Method for judging key moments in whole process of machining step for computer numerical control machine tools

Abstract

Some embodiments of the present disclosure provide a method for judging four key moments in a whole process (a feeding starting moment, an idling process, a cutting starting moment, cutting, a cutting ending moment, an idling process and a feeding ending moment) of a machining step for computer numerical control machine tools. The method includes that: the feeding starting moment and ending moment are determined according to a real-time execution state of a numerical control code; input power of a spindle of a machine tool is compared in real time with idling power to determine the cutting starting moment and ending moment; and for a special machining step in which power does not change obviously in a feeding process, the cutting starting and ending moments are determined in combination with a historical statistical average time of an idling process duration and a feeding moment.

Claims

1. A method for judging key moments in a whole process of a machining step for computer numerical control machine tools, wherein, before judgment, an input power range P.sub.UminP.sub.Umax of a spindle of the computer numerical control machine tools in an idling process state is acquired and stored, and during judgment process, following steps are comprised: when a workpiece is machined, reading an execution state, of a numerical control code of the computer numerical control machine tools in real time, acquiring and recording an execution starting moment t.sub.U1s of a cutting feeding code, and then judging the execution starting moment t.sub.U1s as a feeding starting moment t.sub.U1s in the machining step as well as a starting moment t.sub.U1s of a first idling state; after a first idling process in the machining step is started, acquiring a real-time input power P.sub.i of the spindle of the computer numerical control machine tools, and when the input power P.sub.i increases and exceeds maximum input power P.sub.Umax of the spindle in an idling process state, recording an increasing moment, and then judging the increasing moment as a starting moment t.sub.Cs of a cutting state in the machining step as well as an ending moment of the first idling process state; after the cutting state in the machining step is started and when the input power P.sub.i decreases to be lower than P.sub.Umax and is kept within the input power range P.sub.UminP.sub.Umax of the spindle in the idling process state, recording a decreasing moment and then judging the decreasing moment as an ending moment t.sub.Ce of the cutting state in the machining step as well as a starting moment of a second idling state; and after the cutting state in the machining step is ended, reading the execution state of the numerical control code of the computer numerical control machine tools in real time, acquiring and recording an execution ending moment of the cutting feeding code, and judging the execution ending moment as a feeding ending moment t.sub.U2e in the machining step as well as an ending moment t.sub.U2e of the second idling process state.

2. The method for judging the key moments in the whole process of the machining step for the computer numerical control machine tools as claimed in claim 1, wherein in an execution process t.sub.U1st.sub.U2e of the cutting feeding code, when the real-time input power P.sub.i of the spindle of the computer numerical control machine tools is kept within the input power range P.sub.UminP.sub.Umax of the spindle in the idling process state, the method further comprises following steps: reading first idling process state durations T.sub.U1 and second idling process state durations T.sub.U2 in all historical machining steps of the computer numerical control machine tools, and calculating an average time T.sub.U1 of the first idling process state durations and an average time T.sub.U2 of the second idling process state durations respectively; and judging a sum of the average time T.sub.U1 of the first idling process state durations and the feeding starting moment t.sub.U1s in the machining step as the starting moment t.sub.Cs of the cutting state, and subtracting the average time T.sub.U2 of the second idling process state durations from the feeding ending moment t.sub.U2e in the machining step for judgment as the ending moment t.sub.Ce of the cutting state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a rough turning of external cylinder process;

(2) FIG. 2 is a flowchart of automatic judgment in a machining step; and

(3) FIG. 3 is a structure diagram of a workpiece according to an embodiment.

(4) In FIG. 1: 1, turning tool, 2, workpiece, 11, rapid feed path, 12, first idling process path, 13, cutting path, 14, second idling process path and 15, rapid return path.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) Some embodiments of the disclosure will be further described below in combination with the drawings.

(6) During specific implementation: during machining of a machine tool, a feeding route for a complete step is: a reference point of the machine tool.fwdarw.a clearance plane.fwdarw.workpiece cutting.fwdarw.the clearance plane.fwdarw.the reference point of the machine tool. Herein, the clearance plane refers to a plane created in a space close to a surface of a workpiece to prevent collision between a cutting tool moving fast and the surface of the workpiece, and a speed of the cutting tool between the plane and the surface of the workpiece is a cutting feed speed. In this feeding process, a process that the cutting tool gets close to the surface of the workpiece from the clearance plane at the feeding speed (or returns to the clearance plane from the surface of the workpiece after cutting) is called idling process. Under a normal condition, a complete machining step includes two idling processes: a first idling process refers to a process that, before cutting, the cutting tool leaves the clearance plane and gets close to the surface of the workpiece at the feeding speed; and a second idling process refers to a process that, after cutting is completed, the cutting tool leaves the surface of the workpiece and gets close to the clearance plane or a process that the cutting tool leaves the surface of the workpiece and leads to a coordinate origin of the machine tool at the feeding speed. For example, as shown in FIG. 1, two idling processes in a rough turning of external cylinder process refer to feeding processes in the vicinity of two end faces of the workpiece. Time for completing the whole idling process is idling process time. During practical engineering, the idling process time usually depends on an operation habit of a worker and a machining space of the machine tool, and is almost unrelated to selection of a machining type such as finish machining, semi-finish machining and rough machining.

(7) Therefore, judgment about a key in a whole process of a machining step for CNC machine tools includes the following steps.

(8) In a), an input power P.sub.UminP.sub.Umax of a spindle of the machine tool in an idling process state is acquired off-line and stored.

(9) In b), a feeding starting moment of the machining step is judged.

(10) When feeding is started, there is a distinctive characteristic that a feeding speed of a cutting tool changes obviously and executed codes are obviously different. The feeding starting moment is acquired by reading a numerical control code executed by the CNC machine tools in real time and analyzing this change characteristic. When the numerical control code is changed from a rapid moving code to a cutting feeding code, a feeding starting moment t.sub.U1s (i.e., a first idling process starting moment) of the machining step is recorded. For example, when a code presently executed by a FANUC system changes from a rapid moving code G00 X_Y_Z_ to a feeding code G01 Z_F_, feeding of the machining step is started. In the formula, X_Y_Z_ is a coordinate of the machine tool, and F_ is a feeding rate of the machine tool.

(11) In c), a cutting starting moment and ending moment of the machining step are judged.

(12) After idling process is started, the input power P.sub.UminP.sub.Umax of the spindle of the machine tool in the idling process state is compared in real time with a real-time input power P.sub.i, and when

(13) P.sub.i>P.sub.Umax,

(14) this moment is recorded as the cutting starting moment.

(15) In a cutting state, the input power P.sub.i of the machine tool is acquired in real time, and is compared with the input power P.sub.UminP.sub.Umax of the spindle of the machine tool in the idling process state, and when

(16) P.sub.iP.sub.Umax

(17) and P.sub.UminP.sub.iP.sub.Umax is kept, this decreasing moment is recorded as the cutting ending moment of the machining step.

(18) In d), a feeding ending moment of the machining step is judged.

(19) The feeding ending moment of the machining step is obtained by analyzing and monitoring the NC code executed in real time by the CNC machine tools: when the NC code presently executed by the CNC machine tools changes from a feeding code to a rapid return code, this moment is recorded as the feeding ending moment of the machining step, for example, a moment when a code presently executed by the FANUC system of the machine tool changes from the feeding code G01 Z_F_ to a rapid return code G00 X.sub.0 Y.sub.0 Z.sub.0, X.sub.0 Y.sub.0 Z.sub.0 in the formula is a reference point of the machine tool.

(20) From the above, a method for judging key moments in the whole process of the machining step for the CNC machine tools is implemented as follows: at first, the numerical control code executed in real time by a numerical control system of the machine tool is acquired through a numerical control communication technology, and the feeding starting moment and ending moment of the machining step of the CNC machine tools are judged according to a change characteristic thereof; and then, on such a basis, the starting moment and ending moment of the machining step are judged through the real-time input power of the machine tool and a change characteristic thereof. A flow of the whole judgment process refers to the solid line part in FIG. 2.

(21) However, in some finish machining, due to cutting allowance and power requirement are relatively low, so that judgment for such a machining step according to the power change characteristic is usually low in accuracy and high in misjudgment rate. Therefore, for a machining step in which power does not change obviously in a feeding process, judgment about cutting starting and ending moments thereof is implemented in combination with a historical statistical average time of idling durations and a feeding moment, and a flow of a judgment process thereof refers to a dotted line part in FIG. 2, specifically as follows.

(22) At first, first idling process state durations T.sub.U1 and second idling process state durations T.sub.U2 in all historical machining steps of the machine tool are acquired, and an average time T.sub.U1 of the first idling process state durations and an average time T.sub.U2 of the second idling process state durations are calculated respectively.

(23) Then, judging a sum of the average time T.sub.U1 of the first idling process state durations and the feeding starting moment t.sub.U1s the machining step as the starting moment t.sub.Cs of the cutting state in the machining step, namely
t.sub.Cs=t.sub.U1s+T.sub.U1, and

(24) subtracting the average time T.sub.U2 of the second idling process state durations from the feeding ending moment t.sub.U2e in the machining step for judgment as the ending moment t.sub.Ce of the cutting state, namely
t.sub.Ce=t.sub.U2eT.sub.U2.

(25) There are two conditions for acquisition of the historical idling process state durations.

(26) If machining with obviously changing power is performed by the machine tool before, the idling process duration T.sub.U1 is calculated as
T.sub.U1=t.sub.U1et.sub.U1s
T.sub.U2=t.sub.U2et.sub.U2s

(27) In the formula, t.sub.U1s is a starting moment of a first idling process state during historical machining;

(28) t.sub.U1e is an ending moment of the first idling process state during historical machining;

(29) t.sub.U2s is a starting moment of a second idling process state during historical machining; and

(30) t.sub.U2e is an ending moment of the first idling process state during historical machining.

(31) If machining is not performed by the computer numerical control machine tools before, a first idling process travel of such a machining step is required to be calculated and acquired by means of on-site investigation, specifically as follows: idling process time is estimated according to a habit of an operator of the machine tool and then is input by man-machine interaction, or the idling process time of such a same type of machine tool is manually statistically judged for a long time and then manually input.

(32) Descriptions will be made below in combination with a process that a certain part is machined by a certain CNC machine tools as an example. A schematic diagram of the workpiece is shown in FIG. 3. A machining process includes rough turning of external cylinder, fine turning of external cylinder and rough turning of slot. An adopted sensor is an HC33-C3 electric power measurer, and a numerical control code is read and obtained from a numerical control system in real time at an interval of 0.25s by use of software. Before judgment, a fluctuation range 260 W275 W of input power of a spindle of the CNC machine tools in an idling process state is measured off-line.

(33) First, a Process of Rough Turning of External Cylinder

(34) 1: Acquisition of a Feeding Starting Moment and Ending Moment

(35) A moment when the numerical control code presently executed by the CNC machine tools changes from G00 X8.3 to G1 Z1 is the feeding starting moment for rough turning of external cylinder. It is measured that the moment when such a change occurs to the numerical control code is 15:37:29.000 (time is represented as hour: minute: second. millisecond in this example), that is, the feeding starting moment is 15:37:29.000, and the code changes from G01 X13 W-1.2 to G00 X200 at 15:37:40.000, that is, the feeding ending moment for rough turning of external cylinder is 15:37:40.000.

(36) 2: Acquisition of a Cutting Starting Moment and Ending Moment

(37) After idling process is entered, it is measured that the input power of the spindle is 269 W, and at 15:37:29.500, the input power of the spindle of the machine tool changes from 269 W to 489 W and is far higher than 269, that is, the cutting starting moment for rough turning of external cylinder of the CNC machine tools is 15:37:29.500, and then the machine tool is in a cutting state. It is measured on the spot that the power of the spindle in this state keeps fluctuating about 489 W, a maximum fluctuation range is 13 W and the power changes to 265 W at 15:37:39.000, that is, the cutting ending moment for rough turning of external cylinder is 15:37:39.000.

(38) From the above, a first idling process duration and second idling process duration of this rough machining are 0.5s and 1s respectively.

(39) Second, a Process of Fine Turning of External Cylinder

(40) 1: Acquisition of a Feeding Starting Moment and Ending Moment

(41) The feeding starting moment for fine turning of external cylinder is a moment when the presently executed code changes from G00 X7.935 to G01 X8.05 Z-29.5 F300 and is measured on the spot to be 15:37:43.000, and the presently executed numerical control code changes from G01 X14 F300 to G00 X200 Z1 at 15:37:52.000. Based on this, starting moment and ending moment of feeding for fine turning of external cylinder are 15:37:43.000 and 15:37:52.000 respectively.

(42) 2: Acquisition of a Cutting Starting Moment and Ending Moment

(43) The feeding starting moment 15:37:43.000 (i.e., a first idling process starting moment) and the first idling process duration 0.5s for rough turning of external cylinder are substituted into a formula
t.sub.Cs=t.sub.U1s+T.sub.U1

(44) to obtain the cutting starting moment 15:37:43.500 for fine turning of external cylinder.

(45) Similarly, the feeding ending moment 15:37:52.000 (a second idling process ending moment) and the second idling process duration 1.0s for rough turning of external cylinder are substituted into a formula
T.sub.U2=t.sub.U2et.sub.U2s

(46) to obtain the cutting ending moment 15:37:51.000 for fine turning of external cylinder.

(47) Third, a Process of Rough Turning of Slot

(48) 1: Judgment of a Feeding Starting Moment and Ending Moment

(49) A moment when the numerical control code presently executed by the CNC machine tools changes from G00 Z13.25 to G1 X7.05 F100 is the feeding starting moment for rough turning of slot, and is 15:37:56.000. The presently executed numerical control code changes from G01 X8.5 to G00 X10 Z1 at 15:37:59.000, that is, the feeding ending moment is 15:37:59.000.

(50) 2: Judgment of a Cutting Starting Moment and Ending Moment

(51) After cutting feed is started, the power of the spindle is 269 W, and the input power changes from 269 W to 316 W at 15:37:56.500, that is, the cutting starting moment for rough turning of slot is 15:37:56.500. Then, the machine tool is in the cutting state, the power of the spindle fluctuates within an approximately 12 W range centered about 325 W, and the power changes to 269 W at 15:37:58.000, that is, the cutting ending moment for rough turning of slot of the CNC machine tools is 15:37:58.000.

(52) Fourth, Analysis of a Judgment Result

(53) At the same time of adopting the method to acquire the key moments for the machining step, a stopwatch recording and manual judgment manner is adopted to acquire the cutting moments for precision comparison in some embodiments of the disclosure. For conveniently comparing results and converting stopwatch test results into a time mode in the method, the cutting moments (minute: second. millisecond) acquired by two methods refer to the following table.

(54) TABLE-US-00001 Rough turning of Fine turning of Rough turning of external cylinder external cylinder slot Automatic 37:29.500 37:39.000 37:43.500 37:51.000 37:56.500 37:58.000 judgment Manual 37:29.800 37:39.420 37:44.000 37:50.310 37:56.700 37:58.000 measurement

(55) By comparison between experimental results, it can be seen that judgment accuracy of the key moments of the machining step in the embodiment of the present disclosure is relatively high: a judgment error for a rough machining step is smaller than 0.5s, and an error for a finishing machining step is relatively large but also within 1s.

(56) The above is only the preferred embodiment of the disclosure and not intended to limit the disclosure. Any modifications, equivalent replacements, improvements and the like made within the spirit and principle of the disclosure shall fall within the scope of protection of the disclosure.