Rapid Prototyping: Subtractive vs. Additive

Additive vs subtractive rapid prototyping may be a matter of knowing which process best suits your needs since both have their place

With additive manufacturing and 3D printers being such a hot topic these days, it’s important to remember why subtractive processes like milling are still incredibly important to rapid prototyping. But first, let’s examine some of the benefits and limitations of additive rapid prototyping (or direct digital manufacturing).

Benefits of Additive Rapid Prototyping

The process of additive rapid prototyping joins and fuses materials like liquid resins together, layer upon layer to produce a 3D object from model data. Additive rapid prototyping is generally simple, relatively inexpensive and fast. Additive rapid prototyping also allows for a substantial amount of complexity within cavities or internal areas of a part that would require undercuts and may even be impossible with subtractive processes like milling.

Limitations of Additive Rapid Prototyping

The primary drawback of additive rapid prototyping is that the resulting part usually is not made of an end-use material like metal … and even if it is, it lacks structural integrity. That’s because the point where one layer is joined to another lacks the physical strength exhibited by a solid block of the same material (with no layers or joints).

Subtractive Rapid Prototyping with End-Use Materials

Subtractive rapid prototyping provides the ability to prototype in end-use materials. Since milling or machining removes material from a larger piece of material, the finished part has a solid composition rather than a layered composition as seen in additive rapid prototyping with 3D printers. This yields a higher structural integrity which is critical if the prototype part is to be used in product testing. Product testing with a part made through subtractive prototyping allows for an accurate analysis of the part’s viability and even durability since it is made from the same material that will be used to manufacture production parts.

A Wider Range of Surface Finishes and Textures with Subtractive Prototyping

Subtractive rapid prototyping processes also offer a wider range of surface finishes for the completed prototype as opposed to the standard “stepped finish” often achieved in additive rapid prototyping with a 3D printer. This could range from a completely smooth surface with a mirror-like finish to ones with milled or engraved textures. In this way, subtractive rapid prototyping with a high speed CNC milling machine is capable of producing prototype parts with a repeatability suitable for end-use production. The smooth surface finish that can be achieved with high-speed machining can be functionally beneficial if the given part needs to slide and aesthetically beneficial if the prototype is going to be used in market testing.

Additive Rapid Prototyping vs. Subtractive Rapid Prototyping

To illustrate the points made above, we asked our applications engineers to quickly prototype a part using both additive and subtractive processes. Since our favorite after-hours (wink, wink) past time is foosball, they decided to make a “replacement” foosball man for testing. This decision was based on an actual real-life need – since we had recently broken one of the men that came with our vintage 1985 foosball table. Using additive rapid prototyping (3D printing), they were able to design a very rudimentary foosball man in about 90 minutes. From there, they began printing and in just over an hour the part seen below was complete.

 

Additive rapid prototype made with a 3D printer to compare to a similar subtractive rapid prototype made with a high speed milling machine.
Additive rapid prototype made with a 3D printer shows the typical stepped finish indicative of this process.

 

Using subtractive rapid prototyping (high-speed milling) programming the part took substantially longer and clocked in at 3 hrs. 45 minutes. However, milling the part below was considerably faster than 3D printing and took 28 minutes.

 

Subtractive rapid prototyping processes like machining tend to offer more flexibility in terms of surface finish as well as the ability to prototype in end-use materials that are superior for product testing.
Subtractive rapid prototype showing a smooth surface finish and a solid composition that delivered greater functionality.

 

Product Testing an Additive Rapid Prototype vs. a Subtractive Rapid Prototype

Well, you knew we had to “test” the part right? So, in a series of 4 rather heated games using each prototype, here’s what we found. In terms of functionality and durability, the subtractive prototype was the clear winner. Not only did it last through the 4 games, the solid composition of the part made for stronger shots with high velocity. Plus, it clearly would hold up for hundreds of more games. By comparison, the 3D printed part began to show signs of delamination on its right side half way through game 3 — and by the game 4 we had to mend it with a bit of scotch tape to get through the rest of our “product testing”. The damage to the part revealed the inside composition of the 3D printed part as seen below.

 

Additive rapid prototyping using 3D printing can be fast, but less functional in terms of product or market testing due to both aesthetics and their non-solid composition.
Cross section of 3D printing prototype shows internal construction.

 

The rather hollow nature of this part shined a bit of light on why we couldn’t achieve strong shots using this foosball man. In analyzing the resulting surface finish on both parts, we felt that the subtractive prototype was … well, simply more attractive. Plus, the milling process provided more flexibility to achieve different surface finishes. For example, we were able to make the majority of the subtractive prototype very smooth while giving the foot section a more textured finish for added “grip” or ball control. By contrast, the inherent “stepped” surface finish on the additive prototype served well in terms of ball control … but wasn’t very attractive over the entire part.

The Ultimate Subtractive Rapid Prototyping CNC Machine:

Last year’s introduction of the DATRON neo compact high-speed milling machine makes subtractive rapid prototyping more affordable and viable than ever. Plus it’s compact size and touchscreen operation make it easy to use and easy to fit in the tightest “lab-type” environment. To learn more download the brochure by filling out the form below:

Microsoft R&D Lab Using Datron High Speed Milling Machines For Rapid Prototyping

Microsoft R&D operations in Redmond, WA using DATRON milling machines as seen on both CNN and Bloomberg.

 

Microsoft’s Corporate Vice President, Panos Panay, says, “This is like a big toy factory” when speaking about their R&D operation in Redmond, WA. This state-of-the-art facility, along with the many DATRON high-speed CNC machining centers there, was recently featured by CNN in a piece called “Inside Microsoft’s secret design lab”. Like a kid in a candy store Panay continues, “You can spend days and weeks and build anything on the planet in this building!”

 

Microsoft R&D lab machining thin aluminum housings using DATRON high speed CNC milling machines.
Microsoft R&D lab using DATRON high speed machining center for milling thin aluminum housings.

 

Indeed, Microsoft has amassed the world’s leading technology under one roof and the possibilities are endless. Many of the products and devices that we’ve all grown to love and depend on were developed in this building. More importantly the future of commercial electronics will be born here.

Panay is the man behind Microsoft’s Surface, and when commenting on the competitive landscape he says, “You know, we have a very deep set of competitors right now. We’re not sitting on our heels, we need to go forward every day. We can’t fall behind and the way to do it is you build a product, you test. If it fails you build it again. This is awesome right? You learn right away. Iterate, every hour or couple of hours, you can put something in overnight … you can find success and boom! Right there, you’ve failed and succeeded in almost the same set of 8 hours and now you have a solution that works for your customers.”

This is perhaps, the truest spirit of Microsoft R&D, and the equipment in their lab is akin to an artist’s paintbrush, allowing them to embody and emote this spirit in an efficient and meaningful way that can impact the daily lives of millions of consumers. Commenting on rapid prototyping, Panay says, “It happens quickly and it happens in a way that you get the true feel of the product. That’s so important. Tor really know what your customers are going to use and love you have to feel it.”

DATRON is proud to have consulted with this Microsoft R&D lab regarding the best suited high speed milling equipment for this type of rapid prototyping. What can be seen in the video, is a lineup of DATRON M8 and M8Cube high-speed CNC milling machines that are particularly efficient in milling aluminum parts with superior surface and edge finishes. The quality of surface and edge finish is of paramount importance when evaluating attributes like “feel” discussed by Panay in the video.

 

Microsoft R&D lab in Redmond, WA using DATRON high speed CNC milling machines for the rapid prototyping of consumer electronics parts including these aluminum housings for Surface3.
Microsoft R&D Lab rapid prototyping aluminum housings for Surface 3.

 

Bloomberg broadcasted a different video last year of the Microsoft R&D lab that was titled “Inside Microsoft’s Secret Surface Labs”. In this video, the narrator refers to the DATRON M8 as a “magnesium slicing milling machine” and Panay, who appears in this video as well points out, “You’re starting to see that same billet back there come to life right here … and this is our model shop.” The “Surface” story in this video is very much about the tenacity of Microsoft R&D. In fact, it suggests that the initial launch of the Surface in 2012 was less than successful and that iterations of the design have resulted in the product quietly gaining ground.

 

Brett Ostrum, Surface Development General Manager at Microsoft says, “Thinner and lighter, thinner and lighter, thinner and lighter. Grams, tens of grams are a huge currency for us.” As consumer electronics get smaller, the machines used to develop them have to be able to make tiny parts often featuring thin features, thin walls and other intricate features. This is where DATRON high speed machining centers excel because they were engineered from the ground up around a high speed spindle and for the sole purpose of high speed machining. To learn more about this technology and the science of high speed machining:

Download the High Speed Machining White Paper