Metal Forming Processes PDF

ROLLING BULK FORGING DEFORMATION METAL FORMING EXTRUSION WIRE & BAR DRAWING BENDING DEEP OR C...

ROLLING BULK FORGING DEFORMATION METAL FORMING EXTRUSION WIRE & BAR DRAWING BENDING DEEP OR CUP DRAWING SHEET METAL WORKING SHEARING MISCELLANEOUS 1  BULK DEFORMATION PROCESSES Bulk deformation processes are those where the thicknesses or cross sections are reduced or shapes are significantly changed. Since the volume of the material remains constant, changes in one dimension require proportionate changes in others. Thus the enveloping surface area changes significantly, usually increasing as the product lengthens or the shape becomes more complex. 2  BULK DEFORMATION PROCESSES Starting geometry of the raw material may be: – cylindrical bars and billets – rectangular billets and slabs – or any of the above similar shapes 3 4 5  (1) ROLLING Rolling is a deformation process in which the thickness of the work is reduced by compressive forces exerted by two opposing rolls. Rolling operations reduce the thickness or change the cross section of a material through compressive forces exerted by rolls. 6 (1) ROLLING 7 (1) ROLLING 8  (1) ROLLING Rotating rolls perform two main functions: – Pull the work into the gap between them by friction between workpart and rolls – Simultaneously squeeze the work to reduce its cross section 9  (1) ROLLING Most rolling processes are very capital intensive, requiring massive pieces of equipment, called rolling mills, to perform them. Most rolling is carried out by hot working, called hot rolling, owing to the large amount of deformation required. Hot-rolled metal is generally free of residual stresses, and its properties are isotropic. Disadvantages of hot rolling are that the product cannot be held to close tolerances, and the surface has a characteristic oxide scale. 10  (1) ROLLING Rolling is often the first process that is used to convert material into a finished wrought product (Products such as; sheet, rod, bar, tube, plate and wire that are produced by rolling and extrusion mills as well as forging). Thick starting stock can be rolled into blooms, billets, or slabs, or these shapes can be obtained directly from continuous casting. 11  (1) ROLLING A slab is a rectangular solid where the width is greater than twice the thickness (25cm x 4 cm or more). Or 50 – 150mm thick and width ½ to 1.5 meters Slabs can be further rolled to produce plate, sheet, and strip. A bloom has a square or rectangular cross section, with a thickness greater than 15 cm and a width no greater than twice the thickness. (150 –300mm.) 12  (1) ROLLING A billet is usually smaller than a bloom and has a square or circular cross section (4cm x 4 cm or more). Billets are usually produced by some form of deformation process, such as rolling or extrusion. Plates have thickness greater than 6 mm while sheet and strip range from 6 mm to 0.1 mm. 13  (1) ROLLING SLAB BLOOM BILLET 14 15  (1.1) SHAPE ROLLING In shape rolling, the work is deformed into a contoured cross section. Products made by shape rolling include construction shapes such as I-beams, L-beams, and U-channels; rails for railroad tracks; and round and square bars and rods. The process is accomplished by passing the work through rolls that have the reverse of the desired shape. 16 (1.1) SHAPE ROLLING 17 (1.1) SHAPE ROLLING 18  (1.2) Thread Rolling Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies Important commercial process for mass producing bolts and screws Performed by cold working in thread rolling machines Advantages over thread cutting (machining): – Higher production rates – Better material utilization – Stronger threads and better fatigue resistance due to work hardening 19 (1.2) Thread Rolling 20  (1.3) Ring Rolling Ring rolling is a deformation process in which a thick-walled ring of smaller diameter is rolled into a thin-walled ring of larger diameter. As the thick-walled ring is compressed, the deformed material elongates, causing the diameter of the ring to be enlarged. Ring rolling is usually performed as a hot-working process for large rings and as a cold-working process for smaller rings. 21 (1.3) Ring Rolling Reducing the ring thickness results in an increase in its diameter. 22  (1.4) Roll Piercing Roll Piercing is a specialized hot working process for making seamless thick-walled tubes. It utilizes two opposing rolls, and hence it is grouped with the rolling processes. Mandrel 23 (1) ROLLING MILLS CONFIGURATIONS Various rolling mill configurations are available to deal with the variety of applications and technical problems in the rolling process. – Two-high – two opposing rolls – Three-high – work passes through rolls in both directions – Four-high – backing rolls support smaller work rolls – Cluster mill – multiple backing rolls on smaller rolls – Tandem rolling mill – sequence of two-high mills 24 (1.a) Two-High Rolling Mill 25 (1.b) Three-High Rolling Mill 26 (1.c) Four-High Rolling Mill 27 (1.d) Cluster Mill 28 (1.e) Tandem Rolling Mill 29  FLAT ROLLING ANALYSIS In flat rolling, the work is squeezed between two rolls so that its thickness is reduced by an amount called the DRAFT: (1) 30 31  FLAT ROLLING ANALYSIS Conservation of matter is preserved, so the volume of metal exiting the rolls equals the volume entering (2) 32  FLAT ROLLING ANALYSIS Similarly, before and after volume rates of material flow must be the same, so the before and after velocities can be related (3) 33  FLAT ROLLING ANALYSIS The rolls contact the work along an arc defined by the angle Ɵ. Each roll has radius R , and its rotational speed gives it a surface velocity vr. This velocity is greater than the entering speed of the work vo and less than its exiting speed vf. Since the metal flow is continuous, there is a gradual change in velocity of the work between the rolls. 34  FLAT ROLLING ANALYSIS However, there is one point along the arc where work velocity equals roll velocity. This is called the no-slip point, also known as the neutral point. On either side of this point, slipping and friction occur between roll and work. 35  FLAT ROLLING ANALYSIS The amount of slip between the rolls and the work can be measured by means of the FORWARD SLIP, a term used in rolling that is defined as (4) 36  FLAT ROLLING ANALYSIS There is a limit to the maximum possible draft that can be accomplished in flat rolling with a given coefficient of friction, defined by: dmax = µ2 R (5) 37  FLAT ROLLING ANALYSIS The roll force F required to maintain separation between the two rolls is given by: F =σ w L (6) σ = average flow stress, N/mm2 w L = roll-work contact area, mm2 38  FLAT ROLLING ANALYSIS Contact length can be approximated by (7) 39  FLAT ROLLING ANALYSIS Torque for each roll is (8) 40  FLAT ROLLING ANALYSIS The power required to drive each roll is P = 2πNT (9) 41  FLAT ROLLING NUMERICAL 1 A 40 mm thick plate is to be reduced to 30 mm in one pass in a rolling operation. Entrance speed = 16 m/min. Roll radius = 300 mm, and rotational speed = 18.5 m/min. Determine: (a) the minimum required coefficient of friction that would make this rolling operation possible, (b) exit velocity under the assumption that the plate widens by 2% during the operation, and (c) forward slip. 42  FLAT ROLLING NUMERICAL 1 to = 40 mm tf = 30 mm. vo = 16 m/min. R = 300 mm rotational speed = 18.5 m/min. plate widens by 2% during the operation 43 FLAT ROLLING NUMERICAL 1 (5) 44 FLAT ROLLING NUMERICAL 1 (3) 45 FLAT ROLLING NUMERICAL 1 (4) 46  FLAT ROLLING NUMERICAL 2 A 2.0 in thick slab is 10.0 in wide and 12.0 ft long. Thickness is to be reduced in three steps in a hot rolling operation. Each step will reduce the slab to 25% of its previous thickness. It is expected that for this metal and reduction, the slab will widen by 3% in each step. If the entry speed of the slab in the first step is 40 ft/min, and roll speed is the same for the three steps, determine: (a) length and (b) exit velocity of the slab after the final reduction. 47  FLAT ROLLING NUMERICAL 2 to = 2 in wo = 10 in. Lo = 12 ft. Each step will reduce the slab to 25% of its previous thickness widen by 3% in each step vo = 40 ft/min (same for the three steps) 48 FLAT ROLLING NUMERICAL 2 49 FLAT ROLLING NUMERICAL 2 (2) 50  FLAT ROLLING NUMERICAL 2 (b) Given that entry speed is the same at all three steps (3) 51 FLAT ROLLING NUMERICAL 2 52 FLAT ROLLING NUMERICAL 2 53  FLAT ROLLING NUMERICAL 3 A series of cold rolling operations are to be used to reduce the thickness of a plate from 50 mm down to 25 mm in a reversing two-high mill. Roll diameter = 700 mm and coefficient of friction between rolls and work = 0.15. The specification is that the draft is to be equal on each pass. Determine: (a) minimum number of passes required, and (b) draft for each pass? 54  FLAT ROLLING NUMERICAL 3 to = 50 mm tf = 25 mm. R = 700/2 mm = 350 mm µ = 0.15 draft is to be equal on each pass. 55 FLAT ROLLING NUMERICAL 3 56