JPH04231405A - Preparation of cam shaft - Google Patents

Abstract

PURPOSE: To simply produce a cam shaft from a base axis and compacted parts subjected to preliminary compacting from a sintering powdery mixture and melted and sintered onto the base shaft. CONSTITUTION: For positioning compacted parts 1, a recessed place 5 for a holding and inserting piece 3 to be inserted into a base axis 2 is formed on the edge face of the compacted parts 1, the compacted parts 1 are set onto the base shaft 2 till the holding and inserting piece 2 is engaged to the recessed part 5, and the compacted parts 1 placed on the holding and inserting piece 3 of the standing base shaft 2 are sintered under heating.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention is directed to a molded part preformed from a sintered powder mixture and fitted onto a base shaft with radial play, first by fitting into a radial recess of the base shaft and the molded part. The present invention relates to a method of manufacturing a camshaft, in which the camshaft is positioned on the base shaft by engaging holding inserts, and then melted and sintered while shrinking to exceed the radial clearance.

0002

BACKGROUND OF THE INVENTION In order to meet the demand for relatively light camshafts and to simplify the manufacture of such camshafts, cams, support projections and other molded parts of camshafts have been manufactured using powder metallurgy. However, it has already been proposed to fit it onto a preferably hollow steel base and connect it to the base by melting and sintering (German Patent Application No. 3500653). At this time, the angular position of the pre-sintered molded parts, especially the cam, is guaranteed by pressure fitting, but this is not only difficult due to the precise angular position specification.
There is also the risk that the pressure fit will loosen during the sintering process and that the set angular position will therefore be lost.

[0003] In order to avoid these drawbacks, the molded part to be presintered is placed on the base shaft with radial play, a hole corresponding to the base shaft and the molded part is provided for positioning the molded part, and a holding insert is provided. Push the tube into these holes as a piece,
It is already known to be used for supplying lubricants (DE-A-3209980). The angular position of the molded part with respect to the basic axis can be defined with high precision via the hole for the retaining insert in the basic axis;
It is difficult to subsequently drill holes in presintered cams. Furthermore, in order to make holes in the molded parts, sufficient rigidity is required for these compression moldings, which requires appropriate pre-sintering, so the shrinkage of the molded parts that occurs during pre-sintering is less likely to cause loose molded parts. It can no longer be used to connect to the base axis.

0004

OBJECTS TO BE SOLVED BY THE INVENTION The object of the present invention is therefore to avoid these drawbacks and to improve the method for manufacturing camshafts of the first type mentioned, so as to produce molded parts on the base shaft. The object is to ensure not only a precise positioning of the molded part but also a particularly good connection between the molded part and the basic shaft.

[0005]

[Means for Solving the Problems] In order to solve this problem, according to the present invention, recesses for holding insertion pieces are formed in the end faces of the molded parts during compression molding of the molded parts, and each of the recesses for the holding insertion pieces is arranged in the radial direction at the front. The molded part is inserted onto the base shaft until the retaining insert inserted into the base shaft engages in the recess of the molded part, and then the molded part resting on the retaining insert of the base shaft, which is preferably upright, is melted and sintered.

[0006]

[Effect of the invention] Because of this measure, recesses for the holding inserts are formed in the molded part during compression molding, so the positional accuracy of these recesses is not related to the subsequent processing of the molded part. , as it relates to the accuracy of the compression mold, a particularly advantageous condition is provided for the mass production of camshafts, which have high demands on precision, in conjunction with a base shaft that can be precisely drilled. Furthermore, pre-sintering is advantageously omitted, since no additional processing of the molded part is required before it is fitted onto the basic shaft, and the total shrinkage that occurs during sintering of the molded part is used to connect the molded part to the basic shaft. In other words, a predetermined degree of penetration can be obtained, and since the inner diameter of the molded part that is sintered alone without a base shaft is smaller than the outer diameter of the base shaft, even better bonding with the base shaft of the molded part is possible. Become. For a given degree of penetration, therefore, it is possible to use a material with a smaller shrinkage margin compared to comparable prior art. With comparable shrinkage allowances, the radial clearance between the molded part and the base shaft can be selected to be large, which directly influences the required surface quality of the base shaft.

The recess formed in the end face of the molded part ensures a particularly simple and precise positioning of the molded part on the base axis. This is because it is only necessary to fit the molded part onto the base shaft until the holding insert, which has been previously inserted into the base shaft, engages with the recess of the molded part, and thereby the axial position of the molded part on the base shaft can be adjusted. This is because not only that, but also its angular position is uniquely defined. This position of the molded part allows the retaining insert to be inserted into the radial recess of the base shaft only when the molded part, which is preset with its insertion direction, has been inserted onto the base shaft.

[0008]

[Embodiment] If the molded part is sintered with the base shaft upright and the holding insert forms a support for the molded part, the risk of the molded part shifting in the axial direction is avoided, and during the sintering process the molded part is sintered. This has the great advantage of avoiding bending stress on the base shaft and eliminating the risk of bending the base shaft. If the base shaft is properly supported, the sintering process can be carried out conventionally with the base shaft lying on its side.

In order to facilitate the snug engagement of the retaining insert projecting radially from the base shaft into the end face recess of the molded part, the recess in the molded part provides a symmetrical shape with respect to a plane containing the axis. A centering surface for the holding insert can be formed, so that when the molded part is fitted onto the basic shaft, the holding insert engages in the recess in the end face of the molded part, thereby resulting in self-centering. In this connection, the recess has a U-shaped cross section,
A particularly advantageous situation arises if this cross section is matched to a retaining insert (usually a retaining pin). In order to ensure that the retaining pin fits without play in the radial recess of the base shaft, the retaining pin can be designed conically.

For molded parts that can be fitted onto the base axis with relatively little play, if the base shaft is upright, the slight inclination is eliminated, especially during contraction of the molded part, so that the molded part can be placed perpendicular to the axis. A single retaining insert is sufficient to hold it in the correct orientation. If the radial play is large, additional supports must be provided to prevent tilting of the molded part that rests on the upright base shaft. For this purpose, the molded parts are placed during the sintering process on at least three holding pieces inserted into the basic shaft, one of these holding pieces being fitted into a recess in the respective molded part as a holding insert. It is advantageous for the other retaining pieces to have circumferential movement clearance relative to the molded part. By this measure, an unacceptable tilting of the molded part that fits onto the upright base is prevented, as well as an overspecification of the angular position due to the movement clearance of the holding pieces, with the exception of the holding insert, so that precise positioning is ensured. Guaranteed. In order to be able to arrange the holding pieces in the plane containing the holding pins, the molded part can be provided with end face recesses for all the holding pieces, taking into account the necessary movement clearance in the circumferential direction.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a camshaft according to the present invention will be explained with reference to the drawings.

In order to produce a camshaft with a molded part 1 produced by powder metallurgy, the molded part 1, which is compression-molded from a sintered powder mixture, is fitted onto the basic shaft 2 with a radial play and positioned. and then melted and sintered. To position the molded part 1, a pin-shaped holding insert 3 is used which is inserted without play into the radial recess 4 of the base shaft 2, and
It engages with the end face recess 5 of the molded part 1 with a fit. For this purpose, the molded part 1 is pushed onto the basic shaft 2 until the retaining insert 3 engages in the recess 5. In order to guarantee the position of the molded part 1 perpendicular to the axis on the upright base shaft 2 even with large radial play, in addition to the holding insert 3, a holding piece 6 can also be provided. These additional holding pieces 6, which are also pin-shaped, are arranged together with the holding insert 3 in a common plane perpendicular to the axis, as can be seen in particular from FIG. However, these retaining pieces 6 do not fit into the corresponding end face recesses 7 of the molded part 1, but have a movement clearance in the circumferential direction within these recesses 7, so that the retaining insert pieces 3 only defines the angular position of the molded part 1. As can be seen in FIG. 3, the recess 7 has a suitably larger width than the recess 5. If there is no risk of an unacceptable tilting of the molded part 1 on the upright base shaft 2 due to the small radial play, the additional holding piece 6 can be omitted, as shown in FIGS. 5 to 7.

In order to facilitate the play-free engagement of the retaining insert 3 into the end face recess 5 of the molded part, the recess 5 is in the plane containing the axis, as in the case of a U-shaped recess cross-section. A symmetrical centering surface can be formed for the holding insert 3. If the retaining insert 3 is located in the end face of the molded part 1, the recess 5 must have a depth greater than the diameter of the retaining insert 3 in order to be able to take into account the axial shrinkage of the molded part 1. No. The same applies to the length of the recess 5 in the molded part 1.

According to FIG. 8, in order to manufacture a camshaft, the prepared base shaft 2 is placed on a rotary table 8 having a vertical rotation axis.
The molded part 1 to be connected to the base shaft 2 can be passed onto the upright base shaft 2. For this purpose, first the lowermost retaining insert 3 on the upright shaft is engaged in the end face recess 5 of this molded part 1. The holding insert 3 for the molded part 1, for example a cam, which follows upwards is then inserted into the recess 4 provided for this purpose in the base shaft 2, and the molded part 1 can be fitted onto the base shaft 2, but the angle of the molded part Location cannot be taken into account. When the molded parts are fed to the base shaft 2 in a unified direction, the base shaft 2 can be rotated to an appropriate angular position via the rotary table 8 to fit the molded parts in the correct position. In FIG. 9, an angular step α between two successive angular positions for fitting successive molded parts 1 is shown. As can be easily understood from this, the rotational displacement of the base shaft 2 by the rotary table 8 is controlled by the insertion recess 4 of the holding insertion piece 3.
can be used to form the correct position.

After fitting the individual molded parts one after another, the bearing race shown at the top of FIG. metal bonding can be performed. This is because, during sintering, the molded part 1 undergoes a shrinkage that significantly exceeds the radial play.

The shrinkage is related to the sintered powder mixture used for the molded part 1 and the iron powder to be alloyed, and is generally between 1 and 6%. The sintered powder mixture can further contain up to 20% by weight of bronze, which not only improves the sliding properties of the molded part, but also allows the molded part and the base to We also perform wax wear. The sintered powder mixture selected for the molded part produces the molded part 1 with a compressed density of 6.5 to 6.7 g/cm3 while simultaneously forming recesses 5 and 7 for the retaining insert 3 and the retaining piece 6. compression molded. This compacted density allows sufficient wet strength for subsequent handling without the need to use pre-sintering. In special cases, a sintering process that increases the wet strength can be followed by compression molding, but in order to avoid too much preceding significant shrinkage of the molded part during the main sintering process, the shrinkage must be kept within limits during this sintering process. Particular care must be taken to ensure that the

As an example, iron powder alloyed with 6% by weight of molybdenum is used for molded part 1, 2.8% by weight of 16% iron-phosphorous alloy powder, 1.85% by weight of graphite. and 0.8% by weight wax as a lubricant. Cams were compression molded from this powder mixture and had a wet density of 6.5 g/cm@3. These molded parts are shown in Figure 8.
It was fitted onto a base shaft made of St58 steel with a polished peripheral surface. The outer diameter of the hollow base shaft with a wall thickness of 5 mm is 2
It was measured to be 5.0 mm. Since the inner diameter of the cam was 25.1 mm, I was able to fit the cam onto the camshaft without any problems. After positioning the molded part according to the invention on a pin-like holding insert with a diameter of 2.5 mm, the camshaft thus assembled was placed upright in a vacuum furnace and sintered for 2 hours at a sintering temperature of 1060°C. The temperature deviation inside the furnace was measured to be ±5°C. The sintering pressure in the furnace was 4.10-2 mb. Following the sintering process, the camshaft was gradually cooled to 900°C and then quenched in nitrogen for hardening. 550℃
After the tempering process, the base shaft had a hardness of HRC51±1. The maximum deflection of the 500 mm long sintered camshaft was less than 0.1 mm due to the upright position during the sintering process. Metallurgical tests showed that a complete metal bond was formed between the molded part and the base shaft by diffusion after melting and sintering. Free shrinkage of the molded part was measured to be 5.3%, so 1.
A penetration degree of 23 mm was obtained. This relatively large degree of penetration ensured a shrinkage fit of the molded part onto the base shaft, and the action of the base shaft against shrinkage caused the molten phase to compress the molded part. The sintered density was determined to be 7.7 g/cm3. Since the torsional strength of the shaft is smaller than the torsional strength of the joint between the molded part and the base shaft, the torsional strength of this joint could not be determined.

In another example, iron powder to be alloyed with 18% chromium, 3.44% by weight of 16% iron-phosphorous alloy powder, 2.40% by weight of graphite, 1.70% by weight of Electrolytic copper, 1
．． 2% by weight of tin powder, 0.8% by weight of molybdenum and 0.5% by weight of wax as a lubricant were mixed, and from this powder mixture a molded part for a camshaft with a compressed density of 6.6 g/cm3 was produced. Compression molded. The hole diameter of the molded part is 31.
The cam width in the axial direction was 15.0 mm. The outer diameter of the hollow base shaft (wall thickness 5 mm) made of St58 steel is 2.
Measures 9.95mm, 0.5mm with 5% free shrinkage
A degree of penetration was obtained. The molded part to be fitted onto the base shaft is heated to 1085 mm in a vacuum furnace with the base shaft upright.
℃ for 2 hours and quenched in the same furnace at a quenching temperature of 1050℃. After tempering at 550℃ for 2 hours,
Hardness of HRC50±1 was confirmed. The maximum deflection of the 500 mm long shaft was 0.14 mm. Metallurgical tests revealed that in addition to the metallic bond between the base shaft and the molded part due to diffusion, there was also additional soldering by the molten bronze phase during sintering. The density of the molded part was 7.63 g/cm3. The torsional strength of the joint was greater than that of the shaft.

[Brief explanation of the drawing]

1 is a side view of a base shaft for a camshaft to be manufactured according to the invention; FIG.

FIG. 2 is a sectional view taken along line II-II in FIG. 1;

FIG. 3 is a front view of a preformed cam.

FIG. 4 is a cross-sectional view of the cam taken along line IV-IV in FIG. 3;

FIG. 5 is a sectional view taken along line V-V in FIG. 1;

6 is a front view of the preformed cam in the area of section V-V in FIG. 1; FIG.

FIG. 7 is a sectional view of the cam taken along line VII-VII in FIG. 6;

FIG. 8 is a side view of an upright pivot inserted into a rotary table and partially fitted with a molded part.

9 is a sectional view taken along line IX-IX in FIG. 8. FIG.

[Explanation of symbols]

1 Molded parts 2 Basic axis 3 Holding insertion piece 5 Recess

Claims (4)

[Claims] Claim 1: A molded part (1) preformed from a sintered powder mixture and fitted onto the base shaft (2) with radial play is first shaped in the radial direction of the base shaft (2) and the molded part (1). In a method of manufacturing a camshaft, the camshaft is positioned on the base shaft (2) by means of a retaining insert (3) that fits into the recess (5), and is then melted and sintered while shrinking to exceed the radial clearance. , during compression molding of the molded part (1), a recess (5) for the holding insertion piece (3) is formed in the end face of the molded part (1), and each of the recesses (5) is inserted into the base shaft (2) in the radial direction with the front end. The retaining insert piece (3) located in the recess (5) of the molded part (1)
A method for producing a camshaft comprising a base shaft and a molded part, characterized in that the molded part (1) is fitted onto the base shaft (2) until it engages with the base shaft, and then the molded part (1) is melted and sintered. 2. The recess (5) in the molded part (1) forms a centering surface for the holding insert (3) that is symmetrical with respect to a plane containing the axis. Method described. 3. Method according to claim 2, characterized in that the recess (5) has a U-shaped cross section. Claim 4: At least three parts inserted into the base shaft (2).
The molded parts (1) are placed on the two holding pieces (6) during the sintering process, and one of these holding pieces is inserted into the recess (5) of each molded part (1) as a holding insert piece (3). Claim 1 characterized in that the holding piece (6) is engaged with the molded part (1) by a fit, and the other holding piece (6) has a movement clearance in the circumferential direction with respect to the molded part (1).
The method described in one of 3 to 3.