Motion transmitting remote control cable assemblies of the type for transmitting forces along a curved path are often employed in the automotive industry to manually control such features as acceleration, cruise control, transmission shifting, ventilation, braking, clutching, etc. Some applications, e.g., transmission shift control, require the motion transmitting core element to carry both compressive and tensile loads. In other applications, such as accelerator and clutch control, require only tensile force transmission. In this latter case, it is well known to form a slug on the end of the core element for convenient connection to either a controlled or a controlling device. For example, U.S. Pat. No. 4,624,155 to Wing, issued Nov. 25, 1986, discloses a remote control assembly having slugs at each end connected between a brake pedal and the brake linkages. Also, as shown in U.S. Pat. No. 5,165,298 to Shier et al, issued Nov. 24, 1992, a slug is formed on the end of a core element for simple connection to a throttle cam.
Such slugs are typically formed from zinc in a die casting operation where a pair of die halves defining a slug forming die cavity therebetween are clamped about the end of a core element. A segment of the core element located within the die cavity is frequently upset in some manner, such as by bending or fanning, to increase adhesion with the molten zinc. A sprue located along the axis of the core element injects molten zinc into the die cavity and around the upset portion of the core element. After the zinc has solidified, the core element with the attached slug is removed from the die casting assembly for either further assembly or use.
As shown in the Shier et al '298 patent, as well as in U.S. Pat. No. 4,088,040 to Ross-Myring, issued May 9, 1978, it is often desirable to form the slug with a spherically rounded head to permit free swiveling articulation between the slug and the attached control device. In these instances, the slug is usually formed with a generally spherically shaped head portion truncated at its tail, or base, end where a sprue adjoined the die cavity, thus leaving a flattened sprue scare. So long as the head portion remains spherically rounded, the flattened tail formed by the sprue scar does not hamper swiveling articulation between the slug and the control device.
When a tensile force transmitting remote control cable assembly of the type described above is fabricated, it is usually the case that a core element is first cut to length and a slug molded on one end thereof. The molding of this first slug is not a tolerance critical operation because the finished length of the cable assembly, i.e., from head to head of the slugs on each end, has not yet been established. Therefore, after the first slug is die cast onto the first end of the cable, the remaining cable assembly components are installed, such as the conduit, grommets, retention sockets, etc. Then, a final operation forms a second slug onto the second end of the core element, which then holds the various components together and prevents inadvertent disassembly. The second slug must be exactly positioned on the core element to establish a critical dimensioned length, referred to as the gauge measure, between the head of the first slug and the head of the second slug.
According to prior art technology where slugs having spherically rounded heads are formed in a mold, a sprue injects liquid zinc directly, i.e., axially, on the end of the core element in the die cavity. It is frequently the case that the core element is displaced axially under the pressure of the zinc injection by one or two millimeters out of the die cavity, thereby inadvertently lengthening the gauge measure of the cable assembly once the second slug is formed. Such inadvertent axial displacement of the core element out from the die cavity is not consistent from one slug formation to the next, and thereby prevents precise and calculable tolerances in the gauge measure of the final assembly. Further, such inadvertent axial displacement of the core element out from the die cavity during injection of the zinc can result in the upset portion of the core element becoming located very near to the surface of the spherically rounded head. This phenomena can have several disadvantages, the most important of which are an increased tendency for core element pull out from the slug and premature failure due to exposure or shallowness of the fatigued and stressed upset portion of the cable assembly.