The project of CBN inserts used for hard turning slewing bearing,wind power wheel bearing rings instead of grinding 

The hardness of Slewing bearing/wind power wheel bearing ring after quenching can arrive HRC55~62,The hardened layer usually is 3~5mm,Slewing bearing and wind power wheel bearing ring which materials are 50Mn or 42CrMo turning instead of grinding process usually use dry cutting with vertical lathe. Hard turning slewing bearing process raised large challenge on the toughness and wear-resistance of hardened cutting inserts because of the large machining allowance and strictly requirements on machining accuracy when hardening turning roller path and bearing surface . The balance performance of CBN hard turning inserts become the key process of the slewing bearing/wind power wheel bearing ring turning instead of grinding technology.Cubic boron nitride (CBN) is the most hard cutting inserts materials in current ferrous metal which used for machining cutting tools. CBN is already well known as hard cutting inserts after heat-treatment ,and it usually only use on turning small allowance instead of grinding after quenching because of brittleness limit. Depending on hard turning large allowance in the slewing bearings/wind power bearing ring industry ,We will study turning instead of grinding and hardened CBN inserts in this industry .

CBN inserts performance requirement for hardening turning slewing bearings and wind power bearings ring

The machining allowance of hard turning slewing bearings and wind power wheel bearing ring will be reserved depending on previous heat-treatment process and quenching deformation . Usually the allowance is 2~6mm when hard turning slewing bearings and wind power wheel bearing ring after quenching; hard cutting inserts need excellent impact toughness when machining slewing bearings and wind power wheel bearing inner and outer rings after quenching with large allowance. Thus it can be seen that the difficult point on hard cutting slewing inner and outer bearings is CBN inserts need high toughness and excellent wear-resistance and stability because finish turning slewing ring roller path after quenching require good smooth finish and dimension stability . So people who is in slewing wheel bearings industry will complain that CBN inserts has poor smooth finish because of low CBN inserts hardness, and CBN inserts is too Brittle to chipping ,especially for discontinuous surface cutting part.

Halnn superhard material developed non-metal adhesive BN-S20 grade CBN inserts,which specific to the high performance requirement for CBN inserts on hardened turning slewing bearing/wind power wheel bearing ring, As the only non-metal adhesive CBN inserts ,BN-S20 grade inserts not only ensure CBN inserts toughness ,but also avoid the lifetime reduction which caused by metal adhesive permature softening after CBN inserts was heating .BN-S20 grade cutting inserts suit high speed finishing and tough turning high hardness large-scale workpiece after quenching,which hardness is HRC98.5; and the Machinable Hardness range after heat treatment :HRC45-HRC79.Halnn BN-S20 grade CBN inserts also suit hard turning with long time and large allowance or turning instead of grinding process .

The feasibility of turning instead of grinding process in slewing bearings and wind power steel bearing rings industry and new grade CBN inserts application case

Application Case 1:  For turning wind power steel bearings rings with BN-S20 grade CBN inserts ,the allowance after quenching is 5mm, line speed is 90-150m/min , the roughness and the channel surface roughness of finish turning that work piece after quenching can arrive Ra0.3μm,all can satisfy turning instead of grinding process requirement; hard turning dual peach channel after heat-treatment ,all range is less than 0.005mm.Turning instead of grinding process has very obvious advantage,considering machining efficiency and cost , For example ,machining wind power 1.5MW sets pitch bearing inner and outer rings (Dimension:outer diameter1900mm,thickness 130mm)in bearing industry,if all machining allowance after quenching use grinding ,it need more than 18h;if use turning instead of grinding process ,it just need 4.5h.With the same machining accuracy requirement ,the efficiency of turning is 4 times of grinding ; From the tool life terms,like BN-S20 grade CBN inserts turning 1900 wind power pitch bearing, it can finish turning more than 30 piece bearing rings ;all electric energy and manpower and materials consumption used for turning only cost 20 percent of grinding;The inserts durability is higher and the usage cost is lower.

Application Case 2:Hard turning 50Mn large-scale slewing bearing outer ring after quenching,the hardness after heat-treatment is HRC55, Unilateral machining allowance is 2.5mm. Because of the deformation of the 50Mn rings after quenching,inner hole is irregular circle ,the previous CBN inserts often chipping.In order to reduce the chipping depletion,only can use many turning steps machining ,which cause low machining efficiency ,high equipment share,and the cost increase which include electronic cost,auxiliary materials cost ect. If use non-metal adhesive BN-S20 grade CBN inserts ,the cutting depth is about 2.5mm,the irregular part can arrive about 3mm; If finish machining with one turning step,it will reduce the cutting numbers,the efficiency will increase 3 times than before,the cutting inserts also can not chipping and braking which is most person worry about;and because non-metal has high thermal conductivity rate,with the same rotate speed , BN-S20 grade non-metal adhesive CBN inserts lift time is 50% up to common metal adhesive solid CBN inserts.Compare BN-S20 CBN inserts with common CBN inserts ,the product cost only increase 10 percent ,but at the same time ,the working efficiency is 3 times than before ,and the inserts lifetime is 1.5 times than before ,the consumer’s usage cost will reduce substantially.

Risks and Controls of Turning instead of grinding process

The lathe clearance and the rigidity which is used for hard turning decide the occurrence probability of the cutter shock and cutter back-off problems,also affect the workpiece dimension accuracy and surface roughness ,so we need targeted choose cutting insert geometry microscopic included CBN inserts’ cutting edge micromanage depending on the different requirement of the workpiece and the different equipment condition, in order to minimize risk of turning instead of grinding .

Contraposed turning instead of grinding process which used in the slewing bearing/wind power wheel bearings industry, hoosing the common cutting inserts geometry dimension,according to the wheel bearing type and the technology;Usually ,we often choose BN-S20 grade CBN inserts when turning inner or outer ring part ;It not only suit large diameter slewing bearing and wind power steel bearing ring ,but also suit non-standard bearing turning instead of grinding process and turning large allowance bearing ring which diameter less than 500mm and hardness after quenching above HRC60 instead of grinding ;We can choose BN-H20 grade CBN inserts for turning small dimension bearing ring which machining allowance after quenching less than 0.3mm.

What have to be aware of is that when have large machining allowance or uncontinuous machining,the cutter edge need process 0.2 * 20 degrees negative chamfer for hard turning bearing ring after quenching ,and the inserts holder need design chucking negative rake angle better is 6-7 degree ;and when small machining allowance finish turning after heat-treatment,the cutter edge usually need 0.1mm negative chamfer;choose the cutting inserts and nose of tool radius depend on the work clamp which is used for machining bearing ring , so that the whole turning instead of grinding process will not cutter-shock and cutter back-off. 

More information,http://www.halnntools.com/pro/,Or contact with us halnntools@gmail.com, whatsapp:+8615036165377,skype:cbn_inserts_angels