An Automated Answer for Machining Ball Pins

Ball joints are indispensable vehicle components. Whether used in the chassis or steering system, they not only act as a pivot point between different elements, but are also usually in constant motion and exposed to high physical loads. In this context, ball pins and ball sleeves are among the safety-critical car components that must be produced with a high surface quality and micrometer precision despite high production quantities and general cost pressure.

Until recently, ball pins were not a typical automotive component that passed through an Emag vertical turning center. However, the company has developed a new machine — the VST 50 — to minimize machining cycle times for ball pins. In fact, completed ball pins can be machined in 7 seconds, each subsequently undergoing a comprehensive measurement routine.

Although the part was seemingly atypical for Emag equipment, the company says it is similar to other applications in that it involves large quantities, special surface requirements and low unit production costs.

“We repeatedly ensure these qualities for various components,” explains Frank Haas, Emag project manager and development engineer. “In this respect, it was obvious that a major customer approached us with this task some time ago. The main question was whether we could exceed the performance values of existing machines in ball pin production. This was the starting point for the development of the VST 50.”

The VST 50 has highly automated processes, including the use of three robots. On the other hand, the company says it is intuitive to operate using the Emag DNA (EDNA) apps, which also include various measurement routines.

For the actual turning of the ball and neck of the ball pin, there are two downward-facing workpiece spindles that can be moved independently. As a result, one spindle is always loaded and unloaded while the other is in use during the machining process.

The associated tool compound slides are split in two: the tools on the left-hand side are mounted on a rotary B axis, which enables the ball to be turned and smoothed. In addition, the ball diameter and shape can be adjusted using a linear U axis. Special tools for neck machining are mounted on the right-hand side.

Part loading and unloading are carried out by the three robots, which are arranged in parallel in front of the machine. Each is responsible for a different subprocess. The left-hand robot handles the workpiece between the transfer station and the first spindle. The middle robot performs the same task on the second spindle. The right robot handles the workpiece between the transfer station and the outer automation assemblies.

Haas explains that one robot could perform these three tasks alternately, but this arrangement would extend the overall cycle time. “The various movements are sometimes carried out simultaneously,” he notes. “Our solution ensures that a finished workpiece leaves the machine every 7 seconds and the chip-to-chip time is less than 2 seconds.”

This also explains why the robots mentioned are also used for tool changes, whereby Emag has divided the entire process essentially into two parts. First, there is the operator’s task of monitoring the prediction for the tool change on the central control panel. Changing a tool simply requires a button push to have the tool magazine swivel outwards for the change. It is important to note that the production process is not interrupted during this time. After the exchange, the magazine swivels back to its starting position.

This completed manual process is followed by another that is automated. The left-hand robot first puts down its workpiece gripper and picks up a tool gripper. It then removes the worn tool from the interior of the machine and replaces it with a new one which it takes from the tool magazine. To further increase process capability, each tool is coded with an RFID chip so that the tool data can be transferred to the CNC accordingly. The entire tool change takes fewer than 90 seconds.

To ensure process reliability, each machined component passes through a light-band micrometer, which determines the required measured values in fractions of a second. The final ball and neck diameter is determined and any chips are detected at the same time. In addition, a high-resolution process camera is located directly in front of the loading hatches. Its live image appears on the panel at the touch of a button. The operator can easily check whether, for example, the chip formation is causing a fault in the process.

The company says this production process is flexible as the VST 50 is suitable for both short ball pins (ball diameter 16-40 mm, component length 50-150 mm) and long ball pins (ball diameter 22-35 mm, component length 150-455 mm). It can also be used for machining ball sleeves. According to Emag estimates, the VST 50 is approximately twice as fast as other production solutions for this component, which of course also reduces unit production costs.

“We are convinced that this machine will be very well received by the market and by other industries too, because ball joints are not only found in cars,” Haas believes.