Smart ap­proach to milling tools

DEMM Engineering & Manufacturing - - MAINTENANCE MATTERS -

Re­cently-de­vel­oped milling tools pro­vide the op­er­a­tional flex­i­bil­ity re­quired to ma­chine in­creas­ingly com­plex com­po­nents.

Solid car­bide cut­ters have tra­di­tion­ally pro­vided high metal re­moval rates and ex­cel­lent ac­cu­racy. How­ever, the one-piece na­ture of the cut­ters re­quires they be re­ground when worn. Chang­ing tools for re­grind­ing in­ter­rupts pro­duc­tion, and costs time and money.

As a cost-ef­fi­cient al­ter­na­tive to solid cut­ters, tool­mak­ers have de­vel­oped milling cut­ters with in­dex­able, re­place­able in­serts.

When cut­ting edges wear, in­serts are sim­ply in­dexed or ro­tated. Worn out in­serts can be quickly re­placed with the tool body still in the ma­chine, and dif­fer­ent in­sert ge­ome­tries can be fit­ted to the same cut­ter body to cre­ate a va­ri­ety of con­tours.

The ge­ome­tries of in­dex­able in­serts have evolved as well, with many hav­ing cut­ting edges on both top and bot­tom sides. Turn­ing such a dou­ble-sided in­sert over af­ter in­dex­ing dou­bles the num­ber of avail­able cut­ting edges.

How­ever, the de­sign of dou­ble-sided in­serts does not in­clude space be­hind the cut­ting edge for a clear­ance an­gle, and thereby does not per­mit the tools to be ap­plied in a pos­i­tive-rake ap­proach.

In a pos­i­tive rake tool, the bulk of the in­sert body is tilted back from the cut­ting edge, en­abling the edge to shear the work­piece ma­te­rial. On the other hand, in a neg­a­tive-rake tool the bulk of the in­sert body tilts to­ward the work­piece and the tool essen­tially pushes the ma­te­rial be­ing cut. Be­cause of its de­sign, the cut­ting edge of a dou­ble-sided in­sert must ap­proach the work­piece from a neg­a­tive an­gle.

Neg­a­tive-rake cut­ting tools do of­fer cer­tain ben­e­fits. How­ever, be­cause neg­a­tive rake tools push the work ma­te­rial in­stead of shear­ing it, the cut­ting forces gen­er­ated by a neg­a­tive-rake tool can dis­tort a thin-walled part.

Con­versely, a pos­i­tiver­ake tool is free cut­ting, which min­imises cut­ting pres­sure, and can cut tight con­tours that a neg­a­tive tool can­not reach. Pos­i­tive in­sert ge­ome­tries pro­vide a large de­gree of flex­i­bil­ity to per­form a va­ri­ety of op­er­a­tions in­clud­ing slot­ting, con­tour­ing, and hel­i­cal in­ter­po­la­tion and ramp­ing.

The tools can help sta­bilise ma­chin­ing on older and/ or less rigid ma­chines. And min­imis­ing cut­ting forces is cru­cial when ma­chin­ing tough ma­te­ri­als such as ti­ta­nium, In­conel, and many stain­less steels.

To pro­vide in­dex­able in­serts that can cut in the pos­i­tive mode, tool man­u­fac­tur­ers of­fer one-sided in­serts with clear­ance an­gles be­hind the cut­ting edges. Al­though the in­serts can­not be turned over they can be ro­tated in the holder, pro­vid­ing mul­ti­ple use­ful cut­ting edges.

The free cut­ting na­ture of pos­i­tive-rake tools re­duces cut­ting forces and heat gen­er­ated in the cut. That is im­por­tant be­cause a onesided in­sert must have three times more tool life per edge to be cost ef­fec­tive, com­pared with dou­ble-sided in­serts.

Among the avail­able high-per­for­mance, onesided, pos­i­tive-rake in­serts de­vel­oped for milling are the XO.X10 tools de­vel­oped for the Turbo 10 se­ries of milling cut­ters from Seco Tools. The in­serts are en­gi­neered to min­imise cut­ting forces and con­trol chips while pro­vid­ing the flex­i­bil­ity to cut a wide va­ri­ety of part con­tours and ma­te­ri­als.

For ex­am­ple, up sharp, un­coated pol­ished edges work well in softer ma­te­ri­als such as free-ma­chin­ing alu­minium al­loys. For more dif­fi­cult-toma­chine ma­te­ri­als such as steels, cast iron, or stain­less steels, hon­ing or cham­fer­ing the tool edge is nec­es­sary to pro­tect it from chip­ping.

demm.co.nz/read­eren­quiry #D140231

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