Electron Beam Melting (EBM) is an additive technology that produces high-quality parts and can be used with difficult-to-work-with, high-temperature alloys as well as other more conventional materials such as titanium. While the focus of many of the operational features are centered around build quality and part performance, there are different ways to improve the productivity when using EBM. In this article, we catch up with Mattias Fager, senior staff engineer from Colibrium Additive, to discuss the best ways to achieve a high productivity when using an EBM machine.
What drives productivity in EBM?
In our EBM technology we have a very powerful electron beam. In the Q10, it’s 3kW; in the Spectra L, it’s 4.5 kW; and in the Spectra H, 6 kW. The peak power is mainly used during the preheating and heating phase, whereas in the melting phase we don’t typically utilize 60% of this power, but it’s still a high temperature.
As one of the few metal AM powder-bed technologies on the market, Colibrium Additive’s EBM utilizes an elevated build temperature, the benefits of using this is twofold: the part comes out without any residual stresses and at the same time, the speed of welding can be increased significantly without creating weld defects. When only the melting speed of the EBM is considered, it’s one of the most productive powder-bed technologies.
EBM productivity is, to a high degree, set by these relations in amount of time recoating powder and preheating and heating in relation to the actual melting, implying that EBM in general gets more advantageous the larger the size and height of the build.
Are the supplied generic process themes optimized for productivity?
When it comes to productivity in EBM, we have historically aimed towards creating parts that don’t require any post-build heat treatments, and we work to meet the material requirements as printed. This applies to material properties such as ductility, as well as the static tensile strength.
The themes are set so that they meet certain capabilities to ensure that the degree of fusion is as high as possible, and any lack of fusion is kept to an absolute minimum. These capabilities extend over the entire build envelope, to the entire cathode lifetime, and to the allowed levels of oxygen in the powder so that they can be recycled efficiently, while still maintaining good material properties in the part. Designing the themes with hot isostatic pressing (HIP) or heat treatment (HT) in mind would greatly improve both productivity as well as geometrical coverage of the process. This means that we could build more complex parts faster, with less supports. This is a level of scalability that hasn’t really been utilized yet but could further increase the productivity of EBM machines.
The themes are designed to achieve the highest quality part possible rather than geared towards productivity. This approach also helps to lower the costs of going through validation. However, this means that you can produce high-performance parts every time, and there is still a lot of room left for optimizing the productivity of the product if you know your application and the component that you wish to build.
Once the theme is locked in and production has started, you can incrementally optimize your productivity if you know your components.
Let’s talk about the ability to stack parts in the build chamber and improve productivity. What does stacking parts bring to the machine’s productivity and is there ever a good point to stop?
Stacking parts is a unique EBM feat ure where the thermal management keeps the correct build temperature as well as minimizes the need for physical supports. By stacking parts with free floating supports in the build chamber, you can utilize the entire build envelope and create a lot of small parts in a single build, without need for additional support removal. This is much better utilized with smaller parts than it is with larger, chunkier components, and this ability to stack reduces the reload time of the machine in between builds. Regarding the degree of stackability possible, you can stack as much as you like in the z-direction. If you can stack one part at one height, you can stack one part all throughout the build envelope.
In terms of if there is a good time to stop stacking, there is nothing to say that you have to stop from a technical perspective. The only reason to stop producing more printed layers is going to come from either a validation or batch size perspective—in terms of the production of a certain number of different sized parts, or if there are regulatory conditions that might prevent you from printing further. When it comes to determining when to stop stacking, it’s more based around those aspects rather than from a technical and productivity standpoint, because once you have started the build, it’s always more productive to keep printing.
Another aspect is the ability to overlap parts. If you stack small parts, such as acetabular cups, then you can overlap those parts to make the build even more efficient. Unlike other printing technologies, EBM is not limited by the scanning speed, and so called optimizer will virtually combine, move and optimize the different areas of the build (in a similar manner to fitting Tetris shapes together) to optimize the process.
If the scanning speed doesn’t limit productivity, what does?
When it comes the stackability of components in EBM, it’s the melting power that is the limiting factor towards productivity. Depending upon geometry and packing density, there could be a point where the subsequent heating needed for each layer can reduce the overall build rate.
Our more powerful systems, like the 4.5 kW electron beam in the Spectra L, have been designed so that the required power to print covers the entire build envelope and you can stack as much as you like. You will also not see a decrease in productivity if you add a larger coverage in the x and y directions.
How does a HIP process affect the productivity of EBM parts?
If you have a requirement to HIP your component, the themes can be altered in a more productive way, allowing for a smaller amount of internal porosity, still on a very low level. The supplied standard themes trade those last residual pores in favor of a lower productivity.
Should you still need it, HIP process works well with EBM parts. When creating parts with EBM, any level of porosity is going to react well with a HIP process because the printing is performed in a vacuum. This means that the gas pores consist of vacuum, rather than gas. So, it’s easier to close those gaps with HIP if you have a part that has been created with EBM.
Overall Outlook
While EBM is primarily focused on part quality, rather than productivity, you can still achieve a high level of productivity in your printing processes due to the high power and fast scanning speeds of the electron beam units. Once you add in the ability to stack parts and fill up the build envelope, you can achieve a higher level of efficiency and productivity because you can skip a number of operational steps compared to traditional non-stacked builds.
The insights is sponsored by Lodestar3D, to know more about EBM solutions, visit: https://lodestar3d.com/
