Process and apparatus for plating articles

A process and apparatus utilizing at least one conformable anode (40) in a plating process to apply a plating to an article (10). A wire or other material suitable for an anode is shaped to conform to the approximate shape of a region of the article to be coated. The anode is powered by an electrical power source (44), and the article serves as the cathode. The anode and article are both immersed in a plating bath (38). The article and anode are rotated relative to one another about a central axis (22) of the article. The relative movement between the anode and the article causes a uniform plating (46) to be applied to selected regions of the article that pass the anode. Another anode (50) can be arranged in fixed relation with the article to cause plating to a separate selected region of the article concurrently with the other anode.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to processes and apparatus for plating articles, such as, but not limited to, pistons for combustion engines.

2. Related Art

It is known to plate articles by immersing an article in a plating bath and establishing an anode/cathode arrangement whereby one or more surfaces of the article are plated with material from the bath solution. For example, some articles are plated with chrome using this general technique.

One of the challenges presented in plating articles having contoured surfaces and/or sharp corners is that the shape of the article can interfere with the uniform development of the coating, with some areas getting more coating than is otherwise desired and others getting less than what is otherwise desired.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and process for plating articles with a coating from a plating bath, such as, for example, application of a chrome-based coating to surfaces of a piston. The apparatus includes a shaped anode which is contoured to at least some of the outer contoured features of the article. The article itself is made the cathode, and the cathode and anode are moved relative to one another during plating to control application of the plating to the article.

According to a particular embodiment, the shaped anode is held stationary and the piston is rotated in the plating bath relative to the shaped anode. This relative movement, and particularly the relative rotational movement enables better control of the application of the coating to desired areas of the piston in need of the coating. In this regard, the invention is particularly well suited to articles having rotational symmetry such that the shape of the anode can be fixed and the article rotated relative to the anode to maintain a constant spacing between the article and contours of the anode during plating. In this regard, pistons are particularly well suited in that many of the features, including the outer surface of the piston, the ring grooves, the top surface, and often the combustion bowl, have symmetry relative to a central longitudinal axis of the piston body, or at least approximate symmetry.

In regard to coating a piston, not only is there is an advantage to coating the outer surface, but also coating the surface of the upper ring groove, the top face, as well as the combustion bowl. In some piston configurations, the combustion bowl has a reentrant bowl configuration such that the combustion bowl undercuts a circumferential upper lip of the bowl, thus, making it particularly difficult to plate these areas using a conventional plating bath arrangement. The present invention can accommodate such difficult contours, by extending, in the case of the upper ring groove, a portion of the anode into the ring groove and shaping the anode across the top surface and into the combustion bowl and to include, if necessary, the reentrant feature of the combustion bowl. As such, the desired amount of coating is applied, as desired, to the surfaces during the plating process as the piston rotates relative to the anode about the longitudinal axis of the piston in order to enable a uniform deposition of the plating material in the desired areas associated with the shaped anode.

According to a further particular feature of the invention, the apparatus and process may optionally include at least a second anode that is stationary relative to the article being plated and moveable relative to the first anode. In one preferred arrangement, this second anode is designed to rotate with the article relative to the first anode for simultaneously plating other areas of the article which may not be accessible or convenient for access by the first fixed anode. For example, the article may have internal features or passages that are not accessible from outside the article (for example, passages or bores or non-circular features). In the case of a piston, it may, for example, be desirable to plate the pin bores from the plating bath. A pin-shaped anode may be positioned in the pin bores and supported for rotation with the piston about the longitudinal axis of the piston and coupled to an associated rectifier to impart controlled plating to the surfaces of the pin bores. This may be done at the same time that the outer surface of the piston is being plated as it rotates relative to the rotationally fixed first anode. With this apparatus and method, it makes it possible to coat the piston skirt, top ring groove and combustion bowl of the piston via the first anode while also plating the pin bores via the second anode in the same plating bath and at the same time so as to achieve the desired consistency and uniformity of plating on all the desired surfaces in a single step process.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention provides a process and apparatus that utilizes conformable anodes in a plating process to apply a plating material to an article. A wire or other material suitable for an anode is shaped to conform to the approximate shape of a region of the article to be coated. The anode is powered by an electrical power source, such as a rectifier, and the article serves as the cathode, wherein the anode and article are both immersed in a plating bath. While immersed, there is relative movement imparted between the anode and the article. In one presently preferred embodiment, the article is rotated relative to the anode about a central axis of the article, wherein the anode can be fixed so as to not rotate about the central axis. As a result of the relative movement between the anode and the article, a uniform plating is applied to the regions of the article that pass by the anode, thereby achieving, if desired, a 360 degree plating of the article.

The method and apparatus may also include one or more additional anodes that may be positionally fixed relative to the article (and thus relatively moveable relative to the other shaped anode to plate other areas of the article that are inaccessible or less conventionally coated by the other shaped anode). For example, if the article has a bore that is arranged transverse to the rotation axis of the article, the apparatus and method contemplates inserting a correspondingly shaped anode into the bore that can rotate with the article such that the surfaces of the bore can be plated in the same bath and at the same time as the other surfaces being plated in connection with the shaped anode.

Turning now to the drawings, in which, by way of example and without limitation,FIGS. 1-3show a piston article10, referred to hereafter as piston, as the article to be plated. The piston10includes a piston head12having an upper surface14extending substantially perpendicular to the central axis22in which a combustion bowl16is formed. The combustion bowl16may have an edge or lip18and an undercut region20extending radially outwardly from the lip18. The piston10has a central longitudinal axis22which various outer surfaces of the piston extend at least partially symmetrically about, and also includes a pair of laterally spaced pin bosses24in which aligned pin bores26are formed having a common pin bore axis28. The pin bore axis28extends transversely to the central axis22, and may be perpendicular to the central axis22. The piston10may further include a pair of opposed piston skirt portions30that are formed as one piece with the pin bosses24having an outer surface32. The piston head12is formed with a plurality of ring grooves, including an upper ring groove34that is closest to the upper surface14of the piston article10.

FIGS. 2 and 3illustrate the piston10in conjunction with a plating apparatus36. The apparatus36preferably includes a plating bath38of a selective plating solution (such as, for example, one which will produce a chromium-based coating) in which the piston10may be immersed. The apparatus36includes a first shaped anode40that may be in the form of a wire or other suitable material that can serve as an anode. The anode40is arranged along the outside of the piston10and has an area less than the total area of the outer surface of the piston10. The anode40is formed to have a shape corresponding to the general shape of the outer surface of the piston in relation to the longitudinal cross section of the piston presented to the anode40for the surfaces that are to be plated. As such, even over areas having a geometrically discontinuous shape in axial cross section, such as a surface transforming from a linear surface to a nonlinear and/or curvilinear surface, the anode40is able to be conformed to follow the contour of the surface. This is particularly important in being able to apply a uniform coating across the various ring grooves, as well as the undercut region20.

For example, in connection with the example of the piston10shown inFIGS. 1-3, the shaped anode40is configured relative to the shape of the piston10in order to develop a plating on the outer surface32of the skirt portions30, the upper ring groove34and preferably the entire surface of the combustion bowl16. For this purpose, the shaped anode40extends at least partially in the longitudinal direction generally parallel to the central axis22and along the outer surface of the piston10adjacent the outer surface32of the skirt portions30, along the head of the piston12. The anode40is represented as having a portion42extending into the upper ring groove34generally perpendicular to the central axis22, and also has a portion that wraps around the upper surface14of the piston10and then down into the combustion bowl16. The portion of the anode40in the combustion bowl follows the contour of the undercut region20where it may terminate at the central longitudinal axis22. As such, the undercut region20is able to be plated with a uniform thickness of coating material, as desired. Desirably, the distance in which the anode40is spaced from the adjacent surfaces can be controlled with a high degree of precision. As such, it will be appreciated that if the piston article10were rotated relative to the anode40(or vice versa) that the relative movement would cause the entire outer surface of the regions of the piston10that are desired to be coated to be exposed to the shaped anode. In other words, with each revolution, the outer surfaces would pass by the fixed shaped anode40.

In the plating process, the shaped anode40is coupled to a corresponding electrical power source, such as rectifier44and the piston10is electrically coupled to make it a cathode in relation to the anode40. The piston10, immersed in the plating bath38along with the shaped anode40, is rotated relative to the shaped anode40to develop a controlled thickness of plating46on the targeted areas of the piston10as mentioned. Of course, other areas may be coated as well, but the shaped anode makes certain that these targeted areas are carefully controlled.

It may be further desirable to coat an inner diameter surface48of the pin bores26with the plating material from the bath38. This can be achieved at the same time that the outer surface is coated by positioning another anode, referred to hereafter as a pin bore anode50, within the pin bore26and supporting the pin bore anode50in relative fixed relation to the piston10, while enabling the pin bore anode50to rotate concurrently with the piston10about the longitudinal central axis22, and thus, relative to the shaped anode40during the plating process. The pin bore anode50is coupled to an associated rectifier52which results in deposition of the plating material to the pin bore surface48. Coupling the pin bore anode50to its own rectifier52separate from the other rectifier44enables independent control of the pin bore anode50and the corresponding plating of the pin bore surface48from that of the shaped anode40and the corresponding plating of the other surfaces, including the upper surface14, the combustion bowl16, the skirt portions30, one or more of the ring grooves, if desired.

Accordingly, one aspect of this invention provides the use of anodes which are conformable to varying geometric shapes of surfaces being plated in a plating process, such as a plating process used to coat a heavy duty (HD) steel piston. A wire, such as shown at40, or other preformed anode member conforming to the approximate shape of surfaces being plated on the piston (skirt area30to ring area above the skirt area to top bowl area14) is utilized to allow deposition of the coating to the areas of interest. This is powered by the plating electrical power source, such as the rectifier44. The entire piston assembly is rotated within the plating bath38such that it revolves past the conformable anode40resulting in deposition of the coating over the intended areas. Additionally, the second anode50is utilized, with the common cathode connection being the same steel piston10, whereby this second conformable anode50is placed within the pin bores26resulting in deposition of the coating on the ID) surface48of the pin bores26. This is powered by the rectifier52which, as mentioned, is separate from the rectifier44.

The use of conformable anodes40,50for plating surfaces of the piston10allows the deposition of the coating in those areas where the coating is desired at the desired thicknesses. Spinning the piston10allows for uniform deposition around the entire circumference of the piston10. The use of two separate rectifiers44,52and anodes40,50(with a common cathode designated here as the piston10) allows for deposition of the coating into areas separate from one another that could not be coated in a single rectifier/anode configuration and allows the desired thicknesses of the plating material to be applied where needed.

The piston10will be fitted into a holder or otherwise supported by a member that makes the common cathode connection to the piston10as well as to serve as the mechanism for rotating the piston10about its central axis22so that it can be rotated past the conformable anode40that results in deposition of the coating on the piston skirt30, ring groove area and the upper surface14, including the combustion bowl16. The pin bores26are plated by means of the cylindrical anode50placed within the pin bore area, which as described, is powered by the second rectifier52. This allows for application of the appropriate plating density and thickness for each of the two separate regions being plated. As such, in a single plating process, the piston areas plated by the separate anodes40,50can have differing plating densities and thicknesses.

Obviously, in light of the above teachings, many modifications and variations of the present invention are possible. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.