Process-reliable deburring of bores in serial production

In industries such as automotive, aircraft or fluid power, manufacturing processes are constantly being optimised in order to produce large series as efficiently and cost-effectively as possible. Process steps are simplified, cycle times are shortened and repeatability in terms of quality is improved. 

Burrs on bore edges in particular can be big headache for production managers, who are challenged to find solutions that remove the burrs quickly, cheaply and reliably. 

Important criteria for the choice of deburring method are the position of the burr on the workpiece, the material used and the manufacturing tolerances of the workpiece. The required deburring result, compatibility with the production process, machine capabilities and budget also influence the choice of the deburring solution. The most common deburring methods and their characteristics are listed below. 

• In thermal deburring (TEM), the material to be removed is vaporised by the intense heat caused by a chemical reaction. TEM is used in particular for complex geometries, areas that are difficult to access or for workpieces with many bores. External and internal edges are deburred at the same time. Almost all oxidising materials can be deburred using TEM. The result is a sharp or slightly rounded bore edge. The size of the deburring chamber limits the workpiece size and quantity of parts. The influence of the heat on the material and the geometry of the component must be checked.
   
• Electrochemical deburring (ECM) removes burrs by eroding the metal. It is used for almost all metals, even hardened workpieces. As it is a non-contact technique with very low heat input, there is no tool abrasion, no formation of secondary burrs and no mechanical impact. The maximum burr size is limited to approximately 0.3 mm. The workpiece must be thoroughly cleaned before and after processing.
   
• With high-pressure waterjet deburring (HDW), several edges and difficult-to-reach bores can be deburred at the same time. A water jet is directed with a pressure of up to 1,000 bar onto the parts of the workpiece to be deburred. A post-deburr inspection of the bore edge is required to check if particles have broken off due to mechanical stress and if the surface of the workpiece is still rough due to limited removal of the burr roots.
   
• When blasting with granulates, materials such as sand are directed at the bore edge at speeds of up to 80 m/s. Surfaces next to the edge are also affected by this process. Workpiece cleaning after deburring can be a challenge.
   
• In brush deburring, burrs are removed by special brushing tools. The handling is simple and the range of applications is wide due to the many different tool variations. The limits of brush deburring are large burrs, very hard materials and difficult to access areas.
   
• The term mechanical deburring covers deburring tools that enable the workpiece to be finished directly on a machining centre. The back machining of bores and defined edges are also possible. The techniques are characterised by repeatability and high process reliability. The methods can have their limits in areas of the workpiece that are difficult to access.

The technologies in mechanical deburring are diverse, which is why we shall take a closer look at the individual characteristics. 

In circular deburring (interpolation), a predefined working path is followed by a tool. Depending on the given manufacturing or clamping tolerances, the chamfer may be too large, too small, or there may even be no chamfer at all. 

Tools with moving blades do not start deburring until they come into contact with the edge of the bore. This way, castings, for example, with their typical tolerance variations, can be machined reliably and with a consistent deburring result. 

For all types of mechanical deburring, the great advantage is that it can be integrated into the existing machining centre. The completed workpiece comes off the machine after only a slightly increased cycle time. Additional deburring-related steps are no longer necessary. 

By avoiding cleaning, logistics or external machining costs, the overall process costs and cycle times are reduced. Due to the consistent production technology and the simple handling of the tools, no training is required for the personnel. Existing manufacturing resources and knowledge are therefore optimally utilised.

Once a production manager has decided on a deburring method, it is important to find the right type and the right partner. An example from the field: A manufacturer in the e-mobility sector has to deburr internal and difficult-to-access cooling bores on a rotor shaft. Until now, the deburring was done manually by hand. 

Due to a complaint from a customer resulting from a quality deviation, a more stable and automated deburring process had to be found for the approximately 1 million bores per year. In this deburring situation, the components have variations in the wall thickness and thus in the diameter of the inner main bore. Circular deburring is therefore not an option due to these tolerance variations. 

In the meantime, the customer has also contacted HEULE for further applications, even a customised tool solution is being developed. If there is no suitable tool in the standard range, HEULE offers tools that are customised for the specific application requirements. 

HEULE recommends all customers to involve the deburring specialist in the design stage as early as possible. Together, the geometry of the workpiece can be optimised to be as deburring-friendly as possible, and the burr formation of the pre-operations can also be optimised so that serial production runs at maximum efficiency.