The strengths of combination tools are most clearly recognised in industrial-scale series production, as the combination of several production steps saves both machining and tool changing time. However, the tools often have different tool lives for the different machining operations. When one of the components reaches the end of its tool life, the whole tool has to be replaced. MAPAL therefore offers combination tools of modular design In order to be able to fully exploit the tool life of each component.
MAPAL has now developed a new, modular tool concept for the machining of the valve spring seat and the parent metal bore for valve seat rings and valve guides of an aluminium cylinder head. Two combination tools are employed. Both can be designed for MQL machining and have a hydraulic expansion system that clamps both cylindrical shanks inwards and ring-shaped tools outwards. Additive production makes this type of tool clamping possible. Handling and tool changing are quite straightforward.
Boring and countersinking in one pass
The first of the two tools consists of an uncoated solid carbide Tritan-Drill and a PCD-tipped ring-shaped countersinking tool. The Tritan-Drill rough-machines the blind bore for the valve guide while the counterboring tool finish-machines the valve spring seat. The three cutting edges of the Tritan-Drill allow machining with a considerably higher feed rate as compared to twin cutting drills – and with at least the same quality.
The countersinking tool also has triple cutting. This ensures vibration-free machining of the valve spring seat – and that despite difficult cutting conditions due to the cored contours in the workpiece. Machining without vibration results in a higher workpiece quality and a long tool life.
Protection against twisting ensures the correct fitting of both the drill and the counterboring tool. The optimum position and edge-free transition between the chip spaces of drill and counterboring tool ensure a reliable removal of the chips.
The combination of the two machining steps in one tool shortens the cycle time. In practice the blind bore can be drilled with a spindle speed of 8,000 rpm and a feed rate of 3.2 m/min, while the valve spring seat is finish-machined with a spindle speed of 8,000 rpm and a feed rate of 2 m/min. The combination of the two steps reduces the non-productive times per cylinder head by eight to twelve seconds, depending on the machine. Thanks to the triple cutting possibility of the tools and the high machining values, more than 30 seconds are also saved for the machining of each cylinder head compared with twin cutting tools.
Different diameters with one tool
The second combination tool offers savings thanks to lower tool costs and optimum use of the tool life. It combines a PCD-tipped reamer for fine machining of the blind bore for the valve guide and a ring-shaped PCD-tipped boring tool for fine machining of the parent metal bore for the valve seat ring. Apart from the modular construction to allow optimum use to be made of the tool lives of the two components, this tool offers a further benefit compared with other concepts. The diameter of the blind bore for the valve guide is generally identical over the whole series. This is not true for the diameters of the valve seat rings. These differ not only within one cylinder head between the intake and exhaust sides, but also within one engine series. The modular tool system from MAPAL allows the complete engine range to be machined with just one base tool. Only the ring-shaped boring tool has to be replaced for the different diameters of the valve seat rings. The number of tools required and hence the tool costs are reduced significantly as a result. This second tool is operated with a spindle speed of 10,000 rpm and a feed rate of 6.6 m/min.
The two tools with the additively manufactured hydraulic expansion system offer significant time, and hence cost savings. Furthermore, optimum use can be made of the tool life of the individual components within the combination tools.