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

362 Introduction to Basic Manufacturing Processes and Workshop Technology
3. Method of Activation of Slide
(i)
(ii)
(iii)
Crank shaft presses
Knuckle joint presses
Toggle presses
4. Number of Slides in Action
(i) Triple action single action presses
(ii) Double action presses
18.9 GENERAL PRESS INFORMATION
It is necessary for the sheet metal planner to know certain fundamentals specification
of press machine. Some of them are press tonnages, stroke of the press, die area, shut height
etc., and are explained below.
Press tonnage
It indicates the amount of pressure in tones that a press exerts or works safely and is
used for rating a press. The press may exist in various capacities of tones varying from 5,
10, 20, 32, 50, 75, 200, 500 tons to tackle the sheet metal operation using proper die in press.
The tonnage of a hydraulic press is the area multiplied by the oil pressure in the cylinder.
The tonnage of a mechanical press is equal to the shear strength of the crankshaft metal
multiplied by the area of the crankshaft bearings.
Press stroke
It is the reciprocating motion of a press slide. It is adjustable on a hydraulic press.
Die area
It is the available surface for mounting punches and die components
Shut height
It is the distance from the top of the bed to the bottom of the slide when stroke down
and the adjustment up. The shut height of the die must be equal to or less than the shut
height of the press.
Die shut height = Punch shoe thickness + Die show thickness + Die steel height + Punch
steel Height-bypass of steels. The by-pass of steels may be taken as from 3 mm to 6 mm.
18.10 GENERAL PRESS OPERATIONS
1. Shearing. It takes place in form a cut when punch strikes and enters in the sheet
placed on die. The quality of the cut surface is greatly influenced by the clearance
between the two shearing edges of the punch and dies.
2. Cutting. It means severing a piece from a strip or sheet with a cut along a single
line using suitable punch and die of press tool in press machine.
3. Parting. It signifies that scrap is removed between the two pieces to part them
using suitable punch and die of press tool in press machine.