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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
ken. tang@chengcg.com
Machining and milling technology of CNC parts
Let’s take a look at CNC machining and milling technology!
- Feed line of precision CNC machining and milling plane parts: when milling plane mechanical parts, the side edge of end mill is usually selected for cutting. In order to reduce the tool receiving trace and ensure the appearance quality of parts, the cutting in and cutting out procedures of tools are carefully designed.
- In the machining process, when milling the surface, the cutting in and cutting out points of the cutter and milling cutter should cut in and cut out the surface of the part along the extension line of the part summary curve, rather than directly cutting in the part along the normal direction, so as to avoid scratches on the machined surface and ensure the general lubrication of the part.
- In the process of precision CNC machining and milling, if the inner generalization curve allows extension, it should be cut in and out along the tangent direction. If the inner generalization curve does not allow extension, the tool can only cut in and out along the normal direction of the inner generalization curve, and the cutting in and cutting out points are selected at the intersection of two or more elements of the generalization of mechanical parts. When a few internal elements are tangent without intersection, in order to avoid leaving a notch at the general corner when the tool compensation is cancelled, the cutting point of the tool should be far away from the corner.
The above is about the skills in the process of precision CNC machining and milling. For the machining of simple and complex precision parts, the CNC milling technology will be different, which can be based on the appropriate machining line.
ken. tang@chengcg.com
Precision parameter control of CNC machining
In the machining industry, the accuracy parameters of CNC machining are mainly the level that the specific geometric parameters (specification, shape and position) of CNC parts are consistent with the ideal geometric parameters. Learn the following parameters in detail:
In the process of machining mechanical parts and small batch parts, CNC machining accuracy usually includes three level parameters: specification accuracy, shape accuracy and position accuracy.
- Appearance specification parameters of CNC processing
The specific specification of the surface itself or the middle of the surface after machining of CNC parts is consistent with the middle of the ideal part specification. The ideal part processing specification refers to the median value of the specification indicated on the part drawing.
- Shape accuracy parameters of CNC machining
The specific shape of the machined surface of CNC parts is consistent with the ideal part surface shape. The ideal part surface shape refers to the definite surface geometry shape.
- Precision parameters of machining parts of CNC parts
After machining, the specific parts of each surface of CNC parts are consistent with the parts between the surfaces of ideal parts. The position between the surfaces of ideal parts refers to the certain position between the surfaces.
The above is the accuracy parameter control of CNC machining. For different shapes, shapes, simplicity and complexity, it is necessary to select appropriate machining process parameters to improve CNC machining efficiency and ensure the machining accuracy of parts.
ken. tang@chengcg.com
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