Spin-Pull Process for Self-Clinching Nuts
The spin-pull process enables the automated assembly of self-clinching nuts in one-sided joining positions, including those in closed profiles. For thicker metal plates, a self-clinching nut can be used with a washer or spacer.
The structural connection formed by a nut, metal sheet, and spacer is clearly superior to that formed by a blind rivet nut. A self-clinching nut and washer combination has a wide range of applications and offers cost savings in the manufacturing process.
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How Does the Spin-Pull Process Work?
The graphics below show the sequence of a one-sided assembly in closed profile. The automated spin-pull process is performed in one step.
Operation step 1: A sliding unit brings the clinch nut to the pilot hole inside the profile. Then, the nut is positioned underneath the pilot hole.
Operation step 2: The assembly unit moves into the pilot hole and spins into the nut underneath. The unit carries the optional spacer.
Operation step 3: An axial pulling force is applied to the joint. This creates a form-fit connection between the nut, the metal sheet, and the spacer.
Operation step 4: The pulling mandrel is spinning out.
Advantages of the Spin-Pull Process
- Installation in closed-shape extrusion profiles and hard-to-reach positions.
- There is no need to open the profile, and the part's integrity remains intact.
- Access to the assembly position is one-sided.
- It provides a high-strength structural connection unlike blind rivet nuts.
- The installation process is series-proven and patented.
- Two work steps are combined into one.
- This reduces costs and time due to single-step assembly.
- The process is fully automatic and safe.
- Automatic tolerance compensation (+/-0.5 mm).
- Fast cycle time and high availability.
- High torque, pull-through, and push-out forces.
The spin-pull method is particularly suitable
- for high-strength and heavily loaded screw connections with one-sided accessibility.
- for components with undercuts or overlaps.
- for components with very limited installation space or difficult-to-access areas.
- for the chemical separation of aluminum and steel.
- for components such as crash boxes, module carriers (front modules), and battery trays in electric vehicles.
- for hydroformed parts, aluminum profiles, extruded profiles, and carbon fiber materials.
- The press-fit combination can also be used as a spacer.
- Water and gas tightness can be implemented according to customer requirements.
- Freely variable dimensions of nut and washer, possible depending on requirements.
Function of the Operator Workstation
The A220-Spin-Pull semi-automatic workstation can be used to press self-clinching rivet nuts (as well as self-clinching nuts) and rivet washers into closed profiles. This is how it works in detail:
Inserting and Checking the Component
The component to be processed must be prepared and positioned correctly in the semi-automatic workstation. First, the roller door is opened. Then, the worker inserts the component. Before the process begins, the system checks if the component has been inserted correctly. This is done by sensors. If the component has been inserted correctly, the process can begin.
Aligning and Centering the Component
When the worker activates the position switch, the roller door closes and the centering units secure the component in place. Once the door is closed, the component is pre-positioned and secured in the correct location.
Supply of Fasteners
The feeding units supply fasteners to the setting unit via compressed air. Each separation cylinder provides one fastener: the rivet washer for the top setting unit and the self-clinching rivet nut for the bottom slide-in rail. The setting unit moves in with a short stroke. The pulling mandrel threads the rivet washer. Additional sensors ensure a reliable process.
Movement of the Gantry Axis and Setting Process
Once the fasteners have been supplied, the gantry axis moves from its home position (the loading position) to setting level 1. Then, the setting unit is lowered. The pulling mandrel spins into the non-rotating self-clinching rivet nut, which is held by the slide-in rail. The mandrel pulls the rivet nut up and presses the combination into the component. After a successful setting process, the setting unit moves back up to the home position via the gantry axis. Then, the "Loading of fasteners" process is repeated. This procedure is performed at all insertion points.
Releasing the Component
The cylinders for the centering pins return to their home position. Then, the roller door opens, enabling the worker to remove the component.
Why Use Self-Clinching Nuts for One-Sided Joining Positions?
High Load Capacity
Blind rivet nuts are an obvious solution for closed profiles that can only be accessed from one side. However, even the strongest nuts may not meet the strength requirements of the subsequent screw connection. The weak point of a blind rivet nut connection is the formed rivet bead. Under heavy loads, the connection may deform the sheet metal, shear the rivet collar, or pull through the sheet metal.
However, the self-clinching nut is significantly larger in diameter and height than the rivet bead of a blind rivet nut. This allows self-clinching fasteners to withstand much higher forces in any direction. We have also developed production-ready solutions for applications with high lateral forces at a 90-degree angle to the screw axis.
Preload as Significant Advantage
Using a self-clinching nut creates a consistent preload between connected sheets during subsequent screw connections, meeting the required standards. Even when an additional spacer is used, a consistent preload is created between the nut, the sheet, the spacer, and the counter sheet. This ensures a highly resilient structural connection.
A blind rivet nut connection only attaches to the rivet bead. This is because the counterplate is screwed against the nut's head, regardless of the tightening torque. This prevents preload from building up between the two sheets. The rivet bead is relatively small in diameter and not particularly thick. Therefore, the blind rivet nut quickly reaches its limits when subjected to lateral or axial loads.
Cost Reduction Potential
A self-clinching nut has a shorter thread than a blind rivet nut with the same strength rating. This allows for the use of a shorter screw, reducing installation time and cost. Due to its higher load-bearing capacity, fewer screw connection points may also be necessary. This results in additional potential cost savings.
Conclusion
Blind Rivet Nut Remains Relevant
In general, the choice of an adequate fastener depends on the requirements. Blind rivet nuts remain important, so we continue to offer them. They are ideal for various applications, such as serving as a screw joint in a plastic holder.
Spin-Pull Process Considered as Best Solution
Our method is clearly superior for higher loads. It is also the only way to create a structural connection when access is limited from one side. It opens up new possibilities for handling closed profiles without compromising stability.
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