So, by definition it is defined as the deformation under the condition of temperature and strain rate such that recovery takes. The metal working processes are derived into hot working and cold working processes. Hot rolling, drop forging, extrusion, hot drawing, forming powdered metals. This process is extensively used in pipes and steel rods manufacturing. Crane hook, connecting rod of ic engine, spanner, gear blanks etc. Where the hot work area is accessible to persons other than the operator of the hot work. Where reasonably practicable the need for hot working should be eliminated by the use of other processes that do not involve the application or generation of heat or sparks. If hot working process is performed properly, it does not affect. These advantages make warm forming very suitable for a certain range of parts, but this part range is limited due to certain economical and technical reasons, e. This mode of deformation is found mostly on smooth bottoms of shallow parts and in hydroforming processes. Metal forming processes indian institute of technology. Being above the recrystallization temperature allows the material to recrystallize during deformation. Hot working occurs at temperatures above tjlle recrystallization temperature of the metal. Hot work has the potential to unite all three parts of the fire triangle.
If this deformation is done below the recrystallization temperature the process is known as cold working. Those processes working above the recrystallization temperature are hot working processes where as the below or termed as cold working processes. Forging is one of the oldest known metalworking processes. At high strain rates, heat generated due to the local temperature rise by plastic deformation is not conducted away to the cooler regions of the body since the time available is too short. Comparison of hot working and cold working processes. Metals are generally deformed at specific temperature and strain rate so that recovery. When recovery processes are not effective at the time of deformation, the processes are called cold working processes. Stresses beyond yield strength of the workpiece material is required. This is important because recrystallization keeps the materials from strain hardening, which ultimately keeps the yield strength and hardness low and ductility high.
Therefore, if the deformation process is quick enough the temperature of the workpiece should rise, however, this does not usually happen in practice. Creating this new phase on the work order is creating the permit. Today we will learn about extrusion process working, types, application, advantages and disadvantages. There are many other differences between these processes which are described as. This is mandatory in the state of massachusetts as of july 1, 2018.
Forging is often classified according to the temperature at which it is performed. Safety in gas welding, cutting and similar processes page 8 of 11 if you flame cut outdoors and the metal is clean and unpainted you will not normally need rpe. It describes the provisions of the ptw process, framework of the ptw system and ptw suite of documents that support the system. The division is on the basis of the amount of heating applied to the metal before applying the mechanical force. Hot working refers to the process where metals are deformed above their recrystallization temperature and strain hardening does not occur. The microstructural manifestations of flow instabilities are many but the most common process is the occurrence of adiabatic shear bands.
Hot work definition, responsibility, process and risks onboard ships definition work involving sources of ignition or temperatures sufficiently high to cause the ignition of a flammable gas mixture is termed as hot work. Van tyne colorado school of mines, golden, colorado, u. Thus, warm forming can only be substituted for hot forging to a limited extent. Hot work can cause a pipe to heat up substantially and this heat can easily transfer through the process of conduction to another, potentially flammable surface and cause a fire. Chapter 15 32 advantages of hot working since at temperatures above recrystallization, the metal. It is no longer necessary to send copies of the permit to anyone, all shop permit information will be contained within aim. The gas usually air is heated by electric heating elements mounted within the welding gun.
It is defined as the mechanical working of metal at an elevated higher temperature above a particular temperature. In sheet metal forming practice, we distinguish five basic modes of deformation. Exposure to hot and often corrosive material can occur. Fire prevention hot work procedures stanford university. Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The temperature at which atomic mobility can repair the damage caused by the working process. It is one of the oldest metalworking arts with its origin about some thousands of years back. Processes most of the cold working squeezing processes have identical hot working counterparts or are extension of them. The behavior of the metal is significantly altered, due to the fact that it is.
In recognition of the inherent hazards posed by certain hot work processes, the national fire protection agency adopted standard 51b, standard for fire prevention during welding, cutting, and other hot work. It is defined as the mechanical working of metal at an elevated higher. Hot working process metals are plastically deformed above their recrystallization temperature. Bulk deformation atures relative to the melting point of the metal. Hot working may be explained as plastic deformation of metals and alloys at such a temperature above recrystallization temperature at which recovery and. Plant that has been decommissioned removed existing energies. Conclusions about hot working in most cases, hot working processes indicate higher temperatures but the major factor that determines hot working is the presence of recrystallization. Hot working pdf forging rolling metalworking scribd. Process safety information this booklet summarizes the osha final process safety management psm standard. If you dont properly remove flammable materials or substances from the area before work, they could come into contact with a surface that has become. The most important aspect of any hot working process is controlling the temperature of the workpiece. Forging is a metal working process in which useful shape is obtained in solid state by hammering or pressing metal. Metal remains soft and ductile during process hot working mechanism. Mechanical working processes which are done above recrystallisation temperature of the metal are know as hot working processes.
Safe operating procedure university of nebraskalincoln. In mechanical working process the raw material is converted to a given. Involves deformation above recrystallization temperature, between 0. The use of this book replaces the expensive and time consuming trial and error.
When plastic deformation of metal is carried out at temperature above the recrystallization temperature the process, the process is known as hot working. When recovery processes are not effective at the time of deformation, the processes are called cold working. The process for obtaining the permit is the same as for temporary permits, except that the annual permit box is checked. Hot working is plastically deforming of the metallic material at a temperature above the recrystallization temperature. This mode is typical the material flow from the flange towards the. Safety in gas welding, cutting and similar processes. Some metals, such as lead and tin, have a low recrystallisation temperature and can be hot worked even at room temperature, but most commercial metals require some heating. The city of boston requires a hot work safety certificate for all persons engaged in hot work operations on the work site. Hot working, or hot forming, is a metal forming process that is carried out at a temperature range that is higher than the recrystallization temperature of the metal being formed. All hot work permit program training records shall be maintained by the pai.
Schuler started testing warm forming applications about twenty years ago. Plastic deformation processes operations that induce shape changes on the work piece by plastic deformation. Hot working produces a recrystallized grain structure, while the grain structure due to cold working is unrecrystallized and retains the effects of the working. A compendium of processing maps is a unique source book with flow stress data for hot working, processing maps with metallurgical interpretation and optimum processing conditions for metals, alloys, intermetallics and metal matrix composites.
Fixed hot work permits cover ongoing work in designated areas. Forming processes are commonly hot working and cold working operations. The surface areatovolume of the work is relatively small. Hot working is usually performed at elevated temperatures. Hot work is a process that can be a source of ignition when flammable material is present or can be a fire hazard regardless of the presence of flammable material in the workplace. Operations not requiring a hot work permit operations that produce a flame, sparks, hot slag or. Comparison between hot working and cold working processes can be done in aspects like carried out temperature, stress set up, tolerances, hardening, deformation, surface finish, improved properties, cracks formation. Forming processes rolling, extrusion, forging, drawing dr. Very large amount of deformation can be given by hot working because strain hardening and distorted grain structures are simultaneously eliminated with the formation of new grains. Metals are generally deformed at specific temperature and strain rate so that recovery takes place simultaneously with the deformation. The primary reasons for deforming cold rather than hot are to obtain better dimensional accuracy and surface finish. Some examples of shapes obtained by forging process. The usual route is to start with hot working processes followed by cold working and annealing.
Areas can be protected with the use of welding pads, blankets, or curtains, clearing combustibles from a 35foot radius space around the hot work, or moving the hot work to an area free of combustibles. Working in hot processes roasters autoclaves elution columns. Hot work safety guide 062015 4 hot work is not permitted in. The hot work permit helps the permit authorizing individual, hot work operator, and fire watch recognize potential hazards. Welding and allied processes include arc welding, oxyfuel gas welding, openflame soldering, brazing, thermal spraying, oxygen cutting, and arc cutting. Eeping all completed hot work permits shall be kept on file for a period of at least one year. This lecture describes the fundamentals, working principles, advantages, disadvantages and applications of hot and cold working. If you flame cut indoors or in conditions were there is little air movement, the. Lead, however, is hot worked at room temperature because of its low melting temperature. Employers and employees may prefer to read this booklet and a companion one entitled, process safety management guidelines for compliance osha 33, before studying the rule itself. Common hot work processes involve welding, soldering, cutting, brazing burning and the use of powderactuated tools or similar fire producing operations outside of designated hot work areas.
Pdf fundamentals of metal forming there are four basic. Hot working fundamentals of manufacturing processes. Do not create a hot work phase when an outside contractor is doing the hot work. Hot processes generally involve hot liquids, solids or gases, commonly at high pressure. Rolling is the process of reducing the thickness or changing the cross section of a long workpiece by compressive forces applied through a set of rolls, as shown in figure 51. Most of the coldworking squeezing processes have identical hotworking counterparts or are extensions of them. No welding, cutting, or other hot work shall be performed on used drums, barrels, tanks or other containers until they have been cleaned so thoroughly as to make absolutely certain that there are no flammable materials present or any substances such as greases, tars, acids, or other materials which when subjected to heat, might produce.
In many cases the equipment is basically the same, except that it must be more powerful. Try to work in a position where the wind blows the fume cloud away from you and other people. Metal forming processes mechanical engineering mcq. The torch welding gun directs the heated gas toward the work piece surfaces and a. In many cases, the equipment is basically the same, except that it must be more powerful.