Titanium hip implants have the potential to be 3D printed in the future.
Image credit: stockpackshot / Shutterstock.com
3D printing is hailed as part of a third industrial revolution, but many people only associate the technique with cheap and brittle plastic parts. Metal powders have, up to now, been too expensive to consider as an alternative to polymers. However, recent advancements mean that additive manufacturing using titanium could lead the way for strong, durable 3D printed components.
How Titanium Printing Works
Titanium printing works in a similar way to composite 3D printing.
In the printing of plastics, a plastic filament is pushed through a heated nozzle which creates layers of very thin slices that are stacked one on top of another to create a three dimensional shape.
The nozzle heats the filament as it passes through which melts it, allowing it to fuse with the layer beneath. In this way, extremely complex structures can be formed which would not have been possible with traditional ‘subtractive’ methods.
In titanium printing, the composite plastic filament is replaced with titanium powder which is then sintered together.
New Titanium Powder Production Method
Up until recently, titanium printing was far too expensive to see any form of widespread use or development, with suitable titanium powders usually priced at between $200 and $400 per kilogram. This is far more expensive than the plastic filament used which sells for around $20 dollars per kilogram.
However the impressive strength, durability and light weight of titanium are incredibly desirable. The plastic objects that people usually associate with additive manufacturing can be amazingly intricate, but with this level of detail they can be lacking in the structural integrity that is required to be able to be really taken seriously as an alternative to traditional component manufacturing techniques. Unfortunately the price of titanium powders is currently so high, that only a few groups have been able to experiment with it.
The UK-based company Metalysis hope to change this, with a new method of titanium powder production that they have developed. This process uses drastically less energy and is therefore a lot cheaper than its predecessors.
Titanium is traditionally produced using the four stage, labour intensive, Kroll process. This involves extraction, purification, sponge production and alloy creation. In the new process solid titanium oxide powder is directly converted into pure titanium via electrolysis. In this process, the metal oxide powder is mixed with a molten salt, usually calcium chloride, in a reduction vessel.
Here, the metal oxide forms the cathode and the carbon forms the anode. When a current is passed through, the oxygen moves through the salt to react with the carbon anode, creating carbon dioxide and monoxide. Once the salt is washed away, this leaves pure titanium in powdered form which is perfect for use in 3D printing.
Titanium production process flow chart - Image credit: Metalysis
Not many examples of titanium printing exist to date, but all of them are extremely promising and are driving development in the industry. They are drawing a lot of attention by combining the flexibility and precision of 3D printing with the strength and durability of titanium.
Medical Marvels
Recently, titanium printing has come to the forefront of the medical world when Professor Peter Choong, director of orthopaedics and St Vincent’s hospital in Melbourne, used the technology to save a patient from amputation. 71 year old Len Chandler had been diagnosed with a large tumour in his right calcaneus (the heel bone) which would usually have to be amputated.
Science advances have allowed us to consider 3D printing of bones and we were able to get information from Len’s foot and use that to tell the computers precisely how big his foot is, and reproduce that using the new 3D technology.
Going from the possibility of an amputation to where you preserve the limb on account of one (replacement) bone is rewarding if you can achieve it.
Professor Peter Choong - St. Vincent's Hospital
Instead, Choong’s team decided to try a ground breaking solution. They scanned Chandler’s left foot to produce a 3D model of his healthy heel bone which they then used as the basis of a new model of his right foot. As both of Chandler’s feet had been scanned, the titanium heel implant was able to be designed in such a way that it combined perfectly with the healthy parts of the damaged foot.
In another medical marvel, the skull of Hu Wei was repaired using a custom printed titanium mesh. After falling three stories, the 46 year old farmer’s head caved in, causing him to lose many functions in his brain, such as the ability to speak or to see through his left eye.
Doctors from around the world were brought in to see if they could treat Mr Wei. They decided to 3D print a titanium mesh, replicating the lost skull by mirroring the right side of his skull, which they then inserted below his skin. Titanium was chosen for its remarkable strength to weight ratio as well as the fact it does not usually cause adverse reactions when used for bone replacement.
Competing with Aluminium
In February 2014, bicycle manufacturer Empire built a version of their MX6 aluminium trail bike entirely out of 3D printed titanium.
It was printed using a Renishaw printer, the same one that the University of Sheffield is using to test Metalysis’s new titanium powder. As bikes are too large to print in one piece, Empire’s titanium bike is comprised of nine separate components, all designed to fit perfectly together.
The finished bike weighs 1400 grams, 700 grams lighter than the original aluminium mx6 it was based on. What is astonishing is that there is no compromise on strength. Each part was optimised in such a way that any unnecessary material that did not have a structural benefit was removed. The parts that were created could not have been produced by any other process than 3D printing. The seat tower, for example, looks solid but is actually hollow.
Empire’s Chris Williams had this to say on the future of bicycle manufacturing "It may well be that we end up with a hybrid structure of titanium and carbon components, we don’t know, but we’re never going to know until we try."
Renishaw 3D Printing - Additive Manufacturing - Laser Melting Demonstration
Renishaw 3D Printing - Additive Manufacturing - Laser Melting Demonstration
Video sourced from YouTube - Renishaw
3D printing with titanium has showed some remarkable progress in the last year. Renishaw themselves said that if Empire had approached them six months earlier, they would have had to decline the bike project. The rate of growth for this technology should increase substantially thanks to the new titanium powder manufacturing technique developed by Metalysis.
More companies and research laboratories will have access to the new and more affordable materials in the coming months which should hopefully drive innovation and force additive manufacturing to achieve the true third industrial revolution.
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References and Further Reading
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