G. Zak

Layered-Manufacturing of Fiber-Reinforced Composites

In this paper, we present a rapid manufacturing process for the layered fabrication of polymer-based composite parts using short discontinuous fibers as reinforcements. This process uses a UV-laser-based system for the selective solidification of the composite liquid. The primary components of the prototype are: (1) fiber-resin mixing subsystem, (2) composite-liquid deposition subsystem, (3) liquid leveling subsystem, and (4) laser-light delivery subsystem. Axiomatic Design Theory was used to validate the design selected for the experimental embodiment of the process. Extensive microscopic examination of the layered composite parts verified that the prototype system can yield comparable layer quality, in terms of accuracy and uniformity, to that of pure-resin parts made by a photopolymer-based commercial system. Furthermore, mechanical testing of these composite specimens showed up to 60 percent improvement in modulus over the unreinforced layered specimens.

Estimation of Three-Dimensional Fibre-Orientation Distribution in Short-Fibre Composites by a Two-Section Method

The overall fibre orientation in a composite can be statistically characterized by a fibre-orientation distribution. Fibre-orientation studies have concentrated on two major areas: those dealing with continuous fibres and those dealing with short fibres. This paper presents a novel two-section based method for statistical characterization of the fibre- orientation distribution within short-fibre composites. This method produces unbiased distribution data for the near-zero misalignment angles and simultaneously resolves the orientation-duality problem. The method’s novelty lies in its ability to determine accurately (within 1 µ m) the relative positions of two sections. While taking advantage of the extra information provided by the two sections, the proposed method also makes use of the single-section method’s main principles, namely: (1) intersection of a plane and a cylindrical fibre is an ellipse and (2) the ellipse’s shape is a function of fibre’s orientation relative to the intersecting plane. Therefore, by sectioning a specimen, acquiring images of the cross-sectional surfaces, and collecting the fibre-ellipse data from these images, the orientation of every fibre intersecting the sectioning plane can be determined. The probability distribution for fibre orientations within the sectioning plane is then related to that within the specimen volume.

Estimation of average fibre length in short-fibre composites by a two-section method

A novel and robust experimental technique is proposed for predicting the average fibre length in layered composites by using data generated from two parallel, closely spaced sections of a specimen. The method estimates the average fibre length on the basis of the ratio of matched fibres appearing in both cross-sections to the total number observed in a single cross-section. The experimental results of the two-section method were verified by using a conventional binder burnout process, in which residual fibres were measured and recorded directly. The direct measurement results confirmed the average fibre length predictions of the two-section fibre matching method.

Application of the Weighted Least Squares Parameter Estimation Method to the Robot Calibration

Significant attention has been paid recently to the topic of robot calibration. To improve the robots accuracy, various approaches to the measurement of the robots position and orientation (pose) and correction of its kinematic model have been proposed. Little attention, however, has been given to the method of estimation of the kinematic parameters from the measurement data. Typically, a least-squares solution method is used to estimate the corrections to the parameters of the model. In this paper, a method of kinematic parameter estimation is proposed where a standard least-squares estimation procedure is replaced by weighted least-squares. The weighting factors are calculated based on all the a priori available statistical information about the robot and the pose-measuring system. By giving greater weight to the measurements made where the standard deviation of the noise in the data is expected to be lower, a significant reduction in the error of the kinematic parameter estimates is made possible. The improvement in the calibration results was verified using a calibration simulation algorithm.

The Mechatronics laboratory experience

This paper describes an approach taken to undergraduate laboratories in Mechatronics. A sequence of six laboratories culminate with an apparatus that involves the microprocessor control of a floating ping-pong ball. The apparatus consists of a cooling fan (taken from a PC) located at the base of a vertical tube (in which the ping-pong ball levitates) and an ultrasonic sensor at the top of the tube (to measure the height of the ball). The apparatus was found to be an invaluable supplement to the theory taught in the classroom, and in particular in the areas of microprocessor programming and interfacing, areas that are traditionally foreign to Mechanical Engineering students. Student experience with this apparatus relative to a much more expensive computer integrated manufacturing (CIM) assembly cell available in another course is considered. It is argued that the ping-pong ball apparatus better embodies the underlying principles of mechatronic system design, relative to the formal CIM assembly cell.

Description of transmitted energy during laser transmission welding of polymers

It is important to describe the laser energy distribution in polymers properly when modeling heat transfer during laser transmission welding of thermoplastics. This paper presents an analytical model that describes the energy transmission in laser transmission welding of light scattering polymers. The model considers that the transmitted laser beam in a scattering polymer can be represented by scattered and unscattered components. The distribution of the scattered energy from any point in the incident beam is Gaussian. The transmitted power from the discretized input beam is summed to create a normalized power flux distribution model. The model was validated using the measured laser energy distributions after transmission through parts made of polypropylene, as well as unreinforced and glass fiber reinforced polyamide 6.

A 3-D Thermal Model for Spot Laser Transmission Welding of Thermoplastics

This paper presents a three-dimensional (3-D) transient thermal model of spot Laser Transmission Welding (LTW) solved with the finite element method (FEM). Unreinforced nylon 6 temperature-dependant properties were employed for a lap joint geometry. The heating and cooling stages in a spot laser welding process were addressed. The spot weld dimensions obtained from the model were compared with the experimental weld dimension data, and were in good agreement. It is shown that the thermal model is capable of accurately predicting the temperature distribution.

Estimating Contour Laser Transmission Welding Start-up Conditions using a Novel Non-Contact Method

This study presents a simple technique that can be used to estimate the power and speed required for optimal contour laser transmission welding as a function of material, part and laser characteristics. The technique involves rapidly scanning across a pair of laser transparent and absorbent parts in close proximity using a range of scan speeds and powers. The power and scan speed required to initiate visual degradation in the absorbent part are closely related to the conditions required for maximum shear strength. The technique has been tested successfully on four different polymers over a range of part thicknesses and carbon black levels.

Design of a Slot-Coater-Based Layered-Composites Manufacturing System

This paper addresses the reinforcement of photopolymers, through the addition of short glass fibers, for Rapid Layered Composite parts Manufacturing (RLCM). Novel designs for an (external) fiber-resin-mixing subsystem and a (slot-coating-based) liquid-layer-formation subsystem are presented. These subsystems, when used as integral parts of a lithography-based RLCM system, successfully cope with typical difficulties encountered in the formation of thin layers from a highly viscous fiber-photopolymer composite liquid. Axiomatic Design theory was utilized for the analysis of both subsystem designs. Verification experiments run on an RLCM system confirmed (i) the ability of the fiber-resin-mixing subsystem to supply liquid composite with specified fiber content and to avoid fiber degradation through breakage, as well as (ii) the ability of the liquid-layer-formation subsystem to form solid layers with high fiber content and of uniform thickness.

A two-dimensional thermal finite element model of laser transmission welding for T joint

Recent years have seen wider application of laser transmission welding (LTW) as a means for joining of plastic components. Advantages of LTW arise from it being a contact-free method for delivering precisely controlled energy to the surfaces of the welded components and from flexibility with regard to welding geometry afforded by the laser being under computer control. LTW involves a laser beam passing through a laser-transparent component being absorbed by the laser-absorbent component at the weld interface. Heat generated at the interface melts a thin layer of plastic in both components and thus forms a joint through molecular interdiffusion. To form a strong bond, it is important that the weld interface is exposed to sufficient heat to melt the polymer without degrading it. Delivery of the thermal energy by the laser beam is affected by process parameters, such as laser power, scan speed, beam spot size, and material properties, such as absorptivity, presence of reinforcements, and other additives. Dev...