Metal Forming Rolling Processes PDF

Metal Forming Rolling Process  Rolling Processes 1- Rolling operation. 2- Classification of Rolling. 3- Materials in Rolling. 4- Friction in Rolling. 5- Ring Rolling. 6- Thread Rolling. 7- Tube Rolling. Rolling of Metals  1-ROLLING PROCESS Def...

Metal Forming Rolling Process  Rolling Processes 1- Rolling operation. 2- Classification of Rolling. 3- Materials in Rolling. 4- Friction in Rolling. 5- Ring Rolling. 6- Thread Rolling. 7- Tube Rolling. Rolling of Metals  1-ROLLING PROCESS Deformation process in which work thickness is reduced by compressive forces exerted by two opposing rolls with the same speed and diameter The rolling process (specifically, flat rolling). Hot Rolling for I-beam Product  2-CLASSIFICATION OF ROLLING Based on workpiece geometry : – Flat rolling - used to reduce thickness of a rectangular cross section  Types of Rolling Based on workpiece geometry : – Shape rolling - square cross section is formed into a shape such as an I-beam , v shape  Types of Rolling Based on Rolling Mills: – Two-high non-reversing mill - simplest design from which material can only pass in one direction.  Types of Rolling Based on Rolling Mills: – Two-high reversing mill -permits back-and-forth rolling, rolls may stop, reversed, and brought back to rolling speed between each pass  Types of Rolling Based on Rolling Mills: – The three-high mill -eliminates need for roll reversal but requires some form of elevator on each side of mill to raise or lower material and mechanical manipulators to turn or shift product between passes.  Four-high mills- use backup rolls to support the smaller work rolls. cluster arrangements- use many backup rolls to support the smaller work rolls. – used in hot rolling of wide plate and sheets, and in cold rolling, where small negligence would result in an unacceptable variation in product thickness – Foil is rolled on cluster mills since small thickness requires small-diameter rolls – In a cluster mill, the roll in contact with the work can be as small as 1/4 in. in diameter  Planetary rolling mills- one main roll is surrounded with many small rolls. Tandem Rolling Mill- A series of rolling stands in sequence.  Planetary Tandem 3-ROLLING TEMPERATURE – Hot Rolling – most common due to the large amount of deformation required – Cold rolling – produces finished sheet and plate stock HOT AND COLD WORKING  Comparison Cold Working Hot Working Carried below recrystallization temp. Carried above recrystallization temp. Elongation, area reduction, ductility Ductility, elongation, area reduction and impact strength are reduced and impact strength are increased Crystallization does not occur Crystallization occurs again Uniformity of material is lost and Grain refinement occurs properties are greatly affected Increases ultimate tensile strength, Does not affect ultimate tensile yield point, hardness, fatigue strength, yield point, hardness, strength fatigue strength 17 Internal and residual stresses are Internal and residual stresses are not produced produced Load and energy requirements are Load and energy requirements are high low Less tool wear High tool wear Less costly High cost operation No oxidation of metal occurs High scaling and oxidation occurs No metal loss High metal loss Surface decarbonization of steel Surface decarbonization of steel does not occur occurs Good surface finish Surface finish is not good High dimensional accurcy low dimensional accurcy Easy to control dimensions within Difficult to control dimensions within tolerance limits tolerance limits Material handling is easy Material handling is difficult 18 Cold Rolling Hot Rolling  3-MATERIALS IN ROLLING OPERATION 1- Plain carbon steel 2- Alloy steel 3- Aluminum 4- copper Material Behavior in Metal Forming Tensile Testing Machine  Mechanical properties of materials In order to understand the mechanical behavior of materials we need to perform experimental testing in the lab A tensile test machine is a typical equipment of a mechanical testing lab ASTM (American Society for Testing and Materials)  Stress (σ) – strain (ε) diagrams The strains from zero to point A are so small as compared to the strains from point A to E and can not be seen (it is a vertical line…) Metals, such as structural steel, that undergo permanent large strains before failure are ductile Ductile materials absorb large amounts of strain energy Stress-strain diagram for a typical Ductile materials: aluminium, structural steel in tension (drawn to scale) copper, magnesium, lead, molybdenum, nickel, brass, nylon, teflon  Aluminium alloys Although ductile…aluminium alloys typically do not have a clearly definable yield point… However, they have an initial linear region with a recognizable proportional limit Structural alloys have proportional limits in the range of 70-410 MPa and ultimate stresses in the range of 140-550 MPa Typical stress-strain diagram for an aluminum alloy.  Offset method When the yield point is not obvious, like in the previous case, and undergoes large strains, an arbitrary yield stress can be determined by the offset method The intersection of the offset line and the stress-strain curve FIG 1-14Arbitrary yield stress determined by the offset method (point A) defines the yield Copyright 2005 by Nelson, a division of Thomson Canada Limited stress  Brittle materials Brittle materials fail at relatively low strains and little elongation after the proportional limit Brittle materials: concrete, marble, glass, ceramics and metallic alloys The reduction in the cross- sectional area until fracture (point B) is insignificant and the fracture Typical stress-strain diagram for stress (point B) is the same as the a brittle material showing the ultimate stress proportional limit (point A) and fracture stress (point B) Stress Strain diagram – materials  Plastic region of stress-strain curve is primary interest because material is plastically deformed In plastic region, metal's behavior is expressed by the flow curve: where Yf = flow stress, K = strength coefficient; and Yf = K  n = strain hardening exponent n strain l dl l t =  = ln = ln(1 + e ) l0 l l0  Flow Stress For most metals at room temperature, strength increases when deformed due to strain hardening Flow stress = instantaneous value of stress required to continue deforming the material Yf = K n where Yf = flow stress, K = strength coefficient; and n = strain hardening exponent  Average Flow Stress Determined by integrating the flow curve equation between zero and the final strain  value defining the range of interest  Y d  K  d n 0 f Y = = 0   f K  n +1 K  n +1−1 Yf = =  ( n + 1) n +1 K n Yf = 1+ n Yf  Rolled Products Made of Steel Some of the steel products made in a rolling mill. Blooms, Billets, Slaps After casting, ingots are rolled into one of three intermediate shapes called blooms, billets, and slaps: 1. Blooms have square cross section 6” x 6” or larger. They are rolled into structural shapes. 2. Billets have square cross section 1.5” x 1.5” or larger. they are rolled into bars and rods. 3. Slabs have rectangular cross section 10” x 1.5” or larger. They are rolled into plates, sheets and strips. 33 Steps in the shape rolling of an I–section part. Production Line 5-RING ROLLING  6-THREAD ROLLING (1) start of cycle (2) end of cycle Thread rolling with flat dies: Thread rolling. Rolled and machined threads Rolled and machined threads 8-TUBE ROLLING Tube rolling Tube rolling Tube rolling