Steering knuckles are critical components that present some of the biggest machining challenges in the automotive industry. With numerous features, complex designs, and tightening quality standards, knuckle production promises to get even tougher in the future.

Automotive steering knuckles connect safety-critical vehicle components in steering, braking, and suspension systems.

1) How quickly are aluminum and forged steel replacing cast iron? RM: In one sport utility vehicle (SUV) that tooled up in 2010, out of the four components – front control arm, front knuckle, rear control arm, rear knuckle – three were cast iron, and one was aluminum, the rear control arm. When we did an update to that SUV in 2016, three pieces were aluminum. It’s an entirely different type of machining. You’re also going to run the tools at much higher speeds. And with the irregular shapes of knuckles, fixturing, and machine configurations, you get tools with quite a bit of length, so balancing and runout become a big part of the tool design.

2) How much more complex are knuckle designs getting? RM: Companies are adding more features to get suspensions to work better or add stabilizers or sensors, and they’re getting more particular about processes.

We might have to plunge a feature instead of milling it because of the surface finish they want. The surface finish of each process reacts differently with the seals the automakers want to use, so they’re getting more particular.

We’re seeing tighter tolerances in drilled holes for sensors. Most steering systems are computer controlled now, so you need connections for sensors and cabling, and those features can present challenges.

Increasingly being made from aluminum castings (such as the rear steering knuckle shown), knuckles contain more machined features than most automotive components.

3) Do material changes and complexity demand specialty tools? RM: If you can combine operations, you can save chip-to-chip time from tool changes and machine movement. But you have to pay close attention to the application. If you take a 6" face mill, you can’t combine that with a 1/8" drill. You can’t spin the tool to run that small drill fast enough to cut aluminum. It comes down to cycle times and machine capabilities.

4) How are material and design changes impacting cutting forces? RM: It’s hard to support some areas without deforming components. You can clamp it down tightly, but every clamping risks a slight deformation. By the time you’ve done multiple clampings, features don’t line up properly.

We have to support freer cutting with the geometry of the tool. We have to get positive rakes in the tools to lower cutting forces. So, we’re combining those geometries with higher cutting speeds for aluminum. We usually have to work with engineers on each component, but there are ways of lowering cutting and clamping forces without sacrificing metal removal rates.

5) How can tool users balance increasing orders of complex parts with rising surface finish requirements? RM: We have a large breadth of product. We can tailor our products to the application by making special cutters. Sometimes, we have to do special carbide, but we can do 85% of jobs with standard carbide because of the wide range of geometries and grades we offer.