Abstract:
A machining tool, in particular a drill carrier tool, includes a monolithic base body extending in the axial direction which, at least in one section, has a porous or grid-like core structure that is encased in a solid outer jacket. These measures allow less material to be used, while maintaining good mechanical properties. The porous or grid-like core structure is simultaneously used for transporting coolant. The base body is manufactured in particular by means of a 3D printing method.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a machining tool, in particular a rotating tool such as a drill or milling tool, having a monolithic base body extending in an axial direction. The invention additionally relates to a method for manufacturing a machining tool of this type. 
       BACKGROUND OF THE INVENTION 
       [0002]    Machining tools, in particular drills, usually have a clamping shaft extending in the axial direction to which a slotted cutting part connects which extends up to a front tool tip, in particular to a drill bit. In the case of such machining tools, which are also referred to as shaft tools, coolant channels are often formed in the interior of the base body, as can be seen in EP 0 843 609 B1, for example. 
         [0003]    In what are referred to as solid carbide drills, a monolithic base body is formed as a sintered body. The manufacturing process involves first making a base body by compression from a metal powder as sinter material, for example, which is then sintered. U.S. Pat. No. 7,226,254 B2 discloses a sintered base body in which, to save sinter material, a central recess is made in the base body in the area of the clamping shaft prior to sintering said base body. The sinter material thus saved is used for manufacturing additional tools. 
       SUMMARY OF THE INVENTION 
       [0004]    Based on this, the invention forms a basis for providing a machining tool as well as a method for the manufacturing thereof, in which an efficient use of material and good mechanical properties are both ensured. 
         [0005]    The problem is solved according to the invention by a machining tool having the features of claim  1 . The machining tool is a rotating tool in particular, such as a drill or milling tool, for example. It comprises a monolithic base body extending in the axial direction in which a non-solid core structure is formed, at least in a section extending in the axial direction, which is encased by a solid outer jacket. The outer jacket annularly encases the non-solid core structure preferably at a constant wall thickness. A large part of the base body is deliberately designed to be not solid due to the core structure which is non-solid compared to the solid outer jacket, thereby saving not only weight, but also material. At the same time, sufficiently high mechanical stability is achieved by the special core structure with the solid outer jacket structure. In this way, the core structure provides a type of mechanical support structure. 
         [0006]    In this respect, it is especially important that the base body is a monolithic body. This term is understood to mean that the base body, i.e., in particular also the combination of the core structure with the outer jacket, is constructed from a single body, i.e., is made from one piece and is not assembled from two or more parts, e.g., by welding, soldering, bonding or similar. 
         [0007]    The term non-solid core structure is generally understood to mean that open areas are formed in the core structure in which no material is present. 
         [0008]    The core structure is preferably optionally porous, grid-like or even bionic. The term porous is generally understood to mean a structure in which individual pores are preferably scattered, i.e. unstructured and omnidirectional in the material of the core structure. Both open-pore as well as closed-pore structures are possible. In the case of an open-pore structure, on the whole, the core structure is permeable to a gas or liquid, such as a coolant, for example. 
         [0009]    The term grid-like is understood to mean a structure in which areas that are free of material are separated from one another by partitions, in particular channels, usually in an ordered material structure, for example a periodic material structure. These individual channels preferably extend in the axial direction. 
         [0010]    A bionic structure, in contrast, is understood to be an unordered, in particular non-periodic arrangement of partitions of this type, based, in particular, on patterns from nature. 
         [0011]    According to the invention, the machining tool is manufactured with the aid of a method having the features of claim  12 , which provides that the base body is manufactured with the aid of a 3D printing method. In the meantime, 3D printing methods have been used for a wide variety of applications. These methods basically involve processing a powdery starting material layer-by-layer with a laser, such that the individual powder particles bond to one another, for example, melt with or sinter with one another layer-by-layer into a solid, rigid body. The layer-by-layer, stratified construction makes it possible to easily form undercuts and complex geometrical structures, which, with previous conventional manufacturing methods, was not possible or required considerable effort and expense. In this case, a metal powder having an average grain size ranging between 10 and 50 μm is used as a starting material in powder form. In particular, the material for the metal powder is a tool steel. 
         [0012]    Accordingly, this specific method, which makes it possible to create very fine structures, is provided for forming the specific non-solid core structure in the present invention. 
         [0013]    The machining tool is optionally an monolithic tool taken as a whole having a tool tip integrated into the base body or, alternatively, it is what is known as a carrier tool consisting of a support made up of the base body and a preferably reversibly replaceable cutting element applied thereon. 
         [0014]    The machining tool generally has at its front end a tool tip which is itself designed as a cutting element or one or more cutting elements are arranged in the area thereof. In the present invention, a tool tip is thus generally understood to mean the frontal end area of the machining tool, i.e. a forward face area of the machining tool. If the tool is designed as a modular carrier tool, a replaceable cutting element (cutting insert) is attached to the base body. According to a preferred variant, the tool tip itself is designed as a replaceable cutting insert. This can be reversibly and replaceably attached to the base body by clamping, for example, with the aid of fastening elements such as screws, or alternatively by simple turning. In this way, it is held clamped in particular between two retaining or clamping strips of the base body. Alternatively, the carrier tool is designed with plate seats for attaching (indexable) cutting inserts. In this case, the area of the plate seats is understood to mean the tool tip. In a non-modular, one-piece tool having, for example, major cutting edges cut into the end face area, a front end face area having an axial length in the range of a nominal diameter, for example, constitutes the tool tip. 
         [0015]    Drills and milling tools in general are classified as rotating tools. It is thus understood that, during operation, the machining tool rotates around a center axis which at the same time defines the rotational axis. 
         [0016]    A further advantage of the core structure centrally formed in the base body is that it is of lower density than the solid annular outer jacket. This results in a density distribution with greater density in the outer area, which results in a more stable rotation, particularly in rotating tools. The core structure is preferably designed to be rotationally symmetrical and preferably circular, at least rotationally symmetrical with at least a two-fold to six-fold rotational geometry. 
         [0017]    To give it an especially high mechanical rigidity, the core structure is expediently designed as a honeycomb structure. This constitutes a special type of grid-like core structure in which the individual channels have a hexagonal cross-section. 
         [0018]    In the case of a grid-like core structure, for example a honeycomb structure, a plurality of longitudinally extending channels are formed. In the present invention, the term plurality is understood to mean in particular that at least five, preferably at least eight or even significantly more channels are incorporated. The individual channels expediently have a maximum channel width below 0.5 mm and in particular below 0.10 mm. 
         [0019]    If the core structure is porous, it expediently has a porosity ranging between 5 and 90%. This means that, compared to a solid body, between 5 and 90% of the volume consists of pores. The pores preferably have an average pore size ranging between 15 and 45 μm. 
         [0020]    The core structure expediently has, at least in a shaft part, a circular cross-section and is designed to be concentric in particular to the annular outer jacket. The core structure as well as the outer jacket are thus coaxial to the center axis and in particular to the rotational axis. 
         [0021]    Overall, the core structure covers an area of preferably around 5 to 80% of a total cross-sectional area of the base body. If the core structure is circular, it has a core radius that is preferably between 50 and 90% of an outer radius of the base body. Formed thereon is a comparatively narrower circumferential solid rim forming the outer jacket, preferably of constant wall thickness, which, however, is sufficiently dimensioned for the required mechanical loads, for example the clamping forces present when clamping the base body. The core structure portion expediently varies in the axial direction. In particular, the portion of the core structure differs between a front fluted cutting part and a rear shaft part. In the front cutting part, the portion of the core structure is in the lower range, for example between 5 and 30%, while in the shaft part it is in the upper range, for example between 40 and 80%, relative to the total cross-sectional area (recesses, such as chip flutes for example, do not count toward total cross-sectional surface). 
         [0022]    In a useful embodiment, the core structure comprises a cross-sectional area that changes in the axial direction. In principle, the special manufacturing method of 3D printing allows any desired structure to be created. In the present invention, this method is utilized to the extent that a core structure geometry specifically adapted to the base body geometry is created in different axial sections of the base body. Varying the cross-sectional geometry additionally allows mechanical properties to be suitably adjusted at defined axial positions. In particular, allowance is made for highly loaded sections, for example, by enlarging the wall thickness of the solid outer jacket in these sections. 
         [0023]    In an especially expedient refinement, solid struts are introduced into the core structure in the direction of the center axis to thereby achieve additional improvement in rigidity. Struts of this type are expediently bent in the shape of a sickle, for example, to transmit increased mechanical loads arising at the cutting edges into the interior of the base body, for example. The number of struts introduced is expediently equal to the number of cutting edges distributed circumferentially. If two circumferential cutting edges are present, the two struts preferably merge into one another in the center axis and are, for example, wound on the whole into the shape of an S. The struts form, for example, a structure in the shape of spokes and spoked wheel. The struts basically have a wall thickness significantly greater than the normal wall thickness of the grid-like core structure. For example, they are many times greater than the normal wall thickness. The wall thickness of the struts also preferably varies depending on their radial position, and specifically preferably varies continuously. 
         [0024]    The base body usually comprises a shaft part as a clamping shaft with which it is clamped into a clamping device of a machine tool. The center axis of the machining tool is oriented so that it is precisely coaxial with the rotational axis of the machine tool. Connecting to the front of the shaft part in the axial direction is a front cutting part, which is usually provided with chip flutes. These are designed to either run in a straight line or to run helically. In an expedient design, the core structure further extends into the cutting part starting from the shaft part, so that a continuous core structure is formed. In this case, the core structure preferably has a circular cross-sectional geometry in the shaft part, which transitions into an altered geometry in the cutting part. 
         [0025]    The core structure is expediently designed to be elongated in the area of the fluted cutting part and crossing into a center area of the base body. It additionally comprises widened areas on both sides of the center area, giving its cross-section an overall bone-like appearance. Its opposite end areas are spherical or rounded, so that, in particular, the radially outer course of the core structure runs concentrically to the outer jacket. 
         [0026]    In an especially expedient embodiment, the core structure is designed to be suitable for conducting coolant and extends from a rearward end to a front end face of the base body. For this purpose, in particular, a conventional, standardized coolant connection is expediently formed at the rearward end of the base body. This typically comprises a transverse groove into which a coolant is fed from the machine tool. 
         [0027]    At the front end face, coolant optionally exits the base body or is transferred to an interface with a tool tip into which the coolant can then be further fed. 
         [0028]    Taken as a whole, the machining tool is designed in an expedient embodiment as a carrier tool having at least one cutting element that can be secured to the base body, in particular a tool tip or cutting plates. The base body is preferably manufactured from a tool steel. The cutting element, in contrast, is made of a harder material such as a solid carbide or also a ceramic, for example. It is secured to the base body in particular as a reversibly detachable insert. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    Exemplary embodiments of the invention are explained below in greater detail based on the figures, some of which are simplified illustrations. 
           [0030]      FIG. 1  shows a side view of a machining tool designed as a modular carrier tool; 
           [0031]      FIG. 2  shows a sectional view through the machining tool as shown in  FIG. 1  along intersecting line A-A; 
           [0032]      FIG. 3  shows a sectional view through the machining tool as shown in  FIG. 1  along intersecting line C-C; 
           [0033]      FIG. 4  shows a sectional view through the machining tool along intersecting line B-B; 
           [0034]      FIG. 5  shows a sectional view of a grid-like core structure; 
           [0035]      FIG. 6  shows a sectional view of a bionic core structure in the area of the intersecting line A-A as shown in  FIG. 1 ; and 
           [0036]      FIG. 7  shows a sectional view of a bionic core structure in the area of the intersecting line B-B as shown in  FIG. 1 . 
       
    
    
       [0037]    Parts having the same effect are given the same reference numbers in the figures. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    The machining tool  2  illustrated in  FIG. 1  is designed as a modular drill tool. It has a tool tip  4  in the form of a cutting element made of solid carbide or ceramic, which is reversibly and removably attached to the frontal end of a base body  6 . In the present invention, a tool tip is generally understood to mean the frontal end area of the machining tool  2 , i.e. a front end face area of the machining tool. In the exemplary embodiment according to  FIG. 1 , this is formed by the replaceable tool tip  4 . In the case of a carrier tool having plate seats for attaching (indexable) inserts as a cutting element, the area of the plate seat is understood to mean the tool tip. In a non-modular, one-piece tool, a front end area having an axial length, for example, in the range of a nominal diameter of the machining tool  2  is referred to as the tool tip. In the exemplary embodiment according to  FIG. 1 , the tool tip  4  is clamped as a reversibly replaceable insert between two clamping or retaining webs  7  of the base body  6 . 
         [0039]    The machining tool  2 , and thus also the base body  6 , as well as the tool tip  4  each extend in an axial direction  10  along a center axis  8  from a rearward end to a front end. At the same time, this center axis  8  defines a rotational axis around which the machining tool rotates in a rotational direction D during operation. 
         [0040]    The base body  6  is in turn divided into a rear shaft part  12 , with which the machining tool  2  is held clamped in a tensioning piece of a machine tool during operation. A cutting part  16  provided with chip flutes  14  is connected to the shaft part  12  in the axial direction  10 . In the exemplary embodiment, the chip flutes  14  extend in a helical pattern. The end-face tool tip  4  has major cutting edges  18 , each of which typically transitions into a minor cutting edge  20  on the circumferential side. These are continued in the cutting part  16 . 
         [0041]    A support bevel  24  adjoins the minor cutting edge  20  opposite to the direction of rotation. 
         [0042]    As is described below based on  FIGS. 2 through 5 , the base body  6  is a monolithic base body  6 , which is formed not from a solid material, but rather—at least in axial sections has a non-solid core structure  26 . As  FIG. 2  in particular illustrates, this core structure is designed as a circular structure in the shaft part  12 , as seen in the cross-sectional view. To do this, the core structure  26  in this shaft part  12  is preferably designed to have a constant radius R 1 . A support bevel  24  adjoins the minor cutting edge  20  opposite the direction of rotation. This cylindrical core structure  26  is surrounded by an outer jacket  28 , which, except for a flattening  30  introduced externally, is designed as an annular ring. This outer mantel  28  has a radius R 2 . The radius R 1  of the core structure  26  is preferably approximately 50 to 90% of the outer radius R 2 . The core structure  26  has a core cross-sectional area A 1 , and the machining tool  2  has a total cross-sectional area A 2 . This area is defined by the area enclosed by the outer jacket  28 , including the surface of the outer jacket  28 . 
         [0043]    At the rearward end of the shaft part  12 , the same is optionally closed off with an end face plate formed of a solid material, i.e. the non-solid core structure  26  is formed only in the interior of the shaft part  12  without being visible from the rearward end face. A coolant transfer point is expediently formed and incorporated into this solid end face plate. In particular, a transverse groove having through-holes running to the core structure  26  is introduced. 
         [0044]    In the exemplary embodiment, the core structure  26  is limited, in a similar manner, also in the axial direction  10  in the end area of the shaft part  12  by a solid partition  32  through which at least one, or in the exemplary example, two, cut-outs  34 , penetrate. Alternatively, the core structure  26  also spans uninterrupted from the shaft part  12  into the cutting part  6  and without partition  32 . A partition  32  is provided particularly in machining tools  2  without internal coolant supply. However, coolant supply is made possible in principle via the cut-outs  34  in the cutting part  16 . 
         [0045]    In the front area of the machining tool  2 , i.e. in the area of the tool tip  4 , at least one outlet point  35  for coolant or lubricant is provided. Multiple outlet points  35 , which are oriented for example toward cutting areas, are preferably formed in a front end face or are also formed circumferentially. The outlet point  35  can be designed as a borehole in a conventional manner. However, it is likewise preferably created by means of the 3D printing method and is geometrically complex. The core structure  26  is preferably directed to the outside to form the outlet point  35 . In the exemplary embodiment illustrated in  FIG. 1 , an outlet point  35  is formed for example in a circumferential wall  36  in the area of the tool tip and is formed in particular as a porous structure. The outlet point  35  in the exemplary embodiment is thus generally integrated into the retaining webs  7 . 
         [0046]    The core structure  26  continues into the cutting part  16  itself ( FIG. 4 ). Due to the chip flutes  14  and to the circumferential geometry of the base body  6  modified thereby, the cross-sectional geometry of the core structure  26  is adapted in particular such that it is enveloped entirely by roughly the same wall thickness as that of the outer jacket  28 . In particular, the core structure  26  is designed to be elongated in the cutting part  16  and has a center area  37 , which transitions into widened areas  38  at both ends. The outer edge of each said widened area has an accurate contour, so that they run concentrically to the circumferential line of the base body  6 . 
         [0047]    The core structure  26  is preferably homogeneous even over its entire cross sectional area A 1 . Alternatively, additional supports can be provided in a manner not further illustrated here. Separate coolant channels are expediently not formed in the embodiment variants of  FIG. 1 . 
         [0048]    According to a first embodiment variant, the core structure  26  is designed as a porous structure. According to a second embodiment variant illustrated in  FIG. 5 , in contrast, the core structure  26  is designed as a grid-like structure, in particular as a honeycomb-shaped structure. This structure has a plurality of individual channels  40  extending in the axial direction  10 . Rectangular channels are schematically illustrated in  FIG. 5 . The individual channels  40  are each separated from one another by partitions  42 . These partitions  42  preferably have only a slight material thickness of, for example, below 0.3 mm and, particularly, below 0.15 mm. The individual channels  40  usually have a channel width W of below 0.5 mm. 
         [0049]    Further alternatives for the core structure  26  are illustrated in  FIG. 6  and  FIG. 7 . In these embodiment variants, the core structure  26  is designed to be what is referred to as a bionic structure, in which—in contrast to the grid-like structure illustrated in FIG.  5 —the individual partitions  42  are unordered and do not follow a pattern, at least not a recurring pattern. 
         [0050]    It is possible in principle for the different structures to be combined with one another and, for example, to be formed next to one another within a sectional plane. Alternatively, the structure varies in the axial direction  10 . The specific manufacturing method allows nearly all desired combinations and variations. In particular, different structures, particularly of different porosity, are present in the cutting part  16  and the shaft part  12 . Thus, for example, the cutting part  16  is of greater porosity than the shaft part  12 , or vice versa. 
         [0051]    The base body  6  is manufactured using what is referred to as a 3D printing method. In this method, a metal powder is worked successively and thus layer-by-layer by means of laser treatment according to the desired cross-sectional geometry of each layer and melted or sintered to form a cohesive, monolithic sub-body. In this process, each cross-sectional contour of each layer is predefined by the laser. With this 3D printing method, nearly any arbitrary and complex and, in particular, variable cross-sectional geometries can be created. In particular, the core structure  26  described by  FIGS. 2 through 5  and having the solid enveloping outer mantel  28  is formed using this method. The entire base body  6  is thus formed as a one-piece, monolithic body by utilizing this manufacturing method. This body can also undergo finishing work, if necessary, following the 3D printing process. 
         [0052]    The base body  6  is preferably made of tool steel according to DIN EN 10027, for example with a material number 1.2709 and/or 1.2344.