By combining two Kurt HDL double station hydraulic and a single manually actuated HDL vise on a Fadall 3016 machining center, Tescom Corp achieved a 50% increase in productivity for its valve body machining operations. The Industrial Controls Division of this global supplier of pressure regulators, valves, and electronic controllers manufactures specialty regulators and valves that provide reliable control of fluids (gases and liquids) that involve high pressure, corrosive, flammable, and/or unique performance characteristics. These products are sold to end users in industries that include aerospace, chemical, testing laboratories, automotive, and petroleum.

"We needed to increase our valve body output using our existing machining centers with the goal of transitioning our processes into new machines down the road," reported Brian Caldwell, Tescom's machine shop manager. "At the time, we didn't have a budget for new capital equipment but needed to increase output to meet growing product demand. We studied our workholding for improvements. Permanent fixturing wasn't the answer because of the large number of valve body models and sizes and relatively small quantity requirements. We looked at a variety of workholding options and settled on Kurt's new HD vises as the solution to our expanding needs."

Previously, the company had used manually operated single station Kurt vises. Tescom's workholding upgrade allowed the company to transition economically into a much more productive and flexible workholding setup to accommodate the more than 500 different valve body models and sizes that make up its wide product line.

The workholding change was possible within the capabilities of a Fadall Model 3016 machining center. The change allowed the company to continue to use more than 300 sets of existing quick-change jaws machined to hold its various size valve body components in the new vise setup. Retaining these machined jaws saved Tescom thousands of dollars and the effort of having to purchase, machine, and inventory new jaw blanks.

Vises Clamp Like Custom Fixture, Provide Flexibility for Varied Part Runs

'We focused on the workholding capacity, the workholding setup time, tool change time, and operator attention needed while running the parts. We heard about a new vise Kurt introduced which was available in both hydraulic and manual versions for high density applications so we checked them out to see what they would do to help us increase productivity," said Caldwell.

Tescom's Fadall Model 3016 has a 30 x 16 x 20 in. work envelope and could easily accommodate three of the new Kurt HD vises (two hydraulic and one manual) mounted side by side. Having calculated jaw capacities from the smallest to the largest valve bodies and verifying that all of his existing jaw plates would work in the new vises, Caldwell's next step was to compare the cycle time of the two single-station vises (each holding two parts) versus two double-station HD hydraulic vises holding eight parts.

"There was obvious potential for substantial cycle time reduction, particularly where one tool would machine all 8 parts in both vises before a tool change was made," Caldwell stated. "With hydraulic clamping, the setup process was faster than with a manual vise and it gave us more consistent clamping pressures. The clamping consistency became important because we saw it would eliminate any chance of over-clamping that could mar surface finish, which is very critical."

Another factor in Caldwell's analysis was that the new workholding setup minimizes travel distance between parts (vises align within 1 inch of each other on the machine table) so less machine time is lost when the cutting tool travels between parts. Setup time was cut by more than half, machining 4 instead of 2 parts. Also, these new vises set up much faster than the older, standard vises. Overall, Caldwell said he "could see more free time for the operator between setups so he could check finished parts and still have time to tend to other nearby machines."

Tescom's existing machined vise jaws also played an important part in the workholding decision making. "We had a big investment in over 300 jaw plate sets," said Caldwell. "In effect, we've created custom fixtures because the parts 'nest' inside the jaws so when the vise is clamped up, all outer surfaces are held tightly. There's no chance of part misalignment or spindle chatter even at the highest speeds. With the hydraulic vises and our machined jaw plates, we get the fast, precision clamping advantages of a custom fixture but with all the flexibility of a vise. When a part run for a particular size and model valve body is complete, jaws can be quickly replaced with others for different valve body sizes. They snap in and out of position in an instant."

Caldwell also said he liked the ruggedness of the Kurt HD model vises. Made of 80,000 psi ductile iron, the vise bodies provide strength, rigidity, and long-term accuracy while absorbing machining vibration. Also, the vises have enclosed screws and clamping mechanisms so chips don't foul up the hydraulic actuation -- they clamp quickly and accurately each time.

As for the machining process itself, both accuracy and speed are required while maintaining an overall high quality finish on all part contours. Machining operations call for milling, drilling, and tapping of all valve bodies, which range from 1-7 in. dia. Most are machined of 316 stainless steel with lower quantity models machined of monel, Hastelloy®, aluminum, brass, and 17-4 stainless steel. Depending on material and valve body size, the milling operations for flats run at 3,800 rpm/10 in./min; drilling and tapping of valve body mounting holes (drilling at 800 rpm/4 in./min; tapping at 160 rpm/5 in./min) and thread milling at 5240 rpm/8 in./min.

"Precision tolerances as well as overall surface finish are very important for these valve bodies to function reliably and the Kurt vises clamp them very well," reports Caldwell. "We maintain consistent ±.002 for the sealing area. The entire valve body radius has a 25 ra finish, which acts as a metal-to-metal seal. We get a 32 ra finish below the threads where the valve closes. All contours are machined and have a very consistent, high quality appearance using the new Kurt workholding configuration."

Between three and five different setups are made on the one machine with up to 100 individual valve bodies completed in a given 24 hr period. Most runs average from 5-20 valves with a high of 100.

A Third Manual Double Station Vise Handles Odd Lot Needs

With room for a third vise on the Fadall machining center worktable, Caldwell and his engineers saw the opportunity for a way to handle few-of-a-kind and/or odd-size valve bodies.

"We positioned the manual Kurt HD vise alongside of the hydraulic models to take care of low quantity and less frequently needed valve bodies. Our goal was to keep workholding costs down and using the manual vise helped us to do that. We also liked the feature of the vise being easily convertible to hydraulic operation if we choose to do so. We're looking to acquire new machining centers to replace the old in the near future and this new workholding setup will transition nicely into new machines. The new workholding setup is everything we expected it to be and we've had no problems with it," Caldwell concluded.