Precision forging

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The Forging and precision forging are variants of the swaging without burr with increased accuracy of the manufactured components. They aim to omit subsequent process steps such as machining in order to justify the increased effort for the forging processes. Precision forging is used when the accuracy of the workpieces is two ISO tolerance classes better than conventional closed-die forging, e.g. IT10 or 11. Individual functional surfaces then often do not require any post-processing and are ready for installation. We speak of precision forging from qualities IT8 to 9, in special cases IT6 can also be achieved.

In order to achieve the required accuracy, the mass of the raw part must fluctuate very little. It also requires precise temperature control, precise tools, and uniform lubrication. Ejectors are used instead of the usual bevels.

Typical precision forgings are gears and shafts of steel for the automobile industry. It is mostly used as hot forming for mass or large series parts in order to distribute the high costs for the dies over as many work pieces as possible.

Goals and Benefits

Precision and precision forging is primarily aimed at shortening the process chain to the finished product. In the conventional process chain, after die forging with a burr, the workpiece is subjected to a heat treatment in order to enable subsequent machining. This is followed by hardening and finishing (often grinding ). With precision forging, machining can be omitted. For this reason, the forge's heat can also be used for hardening and tempering , which also shortens the process chain. Another advantage is lower material costs. On the one hand, the material separated in the form of chips is saved; on the other hand, the components can be made smaller thanks to the favorable fiber flow through the forging process, as they have increased strength. Precision forging is therefore also of interest for lightweight construction . Furthermore, there are new design options in terms of function and resilience from the fact that no infeed paths and no tool run-out are required for machining.

  • Crankshaft directly after burr-free precision forging (research project at the IPH ).

  • For comparison, conventionally forged crankshaft. The back two after forging, then after trimming, front after grinding

Requirements for the process

Increased accuracy requirements are made in all process steps, since the process is sensitive to fluctuations. This concerns the design and manufacturing accuracy of the dies, the volume of the raw parts, their temperature and the dies due to thermal expansion, the tool guidance and the reproducibility of the entire process.

Range of components

A large part of the drop forged parts goes to the automotive industry and is used for gear parts such as gears, crankshafts and pinion shafts . Since the machining of these components is particularly complex, there are greater savings here. It is also used to manufacture turbine blades and various parts for the aircraft industry such as window frames.

Range of materials

97% of steels are used because they are easy to form in cold and warm conditions. These include structural steels , alloyed forging steels , hardened steels , and tempered steels .

Tool technology

Locking concepts

Various locking concepts are used to prevent the material from flowing out of the die. One possibility is to use a punch that fits exactly into the die. If the punch rotates during the forming process, it can also be used to produce helical gears. Another possibility is a die that is mounted on springs (so-called floating die ). After inserting the blank, the die is closed by a plate ( upper punch ). The forming movement then takes place through the lower punch.

Volume compensation

The mold filling behavior and the achievable accuracies depend essentially on the volume of the raw parts. The fluctuation must be less than 0.5%. In industrial practice, it is customary to separate raw material from bars or other semi-finished products by means of shear cutting , which allows an accuracy of at most ± 1%. If the volume is too small, the mold will not be completely filled; if the volume is too large, a burr can accidentally form or the tool can be damaged. The position and orientation of the blanks in the die also have an impact on the process. Therefore, contours are used in the tool to always position the blanks in the same way. The fluctuating volume can be compensated for by tool, process or machine solutions. Excess material can be taken up in the tool in compensation rooms. However, these must be placed in places that do not impair the function of the component. On the process side, the change in volume can take place in several steps by forming. The blank then has a small excess volume and is manufactured conventionally in the first step by drop forging with a burr that is then cut off. The final step is the actual precision forging. A force gauge can be integrated on the machine side, which measures the forming force and interrupts the flow of force when a limit is exceeded.

Multi-directional forging

Volume fluctuations can also be compensated for by multi-directional forging . The vertical ram movement is deflected horizontally by mechanical elements.

literature

  • Friedrich-Wilhelm Bach, Kai Kerber (Ed.): Process chain precision forging . Springer, 2014, ISBN 978-3-642-34663-7 .

Individual evidence

  1. ^ Fritz Klocke, Wilfried König: Manufacturing process 4 - forming . 5th edition, Springer, 2006, p. 274.
  2. ^ Fritz Klocke, Wilfried König: Manufacturing process 4 - forming . 5th edition, Springer, 2006, pp. 274f.
  3. ↑ https://www.iph-hannover.de/de/forschung/forschungsprojekte/?we_objectID=2372
  4. ^ Friedrich-Wilhelm Bach, Kai Kerber (ed.): Process chain precision forging . Springer, 2014, p. 22.
  5. ^ Fritz Klocke, Wilfried König: Manufacturing process 4 - forming . 5th edition, Springer, 2006, p. 274.
  6. ↑ Eckart Doege , Bernd-Arno Behrens : Handbook of forming technology. Springer, 2010, 2nd edition, pp. 525f.
  7. ^ Fritz Klocke, Wilfried König: Manufacturing process 4 - forming . 5th edition, Springer, 2006, pp. 275-276.
  8. ^ Friedrich-Wilhelm Bach, Kai Kerber (ed.): Process chain precision forging . Springer, 2014, p. 21.
  9. ^ Friedrich-Wilhelm Bach, Kai Kerber (ed.): Process chain precision forging . Springer, 2014, p. 25f.
  10. ^ Friedrich-Wilhelm Bach, Kai Kerber (ed.): Process chain precision forging . Springer, 2014, pp. 24–28.
  11. ^ Friedrich-Wilhelm Bach, Kai Kerber (ed.): Process chain precision forging . Springer, 2014, p. 28f.