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Selection of deburring processes.

Selection of deburring processes

When planning the production of a workpiece, engineers may often neglect deburring. Because a burr cannot be planned in advance, it's difficult to select the appropriate deburring process. Decisions must wait for tests on parts that are already in production. At that time, however, it's too late to optimize the deburring sequence.

It's almost impossible to deburr during the manufacturing process, because the location and shape of a burr cannot be predetermined. Workpiece design and material affect the burr, and manufacturing sequence, method, and processing steps also can have an influence on burr formation.

Generally speaking, short and thin burrs can be handled much easier than long burrs with deep roots. Another criterion is the required quality of deburring. Sometimes a part is considered deburred only when there is a radius or chamfer at the edge. Many drawings say "all edges deburred" or "edges radiused," which is not precise enough. On the other hand, exact information like "radius 0.5 x 45 deg" is not always needed.

So, the first consideration is whether deburring is necessary, and if so, for what reason it is needed. Three main reasons for deburring are:

* Functional: loose particles in hydraulic or pneumatic parts that would hamper function or destroy other parts--or burrs that interface with the sliding movement of parts.

* Ergonomic: burrs that could cause injuries when assembling or using the parts.

* Aesthetic: part appearance that should be improved.

The variety of deburring methods is as wide as that of machining methods. We cannot mention all methods, but here is information on three important deburring systems.

Electrochemical machining (ECM)

Electrochemical machining includes deburring as well as edge finishing. The underlying idea is dissolution of anode material. With this method, edges can be machined to a predefined radius, and lubrication grooves can be worked into the workpiece. ECM can be applied for all materials that conduct electrical currents. With ECM, there is no thermal or mechanical wear, so edge radii can be controlled by the initial machining parameters.

Internal burrs in crosshole intersections or at hidden edges can be removed easily. Complicated edge shapes can be machined by an electrode shape identical to the edge. Hardened parts or hard-to-mill metals such as high-alloyed steels are no problem for ECM.

EDM units can be automated and integrated into production lines. However, the edges to be deburred must be specified geometrically. The tooling must be adapted to the workpiece, i.e., a different fixture is necessary for each different part. Workpieces must be free of cavities in which a penetrating electrolyte such as saltwater or nitrate solution could enter and cause corrosion.

Thermal-energy deburring

TEM (thermal-energy method) deburring is based on the combustion principle. All sections of the workpiece are oxidized by an intense heat flash. There are many advantages to this method. Internal burrs are safely removed because the gas spreads evenly in all cavities. Burrs and particles that could break off later are removed. The edges of ferrous metals can be radiused easily. Also, the units can serve universally. Because the gas adapts to every contour of the workpiece, no change of fixtures is necessary.

TEM is flexible, and part-changeover time is nominal. The units can be automated and integrated into an existing manufacturing process. It is not necessary to specify the edges that are to be deburred. There is mechanical and thermal work on the parts, but no distortion occurs. However, the material must be able to oxidize, and non-ferrous metals can be deburred only sharp-edged. Chamber volumes limit the size of parts to be deburred.

Mechanical deburring with robots

Industrial robots can meet the demand for replacing manual deburring work with machine process, but there are limitations. The robot can replace the human hand, but not the human eye. Also the robot lacks the sensitivity of a human hand. Further progress can be achieved only with developments in the sensors.

A Cartesian-type robot is good for deburring because it's rigid and can be programmed more easily than a robot with soft joints and complicated kinematics.

Despite some limitations, there are many applications for robot-driven deburring tools. Advantages include the use of serial tools.

In mechanical deburring, burr size determines the choice of tools. Milling, brushing, and grinding can handle most metals that are milled. A toolchanging system and programmed tool-control sequence can carry out a wide variety of tasks--even integrated into an automatic production line. Hard-to-reach burrs that are located within bores can be reached as long as the bore diameter is large enough for the deburring tools.

Examples from practice: Hard cam

On hardened parts such as a cam, either the mechanical deburring method or the electrochemical method could be used. The advantage of ECM on this part is that it can perform small machining jobs simultaneously with the deburring. The deburring and working of a ring groove occur in one process.

Hydraulic part

The TEM or ECM process is suggested for hydraulic workpieces where burrs are located inside and no tooling is available to reach them. Also, the workpieces represent a family of parts with different bore sizes and locations. These would require many different tools for mechanical or ECM processes.

Burrs at the breach can be as long as 2 mm. Because the length of the burr is not important and there is no need for further tooling, the thermal-energy method was chosen. This process can remove all particles.

ABS housing

A combination of two deburring methods can also be a good solution. An example is an aluminum workpiece from an ABS system.

The internal crosshole intersections must be radiused. Because it is an aluminum part, TEM will not work. Brushing is not recommended because of the small boring diameters. The desired result can be attained with ECM. For deburring outer contours and cleaning threads, mechanical deburring is used because of the length of the burrs in the threads.

PHOTO : The underlying principle of electrochemical machining is anode dissolution.

PHOTO : Internal burrs at intersections or hidden edges can be removed easily with ECM.

PHOTO : The thermal-energy method (TEM) of deburring is based on the combustion principle.

Walter Schilling Manager, Deburring Processes SurfTran Stuttgart, Germany
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Author:Schilling, Walter
Publication:Tooling & Production
Date:Jul 1, 1991
Words:1028
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