Deburring metal: What methods are there?

How are burrs generated?

Many manufacturing processes in metalworking produce bodies that protrude beyond the desired workpiece surface: burrs. In some cases, the formation of burrs is accepted, for example during casting or forging.  However, it is often unavoidable to produce burrs. This applies to machining processes, but also to most cutting processes. Autogenous flame cutting and punching in particular cannot do without burrs. Blunt cutting edges and worn punching tools produce even more burrs.

In plasma or laser cutting, burrs can be avoided under ideal conditions. However, with thick material or complex contours, burr formation can be observed again. Even with laser cutting, burrs cannot be prevented if aluminium is to be processed. If newer plasma cutting systems with a constricted plasma beam are used, the interaction of parameters such as cutting speed, cutting current and the distance to the sheet metal must be precisely coordinated if burr-free results are to be achieved.

Burrs are formed when part of the base material is deformed during the machining process, but still remains on the workpiece. In principle, this is not a deviation in shape, but an undesirable material component that is produced by material displacement. In cutting and separating processes, these are usually sharp, pointed material residues. The heat generated by certain cutting processes also causes the material to melt. If this molten material leaves the cutting joint and is deposited on the base material, burrs can also form.

Thermal cutting with oxygen as the cutting gas also produces slag in addition to burrs. This does not consist of the base material, but of its oxidation product, and therefore also behaves differently. In addition, an oxide layer forms on the cut edges of the sheet metal. 

Why is it important to remove burrs?

Burrs can cause damage to the production process as well as in the application of the end product. While they are still attached to the workpiece, they can press into tools such as straightening rollers or forming tools. These imprints in the tool then leave marks on the subsequently processed workpieces. The following also applies to press brake tools: Even if burrs do not cause any damage, they do increase wear. Precision tools, such as milling cutters, can also be damaged by burrs.

Another point is the coating: burrs influence the electrical field during powder coating or cathodic dip coating. The field lines during paint deposition concentrate on these tips during the coating process, comparable to a lightning conductor. The paint is then deposited there in an uncontrolled manner.

Last but not least, adhering burrs can injure employees because they are sharp and pointed. Depending on the size of the burr, work gloves only help to a limited extent during handling or assembly. This risk of injury may also occur with the end product.

Uncontrolled detachment is also associated with risks. A detached burr can cause mechanical damage or short circuits both in production systems and in the end product. This can become safety-relevant or even result in a product recall.

What methods are there for deburring workpieces? 

As the burrs are relatively firmly attached to the workpiece, they can only be removed with a tool. Files or angle grinders are ideal for sheet metal. However, this manual work is tedious and time-consuming. In addition to gloves to protect against the sharp burrs, employees may also need protective masks against grinding dust when deburring.

Machines, on the other hand, work more productively and with greater repeat accuracy. Production companies can thus ensure consistent quality. Depending on the size and properties of the sheet metal or sheet metal parts, a wide variety of plants can be used:

• Vibratory grinding or drum deburring are only suitable for small workpieces.
• Brush deburring machines are intended for thinner sheets, while roller deburring machines are more suitable for thicker material.
• Shot blast plants are particularly flexible when deburring sheet metal. In principle, there are no limits to the workpiece size and thickness, depending on the type of machine. In these cases, tests must be carried out to determine whether the sheet metal component warps when the blasting intensity is applied.

This is due to how the deburring process takes place during wheel blasting: The machine accelerates a solid material consisting of many very small particles. If such a particle hits the workpiece, its kinetic energy causes the workpiece to be removed. If a certain angle of attack is maintained, material is removed from the surface; the optimum angle is usually 45°. If a burr protrudes from the surface at this point, it is preferably removed.

What needs to be considered?

The operating principle also indicates what other advantages wheel blasting offers. In addition to deburring sheet metal, other tasks can be completed in the same operation: The descaling or derusting of the surface takes place in the same process step. If there is still an oxide layer on the sheet edge after a cutting process with oxygen as the cutting gas, the shot blast plant also removes it. This results in a continuously clean and homogeneous surface after the blasting process, not just at the edges. If an area is not to be processed by the shot blast plant, it can be masked. However, this involves a certain amount of effort.

Compared to pure deburring machines, wheel blasting offers further advantages:

• The workpiece throughput will be higher depending on the choice of machine size.
• Even complex-shaped edges can be deburred.
• Depending on the turbine power setting and the alignment of the workpieces to the turbine steel, targeted edge rounding on the sheet metal is also possible.

Conclusion

Shot blast plants are not necessarily the focal point when deburring sheet metal and sheet metal parts. This is due to the fact that these machines process the entire sheet metal surface, while burrs only occur on the sheet metal edges. However, as blasting not only removes the burrs, but also performs other necessary processes such as derusting or descaling at the same time, users save the additional effort for these process steps. As long as the workpieces do not warp during blasting, there is a lot to be said in favour of this process.