Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B55/00—Safety devices for grinding or polishing machines; Accessories fitted to grinding or polishing machines for keeping tools or parts of the machine in good working condition
  • B24B55/02—Equipment for cooling the grinding surfaces, e.g. devices for feeding coolant
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B49/00—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation
  • B24B49/14—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation taking regard of the temperature during grinding

Definitions

• the invention relates to a device according to the preamble of claim 1.
• the grinding process is to produce the final shape, for which partial deviations of only a few micrometers are permissible. Ande hand, require economic considerations, since / is taken two superiors the hard or fine machining in the shortest possible time, to achieve a maximum workpiece output per machine and per unit time.
• the finishing process is carried out with high related chip removal volumes, i. H. with a maximum
• ERSATZBL ⁇ TT (REGEL26) Number of cubic millimeters removed per second of grinding time and per millimeter of grinding wheel width. The limit of the optimization capability is reached, however, where work is carried out with such high feed rates that the grinding wheel is on the contact surface
• the grinding fire can be triggered by different causes.
• the most common causes are:
• the invention is based on the object of developing a device for a method for avoiding thermal overloads on workpieces during grinding according to the preamble of claim 1 in such a way that reliable detection of grinding burn is achieved.
• ERSA ⁇ ZBLA ⁇ (RULE 26) or rubbing, all mechanical energy absorbed is always converted into thermal energy. Almost all the energy supplied to the system by the machine tool spindle in the form of drive energy is converted into thermal energy in the grinding process and must be coped with by the workpiece.
• the resulting grinding burn has the effect of converting too much mechanical energy into thermal energy per unit of time and per processed surface.
• the converted thermal energy is determined for the two tooth flanks to be machined simultaneously. Here it must be determined how the energy introduced is distributed over the two tooth flanks. What is important is not the measure of the total energy introduced, but the maximum value that occurs on each tooth flank. If the measured thermal energy exceeds a predetermined threshold value, the presence of grinding burn must be concluded.
• the feed rate can be increased. If the feed rate is regulated in such a way that the risk dimension always remains below the threshold value, it is possible to drive at a high feed rate under otherwise good conditions (good disc, small measurement problems).
• the orientation of the feed speed takes place on the condition of the grinding wheel and regulates it continuously in accordance with dimensions.
• the spindle speed is detected to determine the energy expended.
• the energy of the drive unit can be determined from this.
• the energy which is converted into thermal energy in the tooth gap during the grinding process is essentially determined by the dimensions and the grinding force of the grinding wheel.
• the temperature in turn is determined by the energy used per time and area.
• the time is determined by the feed rate, while the grinding surface is a constant size.
• the surface is not constant only if the pitch error, depending on how centrally the grinding wheel is inserted into the tooth gap, is so great that one side of the flank remains partially or completely unground. But then the other flank has a correspondingly large oversize.
• the pitch error results as a function of how centrally the grinding wheel is inserted into the tooth gap.
• the energy expenditure per time is expressed in the reduction in the speed of the drive spindle and in the change in the spindle current.
• the current of the dividing device is now additionally measured, a statement is made about the measurement distribution on the two sides being machined. If there is a division error, the energy is converted asymmetrically on the flanks and one flank becomes hotter than the other.
• the oversize or the oversize distribution represents a particularly critical grinding burn factor.
• the speeds to be determined can be recorded via inductive sensors or rotary pulse generators. Any other type of speed determination, such as tachometer generators, rotation angle sensors, etc., can also be used.
• the motor current from the dividing head can be or shunt resistance in the control part of the electric motor driving the sub-apparatus can be measured.
• This speed reduction can be up to 8% of the idle speed.
• the speed then attains a stable value during the machining time in the gap.
• the engine speed increases and then reaches idle speed. This speed curve is repeated when machining every tooth gap.
• the detection of the grinding burn is based here essentially on the stable speed value within the gap. This allows the types of grinding burns to be recorded at the end of the gap or across the entire gap.
• the gradient of the speed signal at the gap entry must be evaluated for the grinding fire situation at the gap entry. The steeper the drop, the higher the oversize or the more asymmetrical the oversize distribution.
• the motor current of the sub-apparatus is the current which is necessary to carry out the rotation of the axis of the dividing device during the grinding of a helical toothing.
• the area within the tooth gap is evaluated.
• the motor current changes due to the difference in dimensions between the left and right tooth flank, which causes the grinding wheel to rotate or counter-rotate the axis of the dividing head.
• the dividing device that acts as a workpiece holder serves at the same time as a means for recording the initiated moment.
• the motor current of the antiperspir.- del is used as a further influencing variable. If speed drops caused by the network fluctuations occur, a change in output is also taken into account with the aid of the motor current of the drive spindle. Without this additional consideration, lower speed values would lead to a supposedly high energy conversion and the feed would then be unnecessarily reduced.
• the permanently evaluated influencing variables motor current and speed control the feed speed of the drive spindle internally in the machine.
• the feed speed is always driven in such a way that the determined and calculated values always result in converted energy below a predetermined threshold value.
• the feed speed can be regulated individually so that the energy converted runs with a certain safety distance below the threshold value, almost at a distance that is the same. If there is now an increase in the energy converted, the feed rate is reduced in accordance with this energy increase, so that the threshold value is not exceeded. As a result, no grinding burn occurs in the machined workpiece and the workpiece can be further processed without restriction. The processing time is extended due to the reduced feed rate, but the workpiece does not have to be sorted out due to grinding burn. Thus, if necessary, sic.i reduces the feed rate to a predeterminable minimum value. Experience has also shown, however, that soiled grinding wheels affected by grinding burn.
• REPLACEMENT BUTT (RULE 23) have undergone self-cleaning through the machined workpieces after a certain time. Grinding disks which have once produced grinding burns or which have come close to grinding grinding production can therefore subsequently become grinding wheels again with normal working conditions. Then, with permanent monitoring, the feed speed of the drive spindle can be increased again after the self-cleaning has taken place and the threshold value can be approached again.
• optical display devices for example in the form of light-emitting diodes, scales with liquid crystal displays, screens or other such means, can be provided.
• acoustic display means can also advantageously be provided, which notify an operator of the observation of, for example, optical display means.
• a display device could, for example, be configured as follows:
• Scales for each gear and a scale for the condition of the grinding wheel are provided on a display.
• Each scale has extreme value pointers that show how high that is
• the data determined and the analysis carried out from these values are logged in an internal memory.
• This memory is preferably battery-buffered separately, so that even in the event of a power failure of the processing machine, the backup of the
• a simplified display device in the form of light-emitting diodes can also be arranged.
• a green LED could indicate "no grinding fire” and a red LED "grinding fire”
• the control system works in the processing machine as follows: First, a new mandrel equipped with gears is inserted into the processing machine. The new feed rate for this mandrel is based on the set feed rate of the last dome, but is initially only set to half this value. Then there is a gap across all assembled
• the feed rate is increased or, if necessary, reduced in order to move the processing machine as close as possible below the critical threshold value. This results in a short machining time for the individual workpieces.
• the adjustment of the feed rate to higher or lower values is repeated from tooth gap to tooth gap and is calculated in each case from the determined values.
• This control system is used to orientate each mandrel based on the condition of the grinding wheel. Appropriate caution is used to approach the critical threshold value, which indicates grinding burn, and to regulate in such a way that different dimensional distributions on the tooth flanks of a tooth gap are taken into account.
• the throughput of machined workpieces can be significantly increased by the optimally high feed rate, which takes into account all the parameters currently available.
• a 100 percent grinding fire check is carried out at the same time, so that no rejects are produced by the processing machine. The material losses are therefore almost zero.
• the possibility of cleaning the grinding wheels is taken into account by the control system, so that after Withdrawal of the feed due to a contaminated grinding wheel, the feed speed can be increased again after self-cleaning the wheel.
• the disk remains in use, can be reused, soot cannot be exchanged and removed, but can continue to be used for production. This Aspe also leads to cost reductions without exposing workpieces to the risk of grinding burns.
• the measurement of the current consumption of the dividing device or an equivalent signal, from which the torque that is introduced in the work piece carrying the mandrel can be inferred, leads to a measure for the asymmetry of the dimensional distribution of the two tooth flanks of a tooth gap.
• the cause of the grinding fire is the conversion of too much kinetic energy into thermal energy. Since the thermal energy that is introduced into a workpiece cannot be measured at all on the workpieces or the tools, or can be measured only with great effort, a virtually instantaneous measurement of the kinetic energy of the drive spindle currently present is the corresponding assessment factor.
• the kinetic energy of the drive spindle is composed of the rotational energy of the spindle motor and the drive spindle and of the electrical power that is currently being converted into kinetic energy in the motor.
• the amount of the converted kinetic energy in the tooth flanks is shown directly by the graded speed drop.
• the speed of the drive spindle must therefore be measured and evaluated.
• the drive spindle evaluate impulses.
• a magnetic pick-up can be arranged on the upper part of the spindle housing and measure the periodic rotation of components attached to the spindle. Such components could be screw connections arranged on the spindle. Rotation intervals can then be calculated from this.
• the converted energy is distributed over the two tooth flanks that are currently being processed. As i ⁇ itself *. can be determined from the current of the dividing device.
• the dividing device as a component of the machine tool rotates the mandrel carrying the workpieces, while the grinding spindle moves longitudinally.
• the flanks of the toothed wheel endeavor to support or inhibit the rotation of the dividing device.
• the drive of the king's thorn strives to remove this support or inhibition and exerts a braking or accelerating moment. This is expressed in the size and polarity of the power consumed by the dividing device.
• the current drawn by the dividing device is thus a measure of the asymmetry of the energy input into the two flanks to be ground.
• Strain gauges on the bearing block of the dividing device can provide more precise values of the braking or acceleration torque. They are not subject to a regulation-related hysteresis. This applies equally to a torque measuring shaft, which can be arranged between the dividing head and the kingpin. This measuring shaft delivers a torsional moment as a measure of the asymmetry of the energy input into the flanks to be ground.
• the risk of grinding burn manifests itself essentially in two ways: First, it manifests itself in a slow way, whereby the active surface of the grinding wheel is reduced. This is due to the fact that the spaces between the splinters embedded in the grinding wheel become clogged with abrasion. This process happens purely by chance through the distribution of the splinters and can be triggered by measurement errors. But it is reversible if you give the disc time to recover and clean. The cleaning process required for this is, for example, a
• each tooth flank can offer a measurement error that causes the drive spindle to slow down sharply when the grinding wheel enters the tooth gap.
• the change in the rotational energy of the drive spindle is used as a measured variable and compared with a learned speed degree in order to determine the risk of grinding burns. If the rotational speed drops particularly sharply when entering a tooth gap, this is an indication of the beginning of an initial grinding fire at the beginning of the tooth gap.
• the feed rate is no longer based on a compromise between the tolerable failure probability and the economic limit, but on the current condition of the grinding wheel and gear.
• the drive spindle absorbs little energy when the grinding power is good, while it shows high energy consumption when the grinding power is poor.
• grinding residues on the components to be machined can remain in the tooth gaps, for example, and have to be removed. It may also be necessary to remove grinding residues from the grinding device, for example the grinding wheels.
• the pores clog between the grains with grinding residues embedded in the carrier material of the wheel.
• Clogged grinding wheels lead to an increased risk of grinding burns. It is therefore advantageous to free the grinding wheels from the grinding residues by spraying during the grinding process and thus to maintain the optimum grinding properties of the grinding wheel.
• a fluid stored in a high-pressure accumulator for example a coolant
• This injection can be permanent take place, but it is preferably carried out at intervals. These intervals can be specified, but they can also be derived from the running grinding process with computer assistance. In this way, the intervals in abrasion areas with high stock removal can be made shorter than in areas with smaller stock removal.
• the pressure in the high-pressure accumulator must be sufficiently high to ensure that the tooth gaps are sprayed freely.
• the pressure can also be adapted adaptively with computer support.
• the appearance of grinding burn can serve as an adjustment criterion.
• the filling speed of the high-pressure accumulator can also be adjusted adaptively, for example after the grinding fire has started. If, for example, spraying is carried out at short intervals and at high pressure, the filling speed must be designed to be correspondingly high or determined and set and set by the computer.
• the refilling process of the high-pressure accumulator can be carried out by a suitable pump that runs continuously. However, it is also possible to start the pump only when the pressure in the high-pressure accumulator drops below a predeterminable value, so that the pump depending on. required pressure can be regulated. A small pump can be provided if it does not have to permanently provide high pressure.
• levels of 0%, 1%, 2%, 5% and 10% are carried out in a percentage range between 0 and 10%.
• Levels of 20%, 50%, 80%, 90% and 100% are provided between 10% and 100%.
• Lending levels of 110%, 120% and 150% are arranged for the range between 100% and 150%.
• monitoring circuits which can also be designed to be redundant and / or diverse.
• a monitoring circuit there is, for example, at least one comparator circuit which compares reference values stored in a memory with currently determined values and theirs Plausibility checked. Test values can also be supplied to these comparator circuits at certain intervals so that the comparator circuits are checked for their functionality. Values identified as faulty can be stored in a fault value memory and made available for later review.
• the monitoring can also be formed from various monitoring circuits. For example, in addition to a monitoring circuit made of hard-wired circuit logic, a second monitoring circuit can be set up by a software program running on a computer.
• Fig. 4 is a side view of Detailapparat- and
• Fig. 6 shows a modified switch
• Fig. 7 is a schematic pressure cleaning system.
• the longitudinal grinding process with a single-profile grinding wheel be used.
• the single-profile grinding wheel only has the profile that is to be created lying between two teeth in the gear wheel to be ground.
• the schematic representation of such a single-profile grinding wheel can be seen in FIG.
• 1A shows a gearwheel 2, of which only the two teeth 4 and 6 are shown for better clarity.
• the tooth gap 14 formed by the opposing tooth flanks 8 and 10 and the tooth base 12 lying between them should be ground by means of a single-profile grinding wheel 16.
• the design of the outer contour of this grinding wheel corresponds to the design the inner contour of the tooth gap 14 to be ground.
• a gearwheel 2 is shown in perspective, of which only the two teeth 4 and 6 are also shown, for the sake of clarity.
• the grinding surface underlying the machining is shown hatched in FIG. 1B.
• the gearwheel 2 is arranged on a holder 17 (king pin) which belongs to a grinding machine, as shown in FIG. 2. Due to the grinding of the hatched, emphasized grinding surface, temperature increases occur on this grinding surface, which can lead to thermal structural changes in the workpiece surface layer if these temperature increases exceed certain limit values.
• 2 shows a generally used grinding machine unit 18, which is used for grinding gear wheels.
• a machine table 22 is arranged on a machine bed 20.
• a control cabinet console 24 carries an operating console 26, which is provided with a clamping lever 28, whereby the operating console 26 can be adjusted according to the individual requirements of the operating personnel.
• Such an operating console 26 can contain the above-proposed devices for indicating grinding burn, so that the Operating personnel is always informed about the grinding condition of the workpieces.
• a lifting hydraulic system 30 allows the machine table 22 to be adjusted.
• the operating personnel can access the otherwise encapsulated working area of the machine 18 through frontal sliding doors 31 which, like the doors for an automatic loading 32, belong to the machine cover 34.
• the doors for the automatic loading 32 are activated via pneumatic cylinders 36, while the sliding doors 31 can be opened via operating handles 38.
• the sub-apparatus 40 protrudes into the working space of the machine and carries the workpiece to be machined or the kingpin that carries the workpieces (gearwheels) to be machined, not here shown with
• the dividing device 40 has a tip 42 which engages in a receptacle of the kingpin 44. On the opposite side, the kingpin 44 is held by the tailstock tip 46. Tailstock with tailstock tip 46 and dividing head 40 with tip 42 correspond to the designs known to the person skilled in the art in this area. wheels 2 arranged. Depending on the design of the workpieces to be machined, tailstock tip 46 and dividing head 42 are to be adapted and adjusted. During the machining process, the mandrel 44 is rotated one tooth gap by the dividing apparatus, it not being necessary for tooth gaps lying next to one another to be machined immediately one after the other. Rather, for machine-related reasons, machining of tooth bases further apart can follow one another.
• FIG. 4 shows the adjustment options of the partial apparatus 40
• FIG. 5 shows the arrangement of the grinding head 50 and its adjustment options.
• 4 shows a side view of dividing attachment 40.
• the dividing attachment spindle 52 can thereby perform a rotary movement about the A-axis, specifically by a certain angular amount to the left ⁇ -) and to the right (+).
• the view shows the view of the dividing head spindle in the (+ X) direction according to FIG. 5.
• the machine table 22 carrying the dividing head 40 can be adjusted on a Y axis.
• a table adjustment in the (+) direction means that the grinding head 50 is lifted off the workpiece, while an adjustment in the (-) direction means that the grinding head 50 is immersed in the workpiece to the grinding depth.
• FIG. 4 shows the arrangement of the grinding head 50 with grinding wheel 54 in a front view.
• the height of the grinding head 50 can be adjusted by means of a handle 56 and precisely adjusted to the workpiece to be machined with a very fine division. Adjustment options are also provided which move the entire grinding chute 56 of the machine 18 or cause the grinding head 50 to swivel. Moving the grinding carriage 58 in the (+ X) direction enables a grinding feed and the movement of the
• the grinding wheel 54 has as an outer contour the profiling of the inner contour of the tooth gap to be ground.
• the tooth gaps are ground one after the other.
• the grinding wheel is inclined to the workpiece axis according to the desired inclination. All possible inclinations can be ground.
• the grinding head 50 is fastened to the grinding chute 58 by suitable means, not shown here.
• Bellows 62 are provided on both sides of the grinding carriage 58 and adapt to these movements when the grinding carriage 58 is displaced on the X axis.
• Fig. 6 shows an override switch with a fine gradation with increments of 5%.
• the operator of the grinding device can manually change the preprogrammed feed rate in the displayed jumps of 5% between 0% and 150% using a switching button 64.
• FIG. 7 shows a gearwheel 2 according to FIG. IB.
• a nozzle 66 is connected by a fluid line 68 to a high-pressure accumulator 70, in which a fluid under pressure is stored.
• a pump device 74 is connected to the reservoir 70 via a pressure line 72 and ensures the required pressure in the reservoir 70.
• a pressure switch 76 provided in the accumulator 70 is connected to the pump device 74 by a control line 78 and controls the pump device 74 as soon as the pressure in the high-pressure accumulator 70 has dropped below a threshold value.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Constituent Portions Of Griding Lathes, Driving, Sensing And Control (AREA)

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Citations (9)

• 1994
  • 1994-07-14 DE DE4424829A patent/DE4424829A1/de not_active Withdrawn
• 1995
  • 1995-07-10 WO PCT/EP1995/002678 patent/WO1996002356A1/de active Application Filing

Patent Citations (9)

Non-Patent Citations (2)

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