WO2001053026A1

WO2001053026A1 - Metal cutting inserts with superhard abrasive bodies

Info

Publication number: WO2001053026A1
Application number: PCT/SE2001/000075
Authority: WO
Inventors: Peter Littecke; Scott Horman
Original assignee: Sandvik Ab (Publ)
Priority date: 2000-01-19
Filing date: 2001-01-19
Publication date: 2001-07-26
Also published as: SE0000143D0; SE0000143L

Abstract

The present invention relates to a composite metal cutting insert consisting of cemented carbide having in the corners CBN bodies metallurgically bonded to an unground surface of the cemented carbide. The CBN-bodies have a thickness, T, of 0.5 to 2 mm, extend along the cutting edge on both sides of the nose, L2, 2-6 mm, with the length of the CBN along the rake face perpendicularly to the edge, L1, 0.5-2 mm. The length along the cutting edge consisting of cemented carbide, d, is at least 2 mm and the distance between two opposite CBN-bodies situated in the top and bottom surfaces, H, is at least 0.5 mm. The invention also relates to a method of producing such inserts.

Description

Metal cutting inserts with superhard abrasive bodies

This invention relates to inserts with CBN (Cubic Boron Nitride) or PCD (Polycrystalline Diamond) in the edge and a method of making the same. The purpose is to decrease the cost per edge with increased edge length compared to existing methods .

Inserts for metal cutting purposes with edges of CBN or PCD are made in two different ways; either by sintering CBN or PCD powder into a solid body that is finished into an insert, or by bonding a layer of CBN or PCD to a substrate, usually a cemented carbide disc, from which smaller pieces, "tips", are cut out. These tips are then brazed onto a regular cemented carbide insert and ground to the finished size. Inserts produced that way are normally quite expensive due to the many steps the products must undergo before they are finished.

Two of the most common application areas for CBN inserts are hard part turning and grey cast iron machining. Hard part turning applications, i.e. machining components of hardened steels, normally run at small feeds, 0.05 to 0.15 mm/rev and small depths of cut, but in certain situations the depth of cut can be as big as several millimeters.

In the case of grey cast iron, the ability to machine with depths of cut exceeding 2 mm is quite common, and usually the feed rate is bigger than 0.2 mm/rev. US 5,813,105 describes a way to produce inserts provided with at least one body of PCD or CBN where brazing has been eliminated resulting in a lower manufacturing cost per edge. This technology has been successfully implemented and made commercially available. However, due to the size of the CBN body inserts produced according to US 5,813,105 are quite limited in the depth of cut that they allow.

US 4,702,694 teaches a method to produce round inserts by forming an annular groove on a cylindrical cemented carbide blank, the groove width and height being substantially equal, then filling the groove with PCD or CBN crystals and subjecting it to HP/HT- conditions suitable for the superhard constituents to sinter and adhere to the cemented carbide blank. With this method a number of tools can be manufactured but the method is not suitable for inserts with polygonal shape .

JP-A-4-336903 shows a method of producing inserts by bonding superhard materials like PCD and CBN to horizontal grooves in a cemented carbide column with square cross section followed by cutting the column into smaller pieces. In addition to the high cost for cutting the column into pieces, this method has drawbacks since it not suitable for many of the insert styles presently used in industry.

It is therefore an object of the present invention to provide a method to produce inserts for metal cutting purposes with edges of CBN or PCD without chipbreakers, where the mentioned limitations are lifted. Figs 1-5 illustrate the invention.

The invention will now be described with reference to CBN but it is obvious that it can be applied also to PCD (Polycrystalline Diamond) .

In the preferred embodiment the starting point is a cemented carbide blank preferably of round cross section with at least one horizontal depression preferably formed during pressing of the cemented carbide blank but can also be formed by machining the cemented carbide blank before sintering. The number of depressions depends on the type of insert to be produced, Fig 1, and the same goes for the shape. Preferably there is a depression in each corner. Figure la shows a schematic top view drawing of the depressions.

Figure lb shows a cross section of the same blank with depression with sharp corners. Sharp corners should preferably be avoided and the sidewalls should have enough relief to allow direct pressing without sticking to the punch.

The blank is placed in a container of a material suitable for HP/HT- reatment , such as Nb. The depressions are filled with CBN-particles mixed with other hard and wear-resistant constituents such as carbides, nitrides, carbonitrides, oxides, borides of the metals of groups IVa to Via of the periodical system, preferably titanium, as known in the art.

Preferably presintered bodies as described in Swedish patent application SE 9901221-3 are used. The assembly is then subjected to conventional elevated temperatures and pressures for producing high-pressure materials, e.g., as disclosed in US 4,991,467 and 5,115,697. During this treatment the CBN-material will become bonded to the cemented carbide blank. If the insert has a hole for clamping the method according to Swedish Patent application 9702661-1 can be used. After this, the blank is ground in such a way that the depressions of CBN will end up in the right position for producing inserts. Fig 2 is showing a top view of such an insert .

Figure 2 shows a double-sided insert, but of course it is possible, although less economical to make the insert single sided for example as a positive insert.

Fig 3 is a cross section of Fig 2 showing that the CBN portion of the edge is supported by cemented carbide which is another advantage over the method described in US 8,813,105. The shape, size and cross section of the depressions may vary depending on the finished insert type and size, it may be of the same size and cross section for the whole insert, but it is also possible to mix different shapes and sizes. The preferred shape of the depression is triangular.

Fig 4 shows some typical depressions for a common insert style where the dashed line 1 outlines the finished insert shape, 2 denotes the depressions and 3 is the cemented carbide blank.

In order to reduce further the cost of manufacturing by minimizing periphery grinding the cemented carbide blank can be made up from an assembly of several segments as shown in Fig 5. Treating some of the segments according to Swedish patent application SE 9702661-1 will prevent the parts from bonding to each other. Furthermore, the methods taught in said patent application are practised in order to provide holes for clamping on the finished insert. Finished inserts according to the invention are single or double sided with CBN-bodies metallurgically bonded the unground cemented carbide .

The shape and size of the CBN-bodies and the composition depend on the area of application described above. The bodies are preferably triangular with the size of the sides along the cutting edge being of equal length and the corners along the cutting edge being truncated to from a length Ll . Such an insert is shown in Figs 2 and 3 in which T is the thickness of CBN-bodies

Ll is the length perpendicularly thereto L2 is the length along the cutting edge d is the length along the cutting edge consisting of cemented carbide and H is the distance between two CBN-bodies situated in the top and bottom surfaces .

In the general embodiment the thickness, T, of the CBN-bodies after finish grinding is 0.5 to 2 mm and the length of the bodies along the cutting edge on both sides of the nose, L2 , is 2-6 mm, with the width of the CBN along the rake face perpendicularly to the edge, Ll , being 0.5-2 mm. The length d is at least 2 mm and the distance H at least 0.5 mm. In one preferred embodiment, an insert intended for hard part turning has CBN bodies with a thickness, T, of 0.5-1.2 mm, the CBN extending 2-4 mm, preferably >3 mm, along the edge with a CBN material consisting of between 40% and 60% CBN by volume, preferably in the form of Megadiamond grade MN50, US 5,639,285.

In another preferred embodiment, an insert intended for machining grey cast iron has a CBN thickness of about 2 mm, with the CBN material consisting of 60% to 90% CBN by volume, preferably in the form of Megadiamond grade MN90, US 5,271,749. In such an insert the CBN should extend 3-5 mm, preferably about 5 mm, along the cutting edge.

The above mentioned figures relate to an insert with IC (=inscribed circle diameter) = 8-13 mm and thickness 3-6 mm and they have to be adapted in proportion to IC and thickness .

The CBN-bodies contain in addition to CBN metal binder, such as Co, and other hard and wear-resistant ceramic constituents such as carbides, nitrides, carbonitrides, oxides, borides of the metals of groups IVa to Via of the periodical system as known in the art, preferably titanium. In one preferred embodiment the binder is of ceramic type and in an alternative preferred embodiment the binder is metallic. Since the cemented carbide substrate essentially does not take part in the cutting operation performed by the manufactured inserts, its composition is chosen such that it provides a good bond to the PCD or PCBN abrasive, is easy to grind and contains inexpensive components and has suitable fracture resistance. Preferably, a WC-Co cemented carbide having 10-20% Co by weight, most preferably about 14-16%, is used. Particularly good results have been obtained with a grade of 15%.

Inserts according to the invention can further be provided with thin wear resistant coatings preferably applied by conventional PVD or CVD methods . CVD layers are normally deposited at about 950-1000 °C and PVD- layers preferably a TiN-layer are deposited at about 500 °C using a titanium source and nitrogen atmosphere.

Claims

1. A composite metal cutting insert consisting of cemented carbide having in the corners CBN bodies c h a r a c t e r i s e d in metallurgically bonded to an unground cemented carbide surface said bodies having a thickness, T, of 0.5 to 2 mm, extending along the cutting edge on both sides of the nose, L2 , 2-6 mm, with the length of the CBN along the rake face perpendicularly to the edge, Ll, 0.5-2 mm, the length along the cutting edge consisting of cemented carbide, d, at least 2 mm and the distance between two opposite CBN-bodies situated in the top and bottom surfaces, H, of at least 0.5 mm.

2. A composite metal cutting insert according to claim l c h a r a c t e r i s e d in said thickness, T, being 0.5 - 1.2 mm, the CBN extending 2-4 mm, preferably >3 mm, along the edge, L2 , with a CBN material consisting of between 40% and 60% CBN by volume.

3. A composite metal cutting insert according to claim l c h a r a c t e r i s e d in said thickness, T, being about 2 mm, the CBN extending 3-5 mm, preferably about 5 mm, along the edge, L2 , with the CBN material consisting of 60% to 90% CBN by volume.

4. A metal cutting insert according to claim 1 where there is a hole for clamping in the centre of the insert.

5. Method of making a composite metal cutting insert consisting of a cemented carbide body having in at least one corner a CBN body c h a r a c t e r i s e d in being metallurgically bonded to the unground cemented carbide surface, by

- providing a cemented carbide blank preferably of round cross section with at least one horizontal depression preferably formed during pressing of the cemented carbide blank - placing the blank in a container of a material suitable for HP/HT-treatment , such as Nb

- filling the at least one depression with CBN- particles mixed with other hard and wear-resistant constituents such as carbides, nitrides, carbonitrides, oxides, borides of the metals of groups IVa to Via of the periodical system, preferably titanium, as known in the art

- subjecting the assembly to conventional elevated temperatures and pressures for producing high-pressure materials during which treatment the CBN-material becomes bonded to the cemented carbide blank and

- grinding the blank in such a way that the depressions filled with CBN will end up in the right position for producing inserts.

6. Use of an insert according to claim 2 for hard part turning .

7. Use of an insert according to claim 3 for machining grey cast iron.