On-line measurement of cavity pressure during injection molding

Significance 

Recent technological advancement has led to effective methods of manufacturing plastic products through injection molding. Unfortunately, realizing the desired product quality have remained a challenge due to the unsuitable methods for measuring the cavity pressure curve, which is a key consideration in enhancing and optimizing the molding processes. To this end, effective methods for measuring the cavity pressure curves are highly needed thereby attracting significant attention amongst researchers.

Among the available cavity pressure measurement methods, pressure sensors are widely used owing to their high accuracy. Unfortunately, the sensors are limited to specific set measuring positions and also results in the formation of defects on the surfaces of the final products. Consequently, high initial and installation costs render their use expensive. In a recently published literature, alternatives and non-destructive techniques including ultrasonic and thermocouples have been developed. Alternatively, the need for offline and online monitoring methods have further escalated the development of new technologies. For instance, it is possible to determine material physical properties as well as detecting material defects and deformations using ultrasonic methods. However, most of these methods are not suitable for effective measuring of cavity pressure curves during injection molding.

To this note, a group of Zhejiang University scientists (Professor Peng Zhao, Jianfeng Zhang, Yao Zhao, Junye Huang, Neng Xia, and Jianzhong Fu) developed a non-destructive method for measuring of cavity pressure in injection molding. In particular, they utilized a precise ultrasonic technology to determine the stresses on the tie bars of the injection molding machine and further investigated the possibility of using such method to measure the molding cavity pressure. Their work is currently published in the research journal, Sensors and Actuators A: Physical.

Briefly, the study entailed both theoretical and experiments works. The authors used a magnetic clamping force detector to measure the strains produced by the tie bars as a way of evaluating the relationship between the stress on tie bars and ultrasonic signals. Next, the technique was accurately calibrated with R-squared value up to an average of 0.99962 to enable efficient measurement of the cavity pressure. Lastly, they also investigated the effects of the clamping forces on the pressure cavity measured.

The authors observed minimal errors within 4% in measuring the molding cavity pressure using the developed technique. In addition, accurate measurements were obtained through selection of appropriate clamping forces. Furthermore, the ultrasonic measurements were consistent with those obtained in pressure sensors.

In summary, the study by Professor Zhao’s research group is the first to measure clamping force on tie bars and cavity pressure in injection molding by ultrasonic methods. Consequently, it will enable the efficient optimization of the process through online monitoring to determine the machine variations and product properties. Generally, their work demonstrates a cost-effective, stable and non-destructive method that will ensure high-quality products thus advancing injection molding industries.

On-line measurement of cavity pressure during injection molding via ultrasonic investigation of tie bar - Advances in Engineering

About the author

Peng Zhao received his B.Eng. degree from Huazhong University of Sciences and Technology, Wuhan, Hubei province in 2004, Ph.D. degree in Material Processing Engineering from Huazhong University of Sciences and Technology, Wuhan, Hubei province in 2009. His research area includes advanced polymer molding process and equipment, innovative application of magnetic levitation, and non-destructive characterization of materials. He has over 10 years of experience in polymer processing and characterization. He is currently working as Professor at Zhejiang University, Hangzhou, Zhejiang province, China.

About the author

Jianfeng Zhang received the B.Eng. degree in the Department of Mechanical Engineering from Zhejiang University, Hangzhou, Zhejiang province, China in 2017. He is currently pursuing his MA.Sc course in the Department of Mechanical Engineering from the same university. His research interests include online characterization of injection molding process.

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About the author

Yao Zhao received his B.Eng. degree in the Department of Mechanical Engineering in Yanshan University, Hebei, China in 2016. He is currently pursuing MA.Eng. course in the Department of Mechanical Engineering in Zhejiang University, Hangzhou, Zhejiang province, China. His research interests include material molding and detection.

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About the author

Junye Huang received the B.Eng. degree in the Department of Mechanical Engineering from Zhejiang University, Hangzhou, Zhejiang province, China in 2018. He is currently pursuing his MA.Sc course in the Department of Mechanical Engineering from the same university. His research interests include injection molding process.

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About the author

Neng Xia received his B.Eng. degree in the Department of Mechanical Engineering in Central South University, Chang Sha, Hunan province, China in 2016. He is currently pursuing MA.Eng. course in the College of Mechanical Engineering in Zhejiang University, Hangzhou, Zhejiang province, China. His research interests include modeling and innovative application of magnetic levitation and non-destructive ultrasonic detection.

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About the author

Jianzhong Fu received his B.Eng. degree from Zhejiang University, Hangzhou, Zhejiang province, China in 1990, Ma.Sc degree and his Ph.D. degree in Mechanical Manufacturing and Automation from the same University. His research area includes artificial intelligence and smart manufacturing. He is currently working as Professor at College of Mechanical Engineering in Zhejiang University, Hangzhou, Zhejiang province, China.

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Reference

Zhang, J., Zhao, P., Zhao, Y., Huang, J., Xia, N., & Fu, J. (2019). On-line measurement of cavity pressure during injection molding via ultrasonic investigation of tie bar. Sensors and Actuators A: Physical, 285, 118-126.

Go To Sensors and Actuators A: Physical

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