US2778170A - Method of grinding, including grinding wheel forming - Google Patents

Description

Jan'. 22, 1957 E. v. FLANDERS METHOD OF GRINDING, INCLUDING GRINDING WHEEL FORMING 2 Shee ts-Sheet 1 Filed Nov. 20, 1953 Jan. 22, 1957 E. v. FLANDERS 2,778,170

METHOD OF GRINDING, INCLUDING GRINDING WHEEL FORMING Filed Nov. 20. 1953 2 Sheets-Sheet 2 celerated back to grinding speeds.

will become readily United States Patent METHOD OF GRINDING, INCLUDING GRINDING WHEEL FORMING Ernest V. Flanders, Springfield, Vt., assignor to Jones and Lamson Machine Company, a corporation of Vermont Application November 20, 1953, Serial No. 393,260 4 Claims. (Cl. 51-283) peripheral velocity, and the roll acts in such a way as to crush or pulverize the grinding wheel grains to thereby produce on the wheel a complement of the crusher roll shape. This method is satisfactory in many cases, particularly on work not requiring the utmost in precision and finish. However, it is not possible to crush dress the many so-called resinoid wheels. Such wheels cannot be broken down or pulverized successfully to desired forms by a crushing process.

In diamond dressing, a diamond tool is applied to the wheel and guided in such a path as to produce a desired form on the wheel. Many mechanisms have been proposed for the accurate location and precision movement of the diamond tool. The action is rather analogous to cutting on a lathe or similar machine tool, and is normally done at speeds higher than crush dressing speeds, yet substantially lower than actual work grinding speeds. Typical crushing speeds may be in the order of only 400 peripheral feet per minute; diamond truing speeds may be in the order of 2000 peripheral feet per minute; whereas actual grinding is usually done at'speeds of 8000 feet per minute or higher in modern high level production.

On any known grinding machines, therefore, actual production must be interrupted periodically for a wheel dressing operation, whether it be performed by crusher roll or diamond tool. down of the wheel to wheel truing speeds, and after the dressing operation takes place, the wheel must be ac- This process, it can readily be appreciated, is time-consuming and therefore costly.

In accordance with this invention, I propose a new method of forming wheels which overcomes the difiiculties described briefly above and which provides great advantages as will be pointed out hereinafter.

A further object of my invention is to provide a method of wheel forming suitable for all types of wheels regardless of the bond or grit employed, and to a degree of accuracy equal to that achieved by the best conventional methods.

These and other objects and advantages of my invention apparent from the following specifications and drawings, in which Figure 1 is a view in elevation of wheel forming apparatus embodying my invention;

Figure 2 is a detailed view, partly in section,

i-forming'roll in contact with a grinding wheel;

This operation requires a slowof a wheel 7 or rubber bonded abrading 0 shaft 16 has a second Figure 3 is a view on section lines 33 of Figure 1;

Figure 4 is a plan view of the apparatus shown in Figure 1;

Figure 5 is a detail of the gear train forming part of the mechanism of Figure 4;

Figure 6 is a view on the section lines 66 of Figure 1;

Figure 7 shows a modification of the forming tool drive mechanism;

Figure 8 is a view on the section lines 8-8 of Figure 7;

Figure 9 is a further modification of the drive mechanism shown in Figure 7;

Figure 10 is a view on the section lines 10-10 of Figure 9;

Figure 11 is a view on the section lines 11-11 of Figure 9.

Briefly stated, my invention contemplates the use of a tool which may be in the form of a roll made preferably of a hard and abrasive substance like diamond particles held in a bonding material, or matrix. This roll is formed so as to have on its periphery a complement of the shape which it is desired to produce on a grinding wheel. The roll is forced against the grinding wheel, while the wheel is in rotation under power, and the roll is also rotated or oscillated under power so that successive portions thereof are brought into contact with the grinding wheel.

The wheel may be in continuous operation, rotating at actual grinding speeds, and, if desired, may be performing grinding operations even While the wheel form is being maintained at another point on its periphery.

Referring more particularly to the drawings, I have shown a portion of a grinding machine sufficient to illustrate the invention, having a bed 10 on which is mounted a grinding wheel slide 11. The wheel slide may be mounted on ways (not shown) for motion radially toward and away from a grinding point on the machine as is well understood in the art. The slide 11 carries a cylindrical housing 13 which contains the wheel forming mechanism. The arrangement of this housing 13 and its relationship to the grinding wheel is somewhat similar to that in U. S. Patent 2,578,531, granted December 11, 1951, to Ernest V. Flanders et al.

Mounted on housing 13 is a motor 14 which may be any suitable constant speed motor providing power through belts or the like 15 to the shaft 16. Through worm 17, the rotation of shaft 16 is transmitted to shaft clutch 19 is disengaged by energization of the solenoid 20, the motor 14 merely idles and the entire gear arrangement to the shafts 26, 28 and screw 32 is at rest. I provide a cover'plate 33 which may be removed for conveniently changing the gear ratio in the train, best shown in Figure 3. Through change gears any desired rate of rotation of shaft 26 and screw 32 may be obtained. I prefer to employ a relatively slow rate of rotation, in the order of one-tenth of a revolution per minute, for reasons which will appear hereinafter.

In addition to driving the gear train (Figure3) the power take-01f portion comprising a worm 34 and gear35. This gear combination drives a pinion 36,,which meshes with a wide faced gear 37;

The gear 37 is on a shaft 38 journaled in the housing 13. At the forward end of shaft 38 I provide a pair of bevel gears 40 and 39, best shown in Figure 4, which impart rotary motion to' a wheel forming roll 41. This entire roll driving;- asse bly is slidahly mounted in brackets 42. A collar 43 is pinned to the shell 44. A threaded hole in collar extension 45 engages a threaded end portion on the shaft 26. This thread is of the same pitch as the lead screw 32. A yoke (see Figure 6) slidably engages retaining pin 46 which supports the collar assembly. When shaft 26 is rotated, axial motion is transmitted to the collar 43 and thus the roll 41 is slowly advanced toward the grinding wheel 12.- During this advancing motion, the roll is continuously rotated through the medium of pinion 36 arid gear 37, and bevel gears 39, 40.

Since as heretofore explained the lead screw 32 turns with the -shaft 26, it can readily be seen that through a nut portion 47 on the wheel slide 11 engaging the screw 32, the entire wheel slide also moves in the same direction and at the same rate as the motion of the roll 41 toward the grinding wheel. In this mariner as the wheel is consumed, the working point on the periphery of the wheel, substantially 180 degrees from the point of forming roll engagement, remains in proper position relative to the work piece. This constant relationship assures accurate and automatic maintenance of work size even though the wheel diameter is constantly decreasing.

Figures 7 and 8 illustrate a modification of the wheel forming assembly to provide an oscillatory motion to a roll or roll segment. The bevel gears 39 and 40 impart an oscillatory motion to the wheel forming segment 48 through an adjustable throw eccentric as at 49.

In Figures 9, l0 and ll, I illustrate mechanism for imparting oscillatory straight line motion to a wheel forming tool in the form of a bar 50. In place of the bevel gear combination 39-40 spur gears 51 and 52 drive the bar 50 up and down on ball slide 53 through an adjustable throw eccentric 54.

In each case, the portion of the wheel forming tools 41"., 48 or 50 contacting the grinding wheel is in constant change, while the mechanisms heretofore described advance the wheel forming tool against the wheel at a relatively slow, predetermined rate. This rate may be altered by proper choice of change gears shown in Figure 3 and varies with the character of the grinding wheel itself, the type of workpiece, the complexity of the wheel form being maintained, and the degree of accuracy reqnired. v

If the nature of the work is such as to permit several complete cycles with no dressing action, it is merely necessary to energize solenoid 20, thus interrupting the advance of the wheel forming member. This may be done automatically by a cycle counter set to permit ongagement of clutch 19 after a predetermined number of work pieces have been ground. In any'case, the grinding speed is maintained, and no time consuming slow-down is ne'ce ssary to maintain wheel form. In some applications, where the grinding process causes rapid wheel wear, as, for example, when operations are being performed on eiitre'mely hard orresistant work material, I have found fit 'd's'irable to leave the clutch 19 in continuous engagerhent during grinding. Of course, it is desirable to disengage the clutch 19 during the unloading of the finished work and the loading of a new workpiece toavoid unnee' ss'ary 'wheel consumption. In such a case, the sole- "oid'ZO 'iii'ay be included in an automatic work loading cycle, or interlocked with a work fixture, chuck or the like to operate without further attention.

I have found the methods described herein to be effective on resinoid as well as on vitrified wheels. In conventional crush dressing it is essential to drive the wheel and roll at substantially the same low peripheral velocity. flhegrandom :pulveriz-ation, effective only on vitrified wheels,--leaves a wheel surface which isinfe'rior te -that produced by mycontinuous process carried out at high speeds. My continuous wheel forming. process results in a free-cutting, open grained wheel, yet with a fine structure to insure long life and work of high accuracy and finish.

Continuous wheel forming in accordance with this invention is most advantageous in that it enables the user to combine high accuracy with a high rate of production'. Hretofore, maximum stock re oval rates could not be employed where the grinding 'wheel broke down between the start and the finish of the grinding operation on a single workpiece. Heavy cuts resulted in wheel breakdown which was enough to cause a loss of accuracy. In the typical case the form produced would deviate from the desired standard before the operation was finished. In grinditig a worm gear from the solid, for ex ample, the initial turns of the thread would be correctly formed, but the last threads would be of reduced depth because of wheel breakdown and finish would be impaired because of the declining efficiency of the grinding wheel as the grinding progressed.

In such cases, it has been customary to take an initial heavy roughing cut. A subsequent finishing pass with a freshly trued Wheel was then made with a lighter cutting load such that the entire workpiece could be finished without serious loss in workpiece size, form, or finish. In a thread depth of .250 of an inch, for example, the initial pass might be set to remove .240 of stock, without regard to final accuracy. A subsequent finishing cut could successfully remove the final .010 of stock and produce acceptable work. This method of approach, while achieving the desired end, is time consuming and therefore expensive.

In continuous wheel forming as taught herein, on the other hand, the high stock removal rates (heretofore achieved on roughing cuts only) can now be realized with the heavy cuts producing the final desired form on the workpiece. The grinding wheel is continuously corrected so that the last part of the grinding pass is accomplished with the same accuracy and efiiciency as the rst part of the grinding pass. Thus wheel truing time is not added to total time expended. Furthermore, work usually requiring two or more passes is now finished in a single cutting operation.

The time savings are spectacular and of particular importance in modern mass production where standards of accuracy are becoming higher. It is becoming necessary to achieve close grinding tolerances on more and more parts, and continuous wheel forming with automatic size control has proven to be a significant advance in the art.

The roll 41 may be rotated at a steady, slow rate, for example, 60 R. P. M., in either direction, while the grinding wheel continues to work at normal grinding speeds. If the shaft 26 is geared to turn 30 degrees per minute, and the threaded portion has 10 threads per inch, the wheel forming tool will advance at the rate of one-half inch .per hour. The foregoing example describes typical rates which I have found desirable for a given set of grinding conditions.

While I have illustrated anddescribed preferred embodiments of my invention, the foregoing is by way of illustration only'of a novel wheel forming method which radically departs from conventional practice as hereinbefore described.

Iclaim: p

1. During a grinding operation, the method of maintaining the working point on the periphery of a grinding wheel in proper relation to a workpiece being ground, said wheel having a desired form, that comprises grinding said workpiece with said wheel whereby the diameter of said wheel decreases at a determinable attrition rate, feeding substantially radially'into said wheel a member shaped to the complement of the-desired form of'said wheel at a constant, positive forming jrate I greater than said attrition rate, rotating said wheel and 'said member at diflerent peripheral speeds and simultaneously adfeeding substantially radially into said wheel a member vancing said wheel towards said workpiece at a rate subshaped to the complement of the desired form of said stantially equal to said forming rate. wheel at a constant, positive forming rate greater than 2. During a grinding operation, the method of mainsaid attrition rate, said member comprising a roll of hard taining the working point on the periphery of a grinding 5 abrasive material including diamond particles held towheel in proper relation to a workpiece being ground, gether by a bonding substance, rotating said wheel and said wheel having a desired form, that comprises grinding said member at diiTerent peripheral speeds and simultanesaid workpiece with said wheel whereby the diameter of ously advancing said wheel towards said workpiece at a said wheel decreases at a determinable attrition rate, rate substantially equal to said forming rate.

feeding substantially radially into said wheel a member 0 shaped to the complement of the desired form of said References Cited the file of thls P511tent wheel at a constant, positive forming rate greater than UNITED STATES PATENTS said attrition rate, rotating said wheel and said member at substantially different peripheral speeds and simultaneously advancing said wheel towards said workpiece 15 13137O2 Kriegel. 1919 at a rate substantially equal to said forming rate. 1896533 vuilleumge'lf 1933 3. A method as defined in claim 1 in which said wheel 2100954 Gould N 1937 and said member are rotating in opposite directions. 2333304 Emst 1943 4. During a grinding operation, the method of main- 2347283 Ross Apr 1944 taining the working point on the periphery of a grinding 20 2545730 gz 1951 wheel in proper relation to a workpiece being ground, 2576239 Reimschissgl 1951 said wheel having a desired form, that comprises grinding said workpiece with said wheel whereby the diameter FOREIGN PATENTS of said wheel decreases at a determinable attrition rate, 610,978 Germany Mar. 20, 1935

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