Vikram Cariapa

Material removal model for vibratory finishing

During the past decade, increasing attention has been given to secondary finishing processes as manufacturers seek to improve process efficiency while meeting increasingly stringent cost and product requirements. Although vibratory finishing is widely used, relatively little information is available about material removal and current design practices tend to be empirical. The present paper summarizes the results of a study conducted to investigate material removal in vibratory finishing and to develop a model to describe mass removal rate in terms of key process parameters. The model indicates that the material removal rate remains constant over time and is governed by bowl acceleration, workpiece mass, material properties and workpiece velocity. Results from controlled experimental testing using an instrumented vibratory bowl indicate that the model provides a reasonable representation of the governing process variables.

Investigation of vibratory bowl finishing

Although vibratory finishing has been in commercial use for over 40 years, relatively little fundamental information is known about the process, and industrial practice remains largely based on empiricism and trial and error. An experimental investigation into the vibratory bowl finishing process was conducted using material removal rate and surface roughness as the dependent variables. Bowl performance can best be described in terms of acceleration and depends primarily on the feed weights used, while bowl loading has a relatively minor effect. Furthermore, small changes in bowl loading resulting from normal media wear can be neglected. Results showed that material removal rates were constant over time for aluminium, brass and steel and were sensitive to hardness and bowl acceleration. Surface roughness saturated after a fixed period and was primarily a function of material composition. Surface roughness did not appear to be sensitive to bowl acceleration.

A fixture repeatability and reproducibility measure to predict the quality of machined parts

The production of high quality parts in a flexible manufacturing system is obtained by careful monitoring and control of various operating inputs such as manufacturing processes, fixtures, and gauges that are required to produce these parts. This research focuses on the performance of machining fixtures and develops a measure called the Fixture Repeatability and Reproducibility Measure (FR-R) to evaluate the performance of machining fixtures. This FR-R measure quantifies the variability of a part dimension that is contributed by the fixture under static loading conditions. This measure was used to evaluate the performance of two different fixtures that were utilized to produce two different parts. One part was machined only in parallel planes after location and clamping on the fixture. The second part, of a different geometry, was located and clamped in a different fixture, and then machined in mutually perpendicular planes. An investigation of data for the first part revealed that the FR-R detected the existence of fixture malfunctions. After the fixture was repaired, fresh measurements and further analysis with this FR-R measure revealed inherent problems in the manufacturing process that were addressed by redesigning the part and fixture for the next generation of product. The FR-R measure on the second part confirmed that the current performance of the fixture was satisfactory and matched the historical performance of the fixture. The conclusion was made that this FR-R measure was not only viable, but also desirable. For example, this measure facilitated pre-production evaluation of machining fixtures. Further, the FR-R measure is generated by using an off-line coordinate measuring machine to evaluate fixtures; thus minimizing the use of expensive production machines to do the same job. Finally, this measure showed that it could be used to monitor fixture performance during production, and prevent the production of scrap parts. In summary, this FR-R measure could be used to predict the quality of machined parts in a flexible manufacturing environment.

Application of neural networks for compliant tool polishing operations

Abstract The purpose of this research is to develop a strategy for automating polishing operations using filamentary brushes. In the first stage of the research, the experiments using the Taguchi system of experimental design are performed to identify the effects of various polishing parameters on the surface finish. It is observed that an abrasive impregnated filamentary brush improves the surface finish more substantially than a nylon brush. In addition, an interaction between brush type and rotational speed, and an interaction between brush rotational speed with brush depth, and type of brush with use of lubricant have been identified. In the second stage of the research, the experimental results are utilized to investigate an applicability of using neural networks in predicting and controlling polishing operations. It is shown that neural networks with one hidden layer learn faster than the two hidden layer designs. The neural network trained to predict the surface finish for a given set of polishing parameters performed with an average percent error between 1%–2%. However, the neural network designed to determine the levels of polishing parameters for a desired surface finish did not perform as well.

Contact Zone Force Profile and Machining Performance of Filamentary Brush

Filamentary brushing tools are used in a wide range of surface finishing processes, such as deburring, edge radiusing, polishing, and surface decontamination applications. Moreover, these tools are easily adapted to automation because the filament tips, which perform the machining operation, readily conform to the workpart surface without the need for sophisticated control systems technology. However, little is known about the material removal mechanics of filamentary brushes and, therefore, trial-and-error experimentation is often necessary before the tool is implemented in a production environment. This uncertainty of performance can be traced to a lack of understanding of the actual forces that are generated within the contact zone, that is, along the interface of the filament tip and workpart surface. Although previous experimental research has focused on the overall (i.e., resultant) brush force exerted onto the workpart, no information exists in the literature regarding the variation of force within the contact zone. Such information is essential for understanding the material removal profile within the contact zone, and could provide valuable information regarding the most active machining site along the contact surface. In this paper, a novel experiment is proposed for evaluating the force profile of filament tip forces that are generated within the contact region of a brushed surface. A specially designed workpart fixture is constructed and used in conjunction with a multiaxis force sensor for measuring the detailed force variation within the contact zone. The experiment is conducted using a wire brush at several different rotational speeds, which enables one to ascertain the role of filament inertia in the material removal process. Findings are reported which suggest that a significantly enhanced material removal rate can be achieved at a selective location within the contact zone at moderately elevated spindle speeds.

Automated Deburring with a Filamentary Brush: Prescribed Burr Geometry

In this paper, a dynamic model for removal of edge burrs with a compliant brushing tool is reported. Description of the burr geometry is assumed to be known through on-line measurement methods such as a computer vision system in the flexible manufacturing cell. Dynamic response of the brush/workpiece system is evaluated on the basis of experimentally obtained data. Master Curves are introduced as machining descriptors which characterize the incremental burr removal performance of the brush/workpiece system, leading to the development of an analytical dynamic model for orthogonal burr removal using a finite-width brushing tool. Based upon the dynamic model for material removal, a control strategy for automatic deburring is presented for burr configurations having constant height as well as variable height. A closed-form solution for transverse brush feed rate is obtained which is applicable for removal of burrs having variable height, as described by suitable geometry functions. For illustrative purposes, simulations are carried out for a straight-edge burr profile and sinusoidal burr geometry. Results are reported which identify important relationships among brush feed rate, brush penetration depth, and brush rotational speed. In order to help assess the validity of the proposed analytical model and control strategy, experimental results are reported for a combination ramp/straight-edge burr configuration. The results demonstrate generally good correlation between the predicted and actual profile for the edge burr that has been machined. In addition, some important observations include; (1) burr removal is most rapidly carried out by using the highest brush speed and deepest brush/workpiece penetration depth, subject to the condition that the brush fiber is not damaged, (2) Currently available polymer abrasive brushing tools exhibit very slow machining characteristics and must be improved in order to be used in a production environment where burr size is appreciable, (3) Material removal characteristics of the leading and trailing edge of brushes may be a source of error which merits further investigation.

Multimode machine tools—a concept that improves operations of flexible manufacturing systems

Modern flexible manufacturing systems offer certain benefits when compared to conventional stand-alone systems, but have problems associated with high capital outlays, system integration difficulties and lower than expected utilization because of characteristics of their component machine tools. These problems are addressed in this paper, which introduces a conceptual computer controlled multimode machine tool that can be programmed to execute conventional machining operations. Characteristics of hypothetical manufacturing systems built with these machines, are compared to those of conventional flexible manufacturing systems using established criteria, where it it is shown that these multimode machine tools enhance the operation of flexible manufacturing systems.

Resolving the angular velocity of two-dimensional particle interactions induced within a rotary tumbler

Abstract A horizontally oriented cylindrical tumbler, filled at variable depth with a monoplane of uniform cylindrical media, was rotated at various constant speeds. Resultant motion was captured using a high-speed camera. The images were post-processed with particle tracking velocimetry and image correlation algorithms in order to estimate each particle’s translational and rotational velocity. The particle interactions were then characterized into distance groups based on non-dimensional flow characteristics, where similarities were found with transitions between slip/no-slip and rotation/no-rotation conditions. The results of the particle interactions show rotational chains as analogous to translational force chains. The interactions demonstrated that occurrences of no-slip, no-rotation behavior correspond to areas of confined translational motion. No-slip rotation behavior was lower in areas of high interaction and higher in developing flow areas.Graphical Abstract

A shovel with a perforated blade reduces energy expenditure required for digging wet clay.

Objective: A shovel with a blade perforated with small holes was tested to see whether a worker would use less whole-body energy to dig wet clay than with a shovel with an opaque blade. Background: A perforated shovel is hypothesized to require less whole-body energy on the basis of adhesion theory; a smaller surface area would require less physical effort to dig and release soil from the blade. Method: The study involved 13 workers from an electric utility who dug wet clay with two 1.5-m long-handled point shovels, which differed only in blade design (perforated and opaque). Oxygen consumption was measured with a portable system while each worker dug wet clay at a self-regulated pace for 10 min. Results: There was no significant difference in number of scoops dug during the 10-min sessions, but workers dug 9.5% more weight of clay with the perforated shovel than with the conventional shovel (404 kg vs. 369 kg, respectively). Furthermore, stable oxygen uptake normalized to weight of participant and to the weight of clay dug revealed that participants expended 11.7% less relative energy per kilogram of clay dug with the perforated shovel. Conclusion: A point shovel with a perforated blade is recommended for digging and shoveling wet clay. However, the extra weight that workers chose to dig with the perforated shovel may increase the loading on the spine and may offset the metabolic advantages. Application: Manual shoveling is a common task, and workers may experience less whole-body and muscle fatigue when using a perforated shovel.

Universal Machine Tools Make Flexible Manufacturing Systems More Efficient

The free market principle in the United States has affected it’s economy tremendously. High quality, low cost imported goods are available in abundance and, hence, consumers have become extremely discerning in their choices. Local manufacturers have had to face this competition along with the added handicaps of higher labor costs and more importantly, lower productivity. These two factors have caused many firms to move abroad. This movement has two serious drawbacks, since jobs were not only being exported but the burden of generating real wealth for the country fell on fewer and fewer sectors of the economy. It is a well known fact that manufacturing is one of the real-wealth generating sectors of the economy.Thus, the United States was gradually losing it’s means of creating wealth.