*Electron Beam Melting*

150 Biomedicine

material that is not fused and, if necessary, to be given further post-processing. The most common post-processing techniques are sanding, polishing, homogenization, thermal

It is important to highlight that, in general, material that is not processed (be it powder or liquid) is not capable of supporting fused material. Hence, if a part has overhanging zones, they may need to be supported by a *support structure* (Figure 3). Additionally, the support structure acts as a conductor of excess heat created in the process of selective melting. Finally, in some technologies, the support structure prevents warping of the part due to the thermal stress created during the process. Hence, the first step of pre-processing actually consists in generating an efficient support structure, which is then sliced and fabricated

1. *Time-to-market reduction for customized products*. Due to high speed of the process and being a direct fabrication method, the reconstruction of a model to fit in desired

2. *Product customization with complete flexibility in design & construction of a product.* Unlike conventional processes, AM can produce parts of almost any desired form and can

3. *Maximum material savings.* Material is added and not subtracted. For some applications, especially in the metal sector, case studies show that the waste of raw material is reduced by up to 40% when using additive technologies instead of subtractive (machining) technologies (Reeves, 2008). Also, 95% to 98% of the remaining material

4. *No tools, moulds or punches are needed.* The part is obtained directly from its 3-D CAD

5. *Full-density of final parts.* Unlike other powder based processes (powder metallurgy, MIM), additive technologies produce parts without almost no residual porosity.

together with the part. The support structure is eliminated in the post-processing.

The most important advantages of Additive Manufacturing are:

almost be free from geometrical manufacturing constraints.

(powder or resin that is not processed) may be recycled;

model with the absence of human errors in production.

treatment, etc.

Fig. 3. Support structure for downfacing surfaces

assembly is relatively fast;

EBM is one of free-form fabrication technologies capable of processing ferrous and non ferrous metallic powders to fully-dense material, using layer-by-layer principle. In the case of EBM, the energy is delivered through an electric circuit of 60kV that is created between a tungsten filament placed inside of the electron gun and the building plate (Figure 4).

Fig. 4. Inside the EBM machine (left); scheme of an additive machine (middle); electron beam making the contour of tibia prosthesis.

The filament is heated by electric current and emits a beam of electrons which is conducted by a set of different coils until it impacts the powder surface. During the impact, electric energy is transformed to heat energy which fully melts the powder. The working chamber is kept under deep vacuum (order of magnitude 10-4 mbar). Hence, powder is released from containers and distributed over the build platform in fine 70-100 μm layers. The beam melts powder to a solid slice, following the cross-section of the part at that layer and merging it with previous slices (Figure 4). The build platform descends for the value of layer thickness and a new powder layer is dispatched. The process repeats until the part is completed.

Additive Manufacturing Solutions for Improved Medical Implants 153

Fig. 7. Example of femoral hip stem: a) 3D model of hip stem with superficial porous zone, b) hip stem coupled with femur bone (model) and c) Ti64 hip stem coupled with polyacrilic

a model coupled with the solid hip stem.

Fig. 6. Supply chain flow for medical implants.

bone replica.

additive technologies introduce one important advantage: porous surface for better bone ingrowth (Figure 7). This *controlled* porous coating is designed in a specific software (in the case shown on Figure 7, it was Magics® by Materialise) and exported as

Fig. 5. Some of biomedical parts as produced on the machine (osteosynthesis plates Courtesy of CIMA).

In comparison with other AM processes, EBM has three major advantages very relevant for medical implants manufacturing:

