KR100516876B1 - Metal working drill/endmill blank and method of making the same - Google Patents

Abstract

According to the present invention there is now provided a cemented carbide drill/endmill blank consisting of a core and a surrounding tube with improved technological properties. The difference in Co-content between the core and tube is 1-10 wt.% units and the cubic carbide content is 8-20 wt.% in the tube and 0.5-2 wt.% in the core. The invention also relates to the method of making said cemented carbide drill/end mill blank.

Description

Tungsten Carbide Drills / End Mill Blanks & Manufacturing Methods {METAL WORKING DRILL / ENDMILL BLANK AND METHOD OF MAKING THE SAME}

The present invention relates to a cemented carbide body, preferably a cylindrical body composed of at least two grades having different compositions, microstructures and properties, in particular drilling, end milling or deburring. A body for the purpose of acting as a blank for a tool.

For drill tools, the requirements for the perimeter and center are different for wear resistance and toughness. For drill bits for rock drilling, the requirements differ in surface (wear resistance) and internal parts (toughness) as disclosed in US Pat. No. 5,541,006, which emphasizes the use of two grades in rock drilling bits. This grade is a straight grade with both tungsten carbide and cobalt. In this case, much attention has been paid to the ability to control the cobalt's movement where a sudden or discontinuous composition change at the interface between the zones is desirable. This problem is solved by Fischer et al. As a dual-phase or DP-technique disclosed in US Pat. No. 4,743,515. Tools, rolling rings and slitter / trimming knives as wear parts can be manufactured by the method described in US Pat. No. 5,543,235.

However, these patents only deal with combinations of grades containing tungsten carbide-cobalt or tungsten carbide-nickel. In addition, these patents describe applications in which only one grade is in contact with the workpiece material and the other acts as a 'equalizer' or 'carrier' of pressure or impact.

One patent dealing with cemented carbide drills containing cubic carbides is US Pat. No. 4,971,485, in which case the grade of tungsten carbide-cobalt is used on the shaft to avoid damage due to vibrations from the machine.

1 is a cross-sectional view showing the drill blank according to the present invention in 6 times magnification. In this figure, A is the core and B is the tube.

Figure 2 is a 200x enlarged view showing the diffusion interface between two grades.

The present invention relates to a composite cemented carbide body consisting of a core of toughness grade both in active contact with the workpiece material and a tube of larger abrasion resistant grade surrounding it (hereinafter referred to as a "rounding tube"). A problem in manufacturing such composite bodies is to avoid significant porosity at the interface between the two parts due to the formation of cracks or voids in the outer part and the difference in shrinkage during sintering. In addition, too high stresses at the interface make the manufacturing process impossible, for example slitting and grinding. Another problem may be the shift of the binder phase to equalize the binder phase content of the two parts during sintering. The combination of grades must meet the requirements for toughness and wear resistance at the core as well as at the periphery. The grade should also be applicable to pressurization and sintering conditions.

According to the present invention, it was found that it is possible to avoid the above-mentioned problems by appropriately selecting the composition and microstructure of the two grades. In particular, the present invention relates to a tube of grade containing elements of Groups 4 to 6, preferably carbides and / or carbonitrides of titanium (Ti), tantalum (Ta) and niobium (Nb). A drill blank having a core of tungsten-cobalt grade surrounded by it.

The drill blank according to the invention consists of a core and a surround tube. The core contains less than 30% by weight, preferably 5 to 20% by weight and most preferably 10 to 15% by weight of cobalt in addition to tungsten carbide after sintering. The tube grade is from 5 to 25% by weight of at least one of carbide and / or carbon nitride of more than 5% by weight of cobalt and elements of Groups 4 to 6, preferably titanium (Ti), tantalum (Ta) and niobium (Nb) , Preferably 8 to 20% by weight, most preferably 10 to 15% by weight. The difference in cobalt content between the core and the tube is in the range of 1 to 10% by weight, preferably 2 to 4% by weight. Microprobe analysis of the sample shows a transition zone of 300-500 μm wide, measured as a change in cobalt content. The core contains 0.5 to 2 weight percent cube carbide.

The particle size of the core grade is less than 10 μm, preferably 0.5 to 5 μm, most preferably 0.5 to 3 μm. The tube grade has a particle size of less than 10 μm, preferably 0.5 to 3 μm, most preferably 0.5 to 1.5 μm.

The blank according to the invention is produced by a powder metallurgical method comprising a method of compacting in two steps. First, a rod having a length of about 300 mm and a diameter of 5 to 15 mm, consisting of tungsten carbide having 10 to 30% by weight of cobalt and the remainder being pressurized. Preferably, this rod has a groove shape that provides a keying action between the groove and the tube. Subsequently, a tube of predetermined diameter is pressed at the outer periphery of the rod to the final green density. The size of the core is preferably 40 to 60% of the total diameter of the blank. If desired, the drill blank may be provided with coolant holes by methods known in the art. If the difference in cobalt content between the tube grade and the core grade is from 0 to 15% by weight, preferably 5 to 10% by weight, and the tube contains the above cube carbide, the blank forms cracks or voids between the core and the tube. It can be seen that it can be sintered without.

The pressurization and sintering properties of the original grade powder are extremely important for good results. Pressing conditions are determined by the coefficient of thermal expansion, shrinkage and the predetermined pressurization pressure of the grade used. Determination of these conditions by test is known to those skilled in the art. Sintering is carried out at 1350 to 1450 ° C.

After sintering, the rod is usually cut into drill blanks 50 to 150 mm long, preferably 80 to 120 mm long. The most useful diameter range is 5 to 35 mm, preferably 5 to 20 mm.

The flutes are polished by the diamond wheel at a speed of 18 to 20 m / sec while feeding at a speed of, for example, 60 to 80 mm / min.

In another embodiment a drill top with a length / diameter ratio of 0.5 to 5 soldered to the shaft is used.

After finishing polishing, a drill of the kind as described above is suitable for coating by physical vapor deposition (PVD) as carbide, nitride, carbon nitride or oxide or combinations thereof, such as TiN, TiALN, Ti (C, N).

The drill of the present invention is particularly useful in the processing of stainless steel and ordinary steel.

Example 1

A drill according to the invention has been produced. Pressurization was performed in two steps. First, a cylindrical rod 300 mm long and 11 mm in diameter having a particle size of 2 μm and having a composition of 20 wt% cobalt and 80 wt% tungsten carbide was pressed. The powder of the initial composition, then, with a particle size of 2.5 μm and 11% by weight cobalt, 6.1% by weight TaC, 1.9% by weight NbC, 4% by weight TiC and the balance of tungsten to the final compact density Pressurized around. Some drills have been given coolant holes formed by techniques known in the art. After sintering, the cobalt content of the core grade was reduced from 20 wt% to 14 wt%, and the cobalt content of the tube grade was increased to 12 wt%. In addition, a significant amount of cube carbide can be detected at the center of the core.

After sintering, the rods were cut into drill blanks of 105 mm length and 14 mm diameter. The longitudinal grooves, top and bottom of the blank were polished to the final form.

Example 2

Drills coated with physical vapor deposition (PVD) TiN from Example 1 were tested with stainless steel AISI 316. Two first grades used in the drill from Example 1 and a single grade drill in cobalt grade of 10% by weight of one finely granulated 1 μm tungsten carbide commonly used in these cutting conditions are used as reference.

The following three test data were used with external cooling.

a) v = 50 m / min, f = 0.14 mm / rev

b) v = 82 m / min, f = 0.12 mm / rev

c) v = 32 m / min, f = 0.22 mm / rev

In test a) the drill according to the invention lasted up to drilling 357 holes, whereas the single grade drill had 207 holes (single grade of finely granulated WC-Co), 149 [11 weight % Cobalt, 12 wt% tantalum, niobium, titanium carbide and the rest were worn after drilling 55 holes (single grade of 20 wt% cobalt) and holes of tungsten carbide.

At higher speeds b) the drill and the finely granulated grade according to the invention drill 192 holes, while the other grades are 126 [11 wt% cobalt, 12 wt% tantalum, niobium, titanium carbide And the rest were drilled through tungsten carbide single grade holes and twenty-two (20 wt% cobalt single grade) holes.

At lower speeds with a higher feed rate c) the drill according to the invention drills 179 holes, whereas the finely granulated grade drills 128 holes and the 20% by weight cobalt grade cracks. 41 holes were drilled before stopping operation due to wear or wear.

Example 3

The drill from Example 1, with internal coolant supply, was tested with stainless steel. A normal P40 drill was used as reference in this test.

At increased speeds (100 m / min, f = 0.16 mm / rev) the drill according to the invention drills 550 holes while the P40 reference drill is completely broken after only three holes.

At normal speeds or higher feed speeds (50 m / min, f = 0.25 mm / rev), the P40 reference drill suffers from chipping after drilling 660 holes and the drill according to the invention has 1100 holes. After drilling it was still available.

At normal cutting data (50 m / min, f = 0.16 mm / rev), these two drills were nearly identical in performance and the test was stopped after drilling 1100 holes.

Example 4

The drill from Example 1 with internal coolant supply was tested with different austenitic stainless steels (AISI 304). In this test, normal P40 and sub-micron K20 drills were used as reference.

At normal speeds (50 m / min, f = 0.16 mm / rev), the drill according to the invention works even after drilling 2668 holes, while the P40 and sub-micron K20 drills are used to drill 2011 and 242 holes, respectively. Worn out after drilling.

At increased feed speeds but at normal speeds (50 m / min, f = 0.30 mm / rev), the drill according to the invention completes 520 holes, whereas the P40 and sub-micron K20 drills are 110 and 22 respectively. The hole was completed.

At increased speeds (100 m / min, f = 0.16 mm / rev), the drill according to the invention achieves 198 holes, whereas the P40 and K20 drills break after drilling one or two holes.

Example 5

Drills from Example 1 with internal coolant feed holes, but 10 mm in diameter and coated with Ti (C, N) and TiN were tested with AISI 316 (SS2353), 30 mm through hole drilling. In this test, ordinary finely granulated PVD coated drills were used as reference. Several combinations of cutting data have been used and it is clear from the results that the drill according to the invention has a much wider working range.

The table below shows the number of holes achieved by the drill. The test was stopped after drilling 1300 holes even if the drill did not wear out completely.

Cutting data 400.13 400.20 400.25 600.13 600.20 600.22 Speed, m / min feed speed, mm / rev Plain drill   600 100 -   100     3 - Drill according to the invention > 1300 400 500 > 1300 > 1300 500

Claims (2)

Cemented carbide drill / endmill blank, consisting of one grade core and another grade surround tube,  A cemented carbide drill / endmill blank characterized in that the cobalt content between the core and the tube differs by 1 to 10% by weight, and the cube carbide content is 8 to 20% by weight in the tube and 0.5 to 2% by weight in the core. A method of manufacturing a cemented carbide drill / endmill blank comprising a core of one grade and a surrounding tube of another grade by powder metallurgy comprising compressing the tube in two stages, followed by a core, 10-30% by weight of cobalt for the core and the remainder of the powder consisting of tungsten carbide, and for the tube using a powder with more than 5% by weight of cobalt and 5-25% by weight of cube carbide Method for producing a cemented carbide drill / end mill blank, characterized in that the cobalt content difference between the core powder and the tube powder is 5 to 15% by weight.