MACHINABILITY OF ALUMINIUM ALLOYS

CONTENT:

Definition of Machinability Machinability of Aluminum Alloys How to improve the mach inability of Al

alloy? Cutting force during machining of

aluminum alloys Chip formation and chip segmentation Surface of Machined Aluminium Alloys MACHINABILITY RATINGS

DEFINITION OF MACHINABILITY:

The term machinability refers to the ease with which a metal can be machined to an acceptable surface finish

The term machinability includes all those properties which are relevant for the machining and cutting process:

the wear of tools the necessary cutting force the resulting form of the chips the quality of the surface produced

DEFINITION OF MACHINABILITY:

Then. Machinability is not a material property which

can be defined using a single characteristic parameter. It is, in fact, a complex technological term.

The machinability depends on both the physical and chemical properties of the material_ aluminum as well on the fabrication process used to produce it_.

MACHINABILITY OF ALUMINUM ALLOYS

The use of materials with low specific weight is an effective way of reducing the weight of structures

Aluminum alloys are among the most commonly used lightweight metallic materials as they offer a number of different interesting mechanical and thermal properties.

In fact, aluminum alloys as a class are considered as the family of materials offering the highest levels of machinability, as compared to other families of lightweight metals such as titanium and magnesium alloys.

MACHINABILITY OF ALUMINUM ALLOYS

Aluminum alloys are classified under two classes: cast alloys and wrought alloys

Most wrought aluminum alloys have excellent machinability.

While cast alloys containing copper, magnesium or zinc as the main alloying elements can cause some machining difficulties

HOW TO IMPROVE THE MACHINABILITY OF AL ALLOY? The machinability of alloys can be improved

by different treatment.

Heat treatments, which increase hardness, will reduce the built-up edge tendency during machining.

It has been found that heat treatment of 6061 especially,aging influences the forces only at low cutting speeds, while at high speeds, the influence is negligible because of the low temperature rise seen in the cutting zone.

CUTTING FORCE DURING MACHINING OF ALUMINUM ALLOYS

While the cutting forces during the machining of aluminum alloys are relatively low, they can nevertheless provide a good indicator for a comparison of different alloys under the same machining conditions.

A typical cutting force signal acting on the cutter in the axial direction (thrust force Fz) during drilling is presented in Figure.

CUTTING FORCE DURING MACHINING OF ALUMINUM ALLOYS

Portion a-b of the graph corresponds to the drill point engagement into the workpiece

while the portion b-c corresponds to the real cutting. Portion b-c is usually employed to estimate the cutting force or the energy required to shape metals.

CUTTING FORCE DURING MACHINING OF ALUMINUM ALLOYS

Using an enlarged graph, It is possible to identify the action of each flute of the cutter during the cutting process.

CHIP FORMATION AND CHIP SEGMENTATION

The chip shape and microstructure constitute a good indicator of the deformation having

occurred during the machining process. Several research works have analyzed chip

formation in order to identify the optimal conditions for improving machining and machinability.

Several tests were carried out in the laboratory in order to characterize the chip shape during the machining of aluminum alloys.

Following Figure presents the chip morphology obtained from scanning electronic microscopy (SEM) as a function of cutting speed

SURFACE OF MACHINED ALUMINIUM ALLOYS

In general, the quality of the surface produced by machining depends on three independent parameters:

The kinematical roughness The machined surface roughness External influences

SURFACE OF MACHINED ALUMINIUM ALLOYS

MACHINABILITY RATINGS:

Machinability ratings are “relative” ratings.They compare the ease of machining an alloy to a standard.

TABLES: The tables on the below pages contain

machinability ratings for many alloys. The tables in this Skill Builder were obtained from Tool and Manufacturing Engineers Handbook, Volume 1, Fourth Edition from the Society of Manufacturing Engineers.

MACHINABILITY RATINGS:

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