Press work

Press terminology, press operations, types of presses, basic press cutting action

1. Chapter 5 Press Working 10/27/2017 3:22 PM RAP

2. Press working may be defined as, a manufacturing process by which various components are made from sheet metal. This process is also termed as cold stamping. The machine used for press working is called a press. 10/27/2017 3:22 PM RAP

3. Press Operations Press operations are broadly classified in to two groups:- Cutting operations, Non cutting operations (Forming operations) 10/27/2017 3:22 PM RAP

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5. Cutting Operations 1 : Blanking: Blanking is the operation of cutting a flat shape from sheet metal. The product punched out is called the “blank” and the required product of the operation the hole and the metal left behind is discarded as waste. 2: Punching or Piercing: It is a cutting operation by which various shaped holes are made in sheet metal. Punching is similar to blanking except that in punching, the hole is the desired product. The material punched out from the hole being waste. 10/27/2017 3:22 PM RAP

6. 3: Trimming: This operation consists of cutting unwanted excess of material from the periphery of a previously formed component. 4: Shaving: The edge of a blanked part are generally rough, uneven and un square. Accurate dimensions of the part are obtained by removing a thin strip of metal along the edges. 10/27/2017 3:22 PM RAP

7. 5: Notching: This is cutting operation by which metal pieces are cut from the edge of the sheet , strip or blank. 6: Perforating: This is a process by which multiple holes are very small and close together are cut in a flat sheet metal. 7: Slitting: It refers to the operation of making incomplete holes in a work piece. 8: Lancing: This is a cutting operation in which a hole is partially cut and then one side is bent down to form a sort of tab. Since no metal is actually removed and there will be no scrap. 10/27/2017 3:22 PM RAP

8. Non Cutting Operations 1: Bending: In this operation; the material in the form of flat sheet or strip is uniformly strained around a linear axis which lies in the neutral plane and perpendicular it’s the length wise direction of the sheet or metal. 2: Drawing: This is a process of forming a flat work piece into a hollow shape by means of a punch which cause the blank into a die cavity. 3: Squeezing: Under the operation, the metal is caused to flow to all portions of a die cavity under the action of compressive forces. 10/27/2017 3:22 PM RAP

9. Press Terminology 10/27/2017 3:22 PM RAP

10. 1: Bed: The bed is the lower part of the press frame that serves as a table to which a Bolster plate is mounted. 2: Bolster Plate: This is a thick plate secured to the press bed , which is used for locating and supporting the die assembly. It is usually 5 to 12.5 cm thick. 3: Die Set: It is unit assembly which incorporates a lower and upper shoe, two or more guide parts and guide part bushings. 4: Die Block: It is a block or a plate which contains a die cavity. 5: Lower Shoe: The lower shoe of the a die set is generally mounted on the bolster plate of a press. The die block is mounted on the lower shoe, also the guide post are mounted on it. 10/27/2017 3:22 PM RAP

11. 6: Punch : This is male component of  a die assembly, which is directly or indirectly moved by and fastened to the press ram or slide. 7: Upper Shoe: This is the upper part of the die set which contains guide post bushings. 8: Punch Plate : The punch plate or punch retainer fits closely over the body of the punch and holds it in proper relative position. 9: Back up Plate: Back up plate or pressure plate is placed so that intensity of pressure does not become excessive on punch holder. The plate distributes the pressure over a wide area and the intensity of pressure on the punch holder is reduced to avoid crushing. 10: Stripper: It is a plate which is used to strip the metal strip from cutting a non-cutting Punch or die. It may also guide the sheet. 10/27/2017 3:22 PM RAP

12. Types of Presses 10/27/2017 3:22 PM RAP

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17. Basic Cutting Action The travel for the penetration of the punch, progresses in three zones: Compression Shearing Breakage 10/27/2017 3:22 PM RAP

18. If ‘t’ is the total travel of the punch in the sheet thickness, then ‘t’ can be expressed as – Where, a= Punch progression responsible towards compression; around 10 – 30 % of ‘t’, b= Punch progression responsible towards true shearing; around 40 – 80 % of ‘t’, c= Punch progression responsible towards breakage; around 10 – 30 % of ‘t’, t = a+b+c 10/27/2017 3:22 PM RAP

19. The ratio b/t is known as “Percentage Penetration” and denoted by ‘k’. Then shear force requirement:- Shear Force = Failure stress X Area under cutting = Ultimate s hear stress X Peripheral length of punch X Thickness of material X % Penetration Shear Force = u.s.s . X π .d X t X k (For a circular punch) This expression can be used to calculate press capacity. The factor k depends on: Work piece material Thickness of stock Clearance between die and punch 10/27/2017 3:22 PM RAP

20. Punching Blanking The difference in dimensions between the mating members of a die set is called clearance. This clearance is applied in following manner: 1: when the hole has to be held to size i.e. the hole in the sheet metal is to be accurate (punching operation) , and slug is to be discarded. The punch is made to the size of the hole and the die opening size is obtained by adding clearance to the punch size. 2: In blanking operation , where the slug or blank is the desired part and has to be held to size, the die opening size equals the blank size and the punch size is obtained by subtract. 10/27/2017 3:22 PM RAP

21. Types of Die-Set:- 10/27/2017 3:22 PM RAP

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24. Strip Layout: Percentage utilisation of raw material = (Component area / w x p) X 100 10/27/2017 3:22 PM RAP