Metal Forming Pdf

IPE-3209: METAL FORMING AND SHEET METALWORKING

Nikhil R. Dhar, Ph. D Professor, IPE Department BUET

Course Outlines Fundamental of Metal Forming: Overview of metal forming, material behavior in metal forming, temperature in metal forming, friction and lubrication in metal forming. Bulk Deformation Processes in Metal Working: 

Rolling and Other deformation processes related to rolling



Forging and Other deformation processes related to forging



Extrusion and Other deformation processes related to forging

Sheet Metal Working: Cutting operations, bending operations, drawing, Other sheet metal forming operations, precision forming processes; various features of different types of metal forming dies; principles of powder forming.

Department of Industrial & Production Engineering

107/2

Suggested Reading Manufacturing Processes for Engineering Materials - S. Kalpakjian & S. R. Schmid

Materials and Processes in Manufacturing - E.P. Degarmo, J.T. Black & R.A. Kohser Fundamentals of Modern Manufacturing - M.P. Groover Processes and Design for Manufacturing - S.D.EI Wakil

Metal Cutting Principles - M. C. Shaw Metal Cutting - E. Trent Manufacturing Technology – B. Kumar

Department of Industrial & Production Engineering

107/3

Marks Distribution Total Marks: 100 Class Test (20%) 1

2

3

4

10

10

10

10

Quiz-01 Quiz-02 Quiz-03 Quiz-04

Class Attendance [10%]

Final Examination [70%]

10%

70%

: Fundamental of Metal Forming : Bulk Deformation Processes - Rolling : Bulk Deformation Processes - Forging : Sheet Metal Forming Processes

Department of Industrial & Production Engineering

107/4

LECTURE-01: FUNDAMENTAL OF METAL FORMING

Nikhil R. Dhar, Ph. D Professor, IPE Department BUET

Introduction Large group of manufacturing processes in which plastic deformation is used to change the shape of metal workpieces 

The tool, usually called a die, applies stresses that exceed the yield strength of the metal



The metal takes a shape determined by the geometry of the die

Forming processes tend to be complex systems consisting 

Independent Variables,



Dependent Variables, and



Independent-dependent Interrelations.

Department of Industrial & Production Engineering

107/6

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. Consider some of the independent variables in a typical forming process: 





Starting material : The 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 workpiece: This 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. Tool or die geometry : This 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.

Department of Industrial & Production Engineering

107/7









Lubrication: Since 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. Starting temperature: Many material properties vary greatly with temperature, so its selection and control may well dictate the success or failure of an operation. Speed of operation: Since 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. Amount of deformation: While some processes control this variable through die design, others, such as rolling permits its selection at the discretion of the engineer.

Department of Industrial & Production Engineering

107/8

Dependent Variables: After the engineer specifies the independent variables, the process then determine the nature and values for a second set of variables. Known as dependent variables, these, in essence, are the consequences of the dependent variable selection. Consider some of the dependent variables in a typical forming process:  Force or power requirements: Engineers 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.  Material properties of the product: The 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

Department of Industrial & Production Engineering

107/9



Exit (or Final) temperature: Engineering 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



Surface finish and precision: Both are characteristics of the resultant product that are dependent on the specific details of the process.



Nature of the material flow: Since 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.

Department of Industrial & Production Engineering

107/10

Independent-Dependent Interrelations: The following Figure illustrate a major problem facing the metal-forming engineer. On one side are the independent variables, those aspect of the process for which control is direct and immediate. On the other are the dependent variables, those aspects for which control is totally indirect. It is the dependent variables that we want to control, but the dependent variables are determioned by the process, as consequences of the independent variable selection. If we want to change a dependent variable, we must determine which independent variable is to be changed, in what manner, and by how much. Thus it is important for us to develop a knowledge of the independent variable-dependent variable interrelations. Independen t variables

Schematic of the metal-forming system showing independent variables, dependent variables and the various means of relating the two

Starting material   Starting geometry   Experience Tool geometry  Lubrication  Experiment Starting temperature  Modeling  Speed of deformation   Amount of deformation 

Department of Industrial & Production Engineering

Dependent variables

Forceor Power requirement Product properties    Exit tempe rature Surface finish  Dimensional precision  Material flow details 107/11

The ability to predict and control dependent variables can be obtained in three distinct ways: 

Experience: This 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.



Experiment: While possibly the least likely in error direct experiment is both time consuming and costly.



Process modeling: Here 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 . Most techniques rely on the applied theory of plasticity with various simplifying assumptions.

Department of Industrial & Production Engineering

107/12

General Parameters While much metal-forming knowledge is specific to a given process, there are certain features that are common to all processes, and these will be presented here. Friction and Lubrication: An important consideration in metal deformation processes is the friction developed between the tool and the workpiece. For some processes, more than 50% of the input energy is spent in overcoming friction. The surface finish and dimensional precision of the product are often directly related to friction. Changes in lubrication can alter the mode of material flow during forming and in so doing, create or eliminate defects, or modify the properties of the final product. Production rate, tool design, tool wear and process optimization all depend on the ability to determine and control process friction. 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. Department of Industrial & Production Engineering

107/13

Forming processes tend to be classified as hot working, cold working or warm working based on both the temperature and the material being formed. Hot Working:  Elevated temperatures bring about a decrease in the yield strength of a metal and an increase in ductility. At the temperatures of hot working, recrystallization eliminates the effects of strain hardening, so there is no significant increase in yield strength or hardness, or corresponding decrease in ductility.  The plastic deformation of metals above their recrystallization temperature; it is important to note, however, that the recrystallization temperature varies greatly with different materials  In addition, the elevated temperatures promote diffusion that can remove or reduce chemical inhomogeneities; pores can be welded shut or reduced in size during the deformation; and the metallurgical structure can often be altered through recrystallization to improve the final properties. Department of Industrial & Production Engineering

107/14

Structure and Property Modification by Hot Working: When 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.  Temperature 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. Cold Working:  Plastic deformation of metals below the recrystallization temperature is known as cold working. The process is usually performed at room temperature, but mildly elevated temperatures may be used to provide increased ductility and reduced strength. 

Department of Industrial & Production Engineering

107/15

Advantages of cold working:  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 Disadvantages of cold working:  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  Imparted directional properties may be detrimental  Undesirable residual stresses may be produced Department of Industrial & Production Engineering

107/16

Warm Working:  







Deformation produced at temperatures intermediate to hot and cold working. Compared to cold working, it offers the advantages of reduced loads on the tooling and equipment, increased material ductility, and a possible reduction in the number of anneals due to a reduction in the amount of strain hardening. Compared to hot forming, the lower temperatures of warm working produce less scaling and decarburization, and enable production of products with better dimensional precision and smoother surfaces. The warm regime generally requires less energy than hot working due to the decreased energy in heating the workpiece, energy saved through higher precision and the possible elimination of post forming heat treatments. Tools last longer, for while they must exert 25 to 60% higher forces, there is less thermal shock and thermal fatigue.

Department of Industrial & Production Engineering

107/17

Stresses in Metal Forming Stresses to plastically deform the metal are usually compressive  Examples: rolling, forging, extrusion However, some forming processes  Stretch the metal (tensile stresses)  Others bend the metal (tensile and compressive)  Still others apply shear stresses Material Properties in Metal Forming Desirable material properties:  Low yield strength  High ductility These properties are affected by temperature:  Ductility increases and yield strength temperature is raised Other factors:  Strain rate and friction Department of Industrial & Production Engineering

decreases

when

work

107/18

Basic Types of Deformation Processes Bulk deformation Processes  Rolling  Forging  Extrusion  Wire and bar drawing Sheet metalworking  Cutting or Shearing  Bending  Deep drawing  Miscellaneous processes

Department of Industrial & Production Engineering

107/19

Extrusion Rolling

Forging

Shearing

Drawing

Bulk deformation Processes

Bending Sheet Metalworking

Department of Industrial & Production Engineering

Drawing

107/20

LECTURE-02: BULK DEFORMATION PROCESSES - ROLLING

Nikhil R. Dhar, Ph. D Professor, IPE Department BUET

Rolling Rolling is the most widely used deformation process. It consists of passing metal between two rollers, which exert compressive stresses, reducing the metal thickness. Where simple shapes are to be made in large quantity, rolling is the most economical process. Rolled products include sheets, structural shapes and rails as well as intermediate shapes for wire drawing or forging. Circular shapes, ‘I’ beams and railway tracks are manufactured using grooved rolls.

Department of Industrial & Production Engineering

107/22

Practically all metals, which are not used in cast form are reduced to some standard shapes for subsequent processing.

Manufacturing companies producing metals in form of ingots which are obtained by casting liquid metal into a square cross section. 

Slab (500-1800 mm wide and 50-300 mm thick)



Billets (40 to 150 sq mm)



Blooms (150 to 400 sq mm)

Sometimes continuous casting methods are also used to cast the liquid metal into slabs, billets or blooms.

These shapes are further processed through hot rolling, forging or extrusion, to produce materials in standard form such as plates, sheets, rods, tubes and structural sections. Department of Industrial & Production Engineering

107/23

Sequence of operations

Schematic layout of various flat and shape rolling processes Department of Industrial & Production Engineering

107/24

Basic Principles of Rolling When a piece of metal is rolled in between two rolls, the thickness is reduced as a result of the compressive stresses exerted by the rolls and it can be treated as a two-dimensional deformation in the thickness and length directions neglecting the width direction. This is due to the fact that the length of contact between the rolls and workpiece is generally much smaller than the width of the sheet passing through and the undeformed material on both sides of the roll gap is restraining the lateral expansion along the width direction.

The metal piece experiences both vertical and horizontal stresses caused by the compressive load from the rolls and the restrains by the portions of the metal piece before and after the material in contact with the roll respectively. As the rolls exert a vertical stress on the metal piece, the metal piece exerts the same amount of stress back onto the rolls itself. As such the rolls are subjected to elastic deformation due to this stress induced by the workpiece. As shown in the figure below, the rolls in a 4-high rolling mill are subjected to four kinds of deformation: Department of Industrial & Production Engineering

107/25

 

 

Deflection of the back-up rolls, Deflection of the work rolls, Flattening of the work rolls caused by contact with the back-up rolls and workpiece Flattening of the back-up rolls caused by contact with the work rolls.

Department of Industrial & Production Engineering

107/26

Rolling is the process of reducing the thickess or changing the crosssection of a long workpiece by compressive forces applied through a set of rolls. The rolling processes can be done by  Flat Rolling  Shape Rolling  Production of Seamless Tubing & Pipe Flat Rolling:  Metal strip enters the roll gap  The strip is reduced in size by the metal rolls  The velocity of the strip is increased the metal strip is reduced in size  Factors affecting Rolling Process Frictional Forces Roll Force and Power Requirement

Department of Industrial & Production Engineering

107/27

Department of Industrial & Production Engineering

107/28

Flat-Rolling Practice Hot rolling  The initial break down of an ingot  Continuously cast slab  Structure may be brittle  Converts the cast structure to a wrought structure Finer grains Enhanced ductility  Reduction in defects Continuous Casting  Is replacing traditional methods  Faster & better Product of the first hot-rolling operation - Bloom or slab  Square cross section of 150mm (6in) on one side  Processed father by shape rolling I-beams Railroad rails Department of Industrial & Production Engineering

107/29

Billets – smaller than blooms and rolled into bars and rods Cold rolling  carried out at room temperature  Produces sheet and strip metal  Better surface finish – less scale Pack rolling – when two or more layers of metal are rolled together

Changes in grain structure during hot-rolling Department of Industrial & Production Engineering

107/30

Rolling Defects in Sheets and Plates The elastic deflection of the work rolls results in an uneven widthwise distribution of the workpiece thickness in such a way where the thickness is greater at the center of the width and smaller at the edges. In order to solve the bending of the work rolls, several methods can be adopted.  Smaller work rolls are more prone to greater bending under high rollseparating forces from the vertical stresses induced by the workpiece. As such, back-up rolls are often used to counter this phenomenon.  Another method to reduce or eliminate elastic roll deflection is to use materials of high elastic modulus, such as sintered carbide, for the work rolls.  A more common method to counter the effects of roll bending is the usage of cambered rolls. The degree of cambering depends on the width of the metal piece, flow stress of the material and the reduction per pass. However certain problems arise with improper work rolls cambering. Department of Industrial & Production Engineering

107/31

Lack of camber or insufficient cambering of the work rolls results in producing a workpiece that has a thicker center than the edge. The thicker center implies that the edges are plastically elongated more than the center. This induces a residual stress pattern of compression at the edges and tension along the centerline of the workpiece (Figure a). The consequences of this uneven distribution of stress within the workpiece can be centerline cracking (Figure b), warping (Figure c) or edge wrinkling (Figure d) of the final metal sheet.

Figure a

Figure d Department of Industrial & Production Engineering

Figure b

Figure c 107/32

In the case where the work rolls are over-cambered, the edges of the workpiece will be thicker than the center and the residual stress pattern is exactly the opposite of that of insufficient cambering, i.e. tension at the edges and compression along the centerline (Figure e). Possible undesirable results of the workpiece being produced in such a manner are edge cracking (Figure f), splitting (Figure g) or centerline wrinkling (Figure h).

Figure e

Figure g Department of Industrial & Production Engineering

Figure f

Figure h 107/33

Schematic Illustration of Various Roll arrangements

Department of Industrial & Production Engineering

107/34

Schematic Illustration of various roll arrangements: (a) Two-high; (b) Three-high; (c) Four-high; (d) Cluster mill Department of Industrial & Production Engineering

107/35

Shape-Rolling Operations Various shapes can be produced by shape rolling  Bars  Channels  I-beams  Railroad rails Roll-pass design requires considerable experience in order to avoid external and internal defects

Department of Industrial & Production Engineering

107/36

Stages in Shape Rolling of an H-section part. Various other structural sections such as channels and I-beams, are rolled by this kind of process.

Department of Industrial & Production Engineering

107/37

Ring Rolling A thick ring is expanded into a large diameter ring  The ring is placed between the two rolls  One of which is driven  The thickness is reduced by bringing the rolls together The ring shaped blank my be produced by:  Cutting from plate  Piercing  Cutting from a thick walled pipe Various shapes can be produced by shaped rolls Typical applications of ring rolling:  Large rings for rockets  Gearwheel rims  Ball-bearing and roller-bearing races Can be carried out at room temperature Has short production time Close dimensional tolerances Department of Industrial & Production Engineering

107/38

Thread Rolling Cold-forming process Straight or tapered threads are formed on round rods by passing the pipe though dies Typical products include  Screws and Bolts Threads are rolled in the soft condition Threads may then be heat treated, and subjected to final machining or grinding Uncommon or special-purpose threads are machined

Department of Industrial & Production Engineering

107/39

Production of Seamless Pipe & Tubing Rotary tube piercing (Mannesmann process) 

Hot-working process



Produces long thick-walled seamless pipe



Carried out by using an arrangement of rotating rolls

Tensile stresses develop at the center of the bar when it is subjected to compressive forces

Department of Industrial & Production Engineering

107/40

Department of Industrial & Production Engineering

107/41

Continuous Casting & Integrated Mills and Minimills Continuous casting  Advantages Highly automated Reduces product cost Companies are converting over to this type of casting Integrated Mills utilize everything from the production of hot metal to the casting and rolling of the finished product Minimills  Scrap metal is melted  Cast continuously  Rolled directly into specific lines of products  Each minimill produces one kind of rolled product Rod Bar Structural steel Department of Industrial & Production Engineering

107/42

Continuous Casting Department of Industrial & Production Engineering

107/43

Salient Points about Rolling Rolling is the most extensively used metal forming process and its share is roughly 90%

The material to be rolled is drawn by means of friction into the two revolving roll gap The compressive forces applied by the rolls reduce the thickness of the material or changes its cross sectional area The geometry of the product depend on the contour of the roll gap Roll materials are cast iron, cast steel and forged steel because of high strength and wear resistance requirements Hot rolls are generally rough so that they can bite the work, and cold rolls are ground and polished for good work finish In rolling the crystals get elongated in the rolling direction. In cold rolling crystal more or less retain the elongated shape but in hot rolling they start reforming after coming out from the deformation zone Department of Industrial & Production Engineering

107/44

The peripheral velocity of rolls at entry exceeds that of the strip, which is dragged in if the interface friction is high strip enough.

In the deformation zone the thickness of the strip gets reduced and it elongates. This increases the linear speed of the strip at the exit. Thus there exist a neutral point where roll speed and strip speeds are equal. At this point the direction of the friction reverses. When the angle of contact exceeds the friction angle the rolls cannot draw fresh strip Roll torque, power etc. increase with increase in roll work contact length or roll radius

Department of Industrial & Production Engineering

107/45

LECTURE-03 :BULK DEFORMATION PROCESSES - FORGING

Nikhil R. Dhar, Ph. D Professor, IPE Department BUET

Forging Forging is a deformation process in which the work is compressed between two dies, using either impact or gradual pressure to form the part. Today, forging is an important industrial process used to make a variety of highstrength components for automotive, aerospace, and other applications. These components include engine crankshafts and connecting rods, gears, aircraft structural components, and jet engine turbine parts. In addition, steel and other basic metals industries use forging to establish the basic forms of large components that are subsequently machined to final shape and dimensions. Either impact or gradual pressure is used in forging. The distinction derives more form the type of equipment used than differences in process technology. A forging machine that applies an impact load is called a forging hammer, while one that applies gradual pressure is called a forging press. Another difference among forging operations is the degree to which the flow of the work metal is constrained by the dies. By this classification there are three types of forging operations like  Open-die forging  Impression or Close die forging  Flashless Forging. Department of Industrial & Production Engineering

107/47

Open-Die Forging Most forging processes begin with open die forging. Open die forging is hot mechanical forming between flat or shaped dies in which the metal flow is not completely restricted. The stock is laid on a flat anvil while the flat face of the forging hammer is struck against the stock. The equipment may range from the anvil and hammer to giant hydraulic presses. Open-die hot forging is an important industrial process. Shapes generated by open-die operations are simple; examples include shafts, disks, and rings. In some applications, the work must often be manipulated (for example, rotating in steps) to effect the desired shape change. Open-die forging process is shown in the following Figure. The skill of the human operator is a factor in the success of these operations. Operations classified as opendie forging or related operations include:

Fullering Edging, and Cogging Department of Industrial & Production Engineering

107/48

Fullering is a forging operation performed to reduce the cross section and redistribute the metal in a workpart in preparation for subsequent shape forging. It is accomplished by dies with convex surfaces. Fullering die cavities are often used designed into multicavity impression dies so that the starting bar can be rough formed before final shaping.

Fullering

Edging

Edging is similar to fullering, except that the dies have concave surfaces. Cogging operation consists of a sequence of forging compressions along the length of a workpiece to reduce cross section and increase length. It is used in the steel industry to produce blooms and slabs from cast ingots. It is accomplished using open dies with flat or slightly contoured surfaces. The term incremental forging is sometimes used for this process. Department of Industrial & Production Engineering

Cogging

107/49

Advantages and Limitations Advantages  Simplest type of forging  Dies are inexpensive  Wide range of part sizes, ranging from 30-1000lbs  Good strength qualities  Generally good for small quantities Limitations  Simple shapes only  difficult to hold close tolerances  machining necessary  low production rate  poor utilization of material  high skill required

Department of Industrial & Production Engineering

107/50

Impression or Close Die Forging In impression-die forging, so0metimes called closed die forging, the die surfaces contain a shape or impression that is imparted to the work during compression, thus constraining metal flow to a significant degree as shown in following Figure. In this type of operation, a portion of the work metal flows beyond the die impression to form flash and must be trimmed off later. The process is shown in the following Figure as a three step sequence. The raw workpiece is shown as a cylindrical part similar to that used in the previous open-die operation. Department of Industrial & Production Engineering

107/51

Advantages and Limitations Advantages  Good utilization of material  Better properties than Open Die Forgings  Dies can be made of several pieces and inserts to create more advanced parts  Presses can go up to 50,000 ton capacities  Good dimensional accuracy  High production rates  Good reproducibility Limitations  High die cost  Machining is often necessary  Economical for large quantities, but not for small quantities

Department of Industrial & Production Engineering

107/52

Flashless Forging Flashless forging is sometimes called closed-die forging in industry terminology. However, there is a technical distinction between impression-die forging and true closed-die forging. The distinction is that in closed-die forging the raw workpiece is completely contained within the die cavity during compression, and no flash is formed. This process is shown in the following figure. Flashless forging imposes requirements on process control that are more demanding than impression-die forging. Most important is that the work volume must equal the space in the die cavity within a very close tolerance. If the starting blank is too large, excessive pressures may cause damage to the die or even the press. If the blank is too small, the cavity will not be filled. Because of the special demands made on flashless forging, the process lends itself best to part geometries that are usually simple and symmetrical and to work materials such as aluminum and magnesium and their alloys. Flashless forging is often classified as a precision forging process. Department of Industrial & Production Engineering

107/53

Advantages and Limitations Advantages       

Close dimensional tolerances Very thin webs and flanges are possible Very little or no machining is required Little or no scrap after part is produced Cheaper to produce from less finishing operations and faster production Typical applications are gears, connecting rods, and turbine blades Common materials used in precision forging are aluminum, magnesium alloys, steel, and titanium

Limitations     

High forging forces Thus higher capacity equipment is required Intricate dies leading to increased die cost Precise control over the Blank’s volume and shape Accurate positioning of the Blank in the die cavity

Department of Industrial & Production Engineering

107/54

Other Forging Operations Coining: Coining is a forging process by which very fine and intricate details can be created on the surface of a metal work piece. Coining may be used to control surface quality and detail on parts. One common use of coining, as the name suggests, is in the production of coins. This is a flashless, precision forging operation, that due to the required accuracy of the process, is performed cold. Lubrication is not used, since any substance between the die and work would hinder the reproduction of the most accurate details that are to be formed on the work's surface. In the coining process, a large amount of force is exerted on the forging, over a short distance. Mechanical presses are often used for these operations. Department of Industrial & Production Engineering

107/55

Upsetting: Upsetting is a deformation operation in which a cylindrical workpart is increased in diameter and reduced in length. However, as an industrial operation, it can also be performed as closed-die forging, as shown in the following Figure. Upsetting is widely used in the fastener industry to form the heads of nails, bolts, and similar hardware products.

Department of Industrial & Production Engineering

107/56

Heading: The following Figure illustrates a variety of heading applications, indicating various possible die configurations. Owing to these types of applications, more parts are produced by upsetting than any other forging operation. It is performed as a mass production operation - cold, warm, or hot - on special upset forging machines, called headers or formers. Care must be taken so that work piece does not buckle Can be highly automated

Department of Industrial & Production Engineering

107/57

Swaging and Radial Forging: Swaging and radial forging are forging processes used to educe the diameter of a tube or solid rod. Swaging is often performed on the end of a workpiece to create a tapered section. The swaging process shown is accomplished by means of rotating dies that hammer a workpiece radially inward to taper it as the workpiece is fed into the dies. Radial forging is similar to swaging in its action against the work and is used to create similar shapes. The difference is that in radial forging the dies do not rotate around the workpiece; instead , the work is rotated at it feeds into the hammering dies.

Department of Industrial & Production Engineering

107/58

Roll Forging: Roll forging is a deformation process used to reduce the cross section of a cylindrical (or rectangular) workpiece by passing it through a set of opposing rolls that have grooves matching the desired shape of the part. The typical operation is shown in the following Figure. Roll forging is generally classified as a forging process, even though it utilizes rolls. The 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-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.

Department of Industrial & Production Engineering

107/59

Forging Machines Equipment used in forging consists of forging machines, classified as forging hammers and presses, and forging dies, which are the special tooling used in these machines. In addition, auxiliary equipment is needed, such as furnaces to heat the work, mechanical devices to load and unload the work, and trimming stations to cut away the flash in impression-die forging. Forging Hammers: Forging hammers operate by applying an impact load against the work. The term drop hammer is often used for these machines, owing to the means of delivering impact energy. Drop hammers are most frequently used or impression-die forging. The upper portion of the forging die is attached to the ram, and the lower portion to the anvil. In the operation, the work is placed on the lower die, and the ram is lifted and then dropped. When the upper die strikes the work, the impact energy causes the part to assume the form of the die cavity.

Department of Industrial & Production Engineering

107/60

Drop hammers can be classified as gravity drop hammers and power drop hammers. Gravity drop hammers achieve their energy by the falling weight of a heavy ram. The force of the blow is determined by the height of the drop and the weight of the ram. Power drop hammers accelerate the ram by pressurized air or steam. One disadvantage of the drop hammers is that a large amount of the impact energy is transmitted through the anvil and into the floor of the building. This results in a great deal of vibration for the surrounding area. Department of Industrial & Production Engineering

Gravity drop hammers

Power drop hammers 107/61

Forging Presses: Presses apply gradual pressure, rather than sudden impact, to accomplish the forging operation. Forging presses include  Mechanical Presses  Hydraulic Presses, and  Screw Presses

Mechanical presses typically operate by means of eccentrics, cranks, or knuckle joints, which convert the rotating motion of a drive motor into the translational motion of the ram. These mechanisms are very similar to those used in stamping presses. Mechanical presses typically achieve very high forces at the bottom of the forging stroke.

Department of Industrial & Production Engineering

64/62

Eccentric Press

Crank Press

Department of Industrial & Production Engineering

Knuckle Joint Press 64/63

Hydraulic presses: The basic working principles of the hydraulic press are simple, and rely on differences in fluid pressure. Fluid is pumped into the cylinder below the piston, this causes the fluid pressure under the piston to increase. Simultaneously fluid is pumped out of the top channel, causing the fluid pressure above the piston to decrease. A higher pressure of the fluid below the piston than the fluid above it causes the piston to rise. In the next step, fluid is pumped out from below the piston, causing the pressure under the piston to decrease. Simultaneously fluid is pumped into the cylinder from the top, this increases the fluid pressure above the piston. A higher pressure of the fluid above the piston, than the fluid below it, moves the piston downward. Department of Industrial & Production Engineering

64/64

Screw Presses: Forging screw presses use the rotational energy of a motor to turn a large screw. Typically a friction disk is used to translate the force from the drive shaft to the screw's head. The screw pushes a ram with great mechanical advantage. Screw presses are similar to hydraulic presses in that they are relatively slow and require a longer contact with the work. Screw presses are also similar to hydraulic presses in that they can produce a constant amount of force over a long stroke. Some screw press machines in modern industry can produce 31,000 tons, (62,000,000 lbs), of force. Department of Industrial & Production Engineering

64/65

Department of Industrial & Production Engineering

107/66

LECTURE-04: BULK DEFORMATION PROCESSES - EXTRUSION

Nikhil R. Dhar, Ph. D Professor, IPE Department BUET

Extrusion Process Extrusion is a process that forces metal or plastic to flow through a shaped opening die. The material is plastically deformed under the compression in the die cavity. The process can be carried out hot or cold depending on the ductility of the material. The tooling cost and setup is expensive for the extrusion process, but the actual manufactured part cost is inexpensive when produced in significant quantities. Materials that can be extrudes are aluminum, copper, steel, magnesium, and plastics. Aluminum, copper and plastics are most suitable for extrusion.

Department of Industrial & Production Engineering

107/68

Classification of Extrusion Processes Depending on the ductility of the material used extrusions can be caries out various ways: Hot Extrusion: Extrusion carried out at elevated temperatures  Forward or direct extrusion and  Backward or indirect extrusion Cold Extrusion: Extrusion carried out a ambient temperature. Often combined with forging operations Hydrostatic Extrusion: Pressure is applied by a piston through incompressible fluid medium surrounding the billet

Department of Industrial & Production Engineering

107/69

Hot Extrusion Extrusion is carried out at elevated temperatures-for metals and alloys that do not have sufficient ductility at room temperature, or in order to reduce the forces required. In this extrusion, die wear can be excessive and cooling of the hot billet in the chamber can be a problem, which results in highly non-uniform deformation. To reduce cooling of the billet and to prolong die life, extrusion dies may be preheated, as is done in hot forging operations. Hot billet causes the following problems:  Because the billet is hot, it develops an oxide film unless heated in an inertatmosphere furnace. This film can be abrasive and it can affect the flow pattern of the material.  It also results in an extruded product that may be unacceptable in cases in which good surface finish is important. In order to avoid the formation of oxide films on the hot extruded product, the dummy block placed ahead of the ram is made a little smaller in diameter than the container. As a result, a thin cylindrical shell, consisting mainly of the oxidized layer, is left in the container. The extruded product is thus free of oxides; the skull is later removed from the chamber. Hot extrusion can be done by  Forward or direct extrusion process  Backward or indirect extrusion process Department of Industrial & Production Engineering

107/70

Direct Extrusion: In this extrusion process, the heated billet is placed in the container. A ram towards the die pushes it. The metal is subjected to plastic deformation, slides along the walls of the container and is forced to flow through the die opening. At the end of the extruding operation, a small piece of metal, called butt-end scrap, remains in the container and cannot be extruded. Indirect Extrusion: For the production of solid part, the die is mounted on the end of a hollow ram and enters the container as shown in the following Figure, the outer end of container being closed by a closure plate. As the ram travels, the die applies pressure on the billet and the deformed metal flows through the die opening in the direction opposite to the ram motions and the product is extruded through the hollow ram. In indirect extrusion, there is practically no slip of billet with respect to the container walls.

Extrusion

Direct Extrusion Department of Industrial & Production Engineering

Indirect Extrusion 107/71

Cold Extrusion This process is similar to hot extrusion except that the metals worked possess the plasticity necessary for successful forming without heating them. Usually, these metals have a high degree of ductility. Cold extrusion is also done to improve the physical properties of a metal and to produce a finished part. Cold extrusion is done mostly on vertical mechanical presses because they are fast and simple. The method is fast, wastes no or little materials and gives higher accuracy and tolerance. The widely employed cold extrusion method is Impact extrusion. Impact extrusion is performed at higher speeds and shorter strokes than conventional extrusion. It is for making discrete parts. For making thin wall-thickness items by permitting large deformation at high speed.

Backward impact extrusion

Forward impact extrusion Combined impact extrusion

Department of Industrial & Production Engineering

107/72

Hydrostatic Extrusion With the hydrostatic extrusion the billet in the container is surrounded with fluid media, is called also hydrostatics medium. The container space is sealed on the stem side and on the die side, so that the penetrating stem can compress the hydrostatics medium on pressing power, without the stem touches the billet. Also during extrusion the stem does not touch the billet. The rate, with which the billet moves when pressing in the direction of the die, is thus not equal to the ram speed, but is proportional to the displaced hydrostatics medium volume. For this process it is substantial that the billet seals the container space on applying the pressing power in the hydrostatics medium against the die, since otherwise the pressing power cannot be developed.

It is thus a conical die and a careful sharpening billet a prerequisite of the process. Since the billet does not touch the container's wall, but between billet and container hydrostatics medium exists, prevails negligibly small friction of a liquid at the billet surface. Only the friction between billet and die is of importance for the deforming process. Likewise pressing of the billet is unnecessary at the press begin. Department of Industrial & Production Engineering

107/73

Tube-Drawing Tube-drawing operations, with and without an internal mandrel. Note that a variety of diameters and wall thicknesses can be produced from the same initial tube stock.

Department of Industrial & Production Engineering

107/74

Extrusion Defects Surface Cracking: Cracking on billet materials occurs due to temperature, friction, punch speed.  High Temperatures Crack from along the grain boundaries. Typically occur in aluminum, magnesium, zinc alloys  Cold Temperatures Caused by sticking of billet material at the die land Known has the “Bamboo Defect” because of its similar appearance to bamboo Pipe: The metal-flow pattern tends to draw oxides and impurities toward the center of the billet Internal Cracking: Center of extruded product develops cracks.  Attributed to a state of hydrostatic tinsel stress  Cracks increase with increasing die angle, impurities, and decreasing extrusion ratio and friction Department of Industrial & Production Engineering

107/75

Advantages of Extrusion Processes The range of extruded items is very wide. Cross-sectional shapes not possible by rolling can be extruded, such as those with re-entrant sections. No time is lost when changing shapes since the dies may by readily removed and replaced. Dimensional accuracy of extruded parts is generally superior to that of rolled ones. In extrusion, the ductility of the metals is higher as the metal in the container is in composite compression, this advantage being of particular importance in working poorly plastic metals and alloys. Very large reductions are possible as compared to rolling, for which the reduction per pass is generally  2. Automation in extrusion is simpler as items are produced in a single passing. Small parts in large quantities can be made. For example, to produce a simple pump gear, a long gear is extruded and then sliced into a number of individual gears. It does not need draft or flash to trim and needless machining as it is more accurate than forging. Department of Industrial & Production Engineering

107/76

Disadvantages of Extrusion Processes Process waste in extrusion is higher than in rolling, where it is only 1 to 3% In-homogeneity in structure and properties of an extruded product is greater due to different flows of the axial and the outer layers of blanks. Service life of extrusion tooling is shorter because of high contact stresses and slip rates. Relatively high tooling costs, being made from costly alloy steel. In productivity, extrusion is much inferior to rolling, particularly to its continuous varieties. Cost of extrusion are generally greater as compared to other techniques

Department of Industrial & Production Engineering

107/77

Applications of Extrusion Processes Extrusion is more widely used in the manufacture of solid and hollow sections from poorly plastic non-ferrous metals and their alloys (aluminum, copper, brass and bronze etc.) Steel and other ferrous alloys can also be successfully processed with the development of molten-glass lubricants. Manufacture of sections and pipes of complex configuration. Medium and small batch production Manufacture of parts of high dimensional accuracy The range of extruded items is very wide: rods from 3 to 250 mm in diameter, pipes of 20 to 400 mm in diameter and wall thickness of 1 mm and above and more complicated shapes which can not be obtained by other mechanical methods.

Department of Industrial & Production Engineering

107/78

LECTURE-05: SHEET METAL FORMING PROCESSES

Nikhil R. Dhar, Ph. D Professor, IPE Department BUET

Introduction Sheet metal forming is a grouping of many complementary processes that are used to form sheet metal parts. One or more of these processes is used to take a flat sheet of ductile metal, and mechanically apply deformation forces that alter the shape of the material. Before deciding on the processes, one should determine whether a particular sheet metal can be formed into the desired shape without failure. The sheet metal operations done on a press may be grouped into two categories, cutting (shearing) operations and forming operations. Sheet Metal Forming

Department of Industrial & Production Engineering

107/80

Department of Industrial & Production Engineering

107/81

Cutting (Shearing) Operations In this operation, the workpiece is stressed beyond its ultimate strength. The stresses caused in the metal by the applied forces will be shearing stresses. The cutting operations include: Punching (Piercing) Blanking Notching Perforating Slitting Lancing Parting Shaving Trimming Fine blanking

Department of Industrial & Production Engineering

107/82

Punching (Piercing): It is a cutting operation by which various shaped holes are made in sheet metal. Punching is similar to blanking except that in punching, the hole is the desired product, the material punched out to form the hole being waste. Blanking: Blanking is the operation of cutting a flat shape sheet metal. The article punched out is called the blank and is the required product of the operation. The hole and metal left behind is discarded as waste.

Department of Industrial & Production Engineering

107/83

Notching: This is cutting operation by which metal pieces are cut from the edge of a sheet, strip or blank. Perforating: This is a process by which multiple holes which are very small and close together are cut in flat work material. Slitting: It refers to the operation of making incomplete holes in a workpiece. Lancing: This is a cutting operation in which a hole is partially cut and then one side is bent down to form a sort of tab. Since no metal is actually removed, there will be no scrap. Parting: Parting involves cutting a sheet metal strip by a punch with two cutting edges that match the opposite sides of the blank.

Department of Industrial & Production Engineering

107/84

Shaving: The edge of blanked parts is generally rough, uneven and unsquare. Accurate dimensions of the part are obtained by removing a thin strip of metal along the edges. Trimming: This operation consists of cutting unwanted excess material from the periphery of previously formed components. Fine blanking: Fine blanking is a operation used to blank sheet metal parts with close tolerances and smooth, straight edges in one step.

(a) Shaving a sheared edge. (b) Shearing and shaving, combined in one stroke.

Department of Industrial & Production Engineering

Fine blanking 107/85

Shearing Dies Because the formability of a sheared part can be influenced by the quality of its sheared edges, clearance control is important. In practice, clearances usually range between 2% and 8% of the sheet’s thickness; generally, the thicker the sheet, the larger is the clearance (as much as 10%). However, the smaller the clearance, the better is the quality of the edge. Some common shearing dies are describe below: Punch and Die Shapes: As the surfaces of the punch and die are flat; thus, the punch force builds up rapidly during shearing, because the entire thickness of the sheet is sheared at the same time. However, the area being sheared at any moment can be controlled be beveling the punch and die surfaces, as shown in the following Figure. This geometry is particularly suitable for shearing thick blanks, because it reduces the total shearing force.

Examples of the use of shear angles on punches and dies. Department of Industrial & Production Engineering

107/86

Compound Dies: Several operations on the same strip may be performed in one stroke with a compound die in one station. These operations are usually limited to relatively simple shearing because they are somewhat slow and the dies are more expensive than those for individual shearing operations.

Department of Industrial & Production Engineering

107/87

Progressive Dies: Parts requiring multiple operations, such as punching, blanking and notching are made at high production rates in progressive dies. The sheet metal is fed through a coil strip and a different operation is performed at the same station with each stroke of a series of punches.

Department of Industrial & Production Engineering

107/88

Transfer Dies: In a transfer die setup, the sheet metal undergoes different operations at different stations, which are arranged along a straight line or a circular path. After each operation, the part is transfer to the next operation for additional operations.

Department of Industrial & Production Engineering

107/89

Forming Operations In this operation, the stresses are below the ultimate strength of the metal. In this operation, there is no cutting of the metal but only the contour of the workpiece is changed to get the desired product. The forming operations include: 

Bending: In this operation, the material in the form of flat sheet or strip, is uniformly strained around a linear axis which lies in the neutral plane and perpendicular to the lengthwise direction of the sheet or metal. The bending operations include: V-bending Edge bending Roll bending Air bending Flanging Dimpling

Press break forming Beading Roll forming Tube forming Bulging Stretch forming

Drawing: This is a process of a forming a flat workpiece into a hollow shape by means of a punch, which causes the blank to flow into die cavity. Squeezing: Under this operation, the metal is caused to flow to all portions of a die cavity under the action of compressive forces. Department of Industrial & Production Engineering

107/90

Bending of Flat Sheet and Plate

V-bending

Edge bending

Bending in 4-slide machine Department of Industrial & Production Engineering

Roll bending

Air bending 107/91

Flanging : Flanging is a process of bending the edges of sheet metals to 90o  Shrink flanging – subjected to compressive hoop stress.  Stretch flanging –subjected to tensile stresses

Department of Industrial & Production Engineering

107/92

Dimpling:   

First hole is punched and expanded into a flange Flanges can be produced by piercing with shaped punch When bend angle < 90 degrees as in fitting conical ends its called flanging

Department of Industrial & Production Engineering

107/93

Press Break Forming: Sheet metal or plate can be bent easily with simple fixtures using a press. Long and relatively narrow pieces are usually bent in a press break. This machine utilizes long dies in a mechanical or hydraulic press and is suitable for small production runs. The tooling is simple and adaptable to a wide variety of shapes.

Department of Industrial & Production Engineering

107/94

Beading: In beading the edge of the sheet metal is bent into the cavity of a die. The bead gives stiffness to the part by increasing the moment on inertia of the edges. Also, it improves the appearance of the part and eliminates exposed sharp edges

(a) Bead forming with a single die

Department of Industrial & Production Engineering

(b) Bead forming with two dies, in a press brake.

107/95

Roll Forming: For bending continuous lengths of sheet metal and for large production runs, roll forming is used. The metal strip is bent in stages by passing it through a series of rolls.

Roll-forming process

Stages in roll forming of a sheet-metal door frame. In Stage 6, the rolls may be shaped as in A or B. Department of Industrial & Production Engineering

107/96

Bulging: The basic forming process of bulging involves placing tabular, conical or curvilinear part into a split-female die and expanding it with, say, a polyurethane plug. The punch is then retracted, the plug returns to its original shape and the part is removed by opening the dies.

(b) Production of fittings for plumbing by expanding tubular blanks with internal pressure.

(a) Bulging of a tubular part with a flexible plug. Water pitchers can be made by this method Department of Industrial & Production Engineering

(c) Manufacturing of Bellows. 107/97

Rubber Forming: In rubber forming , one of the dies in a set is made of flexible material, such as a rubber or polyurethane membrane. Polyurethanes are used widely because of their resistance to abrasion, long fatigue life and resistance to damage by burrs or sharp edges of the sheet blank. In bending and embossing sheet metal by the rubber forming method, as shown in the following Figure, the female die is replaced with a rubber pad. Parts can also be formed with laminated sheets of various nonmetallic material or coatings.

Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die. Department of Industrial & Production Engineering

107/98

Hydroform Process: In hydroforming or fluid forming process, the pressure over the rubber membrane is controlled throughout the forming cycle, with maximum pressure reaching 100 Mpa. This procedure allows close control of the part during forming to prevent wrinkling or tearing. Hydroforming processes have the following advantages:  Low tooling cost  Flexibility and ease of operation  Low die wear  No damage to the surface of the sheet and  Capability to form complex shapes.

Department of Industrial & Production Engineering

107/99

Explosive Forming Process: Explosive forming, is distinguished from conventional forming in that the punch or diaphragm is replaced by an explosive charge. The explosives used are generally high explosive chemicals, gaseous mixtures, or propellants. There are two techniques of high explosive forming such as  Contact technique and  Stand -off technique.

Contact Technique: The explosive charge in the form of cartridge is held in direct contact with the work piece while the detonation is initiated. The detonation builds up extremely high pressures (upto 30,000MPa) on the surface of the work piece resulting in metal deformation, and possible fracture. The process is used often for bulging tubes.

Department of Industrial & Production Engineering

107/100

Standoff Technique: The sheet metal work piece blank is clamped over a die and the assembly is lowered into a tank filled with water. The air in the die is pumped out. The explosive charge is placed at some predetermined distance from the work piece. On detonation of the explosive, a pressure pulse of very high intensity is produced. A gas bubble is also produced which expands spherically and then collapses. When the pressure pulse impinges against the work piece, the metal is deformed into the die with as high velocity as 120 m/s.

Department of Industrial & Production Engineering

107/101

Deep Drawing: Drawing operation is the process of forming a flat piece of material (blank) into a hollow shape by means of a punch, which causes the blank to flow into the die-cavity. Round sheet metal block is placed over a circular die opening and held in a place with blank holder & punch forces down into the die cavity. Wrinkling occurs at the edges.

Deep-drawing process on a circular sheet-metal blank Department of Industrial & Production Engineering

107/102

Ironing Process: If the thickness of the sheet as it enters the die cavity is more than the clearance between the punch and the die, the thickness will have to be reduced; this effect is known as ironing. Ironing produces a cup with constant wall thickness thus, the smaller the clearance, the greater is the amount of ironing.

Schematic illustration of the ironing process. Note that the cup wall is thinner than its bottom. All beverage cans without seams are ironed, generally in three steps, after being deep drawn into a cup. Department of Industrial & Production Engineering

107/103

Redrawing Operations: Containers or shells that are too difficult to draw in one operation are generally redrawn. In reverse redrawing, shown in following Figure, the metal is subjected to bending in the direction opposite to its original bending configuration. This reversal in bending results in strain softening. This operation requires lower forces than direct redrawing and the material behaves in a more ductile manner.

Conventional redrawing Department of Industrial & Production Engineering

Reverse redrawing. 107/104

Beverage Can

Steps in Manufacturing an Aluminum Can

Department of Industrial & Production Engineering

107/105

Aluminum Two-Piece Beverage Cans

Department of Industrial & Production Engineering

107/106

THANK YOU FOR YOUR ATTENTION

Department of Industrial & Production Engineering