3D Printing – Panacea or Pandora’s Box?
Much has been said about 3D printing in recent years with some claiming that the technology will become so pervasive that we will all have printers at home for kids’ crafts, and will be able to run by the corner health center for a replacement organ or two. At the same time, frequent users of the technology undoubtedly will have had experiences where 3D printed parts were more trouble than they were worth. So is 3D printing the future, or just something that will soon be in our past?
Rose-Hulman Ventures has been a heavy user of 3D printing technology for nearly 16 years. In that time, the staff have become experts on when, and how to use the various 3D printing technologies for success. While Rose-Hulman Ventures maintains an in-house system that covers most daily 3D printing needs, it is still necessary to work with various external service providers when special materials or other circumstances require it. Working with the vast array for 3D printing providers out here can be daunting, so this article will discuss “Dos and Don’ts” associated with 3D printing.
First, what is 3D printing? 3D printing is the common term for a number of additive machining processes. Whereas traditional machining involves taking a piece of stock material and removing what you don’t need, additive processes start with nothing and build the part up one thin layer at a time.
There are a number of different 3D printing technologies in common use today. Some start with powdered materials that get melted together with a laser. Some use spools of plastic rod stock that gets extruded out of a heated nozzle much like a hot-melt glue gun. Others use liquids that turn solid when exposed to lasers or a flash lamp. The materials vary greatly as well. Most 3D printers work with polymer materials, but directly printed metals are becoming more common. Additionally there are options for directly printing wax parts that can be used for investment casting, and even systems that will directly print sand molds for sand cast parts.
Here are a few common pitfalls that first time consumers of 3D printed parts may run into:
- Parts are expensive – A complex part may be a bargain compared to what it would cost to machine one traditionally, but be prepared to pay real money. Material costs are commonly in the $40/cubic-inch range with some costing much more than that. To compound this, some of the machines require several thousands of dollars of material to fill. Even though only a small percentage of that material is used for a part, there is a limit to the number of times the unused material can be run through the machine so the waste material must be amortized over the parts run. In addition to paying for the amount of material you consume, expect to pay for the time it takes to build the part. Since the parts are built up one layer at a time, the higher the build, the more time will be required, and the higher the cost. Build height is your enemy for another reason. Thicker and more time consuming builds tend to produce more of the tolerance issues mentioned below. Short fast builds are the best bet.
- Tolerance and Part Quality – Most 3D printer technologies produce parts that are within a few thousandths of an inch from nominal, however, there are some other things to consider:
- The tolerances in the X, Y and Z planes may not be that same. This can result in unexpected fit issues such as holes that are not round, or two housing halves not closing well because they were printed in different orientations in the machine.
- Parts run one day may have very different tolerance issues than parts run on another. A prototype assemble using 3D printed parts may fit and work well, but a duplicate made a few days later may have unexpected fit issues.
- Warping of parts is common. Parts with thin cross sections relative to their length or width are very prone to warping because of the uneven heat distribution that is inherent with the 3D printing technologies.
- Hollow parts – All of the additive processes use some sort of support material or structures to stabilize the part as it is being built. This may be a dedicated support material, a printed scaffold to hold the part up, or simply unfused powder from the build process. If your part is hollow, expect to pay for the extra support material required. If your part is also totally enclosed, expect it to arrive full of this extra material that you didn’t want.
- Surface Finish and Part Strength – Strength and finish quality are the major differentiators between the various technologies. Fusion Deposition Modeling (FDM) machines make parts that are generally made from ABS plastic, but have a relatively course surface finish. Stereolithography (SLA) parts tend to have the best surface finishes, but the resins available are not quite as robust. Trade-offs have to be made based on what you need your prototype to do.
- Resolution – Some of the machines in use today can produce parts with amazing resolution. The machine in use at Rose-Hulman Ventures is a mid-level machine and can produce functional threaded parts in the #6-32 or M3 range with no problem. However, there is always a need for more detail, and it is common to be disappointed by limitations of what 3D printers can do.
- Some things should just be machined – Once you get into the mode of having parts 3D printed, it is easy to overlook the pieces in your design that should just be machined. There are many things that could be done with even a manual mill or lathe in less time than a 3D printer, and the parts will be of better quality.
Having your parts 3D printed is very simple. There are a number of service companies out there that utilize all of the technologies available. It is simply a matter of finding one that provides the technology most applicable for your application. Most of the providers utilize an automated quoting and ordering system where you simply upload your part, select the materials and part quantities, and pop in a credit card number. STL files are the normal format for submitting parts, but these days it seems most providers are able to take the native files from your CAD software. This info will help those that are new to 3D printing technology take their first steps into the world of “Grown” parts. Used the right way, the technology can reduce iteration times on designs form weeks to hours. However, it is easy for some of the issues listed above to become red herrings in your development process when prototypes fail to function, not because of design issues, but because of part quality.