Micro Tooling Key to Polymer Seal Machining

Whether it involves hydraulics, gas or water, seals are found wherever high pressures are involved or to prevent the tap at home from dripping. These inconspicuous parts are installed in a large number of devices. The Prädifa Technology Division of Parker Hannifin Corporation is a leader in the development and production of sealing solutions. Its site in Boom, Belgium, specializes in seals made from machinable materials such as polytetrafluoroethylene (PTFE). The specialists rely on tool solutions from Paul Horn GmbH for machining, and Horn’s Supermini and Mini systems are mainly used on the machine tools.

“Due to the variety of our different seals, we use special tools 90% of the time,” explains Peter Schockaert who is responsible for production at Parker Prädifa together with Johan Willems. “The materials and the different sealing profiles require very sharp tools with special cutting edge profiles.” Willems says Horn’s ability to design the cutting edge profiles according to their wishes and requirements is very important, which is why the company has been relying on the tools from Horn in Tübingen, Germany, for years.

The Parker Prädifa Technology Division’s product portfolio includes a wide range of standard sealing elements and sealing systems, customized and application-specific seals, and other technical components. Customers include companies from the aerospace, automotive, pharmaceutical, chemical, hydraulics and other industries. The company is recognized as a leading supplier of polymer sealing solutions made from a variety of sealing materials and in many sizes. This diversity also applies to the sizes of the seals, which range from a diameter of a few millimeters to the world record seal having a diameter of more than 4 meters.

“We often just call the tools ‘blades,’ as they are ground with a very sharp wedge angle,” Schockaert says. One way such a tool is used is to turn an axial thread on a steering shaft seal made from a carbon fiber Teflon material. The thread is needed to make the sealing ring axially flexible. This enables it to be slid over the shaft during subsequent assembly and remain securely attached after it is screwed on.

The first tests were carried out and orders fulfilled with tools that were ground in-house. “We grind prototypes and small quantities of tools ourselves. Then when volumes increase, we look for an appropriate tool solution,” Willems says. In this case, Horn supplied a Supermini with a ground blade for axial machining. The thread to be produced has a depth of 0.2 mm, and the tool machines the thread at a high feed rate. “At first glance, the machining process looks very easy,” Schockaert says. “But the required absence of burrs demands a very sharp cutting edge.”

In fact, no chips flow during machining. The Supermini insert cuts or scores the thread into the surface.

The Supermini system is also used for producing another plastic seal having a diameter of just under 4 mm. In addition to having a face groove, a 1-mm-diameter hole must be bored. “The sharpness of the tools is also very important in this application, as the walls are very thin and could warp if the cutting pressure is too high,” Willems says. After axial grooving with a Supermini type 105, another Supermini of the same type is used to bore the pre-drilled hole to the tightly toleranced final dimension.

Tooling in Use

Schockaert and Willems rely on special twin-spindle lathes that process two seals simultaneously to achieve high throughput. The spindles are mounted above the tools and the bar feeder for the raw material, which is loaded from above, is in line with a tool carrier. The turning process does not require any tool changes. The tools are permanently mounted in line under the spindles. During the process, the spindles move to each tool in turn until all machining operations have been completed.

The Mini system is used alongside Supermini tools. Horn technician Kees van Bers says the Mini system can be adapted very well to the respective machining operations, and a tool is mounted on a platen for each operation. “With the large quantities involved, a very short cycle time was important to us,” Willems explains. “The tools enable us to carry out external copy turning, external grooving, face grooving on both sides, boring and parting off.”

Parker has been working with tool solutions from Horn for approximately 10 years, and the vast majority of the tools used are special solutions designed specifically for the respective processes. “We are pleased to have Horn as a tool partner that fulfills our wishes and requirements precisely in terms of cutting edge design,” Willems says.