8/10/2019 Staying Alive_ Methods to Increase Cutting Tool Life _ the Manufacturing Reliquary

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Staying Alive: Methods to increase cutting tool lifePosted on October 11, 2010

Dont smoke, dont drink, dont swim in the ocean with dead animals strapped to you there are numerous ways

to improve your chances of living longer. Its not so much different for the life of a cutting tool and while there

are an innumerable number of technical factors that may make one tool superior to another for any given task

all things considered equal the most important factor is the human one. Our skill in programming toolpaths

that enter, exit, and cut in a method that insures longer tool life is more important than any coating, substrate or

tool geometry. So in this segment, were going to take a look at some of the most common cutting conditions and

methods of creating more favorable strategies.

Cutter Engagement (Entry)

Left to right, all cuts taken in a climb milling fashion: We have the typical facing/roughing cut at 65-70% of the

cutters diameter, 50% on-center cutting and ae

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None of these are particularly harmful to a milling cutter though the 50% situation is rarely used simply due to

the fact that 65-70% roughing is some 30% more productive. Notice chip formation; the most desirable condition

is a chip that starts thick and thins to zero at the end of the cut. That said, if we were milling our far right

example across the full width, the best strategy would be one that clears the right edge of the part + the radius of

the insert or cutting edge. In general, the ideal cutter would be 20-50% larger than the width of the cutting area.

Should you find yourself in a situation where youd like to mill a 20 mm wide section with your 25 mm diameter

cutter, keep the thick to thin rule in mind when creating that toolpath.

Cutter Exit

For those reading this blog who might not be up on machining terminology, this is a wonderful opportunity toclarify the difference between climb or down milling and conventional or up milling strategies, so lets take a

moment and do just that. The cutter exit examples are all illustrations of conventional or up milling while the

cutter entry examples clearly illustrate climb or down milling . Hopefully this clears up the terminology a bit?

Youll notice that all but one of these milling scenarios creates a favorable cutting condition, especially for the

inserted milling cutter. Matter of fact, short of milling with ceramics which do not do well with the impact loads

like those seen in thick to thin cutting strategies, conventional milling yields no worthwhile advantages over

climbing. Tool exits see high tensile stresses as the chip deforms before being sheared from the workpiece. This

type of cutting also tends to rub or burnish the workpiece at the chip start position, which only exacerbates

milling problems seen in work hardening materials. In short, avoid the conventional cut at all costs and if you

must; take the cut with 65-70% radial engagement to create a more ideal chip shear upon exit.

Entry Strategies

One way to reduce the shock of cutter entry is to reduce the feedrate by 30-50% until the cutter reaches

center of the starting edge. The same is true, and even more important, upon cutter exit.

Use CVD coated carbides for higher engagement angles (roughing/facing). The larger the engagement, the

greater the heat at the cutting edge.

Small engagement angles (peripheral milling) benefit more from PVD coated gradesRoll into the workpiece

The Roll-in

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To our left; the roll-in entry and to the right, a straight-in entry. Notice the chip formation in each scenario and

remember the general rule thick to thin .

Programming the roll-in is rather simple, basically what we are looking to do is take advantage of the CNC

controls corner rounding capabilities. Well take a more detailed look at this and a few other issues in our next

segment stay tuned.

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