Monthly Archive April 29, 2022

How to improve surface finish in CNC machining

In terms of size, the parts meet the blueprint specifications, but the surface finish and overall appearance are not ideal? What should we do?

Consider the following options:

  1. Control chip: chip evacuation is the key factor to produce good surface finish. 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 using air and coolant is a good choice to control chip removal, pay attention to coolant. Avoid using coolant when cutting intermittently. Hot cracks on the cutting edge will occur Due to intermittent heating and rapid cooling of cutting edges And it can lead to premature blade failure, or at least start to affect your surface finish because of over stressed cutting edges and failure.

  1. Improve speed: This is especially true when using cemented carbide tools. Increasing the speed will ensure that the contact time between the material and the tool tip is shorter Therefore, the edge accumulation on the tool is reduced, which may lead to poor surface finish. Increasing the rake angle of the cutting tool also helps to reduce and control edge accumulation.
  2. Use the correct tip radius: a larger tip radius will be able to adapt to a faster speed. The insert can feed at about half of TNR per revolution and still produce good results. If you exceed this TNR to IPR ratio, the tool will create more “linear” surface finish than the glossy smooth surface you want. Therefore, the larger the TNR, the faster the feed speed it can accommodate and still produce the desired results. 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 tip radius means that you must leave more material for completion. To ensure proper operation of the tool, you must set TNR equal to or greater than TNR in order to complete the removal of the tool.

When milling, try to use fillet or spherical end milling cutter instead of plane end milling cutter. Something with a rounded radius will give you a higher finish at sharp corners and will certainly help extend tool life.

  1. Try to insert the wiper: as far as possible. The wiper insert has a small flat area adjacent to the tip radius. 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 a faster feed rate – this allows the use of a smaller TNR to help control chatter.
  2. Increase the lead angle of the tool. Higher lead angle and positive tilt blades produce better surface finish than tools with shallow 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.
  3. 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 try to ensure that the tool never stops or hesitates during the cutting process.