Patent Application
20100101526
The invention relates to a method of preparing the surface of a substrate for applying a thermal spray coating, wherein recesses having undercuts are introduced in the surface to be coated by machining, serving the bonding of the spray coating. To this end, a substrate preferably is the piston running surface of an internal combustion engine, which is configured as a cylinder bore of a crankcase or as a cylinder liner. The invention further relates to a tool that is suitable for this purpose and to a component machined according to the method.
Thermal spray coating is increasingly being used in internal combustion engines. Aluminum alloys are currently used for crankcases or engine blocks in order to save weight, but the surfaces thereof are not suitable for the tribological stress caused by the pistons moving inside the cylinder bores. Nevertheless, in order to benefit from the advantages of lightweight designs, thermal coatings are applied onto the internal surfaces of the cylinder bores, which have the desired tribological properties with regard to friction and wear after finishing. In order to create a firm connection between the thermal spray coating and, for example, the surface of a cylinder bore, it is necessary to pre-treat the substrate by creating a roughened profile onto which the coating adequately adheres.
A method of the above-mentioned type is known from DE 10 2006 045 275 B3 (=WO 2008/034419 A1). With this method, the undercuts are created by means of a complicated movement of at least two cutting plates. The disadvantage not only is the complicated production kinematics, but also the short service life of the cutting plates because of their filigree configuration. Therefore, this method is not appropriate for serial production.
A method is known from DE 10 2006 004 769 A1 (=WO 2007/087989 A1), wherein in a first process step, which may be also be a machining operation, recesses or grooves are introduced in the surface of a substrate having a mushroom-shaped or push button-shaped structure. Subsequently, undercuts are created by means of machining or high-pressure water jets, bending or buckling the raised structures. This process is complex and provides only very imprecisely roughened profiles, which strongly depend on the material used and therefore does not ensure consistent results.
A method is known from DE 101 39 516 A1, in which bound cutting crystals are used as cutting materials for the pretreatment. Undercuts for a positive fit with the adhering coating are not created. Therefore, the adhesive pull strength is only limited. Furthermore, from DE 102 56 460 A1 (=US 2003/0152699 A 1) the creation of a roughened profile by means of fine boring is known. Methods and tools for laser beam machining are also known from the article by T. Abeln, G. Flores and U. Klink, Laserstrukturierung—Verbesserung der tribologischen Eigenschaften von Oberflächen (Laser structuring—Improving the tribological properties of surfaces), VDI-Z. 7/8, 2002, as well as from DE 20 2005 011 772 UI and EP 1 464 436 A1.
A roughened profile having undercuts for the application of heat insulation and heat dissipation layers onto components, which are used in fusion reactors where highly concentrated magnetic field plasma is generated, is known from U.S. Pat. No. 7,220,458 B2. The roughened profile is created by sawing, milling, etching or roughening by means of a laser or electric arc. Apart from heat dissipation, the applied coating serves the provision of soft paths for mechanical stress reduction.
According to the present invention, this object is attained in that a web having a raised plateau surface is created by machining, which is subsequently transformed into a widened region, starting at approximately the center of the plateau surface, said widened region forming roof-shaped projections to both sides, which form undercuts facing the substrate.
Thus, the object is attained, in short, by the combination of producing a preliminary machined profile, preferably using a machining or beam tool, and subsequent shaping, for example by roller burnishing or pressing, by means of which the roughened profile is created.
This method is advantageous in that—with the configuration of a corresponding tool—the production of the roughened profile may be associated with the kinematics of a fine boring spindle. The creation of a roughened profile thus may be integrated in the cycle time of a production line for manufacturing an engine block. To this end, relatively low roughness levels of clearly less than 100 μm may be created, so that the roughened profile only has to be filled in with a small amount of coating agent.
By means of the undercuts configured in this way, a reliable positive fit is obtained between the substrate and the sprayed coating during the subsequent thermal spray coating with melted metal particles. High adhesive pull strength is further achieved in that contraction strains and adhesion of the thermally applied coating are significantly increased by this procedure.
The advantage of the tool and method further is the considerably longer service life of the tools than has been possible with the currently used mechanical roughening processes. Adhesive pull strengths as high as ≧40 MPa are possible.
Exemplary embodiments of the invention and their advantageous refinements are explained in more detail below with reference to the attached drawings. The drawings show:
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
In order to improve the adhesion of the coating 2 to the substrate 3, the surface thereof is provided with a roughened profile. This roughened profile is characterized by a web 4, which extends in a thread-like manner around the periphery of the inner surface of the cylinder bore, a small part of which is shown in cross-section in
a shows sections of a web 4 having a square cross-section,
When the combined machining and shaping tool 20 rotates about the axis of rotation 21 thereof and the shape cutter 25 engages in the surface of the substrate 3 with simultaneous advancement in the direction 30, the web 4 having a trapezoidal cross-section and the flat plateau surface 4-1 is cut in a thread-like manner into the surface of the substrate. Following in the direction 32 of the advancement of the shape cutter 25, the plateau surface 4-1 is then rolled out toward the widened region 6 by the roller burnishing tool 26, starting at an engagement of a raised lug 28 of the roller burnishing tool (26), which starts at the center 5 of the web 4.
The center of the shape cutter 25 is arranged axially offset from the lug 28 by the amount ΔL along a lateral surface line of the rotating tool. In this case ΔL is equal to an integer multiple of the gradient s plus half the profile width b, which is to say (n*s+b/2). Vertical to the advancement direction, which is to say in the radial direction, the lug 28 of the roller burnishing tool 26 is offset by the amount ΔL from the shape cutter 25, which corresponds to the amount by which the widened region 6 is rolled out relative to the previously unwidened plateau surface. This results in the roughened profile illustrated in
The machining tool 25 and shaping tool 26 are configured as two separate units and, as already mentioned, arranged radially and axially offset from one another. While machining a work piece, they are fixed in relation to one another, but may also be adjusted radially as well as axially relative to one another. In this case, machining is a fine boring process, by means of which the webs 4 are created in a thread-like manner along the periphery of the substrate, the thread having a certain pitch.
A machining and shaping tool of the described type may be combined with a tool for position honing according to DE 103 48 419 (=U.S. Pat. No. 7,416,475). This is a method for rough honing the lateral area of a bore, wherein the position of the bore axis is corrected such that it is flush with and/or matches the axis of rotation of the honing tool and consequently of the honing spindle. To this end, the honing tool, which is fixed relative to the axis of rotation thereof, is inserted eccentrically into the bore so that it at first only cuts a part of the cylindrical inner surface of the bore (partial cut). With increasing machining and resultant radial expansion of the honing tool, the part of the periphery of the cylindrical inner surface of the bore being cut becomes enlarged until the bore is completely machined (full width). The position of the bore then matches the position of the axis of rotation of the honing tool. A honing tool of this type may be arranged on the same tool body in the advancement direction in front of the described machining and shaping tool. The above patent specification is hereby expressly incorporated as part of the subject matter of the disclosure of the present application. The process step of position honing, however, may also be carried out with a separate tool.
To this end, the function of position honing is to correct the position of the axis and direction of the bore axis. If a tool for position honing and a combined machining and honing tool are arranged consecutively on a tool body, position honing is carried out as a first step, followed by the machining and shaping steps according to the present invention. Both process steps may be carried out on one or more machining spindles.
It is essential for all exemplary embodiments that the shaping of the plateau surface 4-1 of the web 4 may be consecutively be carried out with shaping tools arranged at a variable radial distance from the axis 27 or on a subsequent spindle.
The radial adjustment of the roller burnishing tool 96, corresponding to ΔR in
A common adjusting system arranged centrically may be used for adjusting the shape cutter 95 and the roller burnishing tool 96. Both adjustments acting independently of one another are then designed as slit cones or are designed as a centric adjusting pin having a concentric adjusting sleeve.
It should be noted that the disclosure is not limited to the embodiment described and illustrated as examples. A large variety of modifications have been described and more are part of the knowledge of the person skilled in the art. These and further modifications as well as any replacement by technical equivalents may be added to the description and figures, without leaving the scope of the protection of the disclosure and of the present patent.
