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M
and M Auto Industries Limited, Gurgaon, India have made
great strides in advancing its production capabilities both quantity
and quality wise.
COILING
This is the primary step in the manufacture of coil springs. This
consists of winding the wire around a central mandrel of a diameter
that will allow for elastic recovery of the spring to the desired
dimension on release. The machine required for mandrel coiling is
essentially simple one involves horizontal rotation on the mandrel
at controlled speeds.
For very small springs, correspondingly small machines operated
by hand are used. For mass production of large quantities of springs,
automatic machines have been developed over the last five decades.
Essentially, the method used for the production of compression springs
is the bending of the wire into the form, wire is pulled from the
coil by a series of one or more pairs of feed rollers. These rolls
can be adjusted to give different lengths of wire for different
springs. The wire is thus passed through guides to coiling fingers
to form the body diameter. The spacing tool (Pitch tool) acts at
right angles to the axis of the spring to provide correct pitch.
The manufacturing cycle is mechanically related or timed by cam
shaft which permit various adjustments to be carried out, and cutting
off occurs at the moment when the wire stops feeding.
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LOOP OR END FORMING
In the case of tension and torsion springs, the additional mechanical
forming of free ends is carried out in special looping or bending
fixtures. The spring end is required to have special shapes for
holding the spring in the mechanical assembly and these shapes from
an integral part of the springs.
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STRESS
RELIEVING
The spring material develops internal stress during the process
of cold deformation (i.e. shaping) of wire. This internal stress
formation can be harmful to the performance of springs under service
conditions. Hence, it is essential to relieve the cold working stresses
by subjecting these springs after the forming operations to the
thermal treatment called stress relieving.
The treatment of temperature generally varies with the steel wire
grade and the treatment cycle, which is dependent on the spring
wire diameter. In general stress- relieving temperature is of the
order of 280 to 450 C. The stress relieving treatment improves the
mechanical properties and enhances the life performance of the spring.
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END
GRINDING
The coil ends of the compression springs are generally required
to have a flat ground surface. This is essentially required for
correct seating of springs in the mechanical assembly. The spring's
ends are grounds to the desired shape by employing ordinary grinding
machines in the case of small production, but for large quantities,
automatic spring end grinding machines with disk feed types are
used.
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SETTING
After the springs are coiled. It is necessary to carryout setting
operation so that while in function spring do not losses its dimension.
This is done by using suitable hand operated press providing the
special tools. For heavier springs Hydraulic presses are used for
the spring free height, diameter and pitch.
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SHOT PEENING
The process of impinging the springs surface by round edged cut
wire steel shots of relatively small size at high velocities is
known as shotpeening. This process is carried out to improve the
Fatigue life of the springs when they are to operate under dynamic
stress conditions. The typical example of these springs are nozzle
holder springs, valve springs in engine assemblies.
The shots for this purpose
should be harder than the springs to be used. Round edged cut
wire shots of high carbon high tensile spring steel wires of size
0.80 mm and 0.90 mm is generally used for this purpose. It is
very important that duration of peening is sufficiently long enough
to ensure the maximum coverage unless the coverage is complete,
the full benefit cannot be achieved.
The action of peening causes the cold work on the surface and
induces the residual compressive stresses which are set in the
opposition to the shear stress created during the working of springs.
Both increased in hardness, and due to cold work and the residual
compressive stress, contribute to the improvement in fatigue life.
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TESTING
In addition to the dimensional check by measuring instruments. The
other tests generally carried out for compression and tension springs
are:
a) Load-Deflection test,
b) Fatigue test.
The mechanical load deflection spring testing machine employed.
It is a highly accurate precision beam balance of knife-edges using
flat parallel adjustable platforms to the lengths upto 300 mm. Electronic
Load testing machines of different capacities are also used for
testing of precision springs.
The mechanical fatigue test machine is equipped with an electrically
driven eccentric can connected to the loading platform (adjustable)
for placing springs under test. The stroke (representing deflecting
under service condition) the springs which are on the adjustable
platform is given. The mechanical counter registers the number of
cycles indicating the number of dynamic cycles. The speed cycle
can also be adjusted by various pulley drives.
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PROTECTIVE COATING
The spring users usually specify the type of protective finish required
on the spring surface depending on the type of environment under
which it functions. The following are the types of protective finish
generally applicable to the springs of various types.
a) ELECTROLYTIC COATING
The most common of these are cadmium, Zinc and Trinickle Plating.
They give excellent protection and attractive finish.
b) BACK DISING OR PHOSPHATING
A chemical process which produces an inexpensive black coating.
Further they are dipped in rust preventive oil to seal the surface.
c) POWDER COATING AND PAINTING
Powder coating and painting is one of the common protective coating
technique used for springs for other extreme environment conditions.
Some time painting also serves as identification.
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PLANT & MACHINERY
M and M Auto Industries Limited possess Plant and Machinery complying
with the latest technological standards. They can be grouped into
different sections as follows :
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PACKAGING & PACKING
Generally packaging & packing of springs and dispatch is made
as per the customer's specifications / requirement.
The packing of springs is quite an important step before the same
is dispatched to the customers. This is particularly true as these
springs may get entangled. Hence special Polythene Bags, Corrugated
boxes with Honey comb partition are used for this purpose to avoid
transit damage.
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