Two-flute deep-hole drill for stainless steels and other high-alloy steel materials

Abstract

Proposed is a two-lip drill for machining stainless steels and other high-alloy steel materials, the flutes of said drill being curved in a cross-sectional view.

Description

[0001] Title: Double-fluted deep hole drill for stainless steels and other high-alloy steel materials

[0002] Description

[0003] The present invention relates to a two-lip deep hole drill which is particularly suitable for machining stainless steels and other high-alloy steel materials.

[0004] Double-fluted deep-hole drills, or double-fluted drills, are available in various designs from the state of the art. Fundamentally, efforts are always being made to improve the tool life, machining accuracy, and process reliability of deep-hole drills. Nowadays, the drill heads are almost always made of carbide.

[0005] Often the shaft of the drill is also made of hard metal (so-called solid hard metal drill).

[0006] A high level of process reliability requires short or compactly shaped chips, since only such chips can be reliably transported out of the bore through the chip flutes of the tools.

[0007] If deep holes are to be drilled in long-chipping materials, it is state-of-the-art to attach chip breakers and / or chip formers to the tool to produce compact chips and ensure reliable chip evacuation from the hole. Chip breakers have an interrupted cutting edge. This has the disadvantage of complex tool manufacturing. In addition, the edges of the chip breaker geometry are particularly susceptible to chipping, which can lead to spontaneous tool failure.

[0008] Chip formers generally cause an increase in feed and cutting forces, which can negatively affect the bore path. Furthermore, their manufacture is complex.

[0009] Single-lip drills are the ideal tools for reliably drilling high-quality holes with depths greater than 5...10 x D in steel materials. However, when drilling stainless steels with single-lip drilling tools using water-miscible cooling lubricant, an undesirable effect occurs which significantly reduces the tool life of the drilling tool: the alloy components nickel and chromium have a strong affinity for the tungsten contained in the cemented carbide of the drill head. This affinity causes the tungsten to be dissolved out of the cemented carbide. As a result, the cemented carbide is structurally weakened and high wear occurs, particularly on the guide rails of the drill head. This significantly deteriorates the surface quality of the hole wall and the tool life of the drill is often only 1 to 2 meters.Due to the very pronounced wear on the guide rails, regrinding is often no longer possible.

[0010] If drilling oil is used as a cooling lubricant, this phenomenon is significantly less pronounced, allowing deep holes to be drilled reliably using single-lip drills. However, many machining machines, especially the widely used machining centers, are generally operated with water-miscible cooling lubricants (emulsion).

[0011] Indexable drills and double-fluted drills are symmetrical tools, which means that the load on the guide pads or guide lands is significantly lower and the phenomenon of heavy wear on the guide lands is significantly reduced. Due to chip removal, deep holes in stainless steel materials, particularly austenitic materials, are often not reliably drilled using these tools, so that unclamping strokes are necessary. The surface quality that can be produced and the achievable diameter tolerance often require reworking, for example by reaming. This increases process times and costs. Indexable deep drilling tools are also expensive to produce and to regrind. JP S 63102814 describes a double-fluted drill with a straight chip flute or bead. With this drill, the chip flutes or bead are...the beads are bordered by a narrow, flat rake face and a narrow, flat wall. The narrow, flat rake face and the narrow, flat wall each form a narrow strip that runs parallel to the center axis of the drill. The flat rake face and the flat wall run radially. Between the flat rake face and the flat wall, the chip flute has a curved cross-section. This cross-section of the chip flute is limited to the drill head; in the area adjacent to the drill head, the chip flutes have a different cross-section.

[0012] It is therefore an object of the present invention to provide a two-flute deep-hole drill that has a long tool life and reliably removes chips, even when machining stainless steels using water-miscible coolants. Furthermore, the holes produced with this drill should be very dimensionally accurate, have a low centerline deviation, and produce good surface qualities. The feed and cutting forces should be as small as possible. Furthermore, the two-flute deep-hole drill according to the invention should be relatively easy to manufacture and regrind.

[0013] This object is achieved in a two-lip deep hole drill with the features of claims 1 and 3.

[0014] The chip flute according to claim 1 results in the main cutting edges being curved from the cutting edges to the secondary cutting edge. This results in a "pulling"

[0015] Cut and the drill centers itself very well in the hole.

[0016] Unlike JP S63102814, in which the main cutting edge comprises a short, straight, radially extending section followed by a curved section, the chip in the drill according to the invention is formed continuously from the outside to the tip of the drill. This has the surprising and positive effect of significantly reducing wear and significantly increasing tool life. It is assumed that the inventive shape of the cutting edges ensures very good centering of the drill and, as a result, reduces the surface pressure between the round ground chamfers and the guide chamfers on the one hand, and the bore on the other.

[0017] A further improvement in the performance of the double-flute drill according to the invention is surprisingly achieved when one of the guide lands is arranged on the same radius as the round ground lands, while the other guide land is arranged on a slightly smaller radius (R - Ax) than the round ground lands. It has proven sufficient if one of the two guide lands is arranged on a radius at least 3 / 100 mm smaller than the round ground lands (Ax is greater than or equal to 0.03 mm and less than or equal to 0.1 mm).

[0018] Resetting by more than 1 / 10 mm is not necessary. This positive effect can be explained by the fact that the drill is very well centered and guided in the hole by the two round ground edges and the one guide chamfer, which are arranged on the same radius as the round ground chamfers. The recessed guide chamfer ensures that the drill does not jam in the hole. In addition, a relatively thick and very stable hydrodynamic lubricating wedge is created between the hole and the recessed guide chamfer, which also has good damping properties.

[0019] These positive effects can also be utilized in a two-lip drill with the features of claim 3. This also results in a two-lip drill characterized by a long tool life and producing very precise holes with a good surface finish and minimal center drift.

[0020] The features of independent claims 1 and 3 can also be combined (see claims 2 and 4). They result in a two-flute drill which, in practical tests in austenitic stainless steel 1.4301 under water-miscible cooling lubricants, had a tool life of significantly more than 50 meters without any noticeable wear.

[0021] A further improvement in performance is achieved when a tangent T of the curved region of the chip flute at the cutting corner and a radius ray RS through the cutting corner enclose an angle ß greater than 0°. It has proven sufficient if the angle ß is less than 10°; preferably, it is 2° or 5°.

[0022] In a further advantageous embodiment of the two-lip drill according to the invention, a circumferential angle y of the chip flutes is less than 90°. The circumferential angle y is a measure of the width of the chip flutes. The guide chamfers are preferably arranged at an angle of more than

[0023] 80 ° and less than 100 ° offset to the circular grinding bevels.

[0024] It has proven advantageous if, in the case of double-fluted drills according to one of the preceding claims, the cross-section of the flutes is the same in the area of ​​the drill head and in the area of ​​the shank. This prevents chip accumulation at the transition between different cross-sections of the flutes and increases process reliability.

[0025] It has also proven effective when the radius of curvature of the chip flutes is not constant. The radius of curvature is particularly preferably largest at the cutting edge. This can be achieved, for example, by using a grinding wheel with a circular segment-shaped profile. By tilting or pivoting this grinding wheel, the desired chip flute profile can be easily created.

[0026] Likewise, in this way it is possible to set an angle ß between a tangent T of the curved cross-section of the chip flute at the cutting corner and a radius ray RS through the cutting corner that is greater than 0 °.

[0027] The two-lip drill according to the invention can be designed as a solid carbide drill or as a built-up drill with a drill head soldered to the shaft.

[0028] The double-fluted deep-hole drill according to the invention is relatively easy to manufacture. This is also due to the fact that the chip flutes are straight and the chip surface according to the invention can be produced in a single grinding process using a profiled (and optionally pivoted) grinding wheel. The drill head according to the invention is advantageously made of hard metal and is coated if necessary.

[0029] Due to the continuously curved main cutting edges and / or the slightly recessed guide chamfer, the two-flute drill according to the invention has excellent performance characteristics. Both features can be implemented individually or in combination on a two-flute drill.

[0030] Further advantages and advantageous embodiments of the invention can be found in the following drawings, their description and the claims.

[0031] All features described in the drawing, its description and the claims can be essential to the invention both individually and in any combination with one another.

[0032] drawing

[0033] It shows :

[0034] Figure 1 is a schematic representation of a two-lip deep hole drill according to the invention,

[0035] Figure 2 shows a detail X of the drill bit according to Figure 1 and

[0036] Figure 3 is a front view of an inventive

[0037] Drill head .

[0038] Description of the embodiment Figure 1 shows a schematic and somewhat simplified representation of a two-lip deep hole drill 1. The deep hole drill 1 consists of a drill head 11, a shaft 12, and a clamping shaft 13. The clamping shaft 13 is used to hold the deep hole drill 1 in a deep drilling machine (not shown) or a machining center. The drill head according to the invention can be used with both solid carbide tools and "assembled" tools. With "assembled" tools, a drill head, a profile tubular shaft, and a clamping sleeve are soldered together.

[0039] A rotation axis or the central axis of the drill head

[0040] 11 has the reference number 23 . In the drill head 11 and the shaft

[0041] 12 has two beads or chip grooves 14 formed therein. Details of the geometry of the chip grooves 14 are explained below with reference to Figure 3.

[0042] As can be seen from detail "X," this example has a tip angle of 150°. Tip angles between 120° and 170° are readily possible.

[0043] It is also possible to provide a chamfer so that the drill has a smaller tip angle in an outer area. In the chamfer area, the tip angle can be between 60° and 140°.

[0044] The deep-hole drill 1 according to the invention is particularly suitable for drilling stainless, high-alloy, and tough steels. This task is very demanding, since these steels, particularly their alloying components nickel and chromium, have the undesirable property of dissolving the tungsten contained in the hard metal drill head, thereby accelerating the wear of the drill head. This property is particularly pronounced when the bore is lubricated with an emulsion of water and drilling oil.

[0045] In order to prevent this, the invention provides several measures which are explained below, particularly with reference to Figure 3.

[0046] The chip groove 14 according to the invention has a curved cross-section, i.e., in a plane extending perpendicular to the central axis 23. In this exemplary embodiment, the radius of curvature of the chip groove 14 is greatest at the cutting corner 16.

[0047] The cutting corner 16 is the place where a main cutting edge 18 and a round ground bevel 20 meet.

[0048] A further improvement in the performance characteristics is achieved when a tangent T of the curved region of the chip groove 14 at the cutting corner 16 and a radius ray RS through the cutting corner 16 enclose an angle ß greater than 0°. It has proven sufficient if the angle ß is less than 10°; preferably, it is in a range from 2° to 5°.

[0049] Two cooling lubricant channels 24 are visible at the tip of the drill head 11. These cooling lubricant channels 24 extend over the entire length of the deep-hole drill 1 in a conventional manner. Cooling lubricant is supplied to the tip of the deep-hole drill 1 via the cooling lubricant channels 24. The cooling lubricant cools the drill tip and simultaneously conveys the chips generated by the drill head 11 through the chip grooves 14 toward the clamping sleeve 13.

[0050] To assist chip removal, coolant grooves 26 can be ground into the end faces 22, establishing a direct hydraulic connection between the coolant channels 24 and the clamping grooves 14. The cross-section of the coolant grooves 26 can be used to adjust the volume flow of the coolant flowing from the coolant channels 24 into the clamping grooves 14.

[0051] As can be seen in Figure 3, the tip of the drill head is "pointed." This "pointing" is achieved by inserting two sharpened edges 30 into the drill tip, which shorten a chisel edge 28 of the drill. This sharpening reduces the feed forces. The grooves 26 and the sharpened edges 30 are also visible in Figure 2.

[0052] Section AA in Figure 2 shows an advantageous design of the flank. Following the main cutting edge 18, the clearance angle is 10°. Following this, the clearance angle is increased to 20°. Of course, the invention is not limited to these clearance angles.

[0053] The arrangement of the circular grinding bevels and the guide bevels according to the invention is now explained with reference to Figure 3.

[0054] The drill head comprises two circular ground chamfers 20 arranged at the cutting corners 16. Two guide chamfers 32 are formed, offset in the circumferential direction by approximately 90° to the circular ground chamfers 20.

[0055] The lower guide chamfer 32.1 in Figure 3 is, like the round ground chamfers 20, arranged at a distance R, corresponding to half the diameter of the drill, from the central axis 23.

[0056] The upper guide chamfer 32.2 in Figure 3 is positioned ("recessed") somewhat closer to the central axis 23 compared to the round ground chamfers 20 and the guide chamfer 32.1. The guide chamfer 32.2 can be recessed by an amount Ax of 3 / 100 mm to approximately 1 / 10 mm.

[0057] This ensures that the drill can rotate freely in the hole and does not jam. Furthermore, a lubricating film (approximately 3 / 100 mm to approximately 1 / 10 mm thick) forms between the hole wall and the guide chamfer 32.2, which has a positive effect on the wear behavior of the drill.

[0058] If the surface pressure between the guide chamfer 32.1, which is positioned on the same radius as the round ground chamfers 20, and the bore wall increases, the drill head can "deviate" slightly toward the guide chamfer 32.2. As a result, the surface pressure between the guide chamfer 32.1 and the bore wall decreases. This significantly reduces wear. A deviation of 1 / 100 mm to 2 / 100 mm can be sufficient.

[0059] In addition, the lubricating film between the bore wall and the

[0060] Guide chamfer 32.2 has a damping effect, which also has a positive effect on the quality of the hole and the tool life of the drill.

[0061] The two-lip drill according to the invention has curved main cutting edges 18 due to the chip flutes 14 which are curved in cross section.

[0062] The double-flute drill according to the invention has excellent performance characteristics due to the continuously curved main cutting edges 18 and / or the slightly recessed guide chamfer 32. 2. Both features can be implemented individually or in combination on a double-flute drill.

[0063] Glossary:

[0064] Double-lip drills are a special variant of deep hole drilling tools. Deep hole drilling tools are tools that operate according to various well-known deep hole drilling systems, i.e., BTA, ejector, single-lip drill, etc.

[0065] Double-flute drills are long and slender and have a central axis. The drill tip coincides with the rotational axis of the double-flute drill. This centers the drill tip in the hole. Double-flute drills are typically used in diameters ranging from approximately 3 mm to 40 mm. Holes with a length of up to approximately 6,000 mm are possible.

[0066] Double-lip drills are characterized by the ability to produce a high-quality hole in a single stroke. They can be used in machine tools such as lathes, machining centers, or special deep-hole drilling machines.

[0067] The machining process occurs through a relative movement of the drill to the workpiece in the direction of rotation around a common central axis or rotational axis, as well as a relative movement of the drill in the direction of the rotational axis (feed movement). The rotational movement can be caused by the drill and / or the workpiece. The same applies to the feed movement.

[0068] During the drilling process, the deviation [mm] of the actual hole path from the theoretical center axis of the drill is considered to be the center line. The center line is an aspect of hole quality. The aim is to achieve the smallest possible center line. Ideally, there should be no center line at all. The center line depends, among other things, on whether the rotary movement is caused by the drill or the workpiece, or by both. Experience shows that the smallest center line values ​​are achieved when the rotary movement is caused by the workpiece or by both the workpiece and drill.

[0069] Cooling lubricant (oil or emulsion) or a mixture of cooling lubricant and air (minimal quantity lubrication) is pumped through the cooling channels in the drill shank and drill tip to lubricate and cool the drill head and guide pads. The cooling lubricant also transports the chips generated by the main cutting edges through the chip flutes.

[0070] The coolant is supplied at the rear end under pressure (for example, at 75 bar), passes through the cooling channel, and exits at the drill head or drill tip. The pressure depends on the diameter and length of the drill.

[0071] The drill head of a double-flute drill has two main cutting edges; it can also have multiple cutting edges. The cutting edge is the area involved in the machining process; it is formed by the rake face and the flank face. The rake face is the area on which the chip runs. In the double-flute drill according to the invention, the chip flute is curved in cross-section (i.e., in a plane whose normal vector runs parallel to the center axis of the drill). As a result, the main cutting edges are also curved. This leads to a "pulling" cut and reduces the cutting forces.

[0072] In a double-fluted drill, the main cutting edges or cutting edges extend from the center axis of the drill head to its outer diameter.

[0073] The flank is the surface at the tip of the drill bit that faces the workpiece surface being machined. A blunt drill bit can be sharpened again by grinding the flanks.

[0074] The cutting edge or (main) cutting edge is the contact line between the chip face and the flank face. If the tip of the two-flute drill according to the invention has a conical and one or more truncated conical sections (e.g., a chamfer), then each cutting edge of the two-flute drill according to the invention consists of two or more curved partial cutting edges. The overall shape of all cutting and non-cutting edges

[0075] Surfaces on the face of the drill head are referred to as grinding. This also includes surfaces that are not directly adjacent to the cutting edges, such as surfaces or grooves for directing the coolant flow, or additional clearance surfaces or a point thinning to reduce the feed force.

[0076] The grinding largely determines the shape of the chips and is tailored to the material being machined. The goals of this adjustment include, among other things, the formation of the most favorable chips, a high machining speed, the longest possible drill life, and compliance with the required quality characteristics of the hole, such as diameter, surface, or straightness (center line).

[0077] The drill head is made of a material suitable for cutting, usually hard metal, but also cermet, ceramic or other suitable materials.

[0078] Sintered carbide with the

[0079] Components used in toilets and other facilities.

[0080] Machining the workpiece wears the cutting edges of the drill bit. A blunt drill bit can be reworked through regrinding. Regrinding involves re-grinding the worn part of the drill bit until all worn areas (especially the chip and flank) are removed and new, sharp cutting edges are created. Afterward, the grind returns to its original shape. If necessary, a coating is applied to at least the tip of the drill bit after regrinding. The drill bit then has the same properties as a brand-new drill bit.

[0081] A drilling tool can be reground as often as necessary until a complete grinding can no longer be applied to the drill head or until the tool can no longer be guided sufficiently due to the shortening of the guide bevels and strips.

[0082] To increase service life, the drill head can be coated with a wear-resistant coating; usually from the metal nitride or metal oxide group; also in several alternating layers. The thickness is usually approximately

[0083] 0.0005 to 0.010 mm. The coating is applied by chemical or physical vacuum coating processes.

[0084] Coating can be provided on the circumference of the drill head, on the flanks or on the chip surfaces; in some cases the entire drill head can also be coated.

[0085] During regrinding, the coating is removed by the grinding wheel, at least from the surfaces being reground. The coating remains intact on the other surfaces of the grinding.

[0086] Two round ground lands are arranged around the circumference of a double-flute drill. These lands guide the drill bit in the hole; they also smooth the hole wall. The round ground lands are cylindrical segments arranged at a distance of radius R (equivalent to half the nominal diameter of the drill bit) from the center axis; they rest against the hole wall during the drilling process.

[0087] The double-fluted drill according to the invention features two circular ground chamfers and two guide chamfers. The circular ground chamfers and two guide chamfers alternate.

[0088] Between a round ground chamfer and a guide chamfer as well as between a guide chamfer and a round ground chamfer, radially recessed segments with a smaller

[0089] Diameter, so that a gap is created between the bore wall and the drill head. The gap serves

[0090] Accumulation of coolant for cooling and lubricating the

[0091] Round ground chamfer and the guide chamfer.

[0092] The secondary cutting edge is the contact line (edge) between

[0093] The rake face and the rounded chamfer run parallel to the drill's center axis.

[0094] The intersection point between the main cutting edge and the secondary cutting edge is called the cutting corner.

[0095] List of reference symbols

[0096] I Double-fluted deep hole drill

[0097] II Drill head

[0098] 12 shaft

[0099] 13 Clamping shaft

[0100] 14 Bead or flute

[0101] 16 Cutting corner

[0102] 18 Main cutting edge

[0103] 20 round ground bevel

[0104] 22 Frontal clearance

[0105] 23 Rotation axis or central axis of the drill head

[0106] 24 coolant channels

[0107] 26 grooves

[0108] 28 Cross cutting edge

[0109] 30 grinding

[0110] 32 guide chamfer ß, Y angle

[0111] RS radius beam

[0112] T Tangent

Claims

Patent claims 1. A two-lip drill comprising a shaft (12) and a drill head (11), wherein two main cutting edges (18), two secondary cutting edges, two round ground chamfers (20), at least one guide chamfer (32) and two straight chip flutes (14) are formed on the drill head (11), and wherein the two chip flutes (14) have a curved region in cross-section, characterized in that the curved region of the chip flutes (14) extends to the secondary cutting edges.

2. Two-lip drill according to claim 1, characterized in that it comprises two guide lands (32), and that one of the guide lands (32.1) is arranged on the same radius as the round ground lands (20), while the other guide land (32.2) is arranged on a smaller radius than the round ground lands (20).

3. Two-lip drill comprising a shaft (12) and a drill head (11), wherein two main cutting edges (18), two secondary cutting edges, two round ground chamfers (20), at least one guide chamfer (32) and two straight chip flutes (14) are formed on the drill head (11), characterized in that a guide chamfer (32.1) is arranged on the same radius as the round ground chamfers (20).

4. Two-lip drill according to claim 3, characterized in that it has two guide chamfers (32.1, 32.2), and that the second guide chamfer (32.2) is arranged on a smaller radius than the round ground chamfers (20).

5. Two-lip drill according to claim 3 or 4, characterized in that the chip flutes (14) have a curved region in cross-section, and that the curved region of the chip flutes extends to the secondary cutting edges.

6. Two-lip drill according to one of claims 1, 2 or 5, characterized in that a tangent (T) of the curved region of the chip groove (14) at the cutting corner (16) and a radius ray (RS) through the cutting corner (16) enclose an angle (ß) greater than 0°.

7. Two-lip drill according to claim 6, characterized in that the angle (ß) is less than 10°.

8. Two-lip drill according to one of the preceding claims, characterized in that a circumferential angle (y) of the chip flutes (14) is less than 90°.

9. Two-lip drill according to one of the preceding claims, characterized in that the guide chamfers (32) are arranged offset by an angle of more than 80° and less than 100° to the round ground chamfers (20).

10. Two-lip drill according to one of claims 2 to 9, characterized in that one of the guide lands (32.2) is set back from the round ground lands (20) by at least 3 / 100 mm and a maximum of 10 / 100 mm.

11. Two-lip drill according to one of the preceding claims, characterized in that the cross section of the clamping grooves (14) is the same in the region of the drill head (11) and in the region of the shaft (12).

12. Two-lip drill according to one of the preceding claims, characterized in that a radius of curvature of the chip flutes (14) is not constant.

13. Two-lip drill according to claim 12, characterized in that the radius of curvature is greatest at the cutting corner (16).

14. A two-flute drill according to one of the preceding claims, characterized in that there are no chip formers on the main cutting edges (18).

15. A two-flute drill according to one of the preceding claims, characterized in that the main cutting edges (18) are curved.

16. Two-lip drill according to one of the preceding claims, characterized in that the drill head (11) is soldered to the shaft (12) and that the chip grooves (14) in the region of the shaft (12) also have a curved region.

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