Case Studies

1. Hydraulic Actuator
2. Stamping Line
3. Welding Line
4. Machining Transfer Line

HYDRAULIC ACTUATOR
TRANTEK DRIVE SYSTEMS INC., ELIMINATES HYDRAULIC ACTUATORS FOR PRODUCTION ASSEMBLY AND FABRICATION PLANTS

Many Manufacturers have installed numerous hydraulically actuated transfer devices over the years. These devices can develop leaks and the associated maintenance and environmental removal/disposal costs are excessive. Older systems also have controls that don’t control the motion as well as newer servo controlled systems.

TranTek Drive Systems, Inc. has retrofitted several of these hydraulically actuated rack and pinion systems with its high lead screw and patented Dri-Tran® polymer nut assembly. In addition, new updated controls have resulted in smoother, quieter, and faster motion. The existing structure and frame can be used. Typically, several used shuttles are shipped to TranTek for refurbishment. The transfer devices are taken apart and the hydraulic devices are removed. The high lead screws and Dri-Tran® polymer nut assembly is then added. New bearings, cam followers, and rails can be provided as needed. These units can also be refurbished in the plant over a non production weekend to get additional units done throughout the year.

For example, in the application shown below, a major automotive OEM was experiencing the following problems:

• Accounting for the volume of hydraulic fluid coming into the plant compared with the documented volume of hydraulic fluid being environmentally removed from the plant. The difference was the amount leaking and not accounted for.
• The housekeeping, cleaning, and safety issues associated with excessive hydraulic fluid leaking onto the floor.
• The cost of replacing fluid that leaked and the cost of environmentally disposing of the recovered leaked fluid.
• The labor cost for cleaning up the fluid.
• The cost of downtime and machine repair as a consequence of a leak and subsequent system device failure.
• Poor motion control with the hydraulic system resulting in controlled crashes at either end of the index. This caused excessive wear on the mechanical components including bearings, cam followers, and rails. In addition, the resulting noise pollution aggravated plant management personnel whose offices were nearby.
• Poor motion control also prevented the speeding up of the transfer cycle to meet increased production throughput requirements.

TranTek Drive System Engineers evaluated all the above issues and concluded that an electric servo drive coupled with a 4 inch high lead screw and Dri-Tran® polymer nut would address all of the undesirable issues described. The hydraulics were eliminated and the 4 inch high lead screw provides an additional 30% speed increase. The noise pollution was eliminated since the interface between the polymer and screw generates negligible sound compared to multiple pinions engaging with the racks and the smooth motion and controlled stops (no crashes) addressed noise and excessive wear and tear concerns.

The cost of the retrofit was much less that the alternative of a total automation transfer device replacement. The existing frame, carriage assembly, cam followers, rails, stops, shocks, mounting brackets, tooling, etc. were re-used. The return on investment was a couple months since additional hydraulic fluid, leaked fluid clean-up & disposal costs were eliminated and machine maintenance costs were acutely reduced. Additional benefits were the production rate increases and reduced noise pollution.

Hydraulically actuated transfer device (Style 1).		High lead screw and DriTran® polymer nut.		Discarded hydraulic cylinders and rack & pinion components

Feature		Benefit
No hydraulic fluid.		Cleaner production environment Elimination of disposal costs Elimination of hydraulic power unit
High leadscrew/Dri-Tran® polymer nut		Faster speeds with high lead screw: The 4 inch lead provides significant speed increases since a high lead screw can have a lead up to 3 times its diameter (a ballscrew is generally limited to a lead equal to or less than its diameter) Quieter operation with polymer nut: The interface between the screw and polymer nut has negligible noise pollution compared with a ballnut/ballscrew or rack/pinion interface Higher loads with polymer nut: Screw stand-offs with a split nut are available to move heavier loads faster and stay away from screw critical speed concerns Lower vibration and associated component wear
Refurbish existing system		Lower overall costs Shorter lead-times
Electric servo-controlled motion		Lower transfer vibration and associated wear More accurate Readily available service parts compared with systems 10+ years old

STAMPING LINE Back to top>
A Big Three stamping plant had installed 11 door weld lines, each propelled by a ball screw/rack and pinion driven shuttle. Two years after the installation, all the lines were encountering costly maintenance and downtime. One shuttle had been down and out of the line 12 times in 24 months.

Factors: Each shuttle included three slave carriages and was required to move the 6500 pound payload 108 inches in 2.4 seconds. The proposed retrofit of the drive system had to be accomplished within the existing framework of the ball screw shuttle and adapted to the existing VFD drive motor.

Solution: The first retrofit, of the worst performing shuttle, was accomplished by replacing the ball screw/rack and pinion drive with a 2-3/4" diameter x 6.0" lead screw with a DriTran polymer nut and new bearing blocks. It was reinstalled on the same door line and achieved six years of trouble-free service before the DriTran polymer nut was replaced. The other ten weld lines were similarly retrofitted.

WELDING LINE Back to top>
A Big Three welding operation had tried several drive systems for two weld assembly machines. Even with covers, the drives could not hold up to the continuous weld flash directly over head. The complete drive assembly had to be replaced every 90 days.

Factors: The replacement DriTran screw and nut had to be directly interchangeable with the existing drive system. In addition, there could be no lubrication used on the screw/nut because of the fire danger from the weld flash.

Solution: TranTek replaced the drive system with a 1-7/8" diameter screw with a 4" lead and DriTran polymer drive nut. The DriTran system ran four times longer than the original. When the unit required service, only the DriTran nut had to be replaced. The original nut was recast and returned as a spare.

MACHINING TRANSFER LINE Back to top>
A Big Three crankshaft machining plant had a 48mm (1.89") diameter 12mm (.472") lead ball screw drive system on four of their transfer lines. The production rate needed to be increased using the existing equipment. Since there was minimal time that could be eliminated from the machining cycle, the improvement in cycle time had to be accomplished by reducing the index time of the transfer bar.

Factors: The replacement screw and nut had to be directly interchangeable with the existing ball screw and nut. They also needed to run more than three times the original speed while maintaining the same positional accuracy. The transfer system had an 8000 pound weight and needed to index 54 inches in less than three seconds.

Solution: TranTek designed a direct replacement 2-3/4" diameter screw with a 6.0" lead and DriTran polymer drive nut. We coupled this with a new two speed AC drive motor and integral gear reducer. This application has been running for almost four years without any drive related problems.