Patent Publication Number: US-6699430-B2

Title: Method and device for producing a sintered metal blank with internally disposed helical recesses

Description:
This is a continuation of PCT/EP00/08603 filed Sep. 2, 2000 and published in German. 
    
    
     The invention relates to the method and a device for producing a substantially circularly cylindrical body, particularly a sintered metal blank, which consists of plastic material and which has at least one helical internal recess extending in the interior of the body, according to the introductory part of patent claim  1  or of patent claim  12 . In addition, the invention relates to a sintered rod produced by the method according to the invention. 
     Such bodies are required particularly in the manufacture of drilling tools or drilling tool inserts of hard metal or ceramic materials. Through the helical course of the at least one internal recess, which serves in the finished drilling tool for the feed of coolant or lubricant to the cutting region, the drilling tool can be furnished with helical cutting grooves which are often of advantage for the provision of favourable cutting and material removal characteristics and consequently are desired. 
     It has previously been attempted to produce such sintered metal blanks or ceramic blanks by an extrusion method, in that the material consisting of sintered metal powder or ceramic powder and binder is forced through an extrusion nozzle which has a cross-section corresponding to the desired blank cross-section and further has at least one internally disposed core in the form of a pin which on extrusion of the plasticised material serves for formation of the internal recess extending through the entire blank. 
     The material issuing from the extrusion nozzle is usually very pressure-sensitive, i.e. the issuing blank deforms extremely easily in the case of external application of force. Since such deformations are no longer reversible and thus lead to blanks which are unusable at least in sections, it has been attempted to further develop the extrusion process so that the blank already has the helically extending cooling channels when issued from the extrusion nozzle. According to one proposal this is achieved in the manner that helically extending guide strips, which impose a twist motion on the issuing plastic material, are mounted at the inner circumference of the extrusion nozzle. Flexible threads with a cross-section corresponding with the cross-section of the internal recess to be produced are fastened in the cross-section of the extrusion nozzle, wherein the threads extend up to the outlet of the nozzle mouthpiece. Due to the flexibility of the threads these can follow the swirl motion or the swirl flow of the plastic material and thus generate the at least one internally disposed cooling channel in the blank. 
     According to a further proposal the nozzle mouthpiece and/or a hub formed in propeller shape, to which the aforesaid flexible or pliable threads are fastened, is set into rotary motion during the extrusion process, whereby again an externally smooth blank with internally disposed helical channels or recesses could be produced. 
     In the production of such tool blanks it is important that the angle of inclination of the at least one helical internal recess is kept constant over the entire length of the blank and within closely toleranced limits. This is required because regular cutting grooves are ground into the tool blank after the sintering process. This grinding is carried out by largely automated machines, so that in the case of imprecise production of the helical internal recesses an uncontrolled high reject rate can result. In that case it has to be taken into consideration that tools with fully hardened metal cutting parts are used inter alia because the high loading capability of the material, particularly the torsional stiffness, has to be utilised. In order to ensure this the internal recess must not extend too close to the cutting groove, which cannot, however, be effectively excluded in the case of inaccurate production of the helical internal recess. In the case of the afore-described attachments for production of blanks with internally disposed helical recesses it is accordingly necessary to monitor as accurately as possible the extrusion tool and/or the sintering devices for the extrusion worm or—if present—for the twist-generating bodies during the extrusion process and to adapt to the material throughput. This has the consequence that relatively lengthy changeover and setting times are required at the extrusion tool with the result that conventional methods are economically usable primarily for large batch production. Disproportionately high machine setting costs result for small batch production or for production of drilling tools with greater nominal diameters, whereby the economics of the production method are called into question. 
     The invention accordingly has the object of creating a method and a device of the aforesaid kind by which the blank or blanks of the kind described in the introduction can be produced more economically and, as before, with high precision. 
     This object is met with respect to the method by the features of patent claim  1  and with respect to the device by the features of patent claim  12 . 
     According to the invention the blank is produced as before in an extrusion process, which is distinguished by a high economy by virtue of high possible throughput rates. The extrusion is carried out so that the at least one inwardly disposed recess is extruded rectilinearly, which has the advantage that the production parameters for the extruding, i.e. the extrusion speed, the material throughput, etc, no longer have an effect on the course of the internally disposed recesses. Instead, a body extruded with substantially rectilinear internal recesses is cut to a predetermined length, i.e. cut to length, and subjected in the cut-to-length state to a special deforming process which is based on the principle of a rolling motion engaging the extruded rod over the entire length thereof. The arrangement is in that case such that the speed of the rolling motion changes linearly and constantly over the length of the extruded rod or body, wherein the inclination of the helically extending internal recess is determined by way of the gradients of the speed distribution of the rolling motion. With the method according to the invention the extruded body is uniformly twisted over its entire length and with maintenance of favourable, i.e. constant, support relationships, wherein a minimal deformation of the blank cross-section results due to the rolling motion taking place in that case. The consistency of the extruded extrusion material is thus of benefit to the attaching in accordance with to the invention. The extruded extrusion material is uniformly of viscous consistency so that by virtue of the friction surface arrangement a largely slip-free entrainment of the outer surface of the extruded blank is ensured. The accuracy of the course of the at least one internally disposed helical recess can thus be kept to a particularly high level. 
     Advantageous embodiments of the method and of the device for production of the substantially circularly cylindrical blank body with a helical internal recess are described in the subclaims. 
     It has proved that with support of the blank along a line it is already possible to produce the at least one helical cooling channel without unacceptably high deformations of the blank cross-section. A particularly simple device for performance of this development in terms of method forms the subject of claims  13  and  14 . Such a device merely requires a support surface and a surface mounted parallel thereto to be pivotable about an axis perpendicular to the support. The inclination of the at least one helical internal recess can be determined by way of the absolute magnitude of the relative pivot angle between the support and the friction surface arrangement. This inclination is directly proportional to the size of the pivot angle. 
     The deformation of the extruded blank during twisting can be kept within even closer limits by the development of the method and the device according to claims  4  and  15 . The support of the extruded blank during twisting preferably takes place with a looping angle of substantially 180°, wherein in this case the external forces due to gravitational force can be kept to a minimum. A particularly simple construction of the device with a minimum of components and in that case at the same time a particularly gentle support of the deformation-sensitive extruded blank results with the development of the device according to patent claim  17 . This device is accordingly suitable in particular measure for extrusion materials with a high proportion of plasticiser. 
     Since the blank tends to shorten during twisting it is of advantage if the surface formed from the film material or textile material is composed of a plurality of part surfaces which are disposed in a line axially along the axis of the body and between each of which a respective gap is provided. The film material or textile material can thus accompany the shortening of the blank rod without excessive force action on the blank, which is of further benefit to the production accuracy of the at least one internally disposed cooling channel. 
     If the drive device engages the side edges of the film material or textile material in accordance with claim  21  then a comparatively wide scope is created for the design of the drive device. The drive device can, through appropriate selection of the length of the film material or textile material or of a corresponding fabric, be placed in a desired region above the fabric bend, i.e. above the blank to be reshaped. Thus, many possibilities for the accommodation of a drive device are left to the constructer. 
     It has proved that in the case of use of a fabric connected to the side edges, four raising and lowering drives engaging at the corners are sufficient in order to uniformly twist the extruded blank over the entire length. Stepping motors, which are preferably program-controlled, are preferably used as drive units. The deforming can thus be set in simple manner and, for example, adapted to different nominal diameters of the drilling tool to be produced, whereby a minimum of re-equipping effort is needed. 
     Further advantageous embodiments are the subject of the remaining subclaims. 
    
    
     A number of embodiments of the invention are explained in more detail in the following by reference to schematic drawings, in which: 
     FIG. 1 shows a plan view of a first embodiment of the device for producing a sintered metal blank, which consists of a plastic material, with an internally disposed helical recess; 
     FIG. 2 shows the view corresponding to II in FIG. 1; 
     FIG. 3 shows, in a view corresponding to FIG. 1, the device after twisting of the extruded blank; 
     FIG. 4A shows a schematic view of a further device for producing a sintered metal blank provided with at least one internally disposed helical recess, in a pre-production phase; 
     FIG. 4B shows the device according to FIG. 4A in a second pre-production step; 
     FIG. 5 shows a perspective view of the device according to FIG. 4A or FIG. 4B before the twisting process of the blank; 
     FIG. 6 shows a view, which corresponds with FIG. 5, of the device after the twisting process; 
     FIG. 7 shows a view, which is similar to FIG. 5, of a third embodiment of the device for producing a substantially circularly cylindrical sintered metal blank, which consists of plastic material, with a helical internal recess extending in the interior of the body; 
     FIG. 8 shows a representation of a modified cross-section of the sintered metal blank; 
     FIG. 9 shows, schematically, an extrusion of a pasty sintered material; 
     FIG. 10 shows a front view of the extruded pasty sintered material; 
     FIG. 11 shows a twisting device from the side; 
     FIG. 12 shows the twisting device of FIG. 11 from above; 
     FIG. 13 shows a part method sequence of the production method; 
     FIG. 14 shows a sintered rod from the side; 
     FIG. 15 shows the sintered rod of FIG. 14 in cross-section; and 
     FIG. 16 shows the sintered rod of FIG. 15 from the front. 
    
    
     A sintered metal blank, which is cut to a predetermined length L*, i.e. cut to length, and which consists of, for example, a hard metal powder with a kneaded-in binder or adhesive, is denoted by the reference numeral  10  in FIGS. 1 to  3 . This sintered metal blank is produced by, for example, the extrusion method and in particular in such a manner that it has a rectilinear and continuous internal recess  12  which is illustrated in the figures by a dot-dashed line and which extends parallel to the centre axis  14  of the circularly cylindrical blank  10 . 
     The production of the sintered metal blank is preferably carried out by the extrusion method with the use of an extrusion nozzle with a suitable core. The blank  10  has a comparatively soft consistency so that handling, for example, transport, has to be carried out very carefully in order to prevent irreversible deformations. Accordingly, the blank is preferably guided on an air cushion directly after exit from the extrusion nozzle and conducted onto the support  16  which is shown in the figures and which in FIGS. 1 and 3 coincides with the drawing plane. Due to the consistency of the extrusion material the blank is viscous on its outer side so that a good adhesion with the support surface  16  results. 
     In order to deform the blank  10  in such a manner that the rectilinear internal recess according to FIG. 1 or  2  is reshaped into a helical recess, the arrangement is as follows: 
     A circle-segment disc  18  with a friction surface  20  at the base is arranged parallel to the planar support surface  16  at the vertical spacing AV. The circle-segment disc  18  is rotatable about an axis  22  which extends perpendicularly to the surface of the support  16  or to the friction surface. The vertical spacing AV between the surfaces  16  and  20  is preferably adjustable, as indicated by the double arrow V in FIG.  2 . This vertical spacing AV corresponds with the diameter D of the blank  10 . 
     As shown in FIG. 1, the blank  10  is placed on the support  16  in such a manner that its longitudinal axis  14  intersects the rotational axis  22  of the circle-segment disc  18 . Subsequently, the circle-segment disc is lowered in controlled manner so that it contacts the blank  10  along a line which is offset diametrally relative to the base contact line of the blank  10  with the support  16 . This orientation is shown in FIGS. 1 and 2. 
     The circle-segment disc  18  is now pivoted at an angular speed ω. Due to the friction contact between the surface  20  of the circle-segment disc  18  and the blank  10  the blank is entrained in that it rolls on the surface of the support  16  at a speed which changes linearly and constantly along the axis of the blank  10 . The rolling speed at the inner end of the blank  10  is denoted by VWI and the rolling speed of the outer end of the blank  10  is denoted by VWA. If the segment disc  18  thus runs through a specific pivot angle φ a linear distribution of the rolling path results along the rod-like blank  10  with the consequence that the circularly cylindrical blank  10  is twisted during the rolling motion and, in particular, in such a manner that an angle of inclination of the twisting, and thus an angle of inclination of the helical internal recess  12 , results which is directly proportional to the pivot angle φ. 
     The circle-segment disc  18  is preferably kept in contact with the rod-like blank  10  with the smallest possible support force and, in particular, during the entire twisting process, i.e. during the entire pivotation about the pivot angle φ (see FIG.  3 ). It can be of advantage here to operate with pressure sensors which act on the raising and lowering device, which is not illustrated in more detail, for the circle-segment disc  18 . 
     It is clear from the foregoing description that in the first embodiment a linear support of the sintered metal blank  10  is present during the twisting process. In the following an embodiment is described in which the support during the twisting takes place over an area. For this purpose reference is made to FIGS. 4 to  6 . 
     The twisting device according to the second embodiment essentially consists of a pliable or flexible film material or textile material  26  which is initially placed flat on a base  28 . The plastic blank  10 , which is, for example, extruded and is again furnished with a rectilinear internal recess  12 , is subsequently placed on the film material or textile material  26 . If—as indicated in FIG. 4A by the arrow H—the side edges  30 A and  30 B are now struck upwardly then the state according to FIG. 4B is adopted. In that case the film material or textile material  26 , which in the simplest embodiment can be formed as a fabric, loops around the blank  10  over a looping angle β of 180°. The blank  10  thus hangs in the fabric  26 , which adopts the shape of a ‘U’. 
     Drive devices  32 A and  32 B which will be described in more detail in the following with reference to FIGS. 5 and 6, engage at the ends  30 A and  30 B of the fabric  26 : 
     Two drive devices in the form of lifting and lowering drives, which are denoted by  32 AV and  32 AH or by  32 BV or by  32 BH, engage on each side of the fabric  26 . These drive devices are disposed at the corners of the fabric or of the film material or textile material  26 . The drive now takes place in the manner that the adjacent corners of the fabric  26  are raised or lowered in opposite sense, as indicated by the arrows H and S in FIG.  5 . Since the blank  10  is suspended in the fabric  26 , it is subjected also in this case and with the assistance of the gravitational force of the blank  10  to a rolling motion, the magnitude of which changes linearly and constantly over the length of the blank  10 . The arrangement is preferably such that the rolling motion is zero in the centre M of the blank  10 . The rolling motion is produced in the manner that the support, which is formed by the fabric  26 , under the blank  10  is so moved away that the extent of displacement between the support  26  and the blank  10  over the length of the blank  10  follows a linear distribution. In other words, through the afore-described drive motion of the film material or textile material  26  the effect results that considered in a plane perpendicular to the longitudinal axis  14  of the blank  10  the tangential movement of the fabric  26  with respect to the blank  10  linearly changes along the axis thereof, wherein in the illustrated embodiment this tangential movement is zero at the centre M of the blank  10 . 
     FIG. 6 shows the state of the twisting device and of the blank  10  after twisting has been carried out. The front left corner of the fabric  26  and the back right corner are lifted up, whilst the other two corners were lowered. The internally disposed channel  12  illustrated in FIG. 5 to be rectilinear is helically twisted in the state according to FIG.  6 . The extent of twisting is determined by the extent of raising and lowering movement in correspondence with the arrows H and S. Step motors, which are program-controlled in suitable manner, are preferably used for the raising and lowering drives at the corners of the film material or textile material  26 , so that a rapid adaptation to different parameters to be observed in the production of the blank can be undertaken. 
     Since the blank  10  tends to shorten during the twisting, the film material or textile material—as shown in FIGS.  5  and  6 —is so designed that it can accompany the shorting without significant reaction force effect on the body  10 . For this purpose a number of axially displaced slots  34  are provided in the film material or textile material  26  and, in particular, in such a manner that still interconnected side edges  30 A and  30 B continue to be present. The slots  34  thus enable—as shown in FIG.  6 —a contraction, which is free of reaction force, of the film material or textile material  26 , whereby undesired deformations of the blank  10  and thus dimensional deviations are effectively excluded. 
     In FIG. 7 there is indicated a variant of the device for twisting the sintered metal blank  10  produced with rectilinear internal recesses. In departure from the embodiment according to FIGS. 5 and 6 there is used here a plurality of strips  36  which are disposed at an axial spacing relative to one another and with each of which there is associated a respective separate drive in the form of a raising or lowering unit. The drive of the strips  36  takes place, similarly to the embodiment according to FIGS. 5 and 6, in such a manner that a linear movement distribution along the blank  10  results. This movement distribution is indicated in FIG. 7 by the arrows H 1  to H 5  or S 1  to S 5 . 
     In departure from the previously described embodiments it is obviously possible to undertake modifications without departing from the concept of the invention. Thus, obviously also other drive devices can be used as long as the afore-described effect is achieved. Moreover, in the case of the example shown in FIG. 1 the rod  10  can also be placed so that the rod end extends beyond the rotational centre point  22 , wherein a circular plate is then present as the part  18 . In addition, the blank can have different cross-sectional forms, in particular it can also have a cross-sectional form slightly departing from the circular shape. Whilst the described forms of embodiment of the blank  10  are shown with only one internal recess, it is obviously also possible to provide several internal recesses of different shape. FIG. 8 shows a possible cross-sectional design with two internal recesses  112  which shall form, in the later tool, the channels for the feed of coolant or lubricant to the cutting region. Recesses which are larger in cross-section and which are disposed so that they lie in the profile of the cutting groove  116  which is to be ground in later and is illustrated by dot-dashed lines, are denoted by the reference numerals  114 . In this design, hard metal can be saved and the metal volume to be removed during grinding in of the cutting grooves  116  can be kept smaller. Sufficient material still remains radially outwardly of the recess  114  in order to keep the deformation resistance during rolling of the blank  110  to such magnitude that irreversible deformations are excluded. 
     The afore-described method and the device belonging thereto can obviously also be used when the course of the internally disposed cooling channel in the extruded sintered metal blank simply has to be corrected. The procedure is also not restricted to the processing of blanks which consist of hard metal or ceramic. It is usable on any material which exists with plastic consistency and accordingly has a very high sensitivity to deformation. Finally, it is also not necessary for the looping angle β to amount to 180°. It is also conceivable to operate with looping angles which are substantially smaller. In this case it is merely necessary to operate with a flexible surface which loops the body in a section and is appropriately driven. 
     The invention thus creates a method and a device for producing a substantially circularly cylindrical body, particularly a sintered metal blank, which consists of plastic material and which has at least one helical internal recess extending in the interior of the body. For the avoidance of excessive retooling effort for changeover of a production batch the body present with plastic consistency is initially produced, preferably extruded, with a substantially rectilinear course of the internal recess. The body is subsequently cut to a defined length and finally subjected, whilst supported over its entire length on a support, by means of a friction surface arrangement to a rolling motion, the speed of which changes linearly and constantly over the length of the body so that the body is uniformly twisted. 
     A further embodiment of the invention in which the cross-section of the internal recesses or channels is non-circular is described by reference to the following figures. 
     According to FIG. 9 a pasty sintered material  41  is extruded by an extruder head  42  which is illustrated only schematically. The pasty sintered material  41  consists of a steel powder, hard metal powder or ceramic powder, mixed with a binder. The extrusion is carried out purely linearly in an extrusion direction x at a substantially constant extrusion speed v. When the extruded strand of the sintered material  41  has a sufficient length l it is cut to length by means of a cutter  43 . The cutting to length is carried out in that case selectably manually or automatically. 
     Shaped bodies  44 , which are illustrated by dashed lines, are retained in the extrusion head  42 . In that case according to FIG. 9 two shaped bodies  44  are present. However, a greater or lesser number of shaped bodies  44  could also be present. Channels  45  are formed in the sintered material  41  by means of the shaped bodies  44  during the extruding. The channels  45  extend parallelly, but eccentrically, to a rod axis  46 . The rod axis  46  is the gravitationally central axis of the extruded sintered material  41 . 
     According to FIG. 11 the channels  45  have channel cross-sections which are non-circular. According to the embodiment they are, for example, triangular. Moreover, they have outer edges  47  and longitudinal axes  47 ′. Neither the outer edges  47  nor the longitudinal axes  47 ′ run concentrically to the rod axis  46 . As apparent, the channels  45  are formed identically to one another and are arranged offset relative to the rod axis by a rotational angle. The rotational angle in that case results from 360° divided by the number of channels  45 . In the present case it thus amounts to 180°. 
     The sintered material  41  is still readily plastically deformable after the cutting to length. According to FIG. 12 it is therefore placed on a flat support  48  and, in particular, in such a manner that it is arranged radially relative to the axis  49  of rotation of a turntable  50 . The turntable  50  is then—see also FIG.  13 —lowered onto the sintered material  41  cut to length and pivoted through a pivot angle φ. The extruded sintered material  41  is thereby twisted over the rod length l with a constant twist. 
     The twisted sintered material  41  is then—see FIG.  10 —introduced into a drying oven  51  and dried there. Chip spaces  53  are thereafter formed in the dried sintered material  41  by means of a grinding disc  52 . Rod fields  54  thereby arise between the chip spaces  53  as seen in the rod cross-section. The sintered material  41  thus prepared is then fed to a sintering oven  55  in which it is sintered into a sintered rod  41 ′. 
     A further grinding disc  52 ′ is arranged behind the sintering oven  55 . A subsequent processing of the chip spaces  53  is carried out by means of this grinding disc  52 ′. It is alternatively also possible that the chip spaces  53  are formed in the then already sintered sintered rod  41 ′ only by means of the grinding disc  52 ′. The forming of the chip spaces  53  before the sintering and by means of the grinding disc  52  is, however, to be preferred since at this point in time the sintered material  41  can still be processed relatively easily. 
     FIG. 14 now shows the sintered rod  41 ′ after its further processing into a drill blank, from one side. As apparent, it has two chip spaces  53  which run in helical form around the rod axis  46 . 
     FIG. 15 now shows a cross-section along one of the dashed lines in FIG.  14 . The cross-section is always the same. As apparent, the chip spaces  53  were therefore formed in the dried sintered material  41  or in the sintered rod  41 ′ in such a manner that the channels  45  extend substantially parallel to the boundaries to the chip spaces  53  as seen in the rod cross-section. In addition, since the cross-section is independent of the location at which it was undertaken, the channels  45  necessarily also run with a constant inclination helically about the rod axis  46 . The channel cross-sections remain unchanged relative to the illustration according to FIG.  10 . They are thus again triangular, thus, in particular, non-circular. Moreover, neither their outer edges  47  nor their longitudinal axes  47 ′ extend concentrically to the rod axis  46 . 
     As apparent, the drill blank  41 ′ has two chip spaces  53  and two rod fields  54  arranged between the chip spaces  53 . The drill blank  41 ′ has one channel  45  for each rod field  54 . The two channels  45  are in that case, as evident, formed to be the same. 
     FIG. 16 now shows the drill blank  41 ′ from the front, thus from the direction of the arrows according to FIG.  14 . According to FIG. 16 the drill blank  41 ′ has two cutting edges  56  at its tip. In addition, the channels  45  extend substantially parallel to the cutting edges  56  as seen in the cross-section. Stated more specifically, they have side edges  57  which extend substantially parallel to the cutting edges  56 . 
     By virtue of the shape of the channels  45  in accordance with the invention an enlarged channel cross-section results by comparison with the state of the art. A higher throughput of a medium through the channels  45  is thus achievable. Moreover, the cutting edges  56  can in operation be acted on by the medium over almost their entire length. Cooling, lubrication of the drill and discharge of drilling chips are thus optimised.