CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 202010298280.4, filed on Apr. 15, 2020, the disclosure of which is incorporated by reference herein in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates generally to a forming method in the field of industrial manufacturing technologies, and in particular to a method for manufacturing a combined hollow camshaft by an axial-compression upsetting-deformation technique.

BACKGROUND

A camshaft is a key part of the engine to control valves to open or close. The camshaft has a through-hole in the axial direction to convey a lubricant for achieving cooling and lubricating functions. The earliest manufacturing method of the camshaft is to integrally cast or forge a preformed billet, then secondarily process the preformed billet to obtain each working surface and axial hole. A difficulty is to process an axial through-hole. The axial through-hole can be manufactured only by using a deep hole drill to drill, but there is a problem that it is easy to generate “deviation” or “drill bit breakage” during drilling of the deep hole drill, thereby causing high technical difficulty and low yield.

To avoid the difficulty of processing the through-hole, techniques of hydraulic expansion, interference fit and the like are developed later to manufacture the camshaft. The process of a deep hole is avoided. However, in practical application, a camshaft manufactured by the hydraulic expansion is easy to drop out after undergoing thermal cycle, so there is a security risk. A camshaft manufactured by the interference fit is hard to overcome problems of narrow process window, high rejection rate, high costs and the like.

SUMMARY

To solve the above problems, the present invention proposes a new method for manufacturing a combined hollow camshaft by an axial-compression upsetting-deformation technique.

In accordance with an embodiment of the invention, a method of forming a single camshaft is provided. The structure of the single camshaft is as follows: in a camshaft, two independent units, namely a cam and a shaft tube, are combined to form working surfaces and through holes as required. A combination manner of the two units is as follows: first, a first countersink and a second countersink are distributed on two sides of the cam. The bottom surface of the first countersink and the bottom surface of the second countersink may be flat surfaces, inclined surfaces or male and female surfaces, preferably the inclined surfaces. The cross sections of the first countersink and the second countersink are non-circular or circular. The first countersink and the second countersink match with a first step and a second step to lock a translational degree of freedom and a circumferential rotational degree of freedom of the cam. Second, the shaft tube is a hollow tube with the first thrust step and the second thrust step. The cam is displaced between the first thrust step and the second thrust step of the shaft tube. Then, the cam is locked by the compression force of the first thrust step and the cam and the compression force of the second thrust step and the cam.

A method for manufacturing a combined hollow camshaft by an axial-compression upsetting-deformation technique according to an embodiment of the invention comprises the following steps:Step 1: selecting a tube billet, wherein the inner diameter of the tube billet is as same as the inner diameter of the shaft tube, the outer diameter of the tube billet is slightly larger than the outer diameter of the shaft tube, and specifically the outer diameter of the tube billet is 1.0-1.2 times of the outer diameter of the shaft tube; selecting a cam, wherein the inner diameter of the cam is slightly larger than the outer diameter of the tube billet, and specifically the inner diameter of the cam is 1.0-1.2 times of the outer diameter of the tube billet; the outer contour of a selected cam blank is slightly larger than the outer contour of a fine-processed cam, and specifically, the shape error is less than 2 mm;Step 2: heating a region A of the tube billet, wherein the axial width of the region A is 1-2 times of the axial width of the cam;Step 3: stopping heating when the temperature of the region A is up in the range of 50-1400 DEG C.;Step 4: placing the cam in the region A;Step 5: applying a support inner pressure p to an inner cavity of the tube billet;Step 6: compressing the tube billet in the axial direction, wherein the temperature of the region A is high, so the material of the region A is thickened and deformed in an upsetting manner and also fills the first countersink and the second countersink of the cam; stopping compressing when the first thrust step and the second thrust step are formed, wherein Step 3 to Step 6 should be finished within 60 s;Step 7: locking the cam, wherein with the temperature reducing, the material of the region A is shrunk in the axial and radial directions to generate the compression force between the first thrust step and the bottom surface of the first countersink as well as between the second thrust step and the bottom surface of the second countersink, so the cam is locked.Step 8: the shaft tube and the outer contour of the cam are fine processed, which is as same as the prior art.

Further, the support inner pressure p is zero (0), and the other steps are the same.

Further, the support inner pressure p is in the range of 0.1-500 MPa, and the other steps are the same.

Further, the non-circular shapes of the cross sections of the first countersink and the second countersink distributed on the two sides of the cam are polygon, and the other steps are the same.

Specifically, another embodiment of the invention is characterized in that: a camshaft combiner is formed based on the first invention. The assembly and manufacture of a second cam can be completed by repeating Step 1 to Step 5; or two or more cams can also be manufactured according to Step 1 and Step 5 at the same time; by that analogy, the method can manufacture any amount and shape of the camshaft as required.

Compared with the prior art, the present invention has the following beneficial effects: 1, the cam and the shaft tube are independent units and can be made from different materials to achieve the best match of their performances and costs; 2, the tube billet is utilized to manufacture the shaft tube such that it does not need to drill a hole; 3, the locking force is formed by utilizing thermal expansion and contraction during camshaft formation, which is easy to implement and achieve; 4, the local part is heated and then upset to form the thrust step, which is simple and easy to achieve; 5, the circumferential and axial degrees of freedom of the cam are commonly limited by the thrust steps, the axial locking force and the countersinks of the non-circular cross sections, which is reliable and is easy to implement.

