3D Printing vs. CNC Machining

            

Recently I have been looking into 3D printing for Crosswind Machining.  There is so much buzz all over the news and internet about it and I wondered if we could benefit from adding it to our shop floor. I think companies need to always be open to change.  Not only so that we make quality products with the machines that we already have, but also looking for ways to improve our capabilities to serve our customers with new ideas and new technology. As a matter of fact our Quality Policy states ”…to consistently surpass customers’ expectations in both quality and delivery scheduling.  We make every effort to continually maintain and improve our system.” That includes looking at newer technologies like 3d printing.  After doing quite a bit of research I have no doubt in my mind that this technology will play a large part of the manufacturing industry in the next 10 years.  Additive manufacturing is being utilized in multiple fields already such as medical, manufacturing, art, automotive industry, and defense.

First you need to realize the difference between additive and subtractive machining .  Additive machining is where material is laid out, layer by layer, to create a product (3d printing).  Subtractive machining is where material is subtracted by tooling (drills, laser cutting, etc) to create a product.  This technology is fantastic.  It’s even become so mainstream that people are buying inexpensive 3d printers to use at home for things like school projects, jewelry making, and creating simple tools and useful items for the home out of plastic.  I am fairly sold on the abilities of 3d printing when it comes to plastic materials.  It’s cheap, quick, and the design possibilities are endless. 

One of the great uses for these machines in a machine shop is their ability to produce a component for R&D purposes within hours or days rather than weeks.   If you only need 1 to a few parts there is no need to tie up a more valuable CNC machine and also the valuable employee running it.  A 3d printer doesn’t have to be babysat either because there is no tooling to break or wear out, no material to change, chips to remove, or 2^nd operations like sanding and deburring.  Not to mention the fact that designs can be so much more complex with additive machining that simply cannot be done with a CNC. Complex geometries like cavities, honeycomb patterns, and undercuts are almost impossible with a traditional CNC machine.

Another thing additive machining can do for a machine shop is create usable tooling for the company such as nuts, screws, hand tools, tubing, fixtures, and adapters.  This is where DMLS enters in.  DMLS is short for Direct Metal Laser Sintering, also commonly referred to as 3d metal printing.  There are definitely some pros to DMLS, but some very strong cons also.  First of all, materials for DMLS are more expensive when compared to bar stock, but you won’t have scrap or have to order large quantities either.  When creating parts from metals like iconel or titanium this can be especially helpful.   Titanium and iconel also wear through tooling quickly and need high pressure cooling because of the high temperatures occurring while being machined.  This is not the case with DMLS.  For short run jobs, especially popular in the biomedical, aerospace, and high speed racing fields, this can be a plus. 

Micro parts made on DMLS

However, there are 2 large problems that I am finding when reading into DMLS vs. CNC machining.  The first is the speed of production.  This may be great technology for a short run job of only a few pieces, but if you need 1,000 pieces it doesn’t make sense to use it.  The speed of a CNC machine when churning out large quantities of components cannot be beat.  It may take hours to make 1 part on a DMLS printer, but once the CNC machine is set up, it can take seconds to minutes.  The other problem I am finding is the quality with metal additive machining.  Parts made on a CNC machine are much less porous than those made on a DMLS machine.  The quality of those made through DMLS is similar to something made via injection molding, but needs heat treating to bring it up to strengths closer to that of wrought metal.  After that, if it requires a smooth finish, it will have to have a finish treatment because they are also not as smooth as machined parts.    The parts will typically come off of the printer with a surface roughness of 350 R a- µ inch or R a-µm 8.75.

Typical surface finish of DMLS part

So, to summarize, I do believe that 3d printing is a great compliment to a CNC machine shop.  I believe this especially to be true if you are in an industry where you are doing R&D jobs, hoping they will turn into long production runs.  You can churn out 1 or a few parts relatively quickly without tying up man hours and a machine.  Your customers can have a sample part to hold in their hand, to test, or decide if there are changes that need to be made.  Also, it can be extremely helpful in making in-house tools rather than searching all over the internet and hoping you can just buy 1 or 2 pieces of something for cheap.  The biggest thing that is really driving my interest in 3d printing, whether it be for plastics or metals though, is that I truly believe it will become a regular staple in machine shops all over the world in the next decade.  If you don’t have one, you will be behind the times.   Customers want vendors that are good at what they do, give a good product for a good price, and are using the latest technology.  However, these machines are nowhere near being ready to replace CNC machines.

Take a look at some of the interesting links I have included below for more information on the subject.

Where 3D Printing Fits In

CNC Machining vs DMLS. Which One is Best for You?

Your Shop, Too, Will Have a 3D Printer

Will metal 3D printing replace CNC machines in the near future?
CNC Machine Walkthrough: 3D Printer vs Laser vs Table Router (Video)

EOS M290 3d Metal Laser Pinter in Action  (Video)