Introduction to Basic Manufacturing Processes and ... - always yours

Sheet Metal Work 361
moveable. When the lever is pulled by the operator the lower blade rises and thus the metal
sheet is cut. This particular provision enables the metal sheet to be locked against the upper
blade during the operation on account of the circular motion of the hand lever. With the
result, the metal sheet is prevented from being distorted.
Folding machines are used for bending and folding the edges of metal plates to form
the joint at the seam. Bending machines or bending rollers, as they are better known, are
used for shaping metal sheets into cylindrical objects. The machine consists of three rollers.
These rollers have different adjustments indifferent types of machines. In some-machines
two rollers at the bottom have fixed position and the third one (top roller) can be adjusted
in vertical direction to adjust the pressure and give the required curvature to the sheet.
A still better control is obtained by having two rollers exactly one over the other, out of
which the bottom roller is fixed and the top roller can be adjusted vertically to suit the
thickness of the sheet and the pressure required for rolling. The third roller, called radius
roller can be moved up and down to provide the desired curvature. Improved designs of
these machines are available which contain the rollers, which have grooves of various
shapes and sizes to form corresponding shapes in metal sheets. Conical shaped rollers are
used for tapered cylindrical articles. Similarly other machines named above are used to
perform different operations after which they are named.
Burring machine is used to make a burr on the edges of the bottom and covers. Burr
is the starting of the seam. Double seaming machine is used for double seaming flat bottoms
on straight or flared cylindrical pieces.
Various types of press machines with different capacities are used for mass production
of sheet metal components. These are equipped with different kind of press tools or dies.
These are commonly employed for fast and accurate processing of sheet metal work.
18.8 TYPE OF PRESSES
Presses are classified based upon the method of operation method of power source
method of activation of slide and number of slides in action. The sub-classification of each is
also gien as under.
1. Method of Operation
(i) Arbor Press. It is a hand operated press. It combines the principle of lever with
pinions to a related rack build into the ram. They are used where a very limited
no. of production of parts is required.
(ii) Foot Press. It is also manual operated press. Most of the presses have foot action
in their operating mechanism.
(iii) Open back inclinable press. It is a power operated press. They are having bench
or floor models.
Presses are classified according to
2. Method of Power Sources
(i) Manual presses
(ii) Mechanical power presses
(iii) Hydraulic presses.