Hannover, Germany - Natural stone, like marble or granite, is processed with saw blades with hard-wearing diamond cutting segments. When these are damaged or worn, the cutting segments have to be replaced. Usually, the whole saw blade is sent to a repair shop. Laser Zentrum Hannover eV (LZH; www.lzh.de) and the Institute for Tool Research and Materials (IFW; Remscheid, Germany) have developed a mobile, laser-based process chain for gluing the cutting segments onto the saw blade and subsequently removing them without causing damage.
|FIGURE 1. The innovative laser based gluing process could, in the future, replace soldering for refitting saw blades.|
Until now, the soldered cutting segments are thermally detached, the soldering partners prepared, and the new cutting segments are then soldered onto the saw blade. The thermal stress from soldering leads to axial runout deviations (warpage) and an unfavorable distribution of stress in the saw blade. Consequently, the cutting quality decreases and cutting losses increase. Therefore, additional process steps are necessary to align and preload the saw blades.
Laser for all the process steps
LZH and IFW have developed a laser-based process chain for manufacturing glued saw blades. The laser radiation exerts minimal thermal stress onto the saw blades so that in the best case, the blades can be refitted without preloading or alignment. Ideally, the saw blade can be refitted as often as necessary.
The laser-based process for the first and consequent fittings of the saw blade consists of four steps (FIGURE 2): First, the surfaces of the segments and the saw blade are prepared by structuring them using a pulsed laser system. The segments are then glued onto the saw blade using a one-component epoxy resin adhesive, which is thermally hardened using a continuous-wave (CW) laser system. When the life span of the segments has been reached, they are detached from the saw blade using the CW laser system. A pulsed laser system is then used to remove glue residues and impurities from the gluing partners. Following this, the saw blade can be refitted.
|FIGURE 2. Concept of the process for laser gluing: Removal of the worn cutting segment (a), cleaning of glue residues from the surface (b), surface preparation (c), and hardening of the glue (d). (Courtesy: LZH)|
For demonstration purposes, LZH has developed a mobile unit that carries out refitting directly at the user's premises (FIGURE 3). Such a refitted saw blade has already been used to successfully cut granite.
Compared to soldering, gluing has many advantages. Among these are no thermal distortion, no heat discoloration, a homogeneous distribution of stress in the joining zone, a relatively high joining strength, and high vibration dampening.
|FIGURE 3. The demonstration unit combines all the laser processes for manufacturing fitted and refitted saw blades.|
This project, under the number 17120 N of the Research Association for Tools and Materials (FGW), has been funded within the framework of the program for supporting industrial research of the German Federal Ministry for Economic Affairs and Energy (BMWi), based on a decision of the German Parliament.