Aluminum drilling

In the drilling process, the workpiece material is the most important consideration. It determines the geometry of the drill bit, the matrix material and the coating, the coolant, the cutting speed and the feed rate.
Aluminum is known for its softer hardness and better ductility, but there are many misunderstandings in the drilling of aluminum materials.
Many people think that aluminum is one of the most easily processed materials, but aluminum processing also presents unique challenges. Aluminum is usually a soft, ductile non-ferrous metal material with low density and high corrosion resistance. Drilling of aluminum materials is difficult because of its soft texture and ductility, and it makes continuous contact with the rake face or cutting edge of the drill for long periods of time.
Although there are many aluminum alloys with different machinability, the most widely used aluminum alloy grades for drilling are 6061 and 7075. The aviation and medical industries use a small amount of special aluminum alloys.
Aluminum drilling has two major problems: chip formation and chip removal. "If the tool is improperly designed, the tool is uncoated, and coolant is not used, the fibrous, long chips will quickly wrap around the workpiece." Among other challenges, BUE is also a problem. The built-up edge that builds up and sticks to the edges can affect new chip formation and cause the chips to build up and block the chip flutes. The build-up of BUE will cause more chips to stick to the tool and produce more chip accumulation. “Because the aluminum material is soft, the chips are easy to form long chips. The main method to solve this problem is to avoid such problems through a reasonable chipbreaker. The EJ Carbide aluminum milling cutter has a special chip breaker structure for aluminum processing. In the front corner, chip breaking can be effectively performed when processing more sticky 6061. A larger positive rake angle brings greater shear force, which forces the cut material into the chip breaker of the tool.
Jason Hout, global specialist in deep-hole processing products and applications at Sandvik Coromant, pointed out that the main difference between soft aluminum and harder materials is that the cut-off point of aluminum is low enough to be easily cut by the cutting edge of the tool, while cutting The tool will be pushed open when it is harder. This shows that the tool with a large positive rake angle and minimum edge passivation is very suitable for drilling aluminum.
In general, the flutes are drilled with a high helix angle and polished to a drill angle of 130° to 140° to produce the best chip removal and cutting performance. However, because the aluminum material is very soft, it is difficult to ensure the diameter and finish of the hole with this structure of the drill. If you want to ensure the diameter, smoothness and roundness of the hole, it is more advantageous to use internal cold straight groove drilling. "However, the sharp edges are also more fragile. Because many aluminum materials contain a lot of hard-point elemental silicon like glass particles, the cutting edge of the tool can be quickly chipped. Hout pointed out:" Can use coated tool or super Wear-resistant PCD tool to overcome the wear caused by silicon.
When using carbide tools, it is important not to use aluminum-based coatings because the aluminum in the coating is bonded to the workpiece material. Common coatings such as Al2O3 or AlTiN do not react chemically with aluminum when exposed to temperature and pressure, but rub against each other to cause BUE. Hout recommends using titanium diboride or amorphous diamond film coated tools to machine aluminum.
Without a suitable coated tool, polished non-coated tools can also handle most cutting applications. "The flutes are polished to facilitate chip discharge. The flutes are arc-shaped and do not use rectangular sections or straight grooves. However, in some cases, such as gun drilling, this structure is required."
Usually, coated tools are not used for drilling aluminum because most of the coatings contain aluminum.” Since most coatings use aluminum as a basic component, tool manufacturers have started to use zirconium nitride titanium coatings for aluminum machining. "But the traditional processing experience is still the use of sharp, polished non-coated carbide drills to machine aluminum."
Proper chip removal involves the correct use of coolant. Aluminum drilling is no exception. Although boring can always be used, part manufacturers try to avoid it. The drill bit with polished flutes and internal cooling is the customer's first choice.
“Especially for deep-hole machining, the key to the problem is always to remove chips with coolant. This is no exception for aluminum machining. It is not recommended to use countersinks. If you have to use countersinks, it may be because good chips are not formed. It has been found that the concentration of cutting fluid is more important than the type of cutting fluid. In general, the higher the concentration, the better the chip removal effect."