| 1. IntroductionWith the development of modern science and technology , the use is more andmore widespread of the rigid and crisp materials like optical glass and the ceramicsand so on . We need to use these materials frequently to make each kind ofcomponents and carries in the components drills a hole and make groove and so on,because these materials are very hard, brittle and not electric conduction, thereforethere is very big difficulty in the processing, especially process each kind of holes,the grooves and so on in the hard crisp material components.The micro-abrasive jet machining (MAJM) is use the high-speed air currentaccelerate the micro abrasive, and the high-speed abrasive impact the work piecesurface, the surface layer material to be removed of the hard crisp material workpiece. First, because this processing method is not cuts with the cutting tool,therefore the work piece receives strength extremely small , then cannot cause thework piece crash, and the processing process does not produce heat , has notaffected to the work piece nature;Secondly,the shape processed by this methoddepends upon the path completely which the jet nozzle moves, therefore thismethod may process the arbitrary shape holes and grooves;Finally, the processingequipment of this processing method is very simple, the construction cost isinexpensive, we can save cost greatly with this processing method. Therefore, themicro-abrasive jet machining technology is a very good solution in rigid and crispmaterials processing.2.Test system developmentWe have developed a set of test system through times test and improvement ,fig 1 is the schematic diagram of this system. This system is made up of the airsupply system, the jet control system, the abrasive supplies system and the jetnozzle and so on. This system may realize the micro-abrasive intermittence jetmachining, its switch frequency can reach 15times/min. At present the stand-offdistance of the test system is controlled by the robot which holds on jet nozzle.abrasivetankHigh-speedsovlaelnvoeid solenoid valveFilter and Pressurerelief valveFilter and Pressurerelief valvenozzleaircompressorOn/offsignalton toffControl computerFig 1 the equipment schematic diagramThis system use the air compressor as the air source, the gas rated pressure is0.8MPa, the greatest air displacement is 150l/min。The jet nozzle is the occurrencepart of gas in the micro-abrasive jet machining, the jet nozzle is the key part inabrasive pellet acceleration, its performance direct influence the effect and theefficiency of the jet. Fig 2 is the jet nozzle's three dimensional assembly drawing.This equipment abrasive supplies way uses stirs type, and fig 3 shows is thematerial supplies way schematic diagram.Connectto robotFig 2 nozzle's assembly drawing Fig 3 material supplies way diagramUnifies PCL-818L data acquisition card, uses the following plan realizationthe control which jet to the intermittent type, Programming with Visual C++ toPCL-818L to obtain the 5V TTL signal, builds a control circuit to realize to usesthe 24V solenoid valve the control, thus completes to the entire micro-abrasive jetmachining system the control. This control procedure flow diagram like fig 4shows ,This procedure can realize the following function:ENDStartSet the output port ,Jet timeandOn/off time in a periodThe output portright?Jet time reach0?Jet once andSubtract a periodfrom jet timeNOYESNOYESFig 4 control procedure flow diagram(1)chooses on Which port to output the signal.(2)establishes in a cycle the air course to open with the closure time.(3)establishes the total jet time, after jet had finished the system automaticallystops.(4)indicate the jet the condition and surplus jet time.3. The research on the simulation about abrasive jetUses the ANSYS CFX software for the different jet nozzle diameter, thedifferent jet nozzle length, differently stand-off distance and the different jetpressure carries on the simulation. We has obtained each jet parameter change tothe granule speed influence rule, obtained the distribution of velocity in jet process.This will instruct us further to optimize the structure of the jet nozzle , also willenable us better plan the parameter of jet experimental. The main rule which thesimulation research on micro-abrasive jet obtains to have following several:With the increases of jet pressure the maximum speed of micro-abrasive andthe most tremendous pressure on work piece center also remarkably increases;With the increases of stand-off distance the maximum speed of micro-abrasiveremarkably to increase, after the stand-off distance is big enough the maximumspeed of micro-abrasive starts as the certain degree to reduce;With the increases ofjet nozzle diameter the maximum speed of micro-abrasive to increase gradually, butwhen the jet nozzle diameter enough big the maximum speed of micro-abrasive isnot appears in the jet nozzle central;With the increases of jet nozzle length themaximum speed of micro-abrasive also to increase along, but the influence jetnozzle length change to maximum speed of the micro-abrasive is not very big.4. The experimental research of micro-abrasive jet machiningWe use the micro-abrasive intermittence jet machining equipment to carry onthe hole processing experiment on the K9 optical glass, carried on the injectionpressure, stand-off distance and jet time these three parameters to the holeprocessing diameter and the depth influence experiment. The experiment indicatedthat:Along with the stand-off distance to increase the processing the hole depthgradually to increase first, Then reduces gradually;Along with the time increasesthe hole depth also to increase along with it, the hole depth and jet time have thevery good linear relations, this explained that in the intermittence jet processing themicro-abrasive not to pile up in the hole base, enhanced the processing efficiencytruly;Increases the processing along with the jet pressure the hole depth also toincrease along with it, regarding different stand-off distance, the pressure variationto processes the hole the depth influence is consistent.Along with stand-off distance to increase the hole diameter also gradually toincrease, the big jet pressure processes hole diameter also big, the scope which alsojets the pressure high when the stand-off distance increases to be also big;Alongwith the jet time increase the hole diameter also to increase;Along with the jetpressure increases the hole diameter also to increase along with it, in big stand-offdistance the jet pressure to process the hole the diameter influence to be obvious.5.Main conclusion(1) Developed a set of test equipments for micro-abrasive jet machining technology,this equipment could realize the intermittent type jet machining, enhanced theprocessing efficiency. Also developed the control system of this micro-abrasiveintermittence jet machining, It can realize the control of intermittent type jetvery good。We can set the total jet time and the on time and off time in a cycleof jet machining in this system.(2) In view of the jet nozzle structure which independently designed by ourselveshas carried on the hydrodynamics simulation with ANSYS Corporation'shydrodynamics simulation software CFX, simulated the parameter just likeabrasive's speed, the work piece surface receives the pressure, high-velocity aircurrent speed and high-velocity air current's pressure distributed rule and so on.Through changed the design parameter of the jet nozzle, we simulated theinfluence of the parameters change to abrasive jet one by one .(3) Uses the intermittence jet device which independently designs to carry on theprocessing experiment about the K9 optical glass, obtained the influencerelations of jet time, jet pressure and stand-off distance, because the jet timeand the processing hole depth becomes the linear relations, explained that theintermittent type jet enhanced the processing efficiency truly.4) Through to contrast the experimental result and simulation result, we found thesimulation result and the experimental result consistent, the simulation result iscorrect. |
PDF Full Text Request