FRACTURE SPLIT MACHINE COMPONENT IMPROVEMENTS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This claims the benefit of U.S. Provisional Patent Application No. 60/744,797 filed April 13, 2006.

STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

FIELD OF THE INVENTION

[0003] This invention relates to machine components that are made in one piece, separated and put back together in a precise position of the two separated pieces relative to one another, such as connecting rods.

BACKGROUND OF THE INVENTION

[0004] Certain machine components, most notably connecting rods, are made in one piece and then split along a parting face so as to be put back together along that face for continued manufacturing operations such as machining. In the case of a connecting rod, at the crank end of the connecting rod, the bearing cap portion of the connecting rod is split off from the main rod portion along a diametral line of the crank bore of the rod. As disclosed in U. S. Patent No. 4,923,674, the disclosure of which is hereby incorporated by reference for its disclosure of how powder forged connecting rods are made and split, a notch is formed during the compacting process on each side of the crank bore, adjacent to the bolt holes that hold the bearing cap to the rod portion of the connecting rod. When forging, the notch closes to become a controlled ans stress concentrating crease or slit, but oxidation on the facing surfaces of the slit prevent it from being completely welded closed.

[0005] The slits initiate the splitting of the bearing cap from the rod portion of the connectine rod. when the bearing cap is wedged or otherwise forced apart from the rod portion,

usually by applying forces to the two halves of the crank bore. The cracking starts from the inside, which is where the initiating slit is, and moves outwardly. When the cracking reaches the bolt hole that is used to fasten the bearing cap to the rod portion post-fracture, it must proceed around both sides of the bolt hole, which can sometimes result in inconsistent crack propagation.

[0006] U. S. Patent No. 4,923,674 discloses forming two crack path notches in the inside of the bolt holes to try to achieve more consistent results, which requires a post compaction or forging machining operation. U. S. Patent Nos. 5,594,187 and 5,613,182 provide a different proposal, which is to form a stress riser crease in a side surface of the connecting rod, rather than at the bore, and is not believed to have found wide acceptance.

SUMMARY OF THE INVENTION

[0007] The present invention provides other solutions for achieving more consistent results in the crack propagation from an initiating slit in a fracture split machine component. The present invention provides control of the crack direction after initiation resulting in more predictable and consistent crack propagation.

[0008] In one aspect, in addition to the starter notch formed in a pre-forging workpiece, a target notch directly opposite from the starter notch is formed in the component. One option is to make the pre-forging by powder metal compaction, such that the starter and target notches close when the component is forged, but do not re-weld either due to oxidation of the surfaces of the notch. Another tactic to prevent re-welding is coating the pre-forging with graphite or some other weld-inhibiting substance, either completely or locally, prior to forging to ensure that the surfaces of the notch do not join with one another. The intent of the target notch is to help direct the propagating crack to consistently end at the target notch, making mismatch and/or breakout of the surface of the component where the crack ends less likely.

[0009] Alternatively, rather than making a notch at the target location, a target slot of various shapes can be formed in the forged part to reduce the wall thickness in the section where the crack is intended to propagate. This should serve to direct the propagation in a predictable and consistent manner.

[0010] In another aspect, the desired area of fracture splitting can be made with a more brittle material. This can be done in the compaction of a powder metal compact by simply using a more brittle powder metal material in the desired zone of crack propagation. The material is chosen to be compatible with the other more ductile material of the connecting rod so a multiple material connecting rod is made. Alternatively, rather than using a different material in the zone of desired crack propagation, the same material can be used but of a lower density, which makes that zone more brittle.

[0011] In the case of a connecting rod, starting at the initiating notch on each side of the crank bore, when the crack propagates out to the bolt holes that extend through the legs of the connecting rod, the crack must proceed around both sides of the bolt hole for the cap section to separate properly from the remaining rod portion of the connecting rod. To facilitate this, in one aspect of the invention, the notch formed in the compact is made deep enough to intersect the bolt hole. Thus, the propagating crack more easily travels around both sides of the bolt hole therefore increasing consistency.

[0012] In another aspect of the invention, crack propagation is directed toward target zones which are formed by selectively applying near surface residual stresses. One method is forming areas of high residual stresses on either side of the target zone by needle peening. Needle peening has the effect of increasing the near surface residual stresses, which helps direct the propagating crack to the zone without the residual stresses.

[0013] In another approach, a notch or slot is formed completely or nearly completely around the peripheral edge of the desired fraction separation plane. In the case of a connecting rod, that is around the legs of the connecting rod, between the cap and the remaining portion of the connecting rod, where the fracture is desired to occur.

[0014] As a number of alternatives are aspects of the invention, different aspects can be combined to facilitate and direct crack propagation. For example, brittle materials can be combined with inner and outer notches or slots, or with fracture separation plane edge notches, or with needle peening, or deep slots.

[0015] In addition, many of the aspects of the invention may be applicable to non-powder metal components, such as wrought components.

[0016] The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Fig. 1 is a perspective view of a connecting rod preform (prior to forging) of a first embodiment of the invention having target notches in the front and rear surfaces of the connecting rod opposite from the initiating notches provided in the crank bore;

[0018] Fig. 2 is a view similar to Fig. 1 , but with target slots rather than notches;

[0019] Fig. 3 is a view similar to Fig. 1, but with zones of more brittle or lower density material and no target notches or slots;

[0020] Fig. 4 is a view like Fig. 1, but with no target notches but a deep initiating notch that extends into the bolt holes;

[0021] Fig. 5 is a view like Fig. 1, but without target notches and with peened areas with a target area between them; and

[0022] Fig. 6 is a view like Fig. 1, but with a crack propagation directing notch formed all the way around the legs of the connecting rod at the desired fracture plane between the bearing cap and the rod portion of the connecting rod.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Fig. 1 illustrates a connecting rod preform 10 having a rod portion 12 and a bearing cap 14. A crank bore 16 has its upper half defined in the rod portion 12 and its lower half defined in the cap 14. Initiating stress risers 18 and 20 are formed on opposite sides of the bore 16 as V-shaped notches during the forming of the powder metal preform and closed to become slits when the preform is forged.

[0024] After forging, when the cap 14 is fracture split from the rod portion 12, a crack propagates through the legs on each side of the bore 16, one crack starting at the stress riser 18 and working outwardly and the other crack starting at stress riser 20 and progressing outwardly. To help control the direction of crack propagation, target stress risers 22 and 24 are provided. The stress risers 22 and 24 are V-shaped notches parallel to the corresponding notches 18 and 20 and opposite therefrom in the preform, and are compressed down to slits by forging. The crack propagates outwardly from the stress riser 18 to the stress riser 22 and on the opposite side from the stress riser 20 to the stress riser 24 to create mating faces that are generally parallel to the initiating and target stress risers where those mating faces start and stop. The provision of the target stress risers 22 and 24 also makes less likely breakout of any chips from the front and rear faces of the connecting rod where the cracks terminate.

[0025] In Fig. 2, the connecting rod preform 10 is essentially the same as in Fig. 1 except that the target stress risers 22' and 24' are formed as slots with a bottom radius in the preform, rather than as V-shaped notches. The stress risers 22' and 24' can extend deeper into the front and rear sides of the connecting rod 10 in Fig. 2 and tend to close close less than the V-shaped

notches during forging and so decrease the surface area of the mating faces that must be fractured.

[0026] In both Figs. 1 and 2, and in all embodiments in which stress riser notches or slots are provided that are pressed closed to form a slit during forging, it is desirable to ensure that the faces of the slots or notches do not weld or join with each other during the forging operation. To this end, it is known to purposely oxidize these surfaces to hinder joinder of them during the forging operation. To further ensure against joinder during forging, the stress riser surfaces can be coated locally with graphite, or the whole connecting rod can be coated with graphite or some other weld inhibiting substance including the notch surfaces.

[0027] The preforms 10 can be made, for example, by powder metallurgy.

[0028] Referring to Fig. 3, a connecting rod 10 has initiating stress risers 18 and 20 and in the zones 30 and 32 of desired crack propagation, the connecting rod 10 is more brittle than in the surrounding areas of the connecting rod 10 to either side of the zones 30 or 32. The zones 30 and 32 can be made more brittle either by using a more brittle powder metal material in those zones when compacting the preform or by using the same material but compressing it to a lower density in the zones 30 and 32. Either way, the cracks that are initiated at the stress risers 18 and 20 are more likely to stay within the boundaries of the respective zones 30 and 32 than to wander outside those boundaries into the more ductile material that borders them.

[0029] In the connecting rod 10 of Fig. 4, the initiating stress risers 18' and 20' are significantly deeper than in the prior embodiments, and extend so deep as to intersect the bolt holes 36 and 38 that are for the bolts that fasten the bearing cap 14 to the rod portion 12 after the two parts are split. Thereby, the crack that is initiated at either of the stress risers 18' or 20' is initiated on opposite sides of the adjacent hole 36 or 38 and so is more likely to proceed around

the holes in the desired fracture plane and less likely to deviate from the intended path of propagation.

[0030] Referring to Fig. 5, the connecting rod 10 has initiating stress risers 18 and 20 as in the embodiments of Figs. 1-3, but on the front and rear faces of the connecting rod 10, has areas 40 and 42 of intended crack termination. The area 42 is defined between two areas 44 and 46 of increased surface density, which would repel the crack from approaching them and therefore repel the crack toward the zone 42. Corresponding areas 48 and 50 on the rear face of the connecting rod 10 of increased surface density border the zone 40. The areas 44, 46, 48, and 50 of increased surface density may be made of higher surface density, for example, by needle peening.

[0031] In the connecting rod 10 illustrated in Fig. 6, stress risers are provided for 360° around the legs of the bearing cap 14 and rod portion 12, at the plane of intended fracture. These 360° notches 54 and 56 may be smaller or more shallow than the notches 18 and 20, 22 and 24, or 22' and 24' as they go all the way around the legs. Alternatively, they could be formed more like the slots 22' and 24', rather than V-shaped notches. They should not, however, be made so small that during forging the faces of the notches are joined to one another. Providing stress risers all the way around the legs makes it more likely that the mating faces once separated will be in or close to the same plane as the stress risers.

[0032] Preferred embodiments of the invention have been described in considerable detail. Many modifications and variations to the preferred embodiments described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiments described, but should be defined by the claims which follow.