Dana Corporation manufactures drive shaft components for the big three auto makers. At Northfield, we’re proud of the part we play in helping them solve their production challenges.
For this application, Dana needed us to provide a chuck that would be mounted on a balancing machine to hold a drive shaft on one end gripping the component called a slip yoke. These drive shafts are for the Daimler Chrysler Corporation.
Getting a grip on the situation.
The workholding task was complicated by several factors. The shape of the part – long and thin – the grip force required to hold a 5ft. long drive shaft – the accuracy 1/10,000 T.I.R. – and the speed – as high as 8,000 rpm – during the balancing process.
Normally, balancing operations are performed at only 900 rpm, but Dana needs to balance this part at simulated road conditions. Since the shaft will deflect (bend) at high speeds, this is the state they want it balanced at. For production cars, drive shafts typically rotate up to 3,000 to 5,500 rpm. However, this component would be used in Daimler Chrysler’s stock (racing) cars. These high-performance vehicles hit 200 mph with their drive shafts rotating at 8,000 rpm.
Sometimes, two chucks are better than one.
To solve the problem, Northfield engineers decided to use a diaphragm chuck, rather than a sliding jaw chuck. But before making the final decision, we did several tests using solid models on our CAD systems, to ensure that our diaphragm chuck wouldn’t lose grip force at these high rpms.
Our solution basically consists of two separate diaphragm chucks, with two separate sets of jaws, mounted one in front of the other. This is done to accommodate the long, thin shape of the part. With one set of jaws gripping near the front of the piece and the other gripping near the rear, the result is accuracy of a 1/10,000 T.I.R. and repeatability to 50 millionths of an inch and extreme rigidity. The chuck also uses a male spline driver mounted in the center of the chuck to help drive the shaft on start up and stop, and guide the shaft into the jaws during loading. These drivers are .002in. undersize of the internal spline and must not influence the centering of jaws. The spline driver is a gauge quality piece of tooling supplied by Michigan Spline Gauge Co. that provides a concentricity of less than 50 millionths with the chuck.
In Dana’s production car area, the chuck runs the same component. In the stock car area, however, it is used to run a few different components. Parts and tooling can be switched and still maintain an accuracy of less than a 1/10,000 T.I.R.
One final note, to meet Dana’s safety standards, we designed this chuck to be air opened with a self-contained clamping system (using the spring pressure of the diaphragms for clamping) that would hold the part in the chuck if air pressure and power were lost during the balancing operation.