We use barrelling to machine surfaces and edges of smaller sheet metal parts. Milling or Punching can produce sharp burrs, which hinder further working, impair accuracy of fit or can cause injuries. During laser machining, workpieces can oxidise at the cut edges or the high heat causes slag to deposit on the edges.
Our production facilities
We offer barrelling up to a workpiece size of 220 mm diagonal dimension or a part weight of 3.5 kilogram. Top quality deburring, degreasing and descaling of small parts. Our two barrelling units have containers (barrels), which are filled with a mixture of abrasive products and an aqueous solution. The workpieces to be ground are added to this mixture and the whole barrel is made to vibrate by motors.
Deburring by means of barrelling
Barrelling is an ideal method for removing sharp burrs from small metal parts, to break (chamfer) edges or to round them off. Any burrs produced are removed completely by the effect of abrasive products. The advantage of this method lies in the low amplitude of the vibratory movement, so that the workpieces do not knock each other or catch on each other during machining.
Before and after comparison
The secret of an optimum result lies in the abrasive products. A large number of different abrasive products exist for barrelling. They are available in difference sizes, shapes and are made of plastic or ceramic. Abrasive products made of plastics are suitable for particularly gentle treatment. However, ceramic abrasive bodies last longer and have a stronger grinding effect. The surface quality is similar to that of sandpaper. Abrasive bodies are also available in different roughness grades.
Why are burrs removed?
Burrs are produced by many sheet metal machining methods. They occur particularly frequently as a result of mechanical working methods such as Shearing or punching. For example, during shearing only part of the material is truly cut. Around two thirds of the material is literally torn off by an extreme force of 600 tonnes. Depending on the clearance set, after cutting to size a varying thickness of burr is left, which can be razor-sharp.
Fewer and smaller burrs are produced by punching, as this method is used to machine thinner sheets up to a maximum material thickness of 6 mm. Even in laser cutting, especially of thicker sheets, slag deposits are produced at the point at which the laser beam exits.
A shielding gas is blown into the clearance (cutting gap) to protect the workpiece. The gas is added at very high pressure and blows the liquefied material out of the gap. Due to the gas pressure, burrs can also form at the rear of the workpiece. Burrs affect quality and dimensional accuracy to the same degree as scale. Sheet metal parts with burrs are difficult to work further – they even constitute a safety risk due to their razor-sharp edges.
Our barrelling units vibrate, which causes the workpieces to slide along the abrasive products. This method is very efficient, as we can machine a large number of small parts at the same time in each unit.
In the case of larger workpieces, burrs can be milled off using our machining centre. But this method is very cost-intensive. Therefore, it is used only in a few cases. Deburring is normally carried out using manually operated grinders.
What is burn-off and scale? How can it be removed?
If metal sheets are machined using lasers or welding, extreme heat in conjunction with oxygen causes vigorous reactions at the material edges. Unalloyed metal sheet oxidises after a while – even without the effect of a heat source. Yet by using the laser beam, which acts on the material with a power of up to 10 million watts, the corrosive effect of the oxygen is multiplied. The energy effect causes more rapid bonding with oxygen molecules and iron. Different iron oxides are produced as a result, which deposit on the edges of the workpiece.
Scale is also called burn-off, as the machined workpieces lose material and look burned. The greater the heat effect the more intensively the metal and oxygen react with each other. In extreme cases the metal can event gasify, blisters and can splash several metres in distance. Scale also has negative effects on the workpiece. The burning of the material causes the edges of the workpiece to become uneven. The rough surfaces of corroded material edges prevent further working and provide a very good surface for subsequent oxidation. Splashed scale can also damage sheet metal surfaces outside of the machined area.
Scale can be largely prevented by using an inert gas. Nitrogen-based gas mixtures are mainly used for laser cutting. These gases are very low-reaction. The gas is added directly to the clearance (cutting gap) through a nozzle in the laser cutting head. As this gap is now completely filled with Shielding gas, the oxygen can no longer get into the machining area. All cut edges have a much higher quality after use of inert gases.
In Welding too, use of an argon-helium mixture prevents contact of oxygen with the weld, which means the material edges can be joined together better. Welds welded under shielding gas are far more durable and longer-lasting, as no oxygen is stored in the molten material. Unfortunately, it is not possible to use shielding gas in all cases. For example, it is difficult to use inert gases outdoors, as wind can blow the protective gas jet away, which reduces the protective effect. In such cases workpieces have to be descaled, at least all weld joints.
We offer barrelling for small parts up to a size of 100 x 200 mm. This means that these parts are placed in a barrel filled with abrasive products. These barrels vibrate, so that metal parts slide along the abrasive products. This process is also called barrelling. In the case of larger workpieces the descaling is carried out using hand-held grinders, as well as different grinding attachments, which can be adjusted to the degree of scaling. We plan to buy a professional machine in the new future in order to make this operation more efficient.