machinability of aluminum alloys
TRANSCRIPT
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
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
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
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
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
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