GB2409041A - EDM apparatus for detection of blockages - Google Patents
EDM apparatus for detection of blockages Download PDFInfo
- Publication number
- GB2409041A GB2409041A GB0328681A GB0328681A GB2409041A GB 2409041 A GB2409041 A GB 2409041A GB 0328681 A GB0328681 A GB 0328681A GB 0328681 A GB0328681 A GB 0328681A GB 2409041 A GB2409041 A GB 2409041A
- Authority
- GB
- United Kingdom
- Prior art keywords
- hole
- pin
- workpiece
- movement
- housing
- 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.)
- Withdrawn
Links
- 238000001514 detection method Methods 0.000 title description 7
- 238000000034 method Methods 0.000 claims abstract description 32
- 238000003754 machining Methods 0.000 claims abstract description 31
- 238000003780 insertion Methods 0.000 claims abstract description 6
- 230000037431 insertion Effects 0.000 claims abstract description 6
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 2
- 229910052721 tungsten Inorganic materials 0.000 claims description 2
- 239000010937 tungsten Substances 0.000 claims description 2
- 238000009760 electrical discharge machining Methods 0.000 abstract description 2
- 238000012544 monitoring process Methods 0.000 abstract 1
- 238000001816 cooling Methods 0.000 description 7
- 238000007689 inspection Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000004020 conductor Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 229910001369 Brass Inorganic materials 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000010951 brass Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000003628 erosive effect Effects 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 229910000601 superalloy Inorganic materials 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 101100117236 Drosophila melanogaster speck gene Proteins 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- SBYXRAKIOMOBFF-UHFFFAOYSA-N copper tungsten Chemical compound [Cu].[W] SBYXRAKIOMOBFF-UHFFFAOYSA-N 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010892 electric spark Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- -1 for example Substances 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 230000003252 repetitive effect Effects 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 230000008016 vaporization Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- 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
- B23H11/00—Auxiliary apparatus or details, not otherwise provided for
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
Abstract
Apparatus and method for inspecting a workpiece with a hole defined therein, the apparatus 10 comprising a housing 30 adapted to receive a pin 20 for insertion into the hole, and a measuring unit 50 to measure either resistance to movement of the pin in the direction of the hole or differential movement between the pin and the housing. The method comprises inserting the pin into the hole and monitoring resistance to movement or differential movement between the pin and the housing, as an indicator of a blockage within the hole and therefore a need for re-machining of the hole. The apparatus and method are of particular application in the field of electrical discharge machining (EDM). The measuring unit 50 is either a strain gauge attached to the pin or a movement sensor. The pin may be an electrode. The method may be automated.
Description
240904 1 - 1
IMPROVEMENTS IN DRILLING
This invention relates to an apparatus and method for inspection of machined holes and in particular holes machined by electro-discharge machining, for example in super- alloy components and the like.
Electro-Discharge Machining (EDM), often referred to as "spark-eroding" or"sink erosion" is a process of controlled electrical erosion or vaporization of electrically conductive material, such as metal materials, through a series of repetitive sparks between electrodes, that is, between a workpiece and a tool. This type of machining removes metal from a workpiece by converting the kinetic energy of electric sparks into heat as the sparks strike the workpiece, such that the controlled sparks gradually erode a desired shape in the workpiece. The workpiece forms the cathode and the tool, otherwise referred to as the electrode, forms the anode.
Electrodes are made from conductive materials such as graphite, copper, brass or copper tungsten. A flow of dielectric fluid, such as a hydrocarbon oil, is pumped into the gap between the electrode and the workpiece to allow a path for the electrical discharge and to flush away debris from the arcing. A pulsating do power supply is connected between the two. The discharges travel through, and ionise, the dielectric fluid, and sparks occur where the two surfaces are closest. The region in which the spark occurs is heated to such high temperatures that a small speck of the work surface is melted and removed from the workpiece, and is subsequently swept away by the dielectric flow. This part of the workpiece is now below the average level of the workpiece surface so the next highest areas of the workpiece are removed next.
These discharges occur hundreds or thousands of times per second so that gradually all the area on the workpiece conforming to the electrode is eroded.
EDM can be used to machine virtually any material, as long as it is a relatively good conductor of electricity. These include metals, alloys and carbides which are too hard or delicate to machine by conventional methods. - 2
For example, EDM is used to machine cooling holes in super alloy components of gas turbine airfoils in circumstances where accessibility or hole shape complexity precludes the use of laser drilling. Cooling holes are formed in the airfoil wall sections of nozzle guide vanes to enable cooling air fed, for example, from the engine compressor to pass from the hollow core of the nozzle guide vanes to form a thin film of cooling air over the airfoil surface, thereby protecting the airfoil from the effects of high temperature combustion gasses.
The shape and size of cooling holes varies considerably depending on the shape and size of the component to be cooled and the amount of cooling air required in a specific area of the airfoil. The geometric shape of cooling holes includes cylindrical holes and shaped holes. Cylindrical holes typically comprise a constant area circular cross- section passing through the wall of the airfoil, and these holes are relatively easy to produce using known EDM technologies.
EDM machines typically use a single or multi-electrode "nose-guide" to direct the electrodes at the correct point relative to the workpiece, such that the this nose guide stands off from the components by about 2mm. The electrodes are then pushed out of the nose guide towards the surface of the workplace to be machined. Initially, the electrodes reverse machine or redress on the surface of the workpiece so that all the electrodes are sensed by the EDM machine to be touching the surface. The EDM machine then machines the hole(s), the cross-section of the hole(s) being determined by the geometry of the electrode(s), by creating controlled sparks between the electrode(s) and the workpiece.
One drawback to the machining process is that since the electrodes are required to machine different thickness of component material, the electrodes wear at different rates. Occasionally one or more electrodes will fail to break out the other side of the component being machined, thereby resulting in incomplete machining of a hole through the material. Currently the component has to be removed from the EDM machine, inspected, and if necessary, reworked to correct any blocked holes. This is - 3 very slow and costly, and prone to human error, often resulting in the component being scrapped. Furthermore, there is also the risk that, if not checked properly, a non- conformal component may end up being used in an engine.
Similarly, when holes are formed by alternative methods of machining, any damage to, for example, a laser head or drill bit will result in incomplete machining and the production of a non-conformal component.
There is a requirement therefore for a means of determining, at an early state in the manufacturing process, if the holes have been formed correctly, so that, if not, appropriate action can be taken to avoid the possibility of a non-conformal part being overlooked and subsequently used in an engine.
According to a first aspect of the invention there is provided an apparatus for inspecting a workpiece with a hole defined therein comprising a housing adapted to receive a pin for insertion into the hole, and a measuring unit operable to measure resistance to movement of the pin in the direction of the hole. Such apparatus readily enables inspection of a workpiece when pins are received within the housing. The housing and pins are then moved relative to the workpiece and the pins inserted into the hole in the workpiece such that, should the pin meet any obstacle within the hole, forward movement of the pin into the hole is resisted and such resistance is detected by the measuring unit.
Typically, the measuring unit in the apparatus comprises a strain gauge attached to the pin. However, any other suitable means of detection of resistance available to the skilled person may be used.
A further aspect of the invention provides an apparatus for inspecting a workpiece with a hole defined therein comprising a housing adapted to receive a pin for insertion into the hole and a measuring unit operable to measure differential movement between the pin and the housing. Such apparatus is provided with a pin received within the housing and the apparatus and pin moved towards a workpiece such that the pin is inserted into the hole in the workpiece. If any obstruction is present in the hole, the pin will meet the - 4 obstruction and be pushed back into the housing of the apparatus. Any differential movement occurring between the pin and the housing is detected by the measuring unit and is indicative of a blockage or obstruction within the hole in the workpiece.
Typically, the measuring unit comprises a movement sensor by which to measure differential movement between the pin and the housing. However, any other suitable means of detection of differential movement may be used.
Apparatus according to the present invention is particularly useful for the inspection of a workplace defining an electro-discharge machined hole therein. During EDM, an electrode may become damaged, for example, by welding itself to the workplace or by breaking. If this happens, the hole being machined may be incompletely formed.
Therefore, a pin of appropriate minimum tolerances corresponding to the desired dimensions of the machined hole may be used for insertion into the hole to check for obstruction of the hole.
Preferably, the pin has a diameter equal to the minimum allowable diameter of the hole machined within the workpiece. This provides a double check that the dimensions of the machined hole are in accordance with the desired minimum tolerances. Not only will the pin be obstructed within the hole if the hole is not of the desired depth, which is often a through hole, but also the pin will be obstructed if the diameter of the hole is less that a selected minimum allowable diameter.
In one embodiment, the pin is an electrode. It is particularly preferred that the pin is an electrode where the hole in the workpiece has been formed by electro-discharge machining. Where an obstruction in a hole defined within the workplace is detected by the apparatus, if the pin is an electrode, the formation of the hole can be corrected by further machining of the hole by electro-discharge machining using the electrode present in the apparatus. Where the pin is an electrode, preferably the electrode is a tungsten electrode. However, the electrode may be composed of any other suitable material, such as, for example, graphite, copper or brass. - 5
According to a further aspect of the invention there is provided a method of inspecting a workpiece with a hole defined therein comprising inserting a pin into the hole and detecting resistance to movement of the pin in the direction of the hole.
A further aspect of the present invention provides a method of inspecting a workpiece with a hole defined therein comprising inserting a pin into the hole and detecting differential movement between the pin and a housing on which the pin is mounted.
In a method according to the present invention, typically the hole is machined in the workpiece by electro-discharge machining, particularly when higher precision machining is required in relatively inaccessible areas, although the hole may be machined in the workpiece by any suitable alternative method, for example, laser machining and the like.
A method according to the present invention may further comprise remachining the hole in the workpiece if resistance to movement of the pin in the direction of the hole is detected or if differential movement is detected between the pin and the housing.
Preferably the method of the present invention is automated to avoid the longer periods of "down time', experienced when the inspection is done manually. In addition, automation of the procedure may be more accurate and minimise the opportunity for human error.
A further aspect of the present invention provides a method of machining a workpiece comprising creating a hole by electro-discharge machining and inspecting the workpiece by inserting a pin into the hole and detecting resistance to movement of the pin in the direction of the hole.
A further aspect of the present invention provides a method of machining a workpiece comprising creating a hole by electro-discharge machining and inspecting the workpiece by inserting a pin into the hole and detecting differential movement between the pin and a housing on which the pin is mounted. - 6
An embodiment of the invention will now be more particularly described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a cross section view of an embodiment of an apparatus according to the present invention; and Figure 2 is a flow chart showing the mode of operation of the apparatus of Figure 1.
Figure 1 shows an embodiment of an apparatus 10 according to the present invention in which pins 20 are received within a housing 30 such that the pins 20 protrude beyond the nose guide 40 of the housing 30. In the embodiment shown in Figure 1, the pins 20 may comprise electrodes suitable for electro-discharge machining. The pins 20 are appropriately sized to minimum tolerances of the desired dimensions of the hole. Each pin 20 is connected to a strain gauge 50 also housed within the housing 30 of the apparatus 10. The strain gauge 50 is in communication with a control unit 60 and is operable to supply a signal to the control unit 60 on detection of any strain exerted on the pin 20 to which the strain gauge is connected, indicative of a resistance to movement of the pin 20 in the direction of the hole in a workpiece in which the pin 20 is being inserted, and consequently indicative of a blockage within the hole or incorrect formation of the hole during machining.
In use, the pins 20 are inserted into holes defined in a workpiece, the pins 20 proceeding smoothly through the holes in the workplace where the holes are formed correctly and without obstruction. If, during passage of the pins 20 into the holes in a workpiece, a pin 20 is inserted into a hole containing a deformation or an obstruction, the pin 20 will be prevented from proceeding through the hole and a strain through the pin 20 will be detected by the strain gauge 50 to which the pin 20 is connected. On measuring a strain through the pin 20, the corresponding strain gauge 50 is operable to supply a signal to the control unit 60, such a signal being indicative of an obstruction in the hole. The hole within which the obstruction has been detected is easily identified - 7 as each pin 20 is positioned to correspond with a particular hole machined within the workpiece being inspected and is in connection with a particular strain gauge 50.
It will be appreciated that, if the pins 20 are electrodes, it may be possible to re- machine the incorrectly machined hole using the electrode 20 by EDM.
Alternatively, the pins 20 of the apparatus 10 may be removed from the holes in the workpiece and an EDM cartridge with protruding electrodes lined up relative to the workpiece and the electrodes of the EDM cartridge inserted into the holes within the workpiece, in order to re- machine the incorrectly formed hole. It will be appreciated that if the EDM cartridge to be used in re-machining the incorrectly formed hole is the same EDM cartridge used in the initial machining of the hole, the electrode corresponding to the incorrectly formed hole will require replacement or redressing.
An EDM process including the steps of inspecting the machined holes will now be described with reference to Figure 1 and the flowchart of Figure 2.
In step A, a conventional EDM cartridge is accurately aligned with a workpiece in which a hole is to be machined, and the hole machined using EDM technology. After machining of a hole in a workpiece, the EDM cartridge is then replaced with an apparatus 10 with pins 20 received within a housing 30. The pins are dimensioned to minimum tolerances corresponding to the desired dimensions of the hole which has been machined in the EDM process of step A. Next, the pins 20 of the apparatus 10 are advanced into the machined holes in the workpiece (see step C). If, at step D, strain through any of the pins 20 is detected by the corresponding strain gauge 50 to which the pin 20 is connected, a signal is provided by the strain gauge 50 to a control unit 60 indicative of a resistance encountered by the pin 20 when advancing through the hole in the workpiece. The next step, step E, involves looping back to step A and re-machining the incorrectly formed hole using a conventional EDM cartridge.
Alternatively, if no strain through the pins 20 is detected by the corresponding strain gauges 50, this is indicative that no blockages are present in the holes in which the - 8 pins 20 have been advanced and the manufacturing process may continue without re- machining of the inspected holes (see step G).
Although aspects of the invention have been described with reference to the embodiments shown in the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be effected without further inventive skill and effort. For example, the strain gauge 50 of the apparatus 10 shown in Figure 1 may be replaced, for example, with a movement sensor for detection of differential movement between the pin and housing, the pin being resiliently mounted within the housing, such that on encountering a blockage within a hole in the workplace being inspected, the pin will be pushed back into the housing of the apparatus, the differential movement between a pin and the housing being detected by a movement sensor. The movement sensor is operable, on detection of differential movement between a pin and the housing, to supply a signal to a control means indicative of differential movement detection. On receipt of such a signal, the control unit 60 is operable to output a signal to alert an operator of the apparatus to a blockage within a hole within the workplace being inspected. - 9 -
Claims (21)
1 Apparatus for inspecting a workplace with a hole defined therein comprising a housing adapted to receive a pin for insertion into the hole, and a measuring unit operable to measure resistance to movement of the pin in the direction of the hole.
2 Apparatus for inspecting a workpiece with a hole defined therein comprising a housing adapted to receive a pin for insertion into the hole, and a measuring unit operable to measure differential movement between the pin and the housing.
3 Apparatus according to Claim 1 wherein the measuring unit comprises a strain gauge attached to the pin.
4 Apparatus according to Claim 2 wherein the measuring unit comprises a movement sensor.
Apparatus according to any preceding Claim for inspecting a workpiece defining an electro-discharge machined hole therein.
6 Apparatus according to any preceding Claim wherein the pin has a diameter equal to the minimum allowable diameter of the hole within the workpiece.
7 Apparatus according to any preceding Claim wherein the pin is an electrode.
8 Apparatus according to Claim 7 wherein the electrode is a tungsten electrode.
9 A method of inspecting a workplace with a hole defined therein comprising inserting a pin into the hole and detecting resistance to movement of the pin in the direction of the hole. -
A method of inspecting a workplace with a hole defined therein comprising inserting a pin into the hole and detecting differential movement between the pin and a housing on which the pin is mounted.
11 A method according to Claim 9 or Claim 10 wherein the hole is machined in the workplace by electro-discharge machining.
12 A method according to Claim 9 or Claim 11 further comprising remachining the hole if resistance to movement of the pin in the direction of the hole is detected.
13 A method according to Claim 10 or Claim 1 1 further comprising remachining the hole if differential movement is detected between the pin and the housing.
14 A method according to any one of Claims 9 to 13 wherein the method is automated.
A method of machining a workplace comprising creating a hole by electrodischarge machining and inspecting the workpiece by inserting a pin into the hole and detecting resistance to movement of the pin in the direction of the hole.
16 A method of machining a workplace comprising creating a hole by electro- discharge machining and inspecting the workpiece by inserting a pin into the hole and detecting differential movement between the pin and a housing on which the pin is mounted.
17 A method according to Claim 15 further comprising re-machining of the hole if resistance to movement of the pin in the direction of the hole is detected.
18 A method according to Claim 16 wherein the hole is re-machined if differential movement is detected between the pin and the housing.
19 A method according to any one of Claims 15 to 18 wherein the method is - 11 automated.
Apparatus substantially as hereinbefore described and with reference to the accompanying drawings.
21 A method substantially as hereinbefore described and with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0328681A GB2409041A (en) | 2003-12-11 | 2003-12-11 | EDM apparatus for detection of blockages |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0328681A GB2409041A (en) | 2003-12-11 | 2003-12-11 | EDM apparatus for detection of blockages |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB0328681D0 GB0328681D0 (en) | 2004-01-14 |
| GB2409041A true GB2409041A (en) | 2005-06-15 |
Family
ID=30130004
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0328681A Withdrawn GB2409041A (en) | 2003-12-11 | 2003-12-11 | EDM apparatus for detection of blockages |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2409041A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116481415B (en) * | 2023-05-04 | 2026-01-09 | 安徽水安建设集团股份有限公司 | Test apparatus and test method for stress and strain field state of large conveying pipelines |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1423523A (en) * | 1972-03-23 | 1976-02-04 | Cav Ltd | Method and apparatus for testing components |
| US4510365A (en) * | 1982-05-06 | 1985-04-09 | Raycon Corporation | Electronic depth controller for EDM apparatus |
| US5144753A (en) * | 1991-03-25 | 1992-09-08 | Murphy Gordon J | Probe instrument |
| GB2274711A (en) * | 1993-01-29 | 1994-08-03 | Michael Alfred John Stanton | Illuminated depth checking gauge |
-
2003
- 2003-12-11 GB GB0328681A patent/GB2409041A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1423523A (en) * | 1972-03-23 | 1976-02-04 | Cav Ltd | Method and apparatus for testing components |
| US4510365A (en) * | 1982-05-06 | 1985-04-09 | Raycon Corporation | Electronic depth controller for EDM apparatus |
| US5144753A (en) * | 1991-03-25 | 1992-09-08 | Murphy Gordon J | Probe instrument |
| GB2274711A (en) * | 1993-01-29 | 1994-08-03 | Michael Alfred John Stanton | Illuminated depth checking gauge |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0328681D0 (en) | 2004-01-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |