MXPA99011051A - Method for improving the error of envelope and of passing in metal gears in po - Google Patents

Abstract

The present invention relates to a method for manufacturing a straight product gear from a powder metal, the straight gear has a plurality of gear teeth, each tooth has gear tooth flanks, the gear, has a longitudinal center line , the method can be operated to regenerate the gear alignment, to reduce the misalignment between the flanks of adjacent gear teeth to reduce the misalignment between the gear teeth and to reduce the error of the main line of each gear, the method of The invention is characterized in that it comprises: (a) compressing a powder metal preform of the spur gear, each gear having a longitudinal center line and a plurality of gear teeth, each gear tooth has gear teeth flanks, (b) synthesizing the gear teeth. preformed straight gear to solidify the powdered metal preform in a general way; (c) heat the preformed s interized to a predetermined minimum hardness; (d) provide a hardened milling cutter and a stable hardness milling machine; (e) turn the sintered and heat treated gear with the hardened milling cutter in the hard milling apparatus to remove between approximately 0.013 cm (0.005) in.) and 0.018 cm (0.007 in.) of material on each gear tooth flank, the turning acts to regenerate the relationship formed between the gear and between the gear teeth and the longitudinal centerline of each gear.

Description

METHOD AND APPARATUS TO IMPROVE THE ENVELOPE AND PASSAGE ERROR IN PULVIMETAL GEARS DESCRIPTION OF THE INVENTION The present invention is related to the manufacture of gears by a powder-metal process. More specifically, the present invention provides a method and apparatus for improving the envelope and pitch error of a pulley produced gear, which gear has been heat treated and cooled to approximately a totally hard condition. The gears have historically been manufactured by machining, forging and casting. During the machining separations, a blade can be cut from a soft or green bar stock material, and after this subsequent machining operations have included core drilling, broaching, carving, shaving, heat treatment to harden with a machining after hardening and crushing operations. In more recent years, the gears have been manufactured by means of pulvimetal processes, particularly cylindrical gears, which can have straight or helical dentures. Initially the size of the pulvimetal gears produced were generally smaller gears, but over the years the size of the pulvimetal gears increased.

The gears can generally include cylindrical gears, bevel gears and helical gears and can be classified as straight or helical bevel gears; Straight gear, spiral, zero conical and conical denture and hypoid. This is merely a short list of the various descriptive nomenclature terminologies for gears in general. In addition, these gears can be used in various ranges to provide gear trains. The cylindrical gears are generally those that transmit energy between the parallel axes and have straight teeth parallel to the gear e e. Currently, the production of pulvimetal gear is especially directed to cylindrical gear. In the broadest sense, it is necessary to provide a gear that transmits force and movement to transfer the energy between the parallel axes coupled to the gear. Satisfactorily the durability of the highly loaded gear tooth surface requires that various issues or physical characteristics of the gear be suitably designed and manufactured. Among the parameters required to be restricted to the closest tolerances are the following: (1) the profile of the denture, which must be adequately modified from a real enclosure to suit the operating conditions; (2) the index of the denture and the parallelism of the denture, which must be kept within the close limits; (3) the gear, which must be mounted in such a way that the teeth do not deviate out of line; and the surface of the gear teeth, which must have a sufficient hardness and an adequate finish and which must have a good lubrication, particularly when starting the initial operation. The design of the gear and gear teeth has been observed as a compromise or between the resistance of the denture and the durability of the surface. A large denture provides much more strength but much less surface durability than a smaller denture, and vice versa. A highly loaded gear tooth with adequate rigidity deviates around a point in the middle part of the flange, bending like a rigid body under load rather than as a non-uniform rod only. The unlocking or other modifications of the profile of the denture provides free space to avoid excessive loading on the denture tips due to the deviation of the preceding gear, and ramps at the tips on the denture ensure that the first contact does not extend to the teeth. tips. It is the refinement of the design which needs to be careful in gear production to avoid distortion during carburetion or heat treatment. The denture can be kept parallel within 0.0003 inches in the denture width and the index can be maintained within 0.0002 inches between the adjacent teeth of a gear. The reference to the enclosure of a gear tooth has been roughly defined as being placed along an enclosure, which is a curve generated by a point in a hardened cable as it is unwound from a cylinder. The circle that is generated is called the base circuid of the envelope. The envelope curve sets the denture protrusion out of the base circle. From the base circle inward, the flank of the denture ordinarily follows a radial line and is currentilineated within the base region with a band. The basic zipper shape of the enclosure denture has straight sides. As mentioned above, the above methods were recorded, and of these methods the main technique for the production of gears, as it is for the automotive industry, was the machining of steel bar storage to produce a finished gear. Gears that support lighter loads, such as watches and sewing machines, were occasionally produced by stamping metal sheets, but broadly speaking, gears for load transfer were produced by machining and forming steel bar storage. However, all the gears suffer from the requirement of alignment of the gear teeth with each other and with the centerline of the gear. In addition, maintaining adequate contact between the flanks of the gear teeth meshed at the point of support, which is approximately half of the root towards the crown of each tooth, - an important consideration for proper wear, strength and low noise level Obtaining the proper finished gear surface generally includes finishing the gear surfaces by grinding the bearing surfaces, by translating and causing the gear teeth to match or by grinding the inner hole. In addition, the gears can be mounted on fixtures before heat treatment to minimize distortion during heat treatment. All of these operations are additional costs and require both important equipment and experienced labor to produce a finished and acceptable gear. The production of gear by means of the process of pulvimetal provides parts with lower cost with mechanical properties generally equivalent for an application. That is, the powder is formed in a preform inside a die in a powder press at a speed that is several times faster than a single machining operation. These green or preformed gears are formed with gear teeth and central holes in predetermined dimensions without alignment. In addition, these parts avoid flash losses, avoid a plurality of tools and machines and generally minimize the requirements of a plurality of experienced machinists. These preforms are in a condition for the agglomerate, which is generally carried out in a continuous band in a muffle furnace. The agglomeration and heat treatment operations can in some cases be carried out in different areas of the same furnace. However, if intermediate operations are desired, such as the final pressure after agglomeration, they can be performed before heat treatment and hardening. The specific sequence of operations can be determined with the requirement of the particular part, its size, and the available production equipment. However, the subsequent tournament operations after hardening regenerated the relations between the gear teeth and the center line at least as well as the hard ground with a threaded wheel grinder. It should be noted that the burnishing of a gear is not intended to regenerate the geometry or correct for significant errors during production. More specifically, burnishing will slightly affect the quality of the denture surface of the individual gear but it has very little if any impact on the geometry of the gear. It has been found that the dominant variants of the gears produced by means of powder-coated techniques are the axial misalignment of the flanks of the denture in relation to the gear orifice or the longitudinal center line of the gear., and the inclination or misalignment of the flanks of the denture relative to one another and the gear hole. These geometry variants are generated by any of the following operations either individually or in combination: pressing, agglomerate, final pressure, heat treatment or, grinding of the face and orifice. These gear geometry variants are accommodated by hard burnishing after heat treatment. The present invention provides the manufacture and production of gears, particularly cylindrical gears, by means of powder-coating techniques. The gears currently produced with pulvimetal suffer the same restrictions or faults as the machined gears. As a result, a new technique has been developed to provide gears that solve the constraints of misalignment between the gear teeth and the misalignment between the gear teeth and the center line of the gear, or the error of the pitch line. In addition, the present invention regenerates the relationship between the gear teeth and the center line, provides a surface finish on the gear teeth which avoids the requirements of burnishing and prevents the bending of the root area between the teeth of the adjacent gear. this way improving the strength and durability of the gear. The gears are regenerated by the gear tournament after the heat treatment to realign the gear teeth with each other and the center line of the gear, to solve misalignment and error of the pitch line. In addition, this operation is performed with a hard milling tool, which is . Significantly faster than crushing or reburning.

Milling has a negative roll angle in a shaping machine that expands and prevents the slack generated by a large machine to avoid any need for hard grinding of the gear teeth, the center hole or the end support surface. BRIEF DESCRIPTION OF THE DRAWINGS In the various figures of the Drawing, the reference numbers identify the similar components, and in those drawings: Figure 1 is an oblique view of a central cylindrical enclosure; Figure 2 is a plan view of an illustrative drill for counting gear teeth; Figure 3 is a partial elevation view of intersected gears; Figure 4 is an enlarged segment of the gear denture; Figure 5 is a geometric method illustrative of the generation of the face of a shell gear denture; Figure 6 is a partial side elevation view of a powder press for realizing the powder metal parts; Figure 7 is a cross-sectional view of a cutter for hard cutting, the cutter of which has a negative recess angle cutter; and Figure 8 is an end view of the cutter in Figure 7 noting the negative recess angle of the cut denture. The present invention provides a method for the production and regeneration of gears, especially cylindrical gears, whose gears are made of powder metal. Figure 1 illustrates an exemplary cylindrical gear 10 with a plurality of gear teeth 12 and a central hole 14, whose orifice 14 has a central longitudinal axis 16. The gears have generally been produced by various production methods including machining, casting, toasting and stamping. However, the main manufacturing technique for gears for energy transfer has been through machining practices, such as baking, drilling, boring, milling, brushing, forming, slotting, cutting, broaching, filing and generating, and usually multiple combinations of these. processes. In the case of the generated, this term is frequently used when referring to the milling machines or gear generators. The strawberries or cutters by milling cutters are tools that cut the dentures of the gears, not only the cylindrical gears but gear in eight, which are a splined shaft with four gears cut inside it, splines, helical gears, and other types of gear. The cutters by milling cutter 18 in Figures 2, 7 and 8 are defined as a milling machine, the denture 22 which is in a helical path to the remover of the circumferential surface of the milling machine. The cutter cutter 18 is generally used to cut cylindrical and spiral gears, helical wheels, sprocket dentures, ratchet wheels, splines, square drive shafts and other gears. The cutter cutter 18 with a longitudinal axis 20 is shown in Figure 2 with a plurality of cut teeth 22. Cutting by definition is a continuous milling operation in which the milling cutter and the green or green raw material pull in a timed relationship with each other. In addition to the rotational movement, the milling cutter and the gear blade are fed relatively to each other to produce the cylindrical gear, helical gear, or spline. The cutting of a gear provides a rolling action in relation to the milling cutter. This rotation produces the surrounding contour of the gear teeth. The reference for generating a gear, and the envelope contour, by cutting is performed by the relative rotational movement of a gear blade (not shown) and a cutter cutter 18. A cutter cutter or cutter 18 has been described in FIG. a series of rack teeth 22 arranged in a spiral around the periphery of a hub 24. As the cutter cutter 18 rotates in unison with the mesh blade, provides the generating action, and as the cutter cutter 18 is fed through the face of the gear blade, it cuts the teeth of the gear 12. In Figure 2, the cutter 18 rotates about the axis 20 on the spiral configuration shown in the cutter 18. The gears, particularly the cylindrical gears 10, as illustrated in Figure 1, include a plurality of parameters or features which are used to describe the gear. Figure 3 illustrates the interaction of a geared pinion or conductive gear 26 with a larger diameter or a driven gear 28. This illustration is merely exemplary, it is not a limitation. The primitive circle 30 of the gears 26 and 28 are shown in this figure as are the base circle 32, the pressure line 34 between the gear teeth in contact 12, and at an angle of pressure 36 between the common tangent 38 and the pressure line 34. More specifically, Figure 4 is an enlarged view of a segment of the gear denture 12 showing the primitive circle 30 about the midpoint between the root or root circle 40 and the upper part of the denture 42 each tooth 12. Each gear tooth 12 has a face width 44, face 46, flank 48 and a tooth thickness 50 along the original circle 30. The bottom of the denture 54 between the adjacent teeth 12 is shown as length of the base circle 56 while the client space 52 is provided between the teeth 12 along the primitive circle 30. The root arrangement 60 is shown at the intersection of the bottom of the denture 54 and the flank 48. The face 46 is the tooth surface radially outwardly of the primitive circle 30. The aforementioned envelope is generated on the face of the tooth 46 and the flank 48 by the interaction of the rotation of the cutter cutter 18 and a workpiece (not shown during the traditional process of carving. This enclosing tooth 12 is along an enclosure, as shown in Figure 5, which is the curve 55 generated by a point in a hardened cable as it is unwound from a cylinder. The generation circle is called the base circle of the envelope. This envelope sets the tooth profile out of the base circle 56. The teeth of the gear 12 can interfere with each other when engaged as in Figure 3. Point C in Figure 3 is the initial point of contact between the teeth of the gear , which is then the point of tangency in the pressure line 34 and the base circle 32. If in contact C the tangent point P precedes, this will indicate a premature contact in the non-enveloping surface of the customers, this is a contact which occurs in the non-enveloping portion of the flank of the tooth 48 below the base circle 32. The tip of the tooth 12 thus gets inside the flank 48 of the pinion gear 26. This last condition is undesirable, since the intention of the manufacturer providing gears that run on the envelope surface around a primitive circle 30 of each gear tooth 12. The gear teeth and gears 12 are evaluated or revised by factors or gear. Acterística. ':; such as decentering, tooth separation, eccentricity, tooth shape, pressure angle, and customer alignment. These are some examples of the physical characteristics of the gears, which must be analyzed for the conformation of quality of an acceptable gear. One consequence of poor or low quality gear, for example, is the noise it will generate during its operation. During the manufacture of the gear 10, it is known that the gear teeth 12 can be misaligned in relation to one another and the center line 16 of the gear 10. Therefore, the gears 10 are often regenerated in grinding machines after the treatment of heat to regenerate the relations of the dentures of the gears. The present invention provides gears 10 produced by a powder metal technique. More specifically, the gears 10 are compressed to form a preform in a powder press 62 such as the press illustrated in U.S. Patent No. 5,858,415 to Bequette et al. and in Figure 6. The preform, which has the desired gear shape, but has finishing dimensions, is largely composed of a predetermined mass or volume of a particular powder, which is generally an alloy composition such as for example A -5, A-9, QMP-4600 or Hoeganaes HP-85. The powder mass is compressed to a preform or a predetermined shape and green density. The preform is thereafter transferred to an agglomerate furnace to fuse the discrete particles. This preform is a relatively loose agglomeration of discrete powder particles, whose preform has only a nominal strength and hardness, although the individual metal particles will have their own metal strength characteristics. During the agglomerate, the preform can also be compressed and the bulk density of the preform will increase. Subsequent operations may include the final pressure of the agglomerated preform to further increase the density and conform the shape to a finished dimension. In the case of the cylindrical gear 10, the density of the preform after the final pressure may be adequate, a subsequent heat treatment of hardening may be carried out to raise at least the surface of the gear to a hardness requirement value. As an example, the density of iron at _0 ° is 7,874g./cc. The present invention provides a powder drive gear with a finished density of about 7.3 g / cc, which is about 889; of the theoretical density of the metal material. However, as in most operations with heat treatment, the gears 10 are susceptible to distortion either by agglomeration or hardening operations. Distortion of the preform from its so-formed state can result in a de-aligning between the adjacent gear teeth 12 or between the gear teeth 12 and the center line 16. In the extreme case of distortion, the bearing surfaces at the ends of the gear or gear hole 14 can be misaligned relative to the teeth of the gear 12 or to the center line 16. The prior gear technology has reared that the gear 10 and thus the teeth of the gear 12 are regenerated to realign the teeth 12 to each other or to the center line 16 to provide the gear 10 as an adequate energy transfer device with minimal noise. However, until relatively recent years, known methods for producing an acceptable gear 10 were limited to crushed and hardened gear 10 for the regeneration of gear teeth 12. In 1974, U.S. Patent No. 3,786,719 to Kimura et al. to the. showed a method for carving hardened gears 10 to regenerate gear parameters. More particularly, the specific cutting cutter was provided with cut teeth 22 having a negative backward angle 23 relative to the direction of the cutter 18 as shown in Figure 8. These hard cutter cutters 18 have higher disagreements 25 already removed. that there is no cut in the root region 60 of the gear tooth 12. The suppression of this top cut surface results in a concave shape at the root 60 without a recess.

The present invention utilizes a hardened mill cutter 18 in conjunction with a stable milling apparatus and hardened spindles (not shown) with exact centers will regenerate the gear 10, and particularly a cylindrical gear, with aligned gear teeth 12, whose teeth 12 are also they align with the center line of the gear 16. The teeth of the gear 12 have a uniform transition at the roots 60 without the rebate, since this process serves to turn or remove extremely thin layers of material on the surface 46, 48 of the teeth of the gear 12 to thereby regenerate the surface of the teeth 46, 48. It has been found that the gears 10 are of a quality that is good or acceptable as the gears 10 crushed to regenerate the surface 46, 48. In addition, the carving In hard it is operable at a speed that is in the order of a magnitude faster than the previous crushing operations. The gross errors in gear tooth patterns and profiles have historically been corrected during cutting operations. Alternatively, gear errors sometimes overlap to correct a reasonable amount of errors, but trying to correct excessive errors by overlapping through long cycles is not desirable.

The present invention provides the tournament of small amounts of material of the gear teeth, which is in the order of 0.005 to 0.007 inches of material, to regenerate the alignment of the gear teeth 12 without contacting the root 60 or lowering the root 60 while maintaining the envelope surface 46, 48 of each gear tooth 46 and flank 48. While only one specific embodiment of the invention has been described and shown, it can be appreciated that various alternatives and modifications can be made to the same Those skilled in the art will recognize that certain modifications can be made in these illustrative modalities. It is, therefore, the intent of the appended claims to cover all modifications and alternatives as they fall within the true scope of the invention.

Claims (9)

1. CLAIMS 1. A method for manufacturing a cylindrical gear produced from a powder drive, the cylindrical gear has a plurality of gear teeth, each tooth has gear tooth flanks, the gear has a longitudinal centerline, the method operates to regenerate the alignment of gear to reduce the misalignment between the flanks of the teeth of the adjacent gear, to reduce the misalignment between the teeth of the gear and reduce the error of line of steps of each gear, the manufacturing method is characterized because it comprises: (a) compress a powder preform of the cylindrical gear, each gear has a longitudinal center line and a plurality of gear teeth, each gear tooth has gear tooth flanks; (b) agglomerating the cylindrical gear preform to generally solidify the powder metal; (c) heat treating the agglomerated preform to a predetermined minimum hardness; (d) provide a hardened milling cutter and milling apparatus; (e) turning the heat treated and agglomerated gear with the hardened milling cutter in the milling apparatus to regenerate the relationship formed between the gear teeth and between the gear teeth and the longitudinal centerline of each gear. The method for manufacturing a cylindrical powder-driven gear according to claim 1, characterized in that the heat treatment of the agglomerated and compressed preform produces a gear having a minimum hardness of Rockwell-C52. 3. The method for manufacturing a cylindrical powder-driven gear according to claim 1, characterized in that the heat treatment of the agglomerated and compressed preform produces a gear having a hardness between Rockwell-C52 and Rockwell-C60. The method for manufacturing a cylindrical powder drive gear according to claim 1, characterized in that the two-gear gear tournament moves between approximately 0.005 inches and 0.007 inches of material on each gear tooth flank. The method for manufacturing a cylindrical powder drive gear according to claim 4, characterized in that the adjacent gear tooth has a root between the adjacent tooth, the gear tooth tournament is provided while the root is held untouched and avoid the reduction of the root. 6. The method for manufacturing a cylindrical powder-metallurgical gear according to claim 1, characterized in that the powder is made of any pre-alloyed powder-coated powder A-5, powder-coated A-9, powder-grade grade 4600 powder-coated QMP-4600 and powder-coated HP-85. The method for manufacturing a cylindrical powder-driven gear according to claim 1, characterized in that the heat treatment is provided by a neutral hardening process with a cold-looking cooling to less than 65.5 ° C (150 ° F). 8. The method for manufacturing a cylindrical powder-driven gear according to claim 1, characterized in that the hardened milling cutter has a plurality of milling elements, the milling elements have one of a zero recess angle and a negative recess angle. 9. The method for manufacturing a cylindrical powder-driven gear according to claim 8, characterized in that the cutter has a central line, the negative recess angle of the milling elements is approximately less than 5o from the center line.