Trochoidal milling uses a series of overlapping circular forward movements, in the radial path direction (plane X-Y), repeating these spiral movements in a required number of passes to achieve the final workpiece shape.
It requires specialized programming and the machine needs fast X and Y axes acceleration.
Trochoidal milling is an excellent method for slotting operation when vibration is a problem and it is also suitable for roughing milling in general, mainly when using solid end mills for cavities and pockets.
• Higher depth of cut (4xD) can be applied without vibration thanks to the small load (arc of contact, A.O.C). • Higher feeds can also be applied because of the small A.O.C, it means it will be necessary to adjust the feed in order to keep the right average chip thickness, and also to compensate the speed factor.
Others advantages of trochoidal milling
• Reduced heat, allowing high cutting speeds • Higher productivity • Less cutting forces • Longer tool life • Improved machining accuracy • Same tool can machine many slot sizes
Arc of contact
Arc of contact is generated by the combination of Ae (woc) and tool radius R.
If the Ae is lower than 10% of the end mill diameter, we will need to increase too much the feed and the VC for average chip thickness correction and sometimes the machine won’t be able to achieve the speed and feed.
If the Ae is higher than 20% of the end mill diameter, the Arc of contact will be higher than 53% and we will need to apply lower feed and lower VC ,due to the increased contact between the end mill and workpiece.
Application example on steel
Trochoidal milling application on material 42CrMo4
Stepover W according to material
Aluminium W of 40% from end mill diameter Steels W of 20% from end mill diameter Titanium/ superalloys W of 12% from end mill diameter Stainless Steels W of 20% from end mill diameter Cast irons W of 25% from end mill diameter
Note :The minimum bw should be 1.50 of end mill diameter
Application using the trochoidal milling
Normally it is not necessary to calculate the parameters thanks to the new softwares CAD/CAM that can generate by themselves the correct way to apply the Trochoidal milling strategy.
It is just necessary to add the basic information below: • End mill diameter
• Number of flutes
• The Dm ( width of the slot )
• The W ( Stepover )
• The Ae in between 10-20% of the end mill diameter
• The total axial depth of cut
• The Vc calculated according to the material and speed compensation
• The Vf – calculated according previous slides
Trochoidal milling – Adaptor
Using trochoidal milling strategy we also need to pay attention to the interface between the machine spindle and the tool. Shrink fit style adaptors are preferred (whenever available), because of their improved rigidity and more accurate run-out, which minimizes the risk of vibrations.
In summary, trochoidal milling strategy provides important advantages in slotting operations, such as longer tool life and process security, reasons why this method is becoming more and more popular in customers that are equipped with modern milling machines and CAM softwares. If you are seeing this subject for the 1st time it might look complicated, but in fact it is not, since the tool trajectory is defined by CAM+Machine and all you need to do is to define a few cutting parameters related to the applied tool, as explained above.