Processes
1- Roll bending
Roll_bending
Roll bending produces a cylindrical shaped product from plate or steel metals.
Roll bender
Roll_bender_machine
A Roll bender is a mechanical jig having three rollers used to form a metal bar into a circular arc. The rollers freely rotate about three parallel axes, which are arranged with uniform horizontal spacing. Two outer rollers, usually immobile, cradle the bottom of the material while the inner roller, whose position is adjustable, presses on the topside of the material.
Roll bending may be done to both sheet metal and bars of metal. If a bar is used, it is assumed to have a uniform cross-section, but not necessarily rectangular, as long as there are no overhanging contours, i.e. positive draft. Such bars are often formed by extrusion. The material to be shaped is suspended between the rollers. The end rollers support the bottom side of the bar and have a matching contour (inverse shape) to it in order to maintain the cross-sectional shape. Likewise, the middle roller is forced against the topside of the bar and has a matching contour to it.
Operation
Forming_a_7_foot_diameter_wheel_rim_with_a_roll_bender
After the bar is initially inserted into the jig, the middle roller is manually lowered and forced against the bar with a screw arrangement. This causes the bar to undergo both plastic and elastic deformation. The portion of the bar between the rollers will take on the shape of a cubic polynomial, which approximates a circular arc. The rollers are then rotated moving the bar along with them. For each new position, the portion of the bar between the rollers takes on the shape of a cubic modified by the end conditions imposed by the adjacent sections of the bar. When either end of the bar is reached, the force applied to the center roller is incrementally increased, the roller rotation is reversed and as the rolling process proceeds, the bar shape becomes a better approximation to a circular arc, gradually, for the number of passes required to bring the arc of the bar to the desired radius.
Plastic and elastic deformation
Close_up_of_the_roll_bender_jig
The plastic deformation of the bar is retained throughout the process. However, the elastic deformation is reversed as a section of bar leaves the area between the rollers. This “spring-back” needs to be compensated in adjusting the middle roller to achieve a desired radius. The amount of spring back depends upon the elastic compliance (inverse of stiffness) of the material relative to its ductility. Aluminum alloys, for example, tend to have high ductility relative to their elastic compliance, whereas steel tends to be the other way around. Therefore aluminum bars are more amenable to bending into an arc than are steel bars.
2- Roll forming
Roll_forming
Roll forming, also spelled rollforming, is a type of rolling involving the continuous bending of a long strip of sheet metal (typically coiled steel) into a desired cross-section. The strip passed through sets of rolls mounted on consecutive stands, each set performing only an incremental part of the bend, until the desired cross-section (profile) is obtained. Roll forming is ideal for producing constant-profile parts with long lengths and in large quantities.
Bending_along_rolls
Overview
Flower_pattern
A variety of cross-section profiles can be produced, but each profile requires a carefully crafted set of roll tools. Design of the rolls starts with a flower pattern, which is the sequence of profile cross-sections, one profile for each stand of rolls. The roll contours are then derived from the flower pattern profiles. Because of the high cost of the roll sets, computer simulation is often used to develop or validate the roll designs and optimize the forming process to minimize the number of stands and material stresses in the final product.
Roll-formed sections may have advantages over extrusions of a similar shapes. Roll formed parts may be much lighter, with thinner walls possible than in the extrusion process, and stronger, having been work hardened in a cold state. Parts can be made having a finish or already painted. In addition, the roll forming process is more rapid and takes less energy than extrusion.
Roll forming machines are available that produce shapes of different sizes and material thicknesses using the same rolls. Variations in size are achieved by making the distances between the rolls variable by manual adjustment or computerized controls, allowing for rapid changeover. These specialized mills are prevalent in the light gauge framing industry where metal studs and tracks of standardized profiles and thicknesses are used. For example, a single mill may be able to produce metal studs of different web (e.g. 3-5/8" to 14 inches), flange (e.g. 1-3/8" to 2-1/2") and lip (e.g. 3/8" to 5/8") dimensions, from different gauges (e.g. 20 to 12 GA) of galvanized steel sheet.
Roll forming lines can be set up with multiple configurations to punch and cut off parts in a continuous operation. For cutting a part to length, the lines can be set up to use a pre-cut die where a single blank runs through the roll mill, or a post-cut die where the profile is cutoff after the roll forming process. Features may be added in a hole, notch, embossment, or shear form by punching in a roll forming line. These part features can be done in a pre-punch application (before roll forming starts), in a mid-line punching application (in the middle of a roll forming line/process) or a post punching application (after roll forming is done). Some roll forming lines incorporate only one of the above punch or cutoff applications, others incorporate some or all of the applications in one line.
Process
Roll forming is, among the manufacturing processes, one of the simplest. It typically begins with a large coil of sheet metal, between 1 inch (2.5 cm) and 20 inches (51 cm) in width, and 0.004 inches (0.10 mm) and 0.125 inches (3.2 mm) thick, supported on an uncoiler. The strip is fed through an entry guide to properly align the material as it passes through the rolls of the mill, each set of rolls forming a bend until the material reaches its desired shape. Roll sets are typically mounted one over the other on a pair of horizontal parallel shafts supported by a stand(s). Side rolls and cluster rolls may also be used to provide greater precision and flexibility and to limit stresses on the material. The shaped strips can be cut to length ahead of a roll forming mill, between mills, or at the end of the roll forming line.
Geometric possibilities
The geometric possibilities can be very broad and even include enclosed shapes as long as the cross-section is uniform. Typical sheet thicknesses range from 0.004 inches (0.10 mm) to 0.125 inches (3.2 mm), but they can exceed that. Length is almost unaffected by the rolling process. The part widths typically are not smaller than 1 inch (2.5 cm) however they can exceed 20 inches (51 cm). The primary limitation is profile depth, which is generally limited to less than 4 inches (10 cm) and rarely larger than 6 inches (15 cm) due to roll-imparted stresses and surface speed differentials that increase with depth.
Tolerances can typically be held within ±0.015 inches (0.38 mm) for the width of the cross-sectional form, and ±0.060 inches (1.5 mm) for its depth.
Production Rates
The production rate depends greatly on the material thickness and the bend radius; it is however also affected by the number of required stations or steps. For bend radii of 50 times the material thickness of a low carbon steel 0.7 inches (18 mm) thick can range from 85 feet per minute (26 m/min) through eight stations to 55 feet per minute (17 m/min) through 12 stations or 50 feet per minute (15 m/min) through 22 stations.
The time for one product to take shape can be represented by a simple function: t = (L + n⋅d) / V, where L is the length of the piece being formed, n is the number of forming stands, d is the distance between stands, and V is the velocity of the strip through the rolls.
In general roll forming lines can run from 5 to 500 feet per minute (1.5 to 152.4 m/min) or higher, depending on the application. In some cases the limiting factor is the punching or cutoff applications.
Other considerations
While dealing with manufacturing, Things to consider are, for example, lubrication, the effect of the process on material properties, cost, and of course safety.
Lubrication provides an essential barrier between the roll dies and the work-piece surface. It helps reducing the tool wear and allows things to move along faster. This table shows the different kinds of lubricants, their application, and the ideal metals to use them on.
| Work material | Roll lubricants | Application |
| Nonferrous | Chlorinated oils or waxes, mineral oils | Spray, wiping roller |
| Ferrous | Water-soluble oils | Wiping, drip, spray |
| Stainless steels | Chlorinated oils or waxes | Wiping roller |
| Polished surfaces | Plastic film | Calendaring, covering, spraying |
| Pre-coated materials | Film or forced air | |
The effects of the process on the material's properties are minimal. The physical and chemical properties virtually don't change, but the process may cause work-hardening, micro-cracks, or thinning at bends when discussing the mechanical properties of the material.
The cost of roll forming is relatively low. When calculating the cost of the process things such as setup time, equipment and tool costs, load/unload time, direct labor rate, overhead rate, and the amortization of equipment and tooling must be considered.
Safety is also a bit of an issue with this process. The main hazards that need to be taken into consideration are dealing with moving work-pieces (up to 800 feet per minute (240 m/min)), high pressure rolls, or sharp, sheared metal edges.
Conclusion
Roll forming, roll bending or plate rolling is a continuous bending operation in which a long strip of metal (typically coiled steel) is passed through consecutive sets of rolls, or stands, each performing only an incremental part of the bend, until the desired cross-section profile is obtained. Roll forming is ideal for producing parts with long lengths or in large quantities. There are 3 main processes: 4 rollers, 3 rollers and 2 rollers, each of which has as different advantages according to the desired specifications of the output plate.
3- Flat rolling
Flat_rolling
Flat rolling is the most basic form of rolling with the starting and ending material having a rectangular cross-section. The material is fed in between two rollers, called working rolls that rotate in opposite directions. The gap between the two rolls is less than the thickness of the starting material, which causes it to deform. The decrease in material thickness causes the material to elongate. The friction at the interface between the material and the rolls causes the material to be pushed through. The amount of deformation possible in a single pass is limited by the friction between the rolls; if the change in thickness is too great the rolls just slip over the material and do not draw it in. The final product is either sheet or plate, with the former being less than 6 mm (0.24 in) thick and the latter greater than; however, heavy plates tend to be formed using a press, which is termed forming, rather than rolling.
Often the rolls are heated to assist in the workability of the metal. Lubrication is often used to keep the workpiece from sticking to the rolls. To fine-tune the process, the speed of the rolls and the temperature of the rollers are adjusted.
The rolling is done in a cluster mill because the small thickness requires a small diameter rolls. To reduce the need for small rolls pack rolling is used, which rolls multiple sheets together to increase the effective starting thickness. As the foil sheets come through the rollers, they are trimmed and slitted with circular or razor-like knives. Trimming refers to the edges of the foil, while slitting involves cutting it into several sheets. Aluminum foil is the most commonly produced product via pack rolling. This is evident from the two different surface finishes; the shiny side is on the roll side and the dull side is against the other sheet of foil.
4- Ring rolling
A_schematic_of_ring_rolling
Ring rolling is a specialized type of hot rolling that increases the diameter of a ring. The starting material is a thick-walled ring. This workpiece is placed between two rolls, an inner idler roll and a driven roll, which presses the ring from the outside. As the rolling occurs the wall thickness decreases as the diameter increases. The rolls may be shaped to form various cross-sectional shapes. The resulting grain structure is circumferential, which gives better mechanical properties. Diameters can be as large as 8 m (26 ft) and face heights as tall as 2 m (79 in). Common applications include bearings, gears, rockets, turbines, airplanes, pipes, and pressure vessels.
5- Structural shape rolling
Structural_shape_rolling
Structural shape rolling, also known as shape rolling and profile rolling, is the rolling and roll forming of structural shapes by passing them through a rolling mill to bend or deform the workpiece to a desired shape while maintaining a constant cross-section. Structural shapes that can be made with this metal forming process include: I-beams, H-beams, T-beams, U-beams, angle iron, channels, bar stock, and railroad rails. The most commonly rolled material is structural steel, however other include metals, plastic, paper, and glass. Common applications include: railroads, bridges, roller coasters, art, and architectural applications.
It is a cost-effective way of bending this kind of material because the process requires less set-up time and uses pre-made dies that are changed out according to the shape and dimension of the workpiece. This process can roll workpieces into full circles.
Process
Cross-sections_of_continuously_rolled_structural_shapes showing_the_change_induced_by_each_rolling_mill
Structural shape rolling uses profile rolling techniques where the workpiece is passed through a series of flatteners (of larger magnitude than that of common rolling devices) that match the workpieces' cross-section. The most common method uses 3 rollers; the bending is controlled by varying the distance between the rollers.
Structural shapes can be rolled in different ways such as the “easy-way”, the “hard-way”, heel in/out, ball in/out, leg in/out, stem in/out, and off axis. The hard-way would be bending the workpiece in the orientation where its moment of inertia is the greatest. The easy-way is bending the workpiece along the axis with the smallest moment of inertia. For example, a piece of angle iron rolled the easy-way would be rolling it along one of its flanges, while the hard-way would be along the angle itself.
6- Controlled rolling
Controlled_rolling
Controlled rolling is a type of thermomechanical processing which integrates controlled deformation and heat treating. The heat which brings the workpiece above the recrystallization temperature is also used to perform the heat treatments so that any subsequent heat treating is unnecessary. Types of heat treatments include the production of a fine grain structure; controlling the nature, size, and distribution of various transformation products (such as ferrite, austenite, pearlite, bainite, and martensite in steel); inducing precipitation hardening; and, controlling the toughness. In order to achieve this the entire process must be closely monitored and controlled. Common variables in controlled rolling include the starting material composition and structure, deformation levels, temperatures at various stages, and cool-down conditions. The benefits of controlled rolling include better mechanical properties and energy savings.
7- Forge rolling
Forging
Forge rolling is a longitudinal rolling process to reduce the cross-sectional area of heated bars or billets by leading them between two contrary rotating roll segments. The process is mainly used to provide optimized material distribution for subsequent die forging processes. Owing to this a better material utilization, lower process forces and better surface quality of parts can be achieved in die forging processes.
Basically any forgeable metal can also be forge-rolled. Forge rolling is mainly used to preform long-scaled billets through targeted mass distribution for parts such as crankshafts, connection rods, steering knuckles and vehicle axles. Narrowest manufacturing tolerances can only partially be achieved by forge rolling. This is the main reason why forge rolling is rarely used for finishing, but mainly for preforming.
Characteristics of forge rolling:
* High productivity and high material utilization
* Good surface quality of forge-rolled workpieces
* Extended tool life-time
* Small tools and low tool costs
* Improved mechanical properties due to optimized grain flow compared to exclusively die forged workpieces
Stages_of_closed_die_forging_process
https://en.wikipedia.org