AddMe.Lab is the Additive Manufacturing laboratory established in 2014 at the Department of Mechanical Engineering of Politecnico di Milano. The laboratory was founded with the contribution of research groups of the Department, the Lombardy Region and the support of leading companies of the Italian industry: BLM Group, Marposs Italia, MasperoTech, Sapio, and Titalia.

AddMe.Lab was born with the idea of stimulating the collaboration and the generation of ideas among the different research groups active in the Department specialized in product design, materials, process technologies, as well as with students and professionals of the sector and the Lombard industrial scene. The result is a unique center for experimentation, creation of new process concepts and implementation of metal additive manufacturing techniques for different sectors such as mechanics, biomedicine, aerospace, oil & gas, and industrial design. AddMe.Lab aims to set up and maintain a dense and wide network of knowledge and skills with the aid of various competences and equipment available in the laboratories of the Department of Mechanical Engineering.

Additive manufacturing processes for metals, ceramics, and composites

Additive manufacturing refers to all the technologies that allow obtaining 3D products of complex geometry and with high functional performances thanks to deposition in a layer-by-layer fashion, as opposed to the subtractive fabrication that involves traditional machining processes. The main processes suitable for metallic and ceramic materials are manifold, mainly related to the deposition in a powder bed and to direct deposition.

The powder bed fusion (PBF) processes are instead based on layer-by-layer melting of powder using a laser or an electron beam as the energy source, in order to create a three-dimensional object. The process is carried out inside a chamber of relatively small dimensions under an inert gas atmosphere in the case of a laser-based process, or under vacuum in the case of the electron beam-based process.

The directed energy deposition (DED) processes originate from relatively consolidated surface coating techniques. Today these processes have been modified to achieve 3D objects commonly for thin-walled or solid parts. The DED processes are found to be more suitable for large parts owing to the fact that new volumes are deposited through the melting of powder or wire feedstocks. In AddMe.Lab, laser-based DED processes are developed using powder and wire feedstocks for laser metal deposition and laser metal wire deposition techniques.

Alongside these technologies, which can now be considered almost as standard, more recently binder jetting or extrusion based AM techniques are being developed using polymeric binders together with metal or ceramic powder. A green part is obtained at the end of the deposition stage, which is then subjected to debinding and sintering treatments in order to obtain fully dense components. The main aim of these alternative processes is to process difficult materials and the reduction of the processing costs.

Add.Me Lab processes and systems

The main benefits offered by additive manufacturing technologies can be summarized as the greater freedom of design, the use of lightweight structures using lattices and variable sections, the possibility to use bio-inspired solutions, the implementation of internal channels with complex geometries to improve the heat exchange, the reduction of the number of parts in an assembly, the net-shape fabrication with minimal material waste compared to subtractive processing, the production of parts without the need for molds or other equipment, and the reduced production cycles from the design to the final parts, where the geometric complexity has a marginal influence on manufacturing time and cost. The additive manufacturing processes allow for customized and sustainable production through lightweight design and the reduction of the number of components.

AddMe.Lab was born in 2014 with the acquisition of the first laser powder bed fusion system, the Renishaw AM250. The process capabilities and the machinery available to the lab have grown rapidly throughout the time, as collaborations with other companies and research centres have been established.

Currently, the AddMe.Lab is equipped with several Laser Powder Bed Fusion (LPBF, also known as Selective Laser Melting) systems. The Renishaw AM250 and Trumpf TruPrint 3000 systems represent state-of-the-art industrial solutions that incorporate fiber lasers operating with pulsed and continuous emission modes, respectively. The Renishaw AM250 is equipped with a 200 W laser and a working volume of 250x250x300 mm3. The system can also operate with a reduced build volume (RBV) system capable of working with very small amounts of powder, facilitating the test and production of non-standard materials. The Trumpf TruPrint 3000 is equipped with a 400 W laser, a cylindrical working volume with a diameter of 300 mm and a depth of 400 mm, and an advanced powder management system. In addition to industrial systems, novel prototype systems have been developed and patented. The novel LPBF platforms encompass multi-material sample production, high temperature preheating capabilities as well as advanced defect monitoring and removal systems. Among these, the new "Penelope" system provides real-time identification of defects combining big data analytics and machine learning techniques, with a novel capability of in-situ and in-line removal of the identified defect.

The Department of Mechanical Engineering has been recently awarded the title of "Department of Excellence" receiving significant funding within the LIS4.0 project. Additive Manufacturing has been within the core of the Department of Excellence project and the funding has been used to expand the hardware capabilities with an additional "open" and highly sensorized LPBF system from 3D New Technologies with the ability to obtain high powder bed pre-heating. The new LPBF system will be used to study novel solutions to process difficult materials with complex geometries. The integration of the information flow (images, videos, signals) that support the printing process in-line and in-situ will allow the identification of defects and the development of real-time control solutions.

Within AddMe.Lab, electron beam melting (EBM) is studied with an Arcam A2 system. The system was acquired as part of a collaboration between the Department of Mechanical Engineering, the Department of Aerospace Science and Technology and the Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”. The Arcam A2 system is a system with high flexibility in terms of pre-heating temperature (up to approximately 1200 ° C), with a volume of 210 x 210 x 350 mm3 and a maximum electron beam power of 3500 W. The high scan speeds (up to 8000 m/s) guarantees high productivity, as well as the possibility to exploit the same beam for the pre-heating phase at high temperatures. The high preheating temperatures allow one to process materials such as inter-metallic alloys with brittle behavior, which are difficult to process by using other metal additive manufacturing processes.

The BLM ADDITUBE system is the laser metal deposition (LMD) system of the AddMe.Lab designed and realized in collaboration with the BLM Group. The system consists of a coaxial powder deposition head positioned by an anthropomorphic robot while the workpiece is handled by a rotating and tilting table. The KUKA Reis deposition is equipped with a pyrometer for temperature control and a coaxial vision system for monitoring the molten pool. Powder feeding is provided by a two-cylinder GTV GmbH powder feeder, which allows the realization of multi-material and multi-graded deposits. The designed system configuration enables the production of large components as well as complex and free-form shapes.

The ExOne Innovent System is one of the first units available in Italy based on binder jetting technology. With this technology, it is possible to process materials that are considered as critical or not suitable for the laser, such as refractory metals, hard metals containing carbides, and copper. The system provides the possibility of producing parts with very fine geometric details. The development of suitable sintering atmospheres and cycles to obtain components with optimal mechanical characteristics is relevant to this technology.

In 2014, the researchers of the Department designed the Efesto system, an innovative extrusion based deposition machine for the 3D printing of metallic and ceramic materials by extruding a mixture of powder and binder in the form of pellets, which was later patented in 2016. The deposition technology is very versatile compared to the materials that can be used. The system has been designed to incorporate the machining phase for a successful "hybrid" manufacturing process, as well as the thermal post-processing. The technology is based on the use of pellet feedstock, inheriting the know-how and the materials from Metal Injection Molding (MIM).

Thanks, once again, to the funding obtained with the "Department of Excellence" LIS4.0 project, AddMe.Lab has become one of the first labs in Europe to install a Desktop Metal Studio System+. The Desktop Metal machine is employed for the low-cost 3D printing of commonly used metals for additive manufacturing, as well as copper. The system will be fully operational by the end of 2019.

The AddMe.Lab machine park is completed by a system of collaborating robots for the construction of large free-form structures through an extrusion/pultrusion system for the production of objects in continous fiber composite reinforced thermoplastic and thermosetting polymers.

In order to have a complete grasp on additive manufacturing, the AddMe.Lab has also invested in innovative powder characterization systems. A Malvern Morphologi G3 system is used for powder size distribution measurements and morphological analysis. A Freeman Technology F4 system is used for rheological characterization of the different powder feedstocks. These systems aim to study how the properties of the powder change during their life cycle (following the recycling phase), as well as understanding which powder properties are fundamental for the quality of the final piece. Finally, the non-destructive characterization of the inner defects is analyzed employing a North Star Imaging X25 micro X-ray CT system with a resolution of 1 µm.

From design to product - Research at Add.Me Lab

Within Add.Me lab, research is conducted in different areas to meet the needs of the market by combining the aspects of material, process, design and qualification of the products.

The field of research on new materials for metal additive manufacturing is highly dynamic. The metal additive manufacturing process characteristics are very different from conventional manufacturing processes. Hence, the AddMe.Lab researchers take up the challenge to respond to the demand for the new alloys optimized for the metal additive processes. The designed alloys will provide better material properties and defect-free process conditions. In addition, new frontiers are opened for the design of multi-material parts combining multiple materials alloys with a composition that varies from area to area according to specific functional requirements, as well as lattice structures.

Together with the processes, a great interest towards the powder feedstock has risen over the recent years. AddMe.Lab investigates powder morphology, chemistry, and rheological properties of the powder in order to assess their influence on process defects as well as other issues related to powder recycling and sustainable manufacturing.

The AddMe.Lab researchers work extensively on solving the problems related to the processability of new materials with the metal additive technologies, concerning the optimization of process parameters, and the development of innovative machine architectures. Experimental and modeling techniques are involved both for the solution of feasibility problems and for the basic understanding of physical phenomena.

One of the research topics is the characterization of the defects typical of additive processes and the development of "zero defect 4.0" solutions aimed at reducing defects and improving product quality in terms of resolution, accuracy, repeatability, and geometric complexity. Innovative solutions are studied and developed for the complete digitalization of the process from an Industry 4.0 perspective, such as the on-line monitoring of the process based on data acquired from in-situ sensors. Several techniques involving images and videos with high temporal and spatial resolution in different optical wavelengths are studied and developed. The researchers develop methods able to quickly and robustly identify the occurrence of defects and process errors. Novel methods for the analysis and quality control of products with complex geometries and lightweight structures typical of additive manufacturing processes are studied too.

The possibility of creating components characterized by a high geometric and functional complexity and at different dimensional scales offers new design stimuli for several applications. The development of multi-functional lattice structures and metal-materials, as well as of highly customized solutions represent only some of the design possibilities offered by additive manufacturing technologies. The AddMe.Lab researchers investigate the Design for Additive Manufacturing criteria to fully exploit these possibilities. The new design paradigm requires the renewal and the evolution of both the methods and the design tools.

In the context of Design for Additive Manufacturing, the AddMe.Lab researchers work on the development of innovative solutions that allow one to fully exploit the potential of additive manufacturing technologies, and to support the designers in managing and using these possibilities to their advantage. In a more general perspective, the ultimate aim is to contribute to the development and optimal use of all the hardware and software tools in order to be able to draw the largest benefits.

The AddMe.Lab researcher also investigate the methods for estimating structural integrity (static, fatigue and fracture resistance) of metal additive manufacturing products for an adequate evaluation of the component's performance. The novel metal additive manufacturing process requires the adaptation of the conventional mechanical design criteria methods. In this context, an innovative probabilistic calculation model has been developed, together with the calculation methods for the properties of metamaterials, made of micro-lattice and cellular structures.