2019cnc4-5

CNC WEST April/May 2019 www.CNC-West.com 61 which offers superior finishes than the standard edge preparation. Edge preparation and sharpness can quickly lead to a conversation of sub-micron grade vs course grain carbide and which grade is more prone to aluminum build up. The quick sum- mary of this conversation is that sub-micron grain carbide is accepted as a better material as it’s very hard and maintains a sharper cutting edge. Howev- er, there are numerous studies showing aluminum is more prone to chemically bond to the Cobalt material than it is to sub-micron grade carbide. The same studies show that course grade carbide tools may be ideal in that they contain the right balance of cobalt to provide adequate edge strength to produce a good edge, while minimizing the cobalt content that promotes aluminum build up. DLC (diamond-like coatings) are becoming more popular as a somewhat expensive solution to pro- ducing great finishes with good tool life. The in- credibly smooth and hard surface produced during the diamond coating process is chemically inert and significantly improves tool life and surface quality when cutting aluminum. Select appropriate roughing processes before fin- ishing: As we’ve touched on earlier in this article, a key to producing good, consistent 3D surfaces is to present a consis- tent cutting condition to the tool as much as possible. One important detail is to cut a consis- tent amount of material throughout the finishing toolpath. To present a consistent amount of material to the tool, the roughing, and possibly semi-finishing tool- paths need to be ap- plied thoughtfully. I will often use a 3D Adaptive toolpath in Fusion 360 with a flat or bull nose end mill and then follow that with a rest machining 3D Adaptive toolpath using a ball mill. Sometimes it also makes sense to use a 3D finishing toolpath with a coarse step over and stock to leave to pro- duce a very consistent layer of material to finish machine. Wrapping up the series: In this series we scratched the surface of the ex- tensive topic of 3D machining. It takes experience, thoughtfulness, good resources, and some trial and error to master this aspect of machining. As with anything in our trade, the better I understand the technical details of each intricacy, the better I can predict what is needed to be successful and the better I can think through and react to challenges as they arise. I can’t stress enough how important it is to have a strong network of resources to work through challenges for CAM software, machine tools, coolant, cutting tools etc. etc. My network has been a key factor in the success I’ve had in this trade, large and small. I hope you found this series useful. they do for machining prismatic parts where you are more concerned about side cutting walls and end cutting floors. Good basics such as using the shortest tool possible and holding it with a tool holder that is rigid with as little TIR (Total Indicated Runout) as possible all apply as they would with pris- matic part machining. One key difference in cutting conditions between machining 3D Surfaces and prismatic parts is the previously mentioned zero SFM condi- tion. Some cutting tool companies make the best of this situation by applying an elliptical gash on the ball end improving the shear of the cutting edge which produces better cutting conditions and sur- face finishes. Tool coatings are an important detail to getting good tool life. TiN, TiCN, AlTiN, TiAIN, chrome ni- trides, zirconium nitrides, and DLC (diamond-like coatings) are some of the many choices available. Coatings have different positive and negative characteristics that help for different cutting con- ditions, such as thermal stability at different tem- peratures. It is best to follow your tool companies’ guidelines to quickly find a suitable solution. I will quickly touch on coatings for cutting aluminum. When cutting aluminum, one of the main reasons the tool fails is due to edge build up where the aluminum material adheres to the cutting edge of the tool. The built-up material degrades the cutting edge of the tool, lowering the shear cutting forces and increasing the heat generated which in turn ac- celerates the material build up and compounds the problem. TiN, TiCN, AlTiN, TiAIN are just a few con- ventional PVD (Physical Vapor Deposition) coatings. The PVD application process makes these coatings poor for cutting aluminum for two reasons: the sur- face roughness of the coating and the chemical re- activity between the aluminum and the coating. The peaks and valleys created from the PVD process are rougher than the material of the tool, which caus- es the aluminum material to rapidly collect in the valleys. Addition- ally, coatings such as TiAIN contain aluminum, which easily bond to the cutting material of the same material. Often a raw pol- ished carbide cutting tool is enough to produce great results and achieve acceptable tool life. Many tool companies offer micro polished edge preparation