Preliminary work on a new research project frequently entails proof-of-concept tests and modeling. The current project is investigating friction stir processing to produce small macroscale aluminum solid cylinders. The tooling was designed to be used in a 2-HP Bridgeport Mill for initial proof of concept tests and then later used in a CNC mill. The work pieces for these first tests were A1100 annealed ½ in. (12.7 mm) diameter work pieces, the final diameters were ¼ in (6.35 mm), and 3/18 inches (9.53 mm). The nominal speeds of the mill were 850 and 1000 RPM and were limited by the power available and the age of the mill. The paper discusses tooling design, instrumentation, preliminary results, and analysis. Temperature was measured during the tests but force was not measured due to limits to the available instrumentation. The future directions of this project are discussed.

Friction stir back extrusion (FSBE) has been identified as a manufacturing method for producing tubing with both stronger and more ductile tubing for applications such as hydroforming, biomedical, energy, and MEMS. Additionally, FSBE has been identified as a technology that can be potentially down scaled. However, the process is still not fully understood because of the multitude of process parameters such as geometry, work piece material, friction and heat transfer, and other parameters that go into producing tubes. The goal of this project was to design and test instrumented tooling for FSBE that were capable of producing a wide variety of tubing diameters, measure temperature and force in real-time both, and save process data for further analysis. The current status of this project is that the die has been fully instrumented and tested for measuring temperature, a design for the tool holder and probe capable of measuring plunge force for a CNC mill has been completed, and sample tests measuring temperature have been performed. In addition, a simple steady state heat transfer analysis has shown that the work pieces were approximately 29 degrees hotter than the temperature at the thermal couple. Those temperatures are above the recrystallization temperature of 150°C. Tooling geometry, and a comparison of test results are presented and the future uses for this tooling are discussed.

A microscale/multiscale tube hydroforming system including tooling and controls is being designed and implemented at the University of Louisiana at Lafayette as part of a collaborative effort with Michigan Technological University. The sealing system demonstrates the evolution of the flared tube ends approach for tube end sealing to a spherical metal-on-metal sealing system. One of the features of the tooling is that while the tooling is capable of producing microscale hydroforming, the entire system can now be made using conventional CNC machining operations. Preliminary work has begun for implementing control of the hydroforming process using a PLC and a custom built continuous high pressure system capable of 415 MPa is described. Preliminary results for formed sample tubes are discussed.

Friction stir back extrusion has recently been identified as a method for manufacturing stronger, more ductile seamless tubes. However, most of the work to date has investigated tubes with low length to diameter ratios and there has been little work investigating the change in grain through the thickness of the tube wall. The current project presents preliminary results in an investigation of the effect of the stirring process on developing ultrafine grain through the tube wall. The long term goal of the project is to miniaturize the process in order to produce highly ductile microscale tubes for biomedical applicaions, microscale heat exchangers, and fuel cell manufacturing applications. Friction stir back extrusion is a variation of friction stir processing and friction stir welding in that the end of a non-cutting tool rotates against a metal work piece, heats the work piece, and creates an ultrafine grain structure. The work described here considers tool speed and diameters when forming tubes from A1100-O aluminum work pieces. It was found that for rotations varying from 750 RPM to 2000 RPM that the maximum stir zone was approximately 250 μm at the bottom of the tube and approximately 50 μm in the walls. The outside diameter of the tubes was 12.5 mm and inside diameters of 6.35 mm and 9.3mm were produced.

Friction stir back extrusion has recently been identified as a method for manufacturing stronger, more ductile seamless tubes. The long term goal of the project described here is to miniaturize the process in order to produce highly ductile microscale tubes for biomedical, microscale heat exchanger, and fuel cell manufacturing applications. The process is similar to friction stir welding and processing in that the end of a non-cutting tool rotates against a metal workpiece, heats the workpiece, and creates an ultrafine grain structure. Conventional microtube manufacturing is done by hot direct extrusion using dies with mandrels. After the workpiece passes the mandrels, the tube segments weld together from residual heat. The work described here considers macroscale tooling design prior to down scaling to the multi and microscale. The immediate objective was to develop tooling that can produce 50mm long tubes with 12.5mm outside diameters and 6.35mm inside diameters. Design considerations such as strength, fatigue, buckling, and vibration were considered. This paper documents the development of the tooling design process that was used in order to overcome the various design issues. Tooling failure and analysis is presented as part of the evolution of the tooling design. While majority of the paper discusses the tooling design process, a final design was developed and preliminary results for friction stir back extrusion tests are presented for tubes that are 25 and 50mm long.

Micro- and multiscale material properties must be considered when manufacturing miniature devices, especially when considering utilizing multiscale sheet metal hydroforming processes. One of the critical considerations during the design process is the burst pressure for the sheet metal which is a limiting factor for potential hydroforming operations. In order to simplify determining tearing or rupture conditions, it is sometimes desired to use analytical methods for estimating material properties, including burst pressures, which occur shortly after material instability. Many researchers have developed approximate methods for predicting deformation during open die hydroforming based upon analytical approaches for biaxial conditions for circular and elliptical dies. Additionally, extracting material properties of sheet metal under biaxial conditions such as bulge hydroforming more closely matches forming conditions that the sheet metal will undergo for actual parts. The objective of the current research was to evaluate the analytically developed models’ ability to predict burst conditions and compare those burst results to those obtained from finite element models and experimentation. Stainless steel (annealed 0.2-mm thick AISI 304) was hydroformed in a circular open die with diameter of 11mm. Elliptical dies were also evaluated that had minor diameters of 11mm and aspect ratios down to 0.5. It was found that using the analytical method developed specifically for circular dies was a good predictor for the burst pressure while the more general analytical method for elliptical dies did not agree with either results from finite element analysis or experimental results.

Micro and multiscale material properties are one area that must be considered in order to satisfy the need for increased utilization of miniature devices manufactured with microscale hydroforming processes. The objective of the present research is to evaluate the properties of 0.2-mm thick AISI 304 stainless steel using circular dies of 5 mm and 11 mm diameter and elliptical hydraulic bulge forming processes with minor diameters of 11 mm and various aspect ratios. Macroscale analytical methods for circular dies were compared to experimental results. For the elliptical dies, Banabic’s method and a new modification of Banabic’s method, utilizing work by Rees were used to obtain power law material properties. The Ekineev-Kruglov method was shown to be the best analytical method estimating material properties from circular dies. For elliptical dies, based upon finite element simulations, it was seen that Banabic’s method resulted in the best agreement with experimental results. However, it was found that neither method for elliptical dies resulted in reasonable dome height predictions compared to those from microscale tensile tests.