Anil Mital

Evaluation of disassemblability to enable design for disassembly in mass production

Abstract A comprehensive methodology to enhance disassemblability of products has been presented in this paper. Disassemblability of a product is a function of several parameters such as exertion of manual force for disassembly, degree of precision required for effective tool placement, weight, size, material and shape of components being disassembled, use of hand tools, etc. The study of relevant literature indicates the presence of disassembly evaluation criteria and methodologies that address the problem partially such as disassembly sequence planning or economic analysis. As far as design for disassembly is concerned, there is a plethora of literature on rules to improve recycling end-of-life components. A systematic methodology to incorporate disassembly considerations in product design and enable quantitative evaluation of the design is absent. The current methodology assigns time-based numeric indices to each design factor, which make for easy and quick determination of disassembly time. A higher score indicates anomalies in product design from the disassembly perspective. Addressing these anomalies can result in significant design modifications rendering an overall increase in disassemblability of the product. Decisions regarding design modifications are based on weighing several factors such as technical and economic feasibility, overall functionality and structural rigidity of the product as a whole. Relevance to industry A comprehensive Design for Disassembly methodology is developed which is intended to act as a tool in life cycle engineering.

Potential applications of fuzzy sets in industrial safety engineering

Abstract This paper discusses potential applications of fuzzy set theory to risk analysis in the area of industrial safety engineering. Vagueness and imprecision in mathematical quantification of risk are equated with fuzziness rather than randomness. The concept of risk evaluation, using linguistic representation of the likelihood of the occurrence of a hazardous event, exposure, and possible consequences of that event, is proposed. The approximate reasoning technique based on fuzzy logic is used to derive fuzzy values of risk.

The psychophysical approach in manual lifting--a verification study.

An experiment was conducted to verify the psychophysical methodology used for determining lifting capabilities of workers. After estimating during a 25-min period what they could lift for 8 h, males lifted for 8 h. The amount lifted was only 65% of the estimated value. Females, on the other hand, lifted 84% of the estimated weight. When the lifting duration increased from 8 h to 12 h, males lifted only 70% and females lifted 77% of the estimated weights. The metabolic energy expenditure rate of the subjects also decreased significantly with time as the loads were reduced. Heart rates remained relatively constant at about 100 beats/min, even though energy expenditure rates decreased over the 12-h period. This could indicate that the subjects were sensitive to their general state of physiological strain in such work and adjusted the loads and corresponding energy expenditure rates to maintain a relatively constant circulatory burden.

Psychophysical and physiological responses to lifting symmetrical and asymmetrical loads symmetrically and asymmetrically

Eighteen adult males (mean age 22·6 years, weight 78·6kg and height 176·6cm) participated in a study designed to investigate the effects of symmetrical and asymmetrical lifting on the maximum acceptable weight of lift and the resulting physiological cost. Each subject performed sixty different lifting tasks involving two lifting heights, three lifting frequencies and five containers. For each lifting task, the load was lifted either symmetrically (sagittal lifting) or asymmetrically (turning 90° while continuing to lift). The heart rate and oxygen uptake of the individuals at the maximum acceptable weight of lift were measured. At the end of the experiment, subjects also verbally indicated their preference for symmetrical and asymmetrical lifting. When lifting asymmetrically, subjects accepted approximately 8·5% less weight. There was, however, no difference in the physiological costs when lifting symmetrically or asymmetrically. Lifting asymmetrical loads also resulted in lower maximum acceptable weights...

Surface finish prediction models for fine turning

Surface finish data were generated for aluminium alloy 390, ductile cast iron, medium carbon leaded steel 10L45, medium carbon alloy steel 4130, and inconel 718 for a wide range of machining conditions defined by cutting speed, feed and tool nose radius. These data were used to develop surface finish prediction models, as a function of cutting speed, feed, and tool nose radius, for each individual metal. A general purpose surface finish prediction model is also proposed for ductile cast iron, medium carbon leaded steel, and alloy steel. Statistical analysis of experimental data indicated that surface finish is strongly influenced by the type of metal, speed and feed of cut, and tool nose radius. While the effects of feed and tool nose radius on surface finish were generally consistent for all materials, the effect of cutting speed was not. The surface finish improved with speed for ductile cast iron, medium carbon leaded steel, medium carbon alloy steel, and aluminium alloy, but it deteriorated with speed...

Injuries due to handtools. Results of a questionnaire.

A questionnaire was mailed to various federal and state agencies in the United States to determine the frequency, severity and annual cost of handtool-related injuries in industry and to identify problem areas with regard to tool type, accident type, nature of injury, parts of body affected, type of industry and characteristics of the injured worker. The responses of various state and regional agencies were tabulated and analysed. This paper summarises the findings.

Effect of body posture and common hand tools on peak torque exertion capabilities

An experimental investigation was conducted to investigate the effects of body posture and of different types of common non-powered hand tools on maximum volitional torque exertion capabilities of males and females. Thirty-six males and 14 females applied peak torque in 21 different body postures while using nine different hand tools. The data analysis indicated that, for both males and females, the magnitude of volitional torque is strongly influenced by the type of tool used and the posture assumed. Between the two, however, the effect of hand tool is more profound. The correlation between the tool type and volitional torque was of the order of 0.71. No other variable was as strongly correlated with volitional torque. Maximum volitional torque profiles, as a function of posture and tool type, are provided for males and females.

A quantitative evaluation of gloves used with non-powered hand tools in routine maintenance tasks

Non-powered hand tools are a major means of carrying out routine maintenance and repair activities. The use of gloves in such situations is essential in order to protect the hands from potential injuries. Together, the gloves and hand tools accomplish the task by transmitting the muscle force on to the workpiece. Several studies have reported that the capability of hands to exert force/torque is severely influenced by the use of gloves. The use of gloves could also lead to a cumulative trauma disorder, rapid onset of muscular fatigue, etc. Most previous studies have focused on determining the influence of gloves on grip strength or push/pull forces one would exert while using devices such as knives. The purpose of this study was to determine the influence of a variety of commercially available gloves on the force/torque exertion capability of workers with wrenches and screwdrivers that are commonly used in performing routine maintenance and repairs. Nineteen males participated in the study and, using seven different hand tools and nine varieties of commercial gloves, exerted peak volitional torques on a simulated workpiece. The peak torque and electromyogram of flexor and extensor muscles were recorded. The results indicated that muscle activity did not differ significantly between the glove and no-glove conditions and the peak torque exertion capability of individuals generally increased with gloves. The magnitude of torque exerted on the workpiece was different for different gloves. The results also contradict some of the previously reported findings.

An ergonomic evaluation of dexterity and tactility with increase in examination/surgical glove thickness

Latex gloves of five different thicknesses (0.21 mm, 0.51 mm, 0.65 mm, 0.76 mm, and 0.83 mm) were manufactured in-house and tested for dexterity and tactility; dexterity and tactility measures with the bare hand were used as control values. Fifteen adult males (mean age = 22.8 years, mean stature = 179 cm, mean body weight = 75.4 kg, mean palm width = 9.9 cm, mean palm depth = 10.9 cm, and mean middle finger length = 9 cm) and five adult females (mean age = 21.2 years, mean stature = 168 cm, mean body weight = 53.6 kg, mean palm width = 8 cm, mean palm depth = 8 cm, and mean middle finger length = 8.3 cm) voluntarily participated. The gloves also were tested for punctures resulting from impact forces encountered during routine hand movements. The results indicated that the latex glove with 0.83 mm thickness successfully resisted routine impact forces and at the same time provided dexterity and tactility comparable to the bare hand. Thinner gloves failed the impact test and punctured. This indicates that it is possible to greatly reduce the incidence of exposure to contaminated body fluids through accidental needlesticks without compromising the preferred hands capabilities.

Margin of safety for the human back a probable consensus based on published studies

Despite numerous efforts to control occurrences of work-related low back pain, it continues to be a significant problem. Since the causation of low back pain is under multifactorial control, it is suggested that the factor most vulnerable at any given time will determine the safety. Epidemiological, biomechanical, physiological, and psychophysical information presented in published literature has been analysed. The data available are related to injuries and the projected margin of safety. This paper therefore, is an integrative, inferential synthesis of the published work to discern the margin of safety. An attempt has been made to conclude, on the basis of objective evidence, an all encompassing criterion to ensure the safety of the back. The psychophysical approach appears to integrate biomechanical and physiological variables on a short term basis in the studies surveyed. However, it remains to be proven that the sensory conditioning due to prolonged and repetitive occupational tasks will remain responsive to cumulative load and fatigue failures.