(E-173) Ergonomic Assessment of Assembly Line Hand Tools for the Insertion of Car Body Plastic Spacers

Introduction:: The total cost of reported work-related musculoskeletal disorders (WMSDs) in the United States is estimated at $45-$54 billion each year.¹ Upper extremity work-related musculoskeletal disorders (UE-WMSDs) are strongly associated with high-repetition and/or high force hand intensive tasks.² Nationally, a substantial proportion of all WMSDs, 22.9% of cases, occur in manufacturing industries.² The automotive manufacturing industry uses coin-sized plastic spacers to fill holes in car body parts. Holes are drilled into car body parts for multiple reasons, but largely to aid in positioning during welding. Following car body assembly and welding, the holes need to be plugged. Assembly line associates insert plastic spacers manually with their thumbs. Plastic spacers are stiff and are designed to form a tight seal with the car body, making them difficult to insert. Each assembly line associate inserts thousands of spacers per shift with each spacer requiring high forces of up to 90N to insert.³ The highly repetitive and highly forceful nature of spacer insertion creates a high risk for thumb injury. To combat this risk, ten different ergonomic plastic spacer applicators were designed and developed for use by associates. These hand tools aim to reduce thumb forces by a minimum of 50% during insertion to reduce thumb related injuries. The goal of this research is to evaluate the potential of these ten prototype designs to reduce application forces during spacer insertion.

Materials and Methods:: Car body parts and plastic spacers obtained through collaboration with BMW were used to create a testing set-up. Car body parts were modified to create a flat surface with three separate holes for spacer insertion and were placed on top of a force plate during data collection. A Tekscan pressure mapping sensor model 9801 was wrapped around each hand tool. The sensor covered all areas on the applicator which could be contacted during plastic spacer insertion. Model 9801 sensors were chosen for maximum coverage and resistance to crinkling during data collection. Before sensor placement on the hand tools, equilibration and calibration of the sensors was completed using a pressure bladder which evenly distributed pressure across the sensor. During testing, each hand tool was used to punch a plastic spacer into each of the three car body holes. Punches were completed consecutively within a 20 second window. Each of the ten tools and a bare thumb were tested during each trial. Pressure values recorded from the Tekscan sensor were converted into force values using known sensor areas. Force values recorded on the force plate during testing were compared to forces applied to the applicator and bare thumb using MATLAB. Total force applied to each hand tool were used for comparison values.


Results, Conclusions, and Discussions:: Preliminary data collection included three complete trials. The maximum focal pressure during plastic spacer insertion using a bare thumb was 17.577 kPa. The total force required for plastic spacer insertion using a bare thumb was 9.2391 N. The maximum focal pressure during plastic spacer insertion using an ergonomic plastic spacer applicator ranged from 4.676 kPa to 108.562 kPa depending on which applicator was used. The total force required for plastic spacer insertion using an ergonomic plastic spacer applicator ranged from 8.244 N to 37.956 N depending on which applicator was used. The larger sized knuckle duster hand tool model with padding and a flat application surface provided a reduction in the maximum focal pressure during spacer insertion. Other hand tool prototypes did not provide a reduction in maximum focal pressure but did direct the location of maximum focal pressure away from the thumb joint. The smaller sized knuckle duster hand tool model with padding provided the greatest reduction in total force during spacer insertion. A future study involving 10 participants aims to verify these results. Each participant will insert three plastic spacers into the testing setup with each of the ten hand tools and their bare thumb.


Acknowledgements (Optional): : Funding was provided by the Clemson University Creative Inquiry Program. Spacers and car body rocker panels were provided through collaboration with BMW Manufacturing.


References (Optional): :

1. PANEL ON MUSCULOSKELETAL DISORDERS AND THE WORKPLACE. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington D.C.: National Academy Press; 2001. doi:10.17226/10032


2. Barr AE, Barbe MF, Clark BD. Work-Related Musculoskeletal Disorders of the Hand and Wrist: Epidemiology, Pathophysiology, and Sensorimotor Changes. Vol 34.; 2004.


3. Osten, N. R. (2020). The Design and Development of an Ergonomic Wearable Body Plug Applicator for Use in Automotive Manufacturing (Master’s Thesis). Clemson University, Clemson.