Metal additive manufacturing, also known as metal 3D-printing is a process used to make fully-finished, machine-grade metal parts. It is a viable alternative to more conventional large-scale production methods such as subtractive manufacturing or injection molding, and in some instances is eliminating the need for machining altogether.
Ideal for producing parts with complex geometries, metal additive manufacturing can help maximize production by creating parts that would be too expensive or time-consuming to make using traditional machining methods like CNC, drilling or turning.
With metal additive manufacturing (AM), parts are manufactured using any variety of 3D printing methods including DMLS, SLM or binder jetting processes. Common to all these methods is that the parts are created from a computer aided design (CAD) file and all are fabricated using a metallic construction material. The construction material is either powder-deposited or extruded through a nozzle in progressive layers, level-by-level, until the parts reach their final shape.
In the metal additive manufacturing processes known as binder jetting, the construction material is a combination of fine metal powders and a binding agent. Metals available include stainless steel, tool steel, and many other ferrous and nonferrous alloys. Common types of binders contain paraffin wax, carnauba wax, and specialty polyethylene waxes.
The binders serve a critical purpose in forming the metal powder into a specific shape. However, they are ultimately sacrificial and must be selectively removed (up to 4%) before the green parts can be exposed to the high heat required for the next step of sintering.
Fluid extraction of the binders is easily done with a vapor degreaser. The debinding may be performed in either the vapor or liquid phase in the vapor degreaser depending on the metals used and the binders to be removed. Both vapor degreasing phases rely on the debinder fluid penetrating the parts to efficiently dissolve the wax from the parts interior.
The wax binders are progressively removed to avoid deformation and cracking during sintering while also allowing the parts to maintain their dimensional accuracy, compress uniformly and sinter evenly. Debinding is a balance of selectively eliminating some, but not all, of the binders in the shortest amount of time and with the least amount of damage to the parts structure since as the binders are removed, the parts become fragile.
Once the wax binders are fully removed from the green parts, the parts are ready to be sintered. Any remaining binders in the parts are effectively burned off while the parts are compacted at near melting temperatures. The metal powder bonds together and the finished parts reach their solid mass state. After that, the sintered parts can be post-processed using standard metal finishing techniques like grinding, sanding coating.