Is Precision Parts Manufacturing 3D Print-Ready?
The topic of 3D additive laser printing of metal is frequently in the news. So you might wonder: When is Metal Cutting Corporation going to talk about laser printing? After all, we often talk about various other methods for making metal parts.
At Metal Cutting we make parts that are very small, for our example here often with dimensions that are 1 mm (0.039″) by 2 mm (0.079″), and we make a LOT of them. These parts don’t usually have a lot of complex features or inner voids. They might be a tube or they might be solid.
So, our question for the 3D laser printing experts is, can you use 3D laser printing of metal for such large quantities of such small parts?
Basic Methods Of 3D Laser Printing Of Metal
To begin, let’s take a quick look at the three primary methods for 3D additive laser printing of metal.
Direct Metal Laser Sintering (DMLS)
This most popular method basically melts a 2D design onto a flattened bed of powder, fusing the powder and then adding layer upon layer to build the object. DMLS allows heretofore impossible designs. However, the process is very slow and produces metallurgy that approaches but does not in every instance equal traditional fabrication. DMLS is also known as selective laser sintering (SLS) or selective laser melting (SLM).
Directed Energy Deposition (DED)
In this powder-fed method, a highly concentrated metal powder stream is slowly released through an extruder and is fused as it meets up with a laser, forming layers at the surface of the part. DED is highly accurate for 3D laser printing of metal and is also used for repairing broken parts. This method is known as laser metal deposition (LMD).
Metal Binder Jetting
This method involves applying a liquid binding resin onto a powdered metal material. The layers are, in effect, “glued” together and then sintered in a high-temperature kiln. This process is faster and less expensive than the other two methods; however, the results are not nearly as strong or dense as the results you get with DMLS or DED.
Some Applications For Laser Printing Metal
Laser printing of metal has become popular for a number of applications. These include everything from prototyping to functional component parts in various industries, to mass customized production of everyday items such as jewelry and kitchenware.
Laser printing of metal is highly popular in dental and orthopedic implant applications. It allows these products to be customized to meet individual patient needs. (You can read more in our blog Polishing Metal Parts for 3D Printed Medical Devices.) Laser printing of metal is also a widely used for the aerospace industry. For instance, the next-generation LEAP jet engine has 3D-printed fuel nozzles.
Some Common Mistakes
People make some incorrect assumptions when it comes to 3D laser printing of metal. It sounds silly but bears noting that just because a product is designed using 3D CAD modeling does not make it “3D print-ready”; 3D laser printing processes require unique post-processing.
As with any manufacturing method, the properties of the specific material to be used must also be considered. For example, one assumption is that laser printing of metal is a substitute for metal casting. On the contrary, laser is great for unique, complex parts that cannot be cast. The properties of a 3D laser printed metal object are different from the properties of the “same” object when it is cast in metal.
Also, laser printing of metal parts designed for a process such as CNC milling would be very expensive. That is because subtractively produced parts have more mass and volume, and their designs are not optimized for the inherent advantages of 3D manufacturing — essentially, voids and lightweight, high-strength structures.
Advantages Of Laser Printing Of Metal
From an engineer’s perspective, probably the most significant advantages of 3D laser printing of metal are:
- The ability to produce fully enclosed voids and other features that are impossible to subtractively machine
- Structures that produce extraordinary part strength and a lightweight design that was previously impossible to achieve
For an industry such as aviation, where reduced weight of an aircraft means lower fuel consumption, lightweight is an important goal.
From an application perspective, the most significant advantage of laser printing of metal would be the “mass customization” that 3D additive laser printing ushered into industries ranging from aviation’s replacement parts to dentistry’s crowns and bridges, to orthopedic and prosthetic innovations, and of course, the entire prototyping business. Some of these unique shapes could never be produced subtractively. Even for those that could be machined or cast at a lower per-piece cost, neither method could conceivably approach the almost instantaneous delivery times that 3D laser printing of metal has made possible.
Laser printing of metal also can reduce the amount of waste material in the production process. Where traditional subtractive cutting methods involve the removal of material to create a shape, 3D laser printing of metal achieves a shape through the addition of just the needed material.
As long as the metal powder is available, 3D laser printing is flexible in terms of the metals it can use. They include titanium, stainless steel, Inconel, and cobalt chrome, as well as brass, copper, bronze, and precious metals such as gold, silver, and platinum. However, while the challenges of 3D laser printing in an inert atmosphere have been surmounted, it remains impossible to properly anneal certain metals. For example, while tungsten can be “constructed” via 3D printing, the resulting block of tungsten metal is too brittle to be usable.
Disadvantages Of Laser Printing For Metal Parts
Additive 3D laser printing is certainly famous for making the impossible possible, but what about precision? Is 3D printing a good method for making small precision metal parts?
Let’s looks at DMLS, the most mature and well-developed method, where the important variables driving dimensional precision are:
- The size of the powder particles
- The height intervals of the elevator steps
- The size of the laser beam
Each of these factors determines dimensional tolerances. Large metal powder particle size makes for larger steps. The height of each powder layer similarly determines that tolerances that can be achieved.
And probably the most important variable is the size of the laser. This is where a tiny beam gives you greater precision, and a larger beam produces more imprecise dimensions. The problem is, a smaller laser beam generates less heat — and that means it will take longer to do its job. So, you can have a part that is very precise and/or very small, but it is going to take much longer to produce. That, in turn, raises the cost.
There are other ways in which laser printing of metal is time-consuming. Again look at the very popular DMLS, where every part has a tiny point of attachment, like the tiny thread that keeps a wasp’s nest suspended from a porch. If you have 10,000 laser printed parts, that means you have 10,000 attachment points that must be separated. This task of separating from the base is usually accomplished using EDM; but whatever method is used, doing it 10,000 times defeats most if not all of the additive advantages.
The reality is that true mass production is still not possible with 3D laser printing of metal. This makes it impractical and costly for producing tens of thousands of very small parts. In addition, there is the high upfront cost of the 3D printer: at least $100,000 for some of the newest tabletops, which aim to disrupt the previous disruptors, up to over $1 million for the controlled atmosphere printers used with metals such as titanium or the giant enclosures required for machines designed to make aviation parts. That high cost means whatever application laser printer is proposed for needs to “add” something really unique to “subtract” from the value of traditional metal fabricating methods.
What Does The Future Hold?
We don’t want you to think we are being stubborn or resistant to change. In fact, we’d like to give a shout-out to our friend Scott Cohen and his partner, David Bell, at New Lab. They know the future as well as anyone, and we don’t doubt that someone at New Labs will one day solve some of the problems we are seeing now.
While the development of desktop-sized 3D laser printers — rather than huge, industrial-sized machines — will make the technology more accessible, we still don’t see laser printing of metal to be suitable for high volumes of small precision parts. In this case, small machines do not make for small parts. But of course, one day we may be proven wrong!
For some helpful tips on how to choose the best precision metal cutting method for your metal fabrication project, download our white paper Choose with Confidence: Comparing 2-Axis Precision Cutting Methods.
