Manufacturing Process - Forming & Shaping Processes

MANUFACTURING PROCESSMANUFACTURING PROCESS(BMFG 2323)(BMFG 2323)

LECTURE 6LECTURE 6

~ FORMING & SHAPING PROCESSES ~

Prepared and presented by: Masjuri Bin Musa @ Othman

Faculty of Mechanical Engineering(Department of Innovation & Engineering Design)

Universiti Teknikal Malaysia Melaka

FORMING & SHAPING PROCESSESFORMING & SHAPING PROCESSES 1

@jurie 2007 – Lecture 6

INTRODUCTIONINTRODUCTION

Forming vs Shaping:- Forming generally indicates “changing” the shape of an existing solid body, whereas shaping generally formed by molten metals into desired shape.

- Forming process, in which the starting material usually stock materials (bar, plate, sheet, rod, or tubing), is then formed into desire shapes e.g sheet to car body.

- Shaping process typically involve the molding and casting of soft or molten materials, and the finished product is usually near- net-shape.



Flat- and Shape-Rolling

Processes

The initial process is cast molten metal to ingots and formed into slabs, rods, or pipes.

Figure shows schematic outline of various flat- and shape-rolling processes.



PLATESPLATES

- Generally the thickness > 6mm; can goes up to 300mm for large structural supports.- General purpose: structural applications such as ship hulls, boilers, bridges, machinery.

SHEETSSHEETS

- Generally the thickness < 6mm.-General applications: automobile and aircraft bodies, appliances, food and beverages containers.



Flat-RollingFlat-Rolling

Figure: (a) Schematic illustration of the flat-rolling process. (b) Friction forces acting on strip surfaces. (c) The roll force, F, and the torque acting on the rolls. The width w of the strip usually increases during rolling.



ROLLING OF METALSROLLING OF METALS

- Rolling is the process of reducing the thickness or changing the cross-section of a long workpiece by compresive forces applied thru’ a set of rolls.

- Product: Blooms, billets, slabs, plates, or sheets

- Improved mechanical properties e.g. strength and ductility.

Hot RollingHot Rolling- Roll ingots into blooms, billets, and slabs at elavated temperature e.g. aluminum alloy

4500C, alloy steels 12500C.

- Grains structure: coarse, nonuniform, and porous result to the properties of strength and hardness but brittle.

- Fair surface finish.



Cold RollingCold Rolling- Roll plates or sheets into desired shapes at room temperature.

- Product:Plates > 6mm: ship hulls, bridges, pressure vessels.Sheets < 6mm: car bodies (0.7 mm), aluminum cans (0.28 mm) aluminum foil (0.008

mm).

- Produces very good surface finish but requires high roll force.



Defects in rolled plates and sheetsDefects in rolled plates and sheets

- May present on the surfaces of rolled plates & sheets or internal structural.-Effected to surface appearance as well as the strength, formability and manufacturing characteristics.-Example of sheet’s defects: scale, rust, scratches, cracks.-Caused by: inclusions and impurities in the original cast material or related to material preparation.-Wavy edges: resulted due to roll bending.-Cracks: resulted from poor material ductility at the rolling temperature.-Alligatoring: resulted by nonuniform bulk deformation of the billet during rolling.

Figure shows a schematic illustration of typical defects in flat rolling: (a) wavy edges; (b) zipper cracks in the center of the strip; (c) edge cracks; and (d) alligatoring.



- Sometimes a rolled sheet may not flat once it leaves the roll gap.-This can be due to variations in incoming material or in the processing parameters during rolling process.-To improve the flatness, the rolled strip will undergoes through a series of leveling rolls.

Figure shows a method of roller levelling to flatten rolled sheets.

Four-High Rolling MillFour-High Rolling Mill



- The use of smaller diameter of work rolls is to reduce the contact area so that reducing the interface friction force.

- If worn or broken, small rolls can be replaced at lower cost compare to the large ones.

Figure: Schematic illustration of a four-high rolling-mill stand, showing its various features. The stiffnesses of the housing, the rolls, and the roll bearings are all important in controlling and maintaining the thickness of the rolled strip.



Backing Roll ArrangementsBacking Roll Arrangements

- Figure (a): two-high rolling mills.- Used for hot rolling.- Roll diameters ranging from 0.6 to 1.4m.

Figure 13.11 Schematic illustration of various roll arrangements: (a) two-high; (b) three- high; (c) four-high; (d) cluster (Sendzimir) mill.



- Figure (b): three-high mill (reversing mill)- The direction of material movement is reversed after each pass.

- Figure ( c): four-high mills- As been mentioned before.

- Figure (d): cluster mills (Sendzimir or Z mill)- Suitable for cold rolling thin sheets of high-strength metals.- Common diameter of the rolls – 0.66m to 1.5m.



GEOMETRIC CONSIDERATIONSGEOMETRIC CONSIDERATIONS

ROLL BENDINGROLL BENDING

Figure shows (a) Bending of straight cylindrical rolls, caused by the roll force. (b) Bending of rolls ground with camber, producing a strip with uniform thickness.

- Because of the forces acting on them, rolls undergo shape changes during rolling.

- As a result of roll bending, the rolled strip tends to be thicker at its center than at its edges.

- To overcome this problem – grind the rolls in such away that the diameter at the center of the roll is slightly larger than at the edges.

- Thus, when the roll bends, the strip being rolled now has a constant thickness along its width.



SPREADING OF A STRIPSPREADING OF A STRIP

Increase in the width (spreading) of a strip in flat rolling. Similarly, spreading can be observed when dough is rolled with a rolling pin.

- In rolling plates and sheets with high width-to-thickness ratio, the width of the strip remains effectively constant during rolling.

- However, with smaller ratio such as strip with a square cross section, its width increases significantly as it passes through the rolls.

- Therefore, as a conclusion, the spreading increases with:

a)Decreasing width-to-thickness ratio of the entering strip – due to the reduction in the width constant.

b)Increasing the friction.c)Decreasing ratio of the roll radius to the strip thickness.



Grain Structure During Hot RollingGrain Structure During Hot Rolling

- The product of the first hot-rolling operation is called bloom or slab.- A bloom: a square cross-section, at least 150mm on the side.- A slab: rectangular in cross-section.- A billet: square in cross-sectional area smaller than blooms.-Blooms are processed further by shape rolling into structural shapes such as I-beams and railroad rails.- Slabs are rolled into plates and sheets.- Billets are rolled into various shapes, such as round rods and bars, using shaped rolls.-Before undergo with the hot rolling process, the cast structure typically include coarse and non-uniform grains; this structure usually is brittle and may be porous.-Therefore, hot rolling process converts the cast structure to a wrought structure with finer grains and enhanced ductility.-Both of this result from the breaking up of brittle grain boundaries and the closing up of internal defects especially porosity.



Figure shows the changes in the grain structure of cast or of large-grain wrought metals during hot rolling. Hot rolling is an effective way to reduce grain size in metals, for improved strength and ductility. Cast structures of ingots or continuous casting are converted to a wrought structure by hot working.

Grain Structure During Hot Rolling (cont’)Grain Structure During Hot Rolling (cont’)



Other characteristics of rolled metalsOther characteristics of rolled metals1) Residual stresses.- Because of non-uniform deformation of the material in the roll gap, residual stress can

develop in rolled plates and sheets.- Large diameter rolls or high reduction per pass tend to deform the bulk more than the

surfaces and this is due to the higher frictional constraint at the surfaces along the arc of contact.

Figure shows (a) Residual stresses developed in rolling with small rolls or at small reductions in thickness per pass. (b) Residual stresses developed in rolling with large rolls or at high reductions per pass. Note the reversal of the residual stress patterns.



2) Dimensional tolerances.-Thickness tolerances for cold-rolled sheets usually range from ±0.1 to 0.35mm, depending on the thickness.- Tolerances for hot rolled plates are much more greater because of thermal effect.- Flatness tolerances for cold rolling: ± 15mm/m.- Flatness tolerances for hot rolling: ± 55mm/m.

3) Surface roughness.- Cold rolling can produce a very fine surface finish compared to hot rolling.-Therefore, products made of cold-rolled sheets may not be require additional finishing operation, depending on the application.

4) Gage numbers-The thickness of a sheet usually identified by a gage number depending on the type of sheet metal being classified.- The smaller the number, the thicker the sheet.



VARIOUS ROLLING PROCESSESVARIOUS ROLLING PROCESSES

SHAPE ROLLING (Profile rolling)-Straight and long structural shapes such as channels, I-beams, railroad rails, and solid bar, are formed at elevated temperatures by shape rolling.- In this process of rolling, the stock will go through a set of specially designed rolls.-In cold shape rolling, the starting materials are in the shape of wire with various cross-sections.-Since the material’s cross section is reduced non-uniformly, the design of a series of rolls requires considerable experience in order to avoid external and internal defects, hold dimensional tolerances, and reduce roll wear.



Figure shows the stages in the shape rolling of an H-section part. Various other structural sections, such as channels and I-beams, are also rolled by this kind of process.

SHAPE ROLLING



ROLL FORGING (Cross rolling)ROLL FORGING (Cross rolling)-The cross-section of a round bar is shaped by passing it through a pair of rolls with profile grooves.- Typically this process is used to produce tapered shafts, table knives, hand tools.

SKEW ROLLINGSKEW ROLLING- Typically this process is used to produce ball bearings.-Round wire or rod is fed into the roll gap, and roughly spherical blanks are formed continuously by action of the rotating rolls.



RING ROLLINGRING ROLLING- A thick ring is expanded into a large-diameter thinner one.- The ring is placed between sets of two rolls, one of which is driven while the other is idle.- The thickness is reduced by bringing the rolls closer together as they rotate. -This kind of process can be carried out at room or at an elevated temperature, depending on the size, strength, and ductility of the work piece material.-Advantages compare to other manufacturing methods: short production times, material savings, close dimensional tolerances.





THREAD ROLLINGTHREAD ROLLING- This type of rolling process is a cold-forming process by which straight or tapered threads are formed on round rods or wire by passing them between dies.- Threads are formed on the rod or wire wit each stroke of a pair of flat reciprocating dies.-Other method – threads are formed with rotary dies – which can produced as high as 80 pieces per second.-Advantages: Produce threads with good strength (due to cold working) without any loss of material/scrap, surface finish produced is very smooth, improve fatigue life.

Figure shows thread-rolling processes: (a) and (c) reciprocating flat dies; (b) two-roller dies. Threaded fasteners, such as bolts, are made economically by these processes, at high rates of production.



ROTARY TUBE PIERCING (Mannesmann process)- It is a hot working operation for making long, thick-walled seamless pipe and tubing.-Principle: when a round bar is subjected to radial compressive forces, tensile stresses develop at the center of the bar.-When it is subjected continuously to these cyclic compressive stresses, the bar begin to develop a small cavity at its center which begins to grow.- Rotary tube piercing is carried out using an arrangement of rotating rolls.-The axes of the rolls are skewed in order to pull the round bar through the rolls by the axial component of the rotary motion.-An internal mandrel assists the operation by expanding the hole and sizing the inside diameter of the tube.-The mandrel may be held in place by a long rod, or it may be floating mandrel without a support.

Figure shows cavity formation in a solid round bar and its utilization in the rotary tube piercing process for making seamless pipe and tubing. (The Mannesmann mill was developed in the 1880s.)

ROTARY TUBE PIERCING (Mannesmann process)





TUBE ROLLINGTUBE ROLLING- Reducing the diameter and thickness of pipes and tubing.

- Utilizes shaped rolls.

- Some of the operations can be incorporated with or without an internal mandrel.

- In the pilger mill, the tube shaped and are rotated continuously.

-During the gap cycle on the roll, the tube is advanced and rotated, starting another cycle

of tube reduction.

- As a result, the tube undergoes a reduction both in diameter and wall thickness.



Figure shows schematic illustration of various tube-rolling processes: (a) with fixed mandrel; (b) with moving mandrel; (c) without mandrel; and (d) pilger rolling over a mandrel and a pair of shaped rolls. Tube diameters and thicknesses can also be changed by other processes, such as drawing, extrusion, and spinning.

TUBE ROLLINGTUBE ROLLING

Spray Casting (Osprey Process)Spray Casting (Osprey Process)

Figure shows spray casting (Osprey process), in which molten metal is sprayed over a rotating mandrel to produce seamless tubing and pipe.





FORGING PROCESSFORGING PROCESS- Work piece is shaped by compressive forces applied through various dies and tooling.- Application: oldest – produced jewelry, coins.

nowadays: large rotors for turbines, gears, bolts, rivets, cutlery, hand tools.- Produce discrete parts.-Characteristics: have good strength, toughness, very reliable for highly stressed – all of these is because the metal flow in a die and material’s grain structure can be controlled.-Can be carried out at room temperature (cold forging), or at elevated temperatures (warm or hot forging).-Cold forging – requires higher forces due to the higher strength of the work piece of the material and also the work piece material must possess sufficient ductility at room temperature to undergo the necessary deformation without cracking.- Cold forging’s advantages: parts have good surface finish and dimensional accuracy.-Hot forging requires lower forces and the dimensional accuracy and surface finish of the parts are not as good as in cold forging.-Typically, parts after forging need to have additional finishing operations, such as heat treating to modify properties and machining to obtain accuracy final dimensions and surface finish.



(a)(b)

Figure shows (a) Schematic illustration of the steps involved in forging a bevel gear with a shaft. Source: Forging Industry Association. (b) Landing-gear components for the C5A and C5B transport aircraft, made by forging.



Figure shows general view of a 445 MN (50,000 ton) hydraulic press.

(c)



Outline of Forging and Related Outline of Forging and Related OperationsOperations



Grain Flow ComparisonGrain Flow Comparison

Figure shows a part made by three different processes, showing grain flow. (a) casting, (b) machining, (c) forging.



Characteristics of Forging ProcessesCharacteristics of Forging ProcessesTABLE 14.1Process Advantages LimitationsOpen die Simple, inexpensive dies; useful for small

quantities; wide range of sizes available;good strength characteristics

Limited to simple shapes; difficult to hold closetolerances; machining to final shape necessary;low production rate; relatively poor utilization ofmaterial; high degree of skill required

Closed die Relatively good utilization of material;generally better properties than open-dieforgings; good dimensional accuracy; highproduction rates; good reproducibility

High die cost for small quantities; machiningoften necessary

Blocker type Low die costs; high production rates Machining to final shape necessary; thick websand large fillets necessary

Conventional type Requires much less machining than blockertype; high production rates; good utilizationof material

Somewhat higher die cost than blocker type

Precision type Close tolerances; machining oftenunnecessary; very good material utilization;very thin webs and flanges possible

Requires high forces, intricate dies, and provisionfor removing forging from dies



OPEN-DIE FORGINGOPEN-DIE FORGING- The most simplest forging operation.- General weigh: 15 to 500kg; 270 tonnes have been made.- Parts produced: nails, pins, bolts, long shaft, ship propellers.-Basic operation/process: A solid work piece placed between two flat dies and reduced in height by compressing it. This particular process is known upsetting or flat-die forging. -Due to reduction on height, therefore the diameter of the forged parts will increase as well.-Even though the work piece is deformed uniformly, however, in actual condition, there is a friction, and this will develops a barrel shape, and this particular deformation is also known as pancaking.-Barellling is caused by frictional forces at the die-work piece interfaces that oppose the outward flow of the materials these interfaces.



UpsettingUpsetting

Figure shows (a) Solid cylindrical billet upset between two flat dies. (b) Uniform deformation of the billet without friction. (c) Deformation with friction. Note barreling of the billet caused by friction forces at the billet-die interfaces.



Cogging (drawing out)- The thickness of a bar is reduced by successive forging steps at specific intervals.- The thickness of bars and rings can be reduced by this operation.-Since the contact area between the die and the work piece is small, a long section of bar can be reduced in thickness without requiring large forces.

Figure shows two views of a cogging operation on a rectangular bar. Blacksmiths use this process to reduce the thickness of bars by hammering the part on an anvil. Note the barreling of the workpiece.



COGGING PROCESSCOGGING PROCESS



IMPRESSION DIE-FORGINGIMPRESSION DIE-FORGING

- In this process, the workpiece takes the shape of the die cavity while being forged between two shaped dies.

- Typically this kind of process is done at elevated temperature in order to enhanced the ductility of the metals and to lower the forces.

- During deformation, some of the material flows outward and forms a flash where this flash has an important role in impression die-forging.

- The high pressure and the resulting high frictional resistance in the flash presents a severe constraint to the material in the die for outward flow.

- Based on the principle that in plastic deformation the material flows in the direction of least resistance (because it requires less energy), the material begins to flow into the die cavity, ultimately filling it completely.



Impression-Die ForgingImpression-Die Forging

Figure: Stages in impression-die forging of a solid round billet. Note the formation of flash, which is excess metal that is subsequently trimmed off.



- Instead of being made as one piece, dies may be made of several pieces including die inserts and this particularly for complex shapes.

- The die inserts can be replaced easily in the case of wear or failure in a particular section of the die and usually are made from stronger and harder materials.

Figure shows die inserts used in dies for forging an automotive axle housing. (See Tables 5.5 to 5.7 for die materials.)



Forging a Connecting RodForging a Connecting Rod

Figure (a) Stages in forging a connecting rod for an internal combustion engine. Note the amount of flash required to ensure proper filling of the die cavities. (b) Fullering, and (c) edging operations to distribute the material when preshaping the blank for forging.

- Fullering: material is distributed away from an area.

- Edging: material is gathered into localized area.



Trimming Flash from a Forged PartTrimming Flash from a Forged Part

Figure shows trimming flash from a forged part. Note that the thin material at the center is removed by punching.



CLOSED-DIE FORGINGCLOSED-DIE FORGING-In real situation, flash does not form, and the work piece completely fills the die cavity.-In this particular case, the forging pressure is very high, and accurate control of the blank volume and proper die design are essential in order to produce a forging with the desired dimensional tolerances.

CLOSE-DIE FORGINGCLOSE-DIE FORGING





CoiningCoiningFigure (a) Schematic illustration of the coining process. the earliest coins were made by open-die forging and lacked sharp details. (b) An example of a coining operation to produce an impression of the letter E on a block of metal.



- Coining is a part of a closed-die forging process.- Application: minting coins, medallions, jewelry, marking parts with letters and numbers.-In order to produce fine details, the pressure required can be as high as five or six times the strength of the material.-Lubricants cannot be applied in coining process, because they can become entrapped in the die cavities and prevent the full reproduction of die surface details and surface finish.



HEADING FORGING (UPSET FORGING)HEADING FORGING (UPSET FORGING)

Figure shows (a) Heading operation, to form heads on fasteners such as nails and rivets. (b) Sequence of operations to produce a bolt head by heading.

- Performed on the end of a round rod or wire in order to increase the cross-section.

- Typical application: nails, bolt heads, screws, rivet, other type of fasteners.

- Can be carried out by cold, warm, or hot forging.



Grain Flow Pattern of Pierced Round Billet

Figure shows a pierced round billet, showing grain flow pattern.

- A process of indenting the surface of a w/piece with a punch in order to produce a cavity or an impression.

- The deformation of the w/piece will depend on how much it is constrained from flowing freely as the punch descends.

- Piercing may be followed by punching to produce a hole in the part .



SWAGINGSWAGING

- In this process, a solid rod or tube is subjected to radial impact forces by a set of reciprocating dies of the machine.-The w/piece is stationary and the dies rotate, striking the w/piece at rates as high as 20 strokes per second.-Max. w/piece diameter: ≈ 150mm-Dimensional tolerances range from ±0.05 to ±0.5mm.-Suitable for medium to high rates of production, where rates as high as 50 parts/min depending on the complexity of the parts.

Rotary swaging



Figure shows (a) Schematic illustration of the rotary-swaging process. (b) Forming internal profiles on a tubular workpiece by swaging. (c) A die-closing type swaging machine, showing forming of a stepped shaft. (d) Typical parts made by swaging.



Tube swaging-In this process, the internal diameter and/or the thickness of the tube is reduced with or without the use of internal mandrels.

Figure shows (a) Swaging of tubes without a mandrel; not the increase in wall thickness in the die gap. (b) Swaging with a mandrel; note that the final wall thickness of the tube depends on the mandrel diameter. (c) Examples of cross-sections of tubes produced by swaging on shaped mandrels. Rifling (spiral grooves) in small gun barrels can be made by this process.

DEFECTS IN FORGED PARTSDEFECTS IN FORGED PARTS



Figure shows an examples of defects in forged parts. (a) Labs formed by web buckling during forging; web thickness should be increased to avoid this problem. (b) Internal defects caused by oversized billet; die cavities are filled prematurely, and the material at the center flows past the filled regions as the dies close.

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Manufacturing Process - Forming & Shaping Processes