Roll Forging.
Roll Forging.
Roll Forging is a deformation process used to reduce the cross section of a cylindrical or rectangular work piece by passing it through a set of opposing rolls that have grooves matching the desired shape of the final part.
Roll Forging.
Roll Forging is classified as Forging process even though it utilizes rolls. Rolls do not turn continuously in roll forging but rotate through only a portion of one revolution corresponding to the desired deformation to be accomplished on the part.
Roll Forging.
Roll Forging.
Roll Forged parts are generally stronger and possess favorable grain structure compared to competing processes such as machining that might be used to produce the same part geometry.
Roll Forging products.
In roll forging round or flat bar stock is reduced in thickness and increased in length to produce such products as axles, tapered levers and leaf springs.
Swaging.
Swaging is a process used to reduce the diameter of a tube or solid rod.
Swaging is often performed on the end of a work piece to create a tapered section.
Examples of Parts made by Swaging.
Swaging.
Swaging process as shown in figure is accomplished by means of rotating dies that hammer a work piece radially inward to taper it as the piece is fed in to the dies.
Swaging.
In swaging die the die itself acts as hammer. Repeated blows are delivered from various angles , causing the metal to flow inward and assume the contour of the die. Most of the swaging is usually performed cold.
Swaging.
Some swaging processes are performed hot . For example hot swaging is used to reduce and form the end of a pressurized gas cylinder.
Net shape and near net shape Forging.1
To minimize both the expense and waste considerable effort has been made to develop processes that can form parts close enough to final dimensions that little or no final machining is required. These are referred to as net shape or near net shape processes and may also be referred to as precision forging.
Net shape and near net shape Forging.2
Cost savings usually result from the elimination of reduction or elimination of secondary machining , the companion reduction in scrap and an over all decrease in the amount of energy required to produce the product.
Net shape and near net shape Forging.3
Design and implementation of net shape processing can be rather expensive ,application is usually reserved for parts where a significant cost reduction can be achieved.
Extrusion.
In the extrusion process metal is compressed and forced to flow through a suitably shaped die to form a product with reduced but constant cross section.
Extrusion may be performed either hot or cold , hot extrusion is commonly employed for many metals to reduce the forces required.
Extrusion.2
Extrusion process is like squeezing tooth paste out of a tube. In the case of metals a common arrangement is to have a heated billet placed inside of confining chamber. A ram advances from one end ,causing the billet to first upset and conform to the confining chamber.
Extrusion.3
As the ram continues to advance the pressure builds until the material flows plastically through the die and extrudes.
Extrusion.( Materials)
Aluminum ,Magnesium ,copper , Lead , and alloys of these metals are commonly extruded , taking advantage of the relatively low yield strength and low hot working temperature. Steel , stainless steel ,Nickel based alloys and titanium based alloys are far more difficult to extrude. Their yield strength and the metals have the tendency to weld to the walls of the die and
confining chamber under the required conditions of temperature and pressure.
Extrusion.( Materials)2
With the development and use of phosphate based and molten glass lubricants ,hot extrusion can be routinely produced from these high strength , high temperature metals.
These lubricants are able to with stand the required temperatures and adhere to the billet, flowing and thinning in a way that prevents metal to metal contact through out the process.
Extrusion.
Almost any cross sectional shape can be extruded from the non ferrous metals.
Size limitations are few because presses are now available that can extrude any shape that can be enclosed with in 75 cm diameter circle. In the case of steels and other high strength metals the shapes and sizes are a bit more limited
Extrusion Products.
Extrusion.
Extrusion has a number of attractive features .many shapes can be produced as extrusions that are not possible by rolling such as longitudinal holes. No draft is required. Billet to product cross sectional area ratios can be 100 to 1 for the weaker metals. The major limitation of the process is the requirement that the cross section be uniform for the entire length of the product.
Extrusion.
Extrusion products have good surface finish and dimensional precision. For most shapes tolerances of ±0.003 cm/cm easily attainable. Grain structure is typical of other hot worked metals but strong directional properties ( longitudinal versus transverse ) are usually observed. Standard product lengths are about 6 to 7 m but lengths in excess of 12 m have been produced.
Extrusion methods.
Extrusions can be produced by various techniques and equipment configurations. Hot extrusion is usually done by two methods: 1. 2.
Direct In Direct
Direct Extrusion.
In direct extrusion a solid ram drives the entire billet to and through a stationary die and must provide additional power to over come the frictional resistance between the surface of the moving billet and the confining chamber.
Direct Extrusion.
One of the problems in direct extrusions is the significant friction that exist between the work surface and the walls of the container as the work piece is forced to slide toward the die opening.
This friction causes a substantial increase in the ram force required in direct extrusion.
In Direct Extrusion
In Indirect extrusion the die is mounted to the ram rather than at the opposite end of the container. As the ram penetrates in to the work , the metal is forced to flow through the clearance in a direction opposite to the direction of motion of the ram.
In Direct Extrusion
Since the work is not forced to move relative to the container , there is no friction at the container walls and the ram force is therefore lower than the direct extrusion.
Direct and In direct extrusion.
In Direct Extrusion( Limitations)
Added complexity of the in direct process serves to increase the purchase price and maintenance cost of the required equipment.
In direct extrusions are imposed by the lower rigidity of the hollow ram .
Extrusion speeds.
Speeds of the hot extrusion process are fast so as to minimize the cooling of the billet with in the chamber.
Extruded products can emerge at rates up to 300 m/min.
Extrusion speeds may be restricted by the large amounts of heat that are generated by the massive deformation and the associated rise in temperature.
Extrusion speeds 2
Sensors are often used to monitor the temperature of the emerging product and feed this information back to a control system. For materials whose properties are not sensitive to strain rate , ram speed may be maintained at the highest level that will keep the product temperature below some predetermined value.
Extrusion speeds
Lubrication is another important area of concern. If the reduction ratio is 100 the product will be 100 times longer than the starting billet and if the product has a complex cross section its perimeter will be considerably larger than the starting material.
Extrusion lubricant
Surface area of the product is the length times the perimeter as the length and perimeter both increased the surface area of the final product will be greater than the surface area of the starting work piece. A lubricant that is applied to the starting piece must thin considerably as the material passes through the die and is converted to the product.
Extrusion lubricant 2
An acceptable lubricant is expected to reduce friction and act as a barrier to heat transfer at all stages of the process.
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