An OEM in Iowa differs from that profile, if only slightly, in that it uses a distinctive method to charge the hydraulic circuit on pallet-mounted fixtures used for its horizontal machining centers (HMCs). A nearby contract shop that supplies these fixtures to the OEM also uses the atypical system for some of its high-volume machining jobs.

Rather than using compressed air to charge a fixture's hydraulic circuit to secure parts for machining, this alternate technique is based on a mechanical transfer of energy. It uses a remote cylinder device that is temporarily attached to the fixture and pressurizes a completely sealed hydraulic circuit (think in terms of a car's braking system). Once parts are secured, the remote device is removed, while parts remain firmly clamped and pallet movement unrestrained.

The companies mentioned are located within a short drive of each other in central Iowa—Sauer-Danfoss in Ames and Mid-America Manufacturing (MAM) in the city of Nevada. Sauer-Danfoss produces hydraulic components for mobile equipment, so it's no surprise that the company uses fluid power to hold the pumps, motors and valves it produces at this facility during machining. MAM is both a contract machine shop and a custom fixture manufacturer. It supplies a number of fixtures to Sauer-Danfoss with the mechanical energy transfer system, and also uses that system on some of the seven HMCs in its facility.

Sauer-Danfoss has four Machining Workholding pallet systems that serve a number of HMCs. Because pallets are shuttled back and forth between loading station and machine, and because the pallets are rotated within the machine, it is impractical to have each fixture leashed with continuously attached hydraulic lines for part clamping. So the company began using a quick-disconnect hydraulic system to charge the circuit on each fixture, but found that dirt and debris were prone to enter into the hydraulic stream, leading to maintenance downtime and seal replacements.

Sauer-Danfoss has since standardized on the mechanical energy transfer method to power the hydraulic workholding circuit on the fixture. Tom Taylor, tool designer, says that his Ames facility has nearly 70 fixtures with the mechanical energy system that are used on 36 HMCs. Let's take a closer look at this hydraulic workholding technique and its main components.