Vacuum Furnaces: Maximizing the Work Zone with Creative Fixturing
A shop can spend a million dollars purchasing a new vacuum furnace and hundreds of dollars more on personnel, process gas and electricity each time a batch of parts is run through a brazing or heat-treatment cycle. To obtain more value from their capital expense, many companies add shifts so they can keep the furnace running. Often, however, there is a far simpler remedy: using a custom fixture that allows the maximum number of parts to be processed simultaneously (Fig. 1).
“With a custom fixture, we can get more production out of our furnace,” said Kim Hutchinson, senior project manager for Hitchiner Manufacturing Company, Inc. in Milford, N.H. “The low mass of the plate heats up faster, and we can pack the parts more densely so there are more pieces per load.”
One Size Misfits All
Most vacuum-furnace manufacturers are focused on two things – building and servicing their furnaces. These are the high-ticket items that make or break the company. But, as with so many aspects of life, it is the little things that can make the biggest difference – such as having a few more inches of legroom on an overseas flight or a drink that is a few degrees colder on an August afternoon.
With furnaces, it is easy to find a fixture that fits. What is harder, but can pay the biggest dividends in production and profitability, is a fixture with the right size, materials and design for both the furnace and the parts that are being processed. The trick is to maximize the work zone.
Furnace manufacturers will specify the useable work zone for their equipment. The exact dimensions of the space that they guarantee will reach a uniform temperature. The work zone is often cylindrical, but many fixtures are square or rectangular and don’t efficiently utilize the entire work zone. Switching to a round fixture allows more parts to be processed at a time.
“Many companies don’t realize that even a simple design change to the fixture can allow them to process 25% more parts per load,” said Rob Kornfeld, president of Hi-Tech Furnace Systems, Inc. of Shelby Township, Mich.
Then there are times when the work zone can be utilized beyond what the manufacturer specifies. For example, an individual furnace can be re-surveyed to verify that there is a larger work zone with uniform temperature within specification. Or there are certain types of parts that don’t require the precision heating obtained within the manufacturer’s specified work zone. If the parts can tolerate a wider temperature range and still meet their design purpose, then a larger fixture holding more parts can be designed, recognizing that some of the processed parts will be outside the manufacturer’s specified work zone (Fig. 2).
Alternatively, there is the option of layering the parts. Instead of laying the parts out on a single level, a customized solution can be designed with multiple levels of the precise height needed to allow even heating of the parts while utilizing the full height of the work zone (Fig. 3).
A Layered Approach
Hitchiner – an investment casting company that manufactures parts for the commercial, automotive, aerospace and defense industries – uses an Ipsen vacuum furnace with a 48-inch x 48-inch x 72-inch work zone for solution annealing of turbine blades at 2250°F. A few years ago, they decided to go with a custom fixture from Hi-Tech Furnace Systems.
“I was familiar with the low life span of alloy fixturing at those kinds of temperatures,” Hutchinson said. “I studied switching to graphite, and it seemed an ideal material to use.”
One of his company’s managers had experience with Hi-Tech’s customized fixtures and recommended that Hutchinson contact us to look into a custom fixture. Hi-Tech Furnace designed a stackable graphite fixture that would hold 200 pieces per level. The fixture had five levels with 4-inch spaces between, allowing 1,000 blades to be processed at a time (Fig. 4).
“The ease of stacking the plates and the configuration of Rob’s modular design was really what sold me on it,” Hutchinson said. “Since you can lay out one plate at a time and stack the levels successively, you can minimize the distance between the plates without having to reach your hands into that small space.”
Designing a creative, customized fixture doesn’t always make financial sense. When repairing an expensive jet engine component, for example, it is more important to get that engine back into service in the minimal time possible rather than trying to process the largest number of parts possible. Even for production runs, a standard, off-the-shelf grid, plate or basket may do the job well enough and at a lower cost than a custom solution.
But either way, you won’t know which solution will be best unless you speak with someone who has the experience and expertise to analyze your business needs and show you which option offers the greatest value. We frequently advise customers to purchase a standard fixture rather than order a custom one. In cases like Hitchiner, however, a creative solution provides long-term benefits.
“We bought these fixtures in 2009, and they are still usable,” Hutchinson said. “We haven’t had to buy any since.” IH
For more information: Contact Hi-Tech Furnace Systems – a worldwide designer, manufacturer and installer of retort-style furnace systems – at 586-566-0600, visit www.hi-techfurnace.com or e-mail them at firstname.lastname@example.org.