Moving Outside the Autoclave Box
As Featured in Composite Manufacturing
by: Mary Lou Jay | February 27, 2017
Enhanced Controls Improve Parts Quality
Better ovens have helped improve the quality of OOA parts. Aerospace customers in particular are requesting ovens with more flexible systems and more accurate, higher-end controls, says Mike Grande, sales manager/senior applications engineer at Wisconsin Oven Corporation.
Ovens now offer improved monitoring capabilities. Manufacturers can bag parts individually, embedding thermocouples in each part throughout its thick and thin sections. After the vacuum is drawn and the heating begins, technicians can monitor all the points inside each part, looking for the hottest and the coldest.
“Suppose they have to heat everything up to 350 F, with an allowable range of 340 F to 360 F,” says Grande. “They might start the oven up from cold and run it at 400 degrees for the first half hour while monitoring all points. After they see the hottest points come in and start to approach 360 degrees, the control system senses that, brings the temperature down to 350 degrees. So you have the quick heating without any chance of overshoot because of this advanced control system.”
High-end controls also permit manufacturers to place slightly different vacuum levels on each part in the oven. “Rather than having to compromise and settle for one vacuum level – which might be OK, but not exactly what they want – they can individually tailor it to each part,” Grande said. This improves part quality.
While most ovens have sidewall ductwork that blows heat toward the center, Grande says a few customers have requested ovens with directed hot air impingement. These ovens contain several hoses with nozzles that the manufacturer can clamp into place to direct extra air to certain areas.
Hot air impingement could be useful with a C-shaped part. With the two sides of the C heated by the sidewall ducts, the hot air from the nozzles can be directed into the center of the C. This arrangement allows for faster and more even heating of the composite part.