Design of Revolute Joints for In-Mold Assembly Using Insert Molding

Area of Science:

• Mechanical Engineering
• Materials Science
• Robotics

Background:

• Manufacturing highly articulated miniature structures is complex and costly due to multi-part assembly.
• Insert molding offers a potential single-step solution for creating articulated structures by co-molding metallic bearings with polymers.
• Polymer shrinkage during insert molding typically causes joint jamming, hindering the creation of functional articulated components.

Purpose of the Study:

• To develop a theoretical model for quantifying joint jamming in insert-molded articulated structures.
• To identify optimal design parameters for fabricating functional, multi-degree-of-freedom assemblies using insert molding.
• To overcome limitations of current insert molding techniques for creating articulated components.

Main Methods:

• Development of a theoretical model to estimate joint jamming torque caused by polymer shrinkage on metallic bearings.
• Utilizing the model to determine optimal design parameters considering manufacturing constraints.
• Experimental fabrication and validation of insert-molded articulated structures.

Main Results:

• The theoretical model accurately predicts joint jamming, enabling the selection of optimal design parameters.
• Weld-line strength significantly influences the minimum joint dimensions required for functional revolute joints.
• Successful fabrication of a multi-degree-of-freedom articulated structure for a medical robot prototype.

Conclusions:

• Insert molding can be effectively utilized to produce highly articulated structures in a single step.
• The developed theoretical model provides a pathway to design functional insert-molded articulated components.
• This research demonstrates the first successful application of insert molding for creating multi-degree-of-freedom articulated structures, with potential in medical robotics.