at the moment. The promising results show that this method enables the localization of shrinkage cavities. Furthermore, the influence of product scatter has been analyzed regarding the accuracy of the calculated position of artificial defects

Combining Structural Optimization and Process Assurance in Implicit Modelling for Casting Parts

The structural optimization of manufacturable casting parts is still a challenging and time-consuming task. Today, topology optimization is followed by a manual reconstruction of the design proposal and a process assurance simulation to endorse the design proposal. Consequently, this process is iteratively repeated until it reaches a satisfying compromise. This article shows a method to combine structural optimization and process assurance results to generate automatically structure- and process-optimized die casting parts using implicit geometry modeling. Therefore, evaluation criteria are developed to evaluate the current design proposal and qualitatively measure the improvement of manufacturability between two iterations. For testing the proposed method, we use a cantilever beam as an example of proof. The combined iterative method is compared to manual designed parts and a direct optimization approach and evaluated for mechanical performance and manufacturability. The combination of topology optimization (TO) and process assurance (PA) results is automated and shows a significant enhancement to the manual reconstruction of the design proposals. Further, the improvement of manufacturability is better or equivalent to previous work in the field while using less computational effort, which emphasizes the need for suitable metamodels to significantly reduce the effort for process assurance and enable much shorter iteration times

A test stand for quantifying the core gas release and the gas permeability of inorganically-bound foundry cores

Environmental and work safety aspects necessitate a radical change in the foundry industry. Organic binder systems for foundry sand cores create toxic combustion products and are, therefore, more and more often substituted by inorganic binder systems. While providing an environmental advantage by mainly releasing water vapor, inorganic binder systems impose new challenges for the casting process. The gas release of inorganically-bound foundry cores can lead to increased gas porosity in the cast parts and thus to high scrap rates. The present work aims to gain more understanding of the gas generation and transport in inorganic sand binder systems. We developed a test stand to measure the temperature-dependent core gas release in inorganically-bound foundry cores and their gas permeability. Samples were prepared in a core blowing process and analyzed using the test stand. The measurement results are in good agreement with validation experiments and existing literature

Compensation for geometrical deviations in additive manufacturing

The design of additive manufacturing processes, especially for batch production in industrial practice, is of high importance for the propagation of new additive manufacturing technology. Manual redesign procedures of the additive manufactured parts based on discrete measurement data or numerical meshes are error prone and hardly automatable. To achieve the required final accuracy of the parts, often, various iterations are necessary. To address these issues, a data-driven geometrical compensation approach is proposed that adapts concepts from forming technology. The measurement information of a first calibration cycle of manufactured parts is the basis of the approach. Through non-rigid transformations of the part geometry, a new shape for the subsequent additive manufacturing process was derived in a systematic way. Based on a purely geometrical approach, the systematic portion of part deviations can be compensated. The proposed concept is presented first and was applied to a sample fin-shaped part. The deviation data of three manufacturing cycles was utilised for validation and verification