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Sheet metal basics- stretch forming- explosive forming
- 1. YoucaN Sheet metal basics-Stretch forming- Explosive forming
- 2. • UNIT IVSHEET METAL PROCESSES Sheet metal characteristics – shearing, bending and drawing operations – Stretch forming operations– Formability of sheet metal – Test methods –special forming processes-Working principle and applications – Hydro forming – Rubber pad forming – Metal spinning– Introduction of Explosive forming, magnetic pulse forming,YoucaN
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- 6. • Sheet metalparts offers the advantages of light weight and versatile shape as compared to those made by casting/ forging. • Low carbon steel is the most commonly used sheet metal. • Aluminum and titanium are most common sheet materials for aircraft and aerospace applications. YoucaN
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- 8. • The processof cutting a straight line across a strip, sheet or bar is known a shearing process. • Stage 1- plastic deformation • Stage 2- shear • Stage 3- fracture YoucaN
- 9. • Cutting operations •Blanking(punched out piece is workpiece) • Punching(used to produce a hole in workpiece) • Shearing(cuts along a single line) • Parting(shearing the sheet into two or more pieces) • Notching (metal pieces are cut from the edge of a sheet) • Lancing- cutting the sheet metal through a small length and bending this small cut portion downwards. YoucaN
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- 11. • Bending (Formingthe metal between a suitably shaped punch and forming block. ) • Drawing (consist 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 ) • Sequeezing (metal is caused to flow to all portions of a die cavity under the action of compressive force). • Embossing (producing required shapes on sheet metal blanks means of punches and dies- name plate details) YoucaN
- 12. • For shearingthe blank holder pressure is important. • If the blank holder pressure(depends upon part it vary) is low in drawing operation. YoucaN
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- 22. It denotes theproperty of sheet metal to partially fall back from its bent position when the punch retards after completing the operation YoucaN
- 23. • Angle bending(sheet is bent at an angle to each edge.) • Roll bending (sheet is bent in the form of rolled edges) • Roll forming (desired shapes or any impression in the form of bend is made on the sheet metal) • Seaming (process of providing lock between two edges of different work sheet) YoucaN
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- 26. • Used toproduce large accurate contoured sheets. • Stretching the work beyond its elastic limit by moving a form block towards the blank or sheet metal. • In stretch forming, the sheet metal is clamped along its edges and then stretched over a male die (form block or form punch). • The die moves upward, downward, or sideways, depending on the particular design of the machine • Stretch forming is used primarily to make aircraft wing- skin panels, fuselages, and boat hulls. • Aluminum skins for the Boeing 767 and 757 aircraft, for example, are made by stretch forming-with a tensile force of 9 MN. YoucaN
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- 28. • The rectangularsheets are 12 m >< 2.5 m >< 6.4 mm. Although this process generally is used for low volume production, it is versatile and economical, particularly for the aerospace industry. • In most operations, the blank is a rectangular sheet clamped along its narrower edges and stretched lengthwise, thus allowing the material to shrink in width. • Controlling the amount of stretching is important in order to prevent tearing. • Stretch forming cannot produce parts with sharp contours or with reentrant corners (depressions on the surface of the die). • Various accessory equipment can be used in conjunction with stretch forming, including further forming with both male and female dies while the part is under tension. • Dies for stretch forming generally are made of zinc alloys, steel, plastics, or wood. Most applications require little or no lubrication.YoucaN
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- 33. • Mating diemethod YoucaN
- 34. • Blank canbe stretched in a single operation • Spring back is reduced or eliminated when compared to other forming methods • Plastic deformation is due to pure tension only • Larger parts can be formed YoucaN Materials used Aluminium Alloy Nickel and Cobalt base alloys – Stainless Steel
- 35. • Blank thicknessshould be uniform throughout the length. • Sudden changes in contour surfaces cannot be stretched. • Maintenance cost of hydraulic cylinders is high • The process requires high quality form blocks YoucaN
- 36. •limitations • Uneven thicknessof blank cannot be stretched • Stretching of blank to the required shape of contour is limited • Applications • Production of aircraft wing parts • Production of contoured panels for truck trailer and bus bodies in automobile industry. YoucaN
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- 38. YoucaN Some of theapplications of sheet meta
- 39. YoucaN Some of theapplications of sheet me
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- 41. YoucaN Chemical energy inexplosives- shock waves- Energy transmitting medium(air or water) - work holding die – vaccum – plastic work-milli seconds Explosives: Trinitrotoluene (TNT) Research and development explosives (RDX) Dynamite
- 42. • In explosiveforming the chemical energy stored in explosives is used to process the materials. • The shock waves developed depends on the compressibility of the energy transmitting medium.(water or air) • Water is being less compressible than air is a better medium. • Terms: distance between workpiece and explosive, amount of explosive, energy transmitting medium • Two systems • 1- confined system OR Contact system • 2- unconfined system OR stand off distance methodYoucaN
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- 44. • Two ormore die piece, completely encloses the workpiece. • Between the die and the workpiece vacuum should be produced. • When the explosive is denonated a shock wave is produced in the energy transmitting medium. • This forces the workpiece into the die. • The already created vacuum between the die and workpiece helps to transfer the energy completely. • That vacuum helps to form completely. • Used to small and tubular parts for flaring and bulging operations. • Being a closed system there is a greater hazard of die failure due to high pressure generated.YoucaN
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- 46. • Used toform very thin sheet to large ship plates about 25mm thick. • Workpiece is clamped In die assembly. And the entire die assembly is lowered in to a swimming pool. Vacuum should be created between the plate and die. • An explosive is denoted above or with in the water. • The produced shock waves in the water body forces the workpiece into the die. YoucaN
- 47. • Low pressureexplosives • Black powder and smokeless powder • Pressure is only 700MPa • High pressure explosives • Trinitrotoluene (TNT) • Research and development explosives (RDX) • Dynamite • Pressure is 14000MPa. • Deformation velocity is 9 • 230m/s YoucaN
- 48. • Applications • Radardishes • Rocket motor cases • Parts which are not manufactured in conventional methods can be prepared. YoucaN
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