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TechView


Intelligent Automotive Assembly Continues


To Evolve


In 2004, Promess Inc.’s founder, Larry Stockline, wrote an article describing how two fairly new technologies, real- time process monitoring and signature analysis, were combined to improve the quality of an automotive wheel-stud insertion system. Te system he de- scribed used linear variable differential transformer (LVDT) sensors to monitor the operation and hydraulic cylinders to press the studs. A four-channel


Fast-forward to 2014 where that


relatively simple solution has morphed into an “intelligent” assembly system that does much more than simply insert studs and make sure they are present and seated. Now the hydraulic cylinders have been replaced with instrumented electric servo presses that control and monitor insertion force in real time as well as monitor seating depth. Tis came about because some


clever customer engineers noticed that monitoring the signature during the insertion process told them not only when the stud was seated, but also exactly how much force it had required. With that information available in real time, they rea- soned that a more precisely control- lable cylinder could


be programmed to supply just enough force to seat each stud and no more.


Te attraction of that concept was the inherent ability to mini-


Finite element analysis of a wheel hub showing the deformation which occurs during the pressing of a wheel stud.


Programmable Control Assembly Moni- toring System collected the inputs and ran the signature analysis soſtware. Te goal was to provide missing


and/or wrong stud detection and 100% traceable certification of every assembly. It worked very well, and was the basis for a number of similar systems built for wheel suppliers in several countries.


mize the force applied to the hubs and thereby reduce the number of bent hubs that had to be scrapped. Te hydraulic cylinders in the old system typically applied 12,000 lb (53.4 kN) of force to make sure that even the most mis- matched stud/hole combination would produce a properly seated stud. In real- ity, though, most studs were fully seated at 4000–8000 lb (17.8– 35.6 kN) of force, so excess force was frequently applied to the hub, oſten bending it. Te new insertion system replaces the hydraulic cylinders with Promess’s


Glen Nausley


President Promess Inc. Brighton, MI


programmable Electro-Mechanical Assembly Presses (EMAPs) that are equipped with sensors to measure both force and location. Te control soſtware monitors the signature of each stud in- sertion in real-time and stops the press when the stud is properly seated, limit- ing the force used to only the amount of force required (instead of hitting each stud with the maximum 12,000 lb). In practice that means that most


studs are inserted with 4000–8000 lb of force, well within the plastic deforma- tion limits of the hubs. By inserting the studs “intelligently” rather than by brute force, the system greatly improves the hub end-of-line flatness measurements and also saves energy by using just enough to properly seat each stud. Te technology available for assem-


bly systems today is far more sophis- ticated and capable than that of only a few years ago. Tat will lead to major


The technology available for as- sembly systems today is far more sophisticated and capable than that of only a few years ago.


changes in how technology is applied. In many ways the situation is similar


to the evolution of machining technol- ogy in the last few decades. Where purpose-built transfer lines were once the best solution for high-volume manufacturing, cells of flexible CNC machines are now the norm. It’s only a matter of time until clever


engineers make the same kind of transi- tion in their thinking about assembly systems. Te tools exist now; it’s time to put them to work.


Motorized Vehicle Manufacturing 35


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