Achieving Burr-Free Surfaces Efficiently
For today’s manufacturers of precision metal components, there is 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 is practically impossible to fully avoid the occurrence of burrs when using any of the traditional metalworking processes. Due to the fact that 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 frequently still 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. Thus, it is no wonder that deburring, rounding and polishing are often seen as a necessary and costly evil.
Process Reliability and Costs: A Question of the Process
More and more demanding requirements for process reliability in production and product quality, as well as cost pressure in global competition, necessitate greater economic efficiency for the process steps of deburring, rounding and polishing. At the same time, consistently high quality must be assured in a reproducible manner.
Processes such as automated brush deburring, deburring with special tooling that is integrated into the machining centers, barrel finishing and high-pressure water jets have established themselves to this end. 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
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 (e.g., connecting rods and crankshafts) 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 that complies with the specified requirement.
TEM: Removing Thousands of Burrs in Minutes
Thermal-energy machining (TEM) permits efficient and reproducible lot processing. It is suitable for components made of nearly all metallic materials (as well as some thermoplastics) from which both internal and external burrs need to be removed – even from very difficult-to-access places.
It is used on forgings after machining operations. 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 it 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 only insignificantly heated.
TEM makes it possible to reliably achieve “sharp-edged/burr-free” deburring quality. Depending on the material, a slight rounding of the edges is also possible. Use of this process is limited by the size of the part and the possibility 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. This makes it possible to reliably deburr difficult-to-access areas such as edges, undercuts, internal bore intersections and pockets at a precisely defined location on the workpiece. Forging, casting and press-molding flash can also be removed.
Additionally, ECM makes it possible to produce, for example, highly precise contours, ducts, slots and hollows in a reproducible manner without any thermal or mechanical stressing. Consequently, the ECM process fulfils the 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 (an index of surface roughness) of less than 0.01 µm can be achieved. The process is used for economical and efficient deburring, edge rounding, and polishing of internal and external surfaces. It is used on demanding components destined for use in the automotive and aerospace industries, turbine manufacturing, medical and fluid engineering, food processing, mold 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 are made possible by the so-called PINFLOW process. The workpieces are clamped in a part-specific fixture, which is laid out as a container, filled with a processing medium (small steel balls) and located in the machine’s process chamber. Vibrators then cause the fixture to oscillate horizontally, resulting in relative motion between the workpiece and the deburring medium. The resultant kinetic energy of the steel balls is transferred to the workpiece in order to process its external and internal surfaces, and the deburring effect is also apparent in difficult-to-access places.
DeburringEXPO – Trade Fair for Deburring Technology and Precision Surface Finishing
Oct. 10-12, Karlsruhe Exhibition Center, Germany
Which processes ensure efficient deburring and surface finishing with good process reliability? What new technologies are available for deburring, rounding and polishing? Which manufacturing techniques contribute to the reduced formation of burrs? Answers to these and many other questions can be found by attending the DeburringEXPO.
fairXperts GmbH & Co. has created a platform at which users from all industry sectors can gather comprehensive information about relevant technologies. 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, electrochemical machining (ECM), electron-beam machining, thermal-energy machining (TEM), mechanical deburring, buffing, polish honing, electrolytic polishing, plasma polishing, laser polishing and immersion and brush polishing. It also includes measuring, test and analysis systems, and technical literature.
Further information is available at www.deburring-expo.de.