Press Tools.pptx

PRESS TOOL PPT FOR GTU 3361902

1. Press Tools GTU SEM-6,3361902

2. Press Working Processes- Types, Sketches and Applications Press Working Process: The press working is an economical process for mass production. It is a cold working process. This process proved beneficial in the field like automobile, refrigeration, utensils, making of cabinet and clock due to some characteristics of cold formation, strain hardening, lack of heat treatment, control over properties, energy saving, no necessity of heating source, use of material having less strength, good surface finish etc. are the characteristics of the cold formation. Mainly the processes used in press working are as under. Squeezing: In squeezing operation, the metal is caused to flow to all portions of a die cavity under the action of compressive force. Bending: Bending is the operation of forming the metal between a suitably shaped punch and a forming block Shearing: The process of cutting a straight line across a strip, sheet or bar is known as shearing process Drawing down: Drawing operation consists of a punch forcing a sheet metal blank to flow plastically into the clearance available between the punch and die surfaces so as to acquire top shape, a cylindrical shape or a box shape.

3. The machines used for cold formation are called press and the tools used are called press tool or die. The stock used in press working is generally sheet metal and plates. The sheet metal working is carried on sheets having about 3 mm thickness. This process is carried out on press using die-sets to perform the operations like punching, blanking, bending, drawing on the sheet metal. The products like cupboards, utensils, clock etc. are produced in mass. Today almost all industries are making use of press working. In modern press machine 50 mm thick metal plate can be folded and formed into desired shapes. Today press having capacity of 45,000 Metric tonnes are employed for forging process. In automobile, aero-space, heating and ventilating industries, canning and container industries, domestic appliance manufacturing industries are using the press-working on large scale.

4. Different operations performed by press tools on press are classified as Shearing and Forming operations. Following are the shearing operations performed by press tools: Blanking Piercing Punching Perforating Notching Lancing Trimming Cutting off Parting off Slitting

5. While following are the bending drawing and squeezing press working operations. Bending Drawing Deep drawing Forming Forging Embossing Coining Stretch forming Curling Bulging Swaging

6. Press working processes, sketches and applications: The cutting as well as non-cutting operations can be performed on press. The cutting operations done in press are known as shearing operations. In this operation the cutting is generally done by keeping proper clearance between the edges of punch and die. This operation of cutting can be done in three stages. Plastic deformation Reduction of thickness Fracture If the clearance between punch and die is improper, then cut edge obtained will be defective. It also requires more force. As a result of that life of die reduces and production become costly. Different press working operations are shown in figure 5.1.

7. Blanking: It is a cutting operation by which various shaped blanks are made from sheet metal. The punching is similar to blanking but the hole punched is the desired product while the material punched out for producing hole goes to waste. In blanking the material punched out is the blank which can be used for producing the desired product and the sheet remaining after cutting the blanks goes to waste. Punching or piercing: It is a cutting operation for producing desired shape and size hole in the product. The hole produced is the desired product while the material punched out from the hole goes to waste. Perforating: This is the operation by which multiple holes which are very small and close to one-another are cut in flat sheet metal or plate. Notching: Notching is a cutting operation by which metal pieces are cut from the edge of sheet, strip or a blank.

8. Lancing: The lancing is cutting operation in which a hole is partially cut and then one side is bent down to form a short of tab. This operation does not remove material hence there will be no scrap. Cutting Off: This is an operation in which the material is cut straight or in the shape of the product into two different pieces. Parting Off: This is an operation to cut the work material in such a way that after cutting workpiece gets divided into its different parts. Slitting: Slitting is the operation of making incomplete holes in a workpiece. The cutting of strips from the sheet metal and straight line cut taken in certain length is also called slitting.

9. Trimming: This is a finishing operation in which flash or additional metal from the product is removed. Shaving: The edges of a blanked part are generally uneven, unsquared and rough. To obtain accurate dimension of product a thin strip of metal along the edges are removed by this shaving operation. Bending: Bending is the operation of permanently bending the flat strip of sheet by straining them uniformly around a linear axis which lies in the neutral plane and perpendicular to the lengthwise direction of the sheet or strip. Forming: Forming is the operation in which the shape of punch and die is directly obtained with some or no metal flow in punch and die.

10. Drawing: Drawing is operation in which hollow shape is formed from a flat work piece by means of punch and which causes the blank to flow into a die cavity. Nibbling: The nibbling is an operations in which small quantities of flat parts are cut from sheet metal. The parts may be cut in simple & complex shapes. This operation therefore substituted for blanking. Squeezing: Squeezing is an operation in which the metal is caused to flow to all portions of the die cavity under the action compressive force.

11. Press tools-types, working, components and their functions: The tools used on press-machine to carry out press working operation are called press tools. The press tools are of many types. Its construction is also complicated and having many parts. Working, Components and Functions of Press Tools: Press Working: When electric motor is switched on then the punch fixed on ram of the press is moving downward and enters into the stock material. A stripper provided on the die block is shown in figure 5.2 (a). Maximum compressive force act on the blanking punch is about 1/3 force used to the given thickness. The remaining force get exerted by inertia force. The cut portions is separated due to velocity. Die block is arranged in a die shoe. The shear angle is provided on punch or die as required.

12. The cut land and free land in die block is shown in figure 5.2 (b) which helps to complete remaining cutting work, minimize the effect of burr and burnishing and separates the cut portion from the material. Now the work piece is ready for further operations. This cycle continues and give desired production.

13. Press tool and its components: The punch and die used on press for press working are called press tools. The constructional features of these press tools depends upon the work to be done by them, accuracy and production rate. In simple construction punch is attached to the ram and the die is placed in a bolster plate. For more accuracy and rate of production die block is used having other components like stock stop, pilot, stripper and knock out. These components make the die work easy and simple. The assembly in this fashion is called press tools. Figure 5.6 (a) shows a simple blanking die. Generally following important elements should be included in press tool assembly. Bolster plate Blanking/piercing punch as per operation Stripper and stripper plate Stops Die block Die shoe Back gauge Die set, main body with or without pillars Pins, pilot pins, dowel pins Spring, screw Shaders Knock out mechanism etc.

14. The component from 7 to 12 are not shown in the figure. It is necessary to have components from 1 to 6 in each die. The components in press tools are increases or decreases as per the operation to be performed.

15. Classification of Press Tool: The press tool are classified on basis of Type of operation Type of construction Classification of press tools based on operation: 1. Shearing: Piercing, punching, perforating, blanking, cutting off, parting off, notching, slitting, lancing etc 2. Bending: Angle bending, V-bending and bulging. 3. Forming: Embossing, coining, curling and bulging. 4. Drawing: Cupping, deep-drawing etc. 5. Forging: Drop forging and press forging.

16. B. Classification of press tool based on construction: Single operation press tool: It includes simple types of cutting and non-cutting dies. Multi-operation press tool: One or more dies are used per cycle or stroke to perform the operation. In short simple die, compound die, progressive die and composite or combination die are all press tools based on the die-construction. The work of producing a component is easy and completed in one operation, then it is called the simple die. The name of press tool thus based on type of product, movement of press in one or more stages and the component produced from sheet metal. In compound die, more than one operation of same group are completed at one station and the component is produced. The washer, link of the chain etc. produced in compound die. In progressive die more than one operation of producing the component are completed at different work stations. The key from sheet metal is produced by using progressive die. In a press during one stroke both cutting & noncutting operations are done one after the other at one work station then the component can be produced by using combination or composite die. In lancing operation cutting and bending operations are performed in this fashion, therefore dies used in lancing are called combination die.

17. Concept meaning, definition and calculation of press tonnage and shut height of press tool: Tonnage Capacity: The force required to penetrate and shear the stock material with the punch is the cutting force or tonnage. The cutting force is calculated by the following formula. F = P x t x Fs Where F – Cutting force (N) P – Perimeter in mm t – Thickness of stock in mm Fs – Shearing strength of work material in N/ mm 2

18. Now perimeter for D mm diameter hole (or blank) =  x D Perimeter for l mm side square = 4 x l Perimeter for washer having small diameter d mm and big diameter D mm. =  ( D+d ) when both punches are operated at a time =  x D when punches are operated one after another.

19. Shut Height: Shut height is very important in press tool design and selection of the suitable press. The shut height of press and shut height of die are explained as under: Shut height of press: Shut height of press is the distance from top of the bed plate or bolster to the bottom of the slide, with its stroke down and adjustment up. At the time of measuring shut height, the press tool is not there as shown in the figure 5.5. [Shut height is the distance from the bottom of the die shoe to the top of the punch holder when die is in its closed position. In another words we can say that shut height is the distance from the top of the table or bolster to the bottom of slide with its stroke down and adjustment up. It is an important dimension of a press. The tool designer must know the shut height of the press. He can design punch and die along with punch holder and die shoe for a particular shut height of the press available. Hence shut height determines the length of the punch and thickness to be allowed to die, die shoe, punch holder etc .]

20. 2. Shut height of die: The shut height of die is the distance from the top of the punch holder to the bottom of the die-holder. In this position the die is in inactive position as shown in figure 5.6. The effect of reduction in length due to sharpening of punch is taken care off by deciding the relative length of the guide pin, so that it gets arranged in shut height of the die. [It is the distance from the top of the table or bolster to the bottom of the punch with its stroke down and adjustment up.]

21. Problem 1: Calculate the cutting force required to punch a circular hold of 15 mm diameter in 3 mm thick steel strip having shearing strength 50, 000 N/ cm 2 . (Ans: 70.65 kN Require capacity = 100 kN. )  15mm

22. Problem 2: Calculate the cutting force required to punch a rectangular hole of 30 x 20 mm in a 4 mm thick plate. The shearing strength of material is 60 kN / cm 2 . (Answer: 240 kN Select a press of capacity 250 kN for above operation.) 20 mm 30 mm