Method for manufacturing a piston rod unit and a hollow shaft

Abstract

A piston rod unit and a method for producing a piston rod unit, or a shaft, in light-weight construction, with a rod which is hollowly-drilled by means of a deep bore into the rod shank, and the resulting rod opening is closed subsequently by means of a forging process.

Claims

1. A piston rod unit comprising: a piston rod with a rod shank, wherein the rod shank comprises a bore extending in a longitudinal direction from a piston rod head to a mounted piston; wherein the bore is closed at a rod end of the rod shank by a forging process whereby a cavity of the piston rod is sealed at the rod end of the bore by a material excess left at the rod end during forming of the bore; wherein the piston rod is form-fittingly connected with the mounted piston exclusively via an external connection, and wherein there is no weld inside the piston rod; wherein the bore is formed by deep-hole drilling the rod shank; and during the forging process, the material excess left at the rod end of the piston rod by the drilling is used to close an opening of the bore at the rod end, thereby sealing the cavity of the piston rod; wherein the rod end of the piston rod having the material excess has a greater thickness on either side of the bore than an immediately adjacent section of the piston rod, and wherein an outer diameter of a length of the piston rod extending from the piston rod head to the mounted piston is constant.

2. A mining apparatus comprising the piston rod unit of claim 1.

3. The piston rod unit of claim 1, wherein the piston rod, including the piston rod head, is mechanically formed from a blank.

4. The piston rod unit of claim 3, wherein the piston rod and the piston rod head are a one-piece component.

5. The piston rod unit of claim 1, wherein an end of the bore is of radial shape.

6. The piston rod unit of claim 5, wherein the end of the bore of radial shape is an inner end.

7. The piston rod unit of claim 1, wherein the external connection is a screw connection.

8. The piston rod unit of claim 7, wherein the screw connection comprises a piston nut inside the mounted piston.

9. The piston rod unit of claim 1, wherein there is only one external connection point between the piston rod and the mounted piston.

10. The piston rod unit of claim 1, wherein the bore is completely sealed.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further properties of the disclosure are to be explained in greater detail by means of an exemplary embodiment shown in more detail in the drawings. The Figures show in:

(2) FIG. 1: a hydraulic cylinder according to the disclosure, with a novel piston rod,

(3) FIG. 2: an image of an intermediate product in the manufacture according to the disclosure of the piston rod,

(4) FIG. 3: the piston rod according to FIG. 2 after the effected forging process, and

(5) FIG. 4: the piston rod according to FIG. 2 after the effected forging process in accordance with an alternative configuration.

DETAILED DESCRIPTION

(6) The disclosure proposes a manufacturing method of a hydraulic cylinder in lightweight-construction. Construction according to the disclosure consists in that potential weld connections inside the piston rod can be completely dispensed with and required screw connections are reduced to only one connection point between piston rod and piston. FIG. 1 shows a completely-assembled hydraulic cylinder in the form of a differential cylinder that has been produced in accordance with the method according to the disclosure. The hydraulic cylinder includes the cylinder housing 10 with the piston rod 20 including piston 25 displaceably mounted therein. The piston 25 is screwed to the piston rod end located in the cylinder 10 by means of a screw connection 26. Part of the screw connection is the thread of the piston nut 27 located inside the piston 25.

(7) At the piston rod head 22, a boss for mounting the piston rod unit is provided. The same applies to the closed cylinder end. To achieve lightweight construction, the piston rod 20 comprises a deep bore 21, which extends in the longitudinal direction from the piston rod head 22 to the mounted piston 25.

(8) The manufacturing process of the piston rod unit first provides, in a first step, producing the piston rod 20 including piston rod head 22 from a blank in mechanical ways and manners. The piston rod 20 and the piston rod head 22 are consequently made from one and the same starting material, and are to be considered as a one-piece end product. Furthermore, during the machining process, a radial material excess 30 is left at the rod end of the piston rod 20.

(9) After that, the deep bore 21 is made from the rod end in the direction of the rod head 22 with the bore length B. The inner end 23 of the deep bore 21 is of radial shape, in order to thereby prevent a possible notch effect by means of an edged bore cross-section. The resulting intermediate product is shown by FIG. 2. The piston rod has a length L.

(10) The protruding material 30 is used, after the deep hole drilling 21, to close the bore opening at the rod shank. This is effected by means of open-die forging or another, suitable forging process. In the forging process, the protruding material 30 is made to flow, due to the thermo-mechanical stress, in the radial direction of the cylinder. As a result, it is possible to close the bore opening at the rod shank without having to use other connection techniques that have a negative effect on the dynamic stress resistance.

(11) Prior to the forging, a type of mandrel 40 can be laid into the bore 21 (see FIG. 3), in order to be able to close and seal the bore opening precisely and, on the other hand, be able to control the material flow during the forging in better ways and manners. The proposed method further allows acting more freely both in terms of the material selection and the bore dimensions. This means that the yield in terms of weight reduction can be increased due to the prevented weaknesses that might develop due to previous connection techniques. In large cylinders for the field of mining, up to 400 KG can be saved.

(12) In a further configuration, as shown in FIG. 4, it is also conceivable to configure the geometry of the mandrel 40′ in a wave-like or other non-smooth form, in order to thereby increase the quality of the closure. The internal cavity should be sealed against the entering of the non-compressible medium in each operating situation.