How to improve the surface finish of the workpiece during metal processing

As engineers, we use our skills, knowledge and experience to produce the best looks and the most accurate parts. We are very proud of the products we produce, and we hope others see the pride of the finished product. But what should we do when we do n’t get the results we want? 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 method we know.

We need to look at things like workpiece fixtures to make sure it is sturdy and that it does not promote harmonic problems or vibrations during processing. We need to make sure that we do n’t use unnecessary long tools that can easily turn or increase the chance of chatter. 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 the key factor to produce good surface finish. The control chip may be the first thing you should consider. If the chips produced are in contact with the workpiece during processing, or if you are cutting chips again, 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 break down the chip for better control.

Although the use of air and coolant are good choices for controlling chip evacuation, pay attention to the coolant. Avoid using coolant when cutting intermittently. Thermal cracking of the cutting edge will occur ... due to intermittent heating and rapid cooling of the cutting edge ... and will cause the blade to fail prematurely, or at least it will start to affect your surface finish due to excessive stress on the cutting edge and failure.

2. Increase the speed: This is especially true when using carbide tools. Increasing the speed will ensure that the material will be in contact with the tip of the tool for a shorter period of time ... thus reducing the edge accumulation on the tool, which may result in poor surface finish. Increasing the cutting tool rake angle also helps reduce and control edge accumulation.

3. Use the correct tip radius: a larger tip radius will be able to adapt to a faster speed. The insert can be fed at about half the TNR per revolution and still produces good results. If this TNR to IPR ratio is exceeded, the tool will create more "linear" surface finishes, rather than the glossy smooth surface you want. Therefore, the greater the TNR, the faster the feed rate it can accommodate and still produce the desired result. However, using very large TNR can produce chattering-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 tip radius means you must leave more material for the finish. To ensure the normal operation of the tool, you must set the TNR equal to or greater than the 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 radius of the corner you are cutting-so you can "form" the desired radius-especially on finishing tools. This will help reduce cutting pressure and eliminate chatter.

When milling, try to use a fillet or spherical end mill instead of a plane end mill. Things with rounded radii 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. When the tool is fed 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 smaller TNR to help control chatter.

5. Increase the lead angle of the tool. Higher lead angles and positively inclined blades produce better surface finish 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 traces. Change the process if necessary, but do your best to ensure that the tool never stops or hesitates during the cutting process.