The lubricant research in process of static fluid extruding

Label of document of 4 　 　 piles up: A article number: 1001-0645(2000)02-0174-05Lubrication In The Process Of Hydrostatic ExtrusionZHANG Zhao-hui, WANG Fu-chi, LI Shu-kui(School Of Mechanical Engineering And Automation, beijing Institute Of Technology, beijing 　 100081)Abstract: To Study The Lubrication Situations And The Velocity Conditions For Obtaining The Hydrodynamic Lubrication In The Process Of The Hydrostatic Extrusion, three Lubrication Situations Were Proposed In The Process Of The Hydrostatic Extrusion According To The Lubrication Theory Of The Plasticity Process; A Critical Velocity Formula For Obtaining The Hydrodynamic Lubrication Was Put Forward According To Reyno.

The Results From The Formula Are In Good Agreement With The Experimental Data, and The Critical Velocity Formula May Be Used As A Criterion Of Forming The Hydrodynamic Lubrication In The Process Of The Hydrostatic Extrusion.

Key Words: Technology of extruding of static fluid of 　 of Hydrostatic Extrusion; Hydrodynamic Lubrication; Lubrication Film is a kind of little cutting or the new-style treatment method that do not have cutting and the most efficient technology way that raise brittleness material obdurability. With conventional mechanical extruding technology photograph comparing has a lot of advantages, be like: Static fluid extruding uses medium of complete liquid pressure, impose negative charge by the liquid go up at workpiece, make workpiece does not have the Dui thick phase of common extruding before extruding, be out of shape even; In the meantime, lubricate as a result of high-pressured liquid the effect, make extrusion die is provided and the attrition between workpiece is reduced greatly, accordingly, this kind of technology very be helpful for brittleness metal stuff reaching metallic radical the treatment of composite material. The graph is shown 1 times for static fluid extruding and principle of extruding of general force plunger pursue. Graph extruding of 1 static fluid and basis of author of plan of principle of extruding of general force plunger are adhesion - be out of shape n duality chafes academic [1, 2] , the attrition between the workpiece in analysing process of static fluid extruding systematically quite and mould surface is lubricant circumstance. The lubricant condition between 1 workpiece and mould surface 1.

1 adhesion - be out of shape n duality chafes theory is adhesion - be out of shape n duality chafes academic attrition mechanism but by the graph 2 try to explain. Surface of mould of microcosmic cobbly workpiece, below very high interface pressure, the protruding body A of workpiece surface, c and mould surface produce instantaneous adhesion, as a result of the opposite motion between workpiece and mould, workpiece surface A, c protruding body will by clipping, what its shearing force forms attrition factor is adhesion; When B of another protruding body is running workpiece surface to mould surface A to choose protruding posture place, will be plowed to cut by body of protruding of this bit of mould and be out of shape, form attrition plow cut. Because this attrition factor is two the sum: B of μ of A+ of μ = μ , (1) pursues 2 actual metals are contacted occasionally A of the μ in model type is bit more adhesion by the attrition when clipping factor; μ B is plowed to workpiece surface for mould protruding body cut be out of shape attrition factor of the part. 1.

Motivation of fluid of ① of 　 of 3 kinds of in process of extruding of 2 static fluid lubricant condition lubricates to fall in proper condition, workpiece and mould surface can be shed by body lubricating film is separated, film is deep raisedder than the surface dimension is gotten greatly much. Right now, the pressure of the fluid carries outside the balance, the element in fluid layer does not suffer metallic surface atom to cite the effect of field of force for the most part, OK and free land cuts motion relatively, this kind of lubricant condition calls a fluid to lubricate [3] . When mould interface is in this condition, the active force between lubricant element can perceive the adhesion strength that is broad sense, attrition force results from the active force between element of the lubricant when moving relatively between the interface causes cut obstruction [4] , and without the mechanical and occlusive obstruction between concave and convex body, when fluid motivation is accordingly lubricant, attrition factor includes μ A only, and because the active force between lubricant element is small (include Fan Dehua force, hydrogenous key force to wait for) , make μ A value very little, factor of i.e. whole attrition is very minor (can fall to 0.

001 ～ 0.

008) . At this moment, the attrition obstruction of industry pattern surface depends on completely the property of the fluid, and have nothing to do character with the material of two attrition face. Graph 3a place is shown for fluid motivation lubricant condition leaves feature of appearance of workpiece apparent form. Graph border of ② of 　 of feature of appearance of form of apparent of the workpiece below 3 different and lubricant condition is lubricant this kind of lubricant condition is to show mould and workpiece move relatively the surface by a paper-thin lubricating film (be in normally 0.

1 μ M is the following) separate, the ply of lubricating film cannot arise to lubricate like fluid motivation pool of in that way fluid dynamic pressure, because this won't affect the microcosmic form appearance of industry pattern surface, of mould surface bright and clean degree of meeting is duplicate go up to workpiece, if pursue,3b place is shown. In this kind lubricant condition falls, the attrition obstruction between two surfaces has industry pattern already the between concave and convex body mechanical and occlusive mechanism when two surfaces cut motion relatively is effective, consequently attrition factor includes μ B, have the resistance effect that moves relatively between lubricant element again additionally. Such, total μ is comprised by μ A and μ B, relatively the attrition factor when fluid motivation is lubricant is gotten greatly much, its limits is commonly 0.

050 ～ 0.

150, this kind of lubricant status appears below the work requirement of high pressure, low speed commonly. ③ mixture lubracation mixture lubracation is a kind of when show fluid motivation lubricates to lubricate to coexist at the same time with border lubricant condition, this kind of attrition when lubricating is existing at the same time between element of the lubricant between metallic interface adhesion and the machinery between concave and convex body is occlusive wait for a variety of mechanisms, size of its attrition factor holds proportion on departmental substation definitely. Graph 3c place is shown leave feature of appearance of workpiece apparent form for mixture lubracation condition. Below low speed condition, between workpiece and mould be in attrib border and lubricant condition basically, as extruding speed rise, the lubricant condition between industry pattern surface lubricates to fluid motivation gradually condition transfers, appear right now condition of so called mixture lubracation. Rise further when speed and exceed some when critical value, complete fluid motive force can be formed between industry pattern surface lubricant condition, be versed in the attrition factor between mould surface can be reduced greatly right now. Motivation of the fluid between 2 workpiece and mould surface is lubricant formation condition is in process of static fluid extruding, because extruding mould, workpiece reachs load is axial symmetry, the vertical section of the mould in taking extruding course so and workpiece builds mechanical computation model, if pursue,4 are shown. When undertaking academic derivation, make the following hypothesis [5 ～ 7] : Graph 4 fluids motivation is lubricant extruding 　 ① builds the static fluid below all hypothesis of Reynolds equation all hold water here; ② pressing sticks coefficient to be constant, do not change along with pressure; Effect of ③ oversight temperature rise, consider to press only stick effect; ④ oily film is very thin, ignor to work measure and the influence that contact area size. Introduce one dimension Reynolds equation [8] : (2) among them H is oily film ply; η is the dynamical viscosity of lube; V is the relative speed between industry pattern surface. V=vt+vl, p of α of 0e of η = η , (The Vh in 3) type, vl is fluctuation interface speed, among them, vh=0, vl=-v0(and way of X reference axis are opposite) ;v0 is work shift speed (refer to graph 4); α to stick coefficient; η to press 0 for initiative motivation viscosity, pa.

S. type (3) generation enters type (2) can get 　 (4) general type (4) is integral, get 　 (5) is in in X=x2 of oily film entrance, because interfacial pressure is extremely high, reason can think approximately (1/e α P)(dp/dx)=0.

(6) general type (6) generation enters type (5) can be gotten (P)(dp/dx)=-6v0(h-h2) of α of H3/ η 0e, (7) pursues in area 1(4) , the following condition holds water: H=h0; When X=x0, p=pe; When X=x1, p=p1. type (7) integral offspring enters afore-mentioned attrib border conditions to be able to get 0/h30)v0(h0-h2)(x1-x0) of η of α of Pe+(6 of α of E- α P1=e- . (8) 　 is in area 2 inside, the following condition holds water: H=xtan φ ; When X=x1, p=p1; When X=x2, p=p2. (If 9) 　 makes place denotive the T of osculatory pressure σ of the work that pressure P2 handles than mould entrance and mould is big, criterion pressure medium can flow into workpiece and mould between. Accordingly, the requirement that makes fluid lubricating film is generated continuously is T of P2 ≥ σ . According to elementary analysis, s(of σ of T=pe+ of osculatory pressure σ among them σ S is out of shape for workpiece obstruction) , the requirement that forms fluid motivation to lubricate thereby turns into S of σ of P2 ≥ Pe+ . (Type of 10) criterion basis (9)(10) , in process of static fluid extruding, form fluid motive force the work shift rate with lubricant necessary place is 　 (11) 3 analysis and discussion 　 ① are commonly in process of static fluid extruding, whether to produce the not stable phenomenon such as peristalsis as judgement whether the fluid lubricating film that forms stability namely the mark with fluid lubricant motivation, because this can use a test,lubricant to forming a fluid critical rate value has a test. Graph 5 it is a basis have below the situation of different standard horn that measures in process of copper of static fluid extruding wait without peristalsis flabby the critical rate value with the mobile workpiece that decides phenomenal happening. ○ wriggles to did not happen; △ wriggles to happen. This and according to type (the relation of depend on sb or sth for existence of the V0 that 11) place gets and mould angle is consistent. The formula of critical speed computation that this proves to be based on the workpiece that above assumes derivation comes out 4 times to move is reliable. Graph speed of 5 work shift and modular horn squash to static fluid there is the type of influence 　 ② that does not have peristalsis in the process (11) shows when workpiece floating rate achieves some when critical value, can form fluid motivation to lubricate between workpiece and extrusion die surface, critical value gets this rate workpiece material is out of shape the η of initiative motivation viscosity of medium of half horn φ , pressure mixes obstruction σ S, mould its control the impact that sticks coefficient α and extruding pressure Pe. In extruding workpiece material and lube medium certain condition falls, can through type (the mould angle with 11) logical choice, the critical rate value that makes place corresponding is unapt exorbitant, the metal that because extruding speed crosses what bring greatly to be out of shape temperature rise makes be machined,prevents thereby produces overheat or burn too. When ③ moves with the rate with more critical minor rate when workpiece, think to be in whole be out of shape complete fluid lubricating film had be notted form inside area, and form mixture lubracation state; When floating rate drops work further, can form attrib border and lubricant state. Right now the attrition factor between two surfaces will increase substantially, the not stable phenomenon such as peristalsis also can happen subsequently, should avoid the happening of this kind of lubricant condition in process of static fluid extruding so. CNC Milling