US2402455A - Apparatus for grinding - Google Patents

Description

June 18, 194 6. H. N. SEYFERTH 2,462,455

APPARATUS FOR GRINDING Filed Oct. 6, 1943 FAST DRESSER &

Patented June 18, 1946 APPARATUS FOR GRINDING Harold N. Seyferth, East Detroit, Mich., assignmto Ex-Cell-O Corporation, Detroit, Mich, a corporation of Michigan Application October 6, 1943, Serial No. 505,098

2 Claims. 1

The present invention pertains to a novel apparatus for grinding metal work pieces.

Generally stated, the object of the present invention is to correlate in a novel manner the truing of a grinding wheel or other revoluble grinding element with the grinding operation performed thereby, to facilitate and improve sue:- cessive rough and finish grinding operations.

I have discovered that there is a direct relation between the speed at which a grinding wheel or the like is trued and the character of the surfaces which it subsequently produces on a work piece. More Particularly, if 8- n n wheel is trued at high speed the eflective cutting periphery of the wheel is more roughly dressed so that the wheel is free-cutting, a condition highly desirable for efilcient rough grinding. 0n the other hand, if the same truing device is swept across the active periphery of the same wheel at a low speed which is but a, minor fraction, for example, one-fifth of the high speed mentioned, the wheel will be dressed with a much smoother, less free-cutting surface which, in grinding, leaves on the work a smoother surface than in the case of the high speed truing. It is on the basis of these facts that the herein disclosed procedure is largely predicated.

Another object of the invention is to provide a novel electrical control system adapted to eilect an automatic truing cycle in a grinding machine, correlated with the machine's general cycle of operatlon in such manner that the grinding wheel or the like is trued at high speed preparatory to the rough grinding pass or passes, and subsequently trued at low speed preparatory to the finish grinding pass or passes.

Further objects and advantages of the invention will become apparent as the following descrlption proceeds, taken in connection with the accompanying drawing, in which:

Figure 1 is a generallyschematic perspective view 01' a portion of a grinding machine equipped with an automatic dresser adapted for the present invention. 7

Fig. 2 is a wiring diagram of the dresser con-. trol for the machine of Fig. 1.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail the preierred embodiment. but it is to beunderstood that I do not thereby intend to limit the invention to the specific form or series oistcPs disclosed, but intend to cover all modifications and alternative constructions and methods falling within the mix-i m anally or r 2 of the invention as expressed in the appended claims,

The present invention of the great variety are known in the art and, accordingly, attention need not be given here to specific structural detail of the machine, as such. In Fig. 1 are indicated the principal elements commonly found, for example, in a center type grinder and which is one type of grinding machine to which the present invention is particularly suited. For further data as to the detailed structure of a. representative machine of this type, reference may me made to my prior Patent No. 2,317,226, issued April 20, 1943.

In brief, a workpiece is applicable to any one it is revolubly mounted between a headstock ii and tailstock 12 which are carried on a. table it, the latter being reversely traversable in the usual manner axiall of the work and the work being revolved by a suitable drive (not shown) in the headstock. Engageable with the periphery of the work piece is a rotatable grinding element, shown as an abrasive grinding wheel 45 adapted to be revolved by the usual drive motor (not shown) and carried toward and from the work, transaxially of the latter, by the supporting wheel slide I6 fed by a lead screw l 1, In the usual manner, the wheel slide l8 may be fed forward by the screw l'l, either manuautomatically, a small incremental step after each stroke or pass of the table I4 until the work has been ground to the desired depth.

:As is also customary in grinding machines, provision is made loidressing or truing the wheel 18. this case, the same has been indicated as including a single dressing point l8, although of course a plurality may be employed if desired, together with a dresser mechanism 89 driven by a resersible electric motor 2fl for actuating the dresser mechanism to sweep the dressing point back and forth across the wheel periphery in a fixed path calculated to true or dress it to a desired contour. Rotation of the motor 20 in one direction causes the mechanism "to shift the tool I! in a corresponding direction, rotation of the motor causes the tool to be moved through a corresponding return stroke. Dresser hsnisms, as such, are well-known in the art and the mechanism 19 ma take any desired one or various well-known forms. and as a example reference may be made to Gilbert Stewart Patent No..2,311,263, issued February 18, 1948. The motor 2| is belted to a speed reduction genring within the, casing ii and is thence connected of grinding machines which and reverse anism. A dresser slide 23 supports the dresser mechanism on the wheel slide for movement into and out of operative relation with the wheel.

In accordance with the present invention, the speed at which the dressing or truing too1'l8 is moved across the wheel periphery by the dresser drive motor 20 is correlated with the grinding operations in such manner as to condition the wheel successively for rough and finish grinding in operating upon the work piece. For a full understanding of how that is accomplished, attention should first be given to certain characteristics of grinding wheels or other revoluble grinding members of the class here contemplated.

It is contemplated that the grinding wheel shall consist of abrasive particles bonded or held together by a suitable binder. Wheels of great variety are, of course, used in the art, differing from each other in the abrasive used, the size of the abrasive particles, and the degree of strength with which the particles are bonded together by the particular one of the various available binders which may be used. Such wheels may vary from very hard, dense structures to comparatively soft ones which crumble readily under pressure. It is characteristic of such wheels, however, that the abrasive particles remove metal from the work in minute, and, in fact, many times microscopic, chips as the abrasive particles are dragged across the work surface by the wheel. When the wheel is roughly dressed it is said to be "free cutting, and is capable of removing comparatively large amounts of metal as the surface of the wheel is moved across the work. when the wheel is dressed with a smoother surface the cutting action on the work is correspondingly reduced and a smoother surface is produced on the work piece until a point is reached at which the wheel has largely a rubbing or burnishing action on the work.

I have found that with any given wheel, the freedom with which it cuts can in large measure and with reasonable accuracy be controlled through variation in the speed at which the dressing tool is moved across the wheel in truing the same. What apparently occurs is that if the dressing tool point is swept across the wheel periphery at high speed, the abrasive particles are uprooted so that a freely cutting surface results. On the other hand, if the dressing speed is diminished to a low value which is but a minor fraction, for example, one-fifth or one-fourth of the high speed, a much smoother wheel surface, suited to finish grinding, is produced. After the slow speed dressing, the wheel periphery has an appearance of being filled, that is, the interstices preparatory to the roughing passes, thus producinga freely cutting surface for that purpose, and

is-trued at a comparatively low speed preparatory to thefinish pass. Specifically, the grinding may be carried out with reverse traversing of the work table it -(Fig. 1) and incremental infeed steps of the 'wheel slide [6 after each pass of the work. Each time that a selected number of passes of the work, that is, one or more, has occurred, the

dresser mechanism I9 is operated through a predetermined cycle by its drive motor 20 running at highspeed, thereby effecting a high speed truing of the wheel l5 suited to rough grinding,

When the total infeed of the wheel slide it is completed to a predetermined depth commensu-' rate with the desired final size of the work, but before the last pass of the work, the dresser mechanism i9 is operated through its cycle with the dresser motor 20 running atlow speed so as to condition the wheel 15 for finish grinding of the work in the final pass of the latter.

between the particles of abrasive appear to be' filled and the tendency of the wheel to crumble is reduced. Merely by way of example, if the dressing tool is moved through a, travel of of an inch during truing, it may be moved at a fast speed in conditioning the wheel for roughing such that it completes its truing travel in from three to nine seconds, whereas in conditioning the wheel for finishing the truing tool may be moved throughthe same length of travel at a comparatively slow speed requiring from sixteen to forty-eight seconds. chosen will be governed by the characteristics of the particular wheel which is used, the characteristics of the truing tool, etc.

In utilizing the foregoing phenomena, the general procedure which I employ is to carry out what is otherwise a normal grinding cycle except that the grinding wheel is trued at high speed As indicated above,the alternation between high and low speed dressing is desirably accomplished by a corresponding alteration in the speed of the dresser drive motor 20. The speed of rotation of the wheel itself may be the same during both types of dressing. That. same wheel speed may also ,be retained throughout both the rough and finish grinding operations, although in many instances it may be desirable to diminish the wheel speed during the finish grinding to avoid burning the work.

Attention may now be given to Fig. 2 wherein is shown the novel electric control circuit for carrying out the described cyclic changes in dressing speeds automatically. Included in this circuit are several contactors and relays and in each instance their contacts have been shown as connected at the proper points in the circuit, as well a as duplicated at points adjacent the actuating windings to indicate their relation to the latter.

These include forward and reverse contactors DF and DR having respective main contacts DFI, DB! and DF3 and DRI, DB2 and DB3 interposed between the dresser drive motor 20 and three phase supply lines Ll, L2 and L3 in the usual manner to effect rotation of the motor in respec- .tive opposite directions upon closure of corretacts FI and SI of what may be termed the fast and slow contactors F and S and which condition the two speed dresser motor alternatively for fast or slow speed operation upon closure. Finally, there are three control relays CRI, CR8 and CRI 0 whose functions in the circuit .will appear below, All of these contactors of the relays are arrang to be energized by current derived from supply lines Ll, L3.-

As a means of instituting operation of the dresser after each predetermined series of one or more passes of the work, a counter mechanism of conventional design may be employed. In Fig. 2, I

the clutch coil and actuating coil of such a counter mechanism are indicated, respectively, at A and B, the latter mechanism having a normally open contact C which is closed upon the complethe. counter, it closes its tion of each predetermined series of strokes of the table It which are being counted.

Various control switches are also included in the system. These comprise the switch lSSi which is actuated from the feed screw from the wheel slide it and is closed upon completion of the incremental inieed oi the'wheel slide to a point corresponding to the desired depth of cut on the work. Also included is a table switch 28 which is closed whenever the table i4 is in motion. A manually operated selector switch 21 serves when opened to disable the counter mechanism, while a normally open push button switch 28 conditions the circuit for manually controlled operation upon closure. For use in conjunction with the push button switch 28 is a manually operable selector switch 2s having two sets of contacts 39 and 3i, the former being shown as closed and the latter as open. When the switch 29 is positioned as shown, the circuit is conditioned for slow speed operation, while shifting the push but ton 29 to its alternate position conditions the circuit for fast operation of the dresser motor under the control of the push button 23 and irrespective of the position of the switch LSSi.

To condition the circuit of Fig. 2 for automatic operation, the switches are positioned as shown.

In such case when current is applied to the circuit from the supply lines, the clutch coil A of the counter mechanism is energized,- conditioning the counter for operation, and the actuating winding 18 of the counter is also energized, thereby advancing it one half step. The control relay CR! is also energized through normally closed contacts CRllll of the relay CRH), sealing itself in through its own contacts CRll. The closing of its contact CRl-2 has no effect on the circult at this point. As soon as the work table it starts to move in its first stroke, the table switch 28 is closed, thereby energizing the relay (233% so that it opens both of its normally closed contacts CR3! and CR%2. The former interrupt the flow of current to the counter actuating winding B, while the latter prevent titution or the dresser drive while the table i l is in motion. As soon as the table comes to rest at the end or this stroke, the switch 26 is reopened, thereby deenergizing the relay CR8 so that its contacts recluse, thus applying another current impulse to the counters actuating plication of current to the winding B advances the counter one step so that the counter is actuated for each stroke or the table.

After a predetermined number of actuations of switch C, the latter remaining closed until reopened by starting of the dresser motor 20. Such closure of the switch takes place coincident with the reclosure of contact CBS-2 at the end of a table stroke, wherefore a circuit is complete from line L3 through contact CRt-i and switch 0 to the forward contactor DF for the dresser motor. The contactor thereupon closes its main contacts, seals itself in through its auxiliary contacts DFS, opens its interlock contacts DFS, and closes its contacts DFS to complete an energizing circuit for the fast contactor F. Such closing of the contactors DF and F energizes the dresser motor 20 for 1- tation at fast speed in a forward direction.

At the completion of a predetermined forward movement of the dresser tool i8 by the dresser mechanism 19, a limit switch LSDF associated therewith is opened and a second limit switch LQDR closed. The opening of, the limit switch winding B. Each apwhen the switch the closing of the other limit switch ISD$ picks up the reverse contactor DR. The fast contactor F remains energized, or is reenergize'd by closure of the auxiliary contacts DRE on the reverse contactor, so that the dresser motor 20 is caused to revolve rapidly and in an opposite direction, thus driving the dresser mechanism reversely at high speed. At the end of the reverse stroke or the dresser tool 18, the reopening of the limit switch LSDR drops out the reverse contactor DR, and the other limit switch LSD is reclosed. Such reclosure of the latter switch is ineffective to pick up the forward contactor DF, however, since the counter switch C was only momentarily closed and has now reopened. Consequently, the dresser mechanism comes to rest after thetruing tool 38 has moved forwardly and reversely at high speed through mechanism :9.

The high speed actuation of the dresser tool i8 through a preset cycle of motion in the manner described above dresses the periphery of the wheel it for free cutting action suitable for rough grinding. Such high speed dressing oi the wheel is repeated periodically in accordance with the setting of the counter mechanism throughout the series of passes or" the work piece ill for completing the amount of rough grinding desired.

At the completion of the inieed movement of the wheel slide id, or, in other words, upon the completion of the movement of the wheel slide inward to a position corresponding to the final depth of cut desired on the work but before the table it makes its last pass, the switch LS8: is closed momentarily. This results in a momentary energization of the control relay CRit during which the latter opens its contacts CRlQ-l and CR-itd and closes its contacts CRiG-i, and CRiM. When closed, the contacts CRit2 act in conjunction with the previously closed contacts CRfi-Q and CRil to complete an energizing circuit for the forward contactor IDF. This contactor picks up, sealing itself in through its contacts DF-d as before. In this instance, however, the opening of the contacts CHM-4i and closing of CRiil-Zl disables the fast contaotor F against energization and completes a circuit for the other or slow contactor S. The dresser motor as is thus energized for slow operation in a forward direction so that the trm'ng tool it is moved slowly across the wheel periphery to true the wheel for finish grinding during the final stroke of the table which is to follow.

At the end of the slow forward movement of the truing tool it, the switch LSDF is opened and the companion switch LSDR closed, whereupon the dresser motor 29 is energized for reverse movement, but again at slow speed. At the end or the reverse movement of the truing tool it,

the switch LSDR is reopened to drop out the re verse contactor DR and the companion switch LSDF is reclosed. The dresser motor come to rest, however, since the relay CR! has been dropped out by opening up contacts 13F! during the reversing of the dresser, wherefore reestabiishment oi the circuit for the forward contactor DF is prevented by the opened contacts CRII LSDF recloses. After the last pass of the work table H during which the work is finish ground by the slowly trued wheel, the wheel slide 36 is retracted to its starting position, whereupon the switch LSSI reopens and the dresser control circuit is thus restored to its initial position.

LSDF drops out the forward contactor DP, while 35 Should manually controlled operation be dea path determined by the dresser :forward direction at high speed. It then executes its forward and reverse cycle as before. On the other hand, if switch 29 is shifted to its alternate position and the relay CRIB picked up by manually or otherwise closing LSSI, then closure of switch 28 will cause the dresser to execute a slow speed cycle of forward reverse. For either a slow or fast speed cycle, only a momentary closure of the switch 28 is required to institute it since the forward contactor seals itself in by its contacts DF in shunt with the switch I claim as my' invention:

-1. A dresser control system for a grinding machine having a work support and rotatable abrasive element, arranged for relative reciprocation axially of the element and for relative infeed with respect to each other transversely of the path of reciprocation, as well as a dressing tool for the abrasive element arranged to be swept to and fro across the abrasive element in a predetermined. cycle of movement by a reversible electric dresser drive motor to dress such element. said control system comprising, in combination, a counter mechanism, means for actuating said counter mechanism in response to successive relative reciprocations of the work supp rt and abrasive element, means operable in response to each completion of a predetermined series of ac-' tuations of said counter mechanism for energizing said dresser drive motor to move the dresser tool through its cycle of movement at high speed, to thereby dress the element by each such cycle for rough grinding. and means operable in response to a preselected relative infeed of the work support and abrasive element for energizing said dresser drive motor to move the dresser tool through its cycle of movement at a. low speed which is but a minor fraction of said high speed,

' to thereby prepare-the element for finish grinding of the work. n

2. A dresser "control system for a grinding machine having a work support and rotatable abrasive element, arranged for relative reciprocation axially of the element and for relative infeed with respect to each other transversely of the path of reciprocation, as-well as a dressing tool for the abrasive element arranged to be swept to and fro across the abrasive element in a predetermined cycle of movement by a reversible electric dresser drive motor to dress such element, said control system comprising, in combination, means operable in response to the completion of a predetermined series of relative reciprocations of the work support and abrasive element for energizing the dresser drive motor to move the dresser tool through its cycle of movement at high speed, and means operable in response to a preselected relative infeed of the work support and abrasive element for energizing said dresser drive motor to move the dresser tool through its cycle of movement at a low speed which is but a minor fraction of said high speed.

HAROLD N. SEYFER'I'H.

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