High throughput finishing of metal components

Abstract

A method for finishing a surface of a metal component is carried out in a receptacle containing a quantity of non-abrasive media. The component is at least partially immersed in the media and a quantity of active finishing chemistry is supplied. The chemistry forms a relatively soft conversion coating on the surface. By inducing high energy relative movement between the surface and the media the coating can be continuously removed. The method may be carried out in a drag finishing machine.

Claims

1. A method for finishing a surface of a steel component, comprising: providing a receptacle containing a quantity of non-abrasive media; immersing the surface of the component into the media; flooding the receptacle with a quantity of finishing chemistry capable of forming a soft conversion coating on the surface, to a defined level in the receptacle, such that the surface is immersed in the chemistry; forcing the component through the media at a relative movement between the component and the media greater than0.3 m/s using a fixture connected to the component, thereby continuously removing the conversion coating; and continuing to force the component through the media to achieve a surface roughness Ra of the surface of less than 0.5 micron in less than 10 minutes; wherein the method is carried out at a temperature greater than 40 C.

2. The method of claim 1, wherein at least half of the surface is immersed into the finishing chemistry.

3. The method of claim 1, wherein the method is carried out at a temperature greater than 50 C.

4. The method of claim 1, wherein the defined level of the finishing chemistry is determined by overflow outlets from the receptacle.

5. The method of claim 1, wherein the defined level of the finishing chemistry is adjustable.

6. The method of claim 1, wherein the component is a ring or pinion gear for a rear axle or transaxle of a car or truck.

7. The method of claim 1, wherein the component comprises at least two matched parts and the matched parts are finished together.

8. The method of claim 1, wherein the chemistry is acid based.

9. The method of claim 1, further comprising removing the component from the receptacle and immersing it in a further receptacle comprising a burnishing or coating solution.

10. The method of claim 1, wherein the method is carried out at a temperature greater than 70 C.

11. The method of claim 1, wherein the method is continued until a surface roughness Ra of the surface is less than 0.35 micron.

12. The method of claim 1, further comprising continuously supplying finishing chemistry to the receptacle at a rate of at least 0.5 liters per hour per liter of media.

13. The method of claim 1, wherein the relative movement between the component and the media is at least 0.8 m/s.

14. The method of claim 1, wherein the relative movement between the component and the media is at least 1.5 m/s.

15. The method of claim 1, wherein the method is continued until a surface roughness Ra of the surface is less than 0.20 micron.

16. The method of claim 1, wherein the method achieves a surface roughness Ra of the surface of less than 0.35 micron in less than 10 minutes.

17. The method of claim 1, wherein the method achieves a surface roughness Ra of the surface of less than 0.20 micron in less than 10 minutes.

18. A method for finishing a surface of a steel component, comprising: providing a receptacle containing a quantity of non-abrasive media; immersing the surface of the component into the media; continuously supplying a quantity of finishing chemistry to the receptacle to a defined level in the receptacle; forcing the component through the media at a relative movement between the component and the media greater than 0.3 m/s using a fixture connected to the component, thereby continuously removing the conversion coating; and continuing to force the component through the media for less than 10 minutes to achieve a surface roughness Ra of the surface of less than 0.5 micron; wherein the method is carried out at a temperature greater than 40 C.

19. The method of claim 17, wherein the relative movement between the component and the media is greater than 0.8 m/s.

20. The method of claim 17, wherein the relative movement between the component and the media is greater than 1.5 m/s.

21. The method of claim 17, wherein the finishing chemistry is supplied to the receptacle at a rate of at least 0.5 liters per hour per liter of media.

22. A method for finishing a surface of a steel component, comprising: providing a receptacle containing a quantity of non-abrasive media; immersing the surface of the component into the media; flooding the receptacle with an excess of finishing chemistry capable of forming a soft conversion coating on the surface such that the surface is immersed in the chemistry; forcing the component through the media at a relative movement between the component and the media greater than 0.3 m/s using a fixture connected to the component, thereby continuously removing the conversion coating; and continuing to force the component through the media to achieve a surface roughness Ra of the surface of less than 0.5 micron in less than 10 minutes while maintaining dimensional tolerance of the component; wherein the method is carried out at a temperature greater than 40 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features and advantages of the invention will be appreciated upon reference to the following drawings, in which:

(2) FIG. 1 is a schematic view of a drag finishing machine according to the invention;

(3) FIG. 2 is a plan view of a drag finishing machine according to a further aspect of the invention; and

(4) FIG. 3 is a surface roughness trace of the ring gear of Example 3.

(5) FIG. 4 is a table showing the results of Examples 1 to 13 (operation of the machine 10).

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(6) The following is a description of certain embodiments of the invention as used in the finishing of ring and pinion gears, given by way of example only and with reference to the drawings.

(7) Referring to FIG. 1, a drag finishing machine 10 is schematically shown. The machine 10 is a Mini Drag Finisher available from Rsler Metal Finishing, USA LLC. Nevertheless, the skilled person will understand that many other machines having similar capabilities could be adapted for operation according to the invention.

(8) The machine 10 comprises a receptacle in the form of an annular bowl 12. A spindle 14 carries a component 16 to be treated. The spindle 14 is driven to rotate around an axis X. In this example, the axis X is angled with respect to the vertical at around 15. The spindle 14 is mounted on a turret 22 which rotates around an axis Y. Axes X and Y are offset from one another by a distance of about 50 cm whereby the spindle 14 traces a circle of around 1.0 m diameter.

(9) The bowl 12 is filled with non-abrasive media 18 up to a defined level L. The media used during testing was a non-abrasive ceramic media having a density of about 2.75 grams per cubic centimeter (g/cc) and an average diamond pyramid hardness (DPH) value of about 845. The media had an overall bulk density of about 1.70 grams per cubic centimeter. The media shape was chosen to be a triangular prism of size 3 mm along the edge of the triangles, and 5 mm along the other sides of the rectangular faces. The size and shape of the media was chosen such that it would sufficiently fit all the way into the root of the ring and pinion gear teeth without lodging.

(10) A quantity of chemistry 20 was supplied to the bowl as specified further in the examples below. The chemistry used was FERROMIL FML 7800 available from REM Chemicals Inc of Brenham, Tex., which is a phosphate-based chemically accelerated chemistry that produces a suitable conversion coating when used in a drag finishing environment on steel components. Similar chemistries that may also be used include Microsurface 5132, available from Houghton International, Valley Forge, Pa., Aquamil OXP available from Hubbard-Hall of Waterbury, Conn., the Quick Cut II CSA 550 (CF), available from Hammond Roto-finish of Kalamazoo, Mich. and Chemtrol, available from Precision Finishing Inc of Sellersville, Pa.

(11) The ring and pinion gear sets on which testing was carried out were for light axle ring and pinions for automotive vehicles. The sizes of the gears were approximately 18 cm and 23 cm ring gears and their mating pinion. The gears were manufactured according to standard automotive manufacturing processes.

(12) Operation of the machine 10 was carried out according to the following examples.

EXAMPLE 1

(13) In a first example, the bowl 12 was filled with media 18 to a level of approximately 406 mm depth. The media comprised non-abrasive 35 SCT (straight cut triangles). A quantity of 76 litres of chemistry of type FERROMIL FML-7800 diluted at 35 vol % and pre-heated, was added to the bowl. The media was stirred and then the chemistry was drained, leaving the media wet and at a temperature of around 43 C. (all temperature was measured using an infra-red heat sensor gun reading off the top of the media). A rear axle hypoid ring gear of 23 cm diameter was attached to the spindle 14 and lowered into the bowl to a depth at which the bottom of the ring gear was around 160 mm from the bottom of the bowl. The gear had an initial surface finish of 1.2-1.7 microns. The turret 22 was driven for 10 minutes at about 31 rpm and the spindle rotated at about 40 rpm. After 10 minutes the ring gear was removed and inspected. The surface roughness after processing for 10 minutes was determined to be 0.37-0.5 microns. All surface roughness measurements are given as average Ra based on measurements of the contact area of the teeth at five or six locations on both concave and convex sides. The upper and lower values were taken to determine the Ra range. Measurements were performed using a T1000 Hommel gauge with stylus tip radius of 2 micron.

EXAMPLE 2

(14) As a control, a ring gear of similar type to Example 1 was finished using conventional vibratory finishing in a Sweco approximate 300-liter bowl. The bowl was operated at an amplitude of 4.5 mm and a lead angle of 65. The media comprised 35 SCT as in Example 1. The chemistry used was FERROMIL FML-7800 at a 20 volume % concentration (the chemistry of Example 1 would have been unusable in this example as it would have caused etching), delivered on a flow through based at a rate of 11 litres per hour at ambient temperature. The ring gear had an initial surface roughness of 1.25-1.75 microns. It required 60 minutes of processing time to achieve a surface roughness of 0.15-0.2 microns.

EXAMPLE 3

(15) The procedure of Example 1 was repeated except that instead of draining the bowl it was instead filled with 76 litres of chemistry to a level of around 200 mm. On lowering the ring gear into the bowl, the ring gear was substantially immersed in the chemistry. After 10 minutes of processing, the part has a surface roughness of 0.12-0.2 microns. An example trace taken before and after processing is shown as FIG. 3.

EXAMPLE 4

(16) The procedure of Example 3 was repeated with 114 litres of chemistry, reaching a level of approximately 300 mm within the bowl. In this case, the ring gear was deeply immersed in the chemistry during processing. After 10 minutes, the ring gear was measured and found to have a surface roughness of 0.05-0.1 microns.

EXAMPLE 5

(17) The procedure of Example 3 was repeated with the spindle and ring gear being immersed deeper into the bowl to a distance of approximately 110 mm from the bottom of the bowl. After 10 minutes the ring gear was measured and found to have a surface roughness of 0.07-0.125 microns.

EXAMPLE 6

(18) The procedure of Example 3 was repeated at a temperature of 24 C. After 10 minutes, the ring gear was measured and found to have a surface roughness of 0.75-0.87 micron.

EXAMPLE 7

(19) The procedure of Example 3 was repeated with the temperature within the media held at 49 C. After 10 minutes, the ring gear was measured and found to have a surface roughness of 0.12-0.2 microns.

EXAMPLE 8

(20) The procedure of Example 3 was repeated at a temperature of 57 C. After 10 minutes, the ring gear was measured and found to have a surface roughness of 0.02-0.07 microns.

EXAMPLE 9

(21) The procedure of Example 3 was repeated with a reduced turret speed of about 20 rpm. After 10 minutes, the ring gear was measured and found to have a surface roughness of 0.12-0.2 microns. It was concluded that operation at this speed was sufficient to impart the required energy for fast finishing.

EXAMPLE 10

(22) The procedure of Example 3 was repeated with a reduced turret speed at about 6 rpm. After 10 minutes, the ring gear was measured and found to have a surface roughness of 0.17-0.3 micron. Even at relatively low speeds, the driving of the ring gear through the media caused sufficient action to adequately finish the workpiece in a short time.

EXAMPLE 11

(23) The procedure of Example 3 was repeated without turret rotation. Spindle rotation was maintained at about 40 rpm. After 10 minutes, the ring gear was measured and found to have a surface roughness of 1.0-1.1 microns. Despite the relatively high speed of rotation, the spindle-only action was ineffective in imparting energy to the surface to remove the conversion coating. While not wishing to be bound by theory, it is believed that the relatively stable rotation of the ring gear causes it to effectively plane over the media without significant impacts of the media particles on the gear surfaces.

EXAMPLE 12

(24) The procedure of Example 3 was repeated without literal immersion of the component in the chemistry. Instead, chemistry was supplied at a rate of 6.9 liters per minute onto the spindle path and the drains from the bowl were opened to ensure no excess chemistry was retained. After 10 minutes, the ring gear was measured and found to have a surface roughness of 0.05-0.1 microns. This shows that excess chemistry that essentially immerses the component was as effective as Example 3.

EXAMPLE13

(25) The procedure of Example 11 was repeated at a rate of 0.63 liters per minute onto the spindle path. After 10 minutes, the ring gear was measured and found to have a surface roughness of 0.50-0.76 microns. This delivery rate was more than double that conventionally used in CAVF processes but shows a significant drop off in finishing speed.

(26) The results of Examples 1 to 13 are depicted in FIG. 4. A surface roughness trace of the ring gear of Example 3 is shown in FIG. 3. It can be seen that the combined effects of elevated temperature, high energy relative movement and excess chemistry lead to a suitably planarized and finished surface in an amount of time that was significantly less than that of the conventional CAVF process of Example 2.

(27) Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. In particular, the skilled person will understand that the above examples may equally apply similarly to splines, crankshafts, camshafts, bearings, gears, couplings, journals, and medical implants.

(28) Further modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.