Exentis DNAComplex interaction between different fields of expertise

The Exentis DNA, i.e. the complex interaction of fields of expertise, ranging from the initial material composition to industrial production and suppling of the 3D printed parts, largely involves six pillars, which are used at Exentis in an extensively patented process that has been developed during several decades: Exentis 3D Mass Customization®.

Exentis DNA in a nutshell

Selecting the certification regime

  • Industrial
  • Aerospace
  • Automotive
  • Pharmaceuticals and product requirements
  • Bioprinting
  • Medical engineering

Material development

  • Metal, ceramics, polymer, biomaterials
  • Morphology
  • Grain size/distribution
  • Particle shape/li>
  • Granulates
  • Purity
  • Pre-treatment
  • Quality assurance

Paste system production

  • Viscosity
  • Binders
  • Plasticisers
  • Additives
  • Liquefiers
  • Solvents
  • Storage
  • Pre-treatment
  • Quality assurance

Screen development and production

  • Material for fabric threads
  • Fabric angles
  • Thread diameter
  • Mesh size
  • Screen tension
  • Frames
  • Pre-treatment
  • Templates
  • Screen resolution of up to 19000 dpi
  • Quality assurance

3D screen printing parameters

  • Printing parameters
  • Squeegee material/angle
  • Printing speed
  • Paste consistency
  • Drying technologies
  • Quality assurance

3D production system

  • Full automation in multi-layer operations
  • Multi-table or inline layout
  • Suitable for large-scale industrial production
  • Printing cycle time of 2-3 seconds
  • Integrated material drying
  • Quality assurance

Sintering for industrial parts

  • Exposure time
  • Temperature
  • Cooling
  • Air, inert gas
  • Shrinkage
  • Geometry
  • Object carrier
  • Documentation
  • Traceability
  • Traceability

The technology pillars of Exentis 3D Mass Customization®

The technology pillars of the extensively patented process technology, Exentis 3D Mass Customization®, guarantee the unique features of the Exentis 3D screen printing technology. They also help to anchor the process and achieve technological and business success with this additive manufacturing technology.

Technology pillar 1: choice of materials

The first stage involves defining the specific material requirement for the application in specific material requirements for the application in conjunction with the customer. The selection of material is extremely important in terms of the application properties. The 3D screen printing process is not only able to print metals and alloys based on steel, copper, aluminium, refractory metals or rare earths, but also ceramics, glass, polymers, organic substances and biomaterials. It is also possible to combine different materials as lamellar structures as a result of the layered arrangement. Composite materials complete the range.

The selection of the starting material in powder form is particularly important with ceramic and metal materials to ensure that the parts have the properties specified by the customer after passing through the complete process chain. By selecting a suitable powder for its morphology, grain size distribution and particle form, it is possible to specifically set the sinterability, the porosity, the conductibility and the mechanical properties. Pre-heating the powder, for example, by calcination, and its specific purity are absolutely essential and have a major influence on the chemical properties and printability.

The properties of the powder not only affect the features of the sintered part, but also have a direct effect on the ability to process the powder, for example, to achieve extremely fine structures with wall thicknesses of 60 micrometres, roughly the diameter of a human hair. The particle size distribution, the morphology and the particle form finally determine which screens can be used to print the paste systems. Abrasive particles require different properties to softer materials.

Technology pillar 2: developing paste systems

 
In the case of Exentis 3D Mass Customization®, the production of paste systems, i.e. making powders printable, is the crucial element in the high-tech 3D printing process. We might call it the “Coca Cola formula” for Exentis 3D screen printing technology. 3D screen printing makes it possible to process parts made of ceramics, metal and polymer systems, or even biomaterials. The starting material is available in powder form in most cases and paste systems are made from them by feeding in a number of additives.

When processing polymer systems and biomaterials, it is essential to know all about the processing window in terms of temperature, humidity, oxygen content and light sensitivity. These parameters must be individually defined for each system and do not permit even the slightest tolerances to assure that the desired properties are reproducible, i.e. on an industrial scale.

Choosing the right material and skills in the field of producing paste systems go hand in hand. If the right material is carefully selected, it is possible to influence the rheology, i.e. the flow behaviour, which deals with the forming and flowing performance of the substance, to create the desired properties.  

By making the right selection in terms of binders, plasticisers and other additives, it is possible to modify the viscosity of the paste. They are adapted to what is needed for the printed structure, the screens and the print height. The opportunity of using templates instead of screens or combining the two tools in the production process to maximise the printing height plays a major role when tailoring the rheological behaviour of the pastes. It is not only necessary to consider process technology aspects when making the pastes, but also what is required in the application after it has been sintered.

The chemical composition, the porosity, the mechanical and physical properties and even the surface finish can be significantly affected by feeding in additives to modify the pastes to create what is required.

Technology pillar 3: producing screens for specific applications

The production of precision screens for the 3D screen printing on a large scale involves complex requirements in terms of resolution capability, the perfect flow of the paste, edge sharpness, serviceable life, a stable aspect ratio and the highest level of reproducibility in the vertical structural behaviour.

Thanks to a strategic cooperation arrangement with the global market leader for polymer screen meshes in Japan, Exentis has unique access to screens of outstanding quality as the basis for manufacturing each individual Exentis production screen.

The combination of a statically optimised screen frame, high-performance meshes from Japan and the screen fabrics create a level of screen quality, which provides a long serviceable life for the screens used in the production process.

The ongoing screen production process involves a photopolymer coating in clean room conditions with extremely fine tolerances for applying the thickness and the surface roughness. The specific, final layout is handled using high-resolution plots and it generates structures with predefined aspect ratios that are extremely accurate.

Once it has been completed by technical and optical measurements in the quality control department, the Exentis screen leaves the in-house industrial screen production department and becomes a value-adding tool for each Exentis 3D production system.

Technology pillar 4: the 3D screen printing process

 
Conventional 2D screen printing has been a long-established and accepted procedure in manufacturing industry, e.g. for the large-scale production of solar cells, printed circuit boards and vehicle windows.

By integrating the z axis in the industrial production process using Exentis 3D Mass Customization® and the in-house developed production systems, 3D screen printing makes full use of its capabilities in terms of film thicknesses and enables layer thicknesses of less than 20 micrometres up to more than 150 micrometres. This height is viewed as the benchmark for functional materials like ceramics, metal, glass and organic substances.

The parameter landscape with the pure 3D printing process is extensive with 70 assumptions that can be individually set. The major parameters here, for example, are the snap-off distance, screen lift, squeegee speed, squeegee angle, squeegee material, shore hardness, screen tension, EOM thickness, surface roughness value – and tailoring them to the paste rheology.

The challenge in ensuring a high-quality industrial 3D screen printing production process involves coping with the reciprocal effects of the parameters already mentioned and is founded on the models of dynamics and interface physics.

Exentis 3D screen printing technology as a printing procedure is pre-destined for high z axis figures and ultra-high-resolution capabilities in applications below 20 micrometres. This is the equivalent of two hundredths of a millimetre or one third of the thickness of newsprint. It is therefore a process that enables extremely fine and precise dimensions and geometries for applications.

Technology pillar 5: 3D production systems for specific applications

 
Thanks to Exentis 3D Mass Customization®, new kinds of production concepts are being developed at Exentis on the basis of the 3D screen printing technology and they are increasing productivity to a huge extent and leading to annual production of more than 5 million parts on each manufacturing system for selected items. Exentis designs, develops and documents the production systems, which are then exclusively constructed on an individual basis by special machine manufactures. No one individual production system is therefore the same as any other. Printing heights, process speeds, quality assurance systems, drying paths, the addition of pastes and output quantities are newly optimised for each part.

Quality assurance is ensured by permanently monitoring the print quality properties using electronically controlled optical systems with high-resolution cameras. If necessary, a temperature- and humidity-controlled enclosure makes it possible to use materials, paste systems, drying and hardening procedures that are chemically and technologically challenging.

As the 3D screen printing technology is a cold printing process and therefore the high temperature printing chamber, which is necessary for other procedures, can be avoided, each printed layer is dried in order to enable the adhesive addition of the next layer. This takes place by using infrared radiation (IR) for metallic and ceramic materials.

In addition to using infrared radiation to dry the layers, the process times can be crucially optimised when structuring plastic parts, for example, on the basis of a UV, light-sensitive polymer system. Hardening the item to produce the final part takes place using UV-induced polymerisation and does not require any subsequent heat treatment. This makes it possible, for example, to process plastics or even conductible pastes into 3D structures. By selecting combinations of materials that can be sintered, it is possible to mass-produce miniaturised parts, for example, electrodes, in one production stage.

Biomaterials require different production conditions to ceramics or metals. This involves large-scale production in clean rooms with appropriately certified manufacturing systems. Exentis has appropriately certified control, documentation and production systems, which meet all the common requirements for manufacturing medical and pharmaceutical products.

By using process-automated changes of screens, it is possible to handle modifications to the layout of the application geometry and even optional paste changes to vary the application functions. Exentis has screen change systems, which can be programmed into the production process without the need for an operator by using control software.

Technology pillar 6: multi-phase sintering

 
In addition to choosing materials, making the paste system and screen and the 3D screen printing process for 3D production systems for specific applications, multi-phase sintering is another important element in achieving the desired application behaviour.

The materials only develop their appropriate properties during sintering. New molecular compounds are created, crystal structures are formed and the material gains its density.

Sintering basically consists of a two-stage process. Debinding takes place during the first stage. The additives dissipate completely from the so-called green bodies during this phase. This is the name for the completely printed parts, which are produced with additives to achieve improved workability and ideal bonding in the paste systems in the energy- and material-efficient cold printing process.

The latest methods are used to check these thermal reactions in order to design the sintering programmes and specific sintering curves for applications in a cost-effective manner and give the appications their specified properties.

Exentis has experienced experts who can transform this fundamental data into optimised sintering curves. This not only means considering the temperature profile, but also atmospheric conditions like the inert gas or oxygen, oxidising and reducing gases and their pressure parameters in each case. This is the only way to reproduce the necessary application, material and surface properties in the industrial manufacturing process with high quality levels.

 

These six pillars of the extensively patented process technology, Exentis 3D Mass Customization®, guarantee the unique features of the Exentis 3D screen printing technology. They also help to anchor the process and achieve technological and economic success with this additive manufacturing technology.

Consolidation and diffusion-controlled bonding of the material particles, which finally give the application its pre-defined rigidity and density, take place during the second sintering stage at significantly higher temperatures.

 

Some materials undergo phase transformation during sintering and this can be deliberately controlled or bypassed in order to adapt the physical and mechanical properties as well as the density to meet the customer’s requirements.