Interested in other articles?
Interested in other articles?
Virtually every 3D printed product requires some type of post-processing to improve its strength, quality, and performance as well as look and feel. For this reason, when you’re getting to grips with 3D printing and potential investment costs, it’s vital that you have an overview of additive manufacturing post-processing options.
Post-processing is the final stage in the end-to-end 3D printing process and is crucial to the manufacturing cycle. Finding a suitable additive manufacturing post-processing workflow can significantly impact the surface of the print and the look and feel of your final parts, as well as their mechanical properties.
Additive manufacturing post-processing encompasses two key stages: primary and secondary post-processing.
The additive manufacturing post-processing methods you use will depend on the 3D printer and 3D printing technologies you invest in, and the products you intend to manufacture. When you use any of them, you incur additional expenses you’ll need to factor into your workflow costs.
Surface finishing, coloring, fixing, curing, and cleaning are the most common 3D printing post-processing solutions.
This article offers an overview of the key additive manufacturing post-processing techniques used in combination with the most popular 3D printing technologies, along with a description of some other widely used post-processing methods.
Later on in this article, we explain the key post-processing techniques for HP Multi Jet Fusion 3D printed parts.
Data courtesy 1
The most commonly used 3D printing post-processing methods
Surface finishing
3D printed products that need to appeal to consumers will usually be finished to enhance the look and feel once support structures or excess material has been removed and they have been cured, cleaned, or washed.
Coloring
Colored parts are often used in, for example, the manufacture of toys, prototypes, color-coded jigs or fixtures, and, increasingly, in functional parts.
When you’re coloring after the 3D printed product has been made, the part would ideally be produced using white material. It is generally recommended to apply a layer of primer before the part is painted with a brush or spray.
Fixing
Sometimes small repairs are needed to fill small holes or cracks or even to attach parts that have been 3D printed separately.
The two main methods for attaching parts are snap-fitting or gluing. Gluing is the most common. Snap-fitting is used with complex products that need to be able to move.
Curing
Curing or, as it’s sometimes called, post-curing, involves applying UV light and heat to make 3D printed parts stronger and more aesthetically pleasing. It’s a technique that is an important part of resin-based 3D printing processes, such as Stereolithography (SLA) and Digital Light Processing (DLP) where functional UV-sensitive photopolymers are used.
It’s important to bear in mind that temperature and exposure times vary for different resins.
Powder removal - Powder Bed Fusion
After parts are 3D printed using Powder Bed Fusion (PBF) methods such as Selective Laser Sintering (SLS) or HP Multi Jet Fusion (MJF), it’s highly likely that powder will still be attached, especially in holes or channels. In the early days of 3D printing, residue had to be removed manually, but, fortunately, there are now automated solutions that vibrate or rotate it away.
HP Jet Fusion 3D Printing Solutions include an Automatic Unpacking Station for industrial 3D printing environments, helping to streamline the powder removal workflow for production at scale.
Cleaning
Some 3D printed designs made using Fused Deposition Modeling (FDM) or other material jetting technologies will include overhanging features. If this is the case, you’ll need support structures to support these overhangs, and post-processing will be required to remove them. Support structures are either made of the same material as the part itself or special support materials that will either be soluble or insoluble.
Insoluble material is usually tough for obvious reasons, and you’ll need to remove it with a knife or pliers. When it comes to PLA post-processing or working with other materials, learning how to remove insoluble support material without damaging the part or accidentally knocking off smaller features is an art in itself.
Widely used insoluble materials include Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS) and nylon.
There is less risk of damaging a 3D printed product when you’re using soluble support material because you dissolve support structures with water or Limonene. PolyVinyl Alcohol (PVA), used with PLA material and High Impact Polystyrene (HIP), used with ABS, are common soluble materials.
Washing - SLA and photopolymerization
Parts 3D printed using SLA or other photopolymerization methods can be washed after printing.
Sanding
Sanding is done using high to low grit sandpaper depending on the 3D printed part and the quality of finish needed.
As with removal of powder residue, sanding is now a commonly automated procedure. Apart from making the sanding process far less labor intensive, it leads to consistent results and a more attractive finish.
This method of post-processing takes care of the touch points or layer lines that occur where a support structure was attached to a part, particularly when a layering method was used.
Vapor or chemical smoothing
Another way of removing layer lines is to melt them away using vapor or chemicals that react with the 3D printed part’s outer layer and leave a smooth finish.
Data courtesy 2
Welding and gluing
Sometimes you may need to produce a part or product that is much larger than your 3D printer build area. In this case, your 3D printed parts can be welded together or, if you’re using ABS technology, glued using acetone.
Filling
If cracks or holes appear in the object you are 3D printing, you can use fillers and hardeners to repair them.
What additive manufacturing post-processing can be used with HP MJF ?
As we said at the beginning of this article, post-processing is divided into primary post-processing, usually mandatory, and secondary.
Primary post-processing for HP Multi Jet Fusion
After an HP MJF 3D print job is finished, parts are “uncaked” or unpacked, automatically or manually, in the processing station or industrial 3D printer, depending on the specific HP Jet Fusion 3D Printing Solution. Unfused material is reclaimed in the system for recycling.
When they have been unpacked, printed parts are left with a significant layer of unfused material that has been exposed to fusing and detailing agents at various levels along with high levels of energy, which has altered its properties.
The layer of remaining unfused material can be removed using different techniques.
Bead blasting
Bead blasting involves propelling an abrasive or blast media, usually a bead or sphere, at high pressure against the surface of the part using compressed air. This dislodges unfused material from the surface and provides a more uniform, “satin” finish.
Air blasting - in combination with bead blasting
Air blasting involves propelling a stream of compressed air onto the part’s surface. It is usually combined with bead blasting to remove any remaining powder material and blast media dust that may have been left on the surface without affecting the dimensional or mechanical properties of the part.
Water jetting or water jet blasting
Water jetting or water jet blasting involves jetting a fluid mixture of compressed air and water via blast nozzles onto the part surface to remove the powder. It can also be used for initial surface finishing by including a suspended solid (or blast media) in the fluid mixture.
This technique is ideal for cleaning complex geometries or ducts automatically since the blast nozzles have different orientations, allowing the fluid to penetrate hard-to-reach areas.
Secondary post-processing for HP Multi Jet Fusion
Secondary post-processing is optional and depends on the specific requirements for how the final part will be applied.
Techniques included in this post-processing stage generally provide cosmetic qualities. For example, dyeing and painting or reducing surface roughness by methods such as vibratory tumbling or chemical polishing.
But it’s important to remember that this is not a strict classification. Techniques such as painting or electroplating can also deliver qualities such as connectivity, conductivity, toughness, and resilience as well as, an attractive look and feel.
Providing cosmetic attributes for HP MJF 3D printed parts
The cosmetics category can be subdivided into techniques that provide color uniformity in the raw part and those that offer coloring different to that of the raw part. There are five key techniques.
Dyeing
This is currently the most commonly used secondary post-processing technique for HP Multi Jet Fusion 3D printed parts.
Dyeing involves immersing the part in a hot dye for a prescribed period of time, so the dye penetrates the part completely until a specific color or color homogeneity is achieved. Because the color penetrates the interior when a product is dyed, the process is suitable for applications where the part is visible or subject to wear.
Graphite blasting
Bead blasting is used to clean parts of unfused powder without coloring or impacting the part’s surface roughness, but graphite blasting provides color uniformity.
Parts processed with graphite blasting have a highly attractive, metallic-looking surface. The technique also reduces friction between moving parts, making it suitable for functional and mechanical parts where its lubricative benefit may be an advantage.
Data courtesy 3
Smoothing blasting
Smoothing blasting involves propelling an abrasive media onto the surface of the part at high pressure.
The main purpose of smoothing blasting is to give a better, more resistant surface finish, usually in combination with dyeing. This is achieved by using a more abrasive, round formed blast media, usually plastic or ceramic, rather than the glass used in bead blasting and a higher pressure.
Surface finishes achieved can range from matt to glossy finish depending on the type of media used and the processing time. Afterward, the surface becomes more resistant to scratches, dirt, and liquid absorption.
Painting
Painting involves the application of a pigmented liquid composition to the part in a thin layer which converts to a solid film when dry. This results in improved color uniformity and surface roughness on the part.
Other desirable properties such as UV resistance, wear and scratch resistance, and water tightness can also be achieved depending on the formulation of the paint used.
You can apply solvent and water-based paints to Multi Jet Fusion parts.
Electroplating
Electroplating and metal coating are techniques used to add a layer of metal to the surface of a printed part.
This is done to improve the look and feel of the part for cosmetic applications or to improve physical properties such as conductivity, EMI/RFI shielding, mechanical strengthening, and heat conductivity. As a functional coating, it can also deliver other desirable qualities like antibacterial properties.
Reducing surface roughness
Secondary post-processing treatments help to homogenize the surface finish and reduce roughness. There are two main techniques that can smooth the printed part’s surface.
- Vibratory finishing
Vibratory finishing, also known as tumbling, involves vibrating parts in a tumbler with an abrasive media, causing the media to rub against the parts. The abrasive media have a lapping effect on the surface of the part.
- Vapor smoothing or chemical polishing
Vapor smoothing or chemical polishing smooths the surface of thermoplastic polymer parts, including that of internal cavities.
It acts on the surface of the part without degrading the part’s mechanical properties and can achieve a surface finish similar to that of injection molding and different levels of glossiness.
Want to continue learning?
Next article
Related article
Related content
Footnotes and disclaimers
- Data courtesy of Bernat Cuní.
- Data courtesy GoProto Inc.
- Data courtesy CT CoreTechnologie GmbH