FIGURE I: Complete and Incomplete Axle Assemblies

A leading manufacturer of truck axles approached Neff Press looking for a turnkey production solution.  The customer was looking for a better and more consistent way to press wheel studs into rear axle shafts.  The shafts in question consisted of four different lengths, had two different bolt circle diameters and required either six or eight studs.

Previously, the customer employed "single-hit" tooling that pressed all of the studs in one stroke of the ram.  While it was simple, this method proved problematic because of tolerance variations on the head of the stud.  These variations prevented all of the studs from being pressed flush into the axle.  The resulting gaps between the stud head and the axle created durability problems.

Neff's turnkey solution included a 25-ton C-frame hydraulic press and the optional equipment detailed in Figure II.

FIGURE II: Axle Assembly Press

1. Axle Length Sensor 2. Force vs. Distance Monitor Package 3. Safety Light Curtains and Swing-Away Guard Doors 4. Stud Hopper (500-stud capacity) 5. Common Upper Tool for Pressing Stud 6. Lower Tool Nest (Specific for 6 or 8 studs) 7. Servo-Driven Rotary Index Table 8. Manual Dovetail Slide - Adjusts for Bolt Circle Diameter 9. Neff DF25-15M Hydraulic Press

Neff press designed all of the tooling for this project. Each axle would be hand-loaded into a tool nest that had clearance for the studs to stick through. The tool nest and axle sat concentric to a rotary indexing table that would position one stud at a time underneath the ram.

A key feature that allowed this project to be a success was the servo-driven index unit (rotary table). The servo unit can have variable numbers of stops and even complete complex moves and rotate backwards if necessary. This allowed the customer's 6-stud and 8-stud axles to be completed on the same press. Additionally, the indexing unit was mounted on a dovetail slide that allowed manual adjustment for bolt-circle diameter via a hand crank and lead screw.

The main difference between the customer's old process and Neff's new machine is the pressing cycle. Instead of pressing all of the studs in one hit, the Neff machine presses one stud at a time and then rotates the part the next stud under the ram. This process would continue automatically until the operation is complete. This method has a few distinct advantages. First, each stud head is pressed in fully regardless of tolerance variations on head height. Second, press size does not increase with an increased number of studs. The size is optimized for the individual stud pressing operation. This saves on the overall investment.

Because operators could mistakenly not load one or more studs into the fixture, a method for detecting lack of a stud was necessary. Using photoelectric or proximity sensors was not possible because the tooling rotated 360 degrees and would facilitate a special switch or slip ring coupling to run the signal through the center of the indexing unit. Additionally, the insertion operation created metallic chips that could fool a proximity or photo sensor.

FIGURE III: Close-Up of Tooling and Fixtures

1. Hydraulic Ram 2. Completed Axle Assembly 3. Upper Pressing Tool and Ram Slide Assembly 4. Lower Tool Nest 5. Servo-Driven Rotary Turntable 6. Gib-Guidance for Pressing Tool

Neff solved the problem using its Force-Vs-Distance measuring technology. Knowing that each stud took a certain amount of force to insert, Neff's press control used pressing tonnage and ram position feedback to determine if a stud was actually present. If the required force were achieved at a certain insertion distance, the machine would continue on. If the required force was not achieved, an alarm would be displayed and the operator would be prompted to load a stud.

FIGURE IV: Adjustable Indexer Slide		FIGURE V: Axle Assembly Before Pressing
FIGURE VI: Force Vs. Distance Monitoring Screen