Your average person on the street can’t walk into a CNC machining shop and run a 5-axis CNC mill. Today’s CNC machines are incredibly complicated. They take a tremendous amount of training just to start to use one, and the learning never really ends. Even trained CNC operators have to learn new machines before they can start making chips with them. The fact that all modern machines come with digital read-outs and the milling instructions are loaded for each project does not make them easy machines to run. CNC operators are the first line of defense, so to speak, when the theoretical CAD/CAM work is turned into physical products.
Listening to the CNC Mill
The operator may find that a bit is chattering. This can happen if the bit is set to take too much material off in one pass. It can also happen if the bit is dull or damaged. Carbide inserts are ridiculously strong, but they’re also brittle. One common scenario is a piece of raw material being turned down on a CNC lathe. If the stock is not engaging the insert at all times, when it comes around and connects with the cutting edge, the force can snap the insert. A chattering bit is all but guaranteed to lead to the next possible problem.
Watching the Parts
A poor surface finish is another issue an operator watches for while producing CNC machined parts. This can happen for several different reasons. As noted above, one common cause is a dull or damaged bit. A bit that’s been improperly stored may have tiny nicks on the cutting edges. They may not even be visible to the naked eye, but they can show up when the bit cuts across a part, leaving dozens of little imperfections on an otherwise pristine surface. This is far more common in shops that aren’t rigorous about storing their tools properly.
Materials themselves can cause issues. New alloys may not machine exactly as expected. Rough castings might not be exactly the composition specified, which can cause machining issues. This is why operators always pay particular attention to the first piece for a given production run. That’s when material issues will show themselves.
Smelling a Problem
Another problem a dull bit can cause for a CNC operator is a burned or burnished surface. Especially if the part has to be cut without coolant, if the operator isn’t being careful a less-than-perfect bit can cause the part to overheat.
Doing the Math
Making a cut on a CNC machine requires engineers to consider the amount of material being removed by each tooth of the given bit. There is a delicate balance between how deep the cut will be, the number of teeth on the bit, how fast the bit will be turning, how fast the head will be moving forward, what kind of material the bit is made from, and the material being machined. When you think about all of those variables going into every cut made on a CNC machine, it’s a wonder anyone can make them work. An error with any of those variables will lead to a poor surface finish and possibly other problems.
It is also possible to have geometry problems. That’s not finding the hypotenuse of some triangle, but CNC machines can get what’s called “out of tram”. That’s the squareness between the arbor and the table that workpieces are clamped to. A machine can go out of tram if it’s subjected to a big shock. More commonly, a machine will very slowly and gradually drift out of tram just by being used. Wear on the work surface can result in low areas that are out of tram, just as the movement of the arbor can wear down control surfaces. High-quality CNC machining shops like Ben Machine watch for machines going out of tram. We have the means to spot machine wear issues before they begin to affect our products, and we address those problems immediately. Fortunately, we have enough CNC machines that taking one out of service to be trammed does not affect our production capacity.
Keeping it Clean
Another vector for CNC machining challenges is cleanliness. CNC machines produce copious amounts of chips. If a tiny chip works its way under a piece or gets missed during cleanings between operations, it can throw the positioning of the part off. We strive to be meticulous about waste removal, especially in and around the CNC machines. We also invest in coolant filtering and automated swarf removal.
When people tour Ben Machine, they often comment on how clean and organized everything is. That’s very deliberate. We don’t leave bits and cutting inserts lying around where they can be dinged up. We make sure things are where they need to be, and we keep the shop clean. Our reputation lies in the hands of our CNC operators and the products those machines turn out. We recognize the importance of that. You need your products manufactured to your specifications and dealing with problems like these is part and parcel of making sure that we provide exactly what you’ve contracted for.
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