1、 New tools maximize new machine designs The primary tooling concerns when machining aluminum are: minimizing the tendency of aluminum to stick to the tool cutting edges； ensuring there is good chip evacuation form the cutting edge； and ensuring the core strength of the tools is sufficient to withsta
2、nd the cutting forces without breaking. Technological developments such as the Makino MAG-Series machines have made tooling vendors rethink the any state-of-the-art machine technology. It is vital to apply the right tooling and programming concepts. Materials coatings and geometry are the three elem
3、ents in tool design that interrelate to minimize these concerns. If these three elements do not work together, successful high-speed milling is not possible. It is imperative to understand all three of these elements in order to be successful in the high-speed machining of aluminum. Minimize Built-U
4、p Edge When machining aluminum, one of the major failure modes of cutting tools the material being machined adheres to the tool cutting edge. This condition rapidly degrades the cutting ability of the tool. The built-up edge that is generated by the adhering aluminum dulls the tool so it can no long
5、er cut through the material. Tool material selection and tool coating selection are the two primary techniques used by tool designers to reduce occurrence of the built-up edge. The sub-micron grain carbide material requires a high cobalt concentration to achieve the fine grain structure and the mate
6、rials strength properties. Cobalt reacts with aluminum at elevated temperatures, which causes the aluminum to chemically bond to the exposed cobalt of the tool material. Once the aluminum starts to adhere to the tool, it quickly forms a built-up edge on the tool rendering it ineffective. The secret
7、is to find the right balance of cobalt to provide adequate material strength, while minimizing the exposed cobalt in the tools for aluminum adherence during the cutting process. This balance is achieved using coarse-grained carbide that provides a tool of sufficient hardness so as to not dull quickl
8、y when machining aluminum while minimizing adherence. Tool coatings The second tool design element that must be considered when trying to minimize the built-up edge is the tool coating. Tool coating choices include TiN, TiAIN, AITiN, chrome nitrides, zirconium nitrides, diamond, and diamond-like coa
9、tings(DLC). With so many choices, aerospace milling shops need to know which one works best in an aluminum high-speed machining application. The Physical Vapor Deposition (PVD) coating application process on TiN, TiCN, TiAIN, and AITiN tools makes them unsuitable for an aluminum application. The PVD
10、 coating process creates two modes for aluminum to bond to the toolsthe surface roughness and the chemical reactivity between the aluminum and the tool coating. The PVD process results in surface that is rougher that the substrate material to which it is app lied. The surface”peaks and valleys” crea
11、ted by this process causes aluminum to rapidly collect in the valleys on the tool. In addition, the PVD coating is chemically reactive to the aluminum due to its metallic crystal and ionic crystal features. A TiAIN coating actually contains aluminum, which easily bonds with a cutting surface of the
12、same material. The surface roughness and chemical reactivity attributes will cause the tool and work piece to stick together, thus creating the built-up edge. In testing performed by OSG Tap and Die, it was discovered that when machining aluminum at very high speeds, the performance of an uncoated c
13、oarse-grained carbide tool was superior to that of one coated with TiN, Ticn, TiAIN, or ALTiN. This testing does not mean that all tool coatings will reduce the tool performance. The diamond and DLC coatings result in a very smooth chemically inert surface. These coatings have been found to signific
14、antly improve tool life when cutting aluminum materials. The diamond coatings were found to be the best performing coatings, but there is a considerable cost related to this type of coating. The DLC coatings provide the best cost for performance value, adding about 20%-25%to the total tool cost. But
15、, this coating extends the tool life significantly as compared to an uncoated coarse-grained carbide tool. Geometry The rule of thumb for high-speed aluminum machining tooling designs is to maximize space for chip evacuation. This is because aluminum is a very soft material, and the federate is usua
16、lly increased which creates more and bigger chips. The Makino MAG-Series aerospace milling machines, such as the MAG4, require an additional consideration for tool geometry-tool strength. The MAG-Series machines with their powerful 80-hp spindles will snap the tools if they are not designed with suf
17、ficient core strength. In general, sharp cutting edges should always be used to avoid aluminum elongation. A sharp cutting edge will create high shearing and also high surface clearance, creating a better surface finish and finish and minimizing chatter or surface vibration. The issue is that it is
18、possible to achieve a sharper cutting edge with the fine-grained carbide material than the coarse grained material. But due to aluminum adherence to the fine-grained material, it is not possible to maintain that edge for very long. Coarse compromise The coarse grained material appears to be the best
19、 compromise. It is a strong material that can have a reasonable cutting edge. Test results show it is able to achieve a very long tool life with good surface finish. The maintenance of the cutting edge is improved using an oil mist coolant through the tool. Misting gradually cools down the tools, el
20、iminating thermal shock problems. The helix angle is an additional tool geometry consideration. Traditionally when machining aluminum a fool with a high helix angle has been used. A high helix angle lifts the chip away from the pa rt more quickly, but increases the friction and heat generated as res
21、ult of the cutting action. A high helix angle is typically used on a tool with a higher number of flutes to quickly evacuate the chip from the part. When machining aluminum at very high speeds the heat created by the increased friction may cause the chips to weld to the tool. In addition, a cutting
22、surface with a high helix angle will chip more rapidly that a tool with a low helix angle. A tool design that utilizes only two flutes enables both a low helix angle and sufficient chip evacuation area. This is the approach that has proven to be the most successful in extensive testing performed by OSG when developing the new tooling line, the MAX AL.
