Bore cutting tool and method of making the same

Abstract

A bore cutting tool for cutting metal workpieces includes a tool substrate and a tool coating on a surface of the tool substrate. The bore cutting tool includes a plurality of pits in the surface of the tool substrate and wherein the tool coating extends over the pits such that the pit surface includes the tool coating. In this way, the pit dimensions can be retained over prolonged tool life and the pits, with their coated surface, are particularly effective at retaining lubricant so that the thickness of a lubricant film can be increased as compared to a tool without the coated pits. In the embodiments, the pits are formed by laser etching and are present only on the cylindrical land. Average pit depth is suitably in the range 8 μm to 25 μm, average pit width and pit length is independently selected from 40 μm to 250 μm and average pit density may be 20 to 30 pits/mm.sup.2.

Claims

1. A bore cutting tool comprising: a tool substrate, the tool substrate having an upper surface; a tool coating disposed on the upper surface of the tool substrate, the coating having an uppermost surface; and a plurality of pits formed in and spaced along the upper surface of the tool substrate in an array, such that the plurality of pits are arranged in a plurality of rows and columns with the pits being spaced along the rows and columns, wherein the tool coating extends over the plurality of pits such that the coating follows a contour of each of the plurality of pits to form a plurality of coated pits and over spaces between the plurality of pits, the uppermost surface of the tool coating in the plurality of coated pits extending below the upper surface of the tool substrate at the spaces between the plurality of pits and the tool coating having a thickness that is less than a depth of each respective coated pit of the plurality of coated pits to form a reservoir in each of the plurality of coated pits, the reservoirs being arranged to retain lubricant, the depth extending from the uppermost surface of the tool coating between the plurality of coated pits to the uppermost surface of the tool coating in the plurality of coated pits, wherein an average pit depth is in the range of 8 μm to 25 μm.

2. The bore cutting tool according to claim 1, wherein an average pit cross-sectional area of each of the plurality of pits is about 0.005 mm.sup.2 to less than 1 mm.sup.2.

3. The bore cutting tool according to claim 1, wherein the plurality of pits is present only on one surface of the bore cutting tool.

4. The bore cutting tool according to claim 1, wherein the bore cutting tool is a twist drill having a cylindrical land and the plurality of pits is disposed on the cylindrical land.

5. The bore cutting tool according to claim 1, wherein the tool coating has an average thickness of about 1 μm to about 5 μm.

6. The bore cutting tool according to claim 1, wherein the tool coating comprises TiAIN.

7. The bore cutting tool according to claim 1, wherein the plurality of pits is formed by laser etching or electron beam etching of the tool substrate prior to forming the tool coating.

8. A method of making a bore cutting tool, the method comprising the steps of: providing a tool substrate, the tool substrate having an upper surface; providing a tool coating disposed on the upper surface of the tool substrate, the coating having an uppermost surface; and forming a plurality of pits in and spaced along the upper surface of the tool substrate in an array, such that the plurality of pits are arranged in a plurality of rows and columns with the pits being spaced along the rows and columns, wherein the tool coating extends over the plurality of pits such that the coating follows a contour of each of the plurality of pits to form a plurality of coated pits and over spaces between the plurality of pits, the uppermost surface of the tool coating in the plurality of coated pits extending below the upper surface of the tool substrate at the spaces between the plurality of pits and the tool coating having a thickness that is less than a depth of each respective coated pit of the plurality of coated pits to form a reservoir in each of the plurality of coated pits, the reservoirs being arranged to retain lubricant, the depth extending from the uppermost surface of the tool coating between the plurality of coated pits to the uppermost surface of the tool coating in the plurality of coated pits, wherein an average pit depth is in the range of 8 μm to 25 μm.

9. The method according to claim 8, wherein an average pit cross-sectional area of each of the plurality of pits is about 0.005 mm.sup.2 to less than 1 mm.sup.2.

10. The method according to claim 8, wherein the bore cutting tool is a twist drill having a cylindrical land and the plurality of pits is disposed only on the cylindrical land.

11. The method according to claim 8, wherein the tool coating has an average thickness of about 1 μm to about 5 μm.

12. The method according to claim 8, wherein the tool coating comprises TiAIN.

13. The method according to claim 8, wherein the plurality of pits is formed by laser etching or electron beam etching of the tool substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B show a cross-section of a pit including a coated surface.

(2) FIG. 2 shows a tool blank (twist drill blank) to which an array of pits is applied in the hatched area.

(3) FIG. 3 shows a pattern of pits applied to a tool blank, the pits having an elongate “slot” shape.

(4) FIG. 4 shows an SEM image of a cylindrical land of a twist drill comprising an array of pits.

(5) FIG. 5 shows the results of white light analysis (using a Wyko white light interferometer) of a pit presented as a cross-section or profile in the width direction (short axis of the pit).

(6) FIG. 6 is an SEM image of the pits after coating with TiAlN.

(7) FIG. 7 shows the results of white light analysis (using a Wyko white light interferometer) of a pit presented as a cross-section or profile in the width direction (short axis of the pit).

DETAILED DESCRIPTION

(8) The term “pit” as used herein refers to a closed-end pore or blind hole. The pit dimensions are as described herein.

(9) The term “bore cutting tool” as used herein refers to a cutting tool adapted to cut a workpiece so as to form a bore, including reshaping or modifying an existing bore (whether or not other types of cutting or removal of workpiece material can also be performed by the tool). For example, a class of bore cutting tools is round tools. Round tools include twist drills, end mills, reamers and taps. Twist drills are particularly preferred. Whilst any twist drill geometry can be used, a point angle may be 90° to 180°.

(10) The term “array of pits” as used herein refers to a plurality of pits arranged in an ordered, regular or non-random pattern. An example of an array of pits is a plurality of rows of pits, with substantially equal spacing between adjacent pits and respective rows.

(11) FIG. 1A illustrates a cross-section taken at the surface portion of a bore cutting tool 2 according to the present invention. The tool substrate 4 is provided with a pit 6, for example by laser etching. A tool coating 8 is then applied to the pitted tool substrate. The tool coating follows the contour of the pit so that the surface of the pit 10 includes the tool coating. The resultant pit has a comparatively smooth and homogenous surface. There is a smooth transition from the substantially flat main surface of the tool and the “inner” surface of the pit. When the bore cutting tool is provided with a plurality of such pits, the tool is adapted to work efficiently with lubricant (for example MQL) by retaining lubricant in the pits.

(12) The pits, with their coated surface, are particularly effective at retaining lubricant, for example acting as reservoirs for the lubricant 20 as shown in FIG. 1B.

(13) The thickness of the lubricant film can be increased as compared to a bore cutting tool without the pits. Suitably this generates areas of hydrodynamic lubrication where the fluid is forced into the pits as the tool surface comes into contact with the workpiece 18, as illustrated in FIG. 1B.

(14) The average pit depth is at least 5 μm, or for example, at least 8 μm. Suitably the average pit depth is no more than 50 μm, no more than 25 μm, or no more than 15 μm. A particularly average pit depth is in the range 8 μm to 25 μm. Average pit depth can be measured using white light interferometry as discussed herein.

(15) Suitably the average pit width and average pit length are independently selected from 20 μm to 400 μm, or 40 μm to 250 μm. In the case of circular pits, the diameter is of course the width and length. Average pit width and average pit length can be measured using white light interferometry.

(16) Suitably the average pit cross-sectional area is in the range 0.005 mm.sup.2 to 1 mm.sup.2. Suitably the average pitch (centre to centre spacing) is in the range 50 μm to 350 μm, or 50 μm to 250 μm, or 50 μm to 150 μm. Suitably the average density of the pits is in the range 5 to 50 pits/mm.sup.2, 20 to 30 pits/mm.sup.2 or about 24 pits/mm.sup.2.

(17) The pits can be any suitable shape, for example elongate (e.g. round ended or round cornered rectangles), circular, triangular or rectangular. It is preferred that the pits are round ended or round cornered rectangles, also referred to herein as slot-shaped pits or slots.

(18) Suitably the plurality of pits is an array of pits. That is, the plurality of pits is suitably arranged in a non-random pattern. Suitably the spacing between adjacent pits is the same for at least the majority of, preferably substantially all of, the pits in the array. The pits can be arranged as a plurality of rows of pits, suitably with substantially equal spacing between the rows. For example, a grid pattern.

(19) Suitably the plurality of pits is present only on at least one surface of the bore cutting tool which in use is in frictional contact with the workpiece. As explained herein, a preferred bore cutting tool is a twist drill and in twist drill embodiments the twist drill has a cylindrical land and the plurality of pits is present only on the cylindrical land. Suitably at least 50% of the cylindrical land is provided with pits, preferably substantially all of the cylindrical land is provided with pits. By providing pits on the cylindrical land of a twist drill, considerable improvements in tool performance can be achieved, as discussed in the examples herein.

(20) The tool coating may an average thickness of at least 0.5 μm, or at least 1 μm. Suitably an upper limit for the average thickness is 10 μm, or 5 μm. Thus, the coating may have a thickness is in the range 1 μm to 5 μm.

(21) The bore cutting tool can be partially or fully coated. The coating may be a wear resistant coating having a lower coefficient of friction than the uncoated tool.

(22) Suitable coatings include metal nitride-based coating (e.g. TiN, AlxTiyN, etc.), metal oxide based coating (e.g. AlxO, AlxCryO, etc.), carbon based coating (e.g. DLC, Diamond Coating, etc.) and combinations thereof. The tool coating may include a nitride coating, suitably a metal nitride-based coating, for example, TiAlN.

(23) Suitable coating methods include vapour deposition, for example physical vapour deposition (PVD), or other vacuum deposition techniques, and chemical vapour deposition (CVD).

(24) The pits can suitably be created by a laser. Suitably the pits are formed by laser etching of the tool substrate prior to forming the tool coating. For example, laser etching systems used for marking metal components can be applied to bore cutting tools to produce the desired plurality of pits.

(25) The desired pattern of the array is programmed into the laser controller and the laser is then operated so as to provide the cutting tool with the pits according to that pattern.

(26) Typically, the laser is moved with respect to the tool (or blank). Suitably the tool or blank is rotated. Alternatively, or additionally, the laser source is moved over the surface of the tool.

(27) The bore cutting tool is a round tool. Suitably the bore cutting tool is selected from a twist drill, an end mill, a reamer and a tap. The bore cutting tool may be a twist drill. Suitably the twist drill is a metal working twist drill.

(28) Whilst the bore cutting tool (e.g. twist drill) is generally for cutting metal workpieces, it can also be adapted for other workpiece materials such as composites and ceramics.

(29) The tool substrate can be made of carbide. For example, tungsten carbide. Alternative materials include high speed steel (HSS), HSCo and HSCoXP, silicon nitride and PCD (polycrystalline diamond), or combinations thereof (for example PCD mounted on a metal body).

EXAMPLES AND TESTING

Example 1

(30) A tungsten carbide rod was machined so as to produce a twist drill blank having a diameter of 12 mm. The blank was provided with an ordered pattern (array) of pits in the surface of the blank corresponding to the drill body, by laser etching. The area to which the pattern was applied is shown in FIG. 2. The pattern applied to the blank is shown in FIG. 3. The pattern has “slot” shaped elongate pits arranged in land 11 with their longer axis parallel to the main longitudinal axis of the drill (perpendicular to the direction of drill rotation). The pit density was programmed to be about 24 pits/mm.sup.2.

(31) SEM analysis indicated that burr or flash was present around the periphery of the pits. The blanks were therefore surface cleaned using an outer diameter grind to remove the flash. The resultant pits in the tool blank surface are shown in FIG. 4, which illustrates that substantially no flash remains.

(32) The absence of flash was confirmed by white light interferometry using a Wyko white light analyser. White light analysis permits imaging of the 3D surface of the tool. From the acquired data, cross-sections or profiles of the pits can be viewed and measurements of pit depth (at deepest point), width (at widest point) and length (at longest point) can be made, as well as cross-sectional area (at surface). An example of a pit profile across the short axis (width) of the pit is shown in FIG. 4.

(33) The tool blank was then machined so as to produce a drill geometry corresponding to Dormer Tools' CDX R553 commercial product.

(34) The cylindrical land is the only part of the twist drill that retains the pattern of pits. The rest of the surface of the tool blank is removed during the machining steps.

(35) From SEM and white light analysis the following pit dimensions were obtained:

(36) Average pit width=60 μm

(37) Average pit depth=11 μm

(38) Average pit length=230 μm

(39) Average height of flash=0 μm

(40) Pit spacing was selected by appropriate programming of the laser apparatus: approx 320 μm (centre to centre in length direction) and approx 130 μm (center to center in width direction). Other center to center spacings are possible, for example 100 μm to 200 μm.

(41) The twist drill was then coated with TiAlN using a standard deposition technique. The depth of TiAlN coating on the tool substrate was about 1 μm. The coating was applied to all of the twist drill, including the cylindrical land. The coating extends over the pits so that, in cross-section, the tool comprises pits in the tool substrate with a layer of TiAlN following the contour of the pit (e.g. as illustrated in FIGS. 1A and 1B). Other coatings can be used instead of TiAlN.

(42) The coated pits are shown in FIG. 5. A white light analysis width profile of a pit after coating is shown in FIG. 6.

(43) From SEM and white light analysis after coating the following pit dimensions were obtained:

(44) Average pit width=60 μm

(45) Average pit depth=9 μm

(46) Average pit length=230 μm

(47) Average height of flash=0 μm

Example 2

(48) The same procedure as Example 1 was followed except that the laser dwelling time was slightly longer during the laser texturing step.

(49) After coating, the average pit width was measured as 50 μm, the average pit length 220 μm and the average pit depth 11 μm.

Comparative Example 1

(50) A twist drill without pits was made in the same way as Example 1 except laser texturing was not applied.

(51) Tests

(52) Examples 1 and 2 and Comparative Example 1 were tested using two workpiece materials: AMG 1.5 (steel alloy) and AMG 4.3 (Titanium alloy). AMG 4.3 is particularly demanding because drilling of Ti workpieces is known to generate high temperatures and can even cause combustion of the Ti.

(53) The following conditions and settings were used in Test 1:

(54) Machine: DMU-60

(55) Material: AMG 1.5 (W No. 1.2312)

(56) Drill geometry: R553

(57) Diameter: 12.00 mm

(58) Drill length: 5×diameter

(59) Drill depth: 36 mm blind holes

(60) Coating: TiAlN

(61) Coolant: MQL

(62) Number of holes: 10 holes per test per tool

(63) Monitoring equipment: analySIS software and microscope, and Kistler Dynamometer (9123C 1011, with Dyno Wear Software) to monitor cutting thrust and torque.

(64) Surface speed: 48 mm/min

(65) Feed: 0.15 mm/rev

(66) Spindle speed: 1273 rpm

(67) Penetration rate: 190 mm/min

(68) Once the holes were completed, the holes were measured using a Renishaw probe (MP700 OMP70) at depths of 10 mm and 30 mm.

(69) The thrust force and torque measurements showed that twist drills having an array of pits on the cylindrical land experience acceptable levels of thrust and torque.

(70) The hole size measurements (using the Renishaw probe) showed that both of Example 1 and Example 2 produced “tighter” holes than Comparative Example 1. Indeed, both examples achieved a mean hole tolerance of H7, whereas Comparative Example 1 achieved only H9 (ISO 286 “Limits and fits”).

(71) Furthermore, good hole size reproducibility was also achieved.

(72) The following conditions and settings were used in Test 2:

(73) Machine: DMU-60

(74) Material: AMG 4.3 (Ti-6 Al-4V)/ASTM B265

(75) Drill geometry: R553

(76) Diameter: 12.00 mm

(77) Drill length: 5×diameter

(78) Drill depth: 14 mm through holes

(79) Coating: TiAlN

(80) Coolant: MQL

(81) Number of holes: 3 holes per test per tool

(82) Monitoring equipment: analySIS software and microscope and Kistler Dynamometer (to monitor cutting thrust and torque)

(83) Surface speed: 25 mm/min

(84) Feed: 0.135 mm/rev

(85) Spindle speed: 663 rpm

(86) Penetration rate: 90 mm/min

(87) Once the holes were completed, the holes were measured using the Renishaw probe at depths of 5 mm and 10 mm.

(88) The thrust force and torque measurements showed that twist drills comprising an array of pits on the cylindrical land experience acceptable levels of thrust and torque in the Ti workpiece. Indeed, the torque levels experienced in Ti were significantly lower for Examples 1 and 2 as compared to Comparative Example 1.

(89) The hole size measurements (using the Renishaw probe) showed that both of Example 1 and Example 2 produced “tighter” holes than Comparative Example 1 when used in the Ti workpiece. Furthermore, particularly at a depth of 5 mm, the spread of hole size is smaller for Examples 1 and 2 as compared to Comparative Example 1.

(90) The consistent hole sizes achieved by the laser textured tools indicate that the laser textured tools are reducing the frictional properties of the tool. In particular, the excellent hole size spread at 5 mm suggests that the work piece material begins to cool and restore its original shape, thus minimising the possibility of “snatching”. In particular, the reduction in the heat generation can reduce the extent of expansion of the workpiece material thus reducing the “closing in” of the hole on the tool, which effect can cause “grabbing” of “snatching” of the tool.

(91) The test results demonstrate that excellent hole quality can be achieved, particularly in the case of a Ti workpiece.

(92) Furthermore, especially in the case of the challenging Ti workpiece, a reduced torque value is experienced. This indicates that the tool is under less stress, potentially leading to improved tool life with concomitant improvements in tool productivity. The reduction in torque may also permit reduced power consumption, thus generating savings in machine overheads and of course benefitting the environment.

(93) Furthermore, the results show that laser textured tools may be particularly suitable for use with minimum quantity lubrication (MQL) because they optimise the use of the comparatively small amounts of lubricant which are applied to the tool and workpiece in MQL. This permits a reduction in the environmental impact as a result of reduced waste lubricant and a reduction in the cost for the disposal or reclamation of lubricant.

(94) Although the present embodiment(s) has been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore, that the present embodiment(s) be limited not by the specific disclosure herein, but only by the appended claims.