Patent Application
20090170411
This invention relates generally to a flexible micropolishing assembly for micropolishing a plurality of piston rings.
Microfinishing, superfinishing or micropolishing, as it is known in the art, is a surface finishing process wherein a grinding means is brought to bear against a workpiece which has been previously ground. Micropolishing is a low velocity abrading process which generally follows grinding. Because micropolishing incorporates lower cutting speeds than grinding, heat and pressure variants may be minimized to provide improved size, surface characteristics and geometry control. Those skilled in the art recognize that surface quality or roughness is measured in roughness average values (Ra) wherein Ra is the arithmetical average deviation of minute surface irregularities from hypothetical perfect surfaces. Micropolishing can provide surface quality of approximately 1 to 10 μin. (0.025 to 0.25 μm). Bearing surfaces of crankshafts, cam shafts, power transmission shafts and piston rings and other similar machine components that reciprocate or rotate on journal bearing surfaces generally require this surface finish for satisfactory operation.
Conventional mass production micropolishing machines have the ability to finish all the bearing surfaces on a workpiece in one operation. These machines contain a plurality of abrasive tape segments which are aligned with respect to the bearing or working surfaces. In operation, the workpieces are rotated as the micropolishing machine causes abrasive tape segments to contact and thus finish the bearing or working surfaces.
As is common in large scale production, failures may occur at one or more of the grinding areas or abrasive tape positions. As a result, workpieces may be produced with one or more work or bearing surfaces which are not finished to the required surface quality specifications. In such cases, the grinding machine operator must then remove and scrap the defective workpiece. Because micropolishing is the final stage in surface treatment operations, i.e. after grinding and finish grinding, the scrapping of micropolished parts results in a substantial loss of both material and labor to the machinist.
Micropolishing processes are used in automotive applications in the manufacture, repair and rebuilding of internal combustion (IC) engines. Such engines not only require finely finished bearing surfaces for engine efficiency, but also for increased durability and longevity. In the initial manufacturing stage, crankshaft and camshaft bearing surfaces are microfinished to particular roughness specifications by previously mentioned, conventional mass production micropolishing machines.
Piston rings have unique surfaces that also require a micropolishing process. The piston ring outer surface may have several surface contours, angles and shapes that are not conducive to the engine system. The initial grinding process sizes and shapes the piston ring, but does not correct the surface contour concerns and required surface characteristics. Without correction, the performance and wear characteristics of the piston rings and the mating surface is not consistent.
In the current practice, 50 to 100 piston rings are loaded laterally on a piston arbor. The arbor accepts the pistons rings and they can be adjusted along the length of the arbor. The arbor is designed to be mounted between a headstock and tailstock such as a lathe or grinder set up. The arbor includes a tab or notch to allow the arbor to rotate about its central axis. In the process of manufacturing the piston rings, the rings are ground on an outside diameter with the use of a conventional arbor and grinding machine. The grinding process sizes and shapes the outside diameter of the piston rings. In this process the piston rings do not obtain the desired geometry and surface characteristics on the outside diameter. As noted above, the piston rings may have several surface contours, angles and shapes that need proper surface preparation and may or may not mate or cooperate properly with the engine block cylinder or cylinder liners located in the engine block. The surface contours, angles and shapes will not change due to the micropolishing process, however, the wear and performance of the engine as it changes the surface contact characteristics of the piston ring will improve the relationship to the engine block cylinder or cylinder liners located in the engine block.
Due to the imperfections of the piston ring grinding process, piston rings often require an added surface finishing process after the grinding process. Current practice is place the arbor with the attached piston rings and compress them into a tube. The piston rings are them allowed to expand against the tube inner surface. A liquid slurry type abrasive material is added into the tube and the arbor is pushed and pulled in an repeated motion to allow the liquid slurry type abrasive material to polish the piston ring outside diameters against the inside diameter of the tube. This process allows for micropolishing of the shapes of the piston ring outside diameter and will only polish a flat surface. This process has many variants and is hard to control.
The flexible micropolishing machine of the present invention has been developed to meet the need for a machine that can effectively and quickly polish or micropolish a few or a large number of piston rings in a controlled process.
Accordingly, it is an object of the present invention to provide a flexible micropolishing machine for micropolishing a piston ring comprising an arbor for accepting at least one piston ring, a means for rotating the arbor, a flexible roller arm located adjacent the arbor and an indexable step or continuous abrasive material located between the flexible roller arm and the piston ring wherein the flexible roller arm is movable toward the arbor such that the flexible roller arm applies a micropolishing pressure to the indexable abrasive tape thereby micropolishing the piston ring outer diameter.
Another object of the present invention is to provide flexible micropolishing machine of such that the flexible roller arm includes a flexible roller manufactured from a soft resilient material such as urethane.
It is still another object of the present invention is to provide flexible micropolishing machine of such that the flexible roller arm includes a flexible roller manufactured from a soft resilient material capable of conforming to the shape of a piston ring.
Yet another object of the present invention is to provide a flexible micropolishing arm for micropolishing a piston ring comprising a flexible roller arm and an indexable step or continuous abrasive material system located between the flexible roller arm and the piston ring wherein the flexible roller arm is movable toward the piston ring such that flexible roller arm applies a micropolishing pressure to the indexable abrasive material system thereby micropolishing the one piston ring when the piston ring is rotated.
It is yet another object of the present invention to provide a flexible polishing machine including a flexible roller arm unit including a means for lateral or vertical oscillation to provide a desired surface finishing process.
The above objects and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention to be taken in connection with the accompanying drawings.
Referring now to
As shown in
The flexible micropolishing system 10 including arbor 22 is capable of accepting a plurality of piston rings 12 and the flexible micropolishing system 10 is capable of micropolishing the plurality of piston rings 12 in a single operation. In certain embodiments flexible roller arm 20 of the system 10 applies pressure to operate the flexible roller 14. The rotational speed of the roller 14 is determined by the type and speed of the abrasive tape index which can vary in regards to the tape index length or speed at which the tape 28 is traveling with the continuous tape index method. The flexible roller 14 is rotatable at varying speeds to obtain different micropolishing characteristics.
In addition the flexible micropolishing system 10 abrasive tape 28 is also indexable at the same speed as the flexible roller 14 to provide new abrasive material to the piston rings 12 being micropolished. As shown in
Referring now to
A slidable roller arm 38 is located adjacent arbor 24. The slidable roller arm 38, in a preferred embodiment, is located on a sliding base 50. In this embodiment, the flexible roller arm is slidable along axis 36 and also capable of oscillation in controlled lateral movements along the base guide 52. As shown, the indexable abrasive material 26 is located between slidable roller arm 38 and the plurality of piston rings 12 wherein the slidable roller arm 38 is movable toward the arbor 22 such that the slidable roller arm 38 applies a micropolishing pressure to the indexable abrasive tape 28 thereby micropolishing the plurality of piston rings 12.
More specifically in operation, the arbor 22 with the piston rings 12 is located between the head stock 32 and tail stock 34. The standard rotating machine system 40 is engaged and rotates the arbor 22 about the central axis 36. Flexible roller 14 and abrasive tape 28 are advanced against the piston ring surface 54 as shown in
The rotation of the arbor 22 and piston rings 12 is faster than that of the abrasive tape and therefore the abrasive film micropolishes the outside surface 54 of the piston rings 12. The abrasive tape 28 may be indexed in a step fashion or in a continuous fashion depending on the desires surface geometry or characteristics.
In this operation, the process may take from ten seconds to several minutes depending on the material removal needed to meet the surface specification. In some circumstances, additional movement is necessary. A lateral oscillating movement during micropolishing is sometime desired to acquire the appropriate surface characteristics. The flexible roller 14 and indexable abrasive tape 28 are laterally moved back and forth or oscillated in a line substantially parallel to the central axis 36. This oscillating movement is in a range from 0.010 to 0.080 inches and in the preferred embodiment is in a range from 0.030 to 0.060 inches. It is contemplated by the present invention that other ranges large ranges may be required for certain surface characteristics. This method is used when the piston rings 12 outside diameter 54 is flat and a cross hatch pattern is required on the outside surface.
While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.
