Applications
Numerous applications of hydroforming can
be seen in exhaust manifolds (Fig. 3) made of steel tubes.
The process is being used or is being
considered for use to make a wide range of components for both automotive and
non-automotive applications. Pressure levels over 350 MPa are sometimes used to produce
industrial size parts; however, most parts are typically produced at pressure levels under
350 MPa. Automotive parts currently under development or in production include seat
frames, engine cradles and rails, exhaust manifolds, and space frame components.
Typical pre-forming dimensions for tubing used in these automotive applications range from
about 50 mm to 150 mm in diameter and from 1.4 mm to 2.5 mm in thickness. Note that this
would place typical diameter-to-thickness ratios below the 65. Materials used for these
automotive hydroformed tube applications include 1008/1010 mild steel up to 300 MPa HSLA
steels. Most tend to be uncoated, but there are also some galvanealed steels in use.
Conclusion
Interest in the tube hydroforming process
by the automotive industry is due to the possibility of replacing many multi-piece stamped
and welded assemblies in body, frame, or chassis components with one-piece hydroformed
components. Thus, there is a great potential for not only weight-saving, but also for
tooling and labour cost saving that may occur due to the elimination of multi-stage
stamping and assembly processes through part consolidation. A draw-back of the process is
the need for expensive tooling (dies and presses) that can provide and sustain the
required forming pressures. Thus, numerical simulation is needed in order to reduce the
production cost. Tube hydroforming allows engineers to optimize their designs through
cross sectional reshaping and perimeter expansion. Combined with the ability to
inexpensively create the holes that are required for vehicle subsystem interfaces,
hydroforming has become a critical technology for structural components in mass-produced
vehicles.
Several factors play an important role in selecting material for tube hydroforming,
including final properties of the part, forming process and deformation capabilities,
availability, and cost. In many cases, material selection may entail a trade-off between
cost and structural performance. The quality of the incoming tube is critical for the
success of the hydroforming process. Material properties -- such as material composition,
yield strength, ultimate tensile strength, percent elongation, flow characteristics and
dimensions of the tube must be determined based on the final part requirements. These
properties also must be monitored closely during the manufacturing process.
The number of tube hydroforming
applications will increase by better understanding of materials and the process. In many
cases, reliable computer simulations will help in developing more robust hydroforming
techniques.
Dinesh Kumar Rout did his M. Tech in
Mechanical Engineering from IIT, Kharagpur. He has been working as a Researcher in the
Product Research Group, R&D Division of Tata Steel since February 2001.
His major projects include process
simulation of cold rolling for prediction of mill load and major power requirements in
rolling high strength grade steel at Tata Steel and mathematical modelling of cold rolling
profile and furnace system for prediction of shape deviation of cold rolled sheets.
Mr. Rout is currently stationed at Pune
as a Resident Engineer in customer’s premises for Early Vendor Involvement activities
with Tata Motors for X2 platform vehicles. His area of expertise is simulation of sheet
metal forming, Finite Element method based modelling and simulation and automotive
technology and materials.
He is also associated with Bajaj Autofor
manufacturability assessment of new designs for the future models using the recently
developed steel grades from Tata Steel.
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