WO2009070112A1

WO2009070112A1 - Coated cutting tool insert

Info

Publication number: WO2009070112A1
Application number: PCT/SE2008/051360
Authority: WO
Inventors: Ingemar Hessman
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2007-11-28
Filing date: 2008-11-27
Publication date: 2009-06-04
Anticipated expiration: 2010-05-28

Abstract

The present invention relates to a coated cutting tool insert especially for heavy roughing crankshaft milling comprising a cemented carbide body and a coating. The cemented carbide body has a composition of 12.5-14.5 wt% Co, 0.54-0.62 wt% Cr and balance WC with a coercivity of 12.5-14.5 kA/m. The cemented carbide insert is at least partly coated with a 4.1-6.9 μm thick coating including at least three layers of TiCxNyOz forming an inner coating 1.9-3.6 μm thick followed by an α-Al2O3-layer with a thickness of 1.8-3.6 μm.

Description

Coated cutting tool insert

The present invention relates to inserts particularly for crank shaft milling, heavy roughing with high vibration level where the internal properties of the inserts are balanced against the specific loads in this type of application.

The crankshaft (see Fig. 1) is the part of an engine which translates the reciprocating linear motion of the piston into rotation. It is the central component in any combustion engine. It comes in many shapes and sizes - from those in little two-stroke engines in garden-equipment to giant ones in ship diesel engines. It is highly unsymmetrical, long and relatively slender, made of different material types like steel and pearlitic nodular iron, which is demanding to machine, has close quality limits and is subjected to very competitive manufacturing demands. As a mass-volume component, the crankshaft is ruled by cost-efficiency and has undergone considerable evolvement as regards design, material and machining. Crankshafts are generally forged or cast to essentially final shape. With crankshaft milling is therefore generally meant the machining of the bearing surfaces (mains A) of the shaft including the journal (E) bearings surfaces and the stroke bearings (Pins B) .

Internal milling (see Fig. 2) is used mainly for large-volume machining of large sized truck crankshafts also known as planetary milling. The milling cutter forms a ring through which the crankshaft is rotated or standing still. The inserts (G) are positioned closely pitched on the internal circumference of the ring to machine the pin bearing surface (B) and cheek surfaces (D) of the crankshaft. Typically a cutter can have up to 100 inserts in segments on a cutter diameter of 400 mm and machines bearings (A), pins (B) and tops the cheeks (D) of the crankshafts. This is a very stable set-up, used mostly for larger crankshafts and when a lot of material has to be removed.

External milling (see Fig. 3) is used mainly for large-volume machining of small to medium sized automotive crankshafts. The inserts (G) are positioned closely pitched on the external circumference of the ring to machine the pin bearing surface (B) and cheek surfaces (D) of the crankshaft. Typically a cutter can have up to 350 inserts in segments on a cutter diameter of 700 mm and machines bearings (A), pins (B) and tops the cheeks (D) of the crankshafts. This is not as stable as for internal applications, used mostly for smaller crankshafts. EP-A-1798309 discloses a coated cutting tool insert particularly useful for dry and wet machining, preferably milling, in low and medium alloyed steels, stainless steels. The insert is characterized by WC-Co cemented carbide with a W and Cr alloyed Co-binder phase and a coating including at least three TiC_xN_yO₂ layers and a top layer at least on the rake face of a smooth α-Al₂C>3-layer having flattened grains as a result of a final blasting treatment.

Changing inserts in big cutters with a lot of inserts takes a long time and the manufacturer has to have several set ups of cutters in order to get an efficient manufacturing flow. The objective is to obtain a cost efficient and long tool life in order to maximize the time in the machine. The grade has to be designed to meet the loads on each specific crank shaft. The loads in this type of application are depending on vibrations, length of cut, depth of cut, surface zones etc. The object of the present invention is to provide a cutter insert grade for heavy roughing with vibrations, with cost efficient tool life in milling of steel crank shaft.

Fig 1 shows an example of a crankshaft in which

A=Mains B=Pins

C=Top of cheeks

D=Cheeks

E=Journal

F=flange Fig 2 shows an example of an internal milling cutter in which

G= Insert

Fig 3 shows an example of an external milling cutter in which

H=Insert

The insert has an improved cutting performance in medium alloyed steel, with or without raw surface zones preferably under unstable conditions such as vibrations, long overhang, chip-hammering or recutting of chips or in generally toughness demanding operations in dry conditions .

According to the present invention a coated cutting tool insert is provided consisting of a cemented carbide body with a composition of 12.5-14.5 wt% Co, preferably 13-14 wt% Co, 0.54-0.62 wt% Cr, preferably 0.55-0.61 wt% Cr and balance WC.

The coercivity is 12.5-14.5 kA/m, preferably 12.7-14.0 kA/m. The cobalt binder phase is alloyed with a certain amount of W and Cr giving the cemented carbide its desired properties. W and Cr in the binder phase influence the magnetic properties of cobalt and can hence be related to a value CW, defined as

CW= magnetic-% Co/ wt-% Co, where magnetic -% Co is the weight percentage of magnetic material and wt% Co is the weight percentage of Co in the cemented carbide. The CW-value varies between 1 and about 0.6 depending on the degree of alloying. Lower CW-values correspond to higher W and Cr contents in the binder phase and CW =1 corresponds practically to an absence of W and Cr in the binder phase.

The cemented carbide has a CW-value of 0.76-0.84, preferably 0.78-0.82, and most preferably 0.79-0.81. The cemented carbide may also contain small amounts, <1 volume %, of η-phase (M₆C), without any detrimental effects.

The cemented carbide insert is at least partly coated with a 4.1-6.9 μm thick coating including at least three layers of TiC_xN_yO₂. The three layers form an inner coating with an α-Al₂C>₃-layer as the outer layer at least on the rake face. The TiC_xN_yO_z-layers have a total thickness of 1.9-3.6 μm and comprise: a first TiC_xN_yO_z-layer, 0.1 to 1 μm, adjacent to the cemented carbide having a composition of x+y=l, x>=0, preferably x<0.2 and z=0. a second TiC_xNyO₂ layer, 1 to 3.4 μm, having a composition of x>0.4, y>0.4 and 0=<z<0.1, preferably z=0. a third TiC_xNyO₂ layer, 0.1 to 1 μm, adjacent to the α-Al₂O₃- layer having a composition of x+y+z>=l and z>0, preferably z>0.2, x+y+z=l and y<0.2.

The outer α-Al₂θ3-layer has a thickness of 1.8-3.6 μm. The edges on the insert have been subjected to a brushing treatment .

In a preferred embodiment, the insert has a thin 0.1-1 μm colored top layer preferably of TiN or Ti (C, N), most preferably deposited by CVD technique.

The present invention also relates to a method of making a coated cutting tool insert by powder metallurgical technique, wet milling of powders forming hard constituents and binder phase, compacting the milled mixture to bodies of desired shape and size and sintering, of a cemented carbide body with a composition of 12.5-14.5 wt% Co, preferably 13-14 wt% Co, 0.54-0.62 wt% Cr, preferably 0.55- 0.61 wt% Cr and balance WC. The cemented carbide body may also contain smaller amounts of other elements, but on a level corresponding to a technical impurity. The milling and sintering conditions are chosen to obtain an as sintered structure with a coercivity of 12.5-14.5 kA/m, preferably 12.7-14.0 kA/m and a CW- ratio of 0.76-0.84, preferably 0.78-0.82, and most preferably 0.79- 0.81.

The cemented carbide insert is at least partly coated with a 4.1-6.9 μm thick coating including at least three layers of TiC_xN_yO₂ forming an inner coating with an α-Al₂C>₃-layer as the outer layer. The TiC_xN_yO_z-layers having a total thickness of 1.9-3.6 μm comprise: a first TiC_xN_yO_z-layer, 0.1 to 1 μm, adjacent to the cemented carbide having a composition of x+y=l, x>= 0, preferably x < 0.2 and z=0 using known CVD methods using a reaction mixture consisting of TiCl₄, H₂ and N₂, a second TiC_xN_yO_z-layer, 1 to 3.4 μm, having a composition of x>0.4, y>0.4 and 0=<z<0.1, preferably z=0 using the well-known MTCVD- technique at a temperature 885-850⁰C and CH₃CN as the carbon/nitrogen source, a third TiC_xN_yO_z-layer, 0.1 to 1 μm, adjacent to the α-Al₂O₃- layer having a composition of x+y+z>=l and z>0, preferably z>0.2, x+y+z=l and y<0.2 using known CVD methods using a reaction mixture of TiCl₄, H₂ and N₂. The outer α-Al₂O₃-layer has a thickness of 1.8-3.6 μm and is deposited using known CVD-techniques .

The edges on the insert are subjected to a brushing treatment. In one embodiment an additional 0.1-1 μm coloured layer is deposited on top of the α-Al₂O₃-layer preferably of TiN or Ti (C, N), preferably using CVD technique prior to the brushing treatment.

The coated cutting tool insert according to the invention is preferably a cutting tool milling insert for heavy roughing crankshaft milling

The present invention also relates to the use of an insert according to the invention for crank shaft milling or cam shaft milling of steel with a carbon content of about 0.30-0.43 wt% of medium alloyed steels, with raw surfaces such as cast skin, forged skin, hot or cold rolled skin or pre-machined surfaces at cutting speeds and feed rates according to following:

Internal milling Speed: 100-180 m/min Feed per tooth: 0.23-0.32 mm Radial depth of cut: 3-12 mm.

External milling Speed: 140-250 m/min Feed per tooth: 0.17-0.27 mm Radial depth of cut: 3-8 mm.

Example 1

Cemented carbide specially designed milling inserts in the having a composition of 13.2 wt-% Co, 0.58 wt-% Cr and balance WC and with a Hc value of 13 kA/m and a CW-value of 0.80 were prepared.

The inserts were then coated as follows:

- a first layer of 0.5 μm CVD TiN,

- a second layer of 2.7 μm columnar TiC_xN_y with a composition of about x=0.55, y=0.45 by using the well-known MTCVD-technique, tem- perature 885-850°C and CH₃CN as the carbon/nitrogen source and

- a third, bonding layer of 0.5 μm TiN

A fourth layer consisting of 2.5 μm Cf-Al₂O₃ and finally a top layer of about 0.3 μm TiN was deposited using known CVD-technique . Finally the inserts were brushed with nylon brushes with SiC- particles . Example 2

Inserts according to the present invention were tested in an internal crank shaft milling, heavy roughing, circular interpolation operation in steel 0.38 wt% C for large six cylinder engine. Tool: Special milling cutter dia. 400 mm

Number of inserts: 3x28 Pes

Criterion: Surface finish and dimensions.

Reference: Competitor inserts 3x28 Pes

Cutting data Cutting speed: Vc = 160 m/min

Feed per tooth: Fz= 0.28mm per tooth

Radial depth of cut: Ap=5 mm

Dry conditions

Tool life reference (prior art) 400 crank shafts std. production Tool life of invention was 1050 crank shafts, average of five tests .

Increase of tool life 162 % with improved surface finish and productivity.

Example 3

Inserts according to the present invention were tested in a external cam shaft milling roughing operation in steel C 0.40 for a six cylinder truck engine.

Tool: Special milling cutter dia. 450 mm Number of inserts: 3x56 PCs

Criterion: Surface finish and dimensions. Reference: Competitor inserts 3x56 PCs Cutting data

Cutting speed: Vc = 157 m/min Feed per tooth: Fz= 0.3 mm per tooth

Radial depth of cut: Ap=3-8 mm full width 30 mm. Dry conditions

Tool life reference (prior art) 250 cam shafts standard production Tool life of invention was 500 cam shafts, average of five tests . Increase of tool life 100 % with improved surface finish and productivity.

Claims

1. A coated cutting tool insert comprising a cemented carbide body and a coating, wherein said cemented carbide body has a composition of 12.5-14.5 wt% Co, 0.54-0.62 wt% Cr, and balance WC with a coercivity of 12.5-14.5 kA/m, with a CW-value of 0.76-0.84, defined as

CW= magnetic-% Co/ wt-% Co where magnetic-% Co is the weight percentage of magnetic material and wt% Co is the weight percentage of Co in the cemented carbide, the cemented carbide insert being at least partly coated with a 4.1- 6.9 μm thick coating including at least three layers of TiC_xN_yO₂ forming an 1.9-3.6 μm thick inner coating and an outer α-Al₂C>₃-layer, the TiC_xN_yO_z-layers comprise:

- a first TiC_xN_yO_z-layer, 0.1 to 1 μm, adjacent to the cemented carbide having a composition of x+y=l, x>=0,

- a second TiC_xN_yO_z-layer, 1 to 3.4 μm, having a composition of x>0.4, y>0.4 and 0=<z<0.1,

- a third TiC_xN_yO_z-layer, 0.1 to 1 μm, adjacent to the outer α-Al₂C>3- layer, having a composition of x+y+z>=l and z>0, the outer α-Al₂C>3-layer has a thickness of 1.8-3.6 μm, the edges on the insert have been subjected to a brushing treatment.

2. A cutting tool insert according to claim 1, wherein the cemented carbide body has a composition of 13-14 wt% Co, 0.55-0.61 wt% Cr and balance WC with a coercivity of 12.7-14.0 kA/m with a CW- value of 0.78-0.82.

3. A cutting tool insert according to any one of claims 1-2, wherein - for the first TiC_xNyO_z-layer, x<0.2 and z=0,

- for the second TiC_xN_yO_z-layer, z=0,

- for the third TiC_xNyO_z-layer, z>0.2, x+y+z=l and y<0.2.

4. A cutting tool insert according to any one of claims 1-3, comprising an outermost 0.1-1 μm coloured top layer of TiN or

Ti (C, N) .

5. A coated cutting tool insert according any one of claims 1-5, wherein it is a cutting tool milling insert for heavy roughing crankshaft milling.

6. Method of making a coated cutting tool insert comprising a cemented carbide body and a coating, comprising preparing by powder metallurgical technique, wet milling of powders forming hard constituents and binder phase, compacting the milled mixture to bodies of desired shape and size and sintering, of a cemented carbide body with a composition of 12.5-14.5 wt% Co, 0.54-0.62 wt% Cr, and balance WC the milling and sintering conditions being chosen so as to obtain an as sintered structure with a coercivity of 12.5-14.5 kA/m, and a CW-ratio of 0.76-0.84, and, at least partly coating the insert with a 4.1-6.9 μm thick coating including at least three layers of TiC_xN_yO₂ forming an inner coating with an α-Al₂O₃-layer as the outer layer whereby the TiC_xN_yO_z-layers having a total thickness of 1.9-3.6 μm comprise:

- a first TiC_xN_yO_z-layer, 0.1 to 1 μm, adjacent to the cemented carbide having a composition of x+y=l, x>= 0, using known CVD methods using a reaction mixture consisting of TiCl4, H₂ and N₂,

- a second TiC_xN_yO_z-layer, 1 to 3.4 μm, having a composition of x>0.4, y>0.4 and 0=<z<0.1, using the MTCVD-technique at a temperature 885-850 ⁰C and CH₃CN as the carbon/nitro-gen source,

- a third TiC_xN_yO_z-layer, 0.1 to 1 μm, adjacent to the α-Al₂O₃-layer having a composition of x+y+z>=l and z>0, using known CVD methods using a reaction mixture of TiCl4, H₂ and N₂,

the outer α-Al₂O₃-layer has a thickness of 1.8-3.6 μm and is deposited using known CVD-techniques, the edges on the insert are subjected to a brushing treatment.

7. Method according to claim 6, wherein the cemented carbide body has a composition of 13-14 wt% Co, 0.55-0.61 wt% Cr and balance WC with a coercivity of 12.7-14.0 kA/m with a CW-value of 0.78-0.82.

8. Method according to any one of claims 6-7, wherein

- for the first TiC_xNyO_z-layer, x<0.2 and z=0,

- for the second TiC_xN_yO_z-layer, z=0,

- for the third TiC_xNyO_z-layer, z>0.2, x+y+z=l and y<0.2.

9. Method according to any one of claims 6-8, comprising depositing an additional 0.1-1 μm coloured layer of TiN or Ti (C, N) on top of the α-Al₂C>₃-layer, using CVD technique prior to the brushing treatment .

10. Method according to any one of claims 6-9, wherein the cutting tool insert is a cutting tool milling insert for heavy roughing crankshaft milling.

11. Use of an insert according to any one of claims 1-5 for crank shaft milling or cam shaft milling of steel with a carbon content of about 0.30-0.43 wt-% of medium alloyed steels, with the following cutting data:

- Internal milling:

- Speed: 100-180 m/min, - Feed per tooth: 0.23-0.32 mm and

- Radial depth of cut: 3-12 mm or

- External milling

- Speed: 140 - 250 m/min, - Feed per tooth: 0.17-0.27 mm and

- Radial depth of cut: 3-8 mm.