Machinability of Aluminum Alloys

Machinability of Aluminum Alloys

OUTLINES

Introduction.

Definition of Machinability.

Factors Affecting Machinability of Aluminum.

- Role of the properties of the work material. - Conditions for machining operations and processing.

Improving Aluminum Machinability.

Machinability Groupings.

Alloy options for machining.

Conclusion.

References

INTRODUCTION

DEFINITION OF MACHINABILITY

Meaning: there is no clear meaning or unique definition.

Machinability has been referred to:

Machining properties of a work material.

Material response to machining.

Ability of Material to be machined.

How easily and quickly the material can be machined.

The term “machinability” refers to the ease with which a work material can be machined to an acceptable surface finish.

Good Machinability of Material Implies:

Low Power Consumption.

Chips Broken Easily. (favorable: short but uniform without Built up edge)

Tool Life Increase.

Good Surface Finish.

Magnitude of cutting Forces acting against Tool (relatively Low).

such materials are said to be “Free Machining”

FACTORS AFFECTING MACHINABILITY OF ALUMINUM

Four factors affect the machinability of aluminum.

The condition of work materials, the particular alloy, its microstructure, and how uniform its mechanical properties are.

Physical properties those of the individual material groups, such as the modulus of elasticity, thermal conductivity, thermal expansion, and work hardening.

Operating conditions, which includes the type of equipment, the cutting tools, cutting speeds, feed rates and lubricants.

Material processing, which involves the alloy chemistry and heat treatment, the extrusion process controls, the reduction ratio and die design, and whether direct or indirect presses were used.

1) Conditions for machining operations and Aluminum processing :

2) Role of the properties of the work material on machinability:

Basic nature – ductile

Mechanical strength – yield

Density

Microstructure

Modulus of elasticity

Less Hardness

Coefficient of linear expansion

Thermal conductivity




Density

Microstructure


Less Hardness






Density

Microstructure


Less Hardness






Density

Microstructure


Less Hardness



IMPROVING ALUMINUM MACHINABILITY:

Aluminum alloying additions

influence chip formation, material

abrasiveness, surface finish, power

consumed, and many other

machinability related factors.

Some of the alloying additions

and their influences are:

Element Properties

Bi Adds lubricity and aids in chip-breaking

Fe, Mn, Cr,

Ni, Mg, Cu

Combine with each other and also with aluminum and silicon to form

hard intermetallic phases

Mg 0.3% decrease friction between chip and cutting tool, tightens curl of

resultant chip.

Pb Adds lubricity and aids in chip-breaking

Si Increase abrasion on the cutting tool.

Machinability decrease as the size of primary silicon phase increase.

Sn Adds lubricity and aids in chip-breaking

Zn Has no positive or negative influence on machinability

Treatment Given to Metal.

Less Hardness, Less Ductility and less Tensile Strength.

By analyzing the stress vs. strain curve for aluminum, as

the material becomes harder, ductility will become less,

therefore causing a reduction in the amount "toughness“

of the material.

Toughness described analytically is the area under the stress

strain curve, in practical sense it is the amount of energy

the material absorbs for the formation of chips.

Therefore the harder the material become the less tough

and better the machinability will become.

MACHINABILITY GROUPINGS:

Difficulties to define and quantify machinability:

Saying material “A” is more machinable than “B” may mean compared to “B” machining of “A” provides:

Lesser cutting forces, or

Longer tool life, or

Better surface finish

In a group, the order of the material will be different considering different criteria

A,B,C,D,E groupings for most commercial aluminum alloys that specify in increasing order

of chip length and descending order of finish quality

Machinability Ratings

Based on chipping characteristics. Because of the volume of chips created

while machining aluminum, their form takes on great significance.

Generally, the goal in machining aluminum is to generate short, tight chips

that do not interfere with tooling or the surface of the part.

Machinability ratings for aluminum

specify expectations for chips and surface finish:

A-rated: Very small chips, excellent surface finish

B-rated: Curled or easily broken chips, good to excellent finish

C-rated: Continuous chips, good surface finish

D-rated: Continuous chips, satisfactory finish

E-rated: Long, continuous chips, difficult to maintain finish

ALLOY OPTIONS FOR MACHINING

The aluminum industry uses a four-digit index system for the designation

of wrought aluminum alloys. The first digit indicates the major elements

used, along with aluminum, in the alloy.

Alloys in the 6xxx series-among the most widely used in production

machining shops-contain magnesium and silicon.

The most common alloys used in production are 6061, 6042, 6082 and

6262. Each has particular benefits for specific machining needs.

Alloy 6061

Least expensive

Most versatile of the heat treatable aluminum alloys

Good mechanical properties

Good corrosion resistance

It is a candidate for most machining techniques

It is popular for medium to high strength requirements

Good toughness characteristics

Typical applications for alloy 6061

The alloy is most commonly used for transportation components, machinery and equipment,

recreation products, and consumer durables.

Alloy 6262

excellent corrosion resistance to atmospheric conditions

good corrosion resistance to sea water.

good finishing characteristics

responds well to all common anodizing methods,

enhancing resistance to corrosion and wear

Typical applications for alloy 6262

Automotive and truck brake components, air conditioning components, manifolds, hydraulic valve

blocks, electrical and cable components, and hardware and fasteners.

CONCLUSION

REFERENCES

http://www.alueurope.eu/

Aluminum and Aluminum Alloys by Joseph R. Davis.

Aluminum Alloys, Theory and Applications by Prof. Tibor Kvackaj

Tool and Manufacturing Engineers Handbook, Volume 1, Fourth Edition from the Society of Manufacturing

Engineers

http://www.alueurope.eu/

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Machinability of Aluminum Alloys