Viewpoints: Are You Getting the Most from Your Cutting Tools?
We live in an age of speed and flash—the quicker we can get information, the better we can accomplish a task. But, is this always true on the shop floor?
Computers and software have made incredible differences in the way companies do business and in the way they manufacture products. CAD/CAM products allow manufacturers to draw upon stored knowledge and experience, eliminating the need to recreate the wheel with each new product or part introduction—saving time and money. It has also become an almost effortless task to generate a part program with standard feeds and speeds. Just plug in the basics and let the software do the rest.
Unfortunately, since a lot of the programming done at the machine or at the workstation does not fully utilize new process technology, it’s not uncommon to hear people say, “I can’t take the time to program the right tool path or the right speeds and feeds.” The problem with this thinking is that you only have to write the part program one time, but you may run that part 10,000 times in a month. So think about this: It may take 20 hr longer to write a part program, but that investment may save 15 sec per part on a part running 10,000 times a month. This results in a savings of over 40 hr of process time per month. The wiser choice seems pretty obvious.
It all comes down to improving productivity. This is certainly our focus: improving productivity through knowledgeable application. And we measure productivity in cubic inches of metal being removed per minute (metal removal rate or MRR). This is key—the higher the MRR, the better the productivity. We believe that most of the shops we visit today are underutilizing the technology and not optimizing their productivity.
Cutting machine operators should learn to trust their own senses: A simple clue as to whether a cutting operation is getting the most from its technology can be found in both the sight and the sound of the cutting chips. In a typical CAD/CAM program, a cutter path is generated that may or may not be using the full width of the cutter. Once you run below half the diameter of the cutter, bad things start to happen. The chip starts thinning and then heat starts to build up. The metal cutter starts to become a piece of sandpaper. Because the chip is too thin to hold the heat, that heat spreads to the workpiece. If it’s going into the workpiece, problems in holding size result. Additional problems, such as work hardening can also result if the piece is stainless or another high-temp alloy material.
If the heat is going into the insert, then there will be tool life problems. Tool life is not just about the cost of having to use more inserts. It’s about the cost of machine downtime every time you have to change the tools—it’s about productivity.
If the chips are on the thick side, you have to worry about fatigue and fracturing the insert or stalling out the machine. In my experience, most machines are being under-run, and the optimal depth of cut is not being used.
The point is, you can’t always take the automatically generated part path and apply your feeds and speeds. You have to manipulate them to make sure you obtain and maintain the proper chip thickness. You need to refer to both the torque curve chart that comes with your machine and the cutting data in the part book. By running this simple formula, ADC × RDC × IPM = MRR, you can figure out your cubic inches of metal removal per minute.
A less technical approach to metal removal is simply listening to your shop. Can you hear the chips fall? We have a customer who says, “If the chips slamming on the side of the machine don’t sound like it’s raining cats and dogs, then I know my cubic inches per machine is not nearly high enough.” You should be able to hear productivity in addition to seeing it through chip thickness.
There are many variables that can be manipulated to influence productivity, including a constant influx of new products and technologies in the market. However, the answer to productivity is not in the latest and greatest machine, software, or cutting tool—but rather in how the technology is applied. This requires application and training. No software program can give you this. Software is only a tool that can help take your knowledge to market a bit faster. Use your senses, especially your common sense, to make sure you are reaching your productivity potential.
This article was first published in the April 2006 edition of Manufacturing Engineering magazine.