Optimising deburring processes with innovative solutions

TODAY, the removal of these remnants from the production process is an absolute must for high quality, precision parts. On the one hand, ever stricter requirements for deburring quality and process reliability have to be fulfilled and, on the other hand, the deburring process has to be made increasingly efficient.

Whether parts are manufactured by means of machining, metal forming or master forming – deburring usually doesn’t fall into one of the part manufacturer’s areas of core competence. And thus the removal of these remnants from the production process is often still seen as a necessary evil which increases unit costs. However, due to ever stricter requirements for product quality and functionality, intermediate and downstream processes like deburring are becoming more and more significant across all industry sectors. In addition to this, component geometry is getting continuously more complex, and parts are being made of new materials and material combinations. This necessitates the use of technologies which are ideally matched to greatly varying deburring requirements and ensure good process reliability. Otherwise, not only does product quality suffer, but rather economic efficiency as well.

Reducing Costs by Predicting and Minimising Burrs

In particular machined workpieces often include difficult to access areas which have to be deburred, for example undercuts, grooves, slots, internal holes and holes which cross through each other. And the more complex the workpiece becomes, the more difficult it is to get at the burrs. But here as well, it’s nevertheless crucial to remove burrs reliably, in accordance with the specified requirements and without adversely affecting the material. A further challenge is presented by so-called secondary burrs, which are caused by the deburring tool during the deburring process.

A model used to predict and minimise burrs makes a significant contribution to reliable and efficient deburring of workpieces made of steel and nonferrous metals. It was developed by Dr.Beier-Entgrattechnik on the basis of a metal forming approach for the formation of burrs as a practical application. The goal is to provide production planning and design engineering with a tool based on a quick and practical means for predicting the formation of burrs, in order to optimise processes and make them more efficient. The model incorporates findings from materials science and an engineering viewpoint of the machining and forming processes. The formation of burrs depends primarily on the material’s stress-strain behaviour and the prevailing cutting forces. Elastic and plastic material characteristics are derived from the results of tensile tests. The determination or specification of cutting forces is based on relationships prevailing in the field of machining technology.

High-Speed Deburring– a Question of the Right Tool

In particular in the case of machined workpieces which are produced in large numbers, deburring takes place at the end of the automated manufacturing process, or after a sub-process. From an economic standpoint, a fully automated, high-speed deburring process which is executed directly in the machining centre or the CNC machine is the ideal solution. In order to prevent any slow-down of manufacturing processes with short cycle times and to assure uniform quality, reliable, automated, and highly effective deburring methods are required on the one hand. On the other hand, the utilised tools have to be matched to the application and must ensure that deburring results meet the specified requirements, even for complex workpieces with difficult to access burrs. Furthermore, no secondary burrs may be caused by the deburring process. Special HSD tools (high-speed deburring) have been developed for applications of this sort. The cutting force required by these tools is not generated by spring elements, but rather by a pressure medium, for example coolant, oil, compressed air or minimum lubrication lines which are already available. This system has the advantage of maintaining force applied to the cutter at a constant level over a broad range of cutting tool deflection. The cutters are pressed in the furthest inside a drill hole by its walls. Since there aren’t any burrs here, excessive force applied to the cutter would alter or even damage the surface, and would result in unnecessary wear. HSD tools develop the most force when the cutters are open very wide, for example at the edges of drill holes where the drill first enters or exits the material, or the edge of a cross-hole or a groove which needs to be deburred – i.e. precisely where force is actually required for deburring, and if necessary for the production of a chamfer. These tools permit forward and reverse deburring, as well as the deburring of cross-holes, without and design changes.

All cross-holes, as well as the main hole’s point of entry and exit, can be deburred through the main hole with and HSD tool in a time-saving fashion in a single work step. Different diameters of the cross-holes and any grooves or oblong holes that need to be deburred don’t play any role in this respect. At the same time, specially shaped cutters assure that the burrs aren’t just bent over or pressed into the cross-holes.

New Process for Burr-Free, Crossing Oil Holes

The new, automated CBD deburring process (cross bore deburring) developed by Heule Werkzeug AG in Switzerland is still being tested. It’s a further development of the time-tested, modular COFA tool system, in the newest generation of which the cutter and the cutter retainer are separate. The COFA design provides for increased economic efficiency, as well as improved productivity, and is opening up a broader range of applications as well. Integrating the tool into the machining centre or CNC machine makes it possible to produce already deburred workpieces. No pre-adjustment of the COFA tool is required – the mechanically, accurately guided deburring cutter can be inserted or replaced manually, or with a jig. Its functional principle ensures uniform, radius-shaped deburring without any secondary burrs with a defined cutter at even and uneven drill-hole edges. Forward and reverse processing is completed in a single work-step without reversing the spindle’s direction of rotation, and without time-consuming turning of the workpiece. Part tolerances are compensated for automatically by the tool’s operating principle. The COFA tool can also be used for workpieces made of difficult to machine materials such as stainless steel, titanium and Inconel^® as of a hole diameter of 2 mm with practically no limits for maximum hole size.

However, use of the COFA system is limited in the case of holes which cross through each other whose diameter ratio approaches 1:1 and have an intersection angle of less than 90°. Heule has developed the CBD process for applications of this sort, for example removal of internal burrs at the back of oil holes. This tool system is also of modular design and can be integrated into the machine. But it makes use of a modified operating principle: deburring is axial (comparable to broaching) and feed is radial. As a result, the CBD process makes it possible for the first time to deburr cross-holes with nearly any diameter ratio and with intersection angles of significantly less than 90° in an automated fashion within the machining process with a defined cutter. And high process reliability is achieved thanks to the strictly mechanical operating principle.