Plasma Cutting Boosts Armor Production

O'Gara-Hess & Eisenhardt (OHE; Cincinnati, OH) first made a name for itself in 1948, when it engineered a bullet-resistant limousine for US President Harry S. Truman. Since then, more than 60 international heads of state and a long list of diplomats have been customers. Part of the Mobile Security Division of Armor Holdings Inc., the company today is the world's largest provider of wheeled vehicle armor.

The armor plate OHE installs ranges from 1/4 to 3/4'' (6.4-19-mm) thick. Because the company retrofits armor to existing vehicles, pieces must sometimes be cut to fit into very tight places with tolerances in the range of ±0.015'' (0.38mm).

Keith Kilpatrick, director of manufacturing engineering at OHE's Fairfield, OH, plant, needed to boost cutting capacity to support the company's increasing business. He had his eye on a plasma cutting system he had seen in a sister plant in Germany, and contacted a representative of ESAB Cutting Systems (Florence, SC).

Developed by a team of US and German engineers, ESAB's Acer 2 plasma cutting system featured highspeed dual side drives, a precision linear rail cross axis guidance system, the company's Precision Plasmarc plasma system, and a Windows-based CNC. It can provide good cut quality on carbon steel, aluminum, and stainless steel

Precision Plasmarc is a proprietary arc constriction technology that results in very low cut edge bevel angle and minimal dross, and requires little or no clean-up. It allows cutting and plasma marking with the same torch when used with an optional integrated flow control and PC. This eliminates the need for a dedicated marking station, improves accuracy by eliminating the need for tool offsets, and speeds cycles by cutting out machine motion between offsets.

The Fairfield facility has grown into two separate production buildings, both using a cellular assembly line process to produce military and commercial vehicles. In both cases, the vehicles are first disassembled and gutted, then the armor package is applied and the vehicles are reassembled.

Armor packages include ballisticgrade steels welded throughout the passenger compartment, transparent armor consisting of multi-layered ballistic glass, battery protection to ensure continued power supply, and Runflat wheels to help the vehicle reach safety in the event of an attack. Suspension upgrades are also included if required.

The machine's integrated flow control uses CNC-controlled proportional valves to control cut, start, and shield gases. Process parameters are selected and stored in the control, but can be manually adjusted and saved for future use, giving the operator flexibility.

Installed in November 2003, the initial Acer machine was so successful a second unit was added in June 2004. The machines have been instrumental in meeting OHE's demanding production schedules, including 350 Up-Armored Humvees per month for the US Army.

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