Hole Milling Research Articles

Residual Stress Analysis in Thermally Sprayed Layer Composites, Using the Hole Milling and Drilling Method

Residual stresses are related to the thermophysical properties of substrate and coating materials and occur after the coated component has undergone thermal spraying and machining processes. All residual stresses in layer composites result from different individual stress mechanisms occurring during the manufacturing process, mainly based on heat and mass transfer during the coating deposition. Using the hole-milling-and-drilling method, residual stress fields can be measured in a quasi-nondestructive way over the drilling depth with appropriate resolution. In several drilling and milling operations, a cylindrically shaped hole is brought step by step into the component surface. The residual stresses are locally relieved due to material removal, deform the surface around the drilled microhole, and are measured by high-resolution measurement tools (e.g., strain gages (DMS)), for every drilling step in the form of relaxed surface strains. Using calibration curves and material data (E, μ), the measured surface strains are converted into nominal strains at the bottom of the drilled hole for every drilling step. Out of the differentiated strains, in-plane stress fields can be incrementally determined by Hooke’s law. This study describes residual stress measurement features, the finite-element method (FEM) calculation, and the idealization of calibration curves, as well as the results of exemplary stress measurements.

Mechanism of ion impact photoemission change of Si and Al during focused ion beam milling of LSI

Focused ion beam milling is an important tool for LSI modification and failure analysis. For both of these applications, the depth control in milling is a major requirement. The FIB machine we used was equipped with an ion impact photoemission detector for use with both Si and Al. We studied the photoemission change mechanism during LSI milling by altering the acquisition area of the photoemission, and by chemical analysis on the side walls of the milled holes. Si emission varies with the surface area of SiO2. Al emission originates in the edge lines of Al and SiO2 at the bottom of the hole, and from the Al redeposited on SiO2 of the side walls. On the edge lines and the side walls, ion mixing of SiO2 and Al enhances the Al photoemission. We demonstrated that an almost 100% modifying yield in both Al wire cutting and contact hole milling is possible by observing the variance of both emissions.

An apparatus for batch fabrication of micromechanical elements by ion beam machining

An apparatus has been constructed for ion beam milling of micromechanical structures. A 3 cm Kaufman type source is used to provide argon ion current densities and energies of up to 25 mA/cm2 and 1.5 kV, respectively. Stencil masks prepared by chemical milling are used to produce an array of microbeams allowing batch fabrication of micromechanical elements by scanning the mask or workpiece. Algorithms have been developed for computer control of workpiece position, orientation, and rotation. Computer control of beam current and energy has also been implemented. A database of sputtering yields and redeposition rates allows optimum operating conditions to be selected for a given application. Investigations include micromachining of refractory metals, milling of slots, holes, and grooves, and surface texturing, polishing, and figuring micromechanical structures.