Abstract:
A wear-resistant surface is formed on a component formed of an AlSi alloy by using a thermal spraying or a laser beam treatment. A thermally conductive device is brought into a thermally conductive contact with the component so that the thermally conductive device touches the component during the step of forming the wear-resistant surface. The thermally conductive device is actively cooled.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of copending International Application No. PCT/EP00/00575, filed Jan. 26, 2000, which designated the United States. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a process for producing wear-resistant surfaces on components made from an AlSi alloy. The invention also relates to a configuration for producing wear-resistant surfaces on components made from an AlSi alloy. 
     Hypoeutectic aluminum-silicon alloys, which are predominantly used for cylinder crankcases, are unsuitable for the tribological loads of the piston/piston ring/cylinder bearing surface system, because of an insufficient level of the wear-resistant silicon phase. Hypereutectic alloys, e.g. the alloy AlSi 7 Cu 4 Mg have a sufficient number of silicon crystallites. This hard, wear-resistant microstructure constituent is raised with respect to the matrix formed of an aluminum mixed crystal by chemical and/or mechanical processing stages and forms a required load-bearing surface component. However, drawbacks are the castability, which is low compared to the hypoeutectic and almost eutectic alloys, poor machinability and the high costs of this alloy. 
     One possible way of avoiding these drawbacks is to cast in sleeves or liners made from a wear-resistant material, such as for example gray cast iron and hypereutectic aluminum alloys. However, a problem in this case is the join between the sleeve and the surrounding casting, because the join is achieved merely by mechanical meshing or interlocking. When using a porous ceramic liner material, it is possible to infiltrate the liner material during the casting process and thus to obtain a material-to-material bond. This requires a slow filling of the casting mold and the use of high pressure, which considerably reduces the economic efficiency of the process. 
     Alternatively, hypoeutectic and almost eutectic alloys of electrodeposition coatings are applied directly onto the cylinder bearing surfaces. However, this is expensive and these coatings cannot sufficiently withstand tribochemical loads. A further alternative are thermally sprayed layers, which are likewise applied directly to the cylinder bearing surfaces. However, the adhesive strength of these layers is insufficient, since they are joined only by a micromechanical interlocking. 
     Therefore, it has already been proposed to carry out the surface modifications of remelting, alloying, dispersing and coating by using a laser, as is disclosed, for example, in Published, Non-Prosecuted German Patent Application No. DE 196 43 029 A1. In this case, it is necessary to sufficiently dissipate the energy which is introduced into the crankcase or the cylinder bearing surfaces by the laser beams. The dissipation of energy is necessary because an excessively high input of heat with high-energy laser beams may lead to undesirable changes to the microstructure in the crankcase. For this purpose, Published, Non-Prosecuted German Patent Application No. DE 196 43 029 A1 has already proposed that the component surface be cooled via cooling-water channels of the crankcase. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a process and a configuration for producing a wear-resistant surface on a component which overcome the above-mentioned disadvantages of the heretofore-known processes and configurations of this general type and which allow components to be coated even with high-energy coating devices, such as high-performance lasers, without causing heat-related changes to the material of the component. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a process for producing a wear-resistant surface on a component, the process includes the steps of: 
     providing a component formed of an AlSi alloy; 
     forming a wear-resistant surface on the component by using a thermal spraying or a laser beam treatment; and 
     bringing at least one thermally conductive device into a thermally conductive contact with the component such that the at least one thermally conductive device touches the component during the step of forming the wear-resistant surface; and 
     actively cooling the at least one thermally conductive device. 
     In other words, a process for producing wear-resistant surfaces on components made from an AlSi alloy is provided, wherein the wear-resistant surfaces are applied by thermal spraying or a laser beam, wherein, during the production of the wear-resistant surface, at least one thermally conductive device is brought into a thermally conductive contact with the component, and wherein this thermally conductive device is actively cooled. 
     The above-defined process has the advantage that a good dissipation of heat in combination with an increased cooling capacity is available during the coating operation, so that in particular a laser alloying and a laser coating can be carried out without the risk of a heat-related change in the structure of the material of the crankcase. This allows to carry out a coating at even higher energies, so that, for example, a greater depth of penetration of the coating material into the material of the component, a better join or connection between the coating and the material of the component and/or a greater layer thickness are achieved. 
     To further improve properties of the coating that is applied, after the formation of the wear-resistant surface in the form of a thermally sprayed layer, this layer is additionally treated with a laser beam. In particular, the layer is remelted with a laser beam. 
     As explained, the wear-resistant surface may be applied through the use of a thermal spraying, in particular a flame spraying, a plasma spraying or a HV (high velocity) spraying, or through the use of a laser beam. 
     According to a preferred mode of the invention, a remelting, alloying, dispersing and/or coating is carried out through the use of a laser beam or by thermal spraying. 
     The component, whose surface is to be treated, is for example a crankcase of a reciprocating internal combustion engine. The coating is to be carried out on cylinder bearing surfaces of cylinders of the crankcase. In this case, according to a preferred mode of the invention, during the production of the wear-resistant surface, a water space or water chamber of the crankcase has a cooling medium, in particular gas, nitrogen or a cooling liquid, flowing through it. 
     According to another mode of the invention, the thermally conductive device or heat-conducting device includes at least one cooling plate with passages for a cooling medium. The at least one cooling plate is put against the crankcase on at least one side on which open ends of the cylinders are situated. 
     According to yet another mode of the invention, the thermally conductive device includes at least one cooling mandrel which is formed such that it corresponds to the cross section of the cylinder and which is brought into contact with the cylinder bearing surface. The at least one cooling mandrel follows a coating zone on the cylinder bearing surface in an axial direction of the cylinder and/or trails the coating zone. 
     According to a further mode of the invention, the thermally conductive device includes a cooling-medium tank, into which the crankcase is dipped during the production of the wear-resistant surface, in such a manner that a cooling-medium level in the cylinder remains below a coating zone as seen in the direction of the force of gravity. In this case, an immersion depth, i.e. a depth to which the crankcase is dipped into the cooling-medium tank, is controlled in such a manner that a constant given distance is maintained between the coating zone and the cooling-medium level. 
     According to yet a further mode of the invention, the active cooling of the thermally conductive device is carried out by using a gas, nitrogen and/or a cooling liquid. 
     According to an advantageous mode of the invention, a honing operation is performed subsequent to the coating process according to the invention, in order to smooth the coated surface. 
     With the objects of the invention in view there is also provided, a configuration for producing a wear-resistant surface on a component, including: 
     a thermally conductive device configured to be disposed in a thermally conductive contact with a component formed of an AlSi alloy; and 
     the thermally conductive device being configured to operate with a cooling medium. 
     In other words, a configuration for producing wear-resistant surfaces on components made from an AlSi alloy, in particular on cylinder bearing surfaces of cylinders of a crankcase of a reciprocating internal combustion engine, includes a thermally conductive device which is disposed in a thermally conductive contact with the component and includes a cooling medium. 
     This has the advantage of a good dissipation of heat with an increased cooling capacity during the coating operation, so that in particular a laser alloying and a laser coating can be carried out without the risk that the heat causes a change in the structure of the material of the crankcase. Consequently, it is possible to carry out a coating using even higher energy levels, so that, for example, an increased depth of penetration of the coating material into the material of the component, a better join between the coating and the material of the component and/or a higher layer thickness are achieved. 
     The cooling medium expediently includes a gas, nitrogen and/or a cooling liquid, which have a high coefficient of heat capacity to ensure a correspondingly high dissipation of heat. 
     According to a preferred embodiment of the invention, the thermally conductive device includes at least one cooling plate with passages through which the cooling medium flows, wherein a cooling plate is disposed on the crankcase on at least one side of the crankcase where the cylinders have their open ends. 
     According to another feature of the invention, the thermally conductive device includes an annular cooling plate that is shaped such that it rests on a circumferential edge of a corresponding cylinder bore and such that it is aligned with the cylinder bore, i.e. it is in line with the cylinder bore. Thus a good dissipation of heat is achieved at the circumference of the cylinder bore. 
     According to another preferred embodiment of the invention, the thermally conductive device includes at least one cooling mandrel which is formed such that it corresponds to the cross section of a cylinder bore. The at least one cooling mandrel has passages through which the cooling medium flows. The at least one cooling mandrel is, in the axial direction of the cylinder, disposed on at least one side of a coating zone, i.e. the at least one cooling mandrel is disposed on one side or on both sides of a coating zone, in such a manner that a thermally conductive contact is formed between the at least one cooling mandrel and the cylinder bearing surface. 
     In order to achieve a high cooling capacity in the vicinity of the cylinder bearing surface, the passages through which the cooling medium flows are helical passages so that the cooling medium flows in a helically encircling manner. 
     In order to collect excess coating material, a cooling mandrel which is disposed beneath the coating zone, as seen in the direction of the force of gravity, is configured to have a collection basin for excess coating material. 
     In order to collect excess coating material and to introduce it into the collection basin, a collection lug or protrusion is formed on a side of the periphery of the cooling mandrel that faces the coating zone. 
     In order to increase the cooling action of the cooling mandrel, the cooling mandrel is formed, on its periphery which faces the cylinder bearing surface, with cooling bristles which are in brushing contact with the cylinder bearing surface. The cooling bristles are expediently made from a thermally conductive material, in particular copper. 
     According to another embodiment of the invention, the thermally conductive device includes at least one cooling-medium tank, into which the component can be dipped in such a manner that a cooling-medium level is at a given distance from a coating zone. 
     With the objects of the invention in view there is also provided, in combination with a component formed of an AlSi alloy, a configuration for treating the component, including: 
     a thermally conductive device including a cooling medium; and 
     the thermally conductive device being in a thermally conductive contact with the component. 
     According to another feature of the invention, the component is a crankcase having a cylinder with a cylinder bearing surface, and the thermally conductive device is in a thermally conductive contact with the cylinder bearing surface. 
     According to yet another feature of the invention, the cooling medium is a gas or a cooling liquid. 
     According to a further feature of the invention, the crankcase has a side formed with a cylinder opening, the thermally conductive device has a cooling plate disposed on the side formed with the cylinder opening, and the cooling plate is formed with channels for the cooling medium to flow therethrough. 
     According to yet a further feature of the invention, the cylinder is formed with a cylinder bore having a circumferential edge, the thermally conductive device has an annular cooling plate disposed along the circumferential edge and aligned with the cylinder bore, and the at least one annular cooling plate is formed with channels for the cooling medium to flow therethrough. 
     According to another feature of the invention, the cylinder has a cross section and has a coating zone on the cylinder bearing surface, the thermally conductive device includes a cooling mandrel formed to correspond to the cross section of the cylinder, the cooling mandrel is disposed in the cylinder on at least one side of the coating zone such that the thermally conductive contact is formed between the cooling mandrel and the cylinder bearing surface, and the cooling mandrel is formed with passages for the cooling medium to flow therethrough. 
     According to yet another feature of the invention, the passages are helical passages. 
     According to a further feature of the invention, the cooling mandrel is disposed, with respect to a direction of gravity, beneath the coating zone, and the cooling mandrel has a collection basin for receiving excess coating material. 
     According to an additional feature of the invention, the cooling mandrel has a peripheral region with a side facing the coating zone, and the cooling mandrel has a collection lug disposed on the side of the peripheral region facing the coating zone. 
     According to another feature of the invention, the cooling mandrel has a peripheral region facing the cylinder bearing surface, and the cooling mandrel has cooling bristles disposed at the peripheral region, and the cooling bristles are in brushing contact with the cylinder bearing surface. 
     According to another feature of the invention, the component has a coating zone, the thermally conductive device includes a cooling-medium tank filled with the cooling medium up to a cooling medium level, and the component is dipped into the cooling medium such that a given distance between the cooling-medium level and the coating zone is maintained. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a process and a configuration for producing wear-resistant surfaces, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, partial sectional view of a preferred embodiment of a configuration according to the invention, which implements three embodiments for an additional cooling of a component; and 
     FIG. 2 is a diagrammatic sectional view of a further preferred embodiment of a configuration according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is shown a preferred embodiment of a configuration according to the invention which includes a coating device  10 . The coating device  10  coats a cylinder bearing surface  14  of a cylinder wall  15  of a cylinder  16  of a crankcase  18  through the use of a plasma jet or plasma beam  12  which is, for example, a laser beam. The coating device  10  can rotate about a longitudinal axis  20 , as indicated by arrow  22 , and can be displaced along the longitudinal axis  20 , as indicated by arrow  24 . The crankcase  18  has a water chamber or water space  26  for a cooling medium. The rotary movement and translational movement of the coating device  10  relative to the cylinder wall  15  allows the cylinder bearing surface  14  to be treated in predetermined regions. In the following, a current working region of a coating device  10 , in which the plasma beam  12  or a laser beam is incident on the cylinder bearing surface  14 , is referred to as a working zone or a coating zone  28 . 
     According to the invention, the configuration includes a cooling plate  30 , which is produced in constructed form, i.e. the cooling plate  30  is produced through the use of a system of plates, or is produced mechanically, or is produced in cast form, and includes cooling passages  32  through which the cooling medium flows. In this way, the cooling plate is actively cooled and, over and beyond simple heat conduction, actively dissipates thermal energy. The cooling passages are, for example, rectangular and/or round in cross section and are formed in particular above a contact surface  34  between cooling plate  30  and cylinder wall  15 . A cooling plate  30  is disposed on either one or both sides of the open ends of the cylinder  16 . Furthermore, the cooling plates have an annular shape so that they correspond to the cylinder cross section and so that they rest on the peripheral cylinder wall  15 . By being annular-shaped or ring-shaped, the cooling plates provide an opening for inserting the coating device  10  into the cylinder. The lower cooling plate  30  in FIG. 1, which has an annular design, has the further advantage that process gases and excess coating material which has not melted or adhered to the cylinder bearing surface  14  can be discharged in the direction of the force of gravity, i.e. downward in FIG.  1 . 
     According to the invention, the configuration also includes a cooling mandrel  36  which is configured in a way so that it corresponds to the cross section of the cylinder  16 , so that that the cooling mandrel  36  can be introduced into the cylinder  16 , where it bears against the cylinder wall  15  in the circumferential direction. Alternatively or additionally to the configuration according to which the cooling mandrel  36  bears directly against the cylinder wall  15 , cooling bristles  38 , for example made from copper, are provided on the lateral surface of the cooling mandrel  36 . These cooling bristles are in contact with the surface of the cylinder wall  15  and, in this way, dissipate heat from the cylinder wall  15  to the cooling mandrel  36 . Furthermore, cooling passages  40 , through which a cooling medium flows and which are used for an active cooling and a dissipation of thermal energy as described above, are provided in the cooling mandrel. The cooling passages are formed so that they extend in a helically encircling manner. 
     Particles which do not adhere to the cylinder wall  15  are collected through the use of a collection basin  42  formed on the lower cooling mandrel  36 , as shown in FIG.  1 . The collection basin  42  is expediently also filled with a cooling medium. An additional collection lug  44  guides excess coating material which drops off into the collection basin  42 . A cooling-medium inlet  46  and a cooling-medium outlet  48  are provided for the cooling medium in the collection basin  42  and/or in the cooling passages  40 . According to the invention, one or both of the cooling mandrels  36  illustrated in FIG. 1 are moved along in the direction of arrow  24  at the rate of advance of the coating device, as indicated by arrow  50 . 
     In addition, in order to smooth the coated surface, it is possible to hone the coating wherein a plurality of steps may be used for the honing operation depending on the surface quality. 
     In a further alternative embodiment as shown in FIG. 2, a thermally conductive device is provided in the form of a cooling-medium tank  52 . The crankcase  18  is dipped into the cooling medium tank. In this case, the dipping tracks (arrow  58 ) the advance of the coating device  10 , in such a manner that a cooling-medium level  54  is always at a constant, given distance  56  of, for example, 20 mm from the coating zone  28 . In this embodiment, therefore, heat is dissipated by dip-cooling or immersion cooling of the crankcase  18 . 
     According to the invention, the three cooling options described above can be used as alternatives or in any desired combination with one another in a single configuration according to the invention. 
     Furthermore, in a preferred refinement of the invention, it is provided that, during the coating of the cylinder bearing surface  14  with the plasma beam  12  or a laser beam, a cooling fluid, such as for example gas, nitrogen or a cooling liquid, is passed through the water chamber  26 . This results in a further cooling of the cylinder wall  15  and therefore in an additional dissipation of heat from the coating zone.