Presses for sheet metal working

PRESSES FOR SHEET METAL WORKING

Press is a metal forming machine tool used to shape or cut metal by applying force. Press working may be defined as a chipless manufacturing process by which various components are made from sheet metal. Many components in our day-to-day life are made by press working operations. Press working is mainly useful for mass production work. They are the fastest and most efficient method to form a sheet metal to the desired shape.

1. Types of Press Working

There are three different ways of working sheet metal in the press.

(i) Shearing

(ii) Bending

(iii) Drawing

(iv) Punching

(v) Piercing

(vi) Blanking etc.

2. Types of Presses

1. According to the source of power

(a) Manually operated – Hand, ball or fly presses

(b) Power presses - mechanical, hydraulic etc.

2. According to the type and design of frame

(a) Inclinable

(b) Straight side

(c) Gap frame

(d) Horning

(e) Adjustable bed

(f) Open end.

3. According to the position of frame

(a) Inclinable

(b) Vertical

(c) Horizontal

(d) Inclined.

4. According to the actions

(a) Single action 

(b) Double action 

(c) Triple action.

5. According to the mechanism used for applying power to ram

(a) Crank

(b) Toggle

(c) Eccentric

(d) Cam

(e) Screw

(f) Rack and pinion.

7. According to the number of crankshafts used

(b) Single crank

(c) Double crank.

8. Method of transmission of power from motor to crankshaft

(a) Direct

(b) Single geared

(d) Double geared

(e) Multiple geared

(f) Non-geared or flywheel.

3. Fly Press

Fly press is manually operated and has a cast iron frame. The screw provided at the top of the frame moves in a nut when it is operated. The arm and screw are rotated by a handle. The arm supports two cast iron weights which act as an energy storage device.

The punch is connected at the bottom of the ram and die is tightly fixed at the press plates called bolster. An improved and heavier form of fly press is called double side press. The main difference in this type is that the arm and weights are replaced by a heavy flywheel.

4. Power Presses

Various power presses have already been discussed in Chapter 3.5 in Page 3.25.

5. Single, Double and Triple-Action Presses

Single-action presses have only one slide. Therefore, only one operation can be performed during one pass of the ram or slide (up + down stroke).

Double-action presses have two slides with two motions properly synchronized for double action. e.g., the outer slide carries the blank and inner slide continues to descend for carrying the draw punch to perform the drawing operation.

In a triple-action press, three slides are properly mounted to ensure three motions for triple action. e.g., drawing, redrawing and forming operations. So, the triple action presses are used for large works such as motorcar body panels.

6. Selection of Presses for Sheet Metal

The following factors should be considered while selecting a press for a given sheet metal workpiece.

● Type of forming operation, dies and tooling required

● Force required to cut the metal

● Size and shape of workpieces

● Size and type of die

● Length of stroke of the slide, stroke per minute, speed and shut height

● Number of slides (single action, double action and triple action)

● Maximum force required (press capacity, tonnage rating)

● Method of feeding and size of sheet blank

● Type of controls

● Die changing features

● Safety features.