Producing More, and Better, Ball-Joint Cages

Dec. 17, 2020
An automatic, servo-driven punching machine improves cutting quality and increases output by more than 40%, with shorter tool-changing times too.

While automotive and commercial vehicle design is in the midst of significant revisions, one aspect of design remains fairly constant – and in high demand. Virtually every motor vehicle has four to eight ball-joint cages installed, circular housings with multiple openings that holds a drive shaft and allows it to transmit power through variable angles at a constant rotational speed. According to production data, the global vehicle manufacturing sector requires at lease 500 million of these ball-joint cages every year.

Most ball-joint cage are produced on automated punching machines operating with a flywheel drive. As such, the cutting speed and surface quality in the cut area are comparatively low, and so is output. The need to manufacture different types of cages also means regular tool changes, resulting in extensive retooling and thus down times.

Machine-builder Karl Klink GmbH has developed a solution: The RT-HLKK1000 punching machine is designed with a servo drive, which reduces the cycle time to 7.3 seconds per piece (for a six-window cage; an 8-window cage can be produced in 4.1 seconds.)

At the same time, better cut quality minimizes finishing costs and time, and the design also cuts tool changing time from several hours to 30 minutes, increasing the machine availability.

“Ball cages are made in over 80 different versions. Automobile manufacturers often outsource variants with low unit quantities and lot sizes to suppliers,” according to Robert Keller, director of stamping technology for Karl Klink GmbH. That presents a great challenge to these companies. “For one thing, these suppliers have to do tool changes, significantly lowering machine availability and raising costs,” reports Keller. “For another, the flywheel drive used so far by most punching machines results in fixed slide kinematics, yielding in relatively low cut quality and output.”

Servo drive, for quality and speed -- The problem was brought to the attention of Karl Klink GmbH by discussions with an automotive supplier at the Blechexpo fair in Stuttgart a few years ago. From that, the company developed a high-performance automatic ball-joint cage punching machine that meets users’ advanced requirements for high cut quality and shorter retooling times. The RT-HLKK1000 automatic punching machine launched recently is based on the prototype presented in 2015, but with several improvements. The power source sets it apart. Instead of a flywheel, it uses a servo drive, which improves both the cutting speed and the cut quality. Thus, it has been possible to combine higher quality with higher productivity.

+40-percent higher productivity -- The machine has two die stations. Workpieces are fed from both sides and can be finished in different variants simultaneously, independently of each other.

Also, the ball-joint cages can be fed from either side, punched at the first station and then trimmed at the second, with feeding as chosen by the operator. The parameters for each station can be set separately via the control panel.

The 100-percent part inspection measures and adjusts the position of the cages in the feeding and discharge unit. The parts are verified in the process: incorrect and out of spec parts are automatically rejected, leading to a higher efficiency. For ball-joint cages with six windows, including punching and trimming, cycle times of 7.3 sec are possible (for 8-window cages with two-side feed without trimming it is as low as 8.2 sec per two pieces respectively 4.1 sec per piece.) This contrasts to 10+ seconds for the same punching operation on comparable presses of conventional design. In three-shift work without retooling, this means an increased volume of 11,835 parts per day or 2,840,547 per year, versus the 8,388 per day or 2,013,203 per year achievable with conventional machines. “This can boost output by 827,344 workpieces per year, which represents a productivity increase of more than 40 percent,” Keller said.

Flexible production, improved retooling -- Another goal was to design the punching machine so that ball-joint cage manufacturers can react as flexibly as possible to all different order scenarios. This flexibility allows production of ball-joint cages with outside dimensions from 45 to 120 mm. The number of windows and position correction per window are likewise freely programmable, making it possible to produce many geometries.

To speed up retooling time, Karl Klink moved the retooling process out of the narrow confines of the machine to an external retooling point. The tool transfer is accomplished with a tool changing cart. Once there, almost all the necessary parameters can be changed with ease. Hydraulic functions are available too, for example to adjust the cutting gap.

“The die for the next order can be set up during ongoing production. Thus, retooling is done in auxiliary process time,” Keller reported. “The cutting punch and its holder can be replaced with the punch tool installed, further shortening the process. The improved access makes tool changes go even faster.”