QRP worked with Boeing and the University of Utah to investigate a new low-cost titanium product developed by Zak Fang and Pei Sun. Their paper was published in the Journal of Minerals, Metals and Materials. A summary can be found here.
Metal Additive Manufacturing (MAM) can be a great tool for rework. This is more often the case with Direct Energy Deposition (DED) but we found an application for it with Powder Bed Fusion (PBF).
The other day we were building some relatively large parts that took a long time to print. We sent them to a machinist to mill off the critical mounting surfaces and they accidentally milled off a little too much material from one surface. We really didn’t want to tie up the machine and loose schedule to reprint this part for another .020 inches if possible. In this case, the surface that was removed was a parallel plane with the opposite surface; so we decided to try and 3D print a little extra material on the top so the machinist could try again.
We started by locating the part on the center of the build plate as close as we could and tried to quantify the positional error along with the laser error with respect to the plate. Double-sided tape was used to attach the part to the plate as shown below. We were careful to ensure that the damaged surface was sufficiently parallel to the build plate.
We created a new CAD model of an oversized ring, the size of which was large enough to account for the errors we expected in the process (print size, ability to register visually, etc.). That error was small enough that the part could hang off any side slightly without any supports. We placed the new part in the printer and proceeded to fill it up until the top of the part was even with the focus plane.
We exposed the first layer of our new ring onto the damaged surface and found the registration to be off slightly. There was a little more overhang seen on one side than another. We proceeded to shift the position of the part incrementally until we saw approximately equal overhang on all sides and then ran the program to apply another .125″ inches to the top of the part.
After a few of hours, we returned the part to the machinist who milled and ground the surfaces such that the re-work plane was invisible and the final part came within spec.
This was a pretty cool effort that saved us a lot of schedule and budget on the project. The same approach could be followed to mix traditional manufacturing methods with MAM.
In the previous two posts in this additive engineering series, we talked about the purpose of support structures and how they work. Here we’ll start to talk about where we can get away without it on overhangs, bridges, and cantilevers.
As can be seen in the figure below, the weld trace-width is quite a bit wider than the layer thickness although a couple layers beneath the latest layer get re-melted. Therefore, the laser can focus on the solid part and have something to draw heat away, and have a part of the weld bead hang off the edge a bit with each layer. By doing this over and over again you can get an overhang. The rough rule of thumb is that you can go 45° before you need supports. This angle can vary depending on the material, power, laser speed, geometry, and approach direction of the recoater blade.
The rough rule of thumb is that you can go 45° before you need supports. This angle can vary depending on the material, power, laser speed, geometry, and attack of the recoater blade. For example, if the overhang is for a cone that is closing up and getting smaller as the layers progress, you can overhang more as the geometry will tend to hold itself together well. Also, if the overhang faces the oncoming recoater blade, the pressure from the new pile of powder will cause it to lift a little and get progressively worse as the layers continue.
If you overhang too far, there is not much material to draw the heat away and the overhang will tend to want to lift. The powder on the underside can also be more partially welded or the laser may even penetrate through and start drawing in larger chunks of metal powder. You can get away with this for a few layers but as this lifting stacks up, it can get to a runaway state where it is lifting quite a bit above the focus plane. The featured image of this post attempts to demonstrate this.
The image below shows some features being printed at different angles. Vertical walls will be very smooth, but the farther the feature tries to hang over, the more roughness you will see on the bottom surface until it tips far enough that supports are needed.
If you have a sudden expansion in cross section, the process can recuperate after a few layers but it can only withstand a cantilever of about 500 microns (.020″). The image below demonstrates what this might look like after a few layers. The faint dashed line shows the intended geometry. On the left, the part had a short cantilever where there was no support beneath the feature. In that area, the weld bead is very deep for that first layer so the overprint will be on the order of 250 microns beyond the intended surface (somewhat like we see in between supports like you can see on the bottom of this example). Sometimes I will shift my surfaces a little in anticipation of this overprint.
I was going to try to cover bridges in this post but I think that will need to be covered in the next post. Thanks for reading. If you want to go to the beginning of this series just click here.
Metal 3D printing is a fantastic tool but the idea that you can now print “anything” is a myth. You need to design for this process just as you do for any other serious fabrication process. For metal Additive Manufacturing, the key concern during design is your support strategy.
What happens if you can’t access the supports to remove? In many cases, you can develop custom build parameters to address it. Most service bureaus use a standard set of print parameters that are optimized for a generic case that yields high density and good surface finish for a variety of parts. However, with thousands of possible parameter combinations, you can optimize on other criteria depending on your objective.
QRP recently worked on a project for the University of Texas-Dallas to print a radiation sensor for a space application. They needed to have a lattice sphere surrounding a solid sphere that is electrically isolated from each other as shown below. We designed the inner “sphere” with a tear-drop shape so that no supports would be needed on the underside as it grew. The space in-between is impossible to reach to remove supports so we needed it to close up on its own.
We conducted many tests on just the critical dome section and investigated the tiny, 125-micron, features where they needed to close up on each other. The result was an optimized set of parameters for this case alone.
For the final part we printed it with 3 different parameter sets each optimized for 3 different bodies with unique needs. We also plated it with 10 to 20 microns of electroless nickel and ended up with a beautiful shiny part. The final result is shown below. This was a great project to work on with possible future iterations that will replace the solid inner sphere with a lattice as well.
QRP participated in a Business Model Canvas pitch competition with the Boom Startup Space-Tech competition. We won the $2500 cash prize and the opportunity to move on to the national NewSpace competition later this year with the chance to win $100,000.
“I’m very grateful to Boom Startup for the chance to pitch and the guidance they’ve given. I think that what we do at QRP has direct applicability to the commercial space industry and can have a big impact at getting us into space for lower cost,” said, Rob Smith, CEO and presenter for QRP.
Reducing the cost of space flight is directly related to lowering weight and reducing the size of components. At QRP, we are passionate about radical size and weight savings by removing any material that isn’t adding value and combining multiple assembled parts into a single piece. Our Additive Engineering skill can do the detailed analysis needed to synthesize a complex set of system requirements into an efficient end-use product.
“Another benefit to metal 3D printing is that these metal parts don’t outgas which is a problem for composite structures”, says Smith. With additive manufacturing, you can replace exotic materials (having a negative connotation where high reliability is important) with advanced geometry.
In our last installment of this series, we discussed the significance of supports in metal 3D printing. For Laser Powder Bed Fusion the supports do 3 things: 1) give the laser something to weld against, 2) hold the part down from curling up, and 3) draw the heat away. The last two are interrelated and will be discussed here.
Different layers cool at different times resulting in stresses that make a flat surface (parallel to the exposure plane) want to curl up like a potato chip. The following two images are of examples of the support structure breaking and the flat surfaces curling up on the corners.
To avoid this you may need to add additional, thick, solid supports at key locations to hold it down as shown in the figure below. These can serve two purposes: 1) they help draw the heat away to the base plate, and 2) they stake the part down to the plate more firmly. Determining the appropriate size, quantity, and location of these requires more computational muscle than most companies can afford. As a result, trial and error leads to experience and experienced support designers are valuable.
Support generating software has a button to create supports automatically. I can’t imagine anyone in their right mind using that. Custom designed supports are very common and play the second biggest role in determining whether the print will go well or poorly. (The biggest player being Design For Additive Manufacturing [DFAM]).
In our next post we will talk about overhangs, bridges, and cantilevers.
To start at the beginning of this series, click here.
The Governor’s Office of Economic Development (GOED) for the state of Utah recently announced its awardees for this round of Technology Commercialization and Innovation Program (TCIP) funding. QRP was one of 20 awardees from the 183 applicants…
Below is an excerpt from the GOED news release dated 1/18/2017
GOED Announces Recipients of 2017 Tech Commercialization Grant
SALT LAKE CITY (Jan. 19, 2017)—The Governor’s Office of Economic Development (GOED) Technology Commercialization and Innovation Program (TCIP) has awarded grants to 20 Utah companies and university teams to help bring their cutting-edge technologies to market.
“Innovation and entrepreneurship drive Utah’s diverse economy,” said Val Hale, GOED executive director. “The grant recipients represent a wide range of technologies, from consumer software to medical devices and manufacturing advances. We are excited to see these companies develop and grow.”
TCIP helps small businesses secure non-dilutive funding at critical stages of technology development. This year’s grant solicitation was the most competitive in the history of the program, with 183 applicants requesting funds in excess of $18 million out of $1.8 million available. Qualified technologies may receive grants of up to $100,000. Recipients may also take advantage of mentorship opportunities and entrepreneurial curriculum.
“There are many challenges to starting a new business, and one of those challenges is turning an idea into a marketable reality,” said Clark Cahoon, TCIP fund manager. “TCIP helps small business take the next step by offering small amounts of funding and mentorship opportunities.”
Applicants are vetted through volunteer review panels made up of local industry experts. The volunteer review panels recommend awards based on technical merit, team experience, level of matching funds and potential for job creation in the state. Companies receive funding upon meeting required performance metrics, such as the completion of technical or business milestones.
TCIP has been instrumental in the successes of local companies such as Myriad Genetics, BioFire and ENVE Composites.
We are happy to announce that our additive manufacturing capabilities have just been augmented by a larger 3D printer. The 400 Watt eos m280 is a metal DMLS machine capable of printing parts that are 10 inches wide and 11 inches tall. This new printer greatly enhances QRP’s capacity by enabling us to print much larger parts.
This printer became available to QRP by a special offer made by eos, one of the most dominant metal 3D printer suppliers. The printer is capable of printing in any weldable metal including titanium and aluminum. This acquisition includes open parameters for aluminum and stainless steel which will be a springboard for development of custom parameter sets for niche applications. Installation is scheduled for the first week in February and we have orders lined up to produce as soon as it is online.
This acquisition represents a quantum leap in capabilities for our company. We look forward to pushing the envelope of what this process can do for our customers.
In today’s second installment in this series, we begin to explain why supports are unique for DMLS (a.k.a. Powder Bed Fusion – Laser). Unlike other processes, with laser melting the parts end up being welded securely to the baseplate with no parts suspended loosely in the powder. For other processes, supports keep the part supported against gravity. For PBF-L the supports do 3 things: 1) give the laser something to weld against, 2) hold the part down from curling up, and 3) draw the heat away. This post talks about the first of these.
With this form of additive manufacturing, the melting of the top layer of powder is called “exposure”. That exposure has to take place on top of solid metal. The laser actually re-melts 2 or 3 layers beneath the current print layer which results in fully dense parts (once more I’ll reiterate that this is not a “sintering” process). Doing so requires a very high level of energy because the thermally conductive metal quickly draws the focused heat away.
So what would happen if you exposed a layer into loose powder with no solid directly beneath it? There would be nothing to draw the heat away so an unusually large glob of overheated metal would form. Instead of being 2 or 3 layers deep, it could be 10-20 layers deep. It would be severely misformed and if a line is drawn in the powder, the shrinkage would cause the line to break up or lift a lot.
The higher-than-normal temperatures result in lifted edges that rise significantly above the focus plane. This is a problem because when the printer tries to re-coat the part with a new layer of powder, these lifted edges snag the “coater blade”. As the blade drags across it will lift the stray glob away leaving an ugly void beneath it that can interfere with future layers.
To avoid this, supports are formed in earlier layers with a single pass of the laser that are pointed at top so that they can be broken off later on. When a new exposure plane needs to melt powder out into open space, it can bridge across these supports. This keeps that new layer below the next exposure plane and draws some of the heat away so that the over-melt depth isn’t so drastic.
In our next entry of this series, we’ll talk about the other purposes for supports.
(To see the first part of this series click here).
QRP recently printed some LaserCUSING (a.k.a. DMLS) printed aluminum foam for the Mechanical Engineering Department at the University of Utah with Dr. Ashley Spear. This series of foam cylinders were used in crush tests to characterize their mechanical properties relative to aluminum foam fabricated with conventional methods. A paper resulted which was published in a Material Science & Technology conference held in Salt Lake City, Utah.
The study compared conventionally cast aluminum foam with 3D printed foam. The original foam was scanned and then replicas of those parts were 3D printed in 6061 aluminum. The additive manufacturing resulted in parts that were topologically identical to the cast versions although there were local irregularities relative to details of the process. The results were informative and interesting.
There are many fascinating applications for aluminum foam where strength to weight ratio is critical. The rounded nature of the openings results in low stress concentrations and redundant load paths when one strut does fail. The original foam will be random in nature. But designers may fear using a random mesh for fear that some local feature will be located in a particularly bad location in a design. However, consider a foam that has been scanned and then used in a simulation. If the simulation for that foam meets the needs, the exact same geometry can be printed for consistent results across multiple parts. The result is a “pseudo”-random geometry with predictable local features that can be analyzed with very specific accuracy.
It is also applicable for air-oil separators where high surface area is required in a random configuration to trap the oil (high surface tension and viscosity) and allow air to pass through. The random nature of the mesh ensures that the pressure drop through the foam will be the same in all spherical directions– not just the standard 3 mutually orthogonal axes of a cartesian grid. A mesh made from such a grid would have different flow properties for flow running at an angle in-between the three main axis.