Hydro
gains
Automakers
around the world are opening their eyes to the advantages of hydroforming
as a preferred method for manufacturing automobiles, finds Kaushik Karforma
Automobiles
these days are technological marvels. They are computing powerhouses
capable of working wonders in varying climates and terrains; their roles
in people’s lives have undergone a sea change – from a luxury to a necessity.
But while the technology that goes into making the automobiles work
has progresses by leaps and bounds, such is not the case with automobile
manufacturing itself. Rooted to the Fordian assembly-line tradition,
automakers still resort to stamp-and-weld processes in manufacturing
steel frames and body parts for cars and light trucks.
However,
things seem to be changing. If a new technology that is doing the rounds
of automakers round the world is any indication, manufacturing automobiles
will soon enter the Space Age… straight from the Jurassic!
The
new technology is called hydroforming – because it moulds parts by means
of water spurting under high pressure. It involves cold expansion of
a tubular blank in a closed die by the application of high-pressure
fluid inside the tube. During expansion, the tube is axially compressed
so that material flows from the tube thickness and length to form complex
shapes, often with multiple cross-sections.
In
the hydroforming process, operators feed precut hollow, round steel
tubes, called blanks, into a bender, where they are shaped into the
general form of the final part. Robots place the bent tube into the
lower half of a hydroforming die where the ends are sealed. A combination
of water, mixed with a touch of oil and corrosion inhibitor, is fed
through the seals into the blank and then highly pressurised to shape
the steel into the desired configuration. Often, any required holes
or slots can be pierced into the part while it is in the hydroforming
die. The result is a finished part that may require only trimming before
heading off to the assembly line. Depending on the part, the water pressure
may range anywhere from 5,000 per square inch (psi) to 30,000 psi –
and in special cases, may even near 100,000 psi.
There
are several benefits to hydroforming. The first is improvements in quality.
The traditional stamp-and-weld methods are relatively inaccurate; metal
springs back slightly after stamping, and the heat of welding causes
further distortion. As a result, there is average dimensional variation
of 3 mm from one part to another. With hydroforming, dimensions are
accurate to within one-half of a millimetre, permitting very precise
wheel alignment. Body panels, which bolt to mounts on the frame, line
up better as well.
Hydroforming
also reduces waste. When sheets of steel are run through stamping presses,
a lot of metal at the border of each piece ends up as leftovers. Hydroforming
helps reduce the scrap metal.
Significant
cost advantages also accrue through Hydroforming. Direct saving in per-piece
cost through reduction in tooling, manufacturing operations, material
savings and indirect cost savings through value-added process properties
are easily achievable.
Now
that automakers and their suppliers have some experience with hydroforming,
engineers are figuring out new ways to exploit the method’s advantages.
For instance, by making parts in a single unit instead of welding two
or three together, engineers can dispense with flanges – the flat rims
protruding from the edge of a piece for use as points of attachment
– which, in turn, makes the finished part more compact. This helps designers
.....
....CONTD
