By Mike Bishara
In a nondescript building crammed with hi-tech gear Warwick Downing heads a programme which looks certain to change forever the way we think about manufacturing engineering.
Despite everything you ever heard about how rare titanium is, in fact it is one of the most common elements on earth. Titanium (Ti) exists naturally in an oxide form predominantly with other elements, as in our iron sands, says the Titanium Industry Development Association (TiDA) chief executive Warwick Downing.
“After the iron is removed the remainder is around 40 percent Ti. Extracting Tiis achievable and is done around the world, the majority ending as the white base in paint and in sunblock,” he says.
“The difficult part for the metal is extracting the oxygen. It is the oxygen-free metal that we know as having the biocompatibility, high corrosion resistance, and best strength-to-weight ratio of any metal.
“It is the extraction of the Tithat creates the cost of the final metal.”
The good thing about using Tipowder is that there is almost no waste and it is non corrosive and non toxic.
“Couple this with highly efficient manufacturing methods and the ability to use Ti alloys increases,” he says.
TiDA was formed in 2010 to help New Zealand companies add value and develop new products for the international market, while remaining competitive against cheap labour economies.
A key part of that brief was to introduce titanium powder technology to New Zealand industry and help companies build up and improve consolidation capability.
While receiving strong support from New Zealand Trade and Enterprise, “we encourage customers to come in and see how it is done and what can be done.
“New Zealand manufacturers can compete with China on price because our labour component costs, while more expensive, are spent on design and not labour intensive manufacturing,” Mr Downing says.
Powder metallurgy is a highly efficient process because labour costs have little impact – the design and materials used are of greater importance.
Doctors in the UK have 3D printed a complete jaw which has been produced with composite powders including titanium.
“Small numbers or large numbers make no difference. We can machine sinter 60 differently designed parts at the same time as long as they fit in the 220mm x 220mm build area,” says Mr Downing.
The pride and joy at TiDA is a $1.5 million laser sintering unit which it shares with Triodent Ltd in Katikati.
“In using the laser sinterer we can take a CAD model and build it up layer by layer, melting the powder only where it is needed.
“We prefer a bit of time first time, but we have a fair idea what will work and what will not. Basically in free form manufacturing there are very few boundaries – it is a little more difficult to manufacture parallel to the plate, for example, where we may use a snap-off leg to lift it off the plate.
“In CAD design terms, 3D printing titanium and laser sintering can be cheaper than machining using stainless steel – it is lightweight and does not have to be solid,” says Mr Downing.
Metal injection moulding can be used for larger volumes and profiles similar to aluminium can be extruded using Ti alloy powder, giving properties similar or better than a billet. TiDA works with Advanced Material Engineering for injection moulding and South Auckland Forging Engineering for extrusion and hardness testing.
“The best way to realise the economic potential of the titanium powder industry is to support local companies in developing new products,” says TiDA chairman Ian Macrae and owner of one of the country’s largest engineering operations Page Macrae in Mt Maunganui. He also has taken his own advice and has set up Titanox to produce Tifor local consumption and purchased a machine for physical vapour deposition (PVD) coating, a process that could only be done overseas previously.
“One of the key benefits of these coatings is their superior corrosion resistance. Once coated with a metal nitride or carbide PVD coating, the part surface becomes inert and is impervious to attack in hostile chemical environments such as salt water, chlorine, geothermal steam and sulphuric acid which are found in many process applications and industries,” says the company’s development engineer Bruce McLean.
Powder metallurgy was first developed over 75 years ago and now includes many different consolidation methods which allow extremely high-quality metal components to be manufactured with precision so there is little or no need for further machining.
The metal powder can be consolidated by compacting/sintering, injection moulding, spray forming, laser deposition or sintering, hot and cold isostatic pressing, foam structures, screen printing, PVD and hot extrusion rolling and forging.
As a result, new applications and products can now be made which were not previously possible, opening up opportunities and a whole new world of technologies.
One current TiDA research project focuses on powder compact extrusion of NiTialloy powders. Nickel-titanium alloy near the equi-atomic concentration is well known for its shape memory effect and possesses excellent shape memory properties, good mechanical properties such as good ductility at room temperature, good corrosion properties in sea water, excellent biocompatibility and various tribological applications.
“During tensile testing, on breaking it is like rubber and remembers its shape which can be changed by any number of motivators – at the moment temperature,” says Mr Downing.
Super-elastic NiTialloy is widely used for applications such as surgical staples, orthopaedic implants, orthodontics, endoscopic and endodontic instruments. It is elastic metal developed originally for the US Navy for submarines operating at very deep levels where the pressure is intense. It is also used instead of explosives where it is inserted in a small drill hole into a cliff and a small electric current applied to change the shape, can push out a cliff face.
It is being applied to bridges in Japan to mitigate the effects of earthquakes and looks to have good use in Christchurch.
“As part of the project we are looking at the hardness of the extruded bars and considering ways to increase hardness while maintaining the super elastic properties. The average tensile strength for the NiTialloy extruded bars to date are recorded at 900 MPa,” says Mr Downing.
“The role of the facility in Tauranga is to help companies develop new products and prototypes and to ensure they are fit for purpose. We have an extensive range of analysis and testing equipment and the recent addition of new tools will further enhance the facility and services we are able to offer.”
A FRITSCH laser particle sizer helps accurately measure the distribution of particle sizes within any powder.
“Knowing how big the particles are within a certain sample is important because it will determine the packing density and ultimately affect how strong a product is,” says Mr Downing.
The rotary cone sample divider and vibratory feeder sample divider will also play a crucial role to accurately analyse powders. When loose metal powders are moved around, the smallest particles fall to the bottom. Simply scooping a teaspoon of powder off the top of the pile for analysis will not give a true picture of how that powder will perform.
Accurate sample division is achieved by passing the material to be tested via a hopper onto a rotating dividing cone.
“The sample material then passes over the surface to the rotating cone and is accelerated outwards by centrifugal force of the entire system. From there it is fed into channels and the individual samples are collected in glass sample bottles, ready for analysis or testing,” Mr Downing explains.
A 200 tonne hydraulic press at TiDA pushes titanium powder firmly into both green (cold) and brown (warm) compacts to produce a rough shape which can then be processed further.
“Exerting extra pressure onto the powder while in these moulds will help the particles bond together more tightly,” says Mr Downing.
An automatic grinder and polisher help create a perfectly smooth surface on any sample product to allow TiDA’s high-spec optical and scanning electron microscopes to be used more accurately to view grain boundaries and crystal structure.
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