The Metal forming process process

By, Satha Siva Pandian.M

2nd year MECH “B”

Metal Atom Forming

The distinction between hot working and cold working does not depends solely on the temperature, but rather on the processing temperature with respect to the material recrystallization temperature. When the processing temperature of the mechanical deformation of steel is above the recrystallization temperature, the process is termed as hot working; otherwise, it is cold working.  For hot working processes, large deformation can be successively repeated, as the metal remains soft and ductile. The hardness of the material cannot be controlled after hot rolling and it is a function of chemical composition and the rate of cooling after rolling. The hardness is generally lower than that of cold rolling and the required deformation energy is lesser as well. 

HOT AND COLD PROCESSES (WORKING)

Types of Extrusion

Types of extrusion: (a) indirect; (b) hydrostatic; (c) lateral;

Direct-Extrusion

Schematic illustration of the direct-extrusion process.

Cold WorkingPlastic deformation which is carried out in a temperature region and over a time interval such that the strain hardening is not relieved is called cold working.

Some Cold Working Processes:

Cold rollingCold forgingCold extrusionBendingDrawingShearing

SCHEMATICSROLLING SCHEMATICS

FORGING SCHEMATIC EXTRUSION SCHEMATIC

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The advantages of cold working

A better surface finish may be achieved

Dimensional accuracy can be excellent because the work is not hot so it doesn't shrink on cooling; also the low temperatures mean the tools such as dies and rollers can last a long time without wearing out.

Usually there is no problem with oxidative effects such as scale formation. In fact, cold rolling (for example) can make such scale come off the surface of a previously hot-worked object.

Controlled amounts of cold work may be introduced.

HOT WORKING Hot working refers to the process where metals are defromed

above their recrystallizatıon tempereture and strain hardening does not occur.Hot working performed at elevated tempreature.However is hot working at room temperature because of its low melting temperature.

Some Hot Working Processes: Rolling Forging Extrusion Hot drawing Pipe welding Piercing

Reason for Hot Working:

At elevated temperatures, metals weaken and become more ductile.

The advantages of hot working Lower working forces to produce a given shape, which means

the machines involved don't have to be as strong, which means they can be built more cheaply;

The possibility of producing a very dramatic shape change in a single working step, without causing large amounts of internal stress, cracks or cold working;

Sometimes hot working can be combined with a casting process so that metal is cast and then immediately hot worked. This saves money because we don't have to pay for the energy to reheat the metal.

Hot working tends to break up large crystals in the metal and can produce a favourable alignment of elongated crystals

Hot working can remove some kinds of defects that occur in cast metals. It can close gas pockets (bubbles) or voids in a cast billet; and it may also break up non-metallic slag which can sometimes get caught in the melt (inclusions).

Types Of Forging

Hand forging :-Hand forging is emplayed only to shape a Usually used for small item forging Hammer forgings :-small number of light forgings chiefly in repair shops.Press forging :- Usually used for heavy item forging.Machine forging :- For medium sized and large articles requiring very heavy blows.Drop forging :- For mass production of identicalparts.

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RollingAluminium is first passed through a hot rolling mill and then transferred to a

cold rolling mill.

Hot rolling mils Prior to rolling the aluminium is in the form of an ingot which can be up

to 600mm thick. This ingot is then heated to around 500°C and passed several times through the hot rolling mill. This gradually reduces the thickness of the metal to around 6mm.This thinner aluminium is then coiled and transported to the cold rolling mill for further processing.

Cold rolling mils:

There are various types of cold rolling mill, and they produce various types of rolled product, with thicknesses as low as 0.05mm. In general the type of product depends on the alloy used, the rolling deformation and thermal treatment used in the process as well as careful adjustments to the mechanics and chemistry of the process. Rolling mills are controlled by very precise mechanisms and measuring systems.

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Operation on a Rectangular Bar

Direct extrusion: A metal billet is located into a container, and a ram compresses the material, forcing it to flow through one or more openings in a die at the opposite end of the container.

Indirect extrusion: The die is mounted to the ram rather than at the opposite end of the container. One advantage of the indirect extrusion process is that there is no friction, during the process, between the billet and the container liner.

Cold Extrusion

Cold extrusion is performed at temperatures significantly below the melting temperature of the alloy being deformed, and generally at room temperature.

The process can be used for most materials, provided that sufficiently robust machinery can be designed.

Products of cold extrusion include aluminium cans, collapsible tubes and gear blanks.

The advantages of cold extrusion are:

No oxidation takes place

Good mechanical properties due to severe cold working as long as the temperatures created are below the re-crystallization temperature

Good surface finish with the use of proper lubricants

So….cheap, convenient way to strengthen mat'ls

Work hardening

On the other hand, work hardening can be problem

Example: cold rolling plate to sheet

platesheet

too hard to continue

rolling

harder harder!!

extremely hard - need backup rollsto keep work rolls from deforming

fairly soft

Press Forging

HYDRAULIC PRESSES:-

– Slower– More massive– More costly to operate. – usually more flexible– Have greater capacity. – Can be programmed to have different

strokes for different operations and even different speeds within a stroke.

Thank You!