Making a Metal Machinable

I welcome a better machinable aluminum alloy. When will it be available to small users like myself? and how will I be able to identify it from the current alloys?

I used to cast Tenzaloy (AA713) and machined a bit of it to check for porosity or shrinkage. It cut like butter and chips were clean. Many of my customers loved it and they were machining blow molds and other items where a smooth finish was necessary. It is a self aging alloy which develops almost full strength after 10 days. Had one customer who would pick it up the day after we cast it and still say it machined better at that stage than most other aluminum alloys. He likened it most to 2014 wrought plate as far as machine-ability. You can actually artificially age it at 250 degree F for 8-10 hours and achieve max properties if you're in a hurry. It was the material used to cast an 8 foot diameter parabolic mirror for a telescope. Obviously had to be highly polished and have a tight grain and smooth surface in order to act as a mirror.

The term "machinability" refers to the ease with which a metal can be machined to an acceptable surface finish.As compared with other construction materials, aluminum is relatively easy to machine then the other metals. It responds well to most of the fabrication methods including milling, drilling and cutting etc.The three factors that affect the machinability of aluminum are:-1.The first factor is the machining process, that includes all the types of equipment, the cutting tools, cutting speeds and feed rates2. The second factor involves the material-specifically, the particular alloy and temper of the aluminum, its microstructure, and how uniform its mechanical properties are. . 3.The third factor is the material processing, which involves the alloy chemistry, heat treatment, the extrusion process controls, the reduction ratio and die design, and whether direct or indirect presses were used in extruding of aluminum.Machinability ratings for aluminum are based on chipping characteristics. 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

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 machine production are 6061, 6042, 6082 and 6262. Each has particular benefits for specific machining needs.1.Alloy 6061:- It is one of the most widely used in the 6000 series, and for good reason. The least expensive and most versatile of the heat treatable aluminum alloys, 6061, offers a range of good mechanical properties along with good corrosion resistance.

For screw machine applications, alloy 6061 has adequate machinability characteristics in the heat-treated T6/T6511 condition. Chips from turning and drilling can be difficult to break in the T6/T6511 temper condition. For that reason, chipbreakers and special machining techniques, such as peck drilling, should be considered in order to improve chip formation. The alloy is most commonly used for transportation components, machinery and equipment, recreation products, and consumer durables.

2.Alloy 6082:- It is very common in Europe and is gaining popularity in the U.S., offers similar-though not identical-physical characteristics to the 6061 alloy, along with slightly higher mechanical properties in the -T6 condition. This alloy is a good choice for structural applications, including rod, bar, tube and profiles. It offers good finishing characteristics and responds well to anodizing. The most common anodizing methods include clear, clear and color dye, and hard coat.

The alloy also offers good welding and brazing capabilities, corrosion resistance, formability and machinability. When bending or forming 6082 alloy, the -0 or -T4 temper should be used. For machining applications, 6082 provides good machinability in the -T5 or -T6 tempers. Chips may be difficult to break, so chipbreakers or special machining techniques such as peck drilling should be used to improve chip formation. For certain thin-wall sections, -T6 temper may not be available because of alloy quenching limitations.

Various commercial joining methods, such as welding or brazing, can be easily applied to 6082 alloy. However, since it is a heat treatable alloy, strength will be reduced in the weld region. For machining applications, alloy 6082 is available in many rod, bar and hex sizes.

3. Alloy 6262:- It is probably familiar to most machine shops, as it is the alloy of choice for applications requiring improved machinability. This alloy is one of the few developed specifically for machining applications, including screw machine and CNC machine products.

Sapa offers the alloy with a variety of standard and special tempers, and to further enhance its machinability, a unique chemical analysis has been developed that conforms to industry standards. Sapa produces extruded 6262-T6 and -T6511, which are listed in ASTM B 221 and ASTM B 241 specifications. For machining applications, alloy 6262 is available in many rod, bar and hex sizes.

For screw machine applications, alloy 6262 has good machinability characteristics in the heat treated -T6, and -T6511 condition. Generally, the alloy produces curled and broken chips while machining. However, in certain applications, the use of chipbreakers or special machining techniques, such as peck drilling, can further improve chip formation.

This alloy has excellent corrosion resistance to atmospheric conditions and good corrosion resistance to sea water. This alloy also offers good finishing characteristics and responds well to all common anodizing methods, enhancing resistance to corrosion and wear. The most common anodizing methods are clear, clear and color dye, and hard coat.

Joining characteristics for welding and brazing of alloy 6262 are significantly improved over alloy 2011, although they are not as good as alloy 6061.

In addition to excellent product, machine shops can enhance machinability by paying close attention to tools and processing. Aluminum is most successfully machined with tools made of tool steel, high-speed steel, cemented carbides and diamond. Ceramic cutting materials are not recommended. Because of its chemical affinity for aluminum, ceramic will not deliver an acceptable operating life. Similarly, the synthetic cutting materials that are used successfully for machining steel are not a good choice for aluminum.

After the proper tools have been selected, other important considerations will also contribute to improved machinability:

• Tools and toolholders must be rigid.
• Tools should have a finely ground edge to minimize buildup.
• Cutting edges should be kept sharp at all times.
• Chips must be directed away from the workpiece or broken up by a chipbreaker to prevent part damage.
• Productivity can be improved by increasing speeds while maintaining feed rates and cutting at moderate depths.
• Excessive cutting pressures should be avoided unless the workpiece is adequately supported.
• Lower feed rates should be used on thin-walled parts.
• Recommended rake angles should be used to reduce cutting forces, thus producing thinner chips and reducing metal buildup.
• Coolant feed drills and high-pressure coolant feed systems should be used.

Rake angle, feed rates, drilling recommendations and lubricant choices are also important to consider when machining aluminum. Extruders can supply detailed recommendations for product that is selected.

After all that we may come to a conclusion that:-

Aluminum remains one of the most machinable metals available. With its reputation for strength and lightness, it continues to be a preferred metal by customers in a range of industries. Extruders and machine production shops enjoy a strong partnership. The extrusion industry remains committed to supplying machine shops with product that features consistent grain structure, tighter dimensions and higher mechanical properties and no other metal can replace Aluminium because of it's very high importance and all these discussed above properties.