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Deburring/Finishing

Finishing in the field

By Nick Wright

Vektek hones fixture cylinder cavities on-site to achieve a proper seal

March 2012 - When urgent situations arise where equipment problems jeopardize production, on-site repairs may be necessary. In such a scenario, the ability to bring the solution to the customer can be the key to avoiding costly downtime.

Ideal metal-finishing scenarios may involve removing burrs or other blemishes before a final product goes out the door, although sometimes secondary finishing is required in the field. Such finishing makes sure a product fits not only its function but also a customer’s specification.

Emporia, Kan.-based Vektek Inc. is an example. Vektek is a global supplier of hydraulic and pneumatic clamping systems for the metalworking, tool and die and production machining industries. The company sells cylinder products, some of which its customer must install in a manufactured cavity. To ensure the cavity into which the cylinder is installed does not cause a leak, it requires a proper finish. Without one, it will not seal and function correctly.

In 2011, one of the company’s customers, a large heavy-equipment manufacturer in China, sourced Vektek’s cylinders for fixtures, provided by a third party, to be used on horizontal machining centers. Rod Nelson, vice president of Vektek’s international sales, says the fixtures were designed for making mass-produced parts.

“The trouble was that the customer’s cavities were not machined to specification. A flaw in their finishing process was missed,” he says. “As a result, it appeared that the Vektek seals were leaking, a problem that was not a shortcoming in the cylinder design or quality but nevertheless had to be solved at the customer’s site or these very expensive fixtures would not be usable.”

To solve the problem, Vektek advised the customer to install new seals and use the Flex-Hone tool, a small-diameter, ball-style hone made by Brush Research Mfg. Co. Inc., Los Angeles. Founded in 1958, Brush Research produces a full line of industrial brushes and abrasive products for finishing applications. Its Flex-Hone is designed for deburring and edge blending where tight tolerances and clean surface finishes are required.

Pressure points
Inside the fixture cavity, hydraulic oil flows through two holes perpendicular to different sides of the cylinder to extend and return it. Vektek’s customers manufacture bores with these feed holes, which must seal and be kept separate by an external body o-ring. This seals to the field-manufactured bore. Both the bore and cross holes must be finished properly and deburred. The custom cylinders are designed for holding workpieces stationary in long-term production machining fixtures.

Gordon King, general manager of Vektek’s Shanghai office, says the end user’s engineers noticed a problem with the machine’s hydraulic pressure and narrowed it down to the manifold mounted cylinders leaking across the external body seals, which were not sealing properly to their installation holes.

“The hydraulic clamps used on these fixtures are designed to operate at a maximum of 5,000 psi oil pressure,” King says. “Although, in this instance, they were being operated at 3,200 psi, any leaks in the system are critical as a drop in oil pressure will result in the cylinders losing clamping pressure and the part possibly moving during machining.”

Aside from the lost costs of production, the seals’ improperly manufactured installation bores caused leaks that may be dangerous to the machine, fixture and operators, King adds. Such losses could amount to thousands of dollars a day.

“Because the required hole size and roundness are within 0.0005 in. and the required surface finish is better than 63 Ra, imperfections such as minute scratches or burrs within the holes will create oil leaks if the holes aren’t finished correctly prior to cylinder installation,” King says.

The Ra value represents the relationship between the microscopic peaks and valleys of a metal surface, according to Mike Miller, vice president of sales at Brush Research.

Self-centering solution
Vektek recommended the BC 158400 Flex-Hone brush for the customer’s technicians in China. Brush Research manufactures it in a range of diameters and sizes. The company paired it with a standard hand-held drill.

“The rework was carried out at the end-user site, where we took control of one machine at a time,” King says. “Production continued on the other machines. It took approximately one day per machine to repair and test their supplier’s mistakes.”

The brushes can be used in an array of rotating spindles, from machining centers in high-volume production to portable hand drills in secondary finishing or do-it-yourself use, according to Brush Research. “Because the tool is oversized for any given bore, it’s self-centering, which makes it really easy to use in the field,” Miller notes. “The globules just float to the workpiece and just follow whatever geometry is there.”

Ultimately, Vektek determined the inside surface of the cavities was finished improperly—too rough for Vektek’s external o-ring seal on its cylinders to seal properly to the roughly machined cylinder wall.

“In all, 300 cavities were Flex-Honed, and 299 of the 300 cavities were saved and polished exactly to specification,” Nelson says. “One cavity was slightly out of spec, but it also provided an adequate seal. So, in the end, we were able to save 300 very expensive holes.”

The improvement of the cavities enabled the cylinders to make a static seal against the finished wall. “It was an improvement of a specified RMS finish, the standard given to us by the customer,” Nelson says. “It was the surface finish that was improved, and the seal from an o-ring to that surface finish made to work. Those were the critical issues.”

The Flex-Hone can be mounted in portable electric drills, which makes it invaluable for field-finishing operations. Brush Research manufactures various Flex-Hone models anywhere from 4 mm (about 0.16 in.) up to 36 in. with custom diameters available. “The tool is very flexible in that we were able to use it on-site,” King says. “To have to take the fixtures off the machine tools would have at least doubled the time required per machine.”

Gritty globules
Brush Research’s Flex-Hone is also known as the ball hone because of its cluster of round, abrasive globules attached to a central shaft with flexible filaments. Because of each individual globule’s ability to conform and align with surface contours, “it is easy to get a uniform hole finish because it exerts the same pressure on all sides,” King says. “This is an example of a true finishing operation done in the field.”

Looking closer, the makeup of the Flex-Hone’s globules is essentially a raw grain abrasive in a proprietary epoxy matrix that compensates itself for wear, says Miller. This means even after some of the abrasive globules wear down with use, the brush still will provide an even finish on metal surfaces. That feature reduces brush replacement costs and eliminates the need for complex setups.

All of the Flex-Hone brushes provide plateau finishing, which removes burrs and torn metal peaks that may remain after initial finishing. Plateau finishing retains the microscopic valleys in metal finishes to enhance lubrication elements while maximizing the surface area of, in this case, the o-ring’s static seal.

The timing of the situation worked out in all parties’ favor, as well, says Miller. “We have distributors in over 30 countries in the world,” he says. “We had the product on the ground and a distributor with knowledge and we knew what he needed. He took it out there, and they were able to get the job done in short order,” he says. “We were able to get a call one day and have them fixed up in China the next day.”

Noting its success with Brush Research’s Flex-Hone, Nelson says Vektek has specified the Flex-Hone for several years in its product catalog and data sheets. “We stock them and have had good success with them. It makes our life easier,” he adds. FFJ

Interested in purchasing reprints of this article? Click here

Sources

  • Brush Research Mfg. Co. Inc. 
    Los Angeles
    phone: 323/261-2193
    fax: 323/268-6587
    www.brushresearch.com
  • Vektek Inc.
    Emporia, Kan. 
    phone: 800/992-0236
    fax: 816/364-0471
    www.vektek.com

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