GB2058614A - Controlling machining operation - Google Patents

Controlling machining operation Download PDF

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Publication number
GB2058614A
GB2058614A GB8029472A GB8029472A GB2058614A GB 2058614 A GB2058614 A GB 2058614A GB 8029472 A GB8029472 A GB 8029472A GB 8029472 A GB8029472 A GB 8029472A GB 2058614 A GB2058614 A GB 2058614A
Authority
GB
United Kingdom
Prior art keywords
signal
machining operation
machine tool
heat
reference signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8029472A
Other versions
GB2058614B (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
British Hovercraft Corp Ltd
Original Assignee
British Hovercraft Corp Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by British Hovercraft Corp Ltd filed Critical British Hovercraft Corp Ltd
Priority to GB8029472A priority Critical patent/GB2058614B/en
Publication of GB2058614A publication Critical patent/GB2058614A/en
Application granted granted Critical
Publication of GB2058614B publication Critical patent/GB2058614B/en
Expired legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
    • B23Q17/09—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool
    • B23Q17/0952—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool during machining
    • B23Q17/0985—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool during machining by measuring temperature
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q11/00—Accessories fitted to machine tools for keeping tools or parts of the machine in good working condition or for cooling work; Safety devices specially combined with or arranged in, or specially adapted for use in connection with, machine tools
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q15/00—Automatic control or regulation of feed movement, cutting velocity or position of tool or work
    • B23Q15/007—Automatic control or regulation of feed movement, cutting velocity or position of tool or work while the tool acts upon the workpiece
    • B23Q15/12—Adaptive control, i.e. adjusting itself to have a performance which is optimum according to a preassigned criterion
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/34—Director, elements to supervisory
    • G05B2219/34492—Time out, decide only after a lapse, period of time
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/37—Measurements
    • G05B2219/37426—Detected with infrared sensor
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/37—Measurements
    • G05B2219/37427—Detected with thermocouple
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/45—Nc applications
    • G05B2219/45129—Boring, drilling
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/49—Nc machine tool, till multiple
    • G05B2219/49072—Action, withdraw, stop feed tool to prevent breakage or lower load

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Drilling And Boring (AREA)

Abstract

A machining operation, such as drilling, is controlled by sensing heat in the workpiece generated by the operation and comparing a signal significant of this with a reference signal representative of the heat- significant signal that would be obtained in an ideal operation. Deviation of the sensed signal from the reference signal is used to change the performance of the operation. An infra-red sensor 14 or thermo-couple senses the heat. A microprocessor 17 compares this with the reference signal. if the deviation exceeds a predetermined amount over a set period of time, the drill 12 is withdrawn to prevent breakage or to clear swarf. <IMAGE>

Description

SPECIFICATION Improvements in or relating to machine tools This invention relates to machine tools and is particularly concerned with reducing the frequency of tool breakage during machining operations.
Tool breakage during machining operations may be expensive because as well as the cost of replacing the broken tool it may also be necessary to scrap the workpiece that was being machined at the time the tool breakage occurred. This is particularly the case when the machining operation involved is one of producing a hole, such as by drilling or boring, because the broken end of the tool may be lodged in the workpiece such that it cannot easily be removed. In mass production machining operations it is generally uneconomic to attempt to recover the workpiece by removal of the broken drill or tool, and the workpiece is scrapped.
Amongst the causes of tool shearing during a hole cutting operation by drilling are swarf blockage, internal contraction of the workpiece due to redistribution of internal stresses, tool wear, and variations in drill speed or feed. To reduce the problem of swarf blockage when drilling a long or deep hole it is usual to withdraw and re-enter the workpiece at a set frequency during the drilling operation, this being known as "woodpecking." For mass produced components, whose production involves a sequence of machining operations on an automatic machine tool, this considerably increases the time that a workpiece is in the machine without metal being cut; and tool breakage may still occur due to swarf blockage in periods when metal is being cut or because all of the swarf is not cleared from the hole on withdrawal of the drill.
The present invention seeks to provide a method and apparatus whereby a machining operation may be monitored and metal cutting discontinued should some factor be present that may lead to tool breakage so that the incidence of tool breakage is substantially reduced.
Accordingly, one aspect of the invention provides a method of controlling a machining operation on a machine tool comprising sensing a heat signal generated during the machining operation, comparing the sensed signal with a reference signal representative of a heat signal generated during an ideal machining operation, using a deviation in the sensed signal of more than a predetermined amount from the reference signal to effect a change in the machining operation.
Another aspect of the invention provides machine tool control apparatus comprising means for sensing a heat signal generated during a machining operation, means for comparing the sensed signal with a reference signal representative of a heat signal generated during a satisfactory machining operation, and means for effecting a change in the machining operation upon deviation of the sensed signal from the reference signal by more than a predetermined amount.
The source of the heat signal may be the workpiece or the cutting tool.
In a hole cutting operation, when the heat signal is derived from the workpiece, the heat may be sensed in the surface of the workpiece adjacent the entry point of the cutting tool or it may be sensed along a surface of the workpiece running in line with the length of the hole.
The heat signal may be sensed by any suitable thermal sensing means such as a capacitance thermo-couple which touches the workpiece. In an embodiment of the invention the heat signal is sensed by an infra-red sensor.
The reference signal may be stored on a microprocessor and may be derived by sensing the heat signal generated during a satisfactory or ideal machining operation on one of the workpieces that are to be machined. The heat signals sensed during subsequent like machining operations on like components are fed to the microprocessor for comparison with the reference signal. A deviation in the sensed signal over a predetermined time period by more than a predetermined amount from the reference signal indicates an increase in the heat being generated at the tool cutting edge to workpiece interface, and this may be as a result of the onset of a problem, such as swarf blockage, that will lead to tool breakage if no remedial action is taken.In the present invention this deviation is used to produce a signal that may be fed back to the machine so as to cause it to take some appropriate remedial action such as switching itself off or withdrawing the cutting tool for a short period. Where the machine is arranged to withdraw the tool and then re-offer it to the workpiece for continuance of the cutting operation, repeated rejection of the tool may indicate that the cutting tool has become worn to an extent where it needs to be sharpened.
The band of permissible deviation of the sensed heat signal about the reference signal will be such as to filter out temperature peaks of short duration which may be caused by hot swarf passing across the sight line of the sensing means.
Two embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic illustration of a machine tool operation wherein a heat signal generated during a drilling operation is sensed by a infra-red sensor, and Figure 2 is a similar illustration to that of Figure 1 but wherein a heat signal generated during a drilling operation is sensed by a capacitance thermo-couple.
Figure 1 shows an oil hole being drilled along the longitudinal centreline of a cam shaft 11 by a drill held in a chuck 13. An infra-red sensor head 14 is attached to the chuck 13 by a support rod 15 and link arm 16 so as to be positioned in line with the tip of the drill 12 and to follow the movement of the drill tip as it cuts through the cam shaft 1 The sensor 14 senses a heat signal generated in the cam shaft 11 by the drilling operation and produces a signal which is passed to a microprocessor 17.
Stored on the microprocessor is a reference signal 18 obtained by sensing the heat signal generated during a satisfactory drilling operation on a like cam shaft. The signal sensed during passage of the drill 12 through the cam shaft 1 1 is compared with the reference signal on the microprocessor, and should it deviate outside of a permissible scatter band at either side of the reference signal then the machine tool control 19 is instructed to withdraw the drill 12 for a brief period and then re-enter it. Should the problem causing the deviation in the heat signal be one of swarf blockage, withdrawal of the drill either pulls out the swarf or permits the coolant (not shown) to wash it out. Should the problem be one of drill wear then the drill will be rejected on its re-entry, and after this or a set number of rejections the machine may be instructed to switch off.
In the embodiment of Figure 2 a heat signal generated during a drilling operation on a pump body 20 is sensed by a capacitance thermo couple 21. The sensing head 22 of the thermo couple 21 is held in contact with the surface of the pump body 20 at a position near to the point of drill entry by suitable means such as adhesive bonding. The sensed signal is passed from the thermo-couple 21 to the microprocessor 17 and iscompared with the reference signal 18 stored on the microprocessor 17. Deviation of the sensed signal from the reference signal by more than a predetermined amount produces a signal which is passed to the machine tool control 19 to cause it to switch the machine off or to withdraw the drill for a short period before re-offering it to the pump body.
We have found that the heat signal generated during a drilling operation follows substantially the form of curve shown in the reference signal box 18. At the commencement of the drilling operation the temperature rises to a peak and then falls away exponentially as drilling continues before falling back to zero after drill break through, or on withdrawal of the drill when the hole has been drilled to the desired depth.

Claims (11)

1. A method of controlling a machining operation on a machine tool comprising sensing a heat signal generated during the machining operation, comparing the sensed signal with a reference signal representative of a heat signal generated during an ideal machining operation, using a deviation in the sensed signal of more than a predetermined amount from the reference signal to effect a change in the machining operation.
2. Machine tool control apparatus comprising means for sensing a heat signal generated during a machining operation, means for comparing the sensed signal with a reference signal representative of a heat signal generated during a satisfactory machining operation, and means for effecting a change in the machining operation upon deviation of the sensed signal from the reference signal by more than a predetermined amount.
3. The method or the apparatus as claimed in either of the preceding Claims, wherein the source of the sensed heat signal is a workpiece undergoing a machining operation.
4. Machine tool control apparatus as claimed in Claim 2 or Claim 3, wherein the means for sensing the heat signal comprises a capacitance thermocouple.
5. Machine tool control apparatus as claimed in Claim 2 or Claim 3, wherein the means for sensing the heat signal comprises an infra-red sensor.
6. Machine tool control apparatus as claimed in any one of Claims 2 to 5, wherein the comparator means comprises a microprocessor having the reference signal stored thereon.
7. Machine tool control apparatus as claimed in any one of Claims 2 to 6, wherein deviation of the sensed signal from the reference signal by more than a predetermined amount is arranged to produce a signal for use in actuating means to switch off the machine tool.
8. Machine tool control apparatus as claimed in any one of Claims 2 to 6, wherein deviation of the sensed signal from the reference signal by more than a predetermined amount is arranged to produce a signal for use in actuating means which cause the machine to withdraw a tool being used to cut a workpiece.
9. Machine tool control apparatus as claimed in Claim 8, wherein the cutting tool is withdrawn for a short period and then re-offerred to the workpiece, repeated rejection of the cutting tool causing the machine to switch off.
10. Machine tool control apparatus substantially as hereinbefore described with reference to and shown in the accompanying drawing.
11. Every novel feature and every novel combination of features disclosed herein.
GB8029472A 1979-09-19 1980-09-11 Controlling machining operation Expired GB2058614B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8029472A GB2058614B (en) 1979-09-19 1980-09-11 Controlling machining operation

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB7932451 1979-09-19
GB8029472A GB2058614B (en) 1979-09-19 1980-09-11 Controlling machining operation

Publications (2)

Publication Number Publication Date
GB2058614A true GB2058614A (en) 1981-04-15
GB2058614B GB2058614B (en) 1983-03-16

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB8029472A Expired GB2058614B (en) 1979-09-19 1980-09-11 Controlling machining operation

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0051771A1 (en) * 1980-11-08 1982-05-19 Feldmühle Aktiengesellschaft Method and apparatus for the supervision of cutting-tools in machine tools
WO1997049523A1 (en) * 1996-06-26 1997-12-31 The Gleason Works Detecting tool wear by thermal monitoring of workpiece

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0051771A1 (en) * 1980-11-08 1982-05-19 Feldmühle Aktiengesellschaft Method and apparatus for the supervision of cutting-tools in machine tools
WO1997049523A1 (en) * 1996-06-26 1997-12-31 The Gleason Works Detecting tool wear by thermal monitoring of workpiece
US5904457A (en) * 1996-06-26 1999-05-18 The Gleason Works Detecting tool wear by thermal monitoring of workpiece

Also Published As

Publication number Publication date
GB2058614B (en) 1983-03-16

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Legal Events

Date Code Title Description
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee