There’s no tolerance for anything less than perfection from manufacturers in the aerospace industry. The aerospace industry covers everything from commercial flights, drones, and has become the basis for many military operations. Commercial flights are one of the major forms of travel and improvements are made constantly to enhance the structures.
One particular change has been the use of composites over metals. Composites were introduced because of their lightweight properties, but also provide significant benefits in durability and performance. The main composite used today is carbon fiber. Although carbon fiber has its benefits, there have been some problems with the material drilling process.
A fairly recent development of drilling composite stackups is that more manufacturers are moving away from wet drilling. By adding the coolant into the process it can damage the integrity of the carbon fiber layer weakening and causing it to fail over time. For that reason manufacturers have begun looking for alternative options.
Dry Drilling without Coolant
Drilling dry seems like the logical way to go in order to remove the coolant from the process. Dry drilling is effective, but not cost friendly. The term stackup refers to the layering process that is used to strengthen the structure. As you see in the picture below, drilling dry is damaging the composite and generating a lot of heat when it reaches the titanium layer. Not to mention the hole tolerance is affected leaving behind frayed holes. Further as the tool heats up, it breaks causing a significant monetary cost to deal with especially when drilling thousands of holes. Check out how it works in the video below.
Cold Air Gun
Another dry form of cooling is using a cold air gun. This coolant system requires no electricity, only a compressed air source. It works by using a vortex tube technology filtering the air to subzero temperatures. The main applications it cools are spot cooling of metal parts. It has minimal heat removal capacity compared to nitrogen, wet coolant, and CO2 cooling. The heat generated when drilling stackups is more extreme than the results offered using a cold air gun coolant system, and would be better served for lighter applications.
Nitrogen Cooling
Nitrogen cooling is an adequate replacement for wet drilling. It also provides more of a benefit than running completely dry. It does have its share of mishaps though. A problem with the method is the cooling is so extreme that it can leave the tool brittle and fragile. Furthermore it would require buying custom tools and spindles, which can increase costs. But the main problem is control. This cryogenic cooling can freeze up around the holes and structure causing more harm than good.
CO2 Cooling
This brings us to CO2 cooling otherwise known as dry ice cooling. The reason that this method has been more successful than the other available options is the level of control. This precision cooling focuses carbon dioxide directly on the cutter or introduced through spindle. It works by drawing liquid CO2 from a cylinder then forcing it through a nozzle where it expands to form solid dry ice particles, or snow crystals, which are then introduced into the heat zone. Similar to cryogenic cooling it cools the drill and the inside of the hole providing better finishes. The difference is that CO2 is readily available and inexpensive. On top of that the process is environmentally friendly, since there is no coolant agent waste. Watch video for full process and benefits.
Conclusion
Drilling dry can not only result in excessive heat damage to tools and materials, but it can also cause de-lamination issues with the CFRP stackup that results in frayed holes and exit damage.
Because they do not contain wet ingredients, nitrogen and cold air are acceptable substitutes to traditional wet coolants. But according to experts in the industry, they do not provide the same level of precision and protection as using CO2 as the coolant.
It is no wonder some of the top manufacturers in the aerospace industry have already made the switch to this clearly superior drilling method.
