Method for manufacturing a piston rod unit and a hollow shaft

Abstract

The invention relates to a method for producing a piston rod unit, or a shaft, in lightweight 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 method for producing a piston rod unit in lightweight construction, comprising: deep-hole drilling a rod shank of a piston rod of the piston rod unit to form a deep bore, wherein during drilling, a material excess is left at a rod end of the piston rod, wherein the rod end of the piston rod having the material excess has a greater thickness than an immediately adjacent section of the piston rod; closing an opening of the deep bore by a forging process wherein the material excess closes the opening of the deep bore due to thermo-mechanical stress during the forging process; wherein the piston rod is form-fittingly connected with a piston of the piston rod unit exclusively via an external connection type.

2. The method according to claim 1, wherein the piston rod, including a piston rod head, is mechanically formed from a blank.

3. The method according to claim 1, wherein a mandrel is inserted into the opening of the deep bore prior to the forging process.

4. The method according to claim 3, wherein the inserted mandrel has a non-smooth, cone-type surface structure.

5. The method according to claim 3, wherein the inserted mandrel has a smooth surface structure.

6. The method according to claim 3, wherein the mandrel is removed after the forging process.

7. The method according to claim 1, wherein an end of the deep bore located in the piston rod shank is of radial shape.

8. The method according to claim 3, wherein the mandrel is inserted into the opening of the deep bore at the rod end of the piston rod.

9. The method according to claim 1, wherein the external connection type is a screw connection.

10. The method according to claim 2, wherein the piston rod and the piston rod head are a one-piece component.

11. The method according to claim 2, wherein the deep bore extends in a longitudinal direction from the piston rod head to the rod end of the piston rod.

12. The method according to claim 1, wherein the material excess is flowed in a radial direction of a cylinder of the piston rod unit.

Description

(1) Further advantages and properties of the invention 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 invention, with a novel piston rod,

(3) FIG. 2: an image of an intermediate product in the manufacture according to the invention 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.

(6) The invention proposes a manufacturing method of a hydraulic cylinder in lightweight construction. An advantage of the construction according to the invention 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 invention. 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, to produce 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 particularly 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.