All-pneumatic punch cuts and places discs

Safety calls for replacing electronics with pneumatics to generate force.

Engineering By Design (EBD), San Jose, Cal., developed the Microplate Gang Punch as a high-volume solution for filling microplates with small- to medium-size discs or frits, as they are called in the industry. With a single stroke, the punch’s air cylinder drives 96 hardenedand- ground pins through a sheet of raw material — held in a punching nest — and then through a 96-hole die plate to cut the frits. The pins complete their strokes by placing the cut pieces into the wells in a standard microplate.

There are many uses for microplates. The standard microplate is basically a tray with 96 wells on a 9-mm pitch in an 8 12 array. The size and shape of the wells vary according to industry and customer requirements. The material is placed in each well either to help with processing (like a chemical filter) or to test a sample using downstream procedures.

Frit diameters range from 0.09 to 0.25 in. Material thickness can run from paper-thin to 0.25-in. foam.

Punching 96 frits at about 0.24-in. diameter simultaneously takes considerable force. A single-station test punch determined that about 10 lb per frit was needed. With 96 frits — and a 2:1 safety factor — the press has to generate almost a ton of force. Due to the repetitive cycling and high force, an air cylinder (5-in. bore, 2.5-in. stroke) was selected to do the work.

Similar punches incorporate electrically operated controls and sensors. However, the National Electric Code (NPFA-79) and CE specify that electrical components must be segregated from pneumatic components — to prevent broken air hoses from spraying moisture and shorting the circuits. Because pneumatics was needed to generate the force, EBD decided to simplify the punch by eliminating anything electric and making it completely pneumatic.

The raw material sheet and an empty microplate are loaded into a carrier. The operator pushes the carrier into the machine manually. (Safety covers and a fail-safe interlock prevent actuation if the carrier is not positio ned properly.) A simple push-button valve on top of the machine triggers the punch process.

Pneumatic relays and a delay timer give the cylinder enough time to complete its punching and fully retract. A typical machine cycle lasts about ten seconds.

The CE-compliant punch weighs 90 lb. It requires clean, dry air at 90 psi . . . and no electricity. In addition, no operator set-up or adjustment is necessary. An internal pressure regulator adjusts cylinder force to match the application and a gauge displays the actual pressure. EBD uses Clippard’s MMA-43WAS 4- way valve with -in. NPT ports. The valve’s CV is 1.68 and it can flow 93 scfm at 100 psi. The exhausts are throttled to limit cylinder speed and mufflers quiet the punch.