Manufacturing engineering - METAL FORMING

In this lecture you will understand about different terminologies of raw material (Such as billet,bloom,slab etc) used in rolling process.

The process of shaping metals into semi-finished or finished forms by passing between rollers is called rolling. Rolling is the most widely used metal forming process. It is employed to convert metal ingots to simple stock members like slabs, sheets, plates, beams, channels, angles, rods and strips etc.

In rolling, the metal is plastically deformed by passing it between rollers rotating in opposite direction. The main objective of rolling is to decrease the thickness of the metal. Ordinarily, there is negligible increase in width, so that the decrease in thickness results in an increase in length.

Rolling is done both hot and cold. It is accomplishes in rolling mills. A rolling mill is a complex machine having two or more working rollers, supporting rollers, roll stands, drive motor, reducing gear, flywheel, coupling gear etc.

Rollers may be plain or grooved depends upon the shape of rolled product. The metal changes its shape gradually during the period in which it is in contact with the two rollers.

PS - This lecture is the first part for understanding rolling mechanism in detail. Don't forget to see the second part in the next lecture.

The process of shaping metals into semi-finished or finished forms by passing between rollers is called rolling. Rolling is the most widely used metal forming process. It is employed to convert metal ingots to simple stock members like slabs, sheets, plates, beams, channels, angles, rods and strips etc.

In rolling, the metal is plastically deformed by passing it between rollers rotating in opposite direction. The main objective of rolling is to decrease the thickness of the metal. Ordinarily, there is negligible increase in width, so that the decrease in thickness results in an increase in length.

Rolling is done both hot and cold. It is accomplishes in rolling mills. A rolling mill is a complex machine having two or more working rollers, supporting rollers, roll stands, drive motor, reducing gear, flywheel, coupling gear etc.

Rollers may be plain or grooved depends upon the shape of rolled product. The metal changes its shape gradually during the period in which it is in contact with the two rollers.

PS - This lecture is the second part for understanding rolling mechanism in detail. Don't forget to see the first part in the previous lecture.

In materials science, slip is the large displacement of one part of a crystal relative to another part along crystallographic planes and directions. Slip occurs by the passage of dislocations on close packed planes which are planes containing the greatest number of atoms per area and in close-packed directions (most atoms per length).

For greater reduction, more frictional force is required, and because it is not available, the rolls start slipping over the strip. Thus it is that maximum possible reduction is achieved when the neutral point is at the exit, that is, when the exit velocity is equal to the circumferential roll velocity.

All the concerned mathematical deductions are explained in this lecture.

Mathematical deductions of rolling force and power is discussed in this lecture.

There is a need to reduce rolling force and power in order to get desired shape and size of the product. This is accomplished by several means as explained in this lecture.

As per the requirement of the process and arrangement of the rolls, the rolling mill rolls can be divided into the following categories:

1.Two High Rolling Mills
It consists of two rollers, which rotate in the opposite direction for the desired movement of the workpiece. The workpiece is fed between the rollers, which apply a full force, and tends to deform a workpiece and convert it into the desired shape. If you want a robust and quality two high rolling mill, you can look for mill rolls manufacturers to know which one suits your purpose.

The two high rolling mills are further divided into two more categories namely high non-reversible machine in which rollers rotate in only one direction, and the workpiece can be fed in only one direction. On the other hand, the second one high reversible machine, which both rollers rotate in both directions.

2.Three High Rolling Mills
The Three High Rolling Mills comprises of a roll stand with three parallel rolls one above another. The adjacent rolls rotate in the opposite direction to pass the material between the top and middle roll in single direction, and the bottom and central roll in the opposite direction. The workpiece is rolled on both forward and return passes. The workpiece passes through the bottom and intermediate rolls, and returns between the middle and top rolls. Various steel roll manufacturers provide top-quality roll mills to meet every type of industrial requirement.

3.Four High Rolling Mills
The Four High Rolling Mills have a roll stand with four parallel rolls placed one above another. The top and bottom rolls work in the opposite direction. The two in the middle are smaller than the top and bottom rolls, which are also known as backup rolls.

4.Tandem Rolling Mills
The Tandem Rolling Mills comprises of a set of two or three strands of roll set in parallel alignment. A continuous pass might be possible through each one with the change in the direction of the material. Many mill rolls manufacturers provide quality tandem rolling mills to various industries.

5.Cluster Rolling Mills
Cluster Rolling Mills is a first four high rolling mills, where each of the working rolls is backed up by two or more larger rolls for rolling hard material. At times, one might need to employ work rolls of minimum diameter.

Roll pass design generally means the cutting of grooves in the roll body through which steel to be rolled is made to pass sequentially to get the desired contour and size. Roll pass design is a set of methods for determining the dimensions, shape, number, and type of arrangement of rolling mill passes.

Edge Cracks

During both hot and cold rolling, the metal might show some cracks on the edges. This phenomenon occurs from secondary tensile stresses induced at the workpiece surfaces. These cracks result from factors such as uneven heating, uneven rolling, or excess quenching.

Wavy Edges

One of the most common rolling defects is the occurrence of fibers at the edge, which are longer than those at the center. This occurs when concave rolls bend leading to elastic deformations. Thickness at the center implies that the edges are more elongated.

Zipper Cracks

The occurrence of small cracks in the middle of the metal sheet explains this phenomenon. Mostly, zipper cracks occur due to the bending of rolls under the high rolling pressure. It causes compressive stress in the edges and tensile stress in the center. It’s this tensile stresses induced at the workpiece by homogeneous deformation that leads to the formation of zipper cracks.

Surface-based defects in hot rolling processes like scale, rust, scratches, cracks, pits, and gouges can significantly impact product quality and durability. Internal structure-based defects in hot rolling, such as wavy edges, zipper cracks, edge cracks, alligatoring, folds, and laminations, often arise due to improper control of material flow, temperature, or rolling forces.

In this lecture you are going to understand how to create a production report for a structural rolling mill.

Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section. The extrusion process can be done with the material hot or cold. Commonly extruded materials include metals, polymers, ceramics, concrete, modelling clay, and foodstuffs.

Various types of extrusion process is explained in this lecture.

Some of the important formula were discussed here regarding extrusion process.

Various advantages and drawbacks of extrusion process is discussed in this lecture.

Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die.

Mathematical formulae for drawing process explained in detail in this lecture.

Tube drawing is a process to size a tube by shrinking a large diameter tube into a smaller one, by drawing the tube through a die. This process produces high-quality tubing with precise dimensions, good surface finish, and the added strength of cold working.

Forged steel is generally stronger and more reliable than castings and plate steel due to the fact that the grain flows of the steel are altered, conforming to the shape of the part.

In this lecture, various types of forging being discussed.

The forgeability of a metal can be defined as its capability to undergo deformation by forging without cracking Metal which can be formed.

A brief analysis of forging process is discussed here.

1.Drawing

This is the operation in which metal gets elongated with a reduction in the cross sedation area. For this, a force is to be applied in a direction perpendicular to the length axis.

2.Up-setting

This is applied to increase the cross sectional area of the stock at the expanse of the length. To achieve the length of upsetting force is applied in a direction parallel to the length axis, For example forming of a bolt head.

3.Fullering

Material cross-section is decreased and length increased.

4.Edging

It is a process in which the metal piece is displaced to the desired shape by striking between two dies edging is frequently as primary drop forging operation.

5.Bending

Bending is very common forging operation. It is an operation to give a turn to metal rod or plate. This is required for those which have bends shapes.

Common defects of forging -

1) Unfilled Section:
As the name implies in this type of defect some of the forging section remain unfilled. This is due to poor design of die or poor forging technique. This is also due to less raw material or poor heating. This defect can be removed by proper die design, proper availability of raw material and proper heating.

2) Cold Shut:
Cold shut includes small cracks at corners. These defects occur due to improper design of forging die. It is also due to sharp corner, and excessive chilling in forging product. The fillet radius of the die should be increase to remove these defects.

3) Scale Pits:
Scale pits are due to improper cleaning of forged surface. This defect generally associated with forging in open environment. It is irregular deputations on the surface of forging. It can be removed by proper cleaning of forged surface.

4) Die Shift:
Die shift is caused by misalignment of upper die and lower die. When both these dies are not properly aligned the forged product does not get proper dimensions. This defect can be removed by proper alignment. It can be done by provide half notch on upper die and half on lower die so at the time of alignment, both these notches will matched.

5) Flakes:
These are internal cracks occur due to improper cooling of forge product. When the forge product cooled quickly, these cracks generally occur which can reduced the strength of forge product. This defect can be removed by proper cooling.

6) Improper Grain Growth:
This defect occurs due to improper flow of metal in casting which changes predefine grain structure of product. It can be removed by proper die design

7) Incomplete Forging Penetration:
This defect arises due to incomplete forging. it is due to light or rapid hammer blow. This defect can be removed by proper control on forging press.

8) Surface Cracking:
Surface cracking occurs due to exercise working on surfaces at low temperature. In this defect, So many cracks arise on work piece. This defect can be removed by proper control on working temperature.

9) Residual Stresses in Forging:
This defect occurs due to improper cooling of forged part. Too much rapid cooling is main causes of this type of defects. This can be removed by slow cooling of forged part.

Sheet metal is one of the most versatile and widely used construction materials, with applications in just about every industry imaginable from mining, construction, farming, catering, hospitality, shipping, manufacturing, aviation, medical and transport.

But sheet metal isn’t only used in industrial situations – we find it in many domestic applications too, such as a metal surround on a kitchen bench top, in a home appliance or as a unique punched metal screen used as an interior design feature.

As a product however, sheet metals (including stainless steel, steel, mild steel and aluminium) do provide a host of advantages whether it’s for engineers, contractors or even the man-in-the-street. Let’s take a look at some of these advantages:

• Sheet metal has a low weight to thickness ratio, which means it’s easy to transport and easy to work with.

  
  

• Sheet metal is extremely strong and durable, making it the ideal high-strength material in a diversity of applications from harsh agricultural environments (e.g. sheep feeders and wheat bins) and high traffic environments (e.g. stair treads or metal scaffold planking) to extreme temperatures (e.g. industrial washing machines and ovens).

  
  

• Sheet metal is malleable, which means it can be formed, cut, bent or stretched into just about any shape, allowing sheet metal fabricators to offer their customers highly specialized solutions and custom-designs to meet just about any specification.

  
  

• Sheet metal can also be repaired relatively easily, which makes it a practical choice in many different applications.

  
  

• Its relatively low cost is also an advantage in both one-off design situations and in situations involving large quantities for mass production.

Both blanking and punching are material forming processes that involve the precise removal of material from a workpiece. The main difference between the two processes lies in the end product produced.

In blanking operations, the final part or product is removed or “punched-out” out of the larger sheet material, with the remaining material being discarded as scrap. On the other hand, in punching operations, the material removed is discarded, and the final product is the remaining material which then undergoes further processing.

Different Types of Sheet Metal Operations are:

• Shearing Operation

• Blanking & Fine Blanking Operation

• Punching Operation

• Piercing Operation

• Perforating Operation

• Slotting Operation

• Notching Operation

• Bending Operation

CONCLUSION - I hope you have liked the course. Please do find the complete content in pdf format attached in this lecture's resource. All the very BEST !!

So this here is the last lecture of the course. I hope you understood everything. The complete contents are attached herewith.

All the very BEST !!