Turning the ball screw instead of grinding  CBN inserts BN-S20 

Part 1 The Mechanism of the PCBN inserts which used turning the ball screw instead of grinding 

Ball screw are divided into Cold rolled ball screw and grinding ball lead-screw two sorts .The technology of turning(instead of grinding process of ball screw not only fit for machining the Rolling screw end bearing support,but also fit for machining part of the Precision grade grinding screw ball. For cold rolled ball screw，this technology solved the traditional solution on machining the Rolling screw end bearing support after annealing;

For grinding screw ball，machining the screw of ball screw after quenching，it not only has high efficiency，but also meet the requirements of part of precision grade on machining the screw of the ball screw.

As we all know ,In the early days ,Hard cutting(which is used turning the ball screw instead of grinding process）technology usually refer to finish machining on Chilled Hardened Steel. For ball screw end bearing support(base/ bed), It will have a large machining allowance after quenching .People usually machining the hardened work piece after annealing as there is no cutting tools which can cutting hardening materials with large allowance . Machining Ball screw after annealing not only has low efficiency ,but bring many problems ,such as heat treatment distortion and cracking.

With the development of the cutting technology ,the appearance of Halnn super hard Non-metallic adhesive CBN cutting tools BN-S20 lay the foundation on cutting hardening materials with large allowance. BN-S20 grade CBN cutting tool is different from common PCBN cutting tools ,which only use ceramics CBN sintering body of the adhesive, machined through high temperature and high pressure .and has better impact resistance,using Nanoscale ultrafine grain, also has more excellent wear resistance. When machining the two bearing support installation end position of the hardened Cold rolled ball screw,BN-S20 grade CBN inserts lifetime is 4 times more than common CBN inserts .Because of the good impact resisting toughness,the cut depth can arrive 7.5mm,and it also fit for intermittent cutting the hardened ball screw screw.

Part 2 The technology of turning instead of grinding process of ball screw

The difficult points on the technology of turning instead of grinding process of ball screw, The hardness of Ball screw Gcr15 after quenching is usually about HRC 62;  the technology of turning instead of grinding process of ball screw is refer to turning the screw directly on the screw rod after quenching.For example, for the ball screw which diameter is 60mm, the hardened turning screw technology should be as follows :
a. Quenching 60mm round steel 
b. Rough turning screw (turning screw with 0.5mm cut depth,the main and minor angle both have cut depth )
c. Finishing (0.2mm cutting depth ,change it depended on the diameter and the deformation)

The cutting parameters of turning instead of grinding process of ball screw :Common lathe Rotating speed 80-120 turns（Line speed about 25m/min）;CNC Lathe Rotating speed 560 turns(Line speed about 100m/min) .Lathe 6130 15*15mm or 20*20 holder ; put 45 degree turning inserts in the mid ;total cut depth about 10mm off, forming 90 degree groove. Then finishing grinding the arc of the ball screw, finishing turning or hardening whirling milling screw ball with CBN turning inserts and turning the sump bottom of the screw root with sharp CBN inserts which can be grinding.

The roughness after finishing machining the raceway of the screw ball with BN-S20 grade CBN inserts is higher than the smooth finish after Cyclones milling the screw ball
The difficult points of this technology :
There is large compressive stress between the CBN inserts and screw ball when GCr15 grade screw ball rough turning the hardened raceway,and CBN inserts can cutting both the main and minor angle,which will lead in chipping and splintering. So most screw ball industry customers are skeptical about CBN inserts. 

Part 3 The technology of hardening machining the two Cold rolled ball screw bearing support

This technology is hardening machining process which used for cold rolled ball screw which hardness is above HRC 60. The difficult machining point is the hardness will be higher and the machining allowance will be larger after the screw is quenching . 

The cold rolled ball screw hardening cutting parameters (only fit for BN-S20 grade CBN inserts)

Cutting depth : cutting depth can arrive 8mm,roughing machining can cut most allowance with one step,and remove the hardening layer.
Line speed :70~90m/min
Cutting distance 0.1mm/r ,range depending on the machining rigidity.

Advantages and characters of BN-S20 grade PCBN inserts

Halnn superhard BN-S20 grade PCBN inserts is PCBN inserts with non-metal adhesive.BN-S20 grade PCBN inserts avoid the chipping and splintering when machining screw ball with common PCBN inserts,because of higher thermal conductivity rate,longer inserts lifetime.and well impact resisting toughness. Halnn superhard BN-S20 grade PCBN inserts fit for both common lathe and CNC lathe .

Compared Halnn superhard BN-S20 grade inserts with PCBN inserts which used common metal adhesives, when turning the hardening raceway screw of the screw ball ,the former inserts lifetime will be about 1.5~2 times of the latter inserts and the most obvious character is that will not become chipping and splintering when roughing machining .All because non-metallic HLCBN superhard inserts has excellent thermal conductivity rate and impact resisting toughness .

Halnn superhard BN-S20 grade PCBN inserts use turning the ball screw instead of grinding process , have higher smooth finish and longer inserts lifetime when finish machining the screw ball ,(Halnn superhard turning tools research department , copyright ,please indicate the resource if reproduced and quoted . 

More information ,please click http://www.halnntools.com/pro/Solid_CBN_inserts/

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Turning Hardened Steel and CBN inserts 

Introduction

We usually meet the following problems when hard turning quenched steel work piece,especially when rough machining quenched steel,interrupted turning,grooving machining,and the roughness of quenched steel after turning.Most people can’t choose the suitable cutting tools for turning quenched steel,kinds of machining problem appeared,such as:roughing,interrupted machining.Now we mainly discuss the common problems and introduce CBN insert.

The problems when hard turning quenched steel

1.Rough machining quenched steel

Turning Gears after heat-treatment,the hardness of gear and gear ring after quenching or cemented quenching was usually above HRC55,some even reach HRC60~HRC65.Common Gear materials are: 20Cr,20CrMnTi,40Cr,42CrMo,35CrMo. Some gear distorted serious,especially the big gear ring,big gear after cemented quenching,like high-speed rail gear, engineered machinery big gear ring,heavy industry big gear ring,etc,those big gears gear rings deformation was very big,this case involved rough machining quenched steel.At the same way,rough machining tool steel usually happened in manufacturing of die steel.

2.The interrupted machining of the quenched steel

Interrupted turning is a challenge,even for quenched steel hardness reach about HRC60.Especially when high speed turning quenched steel,if the work piece has interrupted turning,the cutting tools will stand more than 100 times impact per minute,it's a big challenge for the cutting tools.For example,Turning hardened gear instead of grinding,and the Vehicle gear occupy 62% in the whole gear industry,and auto gear occupy 62% in the Vehicle gear.It is said that the auto gear occupy about 40% in the whole gear market.Although turning quenched steel instead of grinding was wide spread,there are still some problem during machining the auto quenched gear,such as,there some oil hole in the auto gear,this will happen the interrupted turning trouble,many CBN inserts easily happen to chipping when machining the oil hole,its hard to guarantee the gears position tolerance.

3.Grooving machining quenched steel

Such as:hard turning the synchronizer sliding sleeve gate after quenched,the CBN inserts lifetime still not so satisfied though CBN inserts manufacturer research specialized CBN inserts used for synchronizer sliding sleeve.

4.The roughness of hard turning quenched steel

The bearing steel after quenching usually require a much good finish by turning,Gcr15 steel is a common bearing steel,the hardness after quenching is about HRC62,as the precision and finish of the bearing have a high requirement.Even if adjust the CBN insert edge well,it is still impossible to get a Ra 0.4 finish of the quenched steel after turning.

Choosing Cutting tools when machining the quenched steel

There are few aspect to choose CBN cutting tools for hard turning quenched steel in turning field:one is the choice of cutting tools material ,usually when cutting the quenched steel work piece which hardness less than HRC50 and with a small feed rate,a small cutting depth,ceramic cutting tools will be a better choice.CBN insert suit for the work piece which hardness is harder than HRC50,meanwhile ceramic insert need avoid semi-finishing and roughing,but CBN inserts can suit for interrupted turning,heavy rough machining.Another is the choice of CBN inserts manufacturer/grade and edges processing,a good CBN insert not only won’t chipping during rough machining process,but also can keep a longer working life and get a good surface finish when finishing efficiently.

When finish turning quenched steel,we can choose welding CBN insert.When rough machining or interrupted turning,we need choose the solid/overall CBN inserts,there just a few manufacturer produce this type CBN inserts,Halnn did best in China,BN-S10 CBN inserts from Halnn superhard material make it successful to rough machining and interrupted turning quenched steel industry,and Halnn superhard material company enjoy a highl reputation in world cutting tools industry.

More about our products,please click http://www.halnntools.com/pro/,or contact with us :halnntools@gmail.com,whatsapp:+8615036165377,skype:cbn_inserts_angels

Analyze CBN inserts cracking phenomenon

Summary

CBN Cutting tools abnormal cracking is what customers most boring,which will increase Processing cost,work piece scrap or reworking,lower the processing efficiency and other problems.Especially CBN insert with high price,cracking phenomenon will cause lots of waste,so it is so important to choose the most suitable CBN inserts.

Halnn superhard material summarized some chipping reasons as following:

1.CBN inserts itself performance

The overall sintering between main CBN granule and suited binder will exit a high tensile strength,which is the advantages of common CBN inserts when rough machining work piece.Except the high purity require when producing CBN inserts,the CBN(cubic boron nitride) micro powder also need deoxidized and other many process,and test its bulk density,this is just the most important reason for different  quality CBN inserts in the market.In addition,the synthesis process directly decide the dimension and size of the poly-crystalline grain when processing CBN inserts.

2.The selection of CBN inserts

The cutting depth of soldering CBN inserts should be controlled within 0.3mm or even less to ensure using safety, any manufacturers compound CBN inserts can not make sure there is no chipping when facing interrupted turning condition,this condition must choose Solid CBN inserts.

3.The selection of the CBN inserts type

The impact resistances comparison with the same grade CBN inserts:round insert,commonly 25°,45°,75°,83°,90°(the inserts angle after install ),and the width and angle of CBN inserts itself negative chamfer also affect the CBN cutting tools strength.

4.Cutting parameter influence

Reduce the feed rate is the most reliable method from the cutting force;we need turn down the revolving speed when interrupted turning or machining both long and thin shaft.

5.CNC lathe reason

The machinery overall system rigidity must be high,In order to avoid shaking during machining;we also need avoid the jammed when rough machining.

6.The extend length of the inserts arbor

If the inserts arbor extend long length,it will have the  risks on shaking and chipping,the extend length need within the arbor size.

7.The inserts arbors quality reason

Good quality inserts arbor has a excellent heat-conducting property, high machine rigidity, seismic performance;although the price is a little higher,but the total processing cost will not have a big change,and it will reduce the inserts unnecessary waste.

8.The cutting fluid

Cooling liquid can be used when rough machining gray cast iron or other materials,but the thermal stress will cause CBN inserts cracking risk.

In some conditions,CBN inserts own impact resistance and heat-conducting property are not contradictory.For example,YG series cutting tools have a good impact resistance,but there are a strong cutting resistance will also make the inserts cracked,this condition will mislead the researchers and customer thinking that the inserts doesn't have a good impact resistance,but the actually reason is the cutting tools was not good wear resistant.

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

Halnn release Hard turning bearing rings CBN inserts BN-S20

Hard turning bearing ring technology:

Step 1:Finish turning the base level end, the base level end will be less than 0.005 mm after finish turning ,then turning the outer diameter of the shaft washer;

Step 2:Turn to another face for turning

Step 3:Turning the upper end surface (inside the channel); convert  the workpiece platen, then turning the upper end surface.（outside the channel）

Step 4:Hard turning the spherical channel (Halnn superhard CBN spherical inserts ), the channel bottom range will less than 0.005mm after hard turning ,the channel surface roughness will be Ra0.3μm

Step 5:Finish turning inner diameter of the shaft washer.

With above technology ,the wall thickness difference of the push ball bearing ring will less than 0.01mm,which is more than the precision value of P5 grade bearing .

Application Case 1：Hard turning wind power bearing ring.

Machining Targets: variable pitch bearing ring used for 1.5MW wind power machine sets.

Machine:CNC Vertical Lathe

Cutting Inserts Grade:Halnn superhard BN-S20 CBN inserts

Workpiece Dimension: Outer diameter φ1900mm，Thickness 130mm，

Roughness after finish turning：The channel bottom range of double peach channel after finish turning all less than 0.005mm ,and the channel surface roughness will reach Ra0.3μm.

Application Case 2: Turning the bevel of the Precision angular contact bearing ring 

Machining Targets : Precision angular contact bearing

Cutting Inserts Grade:Halnn superhard BN-H20

Inserts Lifetime:Machining about 1000 sets /cutting edge; smooth finish≤Ra0.4

Advantages of hard turning the bearing ring

 1.High working efficiency

For example, like variable pitch bearing ring which is used for machining wind power 1.5 MW machining sets in bearing industry.If grinding machining all the allowance after queching ,the grinding time is above 18 h, but use the turning instead of grinding process,just need 4.5h .At the same machining precision,the turning machining efficiency is 4 times than grinding machining .

2.Low cost

For example , like turning the 1900 variable pitch bearing ring ，use Halnn superhard BN-S20 grade solid CBN inserts can finish turning more than 30 piece bearing ring.

3.Reduce pollution

Compared with the grinding iron grain with the turning iron scraps, it will be more convenient to deal with the iron scraps ,and the irons scraps cost lower as resource ,also reduce the pollution .

Conclusion

When turning the large-scare and high-precision bearings,using hard turning technology (used turning instead of grinding process) has become a trender in bearing industry .This technology has high machining effiency ,low cost ,traditional technology can not contend with it .As BN-S20. BN-H20 grade superhard inserts enter into the market , the smooth finish and reliability which use turning instead of grinding process become better ,and the inserts cost become lower .

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

The lifetime and wear resistance of CBN inserts

Part 1 Summary

The common failure mode of cutting tools is wear,the inserts lifetime has a lot to do with the wear resistance,after testing,the CBN(Cubic Boron Nitride) inserts lifetime is usually several longer times or even more than carbide inserts and ceramic inserts.CBN inserts lifetime is not only relate the tools quality,but also related to the workpieces materials, machining speed etc.So it is necessary to know more about the relationship between CBN inserts lifetime and performance,use the suitable CBN inserts,increase machining efficiency,reduce the the unnecessary machining waste.

1.The comparison between CBN inserts lifetime and other materials inserts

(1)The round CBN inserts from Halnn super hard,with cutting parameters Vc=40m/min,f=0.16mm/r to machining chilled cast iron with HRC55.CBN inserts durability is 500 min ,but the ceramic inserts is just 5 min.CBN inserts durability is 100 times longer than ceramic inserts.The solid Polycrystalline Cubic Boron Nitride(PCBN) inserts developed by Halnn superhard was widely used in roughing application,CBN inserts begin used in roughing process with big feed rate and cutting depth.It has a higher cutting efficiency than carbide inserts.For example,CBN inserts turning chilled cast iron roll,getting a high cutting efficiency.The cutting parameters:Vc=61m/min,ap=/mm,f=0.94mm/r,the metal cutting efficiency can reach 400cm3/min,the inserts almost has no wear.

(2) Halnn superhard CBN inserts machining the gray iron,cutting parameter:linear speed 600m/min,was 2 higher times efficiency than carbide inserts,the lifetime can be improved about 6-12 times longer when roughing,has 15-20 times longer lifetime than carbide inserts when finishing.

Part 2 The relation between CBN inserts grade and its performance

The CBN inserts performance is closely to the CBN inserts grade.The CBN granularity, contect, and the different kind of binder directly decide CBN inserts performance,each manufacturer define them own grade according to the performance and element,the grade cant used universally although they are similar.

CBN inserts can be divided into two categories according to its organization:one is made by CBN grain sintered directly without binder,has a high CBN content(more than 70%),has a high hardness,used for turning machining the heat-resisting alloy,cast iron and iron series sintered metal;another category is base the CBN grain as the main body,according to the ceramic binder(main contain TiN,TiC,TiCN,AIN,Al2O3,etc)sintered,this kind CBN inserts has a low content CBN(less than 70%),has a lower hardness,just suir for machining the hardened steel.

The classification of CBN inserts grade:Halnn superhard CBN inserts can be divide into rough machining and finish turning according to CBN inserts granularity size;The detail classification is based on the CBN grain crystal.

1.The CBN grain crystal classification of CBN inserts

The size of CBN grain crystal can be divide into three categories: coarse grain (the average size is 20-50μm),medium size grain crystal(10-20μm), fine grain(2-10μm).the larger size of the grain,the better wear resistant and longer lifetime the CBN inserts will have.but the blade of the inserts will be worse,its hard to make a high precision inserts. On the contrary,the the fine grain CBN inserts has a good quality blade,the work piece will have a good surface after machining.There are 1μm,less than 0.5μm grain now,we can choose the different size grain according to the different machining process require of roughing and finishing.

2.The corresponding work piece of the different CBN inserts grade

Currently CBN inserts don't have a uniform classification just like carbide inserts,each manufacturer has themselves type and grade,we need choose base on them catalogue during using.The famous CBN inserts grade was BK-K1 and BN-H1 which were developed by Halnn super hard material company,those two grade inserts was used for machining cast iron and hardened steel separately.Later,BN-S20 and BN-S30 grade inserts were the solid PCBN inserts,can machining:High-chromium cast iron,white cast iron, austempered ductile iron,high-temperature alloy, powder metallurgy,gray cast iron,hardened steel and so on,connect the machining condition(roughing , semi-finishing,finishing)require to the CBN grain size to form the CBN inserts grade.

The different CBN inserts grade has a different cutting performance as the different composition,so we need pay more attention when choose the CBN inserts.

Part 3 How to judge the CBN inserts quality

Judge the CBN inserts from the using point of view,the good quality CBN inserts has two characteristic:

1.Has a good impact resistance,especially in the roughing field,the inserts will not crack,this is most basic guarantee use security of CBN inserts.

2.Has a good wear resistance,in the same time for ensure the efficient machining also can reduce the cost and can instead of carbide inserts and ceramic inserts,this is the economical guarantee of CBN inserts.

Part 4 Discriminate the inserts wear resistance and toughness

It is not difficult to improve the cutting tools hardness and toughness,but with increase of the cutting tools materials hardness,the toughness will reduced,so we need consider the work piece material,the CNC lathe,machining condition comprehensive in use,avoid the contradiction between the hardness and toughness.Aim at the CBN inserts character,Halnn seperhard company research one grade CBN inserts which suit for cutting with low speed and roughing,it has a excellent impact resistance,Halnn superhard material company enjoy a high reputation in cutting tools industry.

Part 5 High efficiency machining is not mean machining with high speed

Cubic boron nitirde is the highest hardness cutting tools material for machining the ferrous metals,so most people thought ‘high hardness,low toughness,just suit for high speed cutting or high precision machine tool’ by mistake,but its not.High efficient machining is not mean high-speed machining,the cutting tools lifetime also will reduce with the increased linear speed even the CBN inserts has a very high hardness.

It is more suitable to machining the difficult processing materials with increasing the cut depth and feed rate for improving the machining efficiency.This is the Halnn superhard company purpose to the reason why research the cubic boron nitride inserts,and facts proved that this case solved the customers practical machining problem,The CBN inserts from Halnn superhard company will not crack when machining with high efficient,expeciall in the industry which interrupted cutting the difficult cut material,this is also the biggest success in the hard cutting tools field.

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