Additive Manufacturing is a process of joining material layer upon layer, as opposed to subtractive manufacturing techniques. The most common types of metal additive manufacturing are Laser Sintering and Electron Beam Welding.
This process uses the laser as a power source to sinter the powdered metal, by aiming the laser at points in space defined by slicing a 3-D model into stacked layers of a certain resolution along the Z-axis (height). This results in the binding of the material in order to create a solid structure.
Electron Beam Welding
Electron Beam welding uses an electron beam as a heat source to melt metal powder. The process of Electron Beam welding is similar to that of Laser Sintering. In Electron beam welding, the electrons are boiled off a metal part as the current passes through a filament. The parts are enclosed within a vacuum chamber, using a negatively charged filament and a bias cup, and a positively charged anode, the electrons are accelerated to 50-80% the speed of light. The direction of the electrons is controlled by the electromagnetic fields. The high power density and low heat input results in minimum distortion of the parts. This in turn results in the parts requiring little to no post-weld machining. It produces fully dense metal parts with the characteristics of the target material.
Surface Finish of Additive Manufactured Parts
Metal parts that have been produced through additive manufacturing tend to have a textured surface with an average Roughness (Ra) of approximately 30 microns. The values of Ra may increase at support locations and may decrease depending on the geometry profile. The base of components manufactured using the aforementioned processes generally present a considerably lower roughness.
High Energy Finishing for Surface Roughness Reduction
High Energy finishing is a process that automates the mechanical and chemical finishing of various shaped parts. This is a stage in the manufacturing process of components, which allows small or large numbers of parts to be finished simultaneously.
High Energy Machines are used to reduce surface roughness, deburr and polish processed parts. The action of these machines relies on the high force and speed at which the media chips come in contact with the processed components. The forces can be as great as 15-20 times the force of gravity, depending on the rotational speed and the turret size of the centrifugal machine.
In many cases, the results achieved via High Energy (HE) Finishing cannot be achieved in a standard vibratory process, particularly applications that include achieving a high surface finish, a mirror finish and the removal of manufacturing defects. HE finishing can be 10 times faster than traditional finishing methods, and produces superior finishes. It is one of the most efficient batch finishing methods.
Components can be processed wet or dry. In a wet process, parts are generally loaded as a batch with media and a solution made of a barrelling compound and water. When processing large or fragile components divider plates may be fitted to form compartments within the barrel in order that parts may be processed individually, ensuring no impingement.
The process benefits include:
- Significant reduction in roughness
- Shorter processing time than traditional methods
- Increased part cleanliness
- Removal of surface defects
- Corrosion protection
- Non part specific
- No major tooling required
- No requirement of fixturing
- Consistent and repeatable results