Robot Automation on a 5-Axis CNC Mill

NTE84-11 its hard to give you a good answer to that question because it solely depends on your part and or parts. In summary if you have a good surface and enough suction you shouldn't have a problem with vacuum but there are quite a few factors to consider to ensure it actually fits. I actually always try to replace grippers with vacuum if its possible for many applications.

You will need to do an evaluation on your parts an test various cups to see what fits best i.e. shape, material, bellows. And test on the bench with a set of vacuum generators and parts to make sure that the application works first. Also since its in a mill you will likely have swarf around the machined part so this can easily damage or block a cup depending on the size so put some consideration in to when to engage the vacuum and if you need some screening behind the cup, you could also use a blow off function to first blow the area clear if you have decent pressure and volume and then engage vacuum. Make sure that your air supply is good and also consider if you need to put some compensation in the tool as you may need to press on the part slightly if you don't allow for any compensation in the cups themselves.

Chips and lubricant are also factors. Either might randomly reduce the vacuum cup's grip on the workpiece. Also, vacuum cup venturi don't react well to liquid ingestion, so if your CNC process is "wet", you need to spec vacuum cups and generators that can handle the liquid. Chemical compatibility is another factor -- some machining lubricants will corrode certain types of cups, airlines, and seals.

How much accuracy does this operation need? Picking something with just vac cups is not a high-precision method. If you need precision placement, I would recommend adding some sort of geo-setting blocks or fingers to the end effector, features that would control the way the workpiece is held while the cups just provide some geometrically flexible force pulling the workpiece against those features.