Development of screw-type milling tools for woodworking
Summary
In the research project "Development of screw-type milling tools for woodworking", the influence of the tool inclination angle LambdaS on peripheral milling tools on the machining process was examined in the period from 12/2007 to 01/2010.
In woodworking, only tools with an inclination angle of up to 25° are currently used for peripheral milling. For this reason, the influence of larger inclination angles lS on noise emissions and power consumption during the milling process was to be investigated. Tools with inclination angles of 45°, 55°, 65°, 75° and 85° were manufactured and compared with a reference tool and a standard milling cutter without inclined cutting edges (lS = 0°), with clearly visible and audible differences. The sound pressure level LpA was reduced by up to 10 dB(A) in the tests at an inclination angle of 65° to 75° compared to conventional milling cutters without inclined cutting edges. Considering that a reduction in the sound pressure level of 6 dB(A) corresponds to a halving of the noise, the results are promising and immense. This quantification is one of the most important results of the research project.
The orthogonal rake angle GammaO has shown very little influence on noise emission and power consumption during peripheral milling in the investigated range (Gammao = 65° to 75°).
Due to the inhomogeneous composition of the wood structure, it is very difficult to assess the milling quality of the finished surface on the workpiece using standardized roughness parameters. For this reason, only a few roughness values were determined as examples for a general assessment. The general visual assessment and the observation of test specimens using structured light and scanning electron microscopy showed that milling with large inclination angles achieves qualities that meet the requirements. A special feature is the avoidance of one-sided edge chipping using so-called counter cutting edges, which were successfully manufactured and tested. When processing at very extreme angles of inclination, a slight surface fibrousness was registered. In contrast to tools without a cutting edge inclination, surface compaction could not be detected even when worn.
The cutting performance increases slightly from 0° to 75° inclination angle and then increases exponentially.
During the machining process of screw-type milling tools, the chips fly away from the cutting point almost axially with reduced energy. This effect increases as the angle of inclination increases. They can therefore be collected much more easily than with conventional milling tools. This results in lower dust emissions in the surrounding area and lower energy consumption for particle collection.
The proportion of fine dust (particles smaller than 0.1 mm) in the sieve samples analyzed from screw-type milling processes is at the same level as the chips from the comparison milling cutters.
The tool wear decreases successively with increasing tool inclination angle LambdaS and this leads to longer tool life Lc. This means that the tool change cycles can be significantly extended and the proportion of dead time in production is reduced.
The new milling tools can be reground with relatively little effort, even without knowledge of the manufacturing details.
The principle of milling with large inclination angles was also implemented with a milling wheel set with segmented individual cutting edges while retaining the noise-reducing properties.
Hardened tools made of alloyed cold work steel were used in the project due to the better manufacturing possibilities. For an industrial implementation of the tools, the use of carbide cutting edges as continuous cutting parts or as cutting inserts is essential. Concepts were developed for this.
The project was funded by the German Federation of Industrial Research Associations (AiF) via the German Society for Wood Research (DGfH) and the International Association for Technical Issues Related to Wood (iVTH) (AiF project no. 15424 BR).