Difficulties and Improvement Measures of Aluminum Drilling

Drilling in CNC machining, raw material is the most important influencing factor, it affects the selection of drill shape, material, coating, coolant, cutting speed and feed speed, this article jiahangaero will describe the CNC drilling of aluminum alloy Difficulties and improvement measures.

Aluminum has the characteristics of soft hardness and good ductility, which will give people the illusion that aluminum processing is very easy. In fact, aluminum processing is also very difficult. Because aluminum is usually used in our daily life in the form of aluminum alloy, and because there are many types of aluminum alloys, their properties vary greatly, so it is a science to understand the characteristics of various aluminum alloys and adopt different processing strategies.

Aluminum alloys will form a large amount of aluminum chips during CNC drilling. The treatment of aluminum chips is very important. If the shape of the tool is not designed properly, without coating, and without the use of coolant, aluminum chips will form tumors on the CNC tool. When the accumulation of aluminum chips is generated and bonded to the cutting edge, it will affect the subsequent formation of aluminum chips. This is a chain reaction, which will eventually lead to the accumulation of aluminum chips and block the chip discharge groove. Because aluminum is soft, aluminum chips are often long chips during CNC machining. The main solution is to avoid such problems through reasonable chip breakers. The use of a chip breaker structure with a large positive rake angle can effectively form chip breaks during machining. The greater positive rake angle brings greater shear force, forcing the aluminum chip being cut into the chip breaker of the tool.

The main difference between drilling a soft material like aluminum and a harder material is that aluminum has a low enough intercept point that it can be easily cut, whereas cutting harder materials pushes the tool away. Typically, the flutes are high helix and polished, and drills with a point angle of 130° to 140° produce the best chip evacuation and cutting performance. However, because the aluminum material is very soft, it is difficult to guarantee the diameter error and smoothness of the hole when processing it with a drill bit of this structure. If it is necessary to ensure the roundness, error and finish of the hole, it is more advantageous to use a straight groove drill with internal cooling. Compared with aluminum, aluminum alloy contains a large amount of silicon, a hard point element like glass particles, which will cause the cutting edge of the tool to chip quickly. Silicone-induced wear can be overcome with coated tools or super-abrasive PCD tools.

When using carbide tools, it is important not to use aluminum-based coatings, because the aluminum in the coating will bond to the workpiece material, and if suitable coated tools are not available, polished non-coated tools can also cope Most cutting occasions. Chip flutes are polished for easy chip removal. The chip flute adopts a circular arc cross-section, and may not use a rectangular cross-section or a straight groove. But in some occasions, such as gun drilling processing, this structure is required.

Use fine-grained cemented carbide with a hardness of 92~93HRA to process low-silicon aluminum alloys. But for wrought or cast aluminum alloys, PCD brazed tools or diamond-like carbon (DLC) tools can be used. Aluminum is usually not drilled with coated tools because most coatings contain aluminum. Since most coatings have aluminum as a base, toolmakers are turning to titanium zirconium nitride coatings for aluminum machining. But traditional machining experience still uses sharp, polished, uncoated carbide drill bits to machine aluminum. "

Proper chip evacuation involves proper use of coolant. Drilling is no exception. While peck drilling is always available, part manufacturers try to avoid it. Drills with polished flutes and internal coolant are the first choice for customers. Especially for deep hole machining, the crux of the matter is always chip removal with coolant. This is no exception for aluminum machining. Peck drilling is not recommended. If you have to use pecking, it's probably because you haven't formed a good chip. It has been found that the concentration of the cutting fluid is more important than the type of cutting fluid. Generally speaking, the higher the concentration, the better the chip removal effect. High metal removal rates require rapid application of large volumes of coolant to dislodge chips from the cutting zone. Metal removal rates for aluminum machining are typically very high. The greater the flow rate and the higher the pressure of the coolant, the better the chip removal effect will be. Coolant may be applied intermittently, but the semi-dry cutting method with minimal lubrication is not suitable for drilling, especially deep hole machining.

When machining aluminum with a gun drill, the pressure in the pilot hole can positively or negatively affect the hole finish, depending on the lubricating properties of the coolant. Clean cutting oils produce a good finish, while synthetic water-based coolants can cause aluminum shavings to stick in the pilot hole, scratching the surface of the hole and degrading the finish. Using high cutting speed and sufficient feed rate, applying low-to-medium viscosity high-lubricating coolant is the best way to ensure the surface finish of finishing.