CUTTING TOOL

Abstract

A cutting tool includes a supporting body and a cBN or PCD cutting edge tip attached to the supporting body via a 5-150 ?m braze joint. The supporting body is cemented carbide having 3-25 wt % of a metallic binder, optionally up to 25 wt % of carbides or carbonitrides of one or more elements of group 4, 5, or 6, and the rest WC. The metallic binder includes at least 40 wt % Ni, and the braze joint has, in the order from the supporting body, a first layer of TiC situated next thereto, with an average thickness of 10-400 nm, a second layer, with an average thickness of 0.5-8 ?m, having in average at least 5 wt % metallic Ni, in average 25-60 wt % metallic Cu and in average 15-45 wt % metallic Ti, and a third layer, with an average thickness of 4-145 ?m, having metallic Ag and metallic Cu.

Claims

1. A cutting tool comprising: a supporting body; and a cBN or PCD cutting edge tip, wherein the cBN or PCD cutting edge tip is attached to the supporting body via a 5-150 ?m thick braze joint, the supporting body being cemented carbide including 3-25 wt % of a metallic binder, optionally up to 25 wt % of carbides or carbonitrides of one or more elements of group 4, 5, or 6 in the periodic table of elements, and the rest WC, wherein the metallic binder includes at least 40 wt % Ni, and wherein said braze joint includes, in order from the supporting body, a first layer of TiC situated next to the supporting body with an average thickness of 10-400 nm, a second layer, with an average thickness of 0.5-8 ?m, including in average at least 5 wt % metallic Ni, in average 25-60 wt % metallic Cu and in average 15-45 wt % metallic Ti, and a third layer, with an average thickness of 4-145 ?m, including metallic Ag and metallic Cu.

2. The cutting tool according to claim 1, wherein the metallic binder in the cemented carbide of the supporting body includes 50-90 wt % Ni.

3. The cutting tool according to claim 1, wherein the metallic binder in the cemented carbide of the supporting body includes 10-20 wt % Fe.

4. The cutting tool according to claim 1, wherein the thickness of the braze joint is 10-100 ?m.

5. The cutting tool according to claim 1, wherein the average thickness of the first layer of TiC is 50-300 nm.

6. The cutting tool according to claim 1, wherein the second layer includes in average 10-40 wt % metallic Ni.

7. The cutting tool according to claim 1, wherein the second layer includes in average 35-55 wt % metallic Cu.

8. The cutting tool according to claim 1, wherein the second includes in average 25-40 wt % metallic Ti.

9. The cutting tool according to claim 1, wherein the average thickness of the second layer is 1-5 ?m.

10. The cutting tool according to claim 1, wherein the second layer has a sum of metallic Ni, metallic Cu and metallic Ti of in average 70-100 wt %.

11. The cutting tool according to claim 1, wherein the third layer includes metallic In.

12. The cutting tool according to claim 1, wherein the third layer has a sum of metallic Cu and metallic Ag of in average 60-100 wt %.

13. The cutting tool according to claim 1, wherein the third layer includes in average 60-80 wt % metallic Ag and in average 15-40 wt % metallic Cu.

14. The cutting tool according to claim 1, wherein there is a Ni depleted zone in an outermost portion of the supporting body next to the braze joint, the Ni depleted zone having an average thickness of 0.5-5 ?m.

15. The cutting tool according to claim 1, wherein the tool is a turning insert, a milling insert, or an endmill.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0053] FIG. 1 is a general view of a cutting tool being a turning insert having a supporting body part and a cBN/PCD cutting edge tip.

[0054] FIG. 2 shows a cross section of a cutting tool with braze joint joining a supporting body and a cBN cutting edge tip.

[0055] FIG. 3 shows an enlarged part of FIG. 2.

DETAILED DESCRIPTION OF EMBODIMENTS IN DRAWINGS

[0056] FIG. 1 shows a general view of a cutting tool (1) being a turning insert having a supporting body (2) and cBN/PCD cutting edge tips (3).

[0057] FIG. 2 shows a SEM image of a cross section of an embodiment of a cutting tool of the present invention having a braze joint (4) joining a cemented carbide supporting body (2) and a cBN cutting edge tip (3). The braze joint (4) comprises a layer (5) which comprises Ni, Cu and Ti and a layer (6) which comprises Ag and Cu.

[0058] FIG. 3 shows a SEM image which is an enlarged section of FIG. 2 showing the cemented carbide supporting body (2) and a lower part of the braze joint where a lowermost first layer (7) of TiC is seen next to the cemented carbide supporting body (2). Further a second layer (5) comprising Ni, Cu and Ti is seen and the lower part of a third layer (6) comprising Ag and Cu.

EXAMPLES

[0059] Exemplifying embodiments of the present invention will now be disclosed in more detail. Cutting tools (inserts) were prepared, analysed and tested in a metal cutting operation.

Example 1Manufacture of Cutting Tool Samples

[0060] Cemented carbide cutting insert blanks were manufactured from a powder mixture with a composition of 4.89 wt % Ni, 0.83 wt % Fe, and balance WC. The powder mixture was milled using milling bodies of WCCo based cemented carbide, dried, pressed into an insert geometry DCGW11T308 and sintered at 1410? C.

[0061] The binder content in the cemented carbide was confirmed to be about 6.1 wt %. The sintered cemented carbide comprised about 4.9 wt % Ni, 0.8 wt % Fe and 0.4 wt % Co, being parts of the metallic binder phase. The metallic binder phase itself comprised about 75 wt % Ni, 13 wt % Fe, 3 wt % Co and 9 wt % W. The W dissolved originated from the WC grains. The Co originated mainly from milling bodies of WCCo based cemented carbide that were worn during the milling of the raw material powder mixture. No free graphite or eta phase was visible in a SEM micrograph of a cross section of the cemented carbide substrates.

[0062] A recess, intended for a cBN tip, at the tip portion of the cutting insert blanks was made. The cutting insert blanks now forms supporting bodies for cBN cutting tips. Cutting edge tips of cBN of two types were provided. The first type (cBN 1) had been manufactured from a powder mixture of cBN and TiN which was pressed into cutting edge tips of geometry S01020 and sintered. The sintered blanks contained 47 vol % cBN balanced with TiN+small amounts of reaction products. The second type (cBN 2) had been manufactured from a powder mixture of cBN and TiCN which was pressed into cutting edge tips of geometry S01020 and sintered. The sintered blanks contained 65 vol % cBN balanced with TiCN+small amounts of reaction products. The cBN 1 and cBN 2 cutting edge tips were available commercially on the market.

[0063] The joining of a cutting edge tip of cBN and a cutting insert blank was then made by applying a braze paste onto the cemented carbide supporting body, on the surface of the recess of the cutting insert blank. Two different braze pastes were used, respectively. The first braze paste (TB629 from Tokyo Braze Co. Ltd.) had a composition of Ag.sub.59Cu.sub.27In.sub.13Ti.sub.1) and the second braze paste (TB608 from Tokyo Braze Co. Ltd.) had a composition of Ag.sub.70Cu.sub.28Ti.sub.2.

[0064] The brazing was made in a furnace at three different temperatures, 740? C., 820? C. and 900? C. The brazing processes at 740? C. and 820? C. were made in an Ipsen VFC-124 batch furnace under vacuum while the brazing process at 900? C. was made in a Tokyo Braze continuous belt furnace with Argon as protecting gas. In the brazing processes at 740? C. and 900? C. the first braze paste was used while in the brazing process at 820? C. the second braze paste was used. There was also a slight difference in process time between the processes at 740? C. and 820? C., on one hand, and the process at 900? C. on the other hand.

[0065] Three different brazing processes are thus defined:

TABLE-US-00001 TABLE 1 Process Process Atmosphere Temperature time 1 Vacuum, 740? C. 10 minutes 10.sup.?5 mbar 2 Vacuum, 820? C. 10 minutes 10.sup.?5 mbar 3 Argon 900? C. 12 minutes

[0066] The final cutting insert geometry was DCGW 11 T308S01020. After the brazing process is completed a final grinding of the joint assembly of the supporting body and the cBN cutting tip is made.

[0067] Some of the assemblies of a supporting body and a second type of cBN cutting edge tip were coated with a 2-4 ?m thick layer of TiN according to a commonly PVD process used in the field of cutting tools. The deposition temperature of the TIN was sufficiently low (about 450? C.) so the deposition of the TIN coating did not affect the properties of the braze joint in any way.

[0068] Table 2 summarises the constitution of the samples and the brazing process used when producing them.

TABLE-US-00002 TABLE 2 cBN Braze Process Sample type paste Atmosphere Temperature time Sample 1 1 1 Vacuum, 740? C. 10 minutes 10.sup.?5 mbar Sample 2 1 2 Vacuum, 820? C. 10 minutes 10.sup.?5 mbar Sample 3 1 1 Argon 900? C. 12 minutes Sample 4 1 1 Vacuum, 740? C. 10 minutes (TiN-coated 10.sup.?5 mbar Sample 1) Sample 5 1 2 Vacuum, 820? C. 10 minutes (TiN-coated 10.sup.?5 mbar Sample 2) Sample 6 1 1 Argon 900? C. 12 minutes (TiN-coated Sample 3) Sample 7 2 1 Vacuum, 740? C. 10 minutes 10.sup.?5 mbar Sample 8 2 2 Vacuum, 820? C. 10 minutes 10.sup.?5 mbar Sample 9 2 1 Argon 900? C. 12 minutes

Example 2Analysis on Braze Joints

[0069] The braze joint was analysed using electron probe microanalyzer (EPMA). FIGS. 2-3 show SEM images where a backscattered electron (BSE) detector has been used. This detector resolves elements by means of atomic weight in that lighter materials appear dark and heavy ones appear bright. For example, Ag appears very bright versus Cu.

[0070] The layered structure of the braze joint was also analysed by wave-length dispersive spectroscopy (WDS) using EPMA. EPMA instrument used was JEOL JXA-8530 F Hyperprobe. This provided different images for different elements so that the presence of a certain element (such as Ni, Ti, Cu, Ag, In, C) at a certain position in the braze joint could be visualised as well as an indication of level of its content by the intensity of the signal.

[0071] The content of a certain element (metallic Ni, Ti, Cu, Ag, and In) in a layer was analysed by using energy dispersive X-ray spectroscopy (EDS) equipped in an EPMA. EPMA instrument used was JEOL JXA-8530 F Hyperprobe. A number of randomly selected measuring points were selected in order to obtain a reliable average value.

[0072] Analysis were made on the braze joint of samples Sample 1, Sample 2 and Sample 3. Clear layers 1, 2 and 3 were seen. Table 3 shows the element contents in each layer and the average thickness of each layer.

[0073] The thickness of the TiC layer is suitably measured by considering the thickness of a concentration of C next to the cemented carbide supporting body in combination with the presence of TiN. However, this is suitably made in combination with an SEM-BSE image obtain as described above where the TiC layer will be clearly seen.

[0074] For Sample 1 brazed at 740? C. it is seen from analysis that: [0075] No visible C next to the cemented carbide as well as Ti. However a very thin layer comprising the element Ti is seen. A clear thin layer is seen in a SEM-BSE image. Thus, a very thin first layer of TiC is present. [0076] The second layer contains substantial amounts of Ni, Cu and Ti. However, the layer is very inhomogeneous, comprising several phases and poorly defined. [0077] No Ni depleted zone in the uppermost part of the cemented carbide is seen.

[0078] For Sample 2 brazed at 820? C. it is seen from analysis that: [0079] C is clearly visible next to the cemented carbide, as well as Ti. A clear layer is seen in a SEM-BSE image. Thus, a first layer of TiC is present. [0080] The second layer containing substantial amounts of Ni, Cu and Ti and is well defined. [0081] A Ni depleted zone in the uppermost about 1 ?m of the cemented carbide is seen.

[0082] For Sample 3 brazed at 900? C. it is seen from analysis that: [0083] C is clearly visible next to the cemented carbide, as well as Ti. A clear layer is seen in a SEM-BSE image. Thus, a first layer of TiC is present. [0084] The second layer containing substantial amounts of Ni, Cu and Ti and is well defined. [0085] A Ni depleted zone in the uppermost about 2 ?m of the cemented carbide is seen.

[0086] Table 3 shows further results from analysis.

TABLE-US-00003 TABLE 3 Layer 1, closest to Whole cemented braze Sample carbide Layer 2 Layer 3 joint Sample 1 TiC Ni*: wt % Cu**: (740? C.) Cu*: wt % Ag**: Ti*: wt % In**: Cu + Ag > 90 wt % Sample 1 125 nm ?2 ?m* ?27 ?m 29 ?m Thickness of layers Sample 2 TiC Ni: 20 wt % Cu**: (820? C.) Cu: 47 wt % Ag**: Ti: 31 wt % Cu + Ag ? 100 wt % phase 1: Cu: 41 wt % Ag: 59 wt % phase 2: Cu: 10 wt % Ag: 90 wt % Sample 2 250 nm 1.7 ?m 18 ?m 20 ?m Thickness of layers Sample 3 TiC Ni*: Cu**: (900? C.) Cu*: Ag**: Ti*: In**: Cu + Ag > 90 wt % phase 1: Cu: 94 wt % Ag: 6 wt % phase 2: Cu: 8 wt % Ag: 88 wt % Sample 3 300 nm 2 ?m 17 ?m 19 ?m Thickness of layers *several phases, poorly defined layer, difficult to measure average metallic element content and layer thickness **the metallic element present but in several phases, difficult to measure average content

Example 3Cutting Tests with Samples

[0087] Cutting tools were tested in a metal cutting operation. The samples tested were Sample 5 and Sample 8, i.e., cBN cutting edge tips of different composition, braze paste 2, brazing in vacuum at a temperature 820? C. for 10 minutes. The test method comprised interrupted cuts in hardened steel. A ring of through-hardened steel SS2258 is provided, having a slot prepared in the soft stage in order to provide an interrupted cut. The test method includes a turning operation by running facing cuts on the slotted part, until edge breakage. The cutting parameters are stepped-up per cut taken to give an incremental load. The test method gives a good view of the cutting tool performance in severe cutting, including a judgement of the solidity of its braze joint.

[0088] The cutting data used are seen in Table 4. Feed (fn) and depth of cut (ap) are set to the same value. Recommended start values for fn and ap depend on the insert style and grade to be tested. The cutting speed (vc) was 120 m/min.

TABLE-US-00004 TABLE 4 Depth of No. of Feed (fn) cut (ap) Increment Increment edges start start fn ap tested Sample 5 0.16 0.16 0.02 per 0.02 per 4 pass pass Sample 8 0.2 0.2 0.02 per 0.02 per 3 pass pass

[0089] The test was run until edge failure (checked under optical microscope after each pass), and the test result is reported as the feed/depth of cut (or number of passes) at which the edge fails.

[0090] For each pass, the values for fn and ap were incremented by 0.02.

[0091] A number of edges were tested in order to get reliable results.

TABLE-US-00005 TABLE 5 Feed at Number of passes to failure(fn) failure (average) Sample 5 6.8 (Vacuum) 0.29 (Vacuum) 3.2 (Argon) 0.22 (Argon) Sample 8 0.4 10

[0092] For the samples, the results showed that all failures occurred in the cBN material with an expected size of failures. There were no signs that the braze would be the weakest link. Thus, it is concluded that the braze joint of the present invention performs very well. It must further be noted that the loads used in this test method were significantly higher than what is application relevant in a normal metal machining operation of hardened steel, so all samples tested would perform very well in an application in the industry.