FLOW DRILL

Abstract

 Flow drill made from a sintered cemented carbide material comprising tungsten carbide and a metallic binder, the sintered cemented carbide material comprising: tungsten carbide having a mean grain size in the range from 0.1 µm to 0.8 µm, 9 weight percent to 15 weight percent cobalt, 0.2 weight percent to 1.1 weight percent molybdenum and/or 1 weight percent to 10 weight percent in total of tantalum carbide, niobium carbide and/or tantalum-niobium mixed carbide, 0 weight percent to 1.4 weight percent chromium, 0 weight percent to 0.6 weight percent vanadium carbide, 0 weight percent to 0.1 weight percent unavoidable impurities, 92.8 weight percent to 71.8 weight percent of said tungsten carbide.

Description

[0001] The present invention relates to a flow drill made from a sintered cemented carbide material comprising tungsten carbide and a metallic binder.

[0002] The present invention relates further to a use of said flow drill and to a flow drilling method.

[0003] A flow drill is a drilling tool designed to create holes in at least one material without producing chips or swarf.

[0004] A flow drill works by utilizing heat generated through friction to soften the material(s), allowing the material(s) to flow and typically to also form a bushing or collar.

[0005] Flow drilling offers several advantages over traditional drilling methods since flow drilling requires lower axial force and torque compared to traditional drilling methods, reducing thereby the risk of damage to a workpiece. Additionally, flow drilling can be performed quickly, often resulting in higher production rates.

[0006] EP 4 144 458 A1 shows a tool for flow drilling.

[0007] An objective of the present invention is to provide an improved flow drill for flow drilling high surface quality holes into high strength thin sheet metal(s) and at the same time having an improved tool life.

[0008] The objective is solved by the flow drill according to claim 1. Further developments are defined in the dependent claims, the specification and in Figs. 1 and 2 and their detailed description.

[0009] The flow drill is made from a sintered cemented carbide material comprising tungsten carbide and a metallic binder, the sintered cemented carbide material comprising: tungsten carbide having a mean grain size in the range from 0.1 µm to 0.8 µm, 7 weight percent to 15 weight percent cobalt, 0.2 weight percent to 1.1 weight percent molybdenum and/or 1 weight percent to 10 weight percent in total of tantalum carbide, niobium carbide and/or tantalum-niobium mixed carbide, 0 weight percent to 1.4 weight percent chromium, 0 weight percent to 0.6 weight percent vanadium carbide, 0 weight percent to 0.1 weight percent unavoidable impurities, 92.8 weight percent to 71.8 weight percent of said tungsten carbide. It has been surprisingly found that the combination of said tungsten carbide mean grain size, said molybdenum in its said range and/or said (tantalum carbide, niobium carbide and/or mixed tantalum-niobium carbide) in its/their said total range, said weight percent range of said cobalt and said weight percent range of said tungsten carbide improves the hot deformation resistance of the flow drill thereby increasing tool file, translating into higher number of holes that can be flow drilled, and enabling flow drilling of high quality holes into high strength sheet metals made of e.g. titanium alloys.

[0010] Preferably, the flow drill is a monolithic body made from said sintered cemented carbide material. Preferable, the flow drill has a drill-tip region made from said sintered cemented carbide.

[0011] It is expressively stated that said 0.2 weight percent to 1.1 weight percent of molybdenum is beneficial for the hot deformation resistance on its own and can be present essentially or completely without any of said tantalum carbide, niobium carbide and/or tantalum-niobium mixed carbide.

[0012] The source for said molybdenum can typically be molybdenum powder and/or molybdenum carbide powder added to a powder mixture which can be pressed and sintered to manufacture said sintered cemented carbide material.

[0013] The source for said tantalum carbide, niobium carbide and tantalum niobium mixed carbide can typically be corresponding carbide powder added to a powder mixture which can be pressed and sintered to manufacture said sintered cemented carbide material.

[0014] It is expressively stated that alternatively 1 weight percent to 10 weight percent in total of tantalum carbide, usually present as TaC, niobium carbide, usually present as NbC, and/or tantalum-niobium mixed carbide is/are beneficial for said hot deformation resistance on its/their own and can be present essentially or completely without said molybdenum; "in total" is to be understood that if only tantalum carbide, niobium carbide or tantalum-niobium mixed carbide is present, it lies in said range from 1 weight percent to 10 weight percent, if two or more of these carbides are present, e.g., tantalum carbide and niobium carbide, the weight percentage sum of these carbides lies in the same range from 1 weight percent to 10 weight percent.

[0015] It is expressively stated that especially the combination of 0.2 weight percent to 1.1 weight percent of said molybdenum with 1 weight percent to 10 weight percent in total of said tantalum carbide, niobium carbide and/or tantalum-niobium mixed carbide is beneficial for said hot deformation resistance.

[0016] Said chromium can be present up to 1.4 weight percent and increases said hot deformation resistance even further. The source for said chromium can typically be chromium powder and/or chromium carbide powder added to a powder mixture which can be pressed and sintered to manufacture said sintered cemented carbide material.

[0017] Said vanadium carbide, usually present as VC, can be present up 0.6 weight percent and increases said hot deformation resistance even further.

[0018] The source for said vanadium carbide can typically be corresponding carbide powder added to a powder mixture which can be pressed and sintered to manufacture said sintered cemented carbide material.

[0019] Said tungsten carbide, usually present as WC, can be present as the remainder in said sintered cemented carbide material with respect to said cobalt, if present, said molybdenum, if present, said tantalum carbide, if present, said niobium carbide, if present, said tantalum-niobium mixed carbide, if present, said chromium, if present, said vanadium carbide, and, if present, said unavoidable impurities. Thus, if said tungsten carbide is present as the remainder, said range "92.8 weight percent to 71.8 weight percent of said tungsten carbide" can be adjusted, depending on which and how much of said tantalum carbide, said niobium carbide, said tantalum-niobium mixed carbide, said chromium, said vanadium carbide and said unavoidable impurities are present to yield 100 weight percent for the composition of said sintered cemented carbide material.

[0020] It is hereby directly and unambiguously disclosed that the range of said tungsten carbide, if being said remainder, is calculated by (100 weight percent - (S1 + S2 + S3 + S4 + S5 + S6)), wherein S1 is the weight percentage of said cobalt, S2 is the weight percentage of said molybdenum, S3 is the total weight percentage of said tantalum carbide, niobium carbide and/or tantalum-niobium mixed carbide, S4 the weight percentage of said vanadium carbide, S5 is the weight percentage of said chromium and S6 is the weight percentage of said unavoidable impurities.

[0021] Said unavoidable impurities are preferably not present but cannot always be avoided due to powder processing and/or sintering.

[0022] The mean grain size of said tungsten carbide grains is measured as "linear intercept length" according to the international standard ISO 4499-2:2008(E). EBSD micrographs (EBSD, electron back-scatter diffraction) of sintered samples were used as a basis. The measurement methodology for such micrographs is described, for example, in: K. P. Mingard et al., "Comparison of EBSD and conventional methods of grain size measurement of hard metals", Int. Journal of Refractory Metals & Hard Materials 27 (2009) 213-223.

[0023] It is expressively stated that the mean tungsten carbide grain size is in the range from 0.1 µm to 0.8 µm, being thereby smaller than 1 µm mean grain size. Said range from 0.1 µm to 0.8 µm covers two grain size classes of tungsten carbide grains, typically classified as ultra fine, mean grain size from 0.2 µm to 0.5 µm, and as submicron, mean grain size from 0.5 µm to 0.8 µm.

[0024] Weight percentages are to be understood in the present disclosure with respect to the entire composition of said sintered cemented carbide material, unless otherwise stated.

[0025] "0 weight percent" is to be understood as "at least essentially free from the corresponding constituent", preferably "free from the corresponding constituent".

[0026] Said tungsten carbide grains form a skeleton structure. Said skeleton structure has interspaces filled with at least said cobalt forming the basis of said binder; further elements can be dissolved in said cobalt, e.g., said chromium, if present.

[0027] Preferably, the flow drill is made from said sintered cemented carbide material comprising said tungsten carbide and said metallic binder, said sintered cemented carbide material consisting of: said tungsten carbide having a mean grain size in the range from 0.1 µm to 0.8 µm, 7 weight percent to 15 weight percent of said cobalt, 0.2 weight percent to 1.1 weight percent of molybdenum and/or 1 weight percent to 10 weight percent in total of said tantalum carbide, niobium carbide and/or tantalum-niobium mixed carbide, 0 weight percent to 1.4 weight percent of said chromium, 0 weight percent to 0.6 weight percent of said vanadium carbide, 0 weight percent to 0.1 weight percent of said unavoidable impurities, said tungsten carbide being the remainder.

[0028] Preferably, the flow drill is made from said sintered cemented carbide material comprising said tungsten carbide and said metallic binder, said sintered cemented carbide material consisting of said tungsten carbide having a mean grain size in the range from 0.1 µm to 0.8 µm, 7 weight percent to 15 weight percent of said cobalt, 0.2 weight percent to 1.1 weight percent of said molybdenum and 1 weight percent to 10 weight percent in total of said tantalum carbide, niobium carbide and/or tantalum-niobium mixed carbide, 0 weight percent to 1.4 weight percent of said chromium, 0 weight percent to 0.6 weight percent of said vanadium carbide, 0 weight percent to 0.1 weight percent of said unavoidable impurities, said tungsten carbide being the remainder.

[0029] According to a further development of said flow drill said tungsten carbide has a mean grain size in the range from 0.2 µm to 0.5 µm or wherein said tungsten carbide has mean grain size in the range from 0.5 µm to 0.8µm. Flow drilling of high strength metals, e.g., titanium alloys, involves high temperatures e.g., 1000°C or more, and high-pressure conditions which subjects the flow drill to significant stresses and activates thermally induced plastic deformation processes. If said tungsten carbide has a mean grain size in the range from 0.2 µm to 0.5 µm or in the range from 0.5 µm to 0.8 µm the toughness of the sintered cemented carbide is improved, helping to prevent cracking, premature wear of said flow drill and to reduce the amount of plastic deformation. Preferably, the mean grain size in the range from 0.2 µm to 0.5 µm if selected, when said cobalt ranges 11 weight percent to 15 weight percent. Preferably, the mean grain size in the range from 0.5 µm to 0.8 µm is selected when said cobalt ranges 9 weight percent to 11 weight percent.

[0030] According to a further development of said flow drill said tantalum carbide, niobium carbide and/or mixed tantalum-niobium carbide is in total in a range from 1.5 weight percent to 8 weight percent. Such a narrow band of said tantalum carbide, niobium carbide and/or mixed tantalum-niobium mixed carbide increases the hot deformation resistance even further. "in total in a range from 1.5 to 8 weight percent" is to be understood that the sum of weight percentages of tantalum carbide, if present, niobium carbide, if present, and tantalum-niobium mixed carbide, if present, lies in the range from 1.5 to 8 weight percent. Preferably, tantalum carbide is selected from said tantalum carbide, niobium carbide and/or mixed tantalum-niobium carbide and lies in the range from 1.5 to 8 weight percent.

[0031] According to a further development of said flow drill said cobalt is in the range from 11 weight percent to 13 weight percent or wherein said cobalt is in the range from 9 weight percent to 11 weight percent. Thus, the binder band is narrowed down, increasing thereby the plastic deformation resistance providing for an improved shape stability of said flow drill under temperatures of 1000°C or more.

[0032] According to a further development of said flow drill said molybdenum is in the range from 0.3 weight percent to 1 weight percent. It has been found that when said molybdenum is in the range from 0.3 weight percent to 1 weight percent it improves the hot deformation resistance of said flow drill.

[0033] According to a further development of said flow drill said chromium is in the range from 0.4 weight percent to 1 weight percent. It has been found that when said chromium is in the range from 0.4 weight percent to 1 weight percent it improves the hot deformation resistance of said flow drill.

[0034] According to a further development of said flow drill said vanadium carbide is in the range from 0.3 weight percent to 0.5 weight percent. It has been found that when said vanadium carbide is in the range from 0.3 weight percent to 0.5 weight percent it improves the hot deformation resistance of said flow drill.

[0035] According to a further development of said flow drill said sintered cemented carbide material is free from titanium carbide. It has been found that titanium carbide is detrimental for flow drilling since titanium carbide grains tend to coarsen thereby reducing toughness.

[0036] According to a further development of said flow drill said sintered cemented carbide material is free from carbides other than tungsten carbide, tantalum carbide, niobium carbide, tantalum-niobium mixed carbide, chromium carbide, vanadium carbide, molybdenum carbide and carbides present as part of said unavoidable impurities. Thus, according to this further development, said sintered cemented carbide material comprises said cobalt and carbides and/or elements which are selected only from: said tungsten carbide in combination with least one carbide selected from said tantalum carbide, niobium carbide, tantalum-niobium mixed carbide and/or said molybdenum, and optionally at least one selected from said chromium and/or said vanadium carbide. This limitation is cost reducing and beneficial for the hot deformation resistance.

[0037] According to a further development of said flow drill comprises a friction-shaping shaft and a drill-tip on top of said friction-shaping shaft, wherein said drill-tip transitions smoothly into said friction-shaping shaft. The friction-shaping shaft and the drill-tip are made from the said sintered cemented carbide material forming thereby a monolithic body. Said friction-shaping shaft is preferably designed to smoothen a hole flow drilled under frictional contact without cutting or threading the material surrounding the hole. The drill-tip makes the first contact with the material to be flow drilled and creates the drill point. Preferably, the drill-tip is designed without cutting edges and has a dome-shape.

[0038] According to a further development of said flow drill the friction-shaping shaft is cylindrical having a friction shaft diameter in the range from 1 mm to 10 mm. This friction shaft diameter range has the effect to improve flow drill hole quality in that clean and burr-free holes can be created, which is particularly advantageous for applications that require high precision, such as in electronics and thin sheet metals.

[0039] According to a further development of said flow drill the friction shaft diameter is in the range from 1.1 mm to 1.9 mm. It has been found that this narrower shafter diameter range from 1.1 mm to 1.9 mm suppresses burr-formation even better and thereby improves hole quality even further.

[0040] According to a further development of said flow drill it comprises a shoulder section, wherein the friction-shaping shaft is arranged between the shoulder section and the drill-tip, wherein the shoulder section widens in an axially direction away from said drill-tip.

[0041] The objective is also solved by the subject matter of claim 14, i.e., a use of said flow drill according to any of the preceding developments of said flow drill to flow drill a hole into a workpiece. Said workpiece is preferably made from a titanium alloy.

[0042] The objective is also solved by the subject matter of claim 15, i.e., a flow drilling method comprising the steps: providing the flow drill according to any one of claims 1 to 13, flow drilling a hole into a workpiece with said flow drill. Preferably, said flow drill is moved only along a major flow drill axis being perpendicular to a hole axis. Said workpiece is preferably made from a titanium alloy. Preferably, said workpiece has no hole or gap at the position where it will be flow drilled.

[0043] Further advantages and further developments will become apparent from the following description of an embodiment with reference to the enclosed drawing.

[0044] The Figures show:

Fig. 1:

a schematic illustration of a flow drill made from a sintered cemented carbide material comprising tungsten carbide and a metallic binder according to an embodiment of the invention;

Fig. 2:

enlarged drill-tip detail of the flow drill illustrated in Fig. 1.

[0045] Fig. 1 shows a flow drill 1 made from a sintered cemented carbide material comprising tungsten carbide and a metallic binder. The sintered cemented carbide material comprises tungsten carbide having a mean grain size of 0.4 µm lying in the mean grain size range from 0.2 µm to 0.5 µm which is typically called "ultra fine" (alternatively said mean grain size is in the range from 0.5 µm to 0.8 µm which is typically called "submicron"), 12 weight percent cobalt lying in the cobalt range from 11 weight percent to 13 weight percent (alternatively said cobalt amounts to 10 weight percent when said mean grain size is in the range from 0.5 µm to 0.8 µm), 0.5 weight percent molybdenum lying in the molybdenum range from 0.2 weight percent to 1.1 weight percent, 8 weight percent tantalum carbide lying in the tantalum carbide range from 1 weight percent to 10 weight percent and tungsten carbide as the remainder with respect to said cobalt (said 12 weight percent or said 10 weight percent), molybdenum and tantalum carbide, i.e. said tungsten carbide lies in the tungsten carbide range from 92.8 weight percent to 71.8 weight percent. Optionally said sintered cemented carbide material can further comprise 0.7 weight percent chromium lying in the chromium range from 0.4 weight percent to 1 weight percent chromium and 0.35 weight percent vanadium carbide lying in the vanadium carbide range from 0.3 weight percent to 0.5 weight percent, wherein the tungsten carbide weight percent is the remainder with respect to said cobalt, said molybdenum, said tantalum carbide and said chromium, if present, and said vanadium carbide, if present. Said sintered carbide material can comprise unavoidable impurities up to 0.1 weight percent, wherein the tungsten carbide weight percent is the remainder with respect to said cobalt, said molybdenum, said tantalum carbide and said chromium, if present, and said vanadium carbide, if present, and said unavoidable impurities, if present. Said sintered cemented carbide material is free from titanium carbide to suppress the presence of carbides which coarsen significantly during flow drilling high strength metals.

[0046] The flow drill 1 is a monolithic body made from said sintered cemented carbide material and designed to create holes in a sheet metal by piercing through that sheet metal under rotation with respect to a central axis 2 of the flow drill 1. The flow drill 1 comprises a drill-tip 3, a friction-shaping shaft 4, a shoulder section 5, a further shoulder section 6 and a mounting shaft 7. The drill-tip 3 is positioned on top of the shoulder section 5 and dome-shaped and thereby designed to create a point-like contact with said sheet metal to be flow drilled and to pierce under axial pressure along the central axis 2 of the flow drill 1 without cutting said sheet metal.

[0047] Fig. 2, where drill-tip part within the dashed circle in Fig. 1 is enlarged, shows that the drill-tip 3 has a substructure comprising a conical front tip 3a and a convexly rounded main drill-tip part 3b which is longer than the conical front tip 3a when measured parallel along the central axis 2. The conical front tip 3a has front tip angle 30a of 90° lying in the range from 85° to 95° which enhances positioning and centering of the flow drill 1 under its first contact with said sheet metal. The main drill-tip part 3b is convexly rounded under a curvature radius 30b of 2.5 mm lying in the range from 1.5 mm to 3.5 mm.

[0048] The conical front tip 3a and the main drill-tip part 3b have been found to provide an improved penetration and fast friction heat buildup for the initial penetration of the flow drill 1 into a high strength sheet metal.

[0049] The friction-shaping shaft 4 has the effect to smoothen and stabilize the flow drilled hole part created by the drill-tip 3 under friction contact with a corresponding hole wall of a high strength sheet metal. As such the friction-shaping shaft 4 is longer than the drill-tip 3 when measured parallel along the central axis 2. The friction-shaping shaft 4 is cylindrical with respect to the central axis 2 and has a friction shaft diameter of 3 mm which is in the range of 1.5 mm to 5 mm. It has been found that the friction shaft diameter in the range of 1.1 mm to 1.9 mm has the effect to suppress burr formation during flow drilling, i.e., material buildup around the flow drill hole due to material flow being suppressed.

[0050] The friction-shaping shaft 4 and has a friction shaft length of 6.5 mm when measured parallel along the central axis 2 which is in the range of 5 mm to 8 mm selected for flow drilling into correspondingly thin high strength sheet metals. The drill-tip 3 has a total tip length of 1.6 mm when measured parallel along the central axis 2 which is in the range of 1 mm to 3 mm. The friction-shaping shaft 4 and the drill-tip 3 have a joint length of 8 mm when measured parallel along the central axis 2 which lies in the range form 5 mm to 12 mm which defines a maximum flow drill depth of the flow drill 1 to lie in the range from 5 mm to 12 mm. The lengths of the friction-shaping shaft 4, the drill-tip 3 and their joint length are selected deliberately to flow drill holes into correspondingly thin sheet high strength metals.

[0051] The friction-shaping shaft 4 is arranged between the drill-tip 3 and the shoulder section 5, wherein the drill-tip 3 transitions due to its main drill-tip part 3b smoothly into the friction-shaping shaft 4. The shoulder section 5 widens parallel along the central axis 2 in the direction away from the drill-tip 3 whereby the diameter of the shoulder section 5 increases to become larger than said friction shaft diameter. The further shoulder section 6 is arranged between the shoulder section 5 and the mounting shaft 7 and widens analogously to the shoulder section 5. The mounting shaft 7 has a mounting shaft diameter larger than the friction shaft diameter which provides for a stable mounting to a spindle which drives the flow drill 1 rotationally and axially during flow drilling. The shoulder sections 5 and 6 provide for a smooth and notch-free connection of the friction shaping shape 4 and the mounting shaft 7.

[0052] A use of the flow drill 1 to flow drill a hole into a workpiece is disclosed by virtue of its design shown in Figs. 1 and 2. The use of the flow drill 1 is realized by rotating the flow drill 1 with respect to the central axis 2 and moving the flow drill 1 simultaneously in a direction 8 into a workpiece, e.g., a thin high strength sheet metal made from e.g., a titanium alloy. Said workpiece has typically prior to flow drilling no hole at the position where it shall be flow drilled. When the hole has been flow drilled the flow drill 1 is moved opposite to the direction 8 out of the flow drilled hole. Said used of the flow drill 1 can be repeated to flow drill further holes analogously at different positions and/or workpieces.

[0053] A flow drilling method comprises the steps: providing the flow drill 1, flow drilling a hole into a workpiece, e.g., a thin high strength sheet metal made from e.g., a titanium alloy. During the step of flow drilling the hole the flow drill 1 is rotated with respect to the central axis 2 and moved simultaneously in the direction 8 into the workpiece which typically has no hole at the position to which the flow drill 1 is moved. During the step of flow drilling the hole the flow drill 1 is typically not moved in a direction perpendicular to the central axis 2. When the hole has been flow drilled the flow drill 1 is moved opposite to the direction 8 out of the flow drilled hole. Said step of flow drilling the hole can be repeated to flow drill further holes analogously at different positions and/or workpieces. The workpiece has a maximum thickness in a direction along the central axis 2 which is smaller than said joint length of the friction-shaping shaft 4 and the drill-tip 3.

[0054] The flow drill 1 is - predominately due to the sintered cemented carbide material - capable to flow drill at least 300 holes into a 1.5 mm thick sheet made from a titanium alloy without breakage of the drill-tip 3 and friction shaping shaft 4 and without deformation of the drill-tip 3 and friction shaping shaft 4, both forming a monolithic part together.

[0055] It is expressively stated that further advantageous embodiments of the flow drill 1 can be realized based on the shape and dimensions and the sintered cemented carbide material shown and described with reference to Figs. 1 and 2, for example the shoulder section 6 can be omitted if the shoulder section 5 transitions into the mounting shaft diameter and/or for example by omitting the conical front tip 3a by extending the main drill-tip part 3b further into the direction 8 such that the main drill-tip part 3b terminates in a single point when viewed as in Fig. 1 and 2, i.e., perpendicular to the central axis 2. The shoulder sections 5 and 6 can also be designed differently than shown in Figs. 1 and 2.

[0056] It is expressively stated that further advantageous embodiments can be realized by changing the composition within the disclosed ranges of said cobalt, said molybdenum, said tantalum carbide, said vanadium carbide, said chromium and/or said tungsten carbide. Said tantalum carbide can be omitted when said molybdenum is kept within its disclosed ranges. Said tantalum carbide can be replaced by said niobium carbide or by said mixed tantalum-niobium carbide or said tantalum carbide can be mixed with said niobium carbide and/or mixed with said mixed tantalum-niobium carbide within the correspondingly disclosed total range for tantalum carbide, niobium carbide and tantalum-niobium mixed carbide. Said molybdenum can be omitted if said tantalum carbide is kept within its disclosed ranges.

Experimental results

[0057] An inventive flow drill A having the shape and dimensions of the flow drill 1, e.g., the inventive flow drill A has likewise a friction-shaping shaft with a friction shaft diameter of 1.5 mm, and being made from a sintered cemented carbide material according to the invention was manufacturing to test its performance against a reference flow drill having the same shape and dimensions of the inventive flow drill A, e.g., the reference flow drill has likewise a friction-shaping shaft with a friction shaft diameter of 1.5 mm, but being made from a different sintered cemented carbide material, named hereafter reference material.

[0058] The sintered cemented carbide material of the inventive flow drill A comprises tungsten carbide and a metallic binder, the sintered cemented carbide material consists of: tungsten carbide having a mean grain size of 0.4 µm (measured as "linear intercept length" according to the international standard ISO 4499-2:2008(E), wherein EBSD micrographs (EBSD, electron back-scatter diffraction) of sintered samples were used as a basis and the measurement methodology for such micrographs is described, for example, in: K. P. Mingard et al., Comparison of EBSD and conventional methods of grain size measurement of hard metals", Int. Journal of Refractory Metals & Hard Materials 27 (2009) 213-223), 12 weight percent cobalt, 0.5 weight percent molybdenum, 8 weight percent tantalum carbide, 0.7 weight percent chromium, 0.35 weight percent vanadium carbide and tungsten carbide as the remainder, i.e., 78.45 weight percent tungsten carbide. Said 0.4 µm mean grain size of flow drill A represent the mean grain size range from 0.2 µm to 0.5 µm.

[0059] The reference material the reference flow drill is made from comprises tungsten carbide and a metallic binder, the reference material consists of tungsten carbide having a mean grain size of 0.4 µm (measured analogously to the sintered cemented carbide material of the inventive flow drill A), 12 weight percent cobalt, 0.7 weight percent chromium, 0.35 weight percent vanadium carbide and tungsten carbide as the remainder, i.e., 86.95 weight percent tungsten carbide.

[0060] The inventive flow drill A and the reference flow drill where both used to flow drill holes into a 1.5 mm thick titanium alloy sheet consisting of 6 weight percent aluminum, 4 weigh percent vanadium, remainder titanium, each under the same flow drill parameters.

[0061] The inventive flow drill A was able to flow drill 331 different holes into the 1.5 mm thick titanium alloy sheet without flow drill fracture or plastic flow drill deformation. The reference flow drill was able to flow drill 121 different holes into the 1.5 mm thick titanium alloy sheet and fractured during flow drilling the 122nd hole. The longer tool life of the inventive flow drill A is attributed to its improved hot deformation resistance predominately improved by the presence of molybdenum in combination with tantalum carbide and the mean tungsten carbide grain size of 0.4 µm; the 1.5 mm thick titanium alloy sheet reaches locally approximately 1000°C during flow drilling.

[0062] Further inventive flow drills A were manufactured according to the inventive flow drill A, thus having the same sintered cemented carbide material, shape and dimensions, and further reference flow drills were manufactured according to said reference flow drill, thus having the same reference material, shape and dimensions. The further inventive flow drills A and the further reference flow drills confirmed the longer tool file of the inventive flow drill A during flow drilling said holes into the 1.5 mm thick titanium alloy sheet.

[0063] Further inventive flow drills A* were manufactured according to the inventive flow drill A*, having the same sintered cemented carbide material, but with 10 weight percent cobalt (instead of 12 weight percent), and accordingly adjusted tungsten carbide weight percent as the remainder, and tungsten carbide grains having a mean grain size of 0.7 µm (representing the range from 0.5 µm to 0.8 µm and measured analogously to the mean grain size in flow drill A), shape and dimensions, and further reference flow drills were manufactured according to said reference flow drill, thus having the same reference material, shape and dimensions. The further inventive flow drills A* and said further reference flow drills showed a longer tool file of the inventive flow drill A* during flow drilling said holes into the 1.5 mm thick titanium alloy sheet.

[0064] An inventive flow drill B1 was manufactured according to the inventive flow drill A but with a mean tungsten carbide grain size of 0.2 µm and an inventive flow drill B2 was manufactured according to the inventive flow drill A but with a mean tungsten carbide grain size of 0.5 µm. The inventive flow drills B1 and B2 showed a longer tool life when tested against further reference flow drills according to said reference flow drill.

[0065] An inventive flow drill B1* was manufactured according to the inventive flow drill A but with a mean tungsten carbide grain size of 0.7 µm and an inventive flow drill B2* was manufactured according to the inventive flow drill A but with a mean tungsten carbide grain size of 0.8 µm. The inventive flow drills B1* and B2* showed a longer tool life when tested against further reference flow drills according to said reference flow drill.

[0066] An inventive flow drill C1 was manufactured according to the inventive flow drill A but with 7 weight percent cobalt and accordingly adjusted tungsten carbide weight percent as the remainder and an inventive flow drill C2 was manufactured according to the inventive flow drill A but with 15 weight percent cobalt and accordingly adjusted tungsten carbide weight percent as the remainder. The inventive flow drills C1 and C2 showed a longer tool life when tested against further reference flow drills according to said reference flow drill.

[0067] An inventive flow drill D1 was manufactured according to the inventive flow drill A but with 0.3 weight percent molybdenum and accordingly adjusted tungsten carbide weight percent as the remainder and an inventive flow drill D2 was manufactured according to the inventive flow drill A but with 1 weight percent molybdenum and accordingly adjusted tungsten carbide weight percent as the remainder. The inventive flow drills D1 and D2 showed a longer tool life when tested against further reference flow drills according to said reference flow drill.

[0068] An inventive flow drill E1 was manufactured according to the inventive flow drill A but with 1.5 weight percent tantalum carbide and accordingly adjusted tungsten carbide weight percent as the remainder and an inventive flow drill E2 was manufactured according to the inventive flow drill A but with 8 weight percent tantalum carbide and accordingly adjusted tungsten carbide weight percent as the remainder. The inventive flow drills E1 and E2 showed a longer tool life when tested against further reference flow drills according to said reference flow drill.

[0069] An inventive flow drill F was manufactured according to the inventive flow drill A but with 0 weight percent molybdenum and accordingly adjusted tungsten carbide weight percent as the remainder. The inventive flow drills F showed a longer tool life when tested against a further reference flow drill according to said reference flow drill.

[0070] An inventive flow drill G was manufactured according to the inventive flow drill A but with 0 weight percent tantalum carbide and accordingly adjusted tungsten carbide weight percent as the remainder. The inventive flow drill G showed a longer tool life when tested against a further reference flow drill according to said reference flow drill.

[0071] An inventive flow drill H was manufactured according to the inventive flow drill A but with 0 weight percent chromium and accordingly adjusted tungsten carbide weight percent as the remainder. The inventive flow drill H showed a longer tool life when tested against a further reference flow drill according to said reference flow drill.

[0072] An inventive flow drill I was manufactured according to the inventive flow drill A but with 0 weight percent vanadium carbide and accordingly adjusted tungsten carbide weight percent as the remainder. The inventive flow drill I showed a longer tool life when tested against a further reference flow drill according to said reference flow drill.

[0073] An inventive flow drill J was manufactured according to the inventive flow drill A but where tantalum carbide was replaced by the same weight percent of niobium carbide. The inventive flow drill J showed a longer tool life when tested against a further reference flow drill according to said reference flow drill.

[0074] During further testing it was found that the mean tungsten carbide grain size, in combination with said tantalum carbide and/or said molybdenum in their disclosed ranges, improves the hot deformation resistance. A flow drill was manufactured according to the inventive flow drill A but with a mean grain size of the tungsten carbide grains of 1 µm which fractured earlier than any of the inventive flow drills A, A* B1, B2, B1*, B2*, C1, C2, D1, D2, E1, E2, F, G, H, I and J during flow drilling. It was found that the longest tool life as a function of the mean tungsten carbide grain size was observed when the mean tungsten carbide grain size was in the range from 0.2 µm to 0.5 µm, which is typically classified as "ultra fine".

Claims

1. Flow drill made from a sintered cemented carbide material comprising tungsten carbide and a metallic binder, the sintered cemented carbide material comprising:
tungsten carbide having a mean grain size in the range from 0.1 µm to 0.8 µm,

7 weight percent to 15 weight percent cobalt,

0.2 weight percent to 1.1 weight percent molybdenum and/or

1 weight percent to 10 weight percent in total of tantalum carbide, niobium carbide and/or tantalum-niobium mixed carbide,

0 weight percent to 1.4 weight percent chromium,

0 weight percent to 0.6 weight percent vanadium carbide,

0 weight percent to 0.1 weight percent unavoidable impurities,

92.8 weight percent to 71.8 weight percent of said tungsten carbide.

2. Flow drill according to claim 1, wherein said tungsten carbide has a mean grain size in the range from 0.2 µm to 0.5 µm or wherein said tungsten carbide has mean grain size in the range from 0.5 µm to 0.8µm.

3. Flow drill according to any of the preceding claims, wherein said tantalum carbide, niobium carbide and/or mixed tantalum-niobium carbide is in total in a range from 1.5 weight percent to 8 weight percent.

4. Flow drill according to any of the preceding claims, wherein said cobalt is in the range from 11 weight percent to 13 weight percent or wherein said cobalt is in the range from 9 weight percent to 11 weight percent.

5. Flow drill according to any of the preceding claims, wherein said molybdenum is in the range from 0.3 weight percent to 1 weight percent.

6. Flow drill according to any of the preceding claims, wherein said chromium is in the range from 0.4 weight percent to 1 weight percent.

7. Flow drill according to any of the preceding claims, wherein said vanadium carbide is in the range from 0.3 weight percent to 0.5 weight percent.

8. Flow drill according to any of the preceding claims, wherein said sintered cemented carbide material is free from titanium carbide.

9. Flow drill according to any of the preceding claims, wherein said sintered cemented carbide material is free from carbides other than tungsten carbide, tantalum carbide, niobium carbide, tantalum-niobium mixed carbide, chromium carbide, vanadium carbide, molybdenum carbide and carbides present as part of said unavoidable impurities.

10. Flow drill according to any of the preceding claims, wherein the flow drill comprises a friction-shaping shaft (4) and a drill-tip (3) on top of said friction-shaping shaft (4), wherein said drill-tip (3) transitions smoothly into said friction-shaping shaft (4).

11. Flow drill according to claim 10, wherein the friction-shaping shaft (4) is cylindrical having a friction shaft diameter in the range from 1 mm to 10 mm.

12. Flow drill according to claim 11, wherein the friction shaft diameter is in the range from 1.1 mm to 1.9 mm.

13. Flow drill according to claim 10, 11 or 12, wherein the flow drill comprises a shoulder (5, 6) section, wherein the friction-shaping shaft (4) is arranged between the shoulder section (5, 7) and the drill-tip (3), wherein the shoulder section (5, 6) widens in an axially direction away from said drill-tip (3).

14. Use of the flow drill according to any of the preceding claims to flow drill a hole into a workpiece.

15. Flow drilling method comprising the steps: providing the flow drill according to any one of claims 1 to 13, flow drilling a hole into a workpiece.

Drawing