Right-Sized Additive

In the early days of 3D printing, industry lacked choice. Today, we have the opposite problem: Too many options are keeping some manufacturers on the additive sidelines.

This Markforged Mark Two 3D printer uses continuous carbon fiber to make parts as strong as aluminum. (All images provided by Phillips)

I get it. The stakes can be high when investing in additive. Too often, I see manufacturers spending more money than necessary for machines they don’t need or buying entry-level machines that will never do the job.

And it’s not just about the money. Like traditional manufacturing, 3D printers come in all shapes and sizes. Just as you would never use a lathe for a manifold or a mill for a shaft, it’s critical to find the right additive machine for the project.

The good news is that decades after the invention of 3D printing, we not only have a huge number of options, but we can say with authority what’s going to work and what’s not.

So, how do you find the best 3D printer for you? To help you find the “right-sized” solution, I would like to share some “intel” based on my years of working in this rapidly evolving space. Which material class is used, plastics or metal, makes a difference in how to approach an explanation.

I will discuss 3D printing in plastics, and then in metals.

Fused Deposition Modeling (FDM) with Plastics

Affordable? Yes. Easy to use? No question about it. Right for all industrial uses? Absolutely not.

For a few hundred bucks, almost anyone can buy an FDM 3D printer, sometimes called FFF (Fused Filament Fabrication). These printers feed a filament (think plastic cord in a weed trimmer) into a heated nozzle to melt it. The melted plastic is then deposited, layer by layer, onto a build plate using an XY drive system.

This technology is great for toys, trinkets, and Near Net Shapes (aka non-functional prototype parts). If you want to mock up a plastic part to see if it fits into an assembly, this is your printer. But if you need a strong, usable part, this is not it. Not only does it lack strength in the Z-axis, but it can also delaminate on the build layer lines. FDM also has very low resolution compared to other 3D printing technologies, so it is not suitable for parts with very small details.

Continuous Fiber Reinforcement (CFR) with Plastics

But all is not lost. To industrialize FDM technology, machine makers added chopped carbon fibers to the filaments. While the chopped fibers strengthened the plastic, it is still wasn’t enough for many applications.

The Hybrid is a major breakthrough in 3D printing, combining additive and subtractive in one machine. This Phillips Hybrid is a mix of a Haas CNC and Meltio additive technology. Hybrids can be purchased new, or the additive technology can be installed on an existing CNC.

Enter continuous fiber reinforcement (CFR) technology. These printers use layers of continuous carbon fibers (versus chopped carbon fiber) in order to make plastic parts as strong as machined aluminum.

For maintenance shops, this is your multi-purpose tool. You can make strong parts quickly with no fixing or tooling needed. Job shops can make workholdings, weld fixturing and custom sheet metal tools. Production shops can make drill guides and robotic grippers.

Stereolithography (SLA)

Stereolithography (SLA) is a perfect technology for prototype shops that need to print transparent prototypes in order to see how material flows through them, such as pumps or vascular structures. A power or light source is used to cure the top layer of a vat of plastic resin. The build plate moves down through the liquid resin, layer by layer until the shape is created.

There are several drawbacks. Not only does it require a post-build curing process, but support structures are also needed to hold the part in place in the liquid. Both these facts add time and cost to post-processing. The material is sensitive to light and does not hold up well without coatings and it is not nearly as strong as parts made with CFR or other technologies.

Selective Laser Sintering (SLS) with Plastics

Though it cannot produce transparent parts, Selective Laser Sintering (SLS) is a close cousin of SLA. Instead of using a vat of liquid, parts are made from thermoplastic powder. With this technology, the powder provides the support so there is no need to build additional support structures. Serial production can be achieved by nesting multiple parts into the build. As an added benefit, your kids (or the kid in you) will love this process as it requires “excavating” shapes from the powder, like an archeologist digging for artifacts.

Once the part is powdered, it’s ready for use. Common uses include functional ductwork with internal channels and replacement parts, such as arm rests, brackets, and fluid connectors. Computer generated lattice structures allow the printer to create “digital foam,” which can be used for custom helmets and shoes.

Now let’s take a deep dive into metals. One of the most rapidly evolving areas in additive manufacturing involves metals. While metal 3D printing came a bit later to the game, the technology is seriously taking off.

Metal Binder Jet (MBJ)

Imagine you could make metal parts using a filament (just like the CFR process described above). You can, with a few extra steps, using metal binder jet (MBJ) printers.

This EOS 3D printer is an example of powder bed fusion technology, the gold standard for metal 3D printing. It can print highly complex and strong metal shapes, making it perfect for flight-critical parts.

With this low-cost, easy-to-use technology, printers use a filament with metal suspended in it. After the print, the extremely fragile part must be put in a wash station to remove the binding material and then baked in a sintering oven to create a cohesive metal part.

There are some factors to consider when choosing this technology. First, the same part geometry limitations for FDM (described above) apply to this process. Second, when the part is complete, it will be metal but may not be fully dense. In other words, it’s great for parts that don’t need to be that strong, such as brackets and fixtures, but not for flight-critical parts.

Arguably the biggest challenge is not with the process, but with the software. The sintering process will cause the part to shrink slightly. The way the part shrinks is dependent on its geometry. Symmetrical parts will shrink symmetrically, but each feature of an asymmetrical part will shrink in a unique way. This is where the real innovation starts. If the software is smart enough, it can learn from the build and improve the next one.

One manufacturer of 3D printers in Boston, Markforged, is doing just that. The company is collecting data and using Artificial Intelligence (AI) from each build to improve the machine’s ability to print the part right the first time, a process they are willing to do as they strive to make parts that could never be produced using subtractive manufacturing .

Power Bed Fusion (PBF) with Metal

Powder bed fusion (PBF) is the gold standard for metal printing. It is the preferred technology for any flight-critical part from fuel nozzles to rocket combustion chambers. The process works much like selective laser sintering (SLS), but supports are also added, as the heat required to sinter metal can warp the part. What you get is a fully dense part that has very little restrictions on part geometry and can scale to production.

While this process may sound easy, the technology it uses to make a good part is cutting edge and requires a higher degree of operator skill. Any particulate or smoke that interferes with the laser sinter beam could impact the integrity of the part. This may not mean anything if you are making brackets or battery trays, but if you are making a flight-critical part, it is everything.

Metal PBF printers come in a number of sizes, but all are still relatively small. Some manufacturers have built machines that can print 600 × 600 mm, but the real challenge in PBF is in the higher Z-axis builds. Most builders have found that the complexities of building above 400 mm in the Z-axis is too great. About five years ago, one machine maker, EOS, figured out how to make a machine that can build parts up to 1 m in the Z-axis. The technology breakthrough opened up the market for small rocket combustion chambers.

To get into this technology, you will have to break the piggy bank. PBF printers are generally the most expensive, costing anywhere from about $500,000 to several million. But if you want to be in the aerospace industry, or are interested in producing the most complex parts, such as manifolds, nozzles, and combustion chambers, this is the right technology. Called the gold standard for a reason, it has the ability to reinvent manufacturing.

Direct Energy Deposition (DED) with Metal

Direct energy deposition is something that has hit the market by storm in recent years. This “hybrid” technology combines subtractive with additive technologies to create an affordable, highly agile 3D printer. The technology combines a traditional welding process (using powder or wire) and applies it to a motion system. Rather than joining two pieces of metal together using welding, the process welds to the previous layer of welds in three dimensions, allowing you to build a shape.

Onyx, a micro carbon fiber filled nylon, is one of several materials transforming 3D printing. Onyx, made by Markforged, yields accurate parts with near flawless surface finishes.

As a stand-alone unit, it is good for building up relatively symmetrical shapes to near net tolerances (eg, cylinders, turbines, projectiles). If you move the part and the weld head in multiple dimensions, using positioning tables or a robotic arm, you can build very complex shapes. With this level of design freedom, you can build car frames, complex brackets, or rocket combustion chambers.

DED comes in several forms. You can use a traditional power source such as an arc welder if you want to add a lot of material quickly, or a laser welder for greater precision. The material can be powder or wire, depending on the desired result. (Powder is generally faster but compared to wire it’s tough to store and transport due to its material volatility and sensitivity to environmental factors).

Most of the parts created using DED require machining. Much like peanut butter and chocolate, DED and machining fit together nicely, and open up a new field for additive: part repair. All of the other processes described are focused on new part production, but this hybrid process can be used on an existing part to repair a component. Think about a screwdriver. The only part of the tool that ever gets damaged is the tip. Once that happens, we throw it away. What if we could machine away the damaged area, add new material through DED, and then re-machine to the original dimensions? I’m not saying you should start a business to repair screwdrivers as they are cheap. But what if your tool was expensive? What if it was a custom die mold? In that case, repair may be a lot more affordable than replacement, and quicker as well.

There are a lot of hybrid machines on the market, and your choice may depend on what CNC machine tool you have in your shop right now. Brand loyalty is strong among CNC shops, as it is in many home garages. (My shop is all Milwaukee, and my neighbor is outfitted with Dewalt.) As traditional CNC manufacturers start to adopt additive, customers will want additive from brands they know, from suppliers they trust.

If I had my choice, I would have one of every type of 3D printer in my garage. But like you, I live in the real world and need to make hard choices.

The good news is that there are a lot more options than ever before. It’s all about finding the one that fits your manufacturing needs.

New Technology Era

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