Stahlin opts for automated press for SMC processing

The enclosure manufacturer acquires two 400-ton hydraulic compression molding machines from Greenerd Press & Machine Co. Inc.

When Stahlin Non-Metallic Enclosures (Belding, Mich., USA) reached its manufacturing capacity limit, it knew that new capital equipment was a necessity. Stahlin produces fiber reinforced polymer (FRP) composite boxes and enclosures for electrical systems and components, using sheet molding compound (SMC) that it formulates and manufactures in-house with polyester resin and chopped fiberglass. The plant, outfitted with eight compression molding presses as well as CNC cutting equipment, SMC compounding equipment and other automated machines, was running three 8-hour shifts per day, six days per week to meet demand, and additional presses were required.

Stahlin looked for an equipment vendor who understood the technical issues related to the compression molding process, including how to minimize part cycle time and reduce scrap rate for the thermoset resin-based SMC material. The company eventually selected Greenerd Press & Machine Co. Inc. (Nashua, N.H., USA) and purchased two 400-ton, 4-post hydraulic presses. The large tonnage and bed size accommodates the majority of Stahlin’s existing mold tools and the 4-post design minimizes deflection and ensures repeatable die alignment. A die lift allows faster setups so that operators can quickly change molds without having to set the stroke, says Stahlin press operator Chuck Edmonds, and the press can be loaded from any of four sides, further increasing efficiency by accommodating various work cell designs. Tonnage can be adjusted easily to accommodate different part molds for production flexibility, and computer touch screen controls have resulted in more consistent parts with less scrap — the company’s older presses required manual, mechanical adjustments. The molds’ open bed design also means that operators do not have to physically bend down to retrieve molded parts and have less chance of contacting hot surfaces.

Dean Childs, Stahlin’s composites supervisor, adds that the Greenerd presses meet all relevant rules for worker safety, including light curtains, and also feature a degassing cycle that allows gases to be evacuated from the mold during part cure, relieving pressure inside the mold for better part quality. “With the computer controls, the parts aren’t pressed too quickly, which can cause the resin to squeeze out of the mold, or too slowly, which causes premature cure of the SMC,” he notes. Scrap rate has been reduced by at least 20 percent, says the company, and productivity has improved along with part quality.