Engineering applications that require screwed fixings into thin-walled components pose a problem that international fastenings specialist Böllhoff solved with the development of its range of RIVNUT blind rivet nuts and RIVSTUD blind rivet studs.
These clever devices enable strong thread fixings where traditional threading techniques are impossible. Moreover, because the fasteners are mounted without counter pressure (fixed blind), they can also be used in hollow sections.
RIVNUT blind rivet nuts and RIVSTUD blind rivet studs are available in many variations and sizes, and therefore offer numerous fastening solutions with additional functions.
The nature of the components makes them suitable for a broad range of adaptations and flexible usages. One such example was designed for a major international supplier of automotive body in white products, aluminium and steel stampings, assemblies and facilities design. The application was for a body-in-white rear corner panel for a prestige British car.
Spin-out resistance
The fastener selected for the task was a RIVNUT M6 closed end, knurled and with an under head seal. The RIVNUT chosen has a flat head round body and is fully cold-formed. It also has a knurled body for increased spin-out resistance. The flat head and tapered shank make automation and insertion easy. Internal rolled threads give increased thread strength.
The volumes of fasteners to be fitted were significant – anything from 1.4-2 million pieces per annum – so manual insertion was out of the question, from productivity, health and safety and quality perspectives.
The solution was Böllhoff’s development of automatic hydraulic setting equipment – designated HSA. This equipment proffered a number of advantages for the customer. The HSA automatic setting tool allows the fasteners to be set continuously, thanks to its automatic loading system, which delivers the RIVNUT directly onto the mandrel of the HSA machine.
The fasteners are conveyed to the mandrel, inserted and retracted to deform the fastening against the rear side of the component wall at break neck speed, every cycle, without fail
The hydraulic setting equipment has been well tried and tested by Böllhoff in other applications of RIVNUT, while the automated feeding and setting eliminates operator error. The equipment also checks the fastener dimensions before blow feeding to the setting head, thereby ensuring no quality problems or machine jams. Thereafter, the RIVNUT insertion is monitored, the stroke and pressure checked, with the outcome that both the equipment and the fastenings are failsafe.
System integration
The HSA has been designed with system integration in mind. The use of a single external PLC enables standard protocols to be deployed to communicate between the hydraulic setting equipment and other machine tools or robots.
The electrical supply can be configured to suit the user’s needs. The setting force is 26 KN – for M4 to M10 fasteners. Setting stroke is 15mm and the weight loading time is just 3.5 seconds. Spin on and spin off time is a rapid 2.0 seconds (movement of the robot and of the workpiece not included).
