High-Strength M8 Hex Bolt Wrench

Introduction

I designed and manufactured a high-strength M8 hex bolt wrench to provide a durable and reliable solution for fastening applications. The goal was to optimize the structural integrity of the wrench while ensuring precision fitment for M8 bolts. During development, we identified the need to incorporate an additional feature to improve usability and functionality. The design process involved SolidWorks modeling, structural FEA analysis, and CNC machining to achieve a balance between strength, manufacturability, and user ergonomics.

Concept Development & Design Iterations

I developed multiple design iterations for the M8 hex bolt wrench, focusing on optimizing strength, manufacturability, and ergonomics. After evaluating each concept, I down selected the final design based on structural feasibility and ease of use (shown below).

Final Design

This design allowed for minimal weight to remain under the limit while providing ease of manufacturing. According to the hand calculations for the handle and the FEA simulations for the head and handle, this design will hold up when loosening our assigned bolt and torque. As our additional feature, we decided on a ⅛ inch Allen wrench, easily 3D printable and accessible at the end of the wrench.

Structural Analysis- ANSYS Deformation Simulation

To ensure the wrench could withstand real-world torque loads, we conducted structural deformation analysis using ANSYS. The simulations focused on both the 3D-printed wrench head and the CNC-machined aluminum handle, using an applied torque of 60 lb-in to evaluate stress distribution and potential failure points.

Key Findings:

Handle Strength: Hand calculations confirmed the aluminum handle could sustain the applied torque without excessive deformation.
Wrench Head Performance: ANSYS simulations revealed stress concentrations around the hex profile, guiding design refinements to improve durability.
Material & Design Validation: The results verified that the final design met structural requirements, ensuring reliable performance during testing.

Fabrication- 3D printing & CNC Machining

After finalizing the design and validating its structural integrity, we fabricated the wrench components using a combination of 3D printing and CNC machining. The wrench head was 3D printed to allow for rapid prototyping and easy customization, while the handle was CNC-machined from aluminum for strength and durability.

Manufacturing Process:

Wrench Head: Printed using [mention material if applicable, e.g., PLA, PETG, or resin], ensuring dimensional accuracy and strength while keeping production time low.
Aluminum Handle: CNC machined to precise tolerances, maintaining tight fitment between the wrench head and handle.
Post-Processing: The 3D-printed wrench head was smoothed and reinforced, and the aluminum handle was deburred to ensure a comfortable grip.
Assembly Preparation:
After machining and printing, each component was inspected for accuracy before assembly and testing.

Assembly & Performance Testing

After fabrication, we assembled the 3D-printed wrench head and CNC-machined aluminum handle to verify fitment and structural integrity. The assembled wrench was then subjected to a 60 lb-in torque load to evaluate its real-world performance.

Testing Process & Results:

Fitment Check: The wrench head and handle interface aligned securely, ensuring proper engagement with the M8 hex bolt.
Torque Testing: Under 60 lb-in of applied torque, the wrench performed as expected until failure occurred.
Failure Location: The fracture occurred at the exact high-stress region identified in the ANSYS simulation, validating the accuracy of our finite element analysis (FEA) predictions.

🔹 Final Outcome & Lessons Learned:
The fully assembled wrench failed at the stress concentration area highlighted in ANSYS simulations, confirming the importance of accurate structural analysis in mechanical design. This result emphasized the need for further material selection adjustments, reinforcement strategies, or design modifications to enhance durability in future iterations.

Reflection

This project highlighted the importance of structural analysis and real-world validation in mechanical design. While hand calculations and ANSYS simulations accurately predicted stress concentrations, physical testing confirmed that the wrench head failed at the exact high-stress region identified in the FEA analysis.

A key takeaway was the need for material optimization and design reinforcement to improve durability under torque loads. Future iterations could focus on modifying the wrench head geometry, adding fillets to reduce stress concentrations, or selecting a stronger material for improved performance.

This experience reinforced the value of finite element analysis (FEA) in predicting failure points, while also demonstrating the limitations of certain fabrication methods when handling high mechanical loads.

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