Additive manufacturing (AM) techniques produce low volumes of complex products with high quality and precision. These products typically include medical and dental prosthetics and implants. With engineering-quality materials, aerospace and automotive components can also be fabricated.
As a form of AM, 3D printing techniques have long been used for rapid prototyping. Some of these low-cost printers help speed the design process. Low-volume AM differs from 3D model and prototype printing in how parts are used and the number of parts produced. Volumes tend to be in the tens, hundreds, or even low thousands. Techniques include laser sintering (LS) and fused deposition modeling (FDM). Materials are generally thermoplastics, but some metals are sintered.
The right and left exhaust manifold, right and left rocker arm housing, and oil filter housing of this HR28TT Honda racing engine were foundry cast from metal using wax patterns made with 3D Systems' ProJet CPX 3000.
"Unlike models and prototypes, end-use production parts often must endure extreme temperatures, humidity, direct sunlight, and sometime abusive handling," Terry Wohlers, principal consultant and president of Wohlers Associates, told us in an interview. "They must hold up over a period of years, maybe even decades, such as in aerospace."
Standard subtractive manufacturing techniques and injection molding don't always make sense in some industries and applications. The high cost of injection molding tools must be amortized over several thousand units. AM can be competitive when producing only 2,000 units, and injection molds cost a lot, making the unit cost for tooling alone very high, says Bryan Crutchfield, managing director for Materialise USA. "With AM, you also have the flexibility to make a design change in CAD data, so you don't have to also change the hard tooling, and you can build on demand."
Injection molding processes run a huge batch at once, necessitating stockpiles of material, but AM saves on material obsolescence costs. Crutchfield says the process needs several hours to build up a part layer by layer, versus three to 40 seconds of cycle time per part in high-volume manufacturing. "But if you take into account all the costs -- including tooling, materials, and investment for shorter runs -- that's when you can favorably compare AM to traditional manufacturing. Stamping dies and injection molds are very expensive to produce up front and much more difficult to change."
Those long lead times RadioGuy quotes for different techniques are one of the big reasons why AM looks so promising to automotive and aerospace manufacturers, among others. One of the biggest applications is for either "bridge" parts--a small run of regular parts made while waiting for the larger order that has been delayed--or for on-the-spot customized replacements, especially in aerospace, especially in remote locations.
My knowledge of die casting comes from plastic and aluminum parts that we use for housings in our products. This parts are much easier than the auto parts which need to stand up to severe thermal and mechanical stresses (whereas our aluminum allow radio housing just need to remain waterproof from -40 degrees to +70 C). I find it interesting to learn that the actual mold used is made of plaster. Makes sense.
When we are ordering up tooling, we typically have a 12 week lead time; I was assuming that an auto engineering site would have the mill in-house and have much shorter lead times. But we are still on the right order of magnitude.
As for what process one uses for what applications: I would think that the "conventional" exhaust manifolds would be stamped/pressed/welded rather than die cast. But the stamp/press processes still require long-lead-time tooling.
I love this forum, where an old softwre guy like myself can learn a bit about mechanical engineering. It is this kind of reaching across between disciplines that helps us all innovate, because it takes a complete outsider who is not steeped in the traditions of "how these things are done" to ask "why are you doing it that was and not ... (insert alternative process here)".
RadioGuy, you're right that the Honda engine parts are cast from molds based on a wax model. The process is a lot like the old lost-wax process. But I disagree with your fine-tuning of the definition. The industry classifies that as part of additive manufacturing. The actual parts made for production uses, such as racing car parts, are another branch of AM and are usually called direct manufacturing, meaning with no model or cast in between the CAD pattern and the output.
And Dave, thanks for all the detailed input on casting.
RNDDUDE, I've seen some of these custom-made dental implants and hearing aids and they are pretty amazing. What's also amazing are the customized surgical guides and other surgeon's tools that are customized to the patient's body, especially in dental surgery.
@Charles: Investment castings have been used in this type of stressful environment for decades. What's new here is that the patterns for the castings are made using additive manufacturing techniques. But the castings are still made by pouring molten metal into a mold.
The human body can be a pretty harsh and corrosive place for parts, but it pales by comparison to an engine's exhaust manifold. I'm very surprised to see this technology being applied to such stressful environments.
@RadioGuy: Your details are a little bit off -- $50,000 is maybe a reasonable price for die casting tooling (depending on the size and complexity of the part), but a typical tooling lead time would be more like six to eight weeks, and a typical tooling life would be several hundred thousand shots -- but your comments capture the spirit of the technology very well.
Basically, if you don't have time and/or money to spend on tooling, and if you only need a small number of parts, then it makes sense to use rapid patterns.
One consideration which isn't mentioned in the article is that casting in a plaster mold is very different from casting in a steel mold. Plaster is a thermally insulating material, while steel is a thermally conductive material. This means that the heat transfer at the metal-mold interface is completely different. A casting will solidify at a much faster rate in a metal mold than in a plaster mold. The solidification rate determines many of the mechanical properties of the casting. So I'm not sure that this is a "realistic substitute" for die casting, at least as far as mechanical properties are concerned.
I'd like to know more about the plaster mold process mentioned in this article. Are the plaster molds thick, or are they shells? If they are shells, do they stand alone, or do they go into a sand flask? Are the molds single-use (which would make this a form of investment casting), or can they be used multiple times?
As RadioGuy points out, in many of these technologies, additive manufacturing techniques are not used to make the final product, but to make a pattern for a casting. As a metallurgist, I would like to see much more emphasis on the metalcasting aspects.
The fact that metalcasting has been around for thousands of years does not make it is old and boring. Advances are constantly being made in foundry technology. The interface between additive manufacturing and metalcasting is just one example.
The automotive parts (exemplified by the Honda racing engine's exhaust manifolds) are not really additive manufactoring. They are metal CASTINGS made in MOLDS based on a WAX MODEL that was sculted by a 3-D printer. This is still cheaper than a mold created from a steel block sculpted by a CMC milling machine. The trade off may be that a steel mold costs $50,000 and takes 3 weeks but is good for 1000 castings, whereas the wax / sand casting is done in a day but has to be repeated with a fresh wax model for each cast.
(I don't really know much about metal manufacturing, but I think the above captures the gross outline of the technology.)
Ann, yes medical has some real potential. Because now one can get very accurate patient topographical data via MRI/cat scan, and have that translated into 3D solid format, customized implants can then be exactly tailored to the patient before and surgery takes place. The result would be perfect fit, faster surgeries, less complications, faster recoveries.
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