Fundamental investigations of micro single-lip deep-hole drilling of challenging drilling situations

The aim of this research project is to obtain the fundamentals for the process combination, consisting of pilot-hole drilling by laser radiation and subsequent micro single-lip deep-hole drilling, for the machining of complex workpiece surfaces. The focus of these investigations is the application of the mentioned process combination to create deep holes with small diameters at non-planar, curved and case-hardened parts. Industrial fields of application are, for instance, the machining of strongly varying and complex-shaped implants in the medical industry, the production of lubrication holes in bearing rings and gear shafts in the automotive industry as well as the production of cooling holes in turbine blades in the aerospace industry.

In order to achieve these objectives, the process advantages of laser drilling, characterized by wearless machining in short primary production times, is combined with the machining of high quality holes with increased aspect ratios enabled by mechanical small diameter single-lip deep-hole drilling. As a first step, drilling tests to assess the material removal in laser drilling based on a design of experiments planning are conducted. After the determination of suitable process parameters for the laser drilling process, considering the requirements that are set for the dimensional and geometrical tolerances of the pilot hole by the subsequent single-lip deep hole drilling, the process combination is applied for the different unfavorable machining situations. The experimental work will be conducted on an existing special-purpose machine, which is designed particularly for this application and allows the process combination of laser pilot-hole drilling and mechanical single-lip deep-hole drilling in one set-up.

In addition, reference tests on a machining center using the conventional process chain, containing end milling for creating a plane face, pilot-hole drilling and single-lip deep-hole drilling, are conducted. The technological and economical evaluation considers the achieved tool life, chip formation, hole quality and process time.

Fig.: Process combination of sequential laser pilot hole drilling and mechanical deep hole drilling for the machining of micro holes with increased length-to-diameter-ratios