manufacturing processes

1. Metal Rolling
Prof. K.N.Wakchaure
Dept. of Mechanical Engineering
SRES COLLEGE OF ENGINEERING,
KOPARGAON
Prof K N Wakchaure

2. METAL FORMING
• Metal forming can be defined as a process in
which the desired size and shape are obtained
through the deformation of metals plastically
under the action of externally applied forces.
• Metal forming processes like rolling, forging,
drawing etc. are gaining ground lately.
• It is due to the fact that metal forming is the
wasteless process which is highly economical.
• They give high dimensional accuracy, easy
formability for complex shapes and good surface
finish with desired metallurgical properties.
Prof K N Wakchaure

3. HOT WORKING AND COLD WORKING
Hot Working
(a) Properties
1. Hot working is done at a temperature above recrystallization but
below its melting point.
2. Hardening due to plastic deformation is completely eliminated
by recovery and recrystallization.
3. Improvement of mechanical properties such as elongation,
reduction of area and impact values.
4. No effect on ultimate tensile strength, yield point, fatigue
strength and hardness.
5. Poor surface finish due to oxidation and scaling.
6. Refinement of crystals occurs.
Prof K N Wakchaure

4. HOT WORKING AND COLD WORKING
Hot Working
6. Refinement of crystals occurs.
7. Due to hot working cracks and blowholes are welded up.
8. No internal or residual stress developed.
9. Force required for deformation is less.
10. Light equipment is used in hot working.
11. Difficult to handle a hot worked metal.
12. Hot working processes are—hot forging, hot rolling, hot
spinning, hot extrusion, hot drawing, and hot piercing, pipe
welding.
Prof K N Wakchaure

5. HOT WORKING AND COLD WORKING
Advantages:
1. Porosity in the metal is largely eliminated.
2. Impurities in the form of inclusions are broken up and distributed throughout the
metal.
3. Coarse or columnar grains are refined.
4. Physical properties are generally improved owing principally to grain refinement.
Ductility and resistance to impact are improved, strength is increased, and greater
homogeneity is developed
in the metal.
5. The amount of energy necessary to change the shape of steel in the plastic state is
far less than that required when the steel is cold.
Prof K N Wakchaure

6. HOT WORKING AND COLD WORKING
Disadvantages/Limitations of Hot Working
1. rapid oxidation or scaling of the
surface with accompanying poor surface finish.
2. Difficult to achieve close tolerances due to
scaling.
3. Hot working equipment and maintenance costs
are high.
Prof K N Wakchaure

7. HOT WORKING AND COLD WORKING
Cold Working
Properties
l. Cold working is done at temperature below recrystallization temperature.
2. Hardening is not eliminated since working is done below recrystallization
temperature.
3. Decreases elongation, reduction of area etc.
4. Increase in ultimate tensile strength, yield point and hardness.
5. Good surface finish is obtained.
6. Crystallization does not occur. Grains are only elongated.
7. Possibility of crack formation and propagation is great.
8. Internal and residual stresses are developed in the metal.
9. Force required for deformation is high.
10. Heavy and powerful equipment is used for cold working.
11. Easier to handle cold parts.
12. Cold working processes are—cold rolling, cold extrusion, press work
(drawing, squeezing, bending, and shearing).
Prof K N Wakchaure

8. HOT WORKING AND COLD WORKING
Advantages of Cold Working
1. Cold working increases the strength and hardness of the
material due to the strain hardening which would be beneficial in
some situations.
2. Since the working is done in cold state, hence no oxide
formation on the surface and consequently,
good surface finish is obtained.
3. Greater dimensional accuracy is achieved.
4. Easier to handle cold parts and also economical for small sizes.
5. Better mechanical properties are achieved.Prof K N Wakchaure

9. HOT WORKING AND COLD WORKING
Disadvantages/Limitations of Cold Working
1. Only small sized components can be easily worked as
greater forces are required for large sections
2. The grain structure is not refined and residual stresses
have harmful effects on certain properties of metals.
3. Many of the metals have less ductility e.g., carbon steel
and certain alloy steels, cannot be cold worked at room
temperature. It is therefore, limited to ductile metals and the
range of shapes produced is not as wide as can be obtained
by machining.
4. Tooling costs are high and as such it is used when large
quantities of similar components are required.
Prof K N Wakchaure

10. Sr.
No.
Parameters Hot Working Cold Working
1. Recrystalization
temp.
Above Below
2. Residual stresses Not induced Induced
3. Pressure required Lower Higher
4. Grain refinement Yes NO
5. Hardening No Yes
6. Oxidation &
Scaling
Yes NO
7. Closed
dimensional
tolerances
Can not be
maintained
Can be maintained
Prof K N Wakchaure

11. Metal rolling
Prof K N Wakchaure

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16. • Metal rolling is one of the most important manufacturing processes
in the modern world.
• The large majority of all metal products produced today are subject
to metal rolling at one point in their manufacture. Metal rolling is
often the first step in creating raw metal forms.
• The ingot is hot rolled into a bloom or a slab, these are the basic
structures for the creation of a wide range of manufactured forms.
• Blooms typically have a square cross section of greater than 6x6
inches.
• Slabs are rectangular and are usually greater than 10 inches in
width and more than 1.5 inches in thickness. Rolling is most often,
Prof K N Wakchaure

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18. Principles Of Metal Rolling
• Most metal rolling operations are similar in that the work material
is plastically deformed by compressive forces between two
constantly spinning rolls.
• These forces act to reduce the thickness of the metal and effect its
grain structure.
• The reduction in thickness can be measured by the difference in
thickness before and after the reduction, this value is called
the draft.
• In addition to reducing the thickness of the work, the rolls also act
to feed the material as they spin in opposite directions to each
other. Friction is therefore a necessary part of the rolling operation,
but too much friction can be detrimental for a variety of reasons.
• It is essential that in a metal rolling process the level of friction
between the rolls and work material is controlled, lubricants can
help with this. Prof K N Wakchaure

19. Video
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22. • This technique will assist the forces necessary
to form the work, and is usually used on hard
to roll materials.
Prof K N Wakchaure

23. Spreading In Roll Forming
• In metal rolling operations the plastic deformation causing a
reduction in thickness will also cause an increase in the width of
the part, this is called spreading.
Prof K N Wakchaure

24. • Vertical rolls can be employed to edge the
work and maintain a constant width.
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25. Grain Structure In Metal Rolling
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27. Rolls For Forming
• Metal rolling operations can produce a wide range of
different formed products. The width of rolled work can be
as much as several meters, or narrower than a thousandth
of an inch.
• Metal forming manufacture also creates rolled work over a
wide range of thicknesses. Metal plates for some boilers
may be rolled to a thickness of 12 inches, while foil for
wrapping cigarettes and candy can be .0003 inches thick.
• Rolls used in metal forming are of various sizes and
geometries. In flat rolling industrial manufacture, the rolls
may typically be 24 to 54 inches in diameter.
• In some rolling operations, in the forming of very thin work,
the rolls can be as small as 1/4 inch.
Prof K N Wakchaure

28. • Rolls are subject to extreme operating conditions including,
tremendous forces, bending moments, thermal stresses, and wear.
• Roll materials are selected for strength, rigidity, and wear
resistance. Roll materials vary dependent upon the specific forming
process.
• Common roll materials are cast iron, cast steel, and forged steel.
Forged rolls are stronger and more rigid than cast rolls but are
more difficult to manufacture.
• In some industrial forming processes rolls are made from nickel
steel or molybdenum steel alloys.
• With metal rolling operations of certain materials, rolls made of
tungsten carbide can provide extreme resistance to deflection.
Prof K N Wakchaure

29. Roll Deflections
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31. Defects In Metal Rolling
• Surface defects commonly occur due to impurities in the
material, scale, rust, or dirt. Adequate surface preparation
prior to the metal rolling operation can help avoid these.
• Most serious internal defects are caused by improper
material distribution in the final product.
• Defects such as edge cracks, center cracks, and wavy edges,
are all common when metal forming by this method.
• Another interesting defect that can occur in flat rolling is
alligatoring, where the work being rolled actually splits in
two during the process. The two parts of the work material
travel in opposite directions relative to their respective
rolls.
Prof K N Wakchaure

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33. Different Types Of Metal Rolling Mills
• In metal forming industry, rolls themselves do not function
in isolation. In a metal rolling process, rolls stands, bearings,
housing, motors, and other mechanical equipment are all a
necessary part of the manufacturing operation.
• The place where all the equipment for metal rolling
manufacture is set up is called a rolling mill. Rolling mills
often vary in the type, number, and position of rolls.
• Rolling mill arrangements commonly used in manufacturing
industry today include the two high mill, the three high
mill, the four high mill, the cluster mill, and the tandem
rolling mill.
Prof K N Wakchaure

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35. • In the two high reversing mill the direction of spin of the rolls
can be reversed. This enables the work to travel through in
one direction, then back through in the other direction.
• A series of reductions can be made using the same set of rolls,
by passing the work back and forth.
• Disadvantages of the two high reversing mill include the
mechanical requirements and power to constantly overcome
and reverse the angular momentum of the rolls.
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38. • The three high rolling mill utilizes the principle
of passing the work back and forth to achieve
a series of reductions.
• Unlike the two high reversing mill, the three
high mill has three rolls that always spin in the
same direction.
• An elevator mechanism lifts and lowers the
work so that it can be passed back and forth
through the rolls.
Prof K N Wakchaure

39. • It is known that the amount of roll force is reduced
with a smaller radius of the rolls. Smaller radius rolls
however deflect easier and must be supported by
other rolls.
• The four high mill uses this principle with two smaller
work rolls each supported by a larger backing roll.Prof K N Wakchaure

40. • The cluster mill or Sendzimir mill, uses a small work roll
backed up by many other rolls. This extremely rigid setup is
often used for cold rolling high strength material to a very
thin width. Prof K N Wakchaure

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42. Shape Rolling
• Shape rolling is a broad term for a range of metal
rolling operations, that involve forming the work
with rolls of a certain geometry.
• The rolls form the part to a specific shape. Most
shape rolling involves passing the material
through several steps.
• Two very common examples of continuous shape
rolled product are the I beam for structural
purposes and the rail for railroad track.
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45. Video
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47. Ring Rolling
• Ring rolling is a particular category of metal rolling in which a
ring of smaller diameter is rolled into a precise ring of larger
diameter and a reduced cross section.
• This is accomplished by the use of two rollers one driven and
one idle acting on either side of the ring's cross section.
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52. Thread Rolling
• Thread rolling is a metal rolling process used extensively in
manufacturing industry to produce screws, bolts and other
fasteners.
• A common thread rolling process used in industry to manufacture
threaded parts involves forming the threads into the metal of a
blank by a pressing and rolling action between two die.
• The die surfaces hold the shape and the force of the action forms
the threads into the material. A similar metal forming process has
been developed for the production of gears.
• Producing threads by this method has several other benefits over
machining. Forming will harden the metal through cold working,
does not waste material by cutting, and produces a favorable grain
structure to strengthen the part with respect to its function.
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55. Rotary Tube Piercing
• Rotary tube piercing, also called roll piercing,
or the mannesmann process, is a hot forming
process that can manufacture long lengths of
seamless tube and pipe.
• Compressive forces applied to a cylinder will
create internal stresses at the center.
• These stresses result in crack propagation.
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