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The perfect finish

20th April 2017

Posted By Paul Boughton


Before and after deburring, a microscopic view. Image: ATL Luhden
In the case of abrasive flow machining, processing is accomplished by means of abrasive particles which are embedded in a polymer plastic mass of defined viscosity. Image credit: Perfect Finish
In this system for high-pressure water jet deburring, CNC positioned nozzles that generate water jets with pressures of up to 50MPa remove chips and burrs from cross-holes, threaded holes and deep holes, as well as from inside the workpiece. Image credit: Zippel

Why deburring, rounding and polishing are more than just necessary evils

For today’s manufacturers of precision components, there’s no getting around deburring, rounding and polishing. These production steps are often seen as a necessary evil due to the high costs associated with them in some cases.

Use of the right technology permits reliable processing at reduced costs.

It’s practically impossible to fully avoid the occurrence of burrs when using any of the traditional metalworking processes.

Because these manufacturing or processing remnants represent a risk from both a functional and an ergonomic standpoint, they have to be removed. As was also the case in days of old, this is still frequently done manually.

Quite apart from the fact that the necessary process reliability and reproducibility is not assured, this manual work results in high costs and often leads to time-consuming rework – in both cases at the expense of economic efficiency and the company’s competitive edge.

And thus it’s no wonder that deburring, rounding and polishing are often regarded as a necessary and costly evil.

More and more demanding requirements for process reliability in production and product quality, as well as cost pressure in global competition, necessitate more economic efficiency for the manufacturing steps of deburring, rounding and polishing.

At the same time, uniform high quality must be assured in a reproducible manner.

Various processes have established themselves to this end, for example automated brush deburring, deburring with special tooling that is integrated into the machining centres, barrel finishing and high-pressure water jets. Many of these processes have been further developed in recent years, and new technologies have been introduced to the market as well.

A new dimension of barrel finishing

Various developments such as drag finishing and so-called ‘surf or stream’ finishing make reliable and economical lot processing by means of barrel finishing possible for parts that are sensitive to damage and could previously only be deburred, ground, polished or smoothed by means of a costly, non-reproducible manual procedure or at great expense with the help of a machine.

In the case of drag finishing, the parts are clamped to workpiece carriers that are then dragged through a barrel with abrasive particles or a polishing medium.

Uniform flow of the abrasive particles or polishing medium around all sides of the workpieces results in effective but nevertheless gentle processing.

Even in the case of workpieces with complex geometries, ideal, reproducible processing results of ‘handmade quality’ can be achieved within a relatively short period of time. Surf or stream finishing goes one step further.

A robot immerses the workpiece at a precisely defined position into the rotating bowl, which is filled with grinding medium, and accurately guides it. This makes it possible to selectively process certain areas, or different radii can be achieved by variously positioning the robot arm.

High grinding pressure is generated by rotating the bowl while the component is surfing in the grinding medium. This results in intensive, reliable processing with short cycle times and a surface finish which complies with the specified requirement.

Reliably removing thousands of burrs in minutes

Thermal energy machining (TEM) also permits efficient and reproducible lot processing. It’s suitable for components made of nearly all metallic materials and thermoplastics from which internal as well as external burrs need to be removed – even from very difficult to access places.

The parts are positioned inside the system for the deburring process, and the system is sealed.

A precisely specified gas mixture is fed to the deburring chamber by means of a gas dosing system and flows through the entire component or production lot.

After the gas is ignited, all of the internal and external burrs are fully burned away, and the roots of the burrs are sealed.

No material is removed from the surface. Due to the fact that the process only lasts a few milliseconds, the workpieces are not significantly heated up. TEM makes it possible to reliably achieve ‘sharp-edged/burr-free’ deburring quality. Depending on the material, slight rounding of the edges is also possible. Use of this process is limited by the size of the part, as well as in the event that targeted edge rounding is required during deburring.

Deburring with additional function

Contactless electrochemical machining (ECM) demonstrates its strengths in this respect.

The process is based on the principle of electrolysis. A cathodic electrode used as a tool is connected to a source of direct current. The other electrode is the anodic workpiece itself.

A charge exchange between the cathode and the workpiece takes place in an aqueous electrolyte solution and processes the workpiece in a targeted fashion. On the one hand, this makes it possible to reliably deburr difficult-to-access areas such as edges, undercuts, internal bore intersections and pockets at precisely defined location on the workpiece.

Casting, press moulding and forging flash can also be removed. On the other hand, ECM also makes it possible to produce, for example, highly precise contours, ducts, slots and hollows in a reproducible manner without any thermal or mechanical stressing. Thus the ECM process fulfils the more and more frequently specified requirement for burr-free processing – with a high quality surface finish as well.

This is also one of the characteristics of abrasive flow machining, by means of which Ra values off less than 0.01 µm can be achieved. The process is used for economically efficient deburring, edge rounding and polishing of internal and external surfaces of demanding components from the automotive and aviation industries, turbine manufacturing, medical and fluid engineering, food processing, mould and toolmaking, general machinery manufacturing and other industry sectors.

Processing is accomplished by means of abrasive particles, the type, size and concentration of which are matched to the respective task, and which are embedded in a polymer plastic mass of defined viscosity. This grinding medium is caused to flow through or over the area of the component to be deburred in alternating directions at a defined pressure level by means of hydraulically powered pistons.

Deburring, cleaning, rounding and hardening of the surface in a single step is made possible by the so-called pinflow process. The workpieces to be processed are clamped in a part-specific fixture that is laid out as a container, is filled with a processing medium (small steel balls) and is located in the machine’s process chamber.

Vibrators then cause the fixture to oscillate horizontally, thus resulting in relative motion between the workpiece and the deburring medium. The resultant kinetic energy of the steel balls is transferred to the workpiece to process its external and internal surfaces, and the deburring effect is also apparent in difficult to access places.

Expert advice at specialist show

Which processes ensure efficient deburring and surface finishing with good process reliability? What new technologies are available for deburring, rounding and polishing? Which measures contribute to the reduced formation of burrs? Answers to these and many other questions are provided by DeburringExpo. With its technical trade fair for deburring technologies and precision surface finishing, fairXperts has created a platform at which users from all industry sectors can gather comprehensive information about relevant technologies.

The second DeburringExpo will take place at the Karlsruhe Exhibition Centre in Germany from October 10-12, 2017. The exhibition portfolio includes equipment, systems and tools for belt grinding, brushing, abrasive flow machining, vibratory grinding, blasting with solid and liquid media, abrasive water-jet blasting, magnetic-abrasive deburring, ultrasonic deburring, chemical bath deburring, ECM, electron beam machining, TEM, mechanical deburring, buffing, polish honing, electrolytic polishing, plasma polishing, laser polishing, immersion and brush polishing, as well as measuring, test and analysis systems, and technical literature.

For more information visit www.deburring-expo.de









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