The Electron Beam (EB) Welding machine was custom built by Sciaky, Inc. to SLAC specifications for PEP II construction. It is one of the largest of its kind in the world. (Photo courtesy of MFD)

The Mechanical Fabrication Department (MFD) has an advanced manufacturing resource housed in a class-1000 clean room in Building 31. Few facilities in the world have this unique tool.

The Electron Beam (EB) welding machine was custom built by Sciaky, Inc. to SLAC specifications for PEP-II construction. It is one of the largest of its kind in the world.

What makes it special is the low contamination vacuum pumping system with a very large capacity vacuum work chamber. Particulate and hydrocarbon contamination, which are destructive to vacuum systems, are minimized in this machine by using cryogenic pumps (as opposed to diffusion pumps that emit hydrocarbons), special vacuum clean lubricants and stainless steel construction.

The machine has five axes of motion and a computer controlled articulated head with 30 kW of welding power.
It can be line-of-sight focused on large parts up to 22 feet long, 23 inches wide and 15 inches tall.

EB welding uses an electron beam to fuse two pieces of metal together without a filler material. The high power and the narrow beam allows the welding of thick and difficult materials with minimal heat-related deformities. The EB welder can penetrate into two inches of copper, four inches of steel and six inches of aluminum.

Example of an EB welded assembly (Photo courtesy of MFD)

Copper is one of the more difficult materials to weld since it can absorb a lot of energy. MFD is a world leader in welding oxygen-free copper. EB welding was the only way to join large, long copper chambers and keep the copper’s structural integrity. Manual welding processes such as GTA-Gas Tungsten Arc, MIG-Metallic Inert Gas, torch welding and stick welding could not achieve the level of control that is needed for the complex assemblies required by SLAC.

EB welding minimizes the turbulent mixing of metals during the welding process. The rapid liquefaction and solidification of the metals to be joined reduces the heat-affected zone and helps keep the structural integrity of the part. This process is performed in a 10-4 torr vacuum with welding parameters developed especially to meet our technical needs.

For more information on the Mechanical Fabrication Department, see: http://www.slac.stanford.edu/grp/mfd/