55 research outputs found
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Position Dependency of Surface Roughness in Parts from Laser Beam Melting Systems
Laser Beam Melting is a promising Additive Manufacturing technology for the production of complex
metal components. During batch production of multiple identical parts in a single build job, we observed parts
with deviating surface roughness in certain areas, which all faced away from the laser. This suggests a dependency
of surface roughness on the part position in the build chamber. In this work we systematically reproduce and
analyze this effect. We place hollow pyramids with twelve faces and two different overhanging angles at nine
positions on the substrate plate and build this setup twice, using an imaging setup for process documentation.
Surface roughness is measured by contact profilometry on three lines for each pyramid face. Our experiments
reproduce the effect. Based on these findings we present a hypothesis for the cause and show metallographic
images to support our theory. As a consequence, the position relative to the laser should be considered in the
design phase for parts with high surface quality requirements.Mechanical Engineerin
Domain types: abstract-domain selection based on variable usage
The success of software model checking depends on finding an appropriate abstraction of the program to verify. The choice of the abstract domain and the analysis configuration is currently left to the user, who may not be familiar with the tradeoffs and performance details of the available abstract domains. We introduce the concept of domain types, which classify the program variables into types that are more fine-grained than standard declared types (e.g., ‘int’ and ‘long’) to guide the selection of an appropriate abstract domain for a model checker. Our implementation on top of an existing verification framework determines the domain type for each variable in a pre-analysis step, based on the usage of variables in the program, and then assigns each variable to an abstract domain. Based on a series of experiments on a comprehensive set of verification tasks from international verification competitions, we demonstrate that the choice of the abstract domain per variable (we consider one explicit and one symbolic domain) can substantially improve the verification in terms of performance and precision
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