Abstract:
The invention proposes a device which prepared a cylinder bore of a combustion engine in one working stroke such that the cylinder bore can subsequently be thermally coated.

Description:
BACKGROUND OF THE INVENTION 
     The processing steps of roughening, thermal coating and honing are used for manufacturing tribologically suitable surfaces in cylinder bores of combustion engines. The roughening has the purpose of creating an adequate topography on the substrate surface, which enables secure connection between the thermal sprayed coating and the substrate. The design of the profile form and the profile depth has an essential influence on the bonding tensile strength of the coating. The coating bonding per se is determined by the adhesion between the two materials, the lateral shrinkage strains resulting between the form elements of the roughening profile and the embedded coating, and the radial form fit resulting due to undercuts of the convex roughing profile elements. 
     The invention concerns a tool and a method for mechanically roughening a substrate surface so that a coating with very good adhesion can be applied to the substrate surface prepared according to the invention. In addition to other methods, such as sand blasting, laser blasting or high-pressure water blasting, methods of mechanical machining are known, wherein chipping and forming are combined with each other in terms of process technology. This latter group, in turn, includes processes which apply chipping and pressing involving a sliding process between the pressing tool and the material. A further combination of chipping and forming consists in chipping with subsequent rolling, wherein the surface profile that is initially generated by fine boring, rotating or milling is formed by rollers rolling over and forming the substrate surface, thereby improving the bonding characteristics. 
     As the invention is concerned with the last-mentioned combination of chipping and rolling (or tumbling), prior art is taken into consideration below. 
     EP 2 267 178 A2 describes a roughening method using a combination of chipping and rolling. The rolling operation is designed such that, with the combination tool, the distance between the roller and the form blade is dependent on the periodicity of the form profile (bridge, breadth and feed) cut in the first method step. Each roller covers one profile bridge. 
     The axial arrangement of the chipping tool and the roller is dependent on the form blade and its kinematic conditions, such as feed, bridge breadth, profile depth. This requires exact adjustment of the working surfaces of the blade and the roller with respect to each other. As the roller always machines only one bridge breadth, a short tool life of the roller must be expected. Furthermore, the roller is not readjustable relative to the blade in a radial direction so that, with varying wear rates, readjustment is no longer possible and the degree of forming is thereby reduced, with smaller undercuts being produced. 
     DE 10 2006 004 769 A1 is based on a roughening method, in which the substrate surface is chipped in a first method step and the previously chipped profile tips are “bent” in a subsequent step. This can be performed by means of rolling, pressing or blasting. For this reason, the substrate surface, i.e. the subsequent contact surface for the coating, is a profile form with undercuts. The roller is not slanted orthogonally with respect to the chipped profile, so that slippage occurs between the roller and the chipped profile. 
     DE 10 2008 024 313 A1 also discloses roller machining after cutting. However, the roller is designed with numerous knife discs, the cutting edges of which are arranged at a distance of the profile bars. This design has the substantial disadvantage that the tool must initially be exactly aligned to the profile tip position of the pre-machined profile form in the axial position, in order to then split the profile at these convex profile bridges by means of radial feed. Furthermore, it is necessary to exactly adjust the distance of the knife discs to the feed and the distance of the raised bridges. Also in this case, the rolling tool is profile-oriented with respect to the axial position and design, which results in complex handling for the process and also complex production as far as the distancing of the knife discs is concerned. 
     DE 20 2009 014 180 U1 also combines a chipping process with a rolling process for forming the profile bridges. In this method, the roller must be provided with a profiling based on the feed and the distance of the profile bridges. These tools are subject to high wear on the roller side, so that economical operation is not possible. The axial distancing of the contours of the roller from the form blade also requires substantial effort during installation of the tool. 
     All above-mentioned methods require tools that are difficult to manufacture and to adjust and are subject to relatively great wear, and some of which cannot be readjusted and therefore complicate or obstruct economical and reliable large-scale production. 
     It is the underlying purpose of the invention to provide a device and a method for mechanical roughening, which can be used independently of the subsequent coating method. The inventive device can thereby be used on a honing machine as well as on a machining center. In dependence on the material and the profile geometries, minimum quantity lubrication or heavy lubrication should both be possible. 
     SUMMARY OF THE INVENTION 
     In accordance with the object, the invention provides a combination tool performing the processing steps of
         fine boring (first tool)   form cutting (second tool), i.e. generating a profiled surface, and   rolling (third tool)
 
in one setting of the workpiece either simultaneously in one working stroke or subsequently in several working strokes in the same (set) position of the workpiece.
       

     This design ensures that all processes have the same kinematics and axial position, and therefore a constant profile depth is obtained along the circumference during profile cutting, since fine bore blades and profile blades are arranged on the same axis of rotation in the same tool. The tool can be used on a honing machine with a double-feed device or on a machining center with comparable feed possibilities. 
     The inventive combination tool is rigidly connected to the machine spindle and starts machining of the upper bore edge with the leading fine bore blades of the first tool. 
     The at least one fine bore blade attributes the position accuracy, concerning rectangularity and position, to the bore. The fine bore blades are tightly installed in the tool, soldered or bonded in and ground to the machining diameter, or they are screwed on or clamped in on a bending support or on a tight mounting fitting and can be adjusted by means of adjusting screws into the required axial position and to the desired working diameter. 
     The cutting plate (form blade) disposed, in the feed direction, downstream of the second tool enlarges the diameter of the bore by a minimal addition of approximately 50 μm so that the surface created by the first tool is completely removed in a coaxial manner. 
     The cutting plate of the second tool preferably consists of several partial blades which successively increase with respect to the cross-sectional surface and thus the effective chipping cross-section. For this reason, the chipping volume of the second tool is divided onto several partial blades resulting in an increased tool life. 
     The chipping cross-section of the partial blades can be changed with increasing depth (i.e. in a radial direction) as well as with increasing breadth (i.e. in an axial direction or feed direction). 
     By means of the form blade of the second tool, rectangular grooves/profiles can advantageously be manufactured, however V-point-, round-, rhombic- or trapezoidal profiles can also be made with the form blade. The form blade is a one-part cutting plate which, according to the respective profile form, is sintered and/or ground or eroded. 
     The profile contains form-cut micro structures such as rectangular, trapezoidal or triangular profiles, on the flanks of which, due to forming of the profile bridges, sub-microprofiles such as lateral undercut-like material overhangs with smallest cracks and shinglings additionally contribute to an increased bonding. The forming process should be designed without slippage so that no chipping, but only an imprint of the roller profile causes the material flow in the forming step. In order to achieve an economical tool life, the method shall be employable in serial production for the manufacture of thermally coated cylinder bores. 
     The form blade of the second tool is supported on a bending support and is e.g. electro-mechanically adjusted to size via a first feed system  1  of the device according to the invention. Thus, readjustment before, during or after machining is possible in order to compensate for the wear of the cutting blade, to work true to size and to increase the tool life. 
     The third tool is arranged opposite to the feed direction at a minimum axial separation and comprises a rotatably supported (forming) roller. The roller is axially and radially supported so that the roller is loaded exclusively by means of rolling friction. The axial support is designed for the stroke direction according to the machining function. 
     The roller (third tool) can preferably be fed in a radial direction. This feed may be position-controlled and/or force-controlled. With force-controlled feed, the roller rests against the form profile previously cut by the first tool and preferably forms it such that undercuts result. Due to the defined feed force, the required forming can be achieved in a reliable and process-secure manner. 
     In addition to an actively controlled feed force, which is generated by a feed device of the machine, a passive feed force in the form of a centrifugal force could also be used. 
     This feed is realized by a second feed rod of the device according to the invention, which is again actuated by a second feed system of the honing machine or the machining center. 
     In order to guarantee a mere rolling function of the roller without slippage or sliding between the workpiece and the roller, the roller is slanted according to the slope resulting from the feed of the device when machining a bore. Thus, the tool life of the roller is significantly increased and the process reliability of the surface structure is improved. 
     The lateral area of the roller is equipped with a bonded hard solid grit, such as e.g. a diamond grit, which is designed with respect to grit structure such that the grit tips are pressed into the raised profile bridges generated by the first tool, which cause lateral displacement of the material and thus form undercut-like profiles due to the material-overhang. 
     The grit is to be designed in dependence on the bridge breadth. It should e.g. amount to one third (⅓) of the breadth of the convex profile bridges. 
     The roller is sufficiently long as to always cover several profile bridges of defined bridge breadths, which are thus simultaneously formed. 
     An exact positioning of the roller in an axial direction relative to the second tool is therefore not necessary. 
     The diamonded length of the forming roller is to be designed as large as possible in order to locally achieve as long a contact time as possible during the axial overrun. 
     As the device according to the invention comprises three tools (fine bore blade, form blade and roller), these tools operate with the same feed. 
     For this reason, and since the axis of rotation of the roller is preferably slanted in accordance with the feed of the device, the axis of rotation of the roller is orthogonal to the longitudinal direction of the profile bridge generated by the first tool. 
     For this reason, a sliding motion overlaying the rolling movement of the roller on the profile bridge is avoided and only imprints of the diamond grit tips, but no grooves, are generated in the convex profile bridges. If, in addition to the imprints of the diamond crystals (forming) a chipping action is desired, this can be realized through a specified non-orthogonal axial position of the roller with respect to the longitudinal axis of the bridges to be formed. 
     Due to these grit imprints, a material flow takes place so that the convex profile bridges are formed and lateral burrs and material overhangs are produced. The feed system can feed the roller against the bore wall in a radial direction and with a predefined contact force for forming the profile bridges. 
     Another variant consists in the conical design of rollers, which build up an increasing pressure with progressing axial overrun of the machined location and thus cause increased forming of the bridges. 
     Both alternatives enable reduction of the height of the previously cut profile bridge by 10% to 50%. The profile depth that remains after forming is approximately 100 μm. 
     It must be mentioned that the diamond crystals are held in a galvanically applied nickel matrix or in a sintered bonding chamfer. The individual diamond crystals are mono-crystalline crystals in a defined variable arrangement density, which are arranged in a defined concentration on the surface of the roller. The crystals should preferably not be splintered, but solid and blocky, however with small wedge angles. 
     It remains to be mentioned that the fine bore blades, form blade and roller completely move past the lower bore edge after crossing the complete bore length in a downstroke. As interfering edges of the bearing seats for the crankshaft support are arranged there at small distances, the fine bore blades, form blade and roller are constructively arranged in the longitudinal direction at a geometrically minimum distance. 
     During movement from the lower reverse point to the upper end position of the tool above the bore, the form blade and the roller are radially reset, so that collision-free crossing of the finished roughened bore surface takes place. 
     As the second tool slightly enlarges the diameter of the machined bore in relation to the bore diameter achieved by the first tool, the first tool need not be radially reset during withdrawal of the device from the bore. 
     With fine boring, form cutting and rolling, the discharge openings for coolant are respectively directed at the location of machining, i.e. toward the blade tips. The device according to the invention can also be operated with dry-machining, if applicable, with cold-air rinsing or dry-ice rinsing or other cryogenic media, as machining with minimum quantity lubrication or with heavy lubrication. The crankcase of a combustion engine shall thereby be subjected to thermal coating substantially without washing and drying. 
     In a further variant of an inventive device, a handling blade is additionally attached in the direction of the upper clamping end of the tool, which, when reaching the lower reversal point, carries out only one rotation for machining the upper bore edge for processing a defined piston joining chamfer. 
     With the device according to the invention, it is possible to generate efficient roughening profiles for high bonding tensile strengths, independently of the subsequent coating-method. As boring up, form cutting and also rolling are carried out in spatial sequence in a downstroke of the tool, minimum machining times for bores of passenger car crankcases of below 30 s can be achieved. The axial arrangement of fine bore blade, form blade and roller is realized with minimum distances, so that cylinder bores in crankcases can also be machined with small overflows. 
     Due to the diamonding of the roller, exact adjustment in the axial direction of the forming tool depending on the previously cut form profile is dispensed with. Thus the process becomes robust and easy to handle. 
     Further advantages and advantageous embodiments of the invention can be extracted from the following drawing and the description thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a profile bridge before and after forming with a roller; 
         FIG. 1.1  shows a sized exemplary cross-section of a surface roughened with the device according to the invention; 
         FIG. 1.2  shows a further sized exemplary cross-section of a surface roughened with the device according to the invention; 
         FIG. 2  shows a longitudinal cut through a tool with fine bore blade according to the invention; 
         FIG. 3  shows a tool with form blade and roller; 
         FIG. 3.1  shows a form blade; 
         FIG. 3.2  shows the arrangement of the roller. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  initially exemplarily shows a profile bridge  1  before forming and a profile bridge  3  after forming with the roller according to the invention (not shown). The profile bridge  1  is manufactured by a correspondingly profiled cutting plate of the first tool. 
     In this example, the profile bridges have a rectangular or a square cross-section. 
     The profile bridge  3  is generated from the profile bridge  1  by rolling with the second tool. The convex surface of the profile bridge  3  is clearly recessed by the forming process relative to the original profile depth. In practice, a recess of up to 50% of the height of the profile bridge  1  has turned out to be advantageous. 
     As the roller of the second tool is preferably provided with diamond grits, the raised surface of the profile bridge  3  comprises crater-shaped indentations/imprints, which were formed by the diamond grit tips during rolling of the roller. 
     Due to the mentioned recess of the profile bridge and the diamond grit tips, the edges of profile bridge  3  are highly deformed, so that material overhang and micro-cracks and thus undercut-like positive-locking contours are generated. 
       FIG. 1.1  shows the diameter relations based on pre-boring for all process steps. An embodiment is also included. 
       FIG. 1  clearly shows that the stationary blade of the first tool, which is adjusted to a diameter D 0  for pre-boring, is not damaged upon withdrawal from the bore, since, in the illustrated example, the bore diameter is 0.2 mm larger than the diameter D 0  after rolling. 
     The division of the chipping volume required for generating the profile bridges  1  into three overall partial blades of the cutting plate of the first tool is clearly illustrated. 
       FIG. 1.2  shows a cross-section through a roughness profile produced by means of the inventive tool. 
     The geometry of the roughness profile is characterized by the following variables:
     Profile depth P E : 50-200 μm   Profile width Pw: 50-400 μm   Size of undercuts GHs: ≦0.5×Pw (25-200 μm)     0 Micro roughness Mrh: ≦0.5×Pt (25-100 μm)   Profile distance Pa: ≧2×GHs   

     The interaction between the above-mentioned parameters produces a high bonding tensile strength and a high shear strength between the substrate and the coating in the axial and tangential directions. 
     In particular, the undercuts produced by forming (rolling) using the inventive tool in connection with a large microroughness on the convex surfaces of the bridges produce the desired properties. 
     The above-mentioned process parameters can be adjusted by the inventive tool. 
     The micro roughening depth is substantially influenced by the size and the shape of the diamond grits on the roller of the tool. 
     The size of the undercuts GHs depends to a large extent on the feed force with which the diamond grits located on the roller are pressed into the substrate, thereby forming the bridges. 
     The roughening result also depends on the feed speed, the type of lubricant, the volume flow and the lubricant pressure. 
       FIG. 2  shows a longitudinal cut through an embodiment of the device  5  according to the invention, wherein the cutting plane is arranged such that the third tool, which serves for fine boring, is visible. 
     The first tool  7  is screwed to a base body  9 . The first tool  7  comprises a fine bore plate  11  being attached to a carrier  13 . The carrier  13  is jointedly or elastically connected to one base body  9 . 
     The fine bore plate  11  can be radially adjusted by a first adjusting screw  15  in order to exactly adjust the diameter D 0 . 
     The fine bore plate  11  can be adjusted in the axial direction by a second adjusting screw  17 . 
       FIG. 2  shows a channel  49  through which coolant can be fed. 
     Several fine bore cutting plates  11  are preferably distributed over the circumference in the base body  9 . The plates can be adjusted to the desired machining diameter before using the tool  5 . The tool life is considerably increased by using several fine bore cutting plates  11 . 
     All fine bore cutting plates  11  are arranged in carriers  13 , which are adjustable both in the radial and the axial direction. 
       FIG. 3  shows the device  5  according to the invention in a longitudinal cut, displaced through 90° relative to  FIG. 2 . 
     In this representation, the second tool  21  for manufacturing the profile bridge  1  (cf.  FIG. 1 ) and the third tool  23  for forming the profile bridge  1  are clearly illustrated. 
     A first feed rod  25  and a second feed rod  27  are guided in the base body  9  such that they can be axially displaced. 
     The feed rods  25 ,  27  enable an independent radial feed movement of the second tool  21  and of the third tool  23 . 
     When the feed rod  25  is moved in the axial direction of the base body  9  in the direction of the second tool  21 , a tubular cone  31  displaces a radially arranged feed pin  33  in a radial direction. The feed pin  33 , in turn, presses a bending support  35  with the form blade plate  37  in a radial outward direction, thereby performing a feed motion of the second tool  21 . 
     The position of the bending support  35 , in turn, is adjustable through axial adjustment. 
     The second feed rod  27  effects the feed of the third tool  23 , which forms, with a roller  39 , the profile bridge  1  previously generated by the second tool  21 . 
     For this purpose, the second feed rod  27  is also moved towards the third tool  23 , thereby actuating a radial feed of the roller  39  towards the bore wall to be machined. It is particularly advantageous for the roller  39  to be radially fed in a positive fashion such that the feed force can be controlled irrespectively of the centrifugal force that acts on the roller  39 . 
     It has turned out to be advantageous to mount, preferably to the base body  9 , a chip deflector (not shown in  FIG. 3 ) with its diamond-equipped roller  39  between the second tool  21  and the third tool  23 . This prevents the chips produced by the second tool  21  from moving between the roller  39  and the bridges  1 ,  3  of the substrate. The roller  39  could thereby be damaged and/or the bridge  1 ,  3  is greatly deformed in an uncontrolled and unpredictable fashion. Both cases are not desirable. 
     The roller  39  is axially and radially supported in a feed frame  41 . The slant of the roller  39  is thereby adjusted such that it is preferably orthogonal to the longitudinal direction of the profile bridge  1 . For this reason, the roller  39  rolls over the profile bridge  1  without sliding movement and effects the requested forming, thereby considerably increasing the tool life of the roller  39 . 
       FIG. 3.1  shows the form blade plate  37  with the stepped partial blades  43 ,  45  and  47 , which successively more deeply penetrate into the material. 
     The axial distance of the partial blades  41 ,  43  and  45  corresponds to the feed during machining of the bore. The partial blades  41 ,  43  and  45  can respectively ablate approximately 0.1 mm of material. 
       FIG. 3.2  shows the support of the roller  39  in the feed frame  41 . The axis of rotation  40  of the roller  39  can be adjusted by adjusting screws relative to the longitudinal axis of the bore or of the profile bridge  1  generated by the first tool  21 . 
     The feed frame  41  is secured against radial unhinging through centrifugal force by means of a leaf spring.