EBM Electron Beam Melting: How High-Energy Electron Beams Make Great

-Reprinted from 3D Wisdom Bay

01
Principles of EBM Technology

Electron beam melting (Electron Beam Melting, EBM) is a metal additive manufacturing technology, first developed and patented by the Swedish company Arcam. The working principle of EBM is similar to that of SLM, and the metal powder is completely melted and formed. The main difference is that SLM technology uses a laser to melt metal powder, while EBM technology uses a high-energy electron beam to melt metal powder.

melting metal powder by high energy electron beam

EBM technology Before printing, after laying a layer of powder, the electron beam will quickly scan the powder layer many times to preheat it, and the powder is in a slightly sintered state without being melted. This is a step unique to EBM technology. SLM can be preheated at a maximum temperature of 300 ℃, while EBM technology can use electron beam scanning to preheat each layer of metal powder, so that the parts can be processed and formed in the range of 600~1200 ℃. The picture below shows the preheating process of the electron beam. Because the electron beam can jump quickly, it seems that there are multiple scan lines heating the powder bed.

Electron beam preheating process of EBM

The specific printing process is that the computer converts the three-dimensional data of the object into 2D data of layers of cross sections and transmits them to the printer. The printer selectively emits electron beams to the powder above the laid powder, the kinetic energy of the electrons is converted into heat energy, and the metal powder in the selected area is heated to be completely melted, then formed, and processed into the current layer. Then the piston lowers the height of the worktable by one unit, a new layer of powder is spread on top of the current layer that has been sintered, and the equipment is transferred to the data of the new layer section for processing and bonding with the previous layer section. This process circulates layer by layer until the whole object is formed.

EBM equipment structure diagram (photo source: South China Institute of Technology)

The manufacturing process of EBM parts needs to be carried out in a high vacuum environment, on the one hand, to prevent electron scattering, on the other hand, some metals (such as titanium) will become very active under high temperature conditions, and the vacuum environment can prevent the oxidation of metals.

02
EBM vs. SLM

Both SLM and EBM equipment use high-energy beams as heat sources to selectively scan and melt metal powder on the powder bed according to CAD layering data, and layer upon layer to form metal parts. There are three main differences between the two:

1. The heat source is different. SLM uses laser as heat source, EBM uses electron beam as heat source;

2. Forming work environment is different. SLM technology is melted and formed under inert gas conditions, EBM technology is melted and formed under vacuum conditions;

3. The working forming heat temperature is different. SLM can be preheated at a maximum temperature of 300 ℃,EBM technology can use electron beam scanning to scan and preheat each layer of metal powder, so that the parts can be processed and formed in the range of 600~1200 ℃;

4. The thickness of powder is different. The powder layer thickness of EBM is between 50-150 μm. The larger the powder thickness, the parts can be manufactured in less time and are therefore more efficient. Usually EBM is 3 times more efficient than SLM.

5. The powder particle size is different. The powder particle size of EBM is relatively coarse, distributed in the range of 45-105um. For the SLM process, too coarse a powder has the risk of not being able to penetrate. The finer the powder particle size, the higher the price, so EBM consumables are more economical.

03
EBM Strengths & Technical Limits

EBM Advantages
The energy conversion efficiency of the electron beam is very high, much higher than that of the laser, so the energy density is high and the powder material melts faster, so the forming speed can be faster and the energy can be saved;
High energy density can melt metals with melting points up to 3400 degrees Celsius;
The scanning speed of the electron beam is much higher than that of the laser, so the electron beam can be used to scan and preheat each layer of metal powder during the molding process to increase the temperature of the powder. The preheated powder has less residual stress after molding, which will be advantageous in the manufacture of specific shapes without heat treatment.

EBM Technical Limitations
The metal powder will become slightly sintered after being preheated by electron beam. After manufacturing, the unmolded powder of EBM needs to be removed by sandblasting and other processes. If it is complicated, it will be difficult to remove the internal molding;
Additional system equipment is required to create a vacuum working environment, so the equipment is relatively large;
The surface roughness of parts formed by EBM technology is greater than that of SLM technology.

04
EBM Applications

EBM Materials
EBM materials are generally multi-metal mixed powder alloy materials, such as the current mainstream Ti6Al4V, cobalt-chromium alloy, high-temperature copper alloy and so on. These materials have their own unique characteristics, such as high temperature copper alloys with high relative strength, potential for high heat flux applications, excellent elevated temperature strength, excellent thermal conductivity, good creep resistance, etc.

At present, EBM materials that have been commercially used are: CoCrMo alloy, pure copper, pure iron, 316L stainless steel, H13 tool steel, niobium metal, nickel-based alloy, pure titanium, titanium alloy, and TiAl-based alloy.

Metal powder for EBM technology (Image: Antarctic Bear)

EBM can be used in the manufacture of models and prototypes, as well as in the production of small batches of metal parts with complex shapes. EBM technology can be widely used in the aerospace and industrial fields of lightweight overall structure, high-performance complex parts manufacturing (such as the manufacture of landing gear components and rocket engine components, etc.), as well as the medical field of porous structure orthopedic implants manufacturing.

The use of EBM technology in orthopedics (Image: Arcam)

EBM application case (photo source: Antarctic bear)

EBM also enables the manufacture of metallic materials that are difficult to manufacture with conventional processing methods, such as superalloys commonly used in aircraft engines.

TiAl-based alloy blades manufactured by EBM technology (Image source: Arcam)

An EBM-made acetabular cup with a porous surface (Image: ARCAM)