grinding
With its sticky, ductile properties, grinding
titanium can be problematic. Unless, that is,
you have the right technology.
By Steed Webzell
Avoiding a sticky end
read more about
grinding at
www.mwponline.com
Features
■ Schutte - strong at
the knees
A Schutte medical
component production
machine has been
delivered to a leading UK
medical component
manufacturer to improve
the manufacturing
process for the
customer’s range of
artificial orthopaedic knee
components
Dorman Machinery
http://tinyurl.com/2kdp3a
THE exceptional strength-to-weight properties of
titanium in combination with its high corrosion
resistance mean this important engineering material is
growing in popularity among design engineers.
Conjoining with other elements such as iron,
aluminium, vanadium and molybdenum, it produces
alloys that are lighter than aluminum and stronger
than steel. Today titanium is used widely for aero
engine and missile parts, as well as medical components
such as prostheses and orthopaedic and dental
implants.The auto industry is also increasing its
consumption of titanium although the price, while
falling in real terms, is perhaps slightly prohibitive for
widespread general adoption in this significant sector.
With so much growing interest in the adoption of
titanium for engineering components, it comes as little
surprise that machine tool, cutting tool and coolant
suppliers are working hard to optimise the necessary
machining processes. However, while the solutions for
milling and turning this material are increasingly well
documented, less is known about the optimum
parameters that govern the successful grinding of
titanium. According to Titanium Industries Inc, a
provider of titanium-related services to manufacturers
around the world, the difference between grinding
titanium and other metals is the activity of titanium at
high temperatures. At localised points of wheel contact,
titanium can react chemically with the wheel material
resulting in grinding wheels clogged with built-up
edge and subsequent thermal damage to the
component. TII states that the most important facts to
consider for successful titanium grinding are:
■ Effective use of coolants. Water-based soluble oils
can be used but, in general, result in poor wheel life.
Solutions of vapor-phase rust inhibitors of the nitrite
amine type give good results with aluminum oxide
wheels.
■ Correct wheel speeds. A good guide is to use one half
to one-third of conventional operating wheel speeds.
■ Selection of proper wheels. Silicon carbide wheels
can be used at 1200 to 1800 surface m/min to give
optimum surface finish at minimum wheel wear but
the high speeds essential with these wheels produces
intense sparking that can cause a fire hazard unless the
work is flooded with coolant. However, vitrified bond
54 MWP november 2007
A60 wheels, hardness J-M have been successfully used
at speeds of 450 to 600 surface m/min while removing
as much as 1300mm 3 of metal per minute.
Remaining in the US, another development to be
announced in the past few weeks is that three retired
Ingersoll International engineers have been awarded a
$2 million grant to develop a way to help cut the
machining cost of titanium. John Osborn, John Hurd
and Kanwar Singh started a company, Rockford
Engineering Associates LLC, last March to research and
develop ways to overcome problems they encountered
in their careers at the now defunct Ingersoll. ‘We
worked a lot on titanium, and Ingersoll was responsible
for some of the better advancements,’ says Osborn, ‘but
we never could make that big breakthrough.’
The implications are major for the manufacturing
technology industry if the three are successful. Osborn
says their idea is to develop machines that can
manufacture titanium parts at super high speeds with
limited or no vibration. Titanium is hard to process
because when machining at high speeds, the alloys tend
to weld themselves to the cutting carbide or grinding
wheels. To combat this, the machines in use now cut at
slower speeds, which lead to greater vibration and more
tooling breakdowns. The company intends to develop
the technology and then license it to other machining
companies.
The announcement of the grant comes at a time
when titanium uptake is increasing across all industry
sectors. ‘Titanium is going to be huge,’ says Osborn. ‘Its
expected use is set to triple or even quadruple in coming
years. Look at cars. If the automotive industry could
afford to use titanium it would, but it’s too expensive
right now. We’re hoping this project can bring the cost
down at least on larger components. If you use titanium
in cars you are saving about 50% of the weight.’
It’s fair to say that in generic terms titanium doesn’t
lend itself to grinding. It’s a sticky, gummy and ductile
material that is better machined by milling or
broaching techniques where possible. But the grinding
processes are coming. In the past two years Raysun
Innovative Design has been a granted a UK patent for
its DIATI 50 grinding process to grind parts such as
titanium turbine/compressor blades. The company
claims that DIATI 50 can grind these features in
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