Metal Forming Operations

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is metal forming also known as?

Metallurgical processing of metals

Chemical processing of metals

Mechanical working of metals (correct)

Thermal treatment of metals

What is the primary objective of metal working processes?

To increase the cost of the metal

To decrease the strength of the metal

To achieve the desired shape and size (correct)

To remove impurities from the metal

What happens to impurities present in the metal during plastic deformation?

They get eliminated from the metal

They get elongated with the grains and broken (correct)

They remain unaffected

They increase in quantity

What is the term for the stress that causes plastic deformation in a metal?

Yield point Signup and view all the answers

What are the two common phenomena governing plastic deformation of a metal?

Deformation by slip and deformation by twin formation Signup and view all the answers

What is the term for the portion of the grains covered between two parallel planes during deformation?

Twinned region Signup and view all the answers

What is the primary reason for the increase in plasticity at higher temperatures?

The bond between atoms of the metal grains is reduced Signup and view all the answers

What is the property of a material that enables it to be drawn into wire with the application of tensile force?

Ductility Signup and view all the answers

What is the process of making a metal harder and stronger through plastic deformation?

Strain hardening Signup and view all the answers

What is the result of continued bending of a metal wire, leading to eventual breakage?

Fatigue cracking Signup and view all the answers

What occurs when strain hardened materials are exposed to elevated temperatures?

The strengthening due to strain hardening is lost Signup and view all the answers

What is the result of the recovery phase in heat treatment?

An adjustment of strain on a microscopic scale and improved corrosion resistance Signup and view all the answers

What is the primary factor that determines the grain size after recrystallization?

The amount of strain hardening Signup and view all the answers

What is the result of grain growth during heat treatment?

Larger grains that reduce the strength and toughness of the material Signup and view all the answers

What is the primary purpose of the embossing process in cold working?

To produce a stiffening effect in the metal Signup and view all the answers

What is the primary concern when starting and stopping hot work on a metal?

Preventing excessive work hardening and overheating Signup and view all the answers

What is a significant advantage of hot working over cold working?

Higher ductility and less force required Signup and view all the answers

What is the primary requirement for the metal to be used in the hot working process?

High plasticity Signup and view all the answers

Which of the following is a limitation of hot working?

Rapid oxidation and scale formation Signup and view all the answers

What is the primary purpose of cold working?

To achieve better surface finish and increased mechanical properties Signup and view all the answers

What is the effect of hot working on the grain structure of the metal?

It refines the grain structure Signup and view all the answers

What happens to the surface layer of a steel piece during hot working?

It loses its strength due to the loss of carbon Signup and view all the answers

What is the primary advantage of hot working over cold working?

It can produce large deformations without work hardening Signup and view all the answers

What is the effect of hot working on the mechanical properties of the metal?

It produces the same net results as cold working and annealing Signup and view all the answers

What is the advantage of cold working over hot working?

Better dimensional accuracy is achieved Signup and view all the answers

What is the purpose of bending in sheet metal manufacturing?

To increase the strength and stiffness of the sheet metal Signup and view all the answers

What is the result of strain hardening in cold working?

Increase in strength and hardness Signup and view all the answers

What is the primary purpose of rolling in metal forming?

To break down ingots into wrought products Signup and view all the answers

What is the problem associated with hot rolling?

Scaling and lack of dimensional accuracy Signup and view all the answers

What is the term for the cast metal with porosity and blowholes?

Ingot Signup and view all the answers

What is the minimum cross-sectional area of a bloom?

230 square centimeters Signup and view all the answers

What is the characteristic of a slab?

Width is greater than or equal to three times of its thickness Signup and view all the answers

What is the minimum cross-sectional area of a billet?

40 square centimeters Signup and view all the answers

What is the type of rolling mill used in pluming and slabing mills and for roughing work?

Two high reversing mill Signup and view all the answers

In what type of rolling mill does the work piece pass through the bottom and middle rolls and then the middle and top rolls?

Three high rolling mill Signup and view all the answers

What is the characteristic of a plate?

Thickness is greater than 6 mm Signup and view all the answers

What is the characteristic of a sheet?

Thickness is less than 6 mm and width is greater than 60 cm Signup and view all the answers

What is the characteristic of a strip?

Thickness is less than 6 mm and width is less than 60 cm Signup and view all the answers

What type of rolling mill is used for the hot rolling of armor and other plates as well as cold rolling of plates, sheets, and strips?

Four high rolling mill Signup and view all the answers

What is the advantage of a three high rolling mill over a two high rolling mill?

Less powerful motor and transmission system is required Signup and view all the answers

Study Notes

Metal Forming

Metal forming operations are used to produce a new shape or improve the properties of a metal.
Shaping in the solid state can be divided into non-cutting shaping (e.g., forging, rolling, pressing) and cutting shaping (e.g., machining operations).

Plastic Deformation

Plastic deformation occurs when a metal is deformed beyond its elastic range.
The main objectives of metal working processes are to provide the desired shape and size, improve mechanical properties, and reduce internal voids or cavities.
Metals are commonly worked by plastic deformation, which can be achieved by applying mechanical force or heating the metal and then applying a small force.

Strain Hardening

Strain hardening (also known as work-hardening or cold-working) is the process of making a metal harder and stronger through plastic deformation.
Dislocations move and interact with each other, resulting in a decrease in their mobility and a strengthening of the material.
Strain hardening can be demonstrated by bending a wire or paper clip repeatedly.

Effects of Elevated Temperature on Strain Hardened Materials

When strain hardened materials are exposed to elevated temperatures, the strengthening that resulted from the plastic deformation can be lost.
Heat treatment can be used to remove the effects of strain hardening, which involves three stages: recovery, recrystallization, and grain growth.

Recovery

Recovery occurs when a stain hardened material is held at an elevated temperature, allowing atoms to move to unstrained positions and relieve internal strain energy.
This results in a reduction in internal residual stresses and a movement of dislocations to lower-energy positions.

Recrystallization

Recrystallization occurs at a higher temperature, where new, strain-free grains nucleate and grow inside the old distorted grains and at the grain boundaries.
This results in a return to the original weaker and more ductile states of the material.

Grain Growth

Grain growth occurs when a specimen is left at a high temperature beyond the time needed for complete recrystallization.
This results in a decrease in the strength and toughness of the material.

Embossing

Embossing is a process that involves stretching a metal sheet to shape under pressure using a punch and a die.
This process gives a stiffening effect to the metal and can produce ornamental wares.

Coining

Coining is a cold working operation that involves producing shallow configurations on a metal surface using a die and a punch.
This process is used for producing important articles such as medals, coins, and stickers.

Bending

Bending is a common process in the manufacturing industry that involves the plastic deformation of a metal sheet over an axis.
This process changes the shape of the workpiece while maintaining its volume.

Hot Working

Hot working is a mechanical working process that occurs above the recrystallization temperature of the metal.
This process is used to produce large deformations and can result in a refined grain structure and improved mechanical properties.

Effects of Hot Working on Mechanical Properties of Metals

Hot working can produce a refined grain structure and improve mechanical properties.
It can also reduce the stresses required to produce deformations and increase the possible amount of deformation.
Hot working can result in a uniform distribution of impurities and improve the surface finish of the metal.

Merits of Hot Working

Hot working can be used to achieve large deformations without strain hardening.
It can improve the grain structure and mechanical properties of the metal.
It can also reduce the stresses required to produce deformations.

Demerits of Hot Working

Hot working can result in a poor surface finish due to oxidation and scaling.
It can also lead to a loss of carbon from the surface of the steel, resulting in a loss of strength.

Cold Working

Cold working is a mechanical working process that occurs below the recrystallization temperature of the metal.
It is used to obtain better surface finish, increase mechanical properties, and produce thinner materials.

Purpose of Cold Working

Cold working is used to obtain better surface finish and increase mechanical properties.
It is also used to produce thinner materials and improve the dimensional accuracy of parts.

Limitations of Cold Working

Cold working can result in a decrease in ductility and an increase in strain hardening.
It requires higher forces and more powerful equipment than hot working.
It can also result in a distortion of the grain structure and the formation of internal stresses.

Advantages of Cold Working

Cold working can produce a smooth surface finish and accurate dimensions.
It can increase the strength and hardness of the material.
It can also result in better dimensional accuracy and a reduction in distortion.

Disadvantages of Cold Working

Cold working can result in a distortion of the grain structure and the formation of internal stresses.
It can also limit the amount of deformation that can be given to the material.
It requires higher forces and more powerful equipment than hot working.

Rolling

Rolling is a metal forming operation that involves the plastic deformation of a material caused by compressive force applied through a set of rolls.
It is used to produce a wide range of products, including blooms, billets, plates, and sheets.
Rolling can be done at high or low temperatures, depending on the desired outcome.### Rolling Process
Hot rolling produces residual stress-free products, but scaling is a major problem, affecting dimensional accuracy.
Cold rolling is gaining importance for sheets, foils, etc., due to high accuracy and lack of oxide scaling, and also strengthens the product through work hardening.

Rolling Mills

Rolling is a major manufacturing process for sheets and other cross-sections of large length, such as I beams, railroads, etc.
It involves compressing a metal workpiece between a set of rolls, reducing its cross-section area and increasing its length.
This process offers high production rates, surface finish, and grain structure, but has high setup costs.

Terminology

Ingot: a cast metal with porosity and blowholes, soaked at 1200°C and rolled into blooms, billets, or slabs.
Blooms: the first rolled product, made by rolling ingot at high temperature, with a cross-section area ≥ 230 cm².
Slab: made by hot rolling of ingot, with a cross-section area ≥ 100 cm² and width ≥ 3 times its thickness.
Billets: made by hot rolling of blooms, with a cross-section area ≥ 40 cm², used to roll into pipes, bars, wire, etc.
Plate: a product of further rolling of slab, with a thickness > 6 mm.
Sheet: a product with a thickness < 6 mm and width > 60 cm.
Strip: a product with a thickness < 6 mm and width < 60 cm.

Types of Rolling Mills

Two high reversing mill: rolls rotate in one direction and then in the other, allowing the metal to pass back and forth through the rolls several times.
Two high non-reversing mill: rolls revolve continuously in one direction, requiring smaller and less costly motive power.
Three high rolling mill: consists of three parallel rolls, with adjacent rolls rotating in opposite directions, reducing thickness at each pass.
Four high rolling mill: used for hot rolling of armor and other plates, as well as cold rolling of plates, sheets, and strips.
Tandem rolling mills: used for rolling multiple stands in a continuous process.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about metal forming, also known as mechanical working of metals, including non-cutting shaping processes like forging and rolling, and cutting shaping like machining operations.