Belt grinding

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The belt grinding is a metal-cutting production method , wherein instead of at the grinding conventional abrasive discs , abrasive belts are used which circulate on at least two rollers. Since the exact shape of the abrasive grains on the belts is just as little known as with conventional grinding, both methods count for cutting with a geometrically undefined cutting edge . The machine tools are belt grinders , the electric hand tool is a belt grinder . The term "belt loop" it is standardized in DIN 8589, in the industry it is also contact loops named after the contact rollers or support rollers that make contact between the abrasive tape and the workpiece. In some process variants, flat contact elements such as support shoes or plates are also used. One advantage of belt sanding is that the support elements do not wear out like grinding wheels and are given a smaller radius during machining. Thus, when grinding the belt at a constant speed of the wheels, the cutting speed also remains constant, while with grinding wheels it slowly decreases. Therefore belt grinding is well suited for automated manufacturing. Another advantage is that the sanding belts are flexible and adapt to the shape of the workpieces, which is also beneficial in fully automated production. In addition, the process can be adapted to the respective application using various process parameters. Influences are the size, hardness and grooves of the supporting disks or rollers, the contact pressure, cutting speed , the abrasive , the grain size and distribution of the abrasive grains and the type of sanding belt backing.

history

Coated abrasives , including abrasive belts, were used as early as the Stone Age. In the following epochs, however, grinding wheels or stones were used almost exclusively . Belt grinding only became widespread in industrial practice after 1945 and was fully developed from the 1970s. The first detailed scientific treatise on belt grinding comes from G. Becker and K. Dziobek in 1980. For a long time, belt grinding was used instead of a bench grinder because of the high surface quality that can be achieved for polishing . Since initial problems such as the short service life of the grinding belts have been overcome since the 1990s, belt grinding is now used in numerous variants and industries.

Material spectrum, workpiece spectrum and applications

The largest customer for grinding belts is the metalworking industry, where mainly workpieces made of steel are processed, but also cast iron, copper or titanium. Belt sanding is also used in woodworking for processing furniture or layers of paint. Otherwise it is also suitable for processing leather, glass, plastic, ceramic or composite materials. The size of the workpieces ranges from cast ship propellers with a diameter of 11.5 m and a weight of 150 t to the tips of surgical needles with diameters of less than one millimeter. Belt grinding is used for flat grinding sheet metal, plates and coils or for processing tubes or bars. It is also suitable for regrinding complicated shapes such as propellers or turbine blades. It is also suitable for external and internal cylindrical grinding. It is used for decorative surface grinding, to improve the surface quality, for deburring or to grind workpieces to size. Shape grinding can be done by machine or manually on a floor grinder, for example to grind the spaces between the prongs on forks. It is also used to sharpen knives and blades or for water fittings made of copper.

Belt sanding is very often used in carpentry or industrial furniture production, for example to sand wooden panels to size or to prepare the surface for painting. Flat support elements are often used for this, as they enable a very high surface quality.

Process variants

Belt grinding can be classified according to several criteria. According to DIN 8589, it is divided according to the kinematics into plane, round, profile and shaped belt grinding. Generating grinding as with conventional grinding with grinding wheels is not possible. Another distinction is according to the support elements used (round or flat), as well as the two variants of belt grinding with constant contact force or constant infeed (cutting depth). High-performance grinding is a special variant.

In addition, belt grinding can be divided according to the degree of mechanization into the grinding of stationary workpieces with belt grinders that are guided by hand or with machine-guided tools in belt grinding machines, as well as grinding with stationary tools and workpieces moved either by hand or by machine.

Kinematic classification

Flat belt grinding

Flat belt grinding, also known as flat grinding, is used to create or process flat surfaces. It can be used to change shape or size or to improve the surface. In a wide belt sander, a belt is used whose width is greater than that of the workpiece together with a support roller. In long-belt sanding machines, the belt is pressed flat onto the workpiece by a support shoe in order to achieve a particularly high surface quality, which is often used in woodworking.

Round belt grinding

Round belt grinding is used to machine rotationally symmetrical workpieces. It can be carried out between centers or without a center , as well as for external and internal machining. Complex workpieces such as crankshafts can also be machined. It is used, for example, for grinding stainless steel tubes, piston rods, stainless steel wires or the inner surfaces of containers. With special controls, so-called “non-round” geometries can also be machined, for example oval cross-sections or tapered workpieces.

Profile belt grinding

Profile belt grinding is used to process profiles. In some cases, support elements are dispensed with, which is referred to as loops in the free belt area. The grinding belt can then adapt to the shape of the workpiece, which is used, for example, to grind the prongs of forks .

Form belt grinding

Shape belt grinding is used to create and process three-dimensional shapes of any shape. A distinction is made between manual, mechanical and CNC form grinding according to the type of motion generation.

  • With manual shape grinding, either the tool or the workpiece is moved by hand and pressed onto the support elements in such a way that the desired shape is created. It is used for smaller quantities or for repair work.
  • With kinematic form grinding, the movement of the tool or workpiece is generated by a gear unit , for example by means of cams . This variant is used for large numbers of identical workpieces, for example for grinding wrenches.
  • In CNC form grinding, the movement is generated by a CNC control and implemented by an industrial robot . This variant is particularly suitable for processing in the free belt area, since the sanding belt adapts to the shape of the workpiece and can thus compensate for minor machine inaccuracies. It is used for example for the grinding of implants made of titanium .

Classification according to contact areas

Either round, flat or no support elements at all can be used. The first two variants can also be combined in a single machine.

  • For circumferential belt grinding according to DIN 8589, a support roller (wide) or a support disk (narrow) is used, on the circumference of which the grinding belt rolls off. They are also known as a contact roll or washer. In industrial practice, this variant is referred to as belt grinding with a support disc or roller. It is the most commonly used variant in metalworking. This enables high metal removal rates , which makes the variant productive. For this, rather low surface qualities are possible.
  • In woodworking, on the other hand, side belt sanding is more common with flat support elements such as support shoes, plates or beams (?). In practice it is usually referred to as belt sanding with a support shoe. This enables high surface quality and dimensional accuracy, but rather low metal removal rates.
  • The belt sanding without support elements on the free belt section between two pulleys. Because of the lack of support, the forces that occur are lower and the metal removal rate is therefore also lower. To do this, the flexible belt adapts to the shape of the workpieces, which is why free belt grinding is mainly used for machining complex shapes, for example for turbine blades or implants.

Belt grinding with constant contact force

When belt grinding with constant contact pressure, the tool follows the shape of the workpiece and is therefore particularly suitable for components with a complex shape. How much material is machined depends on the material, the contact pressure, the topology of the grinding belt and other influencing factors. Since the amount of contact force is not very meaningful without specifying the grinding width, the force F 'related to the grinding width is usually used to be able to compare different experiments.

Because of the wear and tear of the sanding belt, the various process parameters change over time. Since the individual abrasive grains are very firmly connected to the substrate in the case of grinding belts, the grain breakout rarely occurs. Instead, the grains usually wear out by dulling and chipping. New abrasive grains are usually sharp-edged and thus enable high penetration depths of the grains and thus high chip thicknesses, metal removal rates and work interventions, but also high roughness. However, the sharp grains break off or blunt quickly so that the chip thickness, metal removal rate and machining operations decrease as well as the roughness. The somewhat dulled grains wear out more slowly, so that all these values ​​initially drop quickly and with increasing wear more and more slowly until they remain at an almost constant level.

Usually, however, a constant metal removal rate is desired, which can be achieved if the contact pressure is increased slowly over time. The amount of contact pressure has an influence on the wear behavior and the service life of the sanding belts. The standstill criterion is the minimum material removal rate that is economically justifiable. With low metal removal rates, the tool life decreases with increasing forces; with high metal removal rates, the tool life increases. If the contact pressure is low, the grains usually become blunt and can no longer penetrate the material so easily; if the contact pressure is high, the grains splinter and thus remain sharp. Which cutting parameters are best depends on the application. Important influences are the tool change costs and the machine costs as well as the question of whether the worn belts can still be used for other tasks with less high demands.

literature

Individual evidence

  1. ↑ Heinz Tschätsch: Practice of machining technology. Process, tools, calculation. 11th edition, Springer Vieweg, Wiesbaden 2014. ISBN 978-3658049225 , p. 273.
  2. ↑ Heinz Tschätsch: Practice of machining technology. Process, tools, calculation. 11th edition, Springer Vieweg, Wiesbaden 2014. ISBN 978-3658049225 , p. 274.
  3. ↑ Wolfgang Heidtmann, Martin Pischel: Belt grinding with abrasives on a backing , p. 670, 685 f. in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur: Handbuch Spanen. 2nd edition, Hanser, Munich 2014. ISBN 978-3446428263 .
  4. ↑ Wolfgang Heidtmann, Martin Pischel: Belt grinding with abrasives on backing , pp. 685–687, 708, 714–717, 723, in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur: Handbuch Spanen. 2nd edition, Hanser, Munich 2014. ISBN 978-3446428263 .
  5. ↑ Wolfgang Heidtmann, Martin Pischel: Belt grinding with abrasives on a backing , p. 688 f., In: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur: Handbuch Spanen. 2nd edition, Hanser, Munich 2014. ISBN 978-3446428263 .
  6. ↑ Wolfgang Heidtmann, Martin Pischel: Belt grinding with abrasives on a backing , p. 689, in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur: Handbuch Spanen. 2nd edition, Hanser, Munich 2014. ISBN 978-3446428263 .
  7. ↑ Wolfgang Heidtmann, Martin Pischel: Belt grinding with abrasives on a backing , p. 689, in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur: Handbuch Spanen. 2nd edition, Hanser, Munich 2014. ISBN 978-3446428263 .
  8. ↑ Wolfgang Heidtmann, Martin Pischel: Belt grinding with abrasives on a backing , p. 689, in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur: Handbuch Spanen. 2nd edition, Hanser, Munich 2014. ISBN 978-3446428263 .
  9. ↑ Wolfgang Heidtmann, Martin Pischel: Belt grinding with abrasives on a backing , p. 689, in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur: Handbuch Spanen. 2nd edition, Hanser, Munich 2014. ISBN 978-3446428263 .
  10. ↑ Wolfgang Heidtmann, Martin Pischel: Belt grinding with abrasives on a backing , p. 691 f., In: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur: Handbuch Spanen. 2nd edition, Hanser, Munich 2014. ISBN 978-3446428263 .
  11. ↑ Wilfried König, Fritz Klocke: Manufacturing process 2: grinding, honing, lapping. 4th edition. Springer, Berlin 2005, pp. 246–249.