Concurrent machining kickstarts motorcycle production

Harley-Davidson is known for quality, performance, and style among motorcycle aficionados. But building these legendary machines relies less on reputation than on innovative manufacturing techniques and highly automated production.

A case in point is the company's recently installed 12-axis automated system at its York, Pa., plant. It cuts machining time for motorcycle frames by more than 70%. Traditionally, frames for FLT Touring Bikes, including Road Kings and Electra Glides, are processed on a singlespindle machine tool in four sequential operations. To reduce production time while increasing quality, the company turned to Tennessee Rand Co. (tennrand.com), an engineering firm and precision machine builder located in Chattanooga, Tenn. With experience designing automotive robotic systems and welding fixtures, Tennessee Rand's engineers developed a machining center with four separate spindles that perform all metal cutting on the frame simultaneously.

Though simple in concept, turning it into reality was no easy task. The frames are steel, but it is critical they do not flex or bend when secured in the fixture and during machining. Southern Fluidpower of Chattanooga, a Parker Hannifin Technology Center (parker.com), helped develop the hydraulicpneumatic positioning and clamping system that plays a key role in ensuring precision and quality.

After a robot loads the frame into the machining center, a bank of Parker F3 pneumatic valves actuates cylinders on the bike-holding fixture. These extend the tooling components to touch — but not deflect — the bike frame. This engages the frame softly thanks to sandwich-style pressure regulators on the valves.

Then the system hydraulically locks the actuators in place and clamps the part. The goal is to find and lock down the frame without changing its geometry in any way. Sixteen D1VW directional valves provide hydraulic control, and pressure in each valve is regulated separately to prevent the clamping cylinders from accidentally damaging the frame or machine.

Other key components include 2MA air cylinders which counterbalance the gravitational load on the Z-axis ball screws, and PWBA Series pneumatic blocking valves on the grippers that secure the frame in the event of pressure loss.

A Parker V-Pak power unit supplies the hydraulic clamps and work supports. Hydraulics also rotates the tools from one turret position to another on the four spindles, which hold up to five tools each, and locks the turret in place.

Pneumatics supplies purge air to the turret for changing tools and pressurizing the turret housing to keep cooling fluid out of the spindle during machining.

The four separate frame-machining operations include cutting the rear swing-arm bearing mounts from the right and left, as well as the upper and lower steering-head bearing bores. The two top spindles first cut the rear swing-arm bushings to length, followed by a counterboring operation for the hole. The third operation is a tap drill, followed by tapping threads into the bushing. Finally the hole is deburred so the frame is immediately ready for painting. At the same time, front and rear turrets cut the upper and lower steering-head bearing bores.

The 62,000-lb machining center has enough rigidity to withstand vibrations from four simultaneous machining operations. An Allen-Bradley ControlLogix PLC and Tennessee Rand Automation touchscreen provide control. And although it is designed for the FLT frame, the machine can be retrofit for other frames.

The four-spindle operation dramatically cuts machining time necessary to manufacture a complete frame — from 11 min to about 3. Currently the machining center runs three shifts per day.