Basic knowledge Why deburring is important and what you should be aware of
Deburring is an important part of the sheet metal process chain. This is because the burrs that frequently occur on sheet metal components during the machining or manufacturing process can be removed in this way.
Why is it important to deburr and what should be kept in mind? The history of sheet metal deburring began in the 1980s. At that time, thin sheets were mainly punched and nibbled; thicker sheets were cut by plasma and oxyfuel. Many processes enable successful deburring. Deburring was mainly carried out in order to avoid the risk of injury, since, for example stamped parts at the exit side of the stamp have razor-sharp edges. On the one hand, the aim was to eliminate the risk of injury in the company's own production, but also during the subsequent use of the product.
With the introduction of the laser, many thought that deburring would soon no longer be necessary, as these machines could cut almost burr-free - at least if the process parameters were set accurately. Eventually, the opposite was the case. While the punched part had a good side and a bad side, it quickly turned out that laser-cut parts, even if they were perfectly cut, have very sharp edges on both sides.
Deburring as a means of choice against sharp edges
In addition, there was the problem of the oxide layer, which accumulates on the narrow side during oxygen cutting (laser beam flame cutting) and poses a problem both during the subsequent coating and during welding.
People realized that the removal of the oxide layer wasn't sufficient to achieve good coating results, because the coating thickness on the sharp edge of the workpiece was thinner than on the surface in both wet painting and powder coating. Consequently, several producers started to develop machines for rounding workpiece edges.
Today, 0.2 to 0.3 mm edge rounding is almost standard. Frequently one is confronted with requirements of 0.5 mm for thin sheets and 2.0 mm for heavy plates. But there are other reasons for deburring and rounding.
But there are other reasons for deburring and rounding: The tools of bending machines suffer from burr formation and are subject to much faster wear if the burr is not removed beforehand. The same applies to the straightening rolls of widely used roll straightening machines. If sheet metal parts are subsequently machined (especially in the thicker sheet metal area), there is also a reason to remove the burr - be it to protect the tools, to enable positioning or clamping.
Sharp edges can also be dangerous for laboratory gloves or for power and compressed air lines that may chafe against these edges. The reasons are manifold and therefore deburring has become an indispensable part of modern sheet metal production.
Let's summarize the most important reasons for deburring once again:
1. Risk of injury:
- For employees during part transport and assembly
- During use and/or repair of the product
2. Coating quality
- Wet painting
- Cathodic dip coating
- Zinc coating
3. Protection of press brake tools
4. Damage & wear of straightening machines
5. Quality of the weld seam (by oxide)
6. Preparation for machining
7. Compliance with standards, e.g. DIN EN 1090
8. Further technical reasons
9. Drawing default
While the term "deburring" basically only refers to the removal of the primary burr (a sharp, right-angled edge would therefore be considered deburred), the following process steps are in fact commonly assigned to deburring.
What you should heed during deburring
The following aspects should be considered when investing in deburring technology:
Wet or dry machining
Already since the middle/end of the 1980s there have been wet grinding deburring machines available. Since the grinding abrasion in combination with the oil results in a paste-like mass, which clog the grinding tools, it makes sense to use them for heavily oiled parts. In connection with wet grinding, the processing of aluminum is also frequently used. As a matter of fact, aluminum dust is highly combustible. After an aluminium part has been processed on a dry deburring machine, it is important to check that no dust pockets have formed; otherwise they could become a hazard during the subsequent processing of sparking material. Furthermore, dry deburring machines used to process aluminum must be equipped with wet-type dust collectors.
In wet grinding machines this is not necessary at all. Oil is absorbed by the emulsion and, if necessary, separated by a skimmer (no clogging of the tools). Grinding dust (also from aluminum) is separated by a belt filter or a centrifuge. A dust collector is not required. On the other hand, a wet deburring machine requires much more maintenance!
One- or double-sided machining
Machines working on both sides promise significantly higher productivity, as the workpieces do not have to be turned over and fed through the machine a second time. For machines working on both sides the parts are transported on rollers instead of a conveyor belt. On these machines, short parts (usually less than 150 mm in length) can either not be machined at all or only with additional effort.
Depending on the technology selected, some machines for both sides do not round the edges evenly, because on longitudinal edges (seen in the direction of throughfeed) the tools meet in an ideal orientation, while transverse edges are machined somewhat less. However, if this (slightly less pronounced) rounding is sufficient and mainly parts longer than 150 mm are to be machined, a double-sided machine can realize a significant leap in productivity.
As already mentioned above, rounded workpiece edges are a requirement today. Two types of tools are usually used for this purpose. So-called cup or disk brushes and lamellar rollers. Both versions work in an abrasive way.
Many sheet metal processors want to offer intensive rounding. Often however it is overlooked that every doubling of the radius leads to a fourfold expenditure, because four times as much material has to be machined (chip volume). This can be established by drawing the cross-section of the part and calculating the area of the material to be removed by the tools.
Don’t look for a jack-of-all-trades devicee
Another aspect that needs to be considered is rather self-evident. Before the final investment decision, one should consider which range of parts is to be covered. Often, the first thought is: All of them - from coin-sized blanks to large format boards. This results in a jack of all trades device and a correspondingly high investment. It might be appropriate to consider the Pareto principle and determine which 20 % of the expenditure can be used to perform 80 % of the tasks.
Which deburring machine is right one? Markus Lindörfer assists with vendor-independent research. He is a managing partner of Lima Ventures GmbH in Heidelberg. Click here for further information.
This article was first published by belchnet.