Polymer Powder Spread Process Monitoring System
DMRC Project – Low Cost Process Monitoring
Machine and part qualification are always based on the information gathered. For a proper qualification and for confidence gaining
in the LS technology the process itself should be observed and monitored as precisely as possible. Within this DMRC project a high-resolution images-based powder spread monitoring system for the laser sintering process has been developed. For each layer an image is captured and fed to a Region Based Convolutional Neural Network (Mask R-CNN) feature detection software, where it is analysed for powder spread flaws. The software is capable to detect point, line and area flaws within the powder spread and can differentiate those from the exposure area of the parts. The process monitoring system is therefore able to alert the operator, if the powder spread went wrong in a critical way, affecting the part quality. With this information the part can be directly rejected, set to no exposure or the job can be stopped to save powder material, time and costs.
Hardware
The developed system is a retrofittable system, containing four assembly unites plus the processing unit for the software. First the relevant process information as recoater position, preheating phase and exposure areas are collected. A light positioned in front of the process chamber door increases the shadow casting of the
powder surface topology. Powder spread flaws tend to cast much more concise shadows, which helps to identify those imperfections. The image detection software is than able to identify critical areas and highlight the flaws. Additionally, the failure severity, hence the expected intensity of the failure, is rated with a score. This allows to differentiate between minor powder spread imperfections and critical flaws, which show an impact on the part optical and haptical or the mechanical properties.
Achievements
This system is the first powder spread monitoring system for the laser sintering technology, which is running fully automatically and gives in detail insides on the importance of the powder spread process.
