@Doug: Actually, it might be more accurate to call the technique used by the group at UCSB to make the ultralight metallic microlattices which have recently been seen balancing on the head of a dandelion "subtractive manufacturing." First, they made a pattern out of a photocuring polymer, then they coated it with electroless nickel, then they etched away the plastic. It's a fascinating approach. I would never have thought of using electroless nickel plating as a stand-alone structural material!
I agree with you that additive manufacturing is a great way to make patterns for castings - and not just investment castings, but also sand castings.
What kind of rapid patterns are you using? When I worked in investment casting 5 - 6 years ago, we mostly used QuickCast patterns. These are epoxy patterns made using a stereolithography process. What makes them unique is that they have a cellular structure, which allows you to burn them out with a minimum of ash and without cracking your mold. A disadvantage is that they are not autoclavable, so you can't take a QuickCast pattern and put it on a wax sprue. We also used wax patterns made on a ThermoJet 3D printer. They were autoclavable, but the dimensional accuracy was not as good.
Given how quickly things have been developing, I wouldn't be surprised if there have been new developments in the past few years.
Doug, can you tell us what kinds of parts you're making using AM for investment casting? If they're for automotive, medical, aerospace or industrial applications, we'd like to find out more about your application. Please send me an email if you'd like to share some information.
Yes, we are also using additively-manufactured (AM) patterns for investment-casting of various copper and nickel alloys, as well as stainless steel. Another point to consider is that AM is the only means of producing complex patterns effectively. Case-in-point, there are numerous articles being released on the internet discussing the "world's lightest material," produced using an AM pattern.
My point was intended to assert that a means of forging without needing a forging die, strictly a noncontact forging mechanism, such as a bust of laser energy to create a shock wave equivalent to the forging impact. Probably it would not be competitive beyond relatively small production runs. My thought was that if an approximation of a hammer forging process could be developed that would be the way to get 100% density and a desireable grain pattern.
In short, it would wind up being a fundamentally different technology from anything that we have presently.
Laser sintering is, in fact, being used for very small production quantities in aerospace and high-end automotive applications, such as race cars. Dave, you hit the nail on the head--one reason is for very small volumes where the cost of tooling is huge and amortizing it over a few parts make them very expensive parts, indeed. It's also being used to make the pattern for the mold in plaster cast aluminum parts, as a substitute for die-cast parts. Stay tuned--a January feature article looks at low-volume manufacturing with AM techniques, including LS.
@William: There's no reason why you couldn't powder forge a laser sintered part - except that you'd have to build a forging die, which would tend to negate the whole "rapid" aspect of laser sintering. I agree that anyone who could figure out how to make a net shape part with wrought properties through a rapid process with no tooling would probably become a multi-gazillionaire overnight. This would be the Holy Grail of rapid manufacturing. However, like you, I don't have the slightest idea of how this could be done.
I think at some point in the not-too-distant future, laser sintering might become competitive with investment casting for small production volumes - basically, where the production volume is too small to justify the tooling investment. Of course, investment casting foundries could stay competitive by using the same technology to make rapid wax patterns - and, in fact, they already are. In terms of mechanical properties, I would expect an investment casting to be superior to a laser sintered part.
To be fair, investment casting technology has had about a five thousand year head start compared to laser sintering.
Some sintered parts are then forged, which does produce an oriented grain structure, and in addition does increase the density. The ultimate success would be to create a means to do laser forging. I have no ideas on how to do that, but when such a macine is invented I will buy one and go into the laser forged parts business.
From what I've read, metal parts made by direct laser sintering are typically not fully dense. They can be infiltrated with a copper alloy to help fill some of the porosity, or treated by hot isostatic pressing (HIP'ing) to increase the density. But I would not expect them to have the mechanical properties of castings or forgings. I would expect them to be closer to powder metallurgy (P/M) parts in terms of properties. That being the case, I would be very careful about putting them in any application which sees significant amounts of tension, torsion, or bending. Does anyone have any numbers for mechanical properties of laser sintered metal powders?
I think some of the parts being produced by this method are replacing parts that were previously produced by forging with secondary machining. If this is the case, how do the final parts stand up without the grain structures of the forgings? Aren't sintered parts produced from powdered metals fused together with heat and pressure. It would therefore have no grain and be lacking the inherent strength generally associated with that feature. While that would be immaterial on dental crowns and similar items not subjected to torque requirements, engine parts may be problematic. This is akin to plywoood being replaced by particle board. If that is not the case, I wish someone would explain why or why not.
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