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Accumulator bore PCD combination tool 2. Mounting holes PCD step drill 3. Compared to turning, hard milling demands much higher spindle speeds to achieve the same surface speed. To match the surface speed of a turning operation on a three inch diameter workpiece, a three inch diameter milling cutter with four teeth must run four times the turning speed.
With ceramics, the object is to generate a threshold of heat per insert. Therefore in milling operations, each insert must travel faster to generate the heat equivalent of a single point turning tool. Ceramic cutters in many cases demand a new set of application skills from the shop looking to implement them.
Often the process knowledge acquired from sintered carbide insert use is degrees opposite the experience needed to use ceramics.
A major difference is the way ceramics use heat generated in the cut. In most traditional metalcutting, heat is the enemy. It's bad for the tool and generally bad for the workpiece work hardening. The heat dissipation objective for most carbide cutting inserts is to get heat into the chip and quickly out of the cut zone. Not so for ceramics, says Mr. At these temperatures, carbide will soften, deform and fail.
To achieve the elevated operating temperatures for ceramic inserts to prove their mettle, much higher cutting speeds are suggested. Smith, "successful cutting with ceramic inserts demands high surface speed coupled with balanced feed rates.
High speed cutting is necessary to generate the high heat within the cutting zone and to assure that the heat propagates into the workpiece immediately ahead of the cutter. In general, a conservative approach to cutting speeds and feeds is the single largest contributor to process failure when trying to implement ceramic cutters.
When cutting speeds are too slow, insufficient heat is generated. Because heat cannot be transferred ahead of the cutter, in effect, to anneal the already hardened workpiece, cutting forces become too high and insert failure occurs.
In most cases, insert failure is a sign to the machinist to back off speeds and feeds even more. In the application of reinforced ceramic insert cutters, that is the wrong thing to do and only exacerbates the situation.
Assigning numerical values to optimum high speeds and feeds for cutting with ceramics is difficult because of the many process variables that constitute each application. There is, however, an empirical method of analyzing how close a machining operation using ceramic inserts is to optimum. Smith, "the chip produced will be bright red or almost white hot. This is normal for ceramic cutting tools but perhaps is a bit unusual for the machinist or operator who is taught to perceive red or white hot chips as dangerous or undesirable.
For shops looking to use ceramic cutters, there are several key points that, if followed, will help make the implementation smooth and the machining successful. Some of these are intuitive, others are generally good shop practice and a few others are ceramic specific. The relatively high cutting speeds necessary to generate optimum heat put a strain on the cutting insert. Whenever possible the strongest insert shape should be selected.
According to Greenleaf these shapes are—in descending order from strongest to weakest—round, degree diamond, square, degree diamond, triangle, degree diamond and degree diamond. In addition, the larger the corner radius, the stronger the corner.
In roughing, for example, use a large radius to rough the workpiece and then finish with a smaller tool nose radius. Tool holder stiffness is a critical consideration for ceramic machining operations. Deflections will create vibrations that are especially damaging to ceramic cutters, not to mention the surface finish of the workpiece. The shortest overhang possible is the best setup, and the thicker the tool shank or boring bar diameter, the better for cutting with ceramics.
For roughing operations, the programmer should consider varying the depth of multiple roughing passes. Multiple passes at the same depth tend to wear an insert in the same area causing a notch to form. Varying the depth spreads the wear patterns over a larger section of the insert. Another depth-of-cut strategy for flat-sided ceramic inserts is to program fewer passes but deeper ones in order to bury the insert deeper in the workpiece.
This moves the notch formation farther up the face of the insert to an area that has a stronger cross section. Applying ceramics is more than simply slapping on an insert and going at the work. The entire process, which is all factors needed to deliver the cutter to work, is involved to a high degree. Cutting with ceramic tools puts a strain on the machine tool.
High cutting forces, coupled with aggressive feeds and high spindle speed are like red-lining your car. Greenleaf thrives to this day because we've never lost focus of our role as a partner in our customers' success. Greenleaf Corporation has launched redesigned webpages to better help customers find information. Greenleaf Corporation is growing and expanding our global presence, which means we want to see your resume!
We have built a supportive community culture that yields long-term employees. Greenleaf Corporation delivers the latest cutting tool solutions along with exceptional customer service. We have a staff of highly skilled, dedicated, and professional customer service representatives ready to take your call at Greenleaf technical ceramics have established a reputation of superiority and innovation utilizing high quality materials and an extensive array of capable production processes.
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