Additive manufacturing or 3D printing is a relatively new rapid manufacturing technology that has become mainstream in recent years. It covers a wide variety of processes used to produce a multitude of components ranging from automotive and aerospace prototypes to bespoke jewelry.
Before additive manufacturing, prototype products, as well as finished components, were generally machined or moulded in some way that involved processes such as, turning, milling, boring, grinding, spark erosion, injection moulding and casting. These processes are laborious, expensive and time-consuming for one-off and small batch production and sometimes involved many weeks of pattern or tool making before the desired result emerged.
Additive manufacturing has revolutionised this process by providing a rapid, low-cost method of producing components from the simple to extremely complex within a single machine. In most cases, software is used to program the additive manufacturing machine with the desired components parameters which it then produces, for example, from powdered polymers, powdered metals or photopolymer resins depending on the exact additive manufacturing machine and technology employed.
One of the leading authorities in establishing international standards for additive manufacturing technology is the American Society for Testing and Materials, ASTM. ASTM group F42 is the specifically designated body of experts that have compiled a set of standards identifying seven categories of industrial additive manufacturing processes.
A brief and simplistic overview of the seven additive manufacturing processes
1) Powder bed fusion
This category incorporates direct metal laser sintering, (DMLS), selective laser sintering, (SLS), electron beam melting, (EBM) and selective heat sintering, (SHL). These applications utilise a powdered metal or polymer that is selectively targeted by laser or electron beam to melt and fuse the layers of powder into a solid shape.
2) Direct energy deposition
Incorporating 3D laser cladding and direct metal deposition, (DMD). Generally, metals in either powder or wire form are melted using a laser or electron beam and deposited in a layer to build the shape required. Can also be used for polymers and ceramics.
3) Vat polymerisation
Uses a photosensitive resin contained within a vat. The resin hardens when exposed to ultraviolet light. The component is built up in layers on a platform that moves downwards during each cure cycle.
4) Binder jetting
Utilises a powder and a liquid binder. Alternating layers of binder and powder are deposited along “x” and “y” axes from a printing head to build the required shape.
5) Material jetting
Operates in a very similar way to an inkjet printer except that a melted polymer or wax is built up in layers and solidifies in air or sometimes with the aid of UV light.
6) Material extrusion
Polymer material is heated as it is extruded under constant pressure through a nozzle that moves horizontally over a platform that moves vertically. The component is built up layer by layer.
7) Sheet lamination
Is a low temperature, low energy process that bonds but does not melt the material. Thin sheets of metal are laminated one at a time using ultrasonic energy. The process requires further machining or laser cutting to remove the unlaminated metal and produce the final product. Typical metals such as aluminum, copper, titanium and stainless steel can be used.
Of the seven main types of 3D printing, Powder Bed Fusion most commonly uses inert gas to prevent oxidisation during the additive manufacturing process.
The need for inert gas in powder bed fusion
The powder bed fusion process takes place inside a virtually sealed chamber. Powdered polymer or metal is layered onto a platform that moves down in a vertical direction. The required shape is created by a laser melting the appropriate area of each layer of powder. As it solidifies, the platform drops, and the next layer of powder is added.
The chamber needs to be initially purged of ambient air using inert gas before the process starts and then a trickle flow of inert gas is needed to maintain the low oxygen atmosphere to prevent the heated powder from oxidising as it cools and solidifies.
For most applications using polymers and metal powders, nitrogen gas is ideal to use for the chamber inert atmosphere. Depending on the material, a Parker nitrogen generator can produce between 5% to 5ppm maximum remaining oxygen content, continuously, consistently and at very low cost to the most economical purity level required. For use with Titanium powders argon is the preferred choice. This is because nitrogen can react with titanium in a process called “nitriding” that can cause embrittlement.
Because nitrogen gas can be generated at such a low cost compared to cylinder and liquid supplies, it may also mean that expensive chamber gas atmosphere monitoring and recycling systems are unnecessary.
Parker NITROSource gas generation systems are flexible and expandable, producing as little or as much gas as required to exactly the right purity.
There are no cylinders to manage with all of the costs and manual handling risks associated with them or the expense and hassle of a bulk liquid supply.
As the additive manufacturing process takes time to produce the finished component, a small nitrogen generation system with a nitrogen storage vessel is often a very economical solution. The generator is sized to produce the continuous purge flow the chamber requires whilst having a slight overcapacity to replenish a suitably sized storage vessel. The initial chamber higher purge gas flow is provided by this storage vessel, negating the need to size the generation system at the peak flow the initial purge demands.
The Parker nitrogen system can run 24/7 totally uninterrupted for maximum uptime and AM production capacity.
The illustration below details Parker nitrogen generation systems for single and multiple AM machines.
- Air Receiver
- Water Separator
- Clean Dry Air System
- Buffer Vessel
- Nitrogen Generator
- Low-Pressure Storage
- Additive Manufacturing Machine
Parker NITROSource and MIDIGAS have been utilised in many additive manufacturing machine applications saving end users literally thousands per annum in gas cost from traditional methods of supply. To learn more, download the brochures for Parker MIDIGAS and NITROSource nitrogen generators.
This blog was contributed by Phil Green, application and training manager, Parker Gas Separation and Filtration Division, EMEA.