Forming and Shaping ISAT 430 Module 7

Spring 2001ISAT 430 Dr. Ken Lewis 2 Forming and Shaping Meanings blend Forming means changing the shape of an existing solid body. Shaping usually involves molding or casting The resulting product is usually near net shape.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 3 Forming and Shaping Processes Rolling -- Flat Production of flat plate, sheet and foil Long lengths, high speeds Good surface finish Requires High capital investment Incurs low to moderate labor cost.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 4 Forming and Shaping Processes 2 Rolling – Shaped Production of various structural shapes Bars I-beams High speeds Requires shaped rolls, expensive equipment Low to moderate labor costs Moderate operator skill

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 5 Forming and Shaping Processes 3 Forging Production of discrete parts with a set of dies. Some finishing operations usually necessary Usually performed at elevated temperatures Die and equipment costs are high Requires Moderate to high labor cost Moderate to high operator skill Similar parts can be made by casting and powder- metallurgy techniques

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 6 Forming and Shaping Processes 4 Extrusion Production of long lengths of solid or hollow products with constant cross section Product is cut into desired lengths Cold extrusion has similarities to forging and is used to make discrete products. Requires Moderate to high die and equipment costs Low to moderate labor costs Low to moderate labor skill

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 7 Forming and Shaping Processes 5 Drawing Production of long rod and wire with round or various cross sections. Smaller cross section than extrusion Good surface finish Requires Low to Moderate die and equipment costs Low to moderate labor costs Low to moderate labor skill

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 8 Forming and Shaping Processes 6 Sheet metal forming Production of a wide variety of shapes with thin walls Simple or complex geometries Requires Moderate to high die and equipment costs Low to moderate labor costs Low to moderate labor skill

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 9 Forming and Shaping Processes 7 Powder Metallurgy Production of simple or complex shapes by compacting and sintering metal powders Competitive with casting, forging, and machining processes Requires Moderate to high die and equipment costs Low labor costs Low labor skill

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 10 Forming and Shaping Processes 8 Processing of plastics and composite materials Production of a variety of continuous or discrete products Extrusion, spinning, molding, casting Can be competitive with metal parts Requires Moderate to high die and equipment costs High operator skill in composite fabrication

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 11 Forming and Shaping Processes 9 Forming and shaping of ceramics Production of discrete ceramic products by a variety of ways Shaping, drying, firing processes Requires Moderate to high die and equipment costs Low to moderate labor costs Moderate to high labor skill

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 12 Rolling Rolling is a process to reduce the thickness of a long workpiece by compressive forces applied through a set of rolls. First developed in the late 1500’s

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 13 Sequence of events A steel ingot is cast into a rectangular mold Placed in a furnace while just solidified and held for many hours (36) until the temperature is uniform. This process is called soaking Furnaces are called soaking pits. Implies that properties will be uniform throughout the ingot and process that way. The rolling temperature for steel is about 1200°C From here the ingot goes to the rolling mill.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 14 Rolling Starting material depends upon what you are producing. Bloom Square cross section 6 x 6 in or larger Slab Rolled from an ingot or a bloom Rectangular cross section 10 x 1.5 in or more Billet Rolled from a bloom Square cross section 1.5 x 1.5 in or larger.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 15

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 16

Metal behavior in forming An aside

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 18 Stress -- strain Elasticity below the elastic limit Strain hardening above it. In the plastic region, the metal’s behavior is expressed as: Where K = strength coefficient psi (MPa) n is the strain hardening exponent.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 19 Flow Stress As the metal deforms its strength increases (strain hardening) Thus the stress required to deform must be increased Flow stress Instantaneous value of the stress needed to keep the metal “flowing” Shear Rate True Stress Y f = flow stress MPa

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 20 Average Flow Stress The average flow stress is the average stress needed over entire strain region. Just integrate the flow stress over the strain region of interest: Shear Rate True Stress

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 21 Effect of Strain Rate In theory, a metal in hot working should be perfectly plastic with n = 0. The rate of metal deformation is directly related to the speed of deformation v. v is the velocity of the roll or ram h is the instantaneous height of the piece being deformed.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 22 Effect of Strain Rate Note that if v is constant, the strain rate will increase with decreasing h.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 23 Effect of strain rate Similar C is strength constant m is the slope, called the strain rate sensitivity exponent. The effect of temperature is pronounced.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 24 Effect of temperature on stress

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 25 Temperature Cold working (~room temperature) Advantages accuracy Surface finish Strain hardening increases strength Grain flow can provide directional properties No heating required

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 26 Temperature Cold working (~room temperature) Disadvantages Higher forces and power needed Part must be dirt and scale free (stress risers) Ductility and strain hardening limit the amount forming that can be done without part fracture or cracking.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 27 Temperature Warm Working (0.3T m – 0.5T m ) Working above room temperature but below recrystallization temperatures. Advantages Low forces and power More intricate work geometries possible Need for annealing may by reduced T m = melting T.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 28 Temperature Hot working (0.5T m – 0.75T m ) The recrystallization temperature is about one half the melting point. So hot working is above these temperature Disadvantages Deformation process causes localized heating which can cause localized melting (bad Ju Ju) Scale formation increases as the temperature increases. Lower dimensional accuracy Poorer surface finish Shorter tool life. T m = melting T.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 29 Temperature Hot working (0.5T m – 0.75T m ) Advantages Can produce SIGNIFICANT PLASTIC DEFORMATION of the metal. Lower forces and power Brittle metals can be hot worked. Strength properties are usually isotropic No work hardening T m = melting T.

Back to Flat Rolling

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 31 Flat Rolling A strip of thickness h 0 enters the roll gap and leaves at a thickness of h f. The initial velocity V 0 increases to V f at the exit. Note that because the surface speed of the roll is constant, there must be relative sliding between the roll and the strip

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 32 Flat Rolling At one point (no slip point), V strip = V mill. To the left, the roll moves faster than the strip To the right the roll moves slower than the strip Friction is necessary Too much ruins the surface and costs power Too little and nothing happens.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 33 Flat Rolling The draft is (h 0 –h f ) The maximum draft is a function of the coefficient of friction  and the big roll radius R Higher friction and bigger roll, the greater draft. Compare Large tires and rough treads on tractors and off road vehicles.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 34 Flat Rolling The roll force F is shown as perpendicular to the strip (rather than perpendicular to the point of contact) Because R >>> h The roll force may be estimated as:

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 35 Flat Rolling L = roll strip contact length w = strip width Y avg = average true stress on the strip in the roll gap

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 36 Flat Rolling Equation assumes no friction The higher , the further off the formula (low side). The power per roll can be estimated by assuming F acts in the middle of the arc of contact The torque/roll is F x a so in S. I. Units (Newton, meters, seconds) the power per roll is: F is in Newtons L is in meters N is rpm

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 37 Flat Rolling Equation assumes no friction The higher , the further off the formula (low side). The power per roll can be estimated by assuming F acts in the middle of the arc of contact The torque/roll is F x a so in English Units (Pounds, feet, seconds) the power per roll is: F is in Pounds force L is in feet N is rpm

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 38 Example: An annealed copper strip, 9 in (228 mm) wide, and 1 inch (25 mm) thick is rolled to a thickness of 0.8 in (20 mm) in one pass. The roll radius is 12 in (300 mm), and the rolls rotate at 100 rpm. What is the roll force and power required? From Table 3.4 pg 51 Groover, K = 300 MPa, n =.5

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 39 Example: An annealed copper strip, 9 in (228 mm) wide, and 1 inch (25 mm) thick is rolled to a thickness of 0.8 in (20 mm) in one pass. The roll radius is 12 in (300 mm), and the rolls rotate at 100 rpm. What is the roll force and power required? But, there are two rolls so the power is:

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 40 Effect of rolling on Structure This is a typical ingot The outer edges have small grains Faster cooling Note the large interior grains. Slow cooling Plenty of time to grow.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 41 Effect of rolling on Structure The normal forces elongate the grains With enough energy new smaller grains grow Structure becomes much more uniform Better strength and ductility

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 42 Shape Rolling Flat rolling is just the start. Straight and long structural shapes Bars Channels I – beams The material cross section is reduced non-uniformly The sequence and type of rolls is quite complex.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 43 Shape rolling of an H– section part.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 44 Ring Rolling Ring is placed between two rolls, of which one is driven Volume of the ring is constant to the diameter increases during the process Ring blanks Cut from a plate Cutting a thick walled pipe.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 45 Ring Rolling -- shapes Shapes can be quite complex. Uses Large rings for rockets and turbines Gearwheel rims Ball bearing races Flanges.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 46 Thread Rolling Straight or tapered threads put in round rods. Most bolts and screws are made this way. Production rates of up to 80 pieces per second are possible

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 47 Thread Rolling No loss in material Good strength (cold working) Surface finish is very good Process induces residual compressive stresses on surface which improves fatigue life.

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 48 Thread Rolling

Module 7 Spring 2001ISAT 430 Dr. Ken Lewis 49 Thread properties Machining cuts through the grains Rolling compresses them