Metal Forming-cold Working

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Fundamentals of Metal Forming

Manansala, Jeremy

Forming Processes

Forming processes tend to be complex systems consisting independent variables, dependent variables, and independent-dependent interrelations.

Manansala, Jeremy

Independent Variables

Independent variables are those aspects of the process over which the engineer has direct control, and they are generally selected or specified when setting up the process.

Manansala, Jeremy

Independent VariablesStarting materialthe engineer is often free to specify the chemistry and condition. These may also be chosen for ease in fabrication or they may be restricted by the final properties desired for the product.

Starting geometry of the workpiecethis may be dictated by previous processing or it may be selected by the engineer from a variety of available shapes. Economics often influence this decision.

Manansala, Jeremy

Independent Variables

Tool or die geometrythis are has many aspects such as the diameter of a rolling mill roll, the die angle in wire drawing and the cavity details when forging. Since tooling will produce and control the metal flow, success or failure of a process often depends on tool geometry.

Manansala, Jeremy

Independent Variables

Lubricationsince lubricants also acts as coolants, thermal barriers, corrosion inhibitors, and parting compounds, their selection is an aspect of great importance. Specification includes type of lubricant amount to be applied and the method of application.

Manansala, Jeremy

Independent VariablesStarting temperaturemany material properties vary greatly with temperature, so its selection and control may well dictate the success or failure of an operation.

Speed of operationsince speed can directly influence the lubricant effectiveness, the forces required for deformation and the time available for heat transfer. It is obvious that its selection would be significant in a forming operation.

Manansala, Jeremy

Independent Variables

Amount of deformationwhile some processes control this variable through die design, others, such as rolling permits its selection at the discretion of the engineer.

Manansala, Jeremy

Dependent VariablesForce or power requirementsengineers cannot directly specify the force or power; they can only specify the independent variables and then experience the consequences of the selection. The ability to predict the forces or powers however is extremely important for only by having this knowledge will the engineer be able to specify or select the equipment for the process.

Manansala, Jeremy

Dependent VariablesMaterial properties of the productthe customer is not interested in the starting properties but is concerned with our ability to produce the desired final shape with the desired final properties

Exit temperatureengineering properties can be altered by both the mechanical and thermal history of the material thus it is important to know and control the temperature of the material throughout the process

Manansala, Jeremy

Dependent VariablesSurface finish and precisionboth are characteristics of the resultant product that are dependent on the specific details of the process.

Nature of the material flowsince properties depend on deformation history, control here is vital the customer is satisfied only if the desired geometric shape is produced with the right set of companion properties and without surface or internal defects.

Manansala, Jeremy

Independent-Dependent InterrelationsExperiencethis requires long time exposure to the process and is generally limited to the specific materials, equipment and products encountered in the realm of past contact.

Experimentwhile possibly the least likely in error direct experiment is both time consuming and costly.

Manansala, Jeremy

Independent-Dependent InterrelationsProcess modelinghere one approaches the problem with a high speed computer and one or more mathematical models of the process numerical values are provided for the various independent variables and the models are used to compute predictions for the dependent variables

Fajardo, Jeptah Dane

Temperature Concerns

In general, an increase in temperature brings out a decrease in strength, an increase in ductility, and a decrease in the rate of strain hardening all effects that would tend to promote ease of deformation.

Fajardo, Jeptah Dane

Hot Working

In addition, deformationbring aboutabove their in the Elevated temperatures temperatures promote The plastic the elevated of metals a decrease diffusion that of a metal and it increase in to yield strengthcan remove or reduce chemical note, recrystallization temperature;anis important ductility. inhomogeneities; recrystallization temperature At the temperatures of can be welded shut or varies however, that the poreshot working, recrystallization reduced in the effectsmaterials hardening, sothe is eliminates different the deformation; and there greatly withsize duringof strain metallurgical increase in yield strength or hardness, no significant structure can often be altered through recrystallization to improve the final properties. or corresponding decrease in ductility.

Fajardo, Jeptah Dane

Hot WorkingStructure and Property Modification by Hot WorkingWhen metals solidify, particularly in the large sections that are typical cast strands, coarse structures tend to form with a certain amount of chemical segregation. The size of the grains is usually not uniform, and undesirable grain shapes can be quite common, such as the columnar grains. Small gas cavities or shrinkage porosity can also form during solidification.

Fajardo, Jeptah Dane

Hot WorkingTemperature Variations

The success or failure of a hot deformation process often depends on the ability to control the temperatures with the workpiece. To minimize problems, it is desirable to keep the workpiece temperatures as uniform as possible.

Fajardo, Jeptah Dane

Cold Working

The process is usually performed at room Plastic deformation of metals below the temperature, but mildly elevated temperatures recrystallization provide increased ductility and may be used to temperature reduced strength

Fajardo, Jeptah Dane

Cold WorkingADVANTAGES

No heating is required Strength, fatigue and wear properties are improved through strain hardening Superior dimensional control is achieved, so little, if any, secondary machining is required

Better surface finish is obtained Products possess better reproducibility and interchangeability Directional properties can be imparted Contamination problems are minimized

Fajardo, Jeptah Dane

Cold WorkingDISADVANTAGES

Higher forces are required to initiate and complete the deformation Less ductility is available Intermediate anneals may be required to compensate for the loss of ductility that accompanies strain hardening

Heavier and more powerful equipment is required Metal surfaces must be clean and scale-free scaleImparted directional properties may be detrimental Undesirable residual stresses may be produced

Fajardo, Jeptah Dane

Cold WorkingPREPARING METALS FOR COLD WORKING

The success or failure of a cold-working operation colddepends on the quality of the starting material. To obtain a good surface finish and maintain dimensional precision, the starting material must be clean and free of oxide or scale that might cause abrasion and damage to the dies or rolls.

Fajardo, Jeptah Dane

Warm Working

The warm regimeforming, theoffers the advantages hot working, requires less energy Compared to cold generally it lower temperatures Toolsreduced loads produce less scaling and to 60% last longer, foron the the must exert 25 while tooling and intermediate Deformation produced at temperaturesequipment,in than hot of warm working due to theydecreased energy higher forces, there enable production of to hot and material ductility,thermal shock and heating the workpiece, decarburization, andis less and a possible increased cold workingenergy saved through thermal fatigue. higher precision and the possible elimination products in the number of anneals due to and reductionwith better dimensional precision a of postforming heat treatments. smoother surfaces. reduction in the amount of strain hardening.

Cold-working Processes

Ocfemia, Cathrine Joy

Cold-working Processes Squeezing Major Cold-Working Operations Bending Shearing Drawing Presses

Ocfemia, Cathrine Joy

Squeezing ProcessesClassifications of Squeezing ProcessesRolling Cold Forging Coining Peening Riveting Sizing Staking Swaging Extrusion

Burnishing Hubbing

Thread Rolling

Ocfemia, Cathrine Joy

Squeezing ProcessesROLLINGprocess used in sheets, strips, bars, and rods to obtain products that have smooth surfaces and accurate dimensions; most cold-rolling is performed on four-high or cluster-type rolling mills

Ocfemia, Cathrine Joy

Squeezing ProcessesSWAGINGprocess that reduces/increases the diameter, tapers, rods or points round bars or tubes by external hammering

Ocfemia, Cathrine Joy

Squeezing ProcessesCOLD FORGINGprocess in which slugs of material are squeezed into shaped die cavities to produce finished parts of precise shape and size.

Ocfemia, Cathrine Joy

Squeezing ProcessesEXTRUSIONprocess which is commonly used to make collapsible tubes such as toothpaste tubes, cans usually using soft materials such as aluminum, lead, tin. Usually a small shot of solid material is placed in the die and is impacted by a ram, which causes cold flow

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