As engineers, we use our skills, knowledge and experience to produce the best looking and most accurate parts. We are very proud of the products we produce, and we hope that others will see the pride of the finished product. But when we don’t get the results we want, what should we do? In terms of size, the parts meet the blueprint specifications, but the surface finish and overall appearance are not ideal? When this happens, we need to go back to the basics and make sure We use the best processing methods we know.
We need to look at things like work clamps to make sure that it is strong and that it does not promote harmonic problems or vibration during processing. We need to make sure that we don’t use unnecessary long tools that can easily turn around or increase the chance of chattering. In high-speed processes, we need to ensure that a quality-balanced tool is used, which has been rated according to the programming RPM used. But if all the things mentioned above are good, what should we do?
Consider the following options:
1. Control chip: chip evacuation is a key factor in producing a good surface finish. The control chip may be the first thing you should consider. If the produced chips come into contact with the workpiece during machining, or if you are re-cutting the chips, it is likely to affect your surface finish in a negative way. Consider the possibility of changing the style of the chip breaker you are using to help disassemble the chip for better control.
Although the use of air and coolant are good choices for controlling chip removal, pay attention to the coolant. Avoid using coolant when cutting intermittently. Hot cracking of the cutting edge can occur...due to intermittent heating and rapid cooling of the cutting edge...and can cause premature blade failure, or at least start to affect your surface finish due to excessive stress on the cutting edge and failure.
2. Increase speed: This is especially true when using cemented carbide tools. Increasing the speed will ensure that the material is in contact with the tip of the tool for less time... thus reducing edge buildup on the tool, which may result in a poor surface finish. Increasing the rake angle of the cutting tool also helps to reduce and control edge buildup.
3. Use the correct tool nose radius: a larger tool nose radius will be able to adapt to faster speeds. The insert can be fed at about half the TNR per revolution and still produce good results. If you exceed this TNR to IPR ratio, the tool will create more "line-like" surface finishes instead of the glossy and smooth surface you want. Therefore, the larger the TNR, the faster the feed rate it can accommodate and still produce the desired result. However, using a very large TNR can produce chatter-reduce cutting pressure-so be careful and consider the speed required to cut the material-use a TNR tool that meets your needs.
It is also worth mentioning that using a larger nose radius means you have to leave more material for the finish pass. To ensure the normal operation of the tool, you must set the TNR equal to or greater than TNR in order to complete the removal of the tool.
If you encounter chatter around the corner, then you may want to try a smaller TNR. Always use a TNR that is smaller than the corner radius you are cutting-so you can "form" the required radius-especially on finishing tools. This will help reduce cutting pressure and eliminate chatter.
When milling, try to use external fillet or spherical end mills instead of flat end mills. Something with a fillet radius will give you a higher finish at sharp corners and will definitely help extend tool life.
4. Try to insert the wiper: as much as possible. The wiper insert has a small flat area adjacent to the radius of the blade tip. As the tool feeds along the workpiece, this plane actually "wipes" the finish and helps eliminate the linear finish that may be encountered at faster feed rates-this allows the use of a smaller TNR to help control chatter.
5. Increase the lead angle of the tool. Higher lead angles and positively inclined inserts produce better surface finishes than tools with shallower cutting angles. For example: a face milling cutter with a 45° cutting angle will produce a better surface finish than a face milling cutter with a 90° cutting angle.
6. Eliminate dwell and pause: every time the tool stops moving when it comes into contact with the surface of the part, it will leave a trace. Change the process if necessary, but try to ensure that the tool never stops or hesitates during the cutting process.
