Michael Karg

Additive manufacturing in production: challenges and opportunities

Additive manufacturing, characterized by its inherent layer by layer fabrication methodology has been coined by many as the latest revolution in the manufacturing industry. Due to its diversification of Materials, processes, system technology and applications, Additive Manufacturing has been synonymized with terminology such as Rapid prototyping, 3D printing, free-form fabrication, Additive Layer Manufacturing, etc. A huge media and public interest in the technology has led to an innovative attempt of exploring the technology for applications beyond the scope of the traditional engineering industry. Nevertheless, it is believed that a critical factor for the long-term success of Additive Manufacturing would be its ability to fulfill the requirements defined by the traditional manufacturing industry. A parallel development in market trends and product requirements has also lead to a wider scope of opportunities for Additive Manufacturing. The presented paper discusses some of the key challenges which are critical to ensure that Additive Manufacturing is truly accepted as a mainstream production technology in the industry. These challenges would highlight on various aspects of production such as product requirements, process management, data management, intellectual property, work flow management, quality assurance, resource planning, etc. In Addition, changing market trends such as product life cycle, mass customization, sustainability, environmental impact and localized production will form the foundation for the follow up discussion on the current limitations and the corresponding research opportunities. A discussion on ongoing research to address these challenges would include topics like process monitoring, design complexity, process standardization, multi-material and hybrid fabrication, new material development, etc.

Effects of Process Conditions on the Mechanical Behavior of Aluminium Wrought Alloy EN AW-2219 (AlCu6Mn) Additively Manufactured by Laser Beam Melting in Powder Bed

Additive manufacturing is especially suitable for complex-shaped 3D parts with integrated and optimized functionality realized by filigree geometries. Such designs benefit from low safety factors in mechanical layout. This demands ductile materials that reduce stress peaks by predictable plastic deformation instead of failure. Al–Cu wrought alloys are established materials meeting this requirement. Additionally, they provide high specific strengths. As the designation “Wrought Alloys” implies, they are intended for manufacturing by hot or cold working. When cast or welded, they are prone to solidification cracks. Al–Si fillers can alleviate this, but impair ductility. Being closely related to welding, Laser Beam Melting in Powder Bed (LBM) of Al–Cu wrought alloys like EN AW-2219 can be considered challenging. In LBM of aluminium alloys, only easily-weldable Al–Si casting alloys have succeeded commercially today. This article discusses the influences of boundary conditions during LBM of EN AW-2219 on sample porosity and tensile test results, supported by metallographic microsections and fractography. Load direction was varied relative to LBM build-up direction. T6 heat treatment was applied to half of the samples. Pronounced anisotropy was observed. Remarkably, elongation at break of T6 specimens loaded along the build-up direction exceeded the values from literature for conventionally manufactured EN AW-2219 by a factor of two.

A ROUND ROBIN STUDY FOR LASER BEAM MELTING IN A METAL POWDER BED

With recent developments in additive manufacturing, there has been a keen interest in understanding its possibilities and limitations specifically with respect to the conventional engineering and manufacturing standards. Although coined as a prototyping technology at the time of its inception, Additive manufacturing with its characteristic layer by layer fabrication methodology is now the focus of end product manufacturing for many niche applications. One of the key additive manufacturing processes leading this evolution is the process of Laser Beam Melting in metal powder bed. With its ability to fabricate fully dense 3-dimensional structures by selectively melting micro-sized metal powder, Laser Beam Melting is being considered by many as a significant complimentary technology to the conventional forming and subtractive manufacturing processes. In order to completely understand the abilities and limitations of the Laser Beam Melting process, a detailed analysis of the system technology, process and user induced variations in relation to the characteristics of the resultant part needs to be performed. With the above motivations in mind, an initiative at the Collaborative Working Group, Lasers in production at the International Academy of Production Engineering (CIRP) was undertaken to conduct a comparative study in the form of a Round Robin test by analyzing the mechanical characteristics of samples fabricated by various users of the Laser Beam Melting technology from volunteers within the members of the academy. The presented paper illustrates the design and methodology of the round robin test in addition to some preliminary results and makes an attempt to connect these results with the various phenomena occurring in the Laser Beam Melting process. Authors of the paper gratefully acknowledge the contributions from the various members of the Collaborative Working Group, Lasers in production at the International Academy of Production Engineering (CIRP) who volunteered for providing the samples for the conducted round robin test.

High power laser beam melting of Ti6Al4V on formed sheet metal to achieve hybrid structures

Motivated by the desire to combine the advantages of two manufacturing concepts, namely Additive Manufacturing and sheet metal forming, the concept of hybrid processes emerged. Laser Beam Melting process with its characteristic layer by layer fabrication methodology has already been proved to be successful in fabricating fully dense 3D structures with micro sized Ti6Al4V powder. The presented research focuses on direct fabrication of Ti6 Al4V Additive Structures on a thin pre-formed Ti6 Al4V sheet metal substrate. In the state of the art Laser Beam Melting process, fabrication of solid structures is done on a support structure attached to a thick conventionally manufactured base plate. The state of the art process also uses a 200°C pre-heating of the fabrication platform in order to reduce the effect of heat induced stresses on the fabricated structures. Within the hybrid fabrication concept, 3D structures are directly fabricated on a thin sheet metal and the thermodynamic conditions are significantly different in comparison to the conventional process. The research aims at understanding the fundamental aspects of the interaction between the formed sheet metal and additive structure determines the corresponding mechanical characteristics. The interaction process during the fabrication exposes the alloy locally to non-optimum thermal cycles and the research therefore aims to understand the various influencing factors involved during the fabrication process. The system technology modifications required to achieve the aimed fabrication are also discussed in the presented research.

Laser Alloying Advantages by Dry Coating Metallic Powder Mixtures with SiOx Nanoparticles

Up to now, minimizing segregation of free-flowing, microscale metal powder mixtures driven by different mass density is an open challenge. In this work, effects of particle size variation on homogeneity of Al-Cu mixtures, with a density ratio of 3.3, are examined. Dry coating Al particles with 0.3 wt% fumed silica SiOx nanoparticles significantly decreases interparticle attraction. This enlarges the range of free-flowing Al particle sizes to < 20 µm. Powder mixture homogeneity is examined optically in vibrated bulk powder and thinly spread layers. From various powder mixtures, solid samples are built layer by layer with the Additive Manufacturing (3D printing) technology Laser Beam Melting in metal powder bed (LBM). Chemical homogeneity of solids is evaluated via energy-dispersive X-ray spectroscopy, backscattered electron microscopy, metallographic analysis and tensile tests. Persistent homogeneity of Al-Cu powder mixtures and LBM solids is found only with particles < 20 µm dry coated with SiOx nanoparticles. Observed segregation phenomena are explained with a decrease in particle mobility at increasing local concentration and the decreasing effectiveness of mass in smaller particles. The main effects are based on geometry, so they are expected to be transferrable to other nanoparticles, alloying components and powder bed technologies, e.g., binder jetting.

Determination of laser beam focus position based on secondary speckles pattern analysis

Proper positioning of a laser beam focus is a universal problem for various applications that does not have a universal solution. Quite often the taken approach relies on some sort of a calibration and temporal stability of the laser and the optical train. While such an approach can be suitable for a large number of applications its applicability becomes limited in the cases where the laser beam properties uncontrollably change with time. The latter can occur due to the thermal effects, for example. In those cases, the laser focus positioning method should include direct analysis of the laser beam properties. In this contribution we present a simple optical method based on the secondary speckles pattern analysis suitable for determination of the absolute focal spot position. The method does not require any a priori knowledge of the laser beam properties and is suitable for various diffuse or partially diffuse surfaces of interest.