In product design, meeting functional requirements is essential, but achieving this isn’t solely dependent on the design itself. Choosing the right assembly process plays an equally critical role.
It’s vital to align part design with the assembly process. The product design must allow for the process to be successful, and the process must yield the appropriate results to satisfy the joint functional requirements. Below, we outline general guidelines for achieving five common joint requirements:
Articulating joints with or without a torque requirement
Non-articulating joints to withstand torque
Retention (force push-out or pull-out)
Vibration or shear load resistance
Finished form clearance within the product assembly stack-up
Articulating Joints (With or Without a Torque Requirement)
Goal: Minimize or precisely control side load or force induced into the part, rivet, or tenon.
Recommended Processes:
Orbital Forming: Ideal for parts that may have a more precise, smaller acceptable torque range. This process induces less forming force into the joint compared to a press operation.
Radial Forming: Similar to Orbital forming but has a different tool path during the forming process. Suitable for delicate parts with smaller diameter rivets and/or longer shanks, and a lower torque requirement.
Impact Riveting: Can create an articulating joint if gaps are designed into the part, such as with the use of a shouldered rivet where the shoulder height is equal to or greater than the part component stack-up. This process is most often used with semi-tubular rivets. If a solid rivet is required, the amount of shank swell induced into the joint increases, which will influence the consistency of the joint articulation.
Bushing Flare and Flatten: Used to install bushings into parts, where the bushings act as a “bearing surface,” preventing component-to-component contact in the pivoting area. Utilizing a bushing will achieve consistent joint articulation and lead to increased joint life.
Process Intelligence Option - Pivot Joint Testing Equipment: An in-process torque check can be added to the assembly process to ensure joints are within spec during forming. Dedicated torque check stations can also be used to perform offline torque testing. Pivot joint testing equipment is commonly used with articulating joints, but can also be used with non-articulating joints to measure if the joint can withstand a certain amount of torque.
Non-Articulating Joints to Withstand Torque
Goal: Achieve maximum hole fill to secure the joint.
Recommended Processes:
Orbital or Radial Forming: Often used to form the material into a feature designed into the part to provide interference and prevent movement, such as a hex or star hole, keyway, or non-round hole. Process selection is application-based and best determined by assembling sample parts to verify sufficient material flow into the part feature.
Impact Riveting: Provides a secure joint by maximizing shank swell. A pressure pad or stripper is used to apply a clamp load on the part stack-up prior to and during rivet installation to prevent gaps between the components.
Retention (Force Push-Out or Pull-Out)
Goal: Maximize the diameter of the formed head for superior retention. The diameter achieved is dependent on the amount of material or tenon pre-form stick-out from the joint stack-up and the finished height position of the forming tool.
Recommended Processes:
Orbital Forming with Process Intelligence: Ensures consistent forming to a specific height and will result in a consistent finished from diameter if the pre-form stick-out height of the rivet/tenon is consistent. Forming force can also be used to ensure retention. With most applications, there is a direct correlation between the forming force and the push-out force. Forming force limits can be established, allowing monitoring of the forming force to validate the part is within the acceptable tolerance range. Height and force monitoring are often used together to validate finished form requirements.
Vibration or Shear Load Resistance
Goal: Maximize hole fill by inducing force into the rivet/tenon.
Recommended Processes:
Press Forming: Offers the most hole fill of all cold forming processes.
Hot Upset Forming: Heats the material to a malleable state, allowing for maximum hole fill. This is ideal for harder materials that are difficult to cold form.
Impact Riveting: Provides a secure joint by maximizing shank swell. If a solid rivet is used, higher capacity machines are required. A pressure pad or stripper is used to apply a clamp load on the part stack-up prior to and during rivet installation to prevent gaps between the components.
Finished Form Clearance Requirements
Goal: Achieve precise, consistent joint height within assembly print tolerances while satisfying joint functional requirements.
Recommended Processes:
Orbital or Radial Forming with Process Intelligence: Forms the rivet/tenon to a specific height to maintain tight clearance tolerances, while minimizing the force induced into the part. Force and distance monitoring are often used to validate that the forming process is within the acceptable parameters, established by the assembly print tolerances.
Impact Riveting: Ideal process for semi-tubular rivets, especially ≤ ¼" diameter. If solid rivets are used, considerations must be made for rivet shank swell as a result of the process. The advantage of this process is machine cycle time and auto feeding of the rivet.
Press Forming: Similar to Orbital or Radial Forming, this process forms the rivet/tenon to a specific height to maintain tight clearance tolerances. Shank swell considerations need to be made as this process induces the maximum amount of force into the joint.
Importance of Part Design
Even with the correct assembly process and parameters, success ultimately depends on a robust part design. The product design must allow for the process to be successful. Different processes yield different results. Based on the joint functional requirements, choosing the appropriate forming process aligned with the part design will yield results that satisfy these requirements, and lead to assembly success in production.
Orbitform’s Solutions Lab provides expert assembly knowledge with 60+ combined years of experience. With multiple permanent assembly methods to choose from, all available in our lab, we can assemble sample parts and conduct testing to identify the optimal forming process for your application and, if needed, make product design recommendations. Our assembly experts work with you to ensure your design aligns with the appropriate assembly process that will satisfy your part’s functional requirements.
Choosing the right assembly process is as important as designing the part itself. By aligning your joint design with the assembly process, you can optimize performance, reliability, and cost efficiency.
Contact Orbitform to collaborate with our engineers to find the best solution for your joint requirements. Our expertise and state-of-the-art assembly equipment ensure you’ll achieve your desired outcome. Let us help make your product a success!