WO2004050314A2

WO2004050314A2 - Cutting tool with a cooling surface

Info

Publication number: WO2004050314A2
Application number: PCT/SE2003/001853
Authority: WO
Inventors: Tomas Beno
Original assignee: Chalmers Technology Licensing Ab
Priority date: 2002-12-04
Filing date: 2003-12-03
Publication date: 2004-06-17
Also published as: SE0301827D0; SE0301827L; AU2003283916A1; WO2004050314A3; AU2003283916A8

Abstract

The present invention relates to cutting tools having an improved cooling obtained by an enlarged cooling surface in close vicinity to the cutting zone of the tool. The invention further relates to a method for monitoring the wear of a drill tool.

Description

TITLE

TOOLS

DESCRIPTION Technical field

The present invention relates to shaping tools, such as drills, cutters, lathe tool, and the similar having a high cutting efficiency and/or a long life time.

Background of the invention In order to have a high cutting speed and/or a long life time of a cutting tool of the type given in the preamble an efficient cooling of the tool is required. Most often is this done by adding a cooling medium to the cutting point either by spraying or by adding through the tool, such as through a drill being provided with a channel. The more efficient cooling the higher cutting speed which is of great importance to the engineering industry to obtain shorter machining times and an increased through-put of the production and thereby lower costs per machining.

Within the technical field it is previously known via US 5,439,327 to have one or more coolant liquid channels ending in the front edge of a lathe tool or cutter in recesses running up to the cutting edge in order to improve the cooling of the cutting edge. The providing of these coolant Iquid or cutting liquid recesses leads, however, simultaneously weakening of the cutting edge. Further, this type of recesses probably leads to the fact that the cutting liquid will only pass over the recess as an laminar film, or a turbulent film, alternatively, which provides for a restricted cooling.

SU 1215879 describes a rotatable cutting tool having two semi-circular grooves which are joined to each other on a rear surface and having its axis perpendicular to the cutting edge. The design of these grooves is said to prolong the life time of the edge by means of an aerodynamic cooling of the cutting zone.

Summary of the present invention

The present invention is based on increasing the available cooling surface close to the cutting zone so that a larger part of the heat generated can be transferred off with the cutting liquid or more generally the surrounding liquid as also minimum lubrication, cooling using carbon dioxide and compressed air cooling, or a combination of these, are used.

Detailed description of the present invention A further aspect of the invention relates to the supervision of the abrasion of drill tools whereby one monitors the temperature of ingoing and outgoing coolant and/or the torque, whereby at a substantial increase of the temperature according to a determined norm and/or a substantial increase of torque according to a determined norm, the drilling operation is stopped and the tool is optionally exchanged.

Thus a substantially improved tool/tool pad is achieved.

In the accompanying drawing some different embodiments of different tool steels are shown, wherein

FIG. 1-3 shows a cutting-off tool,

FIG. 4-6 shows a cutter,

FIG. 7-10 shows a crown locking drill unit seen from a frward direction (FIG. 7), in a perspective view (FIG. 8), a nozzle (FIG. 9) used in the crown locking unit, and the crown locking unit seen from the rear side (FIG. 10),

FIG. 11-12 shows a cutter holder seen in a front perspective view (FIG. 11) and seen in a view from above (FIG. 12),

FIG. 13-14 shows a graph registered at the operation of drills provided with and without cooling pattern according to the present invention.

FIG. 1-3 shows a cutting-off tool 1 in a perspective view and having essentially a rhombic design and being provided with a throughgoing attachment hole 2. Close to the cutting zone 3 on the upper side of the tool there are channels 4 for a coolant. In the surface being vertical in the figures close to the machining cutting zone 3, the points, there are cooling surfaces 5 present, which are enlarged by means of spark machined recesses 6 in the form of tetrahedrons. FIG. 2 shows a transparent picture of the tool 1 where the configuration of the recesses is clearly evident.

FIG. 4-6 shows a cutter 11 in the same way as the tool 1 provided with a cooling surface 15 on either side of the tool in connection with the operating cutting zone 13, which cooling surface in the same way is provided with recesses 16. FIG. 5 shows a transparent view wherein the shape of the recesses 16 is evident; in this example tetrahedron shaped (pyramid shaped) as well.

Hitherto, all cutting tools used for cutting, lathing, and indexable insert drilling have been smooth. By, as proposed in the present invention, adding a surface enlarging pattern, regular or irregular, on all clearance surfaces and on the parts of the surface on the chip side not having a direct contact with the chips the available cooling surface can be considerably improved. Tests carried out and reported below have shown that the life time of the tools can be considerably prolonged by means of this modification of the surface. The life time is increased independent of cooling method used, including spray cooling. Tests carried out shows that drills according to the present invention in combination with spray cooling provide for an improved life time with > 4 times compared to a standard drill using spray cooling. When using a cutting liquid pressure of 50 bars the increase of life time varied from 2 times to > 4 times compared to standard drills.

When small cutting liquid particles hit a smooth surface there is a great probability that the particle will not obtain a contact time long enough to obtain a phase conversion of the cutting liquid of the surface but this may be take place in the surrounding fluidum (air) in stead or be completely eliminated. If, however, the surface is provided with a pattern according to the present invention then it is obtained, besides a increased available cooling surface, even a possibility for the particle to adhere to the surface long enough to obtain a phase transfer on the surface and thereby a cooling thereof. Phase transfer, e.g., from a liquid to a gas phase means energy consumption, which energy is taken from the heated piece in a machining process, either the tool or the machined piece as such. An important parameter is hereby the particle size of the cutting liquid particle, or water particle, alternatively. Thereby water has an advantage in that it is good from an environmental point of view and possesses physical advantages in that its cp-value is high. Water having an addition of a surface tension reducing agent to produce a small particle may thus be a better coolant with good environmental impact.

In the embodiments shown above there is a patterned surface present in macro form, such as a pyramidal recess or pyramidal protrusion.

Another alternative is to obtain a micro geometry. By producing the macro surface by means of spark machining one obtains a micro geometry which in turn gives rise to a still larger cooling surface. But furthermore, such a machining process gives rise to a to a number of micro cracks, which form cavities which help stimulating a nucleus boiling of the liquid, which produces spray particles. The micro geometry can be obtained by surface coating by means of spark machining, sputtering, oscillating electron beam and laser technology or by means of a surface coating method such as PVD (plasma vapor deposition) or CVD (chemical vapor deposition), alternatively.

Another aspect being a combination of the above described macro technology and micro technology is to obtain baffles on the cooling surface of the tool. The baffles leads to that a fluid flowing towards the baffle will be brought into a strong turbulence when it hits the baffle which turbulence is conveyed to behind the baffle. The turbulence is not dissipative, which means that it continues a way behind the baffle which in turn leads to that the thermal interface is dissolved, which leads to a better contact with the cooling surface and thereby an improved cooling (heat transfer). Studies carried out show that a placement of the baffle haing the form of a "tractor tire", that is to say oblique baffle element angled about 60° to each other provides the best effect. The improvement is thereby most pronounced at liquid cooling but will also function to other fluids (fluidum).

At the application of baffles to the cooling medium, in particular at drills, in particular a indexable insert drills to obtain a turbulent flow studies carried out have shown that the flow at the outlet of the cutting liquid at the drill point is of importance. Thereby it has turned out that a suitable outlet placement is a placement of the baffles on the clearance side of the cutting edge in a semi circular formation to send turbulence vortexes towards the cutting edge on the clearance side where it is most probable that there exists a so called Leiden frost film which normally isolates against an effective heat transfer. Another preferred placement is at the corner of the drill as the corner is one of the weakest points of the drill.

On other tools the baffles are placed onto surfaces where the flow pattern is known. Thus the pattern including baffles may be placed on the cutting tool itself as on the holder of the cutting tool, as well as optional holding pads between cutting tool and holder. At indexable insert drills the cooling requirement is deemed to be high as these pads often are small i.e., 4 to 10 mm in square and having a thickness of 2 to 4 mm. This leads to that the mass of the pad is rapidly heated during operation and thereby the risk for wear increases.

Mist cooling is used today of drills. The disadvantage is hereby that the mist is generated in a sviwel, where the tool is attached to the machine spindle which means that there is de facto mist when the cutting liquid reaches the cutting zone but the mist has been joined to a liquid film when the mist has passed the internal cooling channels of the drill. This is a reason for why mist lubrication has not been accepted as a method due to this uncertain function.

However, if one, in accordance with one aspect of the invention, places nozzles or a spray nozzle at the outlet in the cutting zone the mist will be generated where it shall be present and is useful without any risk for droplet or liquid film formation. Thus one or more nozzles or spray nozzles can be arranged in the helix on the secondary clearance side of a drill. The cutting liquid forced out through the nozzle will then form a mist which is dragged to the clearance side as a common helical drill has a pronounced back flow behind itself. This effect has been established at studies carried out.

FIG. 7-9 show a so called crown locking drill unit, wherein FIG. 7 shows a drill seen in a front view having nozzles applied which comprises a number of spray nozzles, which nozzles are placed in such a way that they enter in the helix of the secondary clearance side. In FIG. 8 21 denotes the cutting edge, 22 the drill point, 23 the secondary clearance side and 24 the primary clearance side which is supported by the return flow which the drill provides at its rotation. FIG. 9 shows an embodiment of a nozzle, whereby 25 denotes the point of he drill provided with nozzles 26, its cylindrical or conical body 27 and its rear end 28 to be introduced into the drill crown holder and its cooling liquid channels. FIG. 10 shows the rear side of the drill crown in a perspective view where the rear part 28 of the nozzle extends for inpassning into its cooling channel of said drill crown holder. In FIG. 8 the cooling surfaces 29 according to the present invention in the form of recesses placed partly on the primary clearance side, partly on the jacket surface of the drill close to the point.

One way of providing the nozzles or dysor at other tools is evident from FIG. 11 where a tubular lin is placed close to a lathe tool on its holder and where cutting liquid under pressure is forced out of diminutive holes in the tubular line. The mist obtained will then hit the cutting point of the cutting tool. FIG. 11 also shows the application of an arch shaped tubular line on the upper side of the holder, which, in the same way, will generate a mist of cutting liquid when forcing cutting liquid under pressure through the diminutive holes. The two tubular lines are connected to a source of cutting liquid (not shown. In FIG. 11 there is further shown a pattern of the present invention applied on the tool holder itself. The present invention thus encompasses tool holders provided with a pattern according to the present invention, as well.

Thus FIG. 11 shows a cutter tool holder 41 being provided with holes 42 in a attachment area 43 for attaching a cutter, or a mounting pad, alternatively, and a cutter. Immediately in front of the attachment area 43 there is a tubular line 44 connected to a source (not shown) of cutting liquid, which source is arranged to force, under pressure, cutting liquid to the tubular line 44. Diminutive openings 45 are provided in the line, in this case directed up towards the non-shown cutter tool and its cutting edge. On the upper side 46 of the holder 41 there is a further tubular line 47 provided, which in the same way is connected to a source (not shown) for cutting liquid, which is arranged, in the same way, to add cutting liquid under force to this second tubular line 47. This line 47, as well, is provided with diminutive holes 48 through which cutting liquid is forced and thereby forms very small droplets, particles or a mist of cutting liquid. The holes 48 are directed towards the cutting edge of the non-shown cutter. FIG. 12 shows the embodiment of FIG. 11 seen from above of which FIG. 12 it is evident that the tubular line 44 runs around the front corners 49 of the tool holder. It is evident from FIG. 11 that the tool holder is provided with a surface enlarging pattern in the form of pyramidal recesses in the surface immediately underneath the attachment area 43 of the cutter tool.

The holes 48 and 45, respectively have such a diameter that a very good distribution of liquid being forced through these openings will be obtained. The aim is to obtain a spray independent of type of liquid having its respective surface tension characteristics. The diameter of the hole may thus vary dependent on which liquid to be used.

In the accompanying graphs, FIGs. 13 and 14, the results of a drilling using a standard drill, and a drill according to the present invention, both having the same steel quality and drill design, where the drill having a diameter of 10 mm and a raise of 1.2 mm per revolution is fed with a speed of 50 m/min, and where spray cooling was used. In FIG. 13 the temperature at the drill point, which temperature is reached during a complete course of action using spray cooling, is shown, and FIG. 14 shows an operation where spray cooling was used after 30 seconds of operation. As evident from FIG. 13 a drill according to the present invention obtains a temperature of 58-59°C after 30 sec. only, while a standard drill obtains 81-82°C after 30 sec. The temperature difference between the cooling liquids can be said to be 33% higher at the standard drill case compared to the drill of the present invention. It is evident from FIG. 14 that the introduction of cooling provides a more rapid cooling at a drill of the present invention than at a standard drill and that the standard drill will not obtain the same degree of cooling as the drill of the present invention as the temperature difference increases with time. In a continuous situation one should reach the values according to FIG. 13.

In other tests carried out at a production industry plant, i.e., in production, it has turned out that one may obtain a life time lengthening of up to 1200% using a tool according to the present invention.

In another aspect of the invention a process for supervision of cutting operation where a cooling liquid is present, is obtained. For example, at the manufacture of air craft details of titanium alloys a critical process is the manufacture of holes as these alloys have a higher concentration of tensions than the remaining parts, up to 4 times.

When a drill tool is worn the cutting forces increase both with regard to axial forces as whell as torque. When this occurs these forces are transferred into heat which leads to a temperature increase of the cutting tool. If the tool should be cooled using a cutting liquid the outgoing cutting liquid will obtain a temperature increase which can be monitored.

In the same way one can monitor the torque by using the spindle effect. The axial force is harder to monitor. However, one can determine if the wear is present at the centre of the tool or along the periphery. If the wear should be found at the periphery both temperature and torque will increase, but if the wear should be found at the centre the temperature of the outgoing cutting liquid will increase without obtaining any increase of the torque.

Thus one can measure the temperature difference between outgoing and ingoing cutting liquid by means of temperature sensors on the tool provided with some type of transferring device, via cable, transmitter, or direct reading of a digital output.

Temperature sensors can also be applied at the spindle point to avoid rotation of the sensor.

By means of a predetermined protocol one mmay later on determine if working operations should be abandoned or not.

If one should drill a bottom hole the wear is important both at centre and at the periphery. If one produces a through going hole the wear at the periphery is decisive when one drills the material away from the centre if this should have been influenced by heat.

Claims

1. Cutting tool, such as drills, cutters, lathe and the similar having a high cutting efficiency and/or long life time, characterized in that the cooling surface close to the cutting zone, or substantially close to the cutting zone is substantially increased by enlarging the surface of the tool in this zone by indents into the surface or by protrusions from the surface.

2. Cutting tools according to claim 1, wherein such indents have the shape of part spheres, tetrahedrons, cones, truncated cones, cylinders, grooves, banks and other suitable geometrical forms.

3. Cutting tools according to claim 1, wherein such protrusions have the shape of shape of part spheres, tetrahedrons, cones, truncated cones, cylinders, grooves, banks and other suitable geometrical forms.

4. Cutting tools according to one or more of claims 1-3, wherein the increased surface is achieved by spark machining, and/or sputtering, or by cutting machining of the tool material.

5. Cutting tool according to one or more of claims 1-4, wherein the tool is a solid drill and cutter, indexable insert drills, drills having an exchangeable tip, lathe tools, cutters and other tools such as threading tools.

6. Cutting tool according to one or more of the claims 1-5, wherein the cooling surface is an increase of the present surface with at least 100%, preferably at least 150%, more preferably 200%, most preferably 400%.

7. Tool holder for cutters and lathe tools, characterized in that the holder is provided with a cooling increasing pattern on a part close to a tool receiving part as defined in claims 1-6.

8. Method for monitoring the wear of a drill tool, characterized in that one monitors the temperature of an ingoing and an outgoing cooling medium and or the torque, whereby at an substantial temperature increase according to a predetermined protocol and/or substantial increase of torque according to a predetermined protocol the drilling is stopped and the tool is optionally exchanged.