Refine
Document Type
Publication reviewed
- peer review (12)
- begutachtet (6)
- nicht begutachtet (1)
Keywords
- EffPro (2)
- Automatic labeling (1)
- Computer vision (1)
- Crystal structure (1)
- Crystallinity (1)
- Gießerei (1)
- Laser sintering (1)
- Online Messung (1)
- Permeation properties (1)
- Physically Based rendering (1)
Laser sintering of polymers is widely used for the production of individual products and small-batch series. However, the qualification of laser-sintered polymeric components for new application fields, e.g. in the food and packaging industry, is still limited due to missing knowledge on physicochemical material properties. This work investigates the mass transfer of low molecular weight substances through laser-sintered polyamide 12 sheets in comparison to an extruded polyamide 12 film. Analysis of structural material properties reveals significant differences between both materials depending on the production processes. Despite their apparent porosity, laser-sintered sheets show lower permeation coefficients for water vapor and oxygen compared to extruded films. This might be related to the higher crystallinity of the laser-sintered vs. the extruded material, arising from the slow cooling rate of the polymer in the laser sintering process.
This research brings knowledge of the different permeation behavior of laser-sintered and extruded polyamide 12 in relation to the structural properties.
Porosity distribution in laser-sintered polymeric thin sheets as revealed by X-ray micro tomography
(2019)
Laser Sintering (LS) is an additive manufacturing technology that is progressively used to manufacture functional products for end-use applications. However, LS technology provides limited ability to produce thin-walled structures that feature high material quality. A key parameter determining the quality of LS polymeric parts is porosity. This article presents a new approach towards clarifying the porosity characteristics of thin-walled structures produced by LS. Therefore, thin sheets of different thickness built in different orientations within the building chamber are examined by means of X-ray micro tomography. The porosity analysis includes the overall porosity, pore number density, pore size distribution and porosity distribution along the thickness of the thin sheets. The results show that the porosity characteristics strongly depend on the thickness and the build orientation of the thin sheets. This investigation helps to estimate the quality of three dimensional hollow bodies produced by LS and moreover, contributes to a better understanding of the pore formation in LS processes.
Punching is a process that is sensitive to a multitude of parameters. The estimation of part and punch quality is often based on expert knowledge and trial-and-error methods, mostly carried out as a separate offline process analysis. In a previous study, we developed an optical inline monitoring system with subsequent image processing which showed promising results in terms of capturing every manufactured part, but was limited by slow image processing. Here, we present a more efficient image processing technique based on neural networks. For our approach, we manually identify the burnish parts in images based on criteria established via an expert survey in order to generate a training dataset. We then employ a combination of region-based and boundary-based losses to optimize the neural network towards a segmentation of the burnish surface which allows for an accurate measurement of the burnish height. The hyperparameter optimization is based on custom evaluation metrics that reflect the requirements of the burnish surface identification problem as well. After comparing different neural network architectures, we focus on optimizing the backbone of the UNet++ structure for our task. The promising results demonstrate that neural networks are indeed capable of an inline segmentation that can be used for measuring the burnish surface of punching parts.
The laser sintering of polymers is an additive manufacturing technology that is becoming increasingly established in the industrial environment. This study investigated the thickness‐ dependent permeation properties of laser‐sintered (LS) polymers as required to design and produce components with a special barrier performance to gaseous substances. Helium and oxygen permeation experiments were carried out on quenched and standard LS polyamide 12 (PA12) sheets generated with two, four, six, and eight layers at a constant powder layer thickness of 100 μm. The structural properties of the sheets were examined by differential scanning calorimetry, light microscopy, and X‐ray micro‐computed tomography. A reduction in thickness resulted in higher diffusion coefficients for both types of LS sheets. An explanation could be the large volume fraction of poorly sintered powder particles adhering to the surfaces and incomplete melting and low consolidation of the polymer at small thicknesses. The thickness‐dependency of the solubility coefficients was the opposite, especially for the standard LS sheets, which might be related to the larger pore volume in thicker sheets. As both effects compensated for each other, nearly constant permeation coefficients for all thicknesses were observed. The results provide further insights into different material characteristics of thin LS PA12 structures and offer new information on factors relevant to their solution and diffusion behavior.
We present a highly miniaturized endoscopic point distance sensor based on a spatial confocal measurement principle. The sensor uses a new technique called spatial confocal point distance measurement. A special feature of the proposed sensor design is the high degree of miniaturization through femtosecond direct laser writing and the use of optical fiber bundles, which enable an endoscopic application. We show the complete sensor measurement principle, sensor head design, experimental setup, and experimental results.
Increasing miniaturization requires improved and highly miniaturized optical 3D metrology systems. In this paper a basic measurement principle and a proposed optical design of a highly miniaturized endoscopic spatial confocal point distance sensor are presented. The sensor uses a, to our knowledge new technique called spatial confocal point distance measurement. A special feature of the proposed sensor design is the high degree of miniaturization, through femtosecond direct laser writing and the use of optical fiber bundles, which enable an endoscopic application.
Um eine hohe Qualität und Zuverlässigkeit der gefertigten Produkte in einer Gießerei sicherzustellen, muss innerhalb der Serienprozesse eine zuverlässige Identifizierung eines jeden Gussteiles und die Rückverfolgbarkeit dessen Produktionsparameter möglich sein. Dabei stellen die oft rauen Umgebungsbedingungen sehr hohe Anforderungen an die Robustheit der Markierungseinheit und die Genauigkeit der zugehörigen Ausleseeinheit. Gleichzeitig müssen eine hohe Anzahl an individuellen Markierungsmöglichkeiten bei geringem Flächenbedarf realisiert werden. An der Hochschule Kempten wird im Forschungsprojekt CastCode in Kooperation mit Partnern aus der Gießereibranche ein ganzheitliches Markierungs- und Auslesekonzept entwickelt, welches diesen hohen Anforderungen genügen soll. Dabei wird die Markierung bereits im Formkasten durchgeführt,sodass sie direkt nach dem Abguss auf der Gussteiloberfläche abgebildet ist und ausgelesen werden kann.
This study aims to investigate the effect of the material thickness and build orientation on the mass transfer of low molecular weight substances through polyamide 12 (PA12) structures produced by laser sintering (LS).
Design/methodology/approach
Disc-shaped PA12 sheets having a nominal thickness ranging from 700 to 2,000 µm were built in horizontal, vertical and diagonal orientations and their permeation properties to oxygen and water vapor were measured. The structural properties of the sheets were examined by X-ray micro-computed tomography, differential scanning calorimetry and polarized light microscopy.
Findings
All the LS sheets that were investigated had water vapor and oxygen permeation coefficients that are in the range of those of PA12 produced by traditional manufacturing technologies. Despite significant differences in the porosity characteristics, the permeation properties of sheets built in different orientations were similar. The pores seem to have no measurable effect on the mass transfer rates in the sheets, and the transport processes seem to predominantly follow the rules of a regular solution-diffusion mechanism. The results showed a non-significant trend toward thickness-dependent permeation coefficients, which agrees with the observed differences in the crystal structures of the sheets.
Practical implications
The results are an important basis for the qualification of LS technology for direct manufacturing in applications requiring special barrier performance.
Originality/value
This study provides new information on mechanisms of mass transport through LS PA12 and the effect of the material thickness and build orientation. Furthermore, the results enhance understanding of the structural properties of thin polymeric sheets produced by LS.
Punching is a wide-spread production process, applied when massive amounts of the ever-same cheap parts are needed. The punching process is sensitive to a multitude of parameters. Unfortunately, the precise dependencies are often unknown. A prerequisite for optimal, reproducible and transparent process alignment is the knowledge of how exactly parameters influence the quality of a punching part, which in turn requires a quantitative description of the quality of a part. We developed an optical inline monitoring system, which consists of a combined imaging and triangulation sensor as well as subsequent image processing. We show that it is possible to capture images of the cutting surface for every part within production. We automatically derive quality parameters using the example of the burnish height from 2D images. In addition, the 3D parameters are calculated and verified from the triangulation images. As an application, we show that the status of tool wear can be inferred by monitoring the burnish height, with immediate consequences for predictive maintenance. Although limited by slow images processing in our prototype, we conclude that connecting machine and process parameters with quality metrics in real time for every single part enables data-driven process modelling and ultimately the implementation of intelligent punching machines.
Zunächst wird die aktuelle Situation der Schnittflächenkenngrößenermittlung innerhalb des Stanzprozesses in der Industrie beleuchtet und den steigenden Qualitätsanforderungen sowie anwendungsindividualisierbaren Produkten/Prozessen gegenübergestellt.
Auf dieser Basis wird ein optisches Inline-System entwickelt. Dieses System ermöglicht die Aufzeichnung der Schnittflächenqualität in einer Prozessgeschwindigkeit von 250 Hub/min mittels Bildaufnahme. Zusätzlich werden über einen integrierten Triangulationssensor dreidimensionale Schnitte der Schnittkante aufgenommen. Eine entwickelte Bildverarbeitung ermittelt aus den Daten der Bildaufnahme automatisiert und reproduzierbar die Glattschnitthöhe. Die Ermittlung weiterer Schnittflächenkenngrößen ist denkbar, wobei dreidimensionale Daten aus dem Triangulationssensor entstehen. Zusätzlich wird die erreichte Genauigkeit der Systems validiert. Abschließend wird ein Ausblick gegeben, welcher im Besonderen dieses System als Grundlage für die Öffnung der Steuerung des Stanzprozesses mittels intelligenter Methoden sieht. Dies wird an einem Praxisbeispiel unterstrichten.
