HUE033240T2 - Eljárás és berendezés alkatrész szilárdságának megnövelésére - Google Patents

Description

LOREMZ & KOLLmm FILI : AW impcmp

European patanf Application Mo, 0$ ?73 450,6

Method end apparatus for increasing the strength of e part

The invention relates to a method for increasing the strength of a component subjected to torsional and flexural stress, in particular or a crankshaft. The inventier; relates, farthermore, to an apparatus for the mechanical strengthening of a component subjected to torsional and flexural stress, in particular of a crankshaft.

Since internal oestrus lion engines are subjected to ever greater stress,· in the coarse of their development, due to the constantly growing increase in power, the engine industry demands very stringent strength requirements precisely tree the crankshaft which undergoes very high load and is extremely important for the functioning of an internal obnibustion engine, while at the: same time, because: of the er trees I y critical apace requirement:, the crankshaft should become only insignificantly larger in spite of the increases in power. This means, for the design of the crankshaft, that an increase in the stress-hearing capacity should not be achieved by increasing the cross section, that is to say via the moment of resistance of the eraxrkshaft, but, as far as possible, via local stress states. For this reason, modern crankshafts are produced, using the moat diverse possible machining and heat treatment methods, so that the crankshafts can be exposed to ever higher engine powers ,

Examples of such methods are thermal treatments, such . as the surface hardening methods of induction hardening and casehardening, laser hardening or nitriding, and also strain hardening methods, such as close rolling, shot peesing and Impact hardening, These are commoni.y employed and largely perfected methods which are suitable for the most diverse possible applications,

As examples of such methods, reference is made to the following publications : EP 1 478 480 M , EF 0 708 819 El, EP 1 14 9 883 A1, DE 41 2B 598 .41, m 2005/063438, BP 1 112 146 Bl, dP 04138463 A, JP 2001254143 A, EF 1 612 290 AX and DE 10 2004 008728 84. A nitriding method, such as is described, for example, in B? 1 812 290 Al, affords the advantage, when used on a crsnxshafv, that both the entire outer region of the cronksOefr and inner regions,, ouch as bores and the like, a re enclosed fey a surf ace nit riding layer. This nitriding layer nay have a depth of up to 0,S mm, depending on the method adopted. The advantage of such a nitriding layer is that the moat diverse possible notches, near-surface material inclusions outside the bearing faces and transition radii are incorporated, with the result that precisely these component regions are neutralised as stress-critical regions due to internal pressure stresses introduced as a consequence of the me shod. As a re sale, overall, a higher stress·· bearing capacity of the erasrotaft can be achlaved» Particularly in the case of high torsional loads which are:' typical in crankshafts, such a nitriding -nethod affords very good results, particularly with regard to fatigue strength. Moreover, as compared with the likewise available and sometimes also used possibility of employing high-ail cy steels for producing the orankshaft, nitriaing is a relatively cost-effeotive method.

However, tbs disadvantage of such nifriding treatments on components subjected to torsional and flexural stress is often that the depth action in notch regions is lower than in other surface treatment methods, In many highly stressed components, such as, for example, crankshafts, however, it is precisely in the transition regions between the bearings and the ' crank webs that such a depth action is desirable, since higher flexural, stresses can thereby be permit red in a lose situation.

In the design of a highly stressed crankshaft, it was therefore often necessary in the past to weigh up whether the flexers 1 or torsional stress entailed the lower reserves, and a suitable method for increasing the strength of the crankshaft was then selected according to this weighing-mp. if the decision on treating the composenr was not in favor of a nitridlag method, higher-grade and higher-tempered materials were often adopted in order to compensate the lower torsional fatigue strength, This mostly led to a cost rise which is undesirable precisely in automobile construction, A generic me shod fcr strengthening crankshafts is known from DE 2 1.41 17S hi.

An apparatus for the close rolling of cranksha fas according to the preamble of claim 11 is known from

Ef I Π2 146 B1, !r; this esse, the fores applied by the close reviling: head is absorbed by two supporting rollers*· axial go i dance being afforded by an axial guide roller,

The object of the present invention is to provide a method for increasing the strength of a component subjected to torsional and flexural stress,, eh rob mates it possible to have high torsional fatigue strength and a high depth action in notch regions for achieving a high flexural fatigue strength and which nevertheless allows the use. of relatively cost^effestive materials .

This object is achieved; according to the invention, by means of the features mentioned in claim 1.,

According to the present invention, therefore, in a first step, essentially' the entire component is nit aided, with the result that the compccent Is afforded the advantages arising from this surface treatment, to be precise, in particular, the high surface hardness, good running properties and high torsional fatigue strength. Owing to the subsequent at least partial removal according to the invention of the nitriding layer in the regions of the component which are subjected to high, flexural stress and to the following mechanical strain hardening of these highly . stressed regions, furthermore, a considerable increase in the strength of these notch regions is achieved., particularly with regard, to their flexural stress-bearing capacity. It is thereby advantageously possible to use less highly tempered materials for producing the component and nevertheless to obtain a torslocally and flexurally stressed component which' is capable of withstanding all the critical loads occurring during use. The force applied to the component during strain hardening can in this case be adapted to the respective conditions, in particular to the stresses to be expected when the component, is being used.

The removal according' to the invention of the nitridmg layer before the strain harden!ng of the highly stressed regions of the component by means of cutting machining ensures that the nit r iding layer is not damaged during the subsequent strain hardening, in particular that no cracks are formed in this, as would be the case if the strain hardening were being carried out on a component region provided with the nitriding layer,.

Overall, therefore, this is a method by means of which the component stresses to be: expected is each case can be influenced in a highly flexible way, thus affording novel possibilities of configuration in the design of composeπ is subjected to tbrsicnal and flexural stress-

An alternative solution results from claim 2.

In order to avoid a final machining of the component in the highly loaded regions, moreover, there is provision for further material of the component also to be removed: in addition to the hitriding layer, in order to form, an undercut in the at least one highly loaded region -

In a highly advantageous development of the method according to the invention, there may .be provision for a final machining of the. component. in terms - of its positional and/or dimensional tolerances to take place after the mechanical strain hardening. A dimensionally accurate component which can be used directly is thus obtained. in a further advantageous refinement of the invention, there may be provision for the mechanical strain hardening to be carried out by means Of close roiling> This, in addition to increasing the strength, gives rise to a very coed surface of the strengthened .region, Aiterhativeiy to this, it . is also possible that the mechanical strain hardening is carried out by means of impact hardening or by means of shot penning <

The method according to the .invention is to be used advantageously particularly when a crankshaft,· in particular an especially highly stressed crankshaft, is used as the oemponent subjected to torsional and flexural stress-.

Moreover, in this respect, there may be prevision for the at least one highly stressed region to be a transition region from a main bear!ng or connecting rod bearing to a crankshaft>

Claim II specifies an apparatus for the mechanical strengthening of a component subjected to torsional and f 1 ox u r a I s tr e s s ,

This apparatus is suitable particularly for carrying out the third step of the method according: to the ievention, to be precise the mechanical strain hardening of the highly stressed regions of the component. In this case, even in the case of slight oblique positions of the strengthening tool, it is ensured that edge pressures Upon the ni or id log layer end therefore possible damage to this are prevented, in a particularly advantageous refinement of this apparatus,· there may he provision for the at least one strengthening tool to have strengthening rollers, further advantageous refinements and developments of the invention, may be gathered from the remaining umbelaims. Ememplary embodiments of the invention are illustrated in principle below, with reference to the drawing in which; fig, 1 shone a highly diagrammatic view of a crankshaft; fig, 2 shows part of the crankshaft from fig. 1 as a component ati oh is subjected to torsional and flexural load and on which a first step of the method actordrug to the invention has been carried out; fig, 3 shows the crankshaft from fig. 2 in a second method step; fig, 4 shows an enlarged illustration of the second method step; fig. 5 shoes the crankshaft from fig- 2 in a third method step,· using an apparatus a o cor ding to the invention; fig, 6 shows the method step from fig, 5 with an alternatively configured apparatus and; fig, 7 shows a further alternative embodiesat of the apparatus for carrying out the third step of the method according to the invention.

Fig. 1 shows a highly diagrammatic view of a crankshaft 1 which has in the way known per se a pin rad. ley of main bearings 2,, via which, it is mounted within a crankcase, not illustrated, of an internal combus 1 ion engine, The oranksh®ft 1 may be both a crankshaft X employed in a motor vehicle end a very large crankshaft 1 used, for example, in ships' drives. Between the main bearings 2 are located respective connecting rod bearings 3, on which connecting rods, likewise net illustrated, of the internal combustion engine can he mounted. In a way known per se, the number of maih bearings 2 and of connecting rod bearings 3 is determined by the number of cylinders of the internal combustion smginc. Between the main bearings 2 and the connecting rod bearings 3 arc loco tod in each case who s are known as crank, webs 1 which bridge the radial distance between the main bearings 2 and the connecting rod bearings 3. The transition region from the crank: webs 4 to the main hearings 2 or connecting rod bearings 3 is generally, in the crankshaft i, id each case a very highly stressed region 5/ that is to say a region in which the crankshaft X has to absorb very high forces during operas: ion. In order to achieve the suff icient strength of the crankshaft 1 even in these highly stressed regions 5, a method described in more detail below has been developed , Instead of being carried out on the crankshaft 1, the .method may in principle also be carried out on another component which is subjected to torsional and flexural stress and the strength of which is to be increased by beans of this method.

In a first step of this method, the entire crankshaft If of which fig, 2 illustrates only one of the main bearings 2 and. parts of the crank webs 4 adjoining them, is πiprided, that is to say is provided writh'd nitriding layer 6 which extends ever the entire crankshaft 1. The nitriding layer 6 may be applied, fox example, by means of gas nitriding/ by means of carbonitriding or by means of plasma nitriding. This outriding layer B also relates to the most diverse possible notches, not illustrated, neat-surface material inciunions and lubricating oil bores and the like, The nitriding layer 6 thus increases the load-hearing capacity and torsional rigidity of the crankshaft 1 end reduces the potential wear of the surface on account of the increased1 surface hardness. The advantages of the nitriding treatment arise particularly in the case of crankshafts 1 which, have relatively narrow crank webs 4> since these are subjected to particularly high torsional stress.

Since only relatively low depth action is obtained precisely in the highly stressed regions: 5 sot the transition between the mat.π bearing 2 or the connecting rod bearing 3, cot iiinstraded in fig, 2, to the crank webs 4 by the nitriding layer 6, in a. second method step illustrated in fig. 3 the nitriding layer 6 is removed in the highly stressed region b of the crankshaft 1 by means of cutting machining. This cut ting machining, for which a: machining tool 7 indicated merely diagmmmaticaliy is employed, may take place, for example, by means of turning, milling or grinding. In addition to the rritriding laynr 6 which, of cour;:e, forms, part of the crankshaft I., farther material, that is to ray material not bo long rug to the nit riding layer 6, of the crankshaft 1 may also be removed, in order in the highly at res sec. region 5 to form an unde rent § which may be provided both radially and axially. This, however, depends on the design of the crankshaft 1 and is not always necessary, The highly stressed region 5 between the main bearing 2 or the connecting rod bearing 3 and the associated crank web 4 is in the present instance in each case provided with a radius or designed at a radios, Irrespective of whether material of the crankshaft 1 is also removed: in addition to the nitriding layer 6 - or net, the transition between the main bearing 2 or the connecting rod hearing 3 and the crank veb 4 may, after machining, be designed as a transition radius tangent to the respective face,

In fig, 4, the nit riding layer 6 is illustrated:, enlarged, and it can be seen that this has a bonding layer ha forming the cuter surface and a diffusion, layer 6b lying beneath it and contiguous to the remaining material of the craxikshaft 1, In contrast to the above-described complete removal of the nitriding layer 6, in which the undercut 3 can also be produced, in this case only the bonding layer 6a is removed, which constitutes an additional meaning of the

Particular tat least partial removal, of the nitriding layer 6" to the above-indicated removal of the nit riding layer 6 only in the 'highly·-· stressed region 5, It is therefore possible to remove only the bonding layer 6a of the nitriding layer 6 solely in the highly stressed region 5, A further possibility is also to remove part of the thickness of the diffusion layer 6b in addition to the bonding layer 6a.

In the third step of the method,, which is illustrated in fig. 4, the.highly stressed region 5 is mechanically stem in-hardened by means Of an. apparatus 2, which has a strengthening tool 10, in those regions in which the nitriding layer 6 has previously been removed, The mechanical strain hardening in this embodiment of the method is close rolling, Alternatively, mechanical strain burdening by moans of impact hardening, or shot penning may also be envisaged, la strain hardening by means of close roiling or impact hardening, a defined force is applied, to the compose rm, whereas, in shot penning, an under inad force action is applied by the balls acting on the crankshaft 1.

As a result of tine strain hardening, dapending on the force applied and on the no cb icing deration,. a non si sPar ably higher depth action of the stresses and of the strength increase arising frog this sod also an increase in the surface hardness are achieved, as compared with the state in. onion the crankshaft 1 is merer y n i t r 1 ded..

During the strain hardening:, it is possible to apply such a high force to the crankshaft X that very fine incipient cracks occur on the surface Of this, but do not have an adverse inf I us non on the strength properties of the crankshaft 1, since they cannot he propagated on account of the internal pressure stresses introduced. On the contrary, as a result of this increase in the close roiling force, an even higher fatigue strength of the .crankshaft l is achieved which is not. diminished by the incipient cracks. . This increase in the strengthening force which leads to the formation of the incipient cracks may in this case lie up to its above the force usually applied by. close rolling,: this advantageous -.v being adopted in order to increase the fatigue strength of the crankshaft 1,

This procedure of increasing the strain hardening force In this way such as to give rise on the surface of the crankshaft 1 to incipient cracks may also be envisaged in the case of drankshafts I which are heat-treated, for example, fey induction hardening: or another suitable method1 instead of by nit.riding.

After the mechanical strain hardening, it is possible to carry out a final, machining of the crankshaft X in terms of its positional and/or dimensional tolerances, this preferably taking piano by means of grinding. This is also possible in the subsequent strain-hardened highly stressed regions u. Such remachining of the surface of the main bearings 2 and/or. of the connecting rod bearings 3 and/or of the crank webs 4 may in many instances also be restricted to a straightforward reduction of surface roughness if a sufficient accuracy of the dimensional and positional tolerances is achieved or maintained by means: of the nitriding •set hod,

Since the highly stressed regions 5 have been strengthened by means of a depth-active strain hardening method, a greater removal of the nitriding layer 6 for dimensional and .positional final machining may bo permit tod. on those cylindrical facoa of tho main bearing 2 or she connecting rod bearing 3 which are, if appropriate.., to be remachined and on Che rue-on collar faces of the crank cobs 4 , The a b o ve ~ d e s c ribe d possible production of the unde rear 8 alto advantageously makes it possible to have a simpler dimensional and positional final much icing, for example by grinding. :fhe highly stressed regions 5 of the crankshaft I which are machined by means of strain hardening may also be .machined by means of a enfting method. In this case, the quantity of material removed, that is to say the depth of the cutting machining, depends on the depth action previously achieved by means of strain hardening, and therefore, in the case of a correspondingly high depth action of,, for example, .! mm, achieved by the strain hardening, it is perfectiy possible to remove 0.2 to 14 Kt of material in the . crankshaft 1, If the -undercut I indicated above is provided, no reworking is necessary in this region during the mechanical remachining of the crankshaft: 1.

Fig, S shown a first embodiment of the apparatus 9 for the mechanical strain hardening of the component subjected to torsional and flexural stress, in the present case the crankshaft 1. the: apparatus S has the strengthening tool 10 suitable for applying the force : to -the crankshaft 1,. and a steading device 11 absorbing the force of the strengthening tool 10. As described below, the steading device 11 prevents damage to the nitriding layer 8 still located on the . main bearing 2 or, in the case of the connecting rod bearing 3, on this . , The sereneihening fool 10. is designed in the present case as a close roiling tool, and has a plurality of . strengthen .ing rollers 12 which are mounted rotatably on a guide roller 1.3 and serve for strain-hardening the highly stressed regions 5 of the crankshaft 1,. that ip to say, as already mentioned, for carrying out the third-step of the method described above.

The steading device 11 has a running roller Id which is connected to the main bearing: 2 and which is mounted oh a bearing bolt 16 via a bearing device IS, The bearing device IS thus supports the stending device 11 in such a way that the latter is capable of absorbing even forces which act on the surface of the crankshaft 1, in the present case on the main bearing 2, at an angle different from 30/°, For this purpose, in the present case, the bearing device 15 is designed as a self·-a lion ing ball bearing, but it could also be a self-aligning roller bearing of another bearing device IS which in the way described absorbs the oblique 1y acting forces, in fig, 5,, the angle a illustrates the required possible oscillation comoonsa·: lag movement in the event of an oblique position of the strengthening tool 10. In general,: that is to say also in the embodiments of the strengthening tool. 10 which are described later, the angle a may amount to up to 15% an oblique position of up to a marlmum of 5 - 10° being more probable. The dimension "x" shows the distance, required for this movement of the guide relief 13, between, the guide roller 11 and the bearing bolt 16, rig , 6 11 loom rates a f urther embodiment: Of the apparatus 9. In this case, two strengthening tools 19 are provided, which have respective strengthening rollers 12 and are offset essentially by ISO* with respect to one another. here, in each case, one strengthening: tool 10 assumes the function of the steading device 11 for the other strengthening tool 10a, although, they act, free of contact and therefore free of force, on the face of the main bearing 21 This freedom from contact and freedom from force is due to the fact that the strengthening rollers 12 act only on the highly stressed r eg ions S a nd therefore are supported only there. Instead of the two strengthening tools 10 and 10a, three or more strengthening tools ID, 10a, etc. could also be provided, which should, then be arranged s;: us to be distributed at uniform, intervals around the orankshaft 1, Ά further embodiment, of the apparatus 9 is illustrated in fig. 7, fere, the strengthening tool 10 has a plurality of rams 17 which are actuated via a deflecting roller 18 in a way hot illustrated in any more detail and which consequently apply the force by pulsating hammer!og to the highly stressed regions 5 of the crankshaft 1. At their ends connected to the highly stressed regions 5, the rams 1? are provided with respective balls If, The; steading device 1.1 which counteracts the force applied by the strengthening tool. 10 is provided with a bearing device 15 which in this case is designed as a plain bearing and which is likewise capable of absorbing even forces which act on the surface of the crankshaft 1 at at angle different from 90*. Of course, forces acting perpeηdiea 1 ar.1 y on the surface of the crankshaft 1 arc also absorbed by the bearing device 15,

With regard to the embodiment of the strengthening tool ID with the rams 17, the design of the bearing device 15 as a plain bearing is an embodiment which is more sui tab.: e than a roiling bearing, since, when a hail bearing or roller bearing is used as the bearing device 15g the pulsating harrier mg of the strengthening tool 10 could present problems with regard to the durability of said bearing device. In this case,· the two faces of the plain .beatring should be adapted as exactly as possible to one another, while oil, grease or another suitable lubricant bay be 1. oca ted between these faces. Said method affords a component subjected to torsional and flexural stress, in the present case the crankshaft I, which not only has the advantages arising from nit riding treatment, such as a higher surface hardness .and higher torsional strength, but, due to the strain, hardening, also possesses a higher strength, in particular higher flexural strength, in the highly1 stressed regions 5. \·' * .. . '·. ^

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Claims (3)

1. Szabadalmi i gény pon t ok

   1 - Kijárás csavarásra és hajUtasra igénybevett alkatrész, különösén fergáttyüstsngeiy |.f| s^ilárdsáfinal iMgr^ygiéséze, amely aljária során első lépésben lényegében a teljes alkatrészt .nitriáréteggel {6} látjuk el, majd második lépésben az alkatrész legalább egy, nagy igén ybevé t e1ne k kitett tartományában {5} forgácsoló me gm u n k á 1. á s s a 1. legalább rés eben. eltávolítlük a nitridritsget 16), és harmadik iépéébeh az a lkat .rés 2: nítridrétegtől (6) mentesített legalább egy, na gy igénybevételnek kitett tartoraányának (5} szí lárdságát m e e h a ni ka 1 áton* h .1 d e g a 1 a k i t á s s a 1 mg g n Ö v e .1 j ü k; a*m3, g nitridrétegböl {6} csüpán egy kötőréteget távolítunk el.
2. 2. Eljárás csavarásra és hajiitásra Igénybevett alkatrész, különösen forgattyústengely (1) sziiárdságának megnövelésére nme ly eljárás során első lépésben lényegében a teljes alkatrészt n.i tridr éteggel · 6) latjuk el, majd második lépésben m. alkatrész legalább egy, négy igénybevételnek kitett tartományában (5) forgácsoló megbán kálássa! legalább részben eltávolítjuk a nitrIdréteget {6}, és harmadik lépésben az alkatrész n i t r i. d r é te g t ő .1 (6} mentesített legalább egy, nagy 1génybevételnek kitett tartományának (5} szilárdságát mechanikai utón, Mdégalákítással megaive Íj ükí azzal jo&amp;loábfctm, hogy alászúrás (8} kialakítása végett a nitridréfcegen (6) kívül további anyagot is eltávolítunk az alkatrészről fi). 3 · Az L vagy 2. igénypont szerinti eljárás, 1 gellemezve, hogy a mechani ka úton, h idegalakitássai történő szilárdságnövelést követően helyzet- és/vagy mérettörés végső megmunkálási. hajtunk végre az alkatrészen (1) > "' i-' ! 2 „ vagy 3« igénypont szerinti eljárás#. «ι&amp;ζ&amp;Χ frnUmmmm, hogy a hideg a la kitassai történő szilirdaágpő^^aést: nengete.res alkalmazásával hajtják végre. Az i*# 2. vagy 3. igénypont szerinti eljárás# at sóssal hogy a hidegalakítással történő sziiárdságnoyéiést ütve sajtoiÉs "alkalmazásával hajtjuk végre. fe. uz 1-2, igénypontok bármelyike szerinti eljárás#. mma.% hogy a n i t r i d r é t e ge t fő) esztergályozás# maré s vagy köszörülés alkalimavásával távolitjuk el. 1... &amp;m- igény pop tök: iblrmelyx ke szerinti élj áráé#: mrnmt 2 ellessen ve # hogy alkatrészként {.1} íorgatkyústengelyt :al.kalmé:Z:nn:k. 8' &amp;"%* igénypont Bzerinti eljárás# azzal jells^euve# hogy a nagy Igénybevételnek kitett tartományt (5) főcsapágy {2} vágy bajtófűdcaásigy (31 éé egy forgattydpbiá (4) közötti •átmeneti tartomány képezi, 3. A 8. igénypont szerinti él járás# a«8al jtóiierif®# tdgy au átmeneti tartomány érintőleges vagy alávigott zidioszMnt van kialakítva,
3. 10, Άζ Χ"·9, igénypontok hSrméiyike szerinti eljárás# mm® 1 JoXX#mez;vó, hogy az alkatrész nagy igénybevételnek kitett tartománya (!) szilárdságának mechani kai úton, hidegalakítással történő megnövelése során olyan erőt alkalmazunk# hogy az alkatrész felületén repedések keletkeznek, és a hengereiéinél: szokásoshoz viszonyítva legfeljebb 40 fmkal megnövelt eröháöist fejtünk ki. 11 < Berendezés csavarásra és haj látásra igénybevett alkatrész# különösen forgattyúatengely (1) szilárdságának mechanikai úton# hidegalákilássál történő megnövelésére# amely berendezés az alkatrészre erőhatást kifejtő s z i I á r ds ágnö ve 1 ö szerszámot (10) és a legalább egy s2ilárdságnovelő szerszám (10) által gyakorolt erőhatást felvevő elientartő szerkezetet (n; foglal magában; azzal jeli aaewa, hogy a a ellentartó szerkezet (11} esapágyszsrkezet (15) által oly módon van csapágyazva, hogy a szAlárdságnövelő -szerszám (.12) csekély mértékben ferdítit helyzete esetén az utóbbi által bevitt, aa alkatrész (1) felületére ferdén ható ereket képes fel venni, 12. A 11 v igénypont szerinti berendezés, azss&amp;l jallemesstm, hogy a legalább egy szila rdságnovelö szerszám {10) több sziiárdságmövelő hengert {12} foglal magában. 13. A 12. igénypont szerinti berendezés, azzal jellemezve, hogy a legalább egy szíláröságnÖveXő szerszám (10) több verőkost í17) foglal magában, 14. A 11-13,. igénypontok bármelyike szerinti berendezés, azzal jellemezve, hogy több, a megmunkalandé alkatrész, körül egymáshoz képest eltolva elrendezett szilárdságnövelő szerszámmal (10, 10a) rendelkezik, és az egyik szilárdságnövelő szerszám :(1Ö, 10a) ellentártó szerkezetként (11, i la) szolgál a másik szí i.árciságnöve fő szerszám (10, 1 Ον ο rámára ,