GB2135602A

GB2135602A - Method of making a ball stud

Info

Publication number: GB2135602A
Application number: GB08405131A
Authority: GB
Inventors: Karl Mettler
Original assignee: Supervis
Current assignee: Supervis
Priority date: 1983-02-28
Filing date: 1984-02-28
Publication date: 1984-09-05
Also published as: IT8467157A0; GB8405131D0; ES530080A0; FR2541605A1; JPS59166339A; GB2135602B; SE8401068L; NL8400462A; AT376915B; IT1179982B; ES8502886A1; ATA68683A; SE450218B; DE3404877A1; SE8401068D0

Abstract

A substantially cylindrical blank having a solid section is used for manufacturing a ball stud, as is used for steering linkages in motor vehicles. A ball (6') is integrally formed on this blank by means of a preferably multi-stage extrusion process, in a press (1') with a pressure plunger (4'). In the final stage of the extrusion process a closed press (1') is used and the ball (6') obtained in this manner is brought to its rated size by means of round forging (Fig. 4). <IMAGE>

Description

SPECIFICATION Method for manufacturing ball studs The invention relates to a method for manufacturing baR studs having a shaft and a ball arranged at the end thereof, wherein, starting from a substantially cylindrical blank having a solid section, the ball is integrally formed thereon by a preferably multi-stage extrusion process by means of a press and an extrusion die.

Ball studs are, for example, used in steering linkages of motor vehicles. In this connection the balls have to have an extremely high degree of dimensional accuracy and, in addition, their surface has to be of high quality, i.e. they have to have a very low degree of surface roughness.

Heretofore, starting from a substantially cylindrical blank of solid section, the ball was preformed by a multi-stage extrusion process in an open press. By means of the extrusion in an open press case an unfinished ball was obtained having ridge extending around its central region which was removed in a subsequent operating stage. In a further operating stage the ball was brought to its rated size by machining and the surface was smoothed by smoothing rollers in a further operating stage.

German Offenlegungsschrift No. 21 07 459 discloses a method for manufacturing hollow steel balls used as connecting elements in skeleton frameworks. These hollow steel balls are produced by drop forging. In this connection, two half shells are firstly formed such that in the forging die each has an edge extending approximately in the form of a sine curve, after which the half shells are placed with their converging edges together and then welded along their continuous separating line, or, however, the hollow balls are forged in one piece in a die, firstly starting from a hollow cylinder as the blank, which is preformed conically at the ends, after which the hollow intermediate product formed in this way is transformed into the spherical end product in a forging die.The forging die consists of two halves which in the final state of preforming of the workpieces form a closed forging die which, in this way, is produced by the halves of the die being knocked onto one another, as a result of which, however, it is only possible to form an incomplete hollow ball. These known hollow steel balls, which are used as connecting elements for skeleton frameworks, are structural parts on which, in view of their dimensional accuracy, only slight demands are to be made, at all events demands which are to some extent comparable with a precision machine part, as represented by a ball stud which is used in connection with steering linkages in motor vehicles.

The above mentioned process is a very expensive shaping process for a high-quality mass-produced article and this is where the invention is of importance since its aim is to simplify the shaping process for ball studs of this type without thereby impairing the quality of the workpiece, on the contrary, obtaining a highquality product in spite of the simplified manufacturing process.

The present invention consists in a method for manufacturing ball studs having a shaft and a ball disposed on the end thereof, wherein, starting from a substantially cylindrical blank having a solid section, the ball is integrally formed thereon by an extrusion process, including a press case and an extrusion die, and wherein at least in the final stage of the extrusion process a closed press is used for shaping the ball and subsequently the surface of the ball obtained in this way is brought to its rated size by round milling and is smoothed.

As a result of this method the manufacture is simplified to an extraordinary degree and is less expensive, and, as a result of the dressing (round milling) of the surface provided a product is obtained which is of higher quality than the products obtained hitherto. The fact that the known method for manufacturing hollow steel balls as connecting elements for frameworks offers no suggestion that the present invention, is obvious to the person skilled in the relevant art.

In the accompanying drawings:- Figure 1 is a perspective view of a solid section cylindrical blank, Figure 2 is a longitudinal sectional view of a known extrusion mould showing the final stage, Figure 3 is a view similar to Fig. 2, but showing an extrusion mould used in a method according to the present invention, Figure 4 is a diagrammatic illustration of a round milling device and Figure 5 is a side view of a finished ball stud formed by the method according to the present invention.

Starting from a cylindrical blank having a solid section, as shown in Figure 1, hitherto in a multistage extrusion process a ball was integrally formed on the end, the latter stage of the extrusion process being shown in longitudinal section in Figure 2. The press 1 used here consists of two shaping members 2 and 3 and is used open, i.e. during the operation of the extrusion die 4 the two shaping members 2 and 3 of the press 1 are at a slight distance a from one another such that the workpiece material can flow into the remaining gap 5 as a result of the action of the extrusion die 4, such that a continuous midcircumferential ridge 7 is formed on the ball 6 to be shaped. The press in this connection is dimensioned so that the ball 6 which is obtained and includes the ridge is over size. In a subsequent operation the ridge 7 is removed and the ball 6 machined to its rated size.Then the surface of the ball is made smooth, in particular by smoothing rollers, and the stud 8 is machined.

In accordance with a preferred embodiment of the present invention a closed press 1' has two shaping members 2' and 3'. The press 1' is in this connection dimensioned in such a way that it has the rated size of the ball 6' to be produced together with the required excess measurement for the subsequent round milling. The degree of surface roughness of the balls 6' formed in this way is thus between approximately 6 and 12 m.

The two shaping members 2' and 3' form the press 1 and pressing die 4' is displaceably mounted in the member 2'. In the method according to the invention the members 2' and 3', which form the press case' and accommodate the blank which may be preformed and has a solid section, are firstly combined to form a closed press mould, whereupon the pressing die 4' is actuated and acts directly on the material, of the blank which forms the ball 6' and has a solid section. During this action the two members 2' and 3' of the press 1 abut one another and thus, together with the die 4' form a closed chamber.

Subsequently the ball 6' is round milled and as a result of this the surface roughness is reduced to a peak-to-height depth which is less than 3 m.

By means of the round milling, on the one hand the surface of the ball 6' is improved and, on the other, the ball is brought to its rated size. The stud is shaped in the conventional manner by machining, however it can likewise be shaped in the desired manner by round milling. The finished ball stud is illustrated in Figure 5.

Apparatus for round milling is shown diagrammatically in Figure 4. It comprises a hammer shaft 10 in which forging dies 12 and hammer rams 1 3 are mounted so as to be radially displaceable. Pressure rollers 14 are inserted in a freely rotatable manner in a roller cage 1 5 which is in turn surrounded by an outer holding ring 1 6.

When the hammer shaft 10 rotates the hammer dies 12 and the rams 13 are guided radially outwardly by centrifugal force. In this connection as the hammer rams 13 run under the individual pressure rollers 14 they receive an inward pressure pulse which is transmitted as deformation force onto the hammer dies 12 and thus onto the workpiece, (not shown).

The ring 1 6 holding the pressure rollers 14 is freely rotatable in a machine housing and is made to rotate by the rotating hammer shaft 10 in the desired relative manner, similarly to a planet gear.

On the path from one pair of pressure rollers to the next the hammer rams 13 are then released again and the resultant opening stroke enables the released workpiece to rotate or to move.

Apparatus of this type is known per se. However, their use in the case of ball shaping is not obvious, since hitherto only cylindrical or conical workpieces were machined in the round milling process.

The shaping of the workpiece described above can be carried out at ambient temperature (cold extrusion) and also at an operating temperature which is increased in relation to the workpiece (warm extrusion). The cold extrusion process is to be preferred, however, since it is not only cheaper (the warming-up process is unnecessary) but it also enables greater manufacturing precision to be obtained.

The stud 8' can be formed by machining. In principle, however, it is also possible to shape the stud in the desired manner by round milling.

As a result of the method according to the invention, ball studs of the type described above can be produced considerably more cheaply than hitherto and, in spite of the cheaper manufacture, a high-quality product is obtained.

Claims

1. A method for manufacturing ball studs having a shaft and a ball disposed on the end thereof, wherein, starting from a substantially cylindrical blank having a solid section, the ball is integrally formed thereon by a process, including a press case and an extrusion die, and wherein at least in the final stage of the extrusion process a closed press is used for shaping the ball and subsequently the surface of the ball obtained in this way is brought to its rated size by round milling and is smoothed.

2. A method as claimed in claim 1, wherein the closed press has a measure of capacity which corresponds to the rated size of the ball to be formed.

3. A method as claimed in claim 1 or 2, wherein a pressing die is displaceably mounted in one of the two shaping members forming the press and acts directly on the material forming the ball.

4. A method as claimed in claim 3, wherein at least in the final stage of the extrusion process the shaping members forming the press abut one another to form a closed mould and subsequently the pressing die is actuated.

5. A method for manufacturing ball studs substantially as described with reference to, and as illustrated in, Figs. 1 and 3 to 5 of the accompanying drawings.