US3697403A - Electrochemical grinding apparatus - Google Patents

Electrochemical grinding apparatus Download PDF

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US3697403A
US3697403A US774009A US3697403DA US3697403A US 3697403 A US3697403 A US 3697403A US 774009 A US774009 A US 774009A US 3697403D A US3697403D A US 3697403DA US 3697403 A US3697403 A US 3697403A
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signal
conductor
gate
voltage
current
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Lester V Colwell
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Hammond Machinery Builders Inc
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Hammond Machinery Builders Inc
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
    • B23H3/00—Electrochemical machining, i.e. removing metal by passing current between an electrode and a workpiece in the presence of an electrolyte
    • B23H3/02—Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
    • B23H5/00—Combined machining
    • B23H5/06—Electrochemical machining combined with mechanical working, e.g. grinding or honing
    • B23H5/08—Electrolytic grinding

Definitions

  • This invention relates to electrochemical (formerly called electrolytic) grinding and relates particularly to both process and apparatus for repetitively sampling at least one selected performance parameter and from the information thereby obtained maintaining selected control parameters at values automatically to maintain at least said selected performance parameter at a desired value.
  • control parameter will refer to the various controllable inputs to the electrochemical grinding apparatus, such as the voltage of the working current and the vfeeding force.
  • the .term performance parameter will refer to relationships, either measurable or computed, to which -the control system is responsive, such as amperage of Working current, power applied to the grinding wheel for driving same, feed rate or resistance across the working gap (space between the workpiece andv the metallic surface of the grinding wheel.
  • the objectives of the present invention include: I
  • control parameters may be selected as the bases for attaining a selected combination of performance parameters and may be then controlled in a manner to attain and maintain such selected operating combination.
  • control parameters may be selected as the bases for attaining a desired combination of performance parameters and may then be controlled in such a manner as to attain such operating combination.
  • a singlelcontrol parameter such as the voltage of the working current
  • a singlelcontrol parameter such as the voltage of the working current
  • the performance parameter being sensed is the working current supplied' to the workpiece and the control parameters being adjusted are the voltage at which such working current is so applied and the feed force applied to the table.
  • sensing means is provided for successively and incrementally changing the voltage at which the working current is applied to the grinding operation and checking the magnitude of working current being supplied to the workpiece after each such incremental change in said voltage, said changes being terminated and/or reversed when a predetermined relationship between voltage and current is attained.
  • sensing means is provided for successively and incrementally changing the voltage at which the working current is applied to the grinding operation and checking the magnitude of grinding current being supplied to the workpiece after each such incremental change in said voltage, said change being terminated and/ or reversed when the change in current magnitude resulting from a given voltage change falls Ibelow a predetermined minimum.
  • 1-6 are graphs of observed and computed relationships between various control and performance parameters.
  • lIG. 7 is an illustration of a surface generated with variations in the voltage and feed force control parameters and the resulting variation in the current performance parameter.
  • FIG. 7A is an enlarged fragment of FIG. 7.
  • FIG. 8 is a schematic side View of one typical electrochemical grinding apparatus wherein the working current is the selected performance parameter.
  • FIG. 9 is an enlarged showing of a portion of FIG. 8.
  • FIG. 10 is a schematic top view of the device of FIG. 8.
  • FIG. 1l is an enlarged showing of a portion of FIG. 1.
  • FIG. 12 is a schematic block diagram representing the system for controlling the selected control parameters of the electrochemical grinding apparatus.
  • FIG. 13A is a schematic electrical diagram of the system shown in FIG. 12.
  • IFIG. 13B is a schematic diagram of certain components of the apparatus shown in FIG. 8 and illustrating the electrical connection of the control thereto.
  • FIG. 14 is a chart illustrating the various functions which occur at predetermined time intervals.
  • iFIG. 15 is a side view of a grinding apparatus similar to that illustrated in FIG. 8 utilizing the spindle power as the selected performance parameter.
  • FIG. 16 is a side view of a modiiied grinding apparatus wherein the table feed rate is the selected performance parameter.
  • the invention contemplates incrementally advancing a control parameter, such as applied voltage, from a selected starting point toward a selected, usually the expected optimum, operating range and after each such advance is effected the performance parameter (such as magnitude of working current) is measured and a record thereof is suitably stored. At a measurable point in time thereafter, the performance parameter is measured again and compared to said record. If the performance parameter change in relationship to the control parameter is, for example at a magnitude above a predetermined minimum value, indicating that the system is operating somewhere to the left of line A in FIG.
  • a control parameter such as applied voltage
  • control parameter continues to be incrementally advanced and is subsequently again sampled and the new sample similarly compared with the record of a previous sample,
  • a given increment of control parameter advance results in a performance parameter change falling below said preselected minimum (such as when the system is between lines A and C of FIG. 11)
  • the apparatus then automatically holds or reverses said control parameter at such values, by suitable subsequent sampling and adjusting, either to maintain said performance parameter within the selected range or to bring about whatever further adjustment is needed to follow such selected range if same should change during a grinding operation.
  • the selected parameters are the applied voltage and the feed force, and the selected performance parameter to be observed is magnitude of working current, other control parameters may be utilized as desired and as further described hereinafter to automatically search for, establish and maintain one or more selected performance parameters in an electrochemical grinding operation.
  • FIGS. 1-6 wherein certain of the above-mentioned relationships are set forth for a work situation wherein tungsten carbide was the workpiece; the stock removal electrode was a rotating metal-bonded diamond impregnated grinding wheel; the electrolyte was a highly dissociatable material of the nature of alkali metal nitrate salts (meaning that in some cases the electrolyte contained a large proportion of such nitrates and in other cases other materials but in each case the electrolyte had a dissociation constant of generally the same order as alkali metal nitrates).
  • FIG. 7 it is seen that a still more complex relationship is involved.
  • the data presented in FIG. 1 is rearranged to show that a surface M is formed by variations in both feed force andvoltage and by the variations in current resulting therefrom.
  • variations in either feed force or voltage will cause variations in current and simultaneous variations in both feed force and voltage will cause relatively complex variations in current.
  • y For illustrative purposes, it will be assumed that the desired operating condition is represented by the range R on the ridge E of the surface M.
  • the shape characteristics of the surface 'M are substantially constant with time, the location of the ridge E, for example within the voltage feed force domain, can change very rapidly ⁇ witlitime due to changes in the area being ground and due further to changes vin the condition of the ⁇ face of the grinding device.
  • FIG. 8 there is schematically illustrated a conventional electrochemical grinding apparatus 10, hereinafter referred to as ECG apparatus, essentially as set forth in the U.S. patent to Keeleric, No. 2,826,540.
  • a grinding device 11 here an abrasive wheel (such as one utilizing diamond or other grit of relatively low electrical conductivity bonded with metal)
  • a spindle motor 13 supplied with electrical power from power lines L1, L2 and L3.
  • a workpiece vW is supported by a ⁇ suitable fixture 14 which in turn may bemounted on a reciprocable table 16.
  • the table 16 is mounted on suitable means such as rollers, one of which.
  • a workpiece feed force may be applied to the table 16 for automatically causing the workpiece W to bear against the abrasive grain of the grinding device with a controllable pressure.
  • the feed force is applied by an air cylinder device 21 which is controlled by a valve 22.
  • An air pressure sounce 23 is connected to an electropneumatic transducer 25 which controls the pressure of air supplied to the valve 22.
  • the valve 22 then commands the direction of movement of the piston 24 in the air cylinder device 21 and the table 16 connected thereto at a force determined by the degree of energization of the electropneumatic transducer 25.
  • the electropneumatic transducer 25 may be of any well known variety such as a Moore Model 77 transducer made by Moore Products Company of Spring House, Pa.
  • the transducer 25 is preset to allow a pressure of 3 p.s.i. to pass therethrough, even when unenergized, to the valve 22 the distance the table 16 can move toward the grinding device 11 in response to the feed force.
  • the limit switch 19 is here responsive to an engagement with the end of the table 16 and is usually adjusted for actuation before, but only slightly before, the table encounters the positive stop 20.
  • a nozzle 26 supplies electrolyte to the grinding zone as further described in the above-mentioned Keeleric patent.
  • the positive side of a source S of low voltage D.C. potential is connected either directly to the workpiece W or it may be applied asv convenient to the workpiece W through the fixture 14, as shown.
  • the negative side of the source S is connected to the shaft or spindle 12 on which the grinding device 11 is mounted by means which, for example, may be the same as that disclosed in U.S. patent to Robischung et al., No. 3,115,454.
  • the source S may be of any convenient source of essentially ripple-free D.C. potential, which may be supplied by storage batteries but, in the practical case, is more usually supplied by an adequately rectified commercial line potential.
  • electropneumatic transducer 25 refers to a typical ECG apparatus utilizing a metal-bonded grinding wheel as the grinding device. It is recognized, of course, that other types of grinding devices already known in ECG processes, may be used with the above-discussed ECG apparatus, such as the abrasive belt means shown in U.S. patent to Bell, No. 3,162,588 or the abrasive disk means shown in U.S. application to Bell, Ser. No. 572,030, filed Aug. l2, l966,n0w abandoned, and assigned to the same assignee as the present invention and further detailed in U.S. Pat. No. 3,334,041.
  • the vECG apparatus described hereinabove forms no part of the present invention and is described solely for convenience in reference.
  • the invention resides in the method and apparatus concepts embodied in the control device, 27 which automatically controls both the voltage applied to the workpiece W by the source S and the table feed force by the electropneumatic transducer 25 to maintain the working current within the range R on the surface M (FIG. 7).
  • control apparatus 27 is responsive to the working current flowing through the conductor 28. This could alsoy be said to be responsive to the resistance across the gap between the workpiece W and the grinding device 11 since the measurement ⁇ of resistance is actually accomplished bythe measurement of current. In this particular system, however, the working current is detected by a shunting device 29 which supplies a signal through the conductor 31 to the control apparatsu 27.
  • the control apparatus 27 also provides a signal through conductor 32 to the electropneumatic transducer 25 for regulating changes in the table feed force above a preselected initial value, such as the force vprovided by a feed pressure of 3 p.s.i., upon the appearance of a Working current through the workpiece W. ⁇
  • the control apparatus 27 is also responsive to signals received from the limit switch 19 through the conductor 33 to control the valve 22 through a pair of conductors 34 and 35 to reverse the pressure applied to the cylinder 21 whereby to initiate a retraction thereof.
  • control apparatus 27 comprises three sections as illustrated in FIG. 12, namely, a timing section 36, an analytical section 37 and a logic section 38.
  • timing section 36 is responsive to timing ⁇ pulses of a predetermined timed interval to control the functions to be performed by the analytical section 37 and the logic section 38.
  • the timing pulses kare generated from a magnetic sensor 39 (FIG. 8) which is positioned in close association with the hub 41 of the grinding device 11.
  • the hub 41 may be provided with a plurality of magnetic pole pieces (not shown), for example, which, as the hub 41 rotates, are detected by the magnetic sensor 39 which in turn supplies a signal through the conductor 42 to the timing section 36.
  • the number of pulses per revolution can be any number so long as the analytical section 37 and the logic section 38 will vbe responsive to the signals generated by the timing section 36. In this particular embodiment, four pulses per revolution are generated and fed through the conductor 42 to the timing section 36.
  • a synchronized pulse train is generated at the output terminals 43, 44 and 4S of the timing section 36 and is applied through conductors 46, 47 and 48 to the analytical section 37 and through conductors 49, 50 and 51 to the logic section 38.
  • the analytical section 37 is responsive to the signal generated in the shunting device 29 and supplied thereto through the conductor 31. This signal represents an analog of the work current actually flowing through the workpiece W.
  • the analytical section 37 analyzes the signal received from the shunting device 29 and determines whether the voltage generated by the source S and the table feed force controlled by the transducer 25 should be increased or decreased. Once that determination has been made, a signal is generated and sent through the conductor 52 to the logic section 38.
  • the analytical section 37 also provides a signal through the conductor 32 to the electropneumatic transducer 25 (FIG.
  • the logic section 38 is responsive both to the synchronized pulse train from the timing section 36 and to the signal from the analytical section 37 which informs the logic section whether the voltage applied to the workpiece should be increased or decreased. The decision of the logic section is then sent through conductors 53 and 54 to the source S for either increasing or decreasing the voltage applied to the workpiece. A feedback signal is generated in the logic section 38 and sent through conductor 55 back to the analytical section 37 so that the analytical section is aware Iat all times of the condition of the source S.
  • the logic section 38 is further responsive to the signal received from the limit switch 19 through the conductor 33, which response is sent through the conductors 34 and 35 to the 'valve 22 for reversing the air pressure in the cylinder 21 and initiating the retraction of the table 16.
  • FIG. 13A illustrates one embodiment of the timing section 36, analytical section 37 and logic section 38 and FIG. 13B illustrates conventional starting and operating mechanism as modified to utilize the present invention. It is recognized that other circuits may accomplish the same result and, therefore, the following description is not intended to be limiting but is instead set forth solely to illustrate the invention.
  • the various gating circuitry is well known and only the symbol for the type of gate has been illustrated for convenience in reference. The gating nmenclature is illustrated and the characteristics are described in a publication by John L. Hughes, entitled Computer Lab Workbook (l968'ed.) published by Digital Equipment Corporation of Maynard, Mass.
  • the timing section 36 is supplied with spiked pulses from the sensor 39 through the conductor 42 and through a sensor converter 56 which converts the spiked pulses to square-wave pulses in order to obtain a more accurate and precise operation of the timing section 36.
  • a conductor 57 connects the sensor converter 56 to a counter 58 of any conventional type having a power input terminal 59 connected to any independent source 61.
  • three outputs are generated at the output terminals 43, 44 and 45, and supplied to the conductors 46, 47 and 48, respectively, and conductors 49, 50 and 51, respectively.
  • the output conductors 43, 44 and 45 of the timing section 36 are energized according to the table illustrated in FIG. 14, the shaded bars indicating the on condition of the respective outputs.
  • Conductors 46, 47 and 48 are connected, respectively, to the inputs of the AND gates 1 and 2, conductor 46 however, being connected to gate 2 through an inverter 69.
  • Conductor 48 is further connected to the winding 62 of a normally open relay 63 to oppose the power source 64.
  • the output 71 of the AND gate 1 is connected through the winding 72 of a normally closed relay 73 to oppose a power source 74.
  • the output 76 of the AND gate 2 is connected to input 1 of the up-down memory circuit 77.
  • the up-down memory circuit 77 may be of any conventional type such as a Data lip-op (one-half of a Digital Equipment Corporation K202) which has the characteristic of transferring the signal at input 2 to the output 122 when input 1 is enabled. That is, if input 2 is HI when input 1 is enabled, the output 122 will also be HI. If input 2 is LO when input 1 is enabled, the output 122 will also be LO.
  • the conductor 31 connects the shunting device- 29 to a pair of conductors 78 and 79 for supplying an analogue of the working current actually appearing in the working circuit to the analytical section 37.
  • the conductor 78 is connected to one terminal 81 of the relay 63, the other terminal 82 being connected through a variable Calibrating resistance GC-1 to the input 83 of amplifier A, which may be of any conventional type.
  • the input 83 is also connected to the terminal 84 of the relay 73.
  • the other terminal 86 is connected to the output 87 of ampliiier A.
  • a capacitor 88 whose function will be described hereinafter, is connected betwee the input terminal 83 and the output terminal 87 of amplifier A.
  • the output terminal 87 of amplifier A is connected to two conductors 89 and 91.
  • Conductor 89 is connected to the input 92 of amplier D.
  • Conductor 91 is connected to the input of ampliiier C.
  • Conductor 79 is connected through a gain control resistor 94 to an input terminal 96 of amplifier B.
  • the output terminal 97 of amplifier B is connected to three conductors 101, 102 and 103.
  • Conductor 101 is connected to the input 104 of the sensor converter 106 and to conductor 32.
  • conductor 32 is connected to the electro-pneumatic transducer 25 illustrated in FIG. 13B.
  • Conductor 102 is connected to the input 107 of ampliiier C.
  • Conductor 103 is connected to the input 108 of amplifier D.
  • amplifiers C and D are very high gain dilerential ampliers of the type which saturate very quickly when the potentials are according to the signs on the input terminals to produce an essentially on-oii output in response to a variable input.
  • the output 111 of ampliier C is connected to an input of AND gate 3.
  • the output 112 of amplifier D is connected to an input of AND gate 4.
  • the output 113 of AND gate 3 is connected to an input of an OR gate 5.
  • the output 114 of AND gate 4 is connected to another input of OR gate 5.
  • the output 116 of the sensor converter 106 is connected through a conductor 117 to one input of the NAND gate 6.
  • the other input of the NAND gate 6 is pre-enabled through the connection to a potential source 118.
  • the output 119 of the NAND gate 6 is connected to the remaining input of OR gate S.
  • the output 121 of OR gate 5 is connected to input 2 of the up-down memory circuit 77.
  • the output 122 of the up-down memory circuit 77 is connected through conductor 52 to an input of AND gate 7 in the logic circuit.
  • the limit switch 19 (FIG. 8) supplies a signal through the conductor 33 to a converter 123 which converts an A.C. signal into a digital signal.
  • the output 124 of the converter 123 is connected to two conductors 126 and 127.
  • the conductor 126 is connected through an inverter 128 to the remaining input to the AND gate 7.
  • the output 129 of the AND gate 7 is connected to three conductors 131, 55, (including 55A and 55B), and 132.
  • the conductors 55 and 55B are connected to the remaining input to AND gate 3.
  • the conductors 55 ,and 55A are connected throughan inverter 136to the remaining input to AND gate 4.
  • the conductor 127 is connected to the input to an adjustabletime delay 137.
  • the output 138 of the adjustable time delay 137 is connected to two conductors 141 and 142.
  • the yconductor 141 is connected to the winding 143 of a normally open relay 144 to oppose a potential source 146.
  • the terminals 147 and 148" of the relay ⁇ 144 are connected through a pair of conductors generally referred by 149 and 150 to supply a signal to the solenoid of the valve 22 in the section 225 (FIG. 13B) described hereinbelow to reverse the pressure in the cylinder to cause a retraction of the table 16.
  • the conductor 142 is connected to an input to NAND gate 8.
  • the other input of the NAND gate 8 is pre-enabled through a connection to a potential source 151.
  • the output 154 of NAND gate 8 is connected to the reset terminal 156 ⁇ on the counter 153.
  • a LO signal at terminal 156 will reset the counter to zero and a HI signal will maintain the counter in its then existing condition.
  • the output 129 of AND gate 7 is connected through conductor 131 tothe up-down controlling terminal 152 on a counter 153. More ⁇ particularly, the up-down controlling terminal .will accept either a HI or a LO signal which will cause the counter to either count up or count down.
  • a HI signal applied to the terminal '152 will result in an up count in the counter 153 during the rise of a pulse appearing at the input terminal 167.
  • a LO signal ⁇ applied to the terminal 152 will result in a down count in the counter 153 during the fall, or at ⁇ the trailing edge of a pulse appearing at the input terminal 167.
  • the power terminal 157 of thhe counter 153 s connected to a source of potential 158.
  • the counter 153 functions in the same manner as the counter 58 in the timing section 36. That is, the various levels 1, 2, 4 and 8 will be turned on and olf in predetermined patterns and in a conventional manner upon the arrival of successive pulses at counting terminal 167.
  • the counter section having the levels and 20 will be connected ⁇ in a conventional manner to count every pulse number 10 and 20, respectively.
  • the output 116 of the sensor converter 106 is also connected through a conductor 161 to an input to AND gate 9.
  • Conductors 49 and 50 from the timing section 36 are connected through inverters 162 and 163, respectively, to two inputs to the AND gate 9 and conductor 51 is connected to the remaining input.
  • the output 164 of AND gate 9 is connected to one input to AND gate 10.
  • the output 166 of AND gate 10 is connected to the counting terminal 167 of the counter 153. Whenever a pulse is received at the counting terminal 167, the counter 153 will be either counted up or counted down, depending on whether a HI or LO signal is present at the terminal '152.
  • the counter 153 is provided with a plurality of output terminals 17.1"-176 Each of the output terminals 171-176 except 172 and 173 is connected to the inputs to AND gate 11. Furthermore, each of the outputs 171-176 is connected through inverters to the inputs to AND gate 12. The remaining input'to AND gate 11 is connected to conductor 132 and the output 129 of AND gate 7. Conductor 132 is also connected through an inverter to the remaining input to AND gate 12. The outputs 177 and 1F78 of AND gates 1.1 and 12, respectively, are connected to the inputs toNOR gate
  • each of the normally open relays 19,1- 196 are connected to shunt, when closed, a plurality of series-connected resistors 201-206, respectively.
  • the resistors 201-206 are connected in any conventional manner to a control connection of a conventional DtC. generator S having output connections 211 and 212 and energized from a source 208.
  • the internal connections of the D.C. generator S are of a coventional type and in this instance arranged so that an increasing resistance in the serial group 201-206 will provide an increasing potential across the output terminals 211 and 212.
  • the resistors 201-206 are all in circuit and the voltage output of the generator S is at its maximum andas each resistor is, or selected groups of resistors are, shunted out of the circuit the voltage output of said generator is decreased by controllable increments.
  • the resistor 209 in the conductor 53- is to insure that a finite starting voltage will be produced by the generator S when the apparatus 10 yis initially energized.
  • the starting section 22'5 (FIG. 13B) is supplied by electrical energy from two of the three power lines L1, L2 and L3 which supply electrical power 'to the spindle motor :13. More particularly, the primary winding 2% of the transformer 227 is connected to the lines L2 and L3. The secondary winding 228 is grounded on one side at 22l9' on one side. The ungrounded side of the secondary winding 228 is connected through a fuse and master stop switch 231 to a conductor 232. The grounded side of the secondary winding 228 is connected to a conductor 233.
  • a series connected pair of switches 23-4 and 236 and a relay winding CRI are connected between the conductors 2%32 and 233'.
  • the switch 234 is normally closed and the switch 236 is normally open.
  • the normally open contacts CRI-1 of the relay ⁇ CRI are connected across the switch 236.
  • the normally open contacts CRi1-2, CRI-3 and CRI-4 are connected in series with the power lines L1, L2 and L3, respectively supplying the spindle motor 13.
  • the normally open contacts CRI-5 are series connected with a relay winding CRZ between the conductors 232 and 233.
  • the conductor (FIGS. 13A and 13B) is connected to the conductor 232.
  • the conductor 149 is connected to one side of a normally open switch 237.
  • the other side of the switch 237 is connected through a normally closed switch 238 and relay winding CR3 to the conductor 233.
  • the start switch 236 (FIG. 13B), is closed to energize the relay winding CR1 to close the contacts CR1-2, CR1-3 and CR1-4 and energize the spindle motor 13 to start the grinding device rotating.
  • Contacts CRil-l close to lock in the relay CR1 so that pressure holding the start switch 236 closed can be removed.
  • Contacts CR1-5 close to energize the relay CR2 to close the contacts CR2-1 and CR2-2 between the source 208 and the generator S (FIG. 13A).
  • the solenoid 239 on the valve 22 and the transducer as yet are unenergized so that the transducer 25 at this point supplies only a force corresponding to a 3 p.s.i. feeding pressure to the cylinder 21 to retract the piston 24 and worktable 16.
  • the apparatus is now in a condition for the operator to load a workpiece W into the fixture 14. After the fixture has been loaded, the operator then closes the manual switch 237. Since the limit switch 19 is not as yet supplying a signal on the conductor 33, the relay 144 (FIG. 13A) is energized by the source 146 to close the contacts between the terminals 147 and 148 and conductors 149 and 150.
  • the apparatus is accordingly started and the workpiece is about to contact the grinding device.
  • working current will oW and the process and apparatus of the invention will be started.
  • the magnetic sensing device 39 (FIG. 8) will pick up pulses from the magnetic pole pieces (not shown) connected to the hub 41 of the grinding device 11 when the grinding device 11 is rotating and will supply a series of pulses spaced apart a predetermined time interval to the control apparatus 27.
  • the timing pulses are transmitted to the timing section 36 through the conductor 42 so that a synchronized pulse train is produced in varying patterns on each of the output terminals 43, 44 and 45 of the timing section 36.
  • FIG. 14 illustrates the intervals during which the output terminals 43, 44 and 45 are respectively turned on and of.
  • the conductor 43 is turned ott during time interval I, turned on during interval II, turned off during interval III and continuing alternately on and oii through the remaining time intervals illustrated in FIG. 14.
  • Output terminal 44 is turned off for two time intervals I and II and then turned on for two time intervals III and IV and then turned off again for two time intervals V-VI and so on.
  • Output terminal 45 is turned off for four time intervals I-IV and then turned on for four time intervals V-VIII and is then turned off for four time intervals I-V during the next cycle of eight time intervals.
  • all of the terminals 43, 44 and 45 are turned oi.
  • At all time intervals VIII all of the output terminals 43, 44 and 45 are turned on.
  • the control 27 is energized and the wheel is rotating but for the moment assume that the operator has not closed the start switch 237.
  • the workpiece W is not engaging the grinding device 11 and, as a result, no working current will iiow.
  • there is no current on conductors 31, 78 and 79 so that capacitor 88 cannot be charged and there is no input to ampliers A and B.
  • This provides a LO signal on the conductor 117 connected to one input of NAND gate 6.
  • the HI signal at input 2 of the up-down memory circuit 77 will remain until time interval VII wherein AND gate 2 is turned on so that the HI output at terminal 76 will be fed to input 1 of the up-down memory circuit 77 to cause the HI signal at input 2 to be transferred to the output terminal 122.
  • the signal at the output terminal 122 will be conducted through conductor 52 to an input of AND gate 7. Since the end of the table 16 is spaced away from the limit switch 19, there will be no signal supplied to the converter 123 and in turn no signal supplied to the conductors 126 and 127. Thus, there is no current through the time delay circuit 137 and none on the winding 143 to oppose the source 146.
  • the relay 144 Will be energized to close the contacts between terminals 147 and 148.
  • the inverter 128 will result in an input to AND gate 7 and since both inputs will then be enabled, a HI signal will exist at the terminal 129 which will be fed through the conductor 131 to the up-down terminal 152 of of the counter 153, -whereby NAND gate 6 assures that the counter 153 will be set to count up to increase the voltage as soon as a working current is present regardless of the condition thereof at its last previous operation.
  • the signal on conductor 48 will be LO whereby there is no potential to oppose the potential source 64 and same will energize the winding 62 of the normally open relay 63 to cause the terminals 81 and 82 to close.
  • AND gate 1 will be turned olf so that the potential at the output 71 will be LO to thereby permit the potential source 74 to energize the winding 72 of the normally closed relay 73 to open the normally closed connection between the terminals 84 and 86.
  • conductor 48 will be HI so that the voltage applied to relay I63 from source 64 will be opposed and relay 63 will thereby become de-energized and the terminals 81 and ⁇ 82 will open.
  • the charging of the capacitor 88 is terminated and the potential thereon is stored.
  • the new value of voltage U above mentioned will result in an increase in the instantaneous current detected by the shunting device 29, which will, in turn, supply a new signal through the conductors 31 and 79 to amplifier B which vwill then supply a signal to the inputs 107 and 108 ofv amplifiers C and D, respectively. If the instantaneous voltage value U is higher than the stored value T on the capacitor 88, amplifier C will saturate and produce an on output so that a HI signal is supplied to an input of AND gate 3.
  • conductor 43 is LO and conductors 44 and 45 are HI.
  • AND gate 2 being turned on so that a HI signal is supplied to input 1 of the up-down memory circuit 77.
  • the signal at input 2 of circuit 77 will be transferred to the output 122 and sent through the conductor 52.to AND gate 7. Since both gates of the AND gate 7 ⁇ are now enabled, a HI signal ⁇ will be present at the output 129, which HI signal will'be supplied to the terminal 152 on the counter 153. ⁇ This will signal the counter 153 to perform an up count upon the occurrence of the next counting pulse to the terminal 167.
  • the varying signal on the conductor 32 represents an analog of the working current and will varyingly energize the electro-pneumatic transducer 25.
  • the transducer 25 will increase the pressure applied to the valve 22 and cylinder 21 with increasing magnitudes of current on the conductor 32.
  • the transducer will decrease the pressure applied to 16 the valve 22 and cylinder 21 with decreasing magnitudes of current on the conductor 32.
  • the value by which the transducer permits the pressure to increase relative to increase in working current is regulatable by the variable resistor GC-2.
  • the amount of pressure increase or decrease can be set so that the values of voltage and working current searched for will be maintained on the surface M as illustrated in FIG. 7.
  • yfurther discussion of the control of the feed force will be deferred until later after the discussion relating to the control of the voltage and the variations in the working current have been more fully developed and as hereinafter described.
  • relays 63 and 73 will perform in the same manner as discussed hereinabove with respect to the first occurrence of a time interval I. However, the capacitor 88 will now charge to the new voltage value U. At the beginning of the second time interval V, relay 63 will again be de-energizled and the contact between terminals 81 and 82 will again be opened. This will result in the capacitor 88 this time storing a voltage equal to the value represented by U and applying said potential to terminals 92 and 93 of amplifiers D and C, respectively.
  • AND gates 9 and 10 will be turned on to supply a pulse to terminal 167 to advance the counter 153 one count. This will result in an incremental increase in voltage to a new value X.
  • This new incremental increase in voltage will be detected by the shuntng device 29, which in turn will supply a signal through conductors 31 and 79 to amplifier B and to the inputs 107 and 108 of amplifiers C and D, respectively.
  • the difference between voltage value U and voltage value X is now below a predetermined minimum.
  • relay 63 will close to connect the terminals 81 and 82 together and the relay 73 will be opened to disconnect the terminals 84 and 86.
  • the capacitor 88 will be charged through the conductors 31 and 78 to the voltage value X.
  • relay 63 is de-energized to discontinue the charging of capacitor 88.
  • the voltage value X will be stored on the capacitor 88 and supplied to the linputs 92 and 93 of amplifiers D and C, respectively.
  • the inputs to AND gates 9 and 10 are enabled so that a counting pulse will appear at the terminal 167 of the counter 153. Since the signal at terminal 152 is LO, the counter will count down to thereby decrease the volt- 17 age by an incremental value. This value has been represented by Yin FIG. 14.
  • the incremental decrease in voltage is detected by the shunting device 29 and a signal is supplied through conductors 31 and 79 to amplifier B and the inputs 107 and 108 to amplifiers C and D. Since, in this particular example, the instantaneous voltage value Y is less than the stored value X on capacitor 88, but said difference being greater in value than said predetermined minimum, amplifier D will saturate and be turned on so that a HI output is generated at 112 and is supplied to an input of AND gate 4.
  • a LO signal is supplied through conductors 55 and 55A to the inverter 136, which inverts the signal to a HI signal to enable the remaining input to AND gate 4 to generate a HI signal at the output 114.
  • This HI output is then supplied to an input to OR gate 5, which HI signal is then transferred to the output 121 and thence to input 2 of the up-down memory circuit 77.
  • the signal on the counter 153 will continue to indicate a down count and the voltage will be reduced again.
  • the signal on the counter 153 will again reverse and call for an up count. In this manner, the cycles will repeat in the manner above described and the voltage and resulting current will cycle back and forth in a region between A and B of said current-voltage curve as appearing in FIGS. 1 and 11.
  • the operation as described will maintain the applied voltage at the desired value and maintain the working current at its maximum even when the sluggish response of the generator to initial voltage increases causes an overshooting of the crest of the current-voltage curve of FIG. 1.
  • the logic decision to decrease voltage even though it does not appear until region B-C of FI'G. 11 has beenvreached will continue until points B or A are reached and finally will stabilize at about point A as previously described.
  • the apparatus will work acceptably for certain purposes as above described if the table feed force is maintained at a constant value. However, the apparatus will work t 18 the full intent of the invention if the table feed force is also made variable. That is, and referring now to the preferred embodiment embodying a control of the feed force with reference being had to FIGS. 7, 11, 13A and 13B, the fluctuations in the working current will be detected by the shunting device 29 and fed to the B amplifier through the conductors 31 and 79. As the working current increases, a signal of increasing magnitude will be fed from the output of amplifier B by conductor 32 to the transducer 25 to increase the air pressure supplied to the valve 22 and cylinder 21 to urge the workpiece against the grinding device with an increasing force. Likewise, when the magnitude of the current diminishes, the magnitude of the pressure will decrease correspondingly to decrease the force urging the workpiece against the grinding device.
  • the conductor -142 will supply a HI signal to NAND gate 8 so that both inputs are then enabled. This will result in a LO signal at output 154 and terminal 156 to reset the counter 153 to zero.
  • the delayed signal at the output 138 will be supplied through the conductor 141 to oppose the source 146 resulting in a de-energization of the winding 143 of the relay 144.
  • the relay 144 is in series with the table advancement circuitry consisting of the relay CR3, the table advancement will be discontinued upon breaking the circuit between the conductors 34 and 35 to de-energize the solenoid 239 of the valve 22 to reverse the air supplied to the cylinder 21 so that the table 16 and workpiece W are retracted from the grinding from the grinding device 11. Since the counter 153 has already been reset to zero, the current is low and the transducer will have reduced the air pressure supplied to the valve 22 to 3 p.s.i. Then, the table 16 will retract at a force corresponding to such 3 p.s.i. feeding pressure.
  • FIG. 15 is essentially identical to the embodiment illustrated in FIG. 8. However, in this embodiment, the working current flowing t0 the workpiece W is not the parameter which is detected. Instead, a sensing device 216 for detecting the power drawn by the spindle motor 13 is placed in sensing relationship with the input lines L1, L2 and L3 to the motor.
  • the control system 27A is constructed so that it will be sensitive to a condition of minimum power at a given operating feed force (lFIG. 3), which minimum power assuming a table feed force of 31 pounds, for example, occurs in the voltage range of approximately 6-7 volts for the grinding conditions above described with respect to which these data were collected.
  • the signal produced by the, sensing device 216 is supplied through a conductor 217 to the control device 27A.
  • the conductor 217 corresponds tothe conductor 31 in FIG. 1-2.
  • the desired operating point would be at the actual point of minimum spindle power. It will be understood that in" many instances of commercial usage, the preferred operating condition may be at some point more or less offset from, and on either side of, such point of absolute minimum. This also parallels the situation in connection with FIGS. v8-14 in which for illustrative purposes the operating condition was assumed to be one of maximum working current but wherein an actual operation might be, and within the scope of the invention could be, located ata selected point more or less Oifset therefrom.
  • the lembodiment illustrated in FIG. 16 is essentially identical to the embodiment illustrated in FIG. 8. However, in this embodiment, a servo 218 is utilized, the output of which has a feed rate detector 219 to sense the rate of rotation of a screw 221 and a feed force sensor 220 to provide proper limits of feed force and to provide a further input signal to theV control 27B.
  • the table 16 is advanced or rretracted- ⁇ by an appropriate rotation of the screw member 221: v,The rate signal indicating the rate at which the screw 221 is rotated will be supplied through conductor 222 to the ⁇ control apparatus 27B.
  • the control device 27B will be responsive to said rate signal to supply a signal through the conductor 223 to control the rotational speed and direction'of rotation to the servo 218.
  • the control apparatus 27B will respond to increase the speed of the servo 218 through a signal sent through the conductor 223, one feed rate being sampled and compared with a subsequent feed rate in the same manner as above described with respect to the shunt current appearing on conductor 31 and the voltage is then adjusted'up or down to maintain the feed rate nearer butto thetleft of the peaks shown in FIG. 2 as associated with feed pressure of
  • the electrical system will be precisely the same for this embodiment as that illustrated and described -above for the gapmbodiment excepting only that the currentuappearing on conductor 31 will be taken from the-sensor 219 and will be proportional to the feed rate rather than as previously to the working current itself.
  • the feed force sensor 220 will maintain the preferred relationship with the feed rate so that the operating point of the machine will be maintained within a predetermined range similar to that shown in FIGS. 7 and 7A.
  • any other means for producing such pulses at a reasonably accurate rate will be acceptable provided only they are rapid enough to control the applied voltage in close relationship to the grinding conditions including such variable conditions as changing of the surface area of the workpiece as a result of the grinding operation, and provided further that they are not so rapid as to exceed the capacity of the rest of the equipment to respond thereto.
  • the rate of such pulses may be freely varied by varying the number of magnets or other magnetic or inductive devices used for this purpose on said spindle or, if necessary to accommodate a relatively slowly responding voltage generator.
  • the counter 36 may be arranged to respond only to multiples of pulses such as counts of 2, 4 and 8 instead of as shown to respond to single pulses in counts of l, 2 and 4.
  • the apparatus shown is sensitive only to one performance parameter, namely, the amperage of current flowing between the workpiece and the grinding wheel and is adapted to control two control parameters, namely, the voltage provided to supply the working current and the feed force.
  • performance parameters may be sensed and either applied jointly to the input 31 of the analytical section 37 or each of such performance parameters to be sensed may be provided with a separate analytical section whose output is then applied jointly to the logic section 38 and to the table feed device.
  • an electrolyte supply for supplying electrolyte between said grinding device and an electrically conductive workpiece and power source means for establish ing a potential difference between said grinding device and said workpiece and establishing a flow of current between said grinding device and said workpiece, the magnitude of said current being proportional to the magnitude of said potential difference and having at least one inlection point therein over the range of variation of said current
  • apparatus for searching through and maintaining a control of the conditions of an electrochemical grinding operation on said workpiece to maintain an optimum operating condition comprising in combination:
  • timing means producing a series of timing pulses foi energizing a plurality of conductors simultaneously in multiple patterns; sampling means connected in circuit with said power source means and responsive to one pattern appearing on said conductors for sampling the value of current applied at a given instant between said workpiece and said grinding device; memory means connected in circuit with said sampling means for remembering the value of said sampled current;
  • logic means responsive to different patterns on said conductors and operative at a period in time subsequent to said sampling for responding to a previous condition of said apparatus and altering the voltage applied between said grinding device and said workpiece, said logic means being responsive in one direction to signals indicative of an increase in current in response to a selected increase in voltage of one magnitude and responding in an opposite direction to pulsesindicative of an increase in current in a different magnitude resulting from a further selected increase in voltage whereby the response in one direction progressively and stepwise increases the voltage applied to ithe system and in response to signals in the opposite direction, stepwise and progressively decreases the voltage;
  • comparison means connected in circuit with said memory means and said sampling means for comparing said remembered current and an instantaneous value of current flowing between said grinding device and said workpiece subsequent to said altering and issuing a signal indicative of the relationship between said remembered value and said instantaneous current;
  • control means applying said signal to said logic means for further altering the voltage applied between said workpiece and said grinding device as needed to maintain said current flow in a zone encompassing said inflection point.
  • the apparatus defined in claim 1 including pressure control means controlling the pressure at which said workpiece is urged against said grinding device, said pressure control means being responsive to the magnitude of the instantaneous value of current to regulate the magnitude of pressure at which the workpiece is urged against the grinding device simultaneously with the above-mentioned changes in voltage.
  • an electrolyte supply for supplying electrolyte between said grinding device and an electrically conductive workpiece and power source means for establishing a potential difference between said grinding device and said workpiece
  • apparatus for automatically searching through and maintaining a control of the conditions of an electrochemical grinding operation on said workpiece to maintain an optimum operating condition,v the combination comprising:
  • control parameter generating means for generating a variable control parameter to control the electrochemical grinding operation on said workpiece about said optimum operating condition
  • performance parameter generating means for generating a varying performance parameter in response to sa-id machining operation, the magnitude of sa-id performance parameter being proportional to the magnitude of said control parameter and having at least one inflection point therein over the range of variation of said performance parameter;
  • detecting means connected in circuit with said performance parameter generating means for detecting said performance parameter and producing a signal proportional to said performance parameter, said detecting means including first means for sampling and remembering a value indicative of the performance parameter, second means for incrementally varying the control parameter to vary the performance parameter, means for comparing with the remembered value a numerical value indicative of the performance parameter following the varying of the control parameter and issuing said signal indicating the manner, if any, by which said performance parameter has changed; and
  • control means connected in circuit with said detecting means and responsive to said signal, said control means including interpreting means for detecting a zero differential at said inflection point in said signal, which zero differential defines said optimum condition, said interpreting means interpreting said signal and altering said control parameter in response to said signal for further altering said performance parameter as required for maintaining said performance parameter at said optimum condition.
  • the apparatus of claim 3 including means for generating a second variable control parameter to further control the electrochemical machining operation on said workpiece, said second control parameter also producing said varying performance parameter, the magnitude of which is also proportional to the second control parameter, said first-mentioned control parameter, said second control parameter and said performance parameter, when varied over a given range, defining a contoured surface having at least one peak condition thereon, said control means being responsive to said signal generated by said detecting means to maintain said performance parameter at said peak condition.
  • a working gap is defined between said workpiece and said grinding device, and wherein said power source means comprises f electrical power generating means connected across said working gap and adapted to cause a working current to flow through said working gap, and wherein said performance parameter is the gap resistance across said working gap- 9.
  • said power source means comprises electrical power generating means connected across a working gap between said workpiece and said grinding device and adapted to cause a working current to flow through said working gap, and wherein said performance parameter is the ratio of working current to the input power to the motor.
  • the performance parameter is the working current
  • said first means samples and remembers the value of the current flowing prior to a predetermined point in time
  • said second means signals the point in time and thereupon incrementally varies the magnitude of the instantaneous current flowing between the workpiece and the grinding device
  • said comparing means compares the magnitude of the altered current flowing after the point in time with the value of the remembered current and issues a signal indicating which thereof is greater
  • said control means is responsive to the last-named signal for maintaining the working current at said optimum condition.
  • said comparing means for indicating the manner of the change of the performance parameter is further adapted to produce a signal indicating both the magnitude of such change and the direction of such change and wherein said interpreting means is vresponsive to the last-named signal for altering the control parameter in one direction if the performance parameterl is changed in one direction and for altering the control parameter in another direction when the change of the performance parameter is in another direction.
  • said interpreting means includes means for altering the control parameter in one direction if the performance parameter changes by a predetermined amount in one direction, for maintaining the control parameter unchanged if the per- Z4 formance parameter changes less than a predetermined amount in each direction and for altering the control parameter in the opposite direction if the performance parameter changes by an amount exceeding a predetermined minimum and in the opposite direction.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Constituent Portions Of Griding Lathes, Driving, Sensing And Control (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
US774009A 1968-11-07 1968-11-07 Electrochemical grinding apparatus Expired - Lifetime US3697403A (en)

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CH (1) CH520540A (de)
DE (1) DE1955515A1 (de)
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4367389A (en) * 1978-10-12 1983-01-04 Inoue-Japax Research Incorporated EDM System with abrasive finisher
US5286355A (en) * 1991-08-12 1994-02-15 The Johns Hopkins University Electrochemical wire sharpening device and method for the fabrication of tips
US20100243430A1 (en) * 2009-03-27 2010-09-30 Biing-Hwa Yan Apparatus and method for magnetic field assisted electrochemical discharge machining
US20160031026A1 (en) * 2014-07-29 2016-02-04 Faraday Technology, Inc. Method and apparatus for pulsed electrochemical grinding

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109108414A (zh) * 2018-10-26 2019-01-01 辽宁科技大学 航空航天3d打印件异形孔内表面光整加工的设备及工艺
RU2768103C2 (ru) * 2020-02-06 2022-03-23 Общество С Ограниченной Ответственностью "Есм" Система для электрохимического абразивного шлифования

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4367389A (en) * 1978-10-12 1983-01-04 Inoue-Japax Research Incorporated EDM System with abrasive finisher
US5286355A (en) * 1991-08-12 1994-02-15 The Johns Hopkins University Electrochemical wire sharpening device and method for the fabrication of tips
US20100243430A1 (en) * 2009-03-27 2010-09-30 Biing-Hwa Yan Apparatus and method for magnetic field assisted electrochemical discharge machining
US8652307B2 (en) * 2009-03-27 2014-02-18 National Central University Apparatus and method for magnetic field assisted electrochemical discharge machining
US20160031026A1 (en) * 2014-07-29 2016-02-04 Faraday Technology, Inc. Method and apparatus for pulsed electrochemical grinding
US9403228B2 (en) * 2014-07-29 2016-08-02 Faraday Technology, Inc. Method and apparatus for pulsed electrochemical grinding

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GB1283083A (en) 1972-07-26
CH520540A (de) 1972-03-31
FR2022799A1 (de) 1970-08-07
DE1955515A1 (de) 1971-12-30

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