A method for determining tool group flexibility with uncertain machine availability - applications in a semiconductor manufacturing process / Adam Terry, Mamidala Ramulu and Posinasetti Nageswara Rao

The production of Integrated Circuits (IC) is a detailed and exacting process requiring tight specifications and precise equipment. The high cost and unique traits of this equipment requires high utilization and maximum throughput to achieve real profits. The design of fabrication facility (FAB) processes requires a thorough understanding of the adverse effects that random machine availability has on system performance. These effects (increased cycle time, decreased and variable throughput, etc) can be offset by tool group flexibility. Tool group flexibility can be described by two measures: machine flexibility (the number of tasks a machine can perform) and task flexibility (the number of machines qualified to perform a specific task). These two measures are related by the ratio of the number of machines in the tool group to the number of tasks that the group must perform. This paper utilizes a combined linear programming and simulation approach in an attempt to model the manufacturing system to gain insight into the production dynamics. The model is based on current production methodology and the use of modular equipment (steppers). The results include some insight into the added cost of flexibility and the associated production ramifications

Experimental study of surface quality and damage when drilling unidirectional CFRP composites

In this study, an experimental investigation on the drilling of unidirectional carbon fiber reinforced plastic (UD-CFRP) composite was conducted using polycrystalline diamond (PCD) tipped eight facet drill. The quality of the drilled hole surface was examined through surface roughness measurements and surface damage by scanning electron microscopy (SEM). It was found that fiber pullout occurred in two specific sectors relative to the angle between the cutting direction and the fiber orientation. The thrust force was highly influenced by the feed rate than the cutting speed and it shows a significant variation throughout the rotation of the drill

MACHINING OF MMCs: A REVIEW

Over the last few decades, Metal Matrix Composites (MMCs) have emerged as a material system offering tremendous potential for future applications. The primary advantages offered by these materials are their improved mechanical properties, particularly in the areas of wear, strength and stiffness. Of the MMCs, Aluminum matrix composites have grown in prominence due to their low density, low melting point and low cost. However, machining these materials remains a challenging task mainly due to the high abrasiveness of the reinforcing phases. Conventional machining processes such as turning, milling or drilling are adopted for machining MMCs. In this article, the existing and ongoing developments in machining MMCs vis-a-vis tool life, tool wear, machinability and understanding chip formation mechanism have been highlighted. Most of the studies discussed in this review will focus on Aluminum matrix composites. Certain areas of machining studies which have hitherto not been investigated have also been detailed

Friction Stir Welding of near α and α + β Titanium Alloys: Metallurgical and Mechanical Characterization

Butt welds of friction stir welded dissimilar titanium alloys (near α: Ti-6242 standard grain (SG) and α + β ; Ti-54M) were produced for varying processing parameters (rotation speed: rpm and traverse speed; mm·min−1). Microstructures, microhardness, and fractured surfaces were analyzed for three different rpms and mm·min−1 with Ti-6242 SG and Ti-54M kept on the advancing and retreating side, respectively. While constant traverse speed (varying rotation speed) has no significant effect on micrographic patterns in weld nugget, constant rotation speed (with increasing traverse speed) results in an increasing number of streaks with specified spacing (advances per revolution) (consisting of material migrating from retreating side) on the advancing side. Although, hardness variation within streaks (due to lower values of v ω ; where v   and   ω are traverse and rotation speed) were challenging to evaluate, yet hardness maps imitated the micrographic morphology of the weld nugget. For varying rotation (225–325 rpm) and traverse speed (100–150 mm·min−1), corresponding microstructure evolutions on the advancing and retreating side were related, with variations in evolving temperatures for corresponding welding parameters. Fractured surfaces revealed an appearance of a combination of transcrystalline and intercrystalline fracture for all the processing parameters. Nature of solid state joining has been shown with a distinct boundary between Ti-6242 SG and Ti-54M, demonstrating the interlocking between streaks of different aspect ratios of these two alloys

Microstructure and microhardness of electron beam melted Ti–6Al–4V components with differential thickness in initial deposition layers

Electron beam powder bed fusion (EB-PBF) is a process to additively manufacture Ti–6Al–4V. Along with process induced defects, the unique microstructure of EB-PBF Ti–6Al–4V leads to anisotropic properties, and therefore an understanding of how the microstructure evolves as layers are added is required. This experimental study presents the microstructural evolution of Ti–6Al–4V during the deposition of initial layers in EB-PBF process. Two geometries of specimens, ramp and step, were fabricated from 0.1 mm thickness (2 layers) to 0.7 mm (14 layers), and 0.2 mm (4 layers) to 1.4 mm (28 layers). The evolution of the microstructure was investigated through optical and electron microscopy, spatial microhardness mapping, and detailed microstructural characterization. Up to the deposition of seven layers, the microstructure comprised of α+β phases with partially retained α′ phase from rapid solidification cooling that resulted in higher microhardness. A unique microstructural gradient composed of three distinct regions (Region I, II, III) appears along the build direction from the deposition of 10 layers until 28 layers. Region I showed a finer α+β microstructure in irregular prior β grain with partial martensitic α’ phase and displayed greater microhardness. Region II showed coarser α+β microstructure and lower microhardness than both Region I and III. The average α-lath thickness and α-volume fraction increased as new layers were deposited. Perpendicular to the build direction, the hardness distribution was observed to be uniform along the longitudinal x-y direction