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Relaxed machining

How to successfully finish milling bimetal without any headaches

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Worldia Europe GmbH

Innovative tools mill engine blocks more economically

Motor block machining typically takes place on horizontal machining centers in a single setup. In the initial machining step, the gray cast iron cylinder liners are pre-machined using a carbide insert milling cutter, leaving only 0.02 to 0.05 mm of material for the finish milling cutter. The cutting depth in aluminum for the finishing cutter is 0.5 mm. After the pre-machining (as shown in Figure 3), the surface is finish-milled with the Worldia BE face mill. The inserts used are universal PCD milling inserts in combination with PCBN bottom cutters that have a thin TiN coating to enhance wear resistance. This approach ensures precise and efficient machining of the cylinder block surfaces by effectively removing the bulk of the material with carbide cutters and achieving a high-quality finish with the combination of PCD and PCBN inserts. The TiN coating on the PCBN cutters further enhances the durability and performance of the tools under the demanding conditions of finishing operations.

The finishing cutter referred to in Figure 2 is the proven multi-tooth cutter from the BE series (diameter 250 mm, FMP250SC60-BE12-36) by Worldia, equipped with fine adjustment of all indexable inserts in the axial direction. This adjustment allows all indexable inserts of the same type to be easily set to a runout of less than 2 μm. The 12 PCBN sub-cutters are set 0.035 to 0.040 mm higher than the 24 PCD inserts, ensuring that the PCD cuts only aluminum and not cast iron. The Worldia tool mills three to four times faster than competitive tools while maintaining the same or better tool life. Cutting data includes: cutting speed (vc) = 1570 m/min, feed rate (vf) = 4000 mm/min, and feed per tooth (fz) = 0.06 mm. Critical to the success is the supply of adequately filtered coolant lubricant (30 to 50 l/min at 10 to 15 bar) through the spindle, directed right at the cutting edge to prevent chip adhesion. This setup ensures efficient, high-quality milling with optimized cooling and chip removal.

Image 3: The semi-finishing of the cast iron liners was carried out with a finishing allowance for the liners of 0.02 to 0.05 mm. For the aluminum surface, it was 0.5 millimeters.
(Image:Worldia)
Image 4: This is what the surfaces of the engine block look like after being machined with the innovative Worldia BE cutter.
(Image:Worldia)

The machined surface is shown in Image 4. The structure of the bimetal block surface meets all requirements, with no chipping or burring visible at the edges of the cast iron liners. As shown in Image 5, the roughness Ra is less than 0.65 µm, the waviness is less than 1.5 µm, and the overall flatness is less than 17 µm.

Image 5: Here you can see additional measurement protocols that demonstrate the surface quality achievable with the Worldia BE cutter. On the left, the roughness and waviness are shown, and on the right, the measurements for flatness are displayed.
(Image:Worldia)

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