Analysis of Melt Pool Characteristics and Process Parameters Using a Coaxial Monitoring System during Directed Energy Deposition in Additive Manufacturing

The growing number of commercially available machines for laser deposition welding show the growing acceptance and importance of this technology for industrial applications. Their increasing usage in research and production requires process stability and user-friendly handling. A commercially available DMG MORI LT 65 3D hybrid machine used in combination with a CCD-based coaxial temperature measurement system was utilized in this work to investigate what information relating to the intensity distribution of melt pool surfaces could be appropriate to draw conclusions about process conditions. In this study it is shown how the minimal required specific energy for a stable process can be determined, and it is indicated that the evolution of a plasma plume depends on thermal energy within the base material. An estimated melt pool area—calculated by the number of pixels (NOP) with intensities larger than a fixed, predefined threshold—builds the main measure in analysing images from the process camera. The melt pool area and its temporal variance can also serve as an indicator for an increased working distance.

Digitalization: Laser Metal Deposition — The Future of Spare Parts and Repairs for Industrial Steam Turbines

Laser metal deposition (LMD) — also referred to as laser deposition welding — has been a well-established process for years. One example of its use is for tip repair for gas turbine blades from Siemens. The decision to also implement laser welding technology for the service of industrial steam turbines was based primarily on the fact that repairs — especially conventional welds and coatings including heat treatment and testing — are very time consuming and are very difficult to reconcile with the overhaul periods planned by customers. The robot supported automation of the LMD process and the fact of its lower heat input, reduced layer thicknesses and the resulting lowered deformation of the part due to reduced coating areas makes it possible to optimize lead times. The high level of process automation and reliability of a laser welding process represents another important benefit. Similarly, process parameters are constantly monitored and tracked, to ensure that the required quality standards are maintained and even increased. Furthermore, laser metal deposition completely replaced the conventional processes such as tungsten inert gas method (TIG), plasma transferred arc (PTA) and detonation spraying. In addition the technology unleashes now the possibility to repair and refurbish parts instead of new manufacturing, and therefore delivery times can be tremendously reduced. Based on the decision to six-axis robots it becomes possible enhancing the LMD process for complex 3D surfaces. After modeling a digital twin in Siemens NX CAM it is possible to generate, optimize and simulate the whole motion-sequences offline before starting the LMD process in the robot cell. So already designed parts in 3D-CAD can be used to develop the final robot program. In addition already existing technologies like 3D surface scanning will be implemented in the chain to support the LMD process. Digitalization turns from a buzzword to an established technology for industrial steam turbine manufacturing and repair.

Generative Fertigung von Verdichterschaufeln einer Blisk*/Additive manufacturing of compressor blades for blisk – Wire-based laser deposition welding for resource efficient production

Generative Fertigungsverfahren erlauben komplexe, individualisierte und anwendungsgerechte Geometrien. Mit Technologien wie dem drahtbasierten Laserauftragschweißen ist es darüber hinaus möglich, ressourceneffizient zu fertigen. So können etwa durch das Auftragen von Schichten auf einen Grundkörper Rohkonturen von Verdichterschaufeln im Turbomaschinenbau hergestellt werden. Dies ersetzt, im Vergleich zur herkömmlichen abtragenden Fertigung, den Schruppprozess und gestattet eine signifikante Kosteneinsparung. Dieser Ansatz wird hier im Rahmen der Fertigung und metallographischen Untersuchung eines Demonstrators beschrieben.   Additive manufacturing allows for complex, individualized and customized geometries. With technologies such as wire-based laser deposition welding, it is also possible to make production more resource-efficient. For instance, this technology helps to produce rough geometries of compressor blades for turbo machinery by depositing layers on a substrate. It substitutes conventional roughing strategies by milling and enables a significant cost reduction. This paper describes the new manufacturing technique in the context of metallographic examination using a demonstrator.