The project of Halnn CBN inserts finish turning hardened steel

1.Turning characteristics and finishing technology of hardened steel

A.Turning characteristics of hardened steel.

Hardened steel means the steel after quenched,the organization is marten site,one kind steel with above HRC50. There are some characteristics when turning hardened steel: 

(1) High hardness, high strength,almost no plastic;

(2) Big cutting force,high cutting temperature ;

(3) Not easy to built-up edge

(4) The cutting edge is easy to chipping,wear and tear;

(5) Low thermal conductivity

B.Technological changes when finishing machine hardened steel

The hardened steel has a high hardness as it after quenched, Grinding is the traditional method to meet the required size precision and finish, but the grinding efficiency is too low. As the increasingly widely used of carbide coated cutting tools,diamond inserts,ceramic inserts and Cubic Boron Nitride(CBN) inserts, diamond, hardened,a new technology appeared,turning the hardened steel,it also called turning instead of grinding.

Advantages of turning instead of grinding :

(1) More efficient , time can be saved more than tenths in some cases

(2) Work piece has a better geometry shape than grinding,

(3) CNC lathe is much easier to maintain .

Following are the case of process the hardened steel by turning replace grinding,briefly introduce the choice of cutting tools materials when finishing hardened steel and the application case of Halnn CBN cutting tools finish turning hardened steel

2. The choice of cutting tools materials during finishing hardened steel

It is a important requirement to choose inserts materials reasonable when finish machining hardened steel .Inserts materials must have characteristic of high hardness ,better wear resistance,heat resistance,and have a certain strength, thermal conductivity according to the hardened steels cutting characteristic.

(1) Carbide alloy inserts: The carbide inserts hardness is about HRA89-89,equal to 71-76 HRC,it is easy happen burning the inserts so that wear quickly and having a low machining efficiency when machining the hardened steel with hardness above HRC40,so carbide inserts is suitable to finish machining the work piece with hardness less than HRC45,and with low turning speed.

(2)Ceramic inserts:As ceramic inserts has a big brittleness,chipping is easy happened, suit for machining the work piece with hardness between HRC40 to HRC55,but its better to avoid the interrupted turning.

(3) Halnn Cubic Boron Nitride(CBN) inserts BN-H20 and BN-S20 grade:suit for machining the steel work piece with hardness above HRC55.You can choose BN-H10 and BN-H20 grade CBN inserts if the cutting depth within 0.3 mm when finish turning,the two grade CBN inserts are both belong to brazed cubic boron nitride(CBN) cutting tools,the difference between the two grades CBN inserts is: BN-H10 grade is only suitable for continuous turning,while BN-H20 can stand medium interrupted turning work piece.

You can choose BN-S20 grade CBN inserts when rough machining the cutting depth reach above 0.5mm or interrupted finish turning hardened steel, this grade CBN inserts belong to non-metallic adhesive,it can not only interrupted turning hardened steel,but also can cut off the hardening layer with big allowance without wear the cutting tools,this is the biggest difference compare with the market common CBN inserts.As this three grade CBN inserts hardness reach about HV8000-HV9000, refractoriness reach 1400℃-1500℃,them cutting speed is few times faster than carbide inserts,CBN inserts lifetime is few dozens longer than carbide insert.Following are the three grade CBN inserts advantage and what material can machining with them.

BN-H10 grade CBN inserts performance advantages and processing material

Cutting tools  grade	Suitable for processing material	Performance advantages	Typical application industry
BN-H10 CBN inserts	Hardened steel  and high strength cast iron	Suitable for high speed finish machining, has a good balance between abrasion resistance and fracture damage resistance.	Baring, gear, gear shaft, constant speed coupling; Pearlitic nodular cast iron, etc.

BN-H20 grade CBN inserts performance advantages and processing material

Cutting tools  grade	Suitable for processing material	Performance advantages	Typical application industry
BN-H20	Hardened steel,materials difficult to turning	More flexible cutting tools, more cutting edges. Have good abrasion resistance and fracture damage resistance when machining the difficult cutting material such as hardened steel	The brake disc, brake drum, cast iron parts, hardened steel gear, etc

BN-S20 grade CBN inserts performance advantages and processing material

Cutting tools  grade	Suitable for processing material	Performance advantages	Typical application industry
BN-S20	Hardened steel, high strength steel, rolling hard steel, heat resistant steel, nickel base alloy and its surface hardening materials	Have excellent heat resistance and wear resistance when machining hardened steel and High strength steel	Hardened steel roller, screw, wind power bearing, high speed steel roll, the wear-resisting layer of oil drill pipe, etc

3. In which condition is more effective when turning instead of grinding with using the above three grade CBN inserts turning hardened steel

(1)It not only can reduce the amount of labor to 1/3～2/3 when cutting several complex surfaces in the CNC lathe,but also can  ensure a very high location accuracy by turning instead of grinding.

(2) when grinding the complex shape inner bore or small bore,the requirement of the grinding wheel is much strict,and cant grinding well sometimes, , then turning is the best way to machining the bore.

(3) If one part has few surfaces (outer circle, inner hole, face, stage, groove) are all required to grinding, just one process can be completed if use turning, you can save the grinding work procedures.

(4) Parts after quenched is easy to deformation and waste when leave a little allowance.You can leave a big allowance first,and then quenching, finally cut off the spare allowance and turning so that reduce the parts waste.

(5)Use CBN inserts machining high frequency parts which used under amount of load change and differ 

4. The case of Cubic boron nitride(CBN) cutting tools BN-H10 grade, BN-H20 Grade and grade BN-S20 machining hardened steel:

(1)BN-H10 grade PCBN inserts finishturning gears steel (after quenching hardness 58HRC-63HRC) :cutting parameters:ap=0.2mm,Fr =0.1mm / r, Vc = 180m/ min.Cutting state: continuous cutting, dry cutting.  

Halnn BN-H10 grade CBN inserts compare to ceramic tool (see below)：The cutting speed of Halnn BN-H10 grade CBN inserts is 1.4 times faster than ceramic inserts ,and the life is 5 times longer . Efficiency has been great improved and the machining time is saved.

Inserts material	Cutting speed	Inserts life	Produce tact
Halnn BN-H10 CBN inserts	180m/min	800pieces/per cutting edge	6 seconds
Other brand ceramic inserts	130m/min	150pieces/per cutting edge	8.5 seconds

(3) BN - S20 grade CBN inserts finishing the ball screw, processing materials: Chinese brand 40CrMo or Gcr15, HRC60-62 hardness, cutting parameter: ap = 4.5 mm, Fr = 0.10 mm/r, Vc = 90 m/min, cutting way: dry cutting.(2)BN-H20 grade CBN inserts finishing synchronizer (after quenching hardness 58HRC-63HRC) case: cutting parameters: ap = 0.15mm, Fr = 0.1mm / r, Vc = 170m / min. Processing Step: finishing groove, continuous cutting, Cutting state: Dry Cutting.                   

Inserts materail	Cutting speed	Cutting depth	The final failure forms
Halnn BN-S20 CBN inserts	90m/min	4.5mm	Normal wear
Other brand ceramic inserts	65m/min	0.5mm	Chipping

BN-S20 brand CBN inserts compare to ceramic blade : The cut depth of Halnn S20 grade CBN inserts is 9 times deep than ceramic inserts under the 1.3 times faster than ceramic inserts cutting speed, the BN-S20 grade CBN inserts case subvert the knowledge which people always thought that Cubic Boron Nitride(CBN) inserts just can finish machining,as the non-metallic adhesive BN - S20 grade inserts impact resistance was improved ,BN-S20 CBN inserts can stand the 7.5mm cut depth,saved the machining time by reducing the feed times,and also reduce the machining cost , realize people rough machining the quenched steel and heavy turning the big size hard work piece. 

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