ADVANCED MANUFACTURING NOW Modern Manufacturing Processes, Solutions & Strategies

Moving ball joint assembly into the 21st

century B

all joints are used in mechani- cal systems on everything from lawn tractors to cars and air-

craft. They’re found virtually anywhere motion in more than one plane is re- quired, and their function is very often critical to performance and safety. In aerospace applications, proper function can literally mean the differ- ence between life and death. Every ball joint used in a critical mechanism must be reliable and smoothly operating with low lash and articulation resis- tance within very tight specifications. Traditional ball joint assembly

processes rely on post-assembly tests to verify operation within functional specifications. Assemblies that fail are scrapped, wasting costly materials, labor and time. It’s not a good choice, but it’s the only one available to a manufacturer using traditional assem- bly processes and technologies. Today, however, there is an assem-

bly technology available that can pro- duce ball joints with virtually identical functional performance while nearly eliminating scrap. This technology combines the decision-making power of computers and software with the precision of electromechanical servo- controlled devices to measure and adjust the functional characteristics of a ball joint while it is being assembled. The technology is closing the loop

between assembly and test. Because lash and articulation resis-

tance are both functions of the fit be- tween the ball and cup of the ball joint, both can be tested by articulating the ball while the joint is being assembled and monitoring the values. This is done by a pair of servo-controlled devices, an


instrumented electromechanical press and an instrumented torque applica- tion and measurement system. Both are controlled and monitored by a com- puter running analytical software. Systems with which Promess is

intimately familiar combine a Promess Electro-Mechanical Assembly Press (EMAP) with a Promess TorquePRO, both controlled by a Promess Ultra- PRO multiaxis controller.

While the cup is being formed, the

TorquePRO articulates the joint through a programmed set of motions while the resulting torque values are monitored, communicated to the UltraPRO and stored. Because this is all done while the joint is being assembled, the real- time data is used to control the ultimate functional characteristics of the joint. If, for example, the ball joint articu- lation torque is too low, then the crimp

Ball joints have to function perfectly in aerospace applications. Historically, materials, labor and time have been wasted getting it all right.

The EMAP is essentially a CNC

press consisting of a ballscrew driven by a servomotor and equipped with sensors to measure position, force and other process parameters that may be necessary. The TorquePRO combines a servomotor and torque transducer in an integrated torque spindle pack- age that delivers plug-and-run func- tionality. The UltraPRO is a Windows- based computer running servo-control and patented force/position signature analysis software. As soon as the component parts

are loaded, the process begins by moving the EMAP down to the programmed initial ball/cup engage- ment point. The EMAP’s onboard sensors feed precise position data back to the control, and it uses the position data to compensate for dimensional variations in the compo- nents and then advances the EMAP a precise distance to begin forming the cup to retain the ball.

is too loose. However, the EMAP can be cycled again, employing a move-to- force strategy that applies a specific force value rather than moving to a position. This press-measure-press assembly strategy is repeated until the articulation torque is optimal, ensuring that every ball joint is assembled to the same functional criteria, every time. Once the assembly is processed to the optimal articulation torque level, the TorquePRO system can run a short “wear-in” routine, exercising the as- sembly through multiple full-range-of- motion cycles, where the performance data is tested again. Additionally, the data generated by the Promess sys- tem can be stored to provide individ- ual ball joint traceability. The data can also be shared with other systems. Traditional 20th

century assembly

processes cannot provide a cost- effective solution here. Fortunately, the technology exists to move the assem- bly of ball joints into the 21st


Director of Software Promess

Andy Joseph

Summer 2016

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