At the end of CNC turning, no shop wants to see its part ruined and scrapped. And while having a combination of the right technique and tools to keep jobs in spec and on time, other variables need to get considered before reaching the final stage. Here are a few of the various things you can consider doing to help you get the best finish on the surface:
Increase in speed. This is the most applicable when using carbide tools. By increasing the surface feet per minute rate (SFM), you will ensure that the material is in contact with the tip of the machine for a shorter amount of time and also reduce the edge buildup on the tool, resulting in cut surface finishes.
Reduce the rate of your feed. Reducing the rate of feed will help improve surface finish. This will also help to reduce wear on the flank and extend the longevity of the insert. Therefore, doubling the diameter of the nose would help improve the surface finish. It is best to use a tool with a high feed rate for roughing applications to remove material quickly. To finish, a lower feed rate and a shallower cut are best.
Increase the angle of the top rake. Positive rake angles will result in a more delicate finish of the surface, requiring lower cutting forces. It will act downwards with a 45 ° cutter, possibly making the part flex. This will result in the back half of the cutter recutting the machined part and creating a poor surface finish. The use of a 90 ° cutter will generate and not flex cutting forces parallel to the component. This will result in a smoother finish on the surface.
Use a breaker of the chip. Improper breaking of chips, downtime to remove chips and higher temperatures at the cutting edge of the tool can also cause a poor surface finish. A chip breaker can quickly produce smaller chips from the cutting area. And because manual clearing of chips is no longer necessary, safety is being improved. If the chip breaker can break or tear the chips apart into sufficient lengths, the vibration will get minimized; the chips will not wrap around the workpiece, and the tools will not be damaged. Chip breakers also reduce the resistance to cutting, which can prevent the cutting edge from chipping or breaking.
Use a wiper plug. Use a special wiper insert with a modified nose radius with more significant corners to wipe the surface smooth to ensure an excellent surface finish. This will enable you to cut at a faster rate of feed.
Use a large radius of the nose. The idea that must be initialized is to use a larger nose radius to achieve a smoother, more beautiful surface finish and decrease the feed rate. This is because the shape and direction of chips are affected by the nose radius and cut depth. Therefore, to achieve the best surface finish and avoid creating chatter (machine vibration), it is best to use the largest possible radius.
Use the proper technique. You want to create a thick-to-thin chip. Your method plays a vital role in rendering surface finishes smooth. Choose a cutter smaller than the diameter of the nose so you can program it from line-to-line for a smooth transition. Do not just restrict yourself to reading your workpiece while running your final cuts; you should also understand your chips. The chips’ characteristics will indicate what set-up or tooling changes are needed.
Use various roughing and finishing tools. Some may suggest that for roughing and painting, the same inserts can be used. But the best way to use different supplements is to roughen one and finish one. A course-pitch cutter with a wide nose radius and a broad rake angle with a fast feed speed can get used for roughing. Use a fine-pitch finishing tool with the correct lead angle and a flat wiper to finish, which will give you a better surface finish.
Clean up the chips. There is a discussion as to whether coolant should get used in milling applications. But it all depends on the type or origin of work nature you do, such as deep cavity friction, the kind of material you use, and the insert you use. In some cases, the use of coolant should get avoided. It can cause thermal cracking and shorten the life of the tool and can negatively affect the surface finish. Nevertheless, using the refrigerant can keep the machine from sticking to the workpiece with titanium, low-carbon steel or nickel-based alloys.
Check your work holding and tool holding. It’s a good idea to check your tool holders’ condition. An old, worn-out tool holder may move the insert. This will cause chatter and adversely affect your part’s surface finish. You also want a stable, rigid work holding, especially with a higher rate of metal removal.
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