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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