Patent Application
20200124085
The present invention relates to a method for producing a ball stud according to the preamble of claim 1.
Such methods are used for producing a ball stud consisting of a shank with a joint ball attached at an axial end. In the process, it is necessary to optimize the ball stud with regard to its surface properties, in particular the resistance to corrosion, and its hardness properties with a view to the concrete application case. Currently, the ball studs (except for the thread region) are completely carbonitrided and oxidized. The low elongation at fracture value of the treated surface is disadvantageous. Due to high-load events, already in the case of slight elastic deformations, cracking of the surface coating in the highly-stressed neck region between joint ball and shank can occur. This incipient cracking can then propagate and lead to component failure. In order to prevent this, in particular, the neck region is currently dimensioned sufficiently large so that no incipient cracking occurs.
WO 2007/148359 A1 describes a method for producing a ball stud with the steps of plastically deforming a blank designed as a metal disk in order to generate a shank and a joint ball and carrying out a fine machining on an outer surface of the ball stud in order to reduce the roughness.
The generic DE 10 2009 011 978 A1 discloses a method for producing a ball stud with an anti-corrosion surface coating, including a joint ball and a shank, wherein the ball stud, viewed in axial direction, is subdivided into several zones, wherein the zones are each provided with a surface coating taking into consideration their stressing and adjusted thereto, including the method steps a) production of the ball stud; b) subdividing of the ball stud, viewed in axial direction, into different zones; c) zone-wise application of an anti-corrosion surface coating by means of a thermal injection method, wherein the zones are each provided with a surface coating taking into consideration their stressing and adjusted thereto.
The aim of the present invention is to provide a process-reliable method for producing a light-weight ball stud.
This aim is achieved by the features of claim 1.
A method for producing a ball stud with a joint ball and a shank, wherein the shank comprises at least a neck region adjoining the joint ball and a fastening section opposite the joint ball, characterized by the steps:
a) plastically shaping a semi-finished ball stud product;
b) mechanically machining, in particular cutting machining, the semi-finished ball stud product;
c) rolling the surface of the joint ball;
d) thermochemically hardening the surface of the semi-finished ball stud product;
e) removing the surface-hardened layer at least in the neck region and/or the fastening section;
f) oxidizing the semi-finished ball stud product;
g) polishing the joint ball.
After the entire ball stud has been treated by the thermochemical surface hardening process, by the subsequent removal of the surface-hardened layer in the corresponding regions and the oxidation, the mechanical properties and the corrosion properties can be influenced in a targeted manner. Thus, the surface-hardened and oxidized regions have a high resistance to wear and good corrosion protection, while the oxidized regions with removed surface-hardened layer are characterized by high ductility and by sufficient corrosion protection. In particular, a high resistance to wear and corrosion is necessary for the joint ball, while the neck region and the fastening section can also get by with a lower resistance to wear and corrosion. As a result, an ideal ball stud is obtained, which has a hard, abrasion-resistant joint ball with optimal protection against corrosion and wear, while the shank has mainly a ductile surface which is not subject to incipient cracking under high stresses. The requirement of corrosion resistance in the shank is clearly lower, so that here an oxidation of the non-thermochemically hardened surface is sufficient. The listing of the method steps moreover does not represent a stipulation of their precise sequential order. Where possible, individual steps can also be switched. Naturally, the method starts with the shaping of the semi-finished ball stud product and its rough machining. However, for example, the joint ball can also be rolled before the polishing of same. Alternatively, the polishing of the joint ball can also occur after the surface hardening of the semi-finished ball stud product. The oxidizing of the semi-finished ball stud product can occur before or after the removal of the surface-hardened layer, at least in the neck region and/or the fastening section.
In a preferred embodiment, the plastic shaping occurs by forging.
In a preferred embodiment, in an additional step, a thread is shaped in the fastening section. In a particularly preferred embodiment, the thread is shaped by thread rolling.
In a preferred embodiment, the surface-hardened layer is removed by cutting. For this purpose, lathing or grinding can be considered, among others.
In a preferred embodiment, at least 25 μm of the surface-hardened layer are removed.
In a preferred embodiment, the surface hardening is a carbonitriding.
In a preferred embodiment, in an additional step, a thermal hardening, in particular an induction hardening, occurs.
Additional details and advantages of the invention result from the following description of a preferred embodiment example in reference to the drawing.
The single FIGURE shows a ball stud.
The ball stud 1 consists substantially of joint ball 2 and shank 3. The shank 3 in turn consists, starting from the joint ball 2, of neck region 4, cylindrical region 5 and fastening section 6, wherein the fastening section 6 in turn consists of conical region 7 and fastening region 8. In the method according to the invention for producing the ball stud 1, first a semi-finished ball stud product is forged from a blank. Subsequently, the regions mentioned at the beginning are carved out by machining, preferably cutting machining. The surface of the joint ball 2 is rolled in the process. The semi-finished ball stud product is carbonitrided as a whole, wherein, in a next step, at least 25 μm of the carbonitrided layer in the neck region 4, the cylindrical region 5 and the thread region 8 are removed by cutting. Thus, the joint ball 2 and the conical region 7 are still provided with a carbonitrided marginal layer. In the thread region 8, a thread is shaped, and the joint ball 2 is polished. The entire semi-finished ball stud product is oxidized at the end of the method.
1 Ball stud
2 Joint ball
3 Shank
4 Neck region
5 Cylindrical region
6 Fastening section
7 Conical region
8 Thread region
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 210 976.9 | Jun 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/064607 | 6/4/2018 | WO | 00 |
