Investment casting

Résumé

Investment casting is an industrial process based on lost-wax casting, one of the oldest known metal-forming techniques. The term "lost-wax casting" can also refer to modern investment casting processes. Investment casting has been used in various forms for the last 5,000 years. In its earliest forms, beeswax was used to form patterns necessary for the casting process. Today, more advanced waxes, refractory materials and specialist alloys are typically used for making patterns. Investment casting is valued for its ability to produce components with accuracy, repeatability, versatility and integrity in a variety of metals and high-performance alloys. The fragile wax patterns must withstand forces encountered during the mould making. Much of the wax used in investment casting can be reclaimed and reused. Lost-foam casting is a modern form of investment casting that eliminates certain steps in the process. Investment casting is so named because the process invests (surrounds) the pat

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https://en.wikipedia.org/wiki/Investment_casting

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Development of High-Strength Aluminum Alloys for Additive Manufacturing

Marvin Lennard Schuster

Metal additive manufacturing (AM) offers the possibility to rapidly produce complex geometries that are not achievable with conventional manufacturing methods. The two most common technologies, Laser Powder Bed Fusion (LPBF) and Direct Metal Deposition (DMD), are characterized by high process temperatures, fast heating, and cooling rates, and an associated far-from-equilibrium solidification. This is problematic when processing materials that were developed and optimized many years ago for conventional manufacturing processes. Common difficulties are the occurrence of gas pores in the component, which are caused by the evaporation of volatile alloying elements during the process, the formation of hot cracks due to large solidification intervals, and the formation of metastable phases. For the processing of high-strength, precipitation-hardening Al-Cu aluminum alloys, this prevents the use of non-modified conventional alloys. However, the development of novel alloys tailored to these processes not only allows these difficulties to be overcome but also opens up the possibility of improving material properties through the targeted exploitation of process-inherent properties. This includes the processing of oxide particle-reinforced alloys, which can not be produced by conventional casting processes. The standard heat treatment usually performed for precipitation hardening, which has also been optimized for conventional materials, must be adapted accordingly to achieve optimum material properties. Within the scope of this work, the microstructure, precipitation, and defect formation after LPBF as well as the heat treatment behavior are thoroughly investigated based on an Al-Cu-Mg-Zr alloy for the first time. The obtained findings are applied to design a novel 2618 Al-Cu alloy for LPBF and DMD, with suitable heat treatment being developed for LPBF. The alloy is characterized with respect to microstructure, precipitation formation, and mechanical properties before, during, and after heat treatment. Furthermore, by modifying elemental Al-Zr powder blends with nm-sized Al2O3, an oxide dispersion strengthened alloy is produced by LPBF and investigated in detail.

EPFL2022

Chargement

Mass is one of the crucial parameters for hardware that has to be placed in Earth orbit. Due to its harsh environment, a material with highest specific properties is desired to achieve space missions. The rise and development of new technologies, such as additive manufacturing (AM), opened new opportunities in part-design complexity, periodic cellular structures (PCS) being one of them. The present thesis investigates the potential implementation of PCS in space applications, particularly for structures and micro-meteoroids and orbital debris (MMOD) impact shields. This was achieved in three steps: Four different types of AlSi12 PCS manufactured by selective laser melting (SLM) were tested under quasi-static compression to measure the mechanical properties dependency versus topology and to characterize the failure mode. Properties ranging from 3 to 4 GPa for the compressive modulus, 5 to 12 MPa for the yield stress, 12 to 20 MPa for the plateau stress, and 2 to 8 MJ/cm3 for the absorbed energy were obtained. An unexpected failure mode was observed when compared to classical cellular metals, namely a brittle failure occurring by global shearing. A predictive failure criterion was established based on topology considerations and correlated to most of the reported results in the literature. A preliminary test campaign on tensile specimens was performed to compute numerical models that were fed into a finite element analysis. Good agreement with experimental data was shown, and the importance of microplasticity effects in this class of material was highlighted. An alternative process was developed to produce AlSi1 PCS by investment casting. The process is based on replication of a polymer preform used to build a NaCl mold. It was observed that the quality of the final cast part depends mainly on the grain size of the salt, with an optimum identified for distributions between 125 and 180 um. Optimization of the process allowed to reduce the drying time by a factor 6. Main process parameters include a drying temperature of 80C and infiltration at 660C under 300 mbar. From this process, PCSs having an energy absorption capacity of 15 MJ/m3 with an efficiency of 80% were produced. Hypervelocity impact tests were conducted on cast PCS and stochastic structures. The objective being to hit the structures with a 2mm-diameter aluminum sphere at velocities close to 7 km/s. Influence of the sample topology, the orientation, and the bumper material was assessed. Stochastic structures successfully stopped the projectile in all configurations. The beneficial effect of the bumper was measured reducing the crater depth from 20 mm to 14 mm. This type of structure exhibited a comparable areal density (0.8 g/cm2) to simple Whipple shield design. PCS poorly performed in mitigating the impact as the debris passed through all the structures, independently of the test configuration due to the open-channels present. PCS are good candidates to be used in space hardware, but their design and the manufacturing process need to be carefully chosen depending on the specific application. AM PCS are suitable for structural application with a high compressive modulus and yield stress. Cast PCS would perfectly fit in shock absorbers. A more random design would be preferable for MMOD shielding applications.

EPFL2018

Chargement

The Investment Casting of Copper at the Microsacle

Jérôme Krebs, Nadja Marxer, Csilla Mikó, Andreas Mortensen

2011

Chargement

Development of High-Strength Aluminum Alloys for Additive Manufacturing

Marvin Lennard Schuster

EPFL2022

EPFL2018