Assembly Ergonomics Research Articles

Detailed design process and assembly considerations for snap-fit joints using additive manufacturing

The use of additive manufacturing (AM) technology has been widely adopted due to the facility to produce highly complex elements compared to conventional fabrication processes. Additionally, AM technology is rapidly developing straightforward systems enabling designers to make products faster, despite current technology limitations (i.e. processing defects, materials properties, etc.). However, not only AM technology or products must be analyzed to have concrete solutions to all existing limitations. This means, it is necessary to take into account AM design process to propose simpler solutions. Elements manufactured by AM technology have dimension limitations on build size regarding printers building capabilities, especially when the elements are more volumetric than the building chamber. In those cases, AM design process takes a significant role and a potential solution is to divide big elements in sections, which are later 3D-printed and joined using snap-fits, as the cheapest and fastest connectors available. Thus, the present work explores the detail design stages of a proposed design methodology for elements´ coupling by snap-fit joints using AM technology. The design methodology is tested on the assembly of parts from a 1-gallon plastic container. A finite element simulation for the parts coupling scenarios is presented and the effects of part’s deflection on the detail design stages are analyzed. In addition, a final design validation regarding assembly ergonomics and retention forces are discussed in order to avoid part decoupling problems or material failure.

Formulation of novel DFMA rules for the advancement of ergonomic factors in non-linear iterative prototype assembly

ABSTRACTThe Design for Manufacturing and Assembly (DFMA) is usually associated with mass production. Iterative prototype construction and assembly have not been taken into account commonly in the planning of assembly ergonomics. This article presents DFMA queries considering factors in geometry and construction that affect the adjustability and adaptability during prototype construction. The example case concerns a paperboard tray press-forming prototype line. The main observation is that a DFMA approach with a systematic ergonomics analysis supports the efforts to avoid unnecessary reassembly cycles of the design. It was found in the study that although the total number of parts was increased, the reassembly times and the number of injuries were reduced significantly. The DFMA rules generated in this article can be applied in any non-linear prototype construction to enable a more clarified and safer operating environment.

On motion planning for narrow-clearance assemblies using virtual manikins

Digital Human Modeling (DHM) is an important tool to improve assembly ergonomics and thereby also productivity and product quality. State-of-art DHM tools can simulate challenging assembly operations by solving inverse kinematic problems so that the positions/orientations of the hands/feet of a manikin match some manually-specified targets. However, it is still difficult and time-consuming for a simulation engineer to perform an assembly with narrow insertion clearances by manually setting hand targets. We present a novel and highly automated approach that explores the 4D space (position of a fingertip plus pronation/supination of the arm) around an initial path for a sphere.

Assembly failures and action cost in relation to complexity level and assembly ergonomics in manual assembly (part 2)

Earlier studies have demonstrated strong relationships between manual assembly at high physical load levels and increased amounts of quality defects compared to assembly at low physical load levels. A recent Swedish interview study of engineers in design and manufacturing engineering indicated that assembly complexity factors are of additional importance for the assembly quality. The objective of this study was therefore to examine the significance of high and low complexity criteria and the relationships between assembly ergonomics and assembly complexity and quality failures by analyzing manual assembly tasks in car manufacturing. In total, 47 000 cars were analyzed and the results showed several significant correlations between assembly ergonomics and assembly complexity, assembly time, failures and action costs. The action costs for high complexity tasks were 22.4 times increased per task per car compared to low complexity tasks. Relevance to industryAssembly ergonomics and assembly complexity factors interact. Both should be proactively considered in order to keep assembly-related failures and action costs as low as possible.

A model for calculation of the costs of poor assembly ergonomics (part 1)

In product development there are many design requirements to meet and often tough project budgets to keep. Requirements that are considered not profitable will often be neglected, which affects assembly ergonomics. The objective of this study was to develop a calculation model for application in practice that enables calculation of costs of poor assembly quality related to assembly ergonomic conditions. The model is meant to be used by engineers and stakeholders in the design or redesign of manual assembly solutions. For that purpose, manual assembly tasks of 47061 cars at high, moderate and low physical load levels were analyzed with respect to assembly-related quality errors and corresponding action costs during production and on the market. The results showed that ergonomics high risk issues had 5–8 times as many quality errors as low risk issues and the earlier these were found the less were the action costs. The action costs for errors that were discovered late in assembly were 9.2 times more costly compared to early repair of errors in the factory. The action costs for quality errors that were found and corrected on the market were further 12.2 times more expensive to correct compared to actions taken in the factory. Examples are shown of how to apply the calculation model that was developed based on the obtained quality data. Relevance to industryBoth ergonomics and quality issues can be proactively solved through simultaneous risk assessment in early product development and hereby late reactive action costs can be greatly reduced.

What are the obstacles and needs of proactive ergonomics measures at early product development stages? – An interview study in five Swedish companies

Despite health and safety legislation and ergonomics regulations for several years many Swedish companies are still unable to effectively prevent the consequences of poor ergonomics. Corrective measures are often made (too) late when employees complain and work-related disorders have already occurred. Besides, several studies have shown that poor ergonomics result in deteriorated assembly quality and reduced productivity and that late measures are often costly. Other studies have proven that design engineers are often unaware of design consequences and do not know how to apply ergonomics principles in new product and production design. Therefore, the purpose of this study was to explore what is required to improve the situation. One way to find out was to ask engineers involved in product and production development. Thus, 64 engineers in design and manufacturing engineering in five Swedish companies were interviewed about ergonomics conditions related to quality and productivity issues. In general, their answers unexpectedly demonstrated a fairly good awareness of the implications of poor assembly ergonomics but also that appropriate product and production design methods and tools to prevent these are missing. 58 of the respondents thought that poor ergonomics could result in reduced product quality. 47 stated that profitability calculations are necessary for changes of poor ergonomic solutions. 37 said that ergonomics risks are accepted due to lack of appropriate calculation methods. Altogether, many suggestions emerged for how to improve product and production design methods and tools in order to achieve more complete and sustainable manufacturing solutions. Relevance to industryThe relationship between ergonomics and assembly quality deserves more attention in order to achieve both good working conditions and sustainable and cost-efficient manufacturing solutions. Assembly ergonomics and quality relationships must therefore be proactively considered already in early design phases of new product and assembly concepts.

The impact of poor assembly ergonomics on product quality: A cost–benefit analysis in car manufacturing

AbstractThe study aimed at analyzing the relationship between assembly ergonomics, assemblability (“ease of assembly”), and product quality and at quantifying these relationships in economic terms. This was in order to better to support the development of more ergonomic product and assembly solutions, particularly at early stages of the car development process. The assembly of 24,443 cars was studied for 8 weeks in an assembly plant and for another 16 weeks as factory‐complete vehicles. The results show increased risks for quality errors of 3.0 and 3.7 times and total action costs that were 8.7 times and 8.2 times higher for high and medium physical load assemblies compared to low physical load assemblies for 55 tasks assessed. © 2009 Wiley Periodicals, Inc.

A participatory and integrative approach to improve productivity and ergonomics in assembly

A participatory and integrative approach was applied to improve the productivity and ergonomics of the assembly lines in two factories, producing magnetic stop valves and office furniture, respectively. Main elements of the approach are the active participation of the company and the integration of two disciplines: assembly engineering and ergonomics. The aims were the analysis of bottlenecks and the definition of solutions. To analyse the main bottlenecks, the assembly process scheme was analysed in close cooperation with company representatives, specific observations were performed on the work floor, and the body postures and the forces on the body measured. To evaluate promising solutions a gaming technique (Ergomix) was applied mixing CAD-drawings of work places with real workers. The approach proved to be successful in the determination of bottlenecks in productivity and ergonomics (regarding the supply of components, the accumulation of materials, body postures, pushing and lifting forces), and the definition of promising solutions (e.g. new assembly concepts, height adjustable working tables, new organization of tasks, and new product design). The potential effects were estimated to be significant: e.g. gains in productivity of 15-20% and substantial reductions of time spent in risky body postures.

ERGOtool for the integral improvement of ergonomics and process flow in assembly

Manufacturers of manually assembled products are increasingly being forced to improve the flow of assembly orders, together with having more efficient employment, in order to meet increasing demands on short delivery times, high product variety, good quality and low manufacturing costs. At the same time, the human factor is increasingly important--a well-motivated workforce is a necessity these days. To improve assembly processes, layout and workstation design, a participatory approach was developed by TNO and applied in various assembly companies. The goals of this approach are the involvement of assembly staff, lead time reduction and an improvement of the assembly tasks in an ergonomic sense. The main elements of the approach are the active participation of the company, the integration of two basic disciplines: assembly engineering and ergonomics, and its stepwise nature. In March 2000, the European project PSIM (Participative Simulation environment for Integral Manufacturing enterprise renewal) was launched. The goal of the project, in which the employees play a central role, is to enable the ongoing and integral improvement of company assembly processes using advanced simulation software. To support this participatory and integral approach to improve production lines, a software tool, the ERGOtool, is developed within the PSIM project. ERGOtool is a software tool that helps in the description and evaluation of current and future assembly processes. It takes factors such as physical load, ergonomic hazards, mental load, and process flow characteristics into consideration.

A Participatory and Integrative Approach to Increase Productivity and Comfort in Assembly

Manufacturers of manually assembled products are more and more forced to improve the flow of assembly orders together with a more efficient employment, in order to meet increasing demands on short delivery times, high product variety, good quality and low manufacturing costs. At the same time, the human factor is increasingly important, for a well-motivated work force is needed more than ever. To improve assembly processes, an approach was developed and applied in various assembly companies. Goals of this approach are both a lead time reduction and an improvement of the assembly tasks in an ergonomic sense. Main elements of the approach are the active participation of the companies, the integration of two basic disciplines: assembly engineering and ergonomics, and its stepwise nature. The initial steps of the approach include the analysis of the assembly process by setting up an ‘assembly process scheme’, and the analysis of bottlenecks with regard to the flow of orders and ergonomics. Latter steps include the selection of improving measures, the implementation of these measures and the evaluation of the effects. This paper describes this approach and its application in two assembly companies: one producing relatively small products (magnetic stop valves) and the other making relatively large products (office furniture). In both companies the approach lead to a new design of the assembly process, a new factory lay-out including new work places, and another involvement of people in the assembling process.