Method for forming hollow shaft with small outside inner hole, large inside inner hole, thick wall, thick end and thin middle part

Abstract

The invention discloses a method for forming a hollow shaft with a small-outside large-inside inner hole, a thick wall, a thick end and a thin middle, which is characterized by comprising the following steps of: firstly, heating a hollow shaft blank to a set temperature, then feeding the hollow shaft blank into a three-roller skew rolling mill, and inserting a core rod into the inner hole of the hollow shaft blank; the hollow shaft blank is pushed to move forwards, the middle section of the hollow shaft blank is thinned and rolled through a first inclined roller set, and a hollow shaft semi-finished product with the inner hole diameter unchanged and the wall thickness of the middle section thinned is obtained; the core rod is pulled out of the hollow shaft semi-finished product, the hollow shaft semi-finished product is pushed to continue to move forwards, meanwhile, the second inclined roller set and the first inclined roller set are controlled to conduct reducing rolling on the front end and the rear end of the hollow shaft semi-finished product at the same time, and a hollow shaft finished product with an inner hole small in outside, large in inside and thick in wall end and thin in middle is obtained; the method has the advantages that integral forming rolling of the hollow shaft with the small outside, the large inside, the thick wall, the thick end and the thin middle is achieved through skew rolling, the process is single, the working procedure is simple, the process cost is greatly reduced, and the machining efficiency of the hollow shaft is improved.

Description

Technical Field

[0001] This invention relates to the field of skew rolling forming technology for hollow shafts, and more particularly to a method for forming hollow shafts with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle wall thickness. Background Technology

[0002] Hollow shafts with unequal wall thicknesses can be used in specific structures, such as increasing the wall thickness at both ends of the shaft, to locally enhance the load-bearing capacity of bearing positions, sealing positions, or connecting positions. This not only avoids material waste caused by thickening the overall shaft material but also enables lightweight applications, greatly expanding the application scenarios and scope of shafts. Traditionally, hollow shafts with thicker ends and thinner middle sections are mainly processed using two methods: one is rotary forging, but this process is costly and inefficient, failing to meet the demands of high-efficiency shaft manufacturing; the other is to first shape the shaft using wedge rolling or precision forging, and then use cutting to thin the wall thickness of the middle section internally. This method involves external forming and internal cutting, requiring two different processes and preventing integrated forming. Furthermore, the shape of the shaft, whether formed by wedge rolling or precision forging, is highly dependent on the mold, and the cutting process thins the inner wall thickness of the shaft, resulting in reduced material utilization. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle wall. The hollow shaft blank is integrally formed by skew rolling, which eliminates the need for multiple different processing steps, reduces process costs and improves processing efficiency.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle wall, comprising the following specific steps: (1) First heat the hollow shaft blank to the set temperature, then send the hollow shaft blank into the three-roll skew mill and insert the mandrel into the inner hole of the hollow shaft blank; (2) Push the hollow shaft blank forward and roll the middle section of the hollow shaft blank through the first skew roll group to obtain a hollow shaft semi-finished product with unchanged inner hole diameter and reduced wall thickness in the middle section; (3) Extract the mandrel from the hollow shaft semi-finished product, adjust the axial relative position between the hollow shaft semi-finished product and the first skew roll group and the second skew roll group, push the hollow shaft semi-finished product to continue moving forward, and at the same time control the second skew roll group and the first skew roll group to perform diameter reduction rolling on the front and rear ends of the hollow shaft semi-finished product. The second skew roll group is used to roll the front end of the hollow shaft semi-finished product, and the first skew roll group is used to roll the rear end of the hollow shaft semi-finished product, so as to obtain a hollow shaft finished product with a small outer hole and a large inner hole and a thick end and a thin middle wall.

[0005] Furthermore, in step (2), when rolling the middle section of the hollow shaft blank, the rolling length is the set length of the middle section plus the compensation length. h The sum, compensation length h for: , Where: M1 is the initial wall thickness of the hollow shaft blank, and M2 is the target wall thickness of the middle section of the hollow shaft semi-finished product. d 1 is the diameter of the mandrel, and β is the roll forming angle of the second roll group.

[0006] Furthermore, the diameter of the said core rod d 1. The initial wall thickness M1 of the hollow shaft blank must satisfy: 1.65M1 < d 1 < 2.5M1.

[0007] Furthermore, the target wall thickness M2 of the middle section of the hollow shaft semi-finished product obtained by rolling in step (2) and the initial wall thickness M1 of the hollow shaft blank must satisfy: 0.15M1 < M2 < 0.75M1.

[0008] Furthermore, the wall thickness M3 at the front and rear ends of the hollow shaft finished product obtained by rolling in step (3) must satisfy the following condition: 0.8M1 < M3 < 0.9M1.

[0009] Furthermore, before rolling, lubricating oil is applied to the outer surfaces of the mandrel, the first skew roll group, and the second skew roll group, respectively.

[0010] Compared with the prior art, the advantages of this invention are that this method realizes the integral forming and rolling of hollow shafts with small outer diameter and large inner diameter and thicker wall at the ends and thinner in the middle through skew rolling. The process is simple, does not require changing different equipment, and the process is simple, which greatly reduces the process cost and improves the processing efficiency of hollow shafts. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the state of the present invention before skew rolling; Figure 2 This is a schematic diagram illustrating the process of thinning and rolling the middle section of a hollow shaft blank according to the present invention. Figure 3 This is a schematic diagram of the process of reducing the diameter of the front and rear ends of the hollow shaft semi-finished product according to the present invention. Figure 4 This is a schematic diagram showing the state of the hollow shaft semi-finished product after the front and rear ends have been reduced in diameter by rolling according to the present invention; Figure 5 This is a schematic diagram of the structure of the hollow shaft product obtained by rolling according to the present invention. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0013] As shown in the figure, a method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle section, includes the following specific steps: (1) First, apply lubricating oil to the outer surfaces of the mandrel 1, the first skew roll group 2, and the second skew roll group 3 respectively. Heat the hollow shaft blank 4 to the set temperature, i.e., the temperature required for skew rolling. Then, send the heated hollow shaft blank 4 into the three-roll skew rolling mill and insert the mandrel 1 into the inner hole of the hollow shaft blank 4. Figure 1 As shown, and the diameter of core rod 1 is... d The initial wall thickness M1 of 1 and hollow shaft blank 4 must satisfy: 1.65M1 < d 1 < 2.5M1, to ensure that after the mandrel 1 is pulled out, the diameter reduction rolling of both ends of the hollow shaft will not cause the inner holes at both ends of the hollow shaft to close. (2) Push the hollow shaft blank 4 forward, and perform thinning rolling on the middle section of the hollow shaft blank 4 through the first skew roll group 2 to obtain a hollow shaft semi-finished product 5 with unchanged inner hole diameter and reduced wall thickness in the middle section, such as Figure 2 As shown, the final wall thickness (i.e. target wall thickness) M2 of the middle section of the hollow shaft semi-finished product 5 obtained by rolling and the initial wall thickness M1 of the hollow shaft blank 4 satisfy: 0.15M1<M2<0.75M1; Because wall thickness accumulation occurs during subsequent rolling of the front end of the hollow shaft, resulting in a reduction in the length of the rolled intermediate section, the rolling length of the intermediate section of the hollow shaft blank 4 in this step is the sum of the set length and the compensation length of the intermediate section. h The sum, compensation length h for: , Where: β is the roll forming angle of the second roll group; (3) Remove the mandrel 1 from the hollow shaft semi-finished product 5, adjust the axial relative position between the hollow shaft semi-finished product 5 and the first skew roll group 2 and the second skew roll group 3, push the hollow shaft semi-finished product 5 to continue moving forward, and at the same time control the second skew roll group 3 and the first skew roll group 2 to simultaneously perform diameter reduction rolling on the front and rear ends of the hollow shaft semi-finished product 5, such as Figure 3 As shown, the second skew roll group 3 is used to roll the front end of the hollow shaft semi-finished product 5, and the first skew roll group 2 is used to roll the rear end of the hollow shaft semi-finished product 5, resulting in a hollow shaft finished product 6 with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle wall thickness. The wall thickness M3 at both ends of the rolled hollow shaft finished product 6 satisfies the following condition with respect to the initial wall thickness M1 of the hollow shaft blank 4: 0.8M1 < M3 < 0.9M1. Figure 4 As shown, Figure 4 After cutting off the excess material, you get the final hollow shaft product, such as... Figure 5As shown.

[0014] In the above embodiments, the distance between the first skew roll group 2 and the second skew roll group 3 can be pre-adjusted according to the length of the middle section and the two ends of the hollow shaft to be rolled, so that in step (3), after the mandrel 1 is pulled out from the hollow shaft semi-finished product 5, the hollow shaft semi-finished product 5 can be directly pushed forward, and the second skew roll group 3 and the first skew roll group 2 can simultaneously perform diameter reduction rolling on the front and rear ends of the hollow shaft semi-finished product 5.

[0015] The scope of protection of this invention includes, but is not limited to, the above embodiments. The scope of protection is defined by the claims. Any substitutions, modifications, or improvements to this technology that are easily conceived by those skilled in the art fall within the scope of protection of this invention.

Claims

1. A method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle section wall, characterized in that... The specific steps include the following: (1) First heat the hollow shaft blank to the set temperature, then send the hollow shaft blank into the three-roll skew mill and insert the mandrel into the inner hole of the hollow shaft blank; (2) Push the hollow shaft blank forward and roll the middle section of the hollow shaft blank through the first skew roll group to obtain a hollow shaft semi-finished product with unchanged inner hole diameter and reduced wall thickness in the middle section; (3) Extract the mandrel from the hollow shaft semi-finished product, adjust the axial relative position between the hollow shaft semi-finished product and the first skew roll group and the second skew roll group, push the hollow shaft semi-finished product to continue moving forward, and at the same time control the second skew roll group and the first skew roll group to perform diameter reduction rolling on the front and rear ends of the hollow shaft semi-finished product. The second skew roll group is used to roll the front end of the hollow shaft semi-finished product, and the first skew roll group is used to roll the rear end of the hollow shaft semi-finished product, so as to obtain a hollow shaft finished product with a small outer hole and a large inner hole and a thick end and a thin middle wall.

2. The method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle section, as described in claim 1, is characterized in that: In step (2), when rolling the middle section of the hollow shaft blank, the rolling length is the set length of the middle section plus the compensation length. h The sum, the compensation length h for: ， Where: M1 is the initial wall thickness of the hollow shaft blank, and M2 is the target wall thickness of the middle section of the hollow shaft semi-finished product. d 1 is the diameter of the mandrel, and β is the roll forming angle of the second roll group.

3. The method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle section, as described in claim 1, is characterized in that: The diameter of the said mandrel d 1. The initial wall thickness M1 of the hollow shaft blank must satisfy: 1.65M1 < d 1 < 2.5M1.

4. The method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle section, as described in claim 1, is characterized in that: The target wall thickness M2 of the middle section of the hollow shaft semi-finished product obtained by rolling in step (2) and the initial wall thickness M1 of the hollow shaft blank must satisfy: 0.15M1 < M2 < 0.75M1.

5. The method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle section, as described in claim 1, is characterized in that: The wall thickness M3 at the front and rear ends of the hollow shaft finished product obtained by rolling in step (3) must satisfy the following condition: 0.8M1 < M3 < 0.9M1.

6. The method for forming a hollow shaft with a smaller outer diameter and a larger inner diameter, and a thicker end and thinner middle section, as described in claim 1, is characterized in that: Before rolling, lubricating oil is applied to the outer surfaces of the mandrel, the first skew roll group, and the second skew roll group.

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