MMS

"Mastercam Delivers Needed Speed for Faster Part Production."

When establishing feed rates for your 3-axis milling machine, The Machinery Handbook is often a place to start, or if you are lucky, you can consult your shop’s feed rate expert. Among other parameters when manually programming feed rates, you have to consider the dynamics of the particular machine tool, the material, the cutter, which roughing pass you are calculating, adjustments when heading into a corner, what the required finish is on the part, when that special tool comes into play, and the list goes on. Because of the many variables, most people play it as safe as possible. They might find The Machinery Handbook figure, back off from that 10 percent or so, and simply maintain that one feed rate throughout the entire process. The logical thinking is, “it will be fine for my cutters, and it will save me days of painstaking programming time to plug in all the different rates during various process stages and particular part features.” Granted, it is a safe approach. However, with today’s CAM software programs, feed rate optimization is one feature you need to be using more often because of compelling benefits.

Feed the bank

Feed rate optimization has a direct link to your company’s bottom line. Optimized cutting gets parts off the machine faster. Feed rate optimization can greatly reduce cycle time by automatically adjusting feed rates based on the volume of material being removed. Basically, where there is more material, the feed rate decreases. Less material and the feed rate increases. This lets the machine run at continuously optimized feed rates and keeps a more constant chip load on the cutter for faster job completion and more efficient tool use.

What is it?

In general, feed rate optimization is a programming tool within many CAM packages that enables the programmer to build feed rate adjustments into the CNC program in the off-line mode. It operates by analyzing the CNC toolpath G-code or ATP format and divides the motion into smaller segments. Based on the volume of material removed in each segment, the software calculates the optimum feed rate for the cutting condition. It then provides a new toolpath that is identical to the original, except with new feed rates.

The Highfeed Machining option in Mastercam represents this technique and gives the programmer additional software tools for enhancing the efficiency, safety, and accuracy of roughing and finishing routines. Essentially, this option is applied after the initial toolpath has been generated. A series of dialog boxes query the programmer, asking for information that defines the stock being removed. This definition is then associated with the performance dynamics of the machine tool and the cutting requirements, such as workpiece material and capability of the cutting tool. These parameters indicate the chip thickness, volume removal rate, entry feed rate and other factors to calculate the optimum feed rate for each section of the cut.

This data allows the software to modify feeds and speeds accordingly to optimize machining conditions. For example, feed rates are increased to maintain full chip load but decreased to negotiate direction changes without over- or undershooting the geometry, given the responsiveness of the servos on the target machine.

Likewise, rapid moves are applied to passes where the tool is not in contact with the workpiece to reduce time "cutting air." The results are machining routines that significantly shorten cycle time without unduly burdening the programming effort.

Improve part quality

Not only will you get parts off the machine faster, but the parts will be more accurate and have an improved, more consistent finish. This is thanks to accurate toolpaths carried out at the optimum rate for that particular move, condition, or function. For some shops, such as moldmakers, the improvement in part quality alone warrants applying the feed rate optimization feature in their software. These shops are accustomed to spending significant time hand polishing molds. With the optimization feature, several Mastercam customers have drastically cut this time. Some have eliminated it altogether!

Extend the life of your cutters and machine tools

There is the safe school of thought, but then there is also the macho school of thought in which the philosophy is to push machines as fast as they can go, hope nothing breaks, and duck when it does. Pushing for speed is commendable, and these folks might think they are productive, but are they truly? What is the cost of speed for speed’s sake? Replacing expensive tools more often? Having your machine down for service frequently? Performing more secondary operations? Risking operator safety? There is a cost associated with all of those. Sharp directional changes at high feed rates can cause excessive servo lag, tool deflection, poor finish, and unnecessary machine tool wear. Feed rate optimization is designed to minimize these problems. Based on the part and the machine tool characteristics, Mastercam’s Highfeed Machining feature, for example, adjusts the feed rate around corners and small radii. It also gradually decreases the feed rate as the tool approaches a corner, and gradually increases the feed rate as the tool leaves for a smoother entry and exit. Efficient machining is like driving. If there is a sharp corner, you naturally must slow down or an accident can occur. After exiting the corner, you can safely pick up the speed again. So, if you are a push-type and apply feed rate optimization, understand that parts may come off the machine more slowly than before, but in the end you can still increase profits because you will not burn your tools up as quickly, your machine tool will have more uptime, your operators are safer, and you will have fewer secondaries to do.

More efficient shop environment

Each machine tool has its own “maximum efficiency zone” where it runs as fast as possible without damaging itself or producing scrap parts. Feed rate optimization is designed to help CNC programmers find that zone and let them save that information. This information is stored in a library of preset parameters based on the shop's own experience with specific combinations of machine tool, cutter type and workpiece material for use again and again. Now when your shop’s feed rate expert takes a vacation, production doesn’t come to a screeching halt. This database is available to everyone and helps maintain part consistency. The variables are minimized.

With Mastercam’s feed rate optimization package, CNC programmers can slice up to 33% or more off their machining time, all while extending tool and machine life. That efficiency spreads throughout the shop. When running optimized programs, often operators are able to run two or more machines at a time. They don’t have to constantly monitor by looking at and listening to the cut and manually override the control when necessary.

Some operators can be hesitant about readily accepting computer-generated feed rates. However, once they experience the results, especially if they participate in a productivity or quality rewards program, they quickly buy into the change.

Select it, don’t reject it!

Even with all of these benefits, we still find some users still bypass feed rate optimization in their CAM software because they have a misconception of it. It is a worthwhile tool for the business owner, programmer, and operator. Cutting air might be safe, but the productivity rewards of cutting material are sweeter.