A Study of Cryogenic Cooling When Reaming Holes in CFRP/Ti/Al Stacks

Abstract

AbstractPrecision holes in CFRP/Ti/Al stacks are usually machined with reamers. Machining modes should meet the requirements for each stack layer. Titanium alloy is machined at low cutting speeds at which aluminum alloy machining problems arise (low hole accuracy, high roughness, and tool build-up). The aim of the article is to study the influence of cooling methods, including the cryogenic one, on the surface quality and hole accuracy in a mixed stack containing aluminum alloy layers. The holes were drilled using the Atlas Copco PFD-1500 machine. The MAPAL built-up reamer 14 mm in diameter with carbide inserts was used for cutting. During the experiment, the reaming process was carried out on various stacks without cooling, with air cooling, and with CO2 cooling. The output data were as follows: deviation from the nominal diameter of the hole in the aluminum alloy, roughness Ra in the aluminum alloy, maximum cutting temperature during reaming, and front surface build-up height after the tool leaves the aluminum alloy layer. Models of the multivariate regression analysis that describe the influence of cooling methods on the quality of holes were built. The use of cooling with liquefied CO2 improved the hole accuracy for complex multicomponent stacks of metals and composite materials. The surface quality of the holes did not deteriorate. It was similar to the surface quality when cooling with compressed air.KeywordsMachiningCarbon fiberTitanium alloyAluminum alloyMetal-composite stackReamingCryogenic coolingCarbon dioxide