Rivet nuts

The rivet nut is a one-piece element with a round or hexagonal shank with an internal thread and a head, which fastens and provides a full thread in a thin-walled workpiece. A pulling tool is required for the setting process, with a mandrel that can spin up and down the blind rivet nut.

The rivet nut is available in closed design, with shaft knurl or under-head serration. The design of the hexagon is partly restricted to the area directly under the head.

The special design with external thread is a blind rivet stud or also blind rivet threaded bolt. The processing is carried out with the same basic device with a corresponding tool with internal thread. The blind rivet stud is usually made of two parts which are welded or pressed together.

The core piece of the processing is the setting unit

The setting tool for the processing of blind rivet nuts has a strong hollow piston cylinder as a base, which is guided at both ends of the piston rod with a large distance between them. Due to the piston diameter of 40 mm it has large power reserves for industrial use. At the extension of the piston rod there is a mandrel with mouthpiece which is matched to the rivet nut used. The setting tool is designed for rivet nuts M4 - M10. The setting force is selectable with 5, 19 or 31 kN depending on the pressure intensifier with oil reservoir. The setting stroke is 12 mm. The brushless gear motor ensures a spindle speed of 500 rpm and a spindle speed of 1000 rpm.

The setting tool is well suited for attachment to a linear unit, for expansion with automatic feeding of the rivet nut and ideal for robot applications. A main focus during the design of the setting unit was the realisation of the process monitoring.

Semi-automatic manual workstation

In semi-automatic solutions, the setting tool is suspended movably in its correct position for processing and the weight is compensated by a balancer. This is a device stand with linear guides. The pressure intensifier is arranged so that the hose length is as short as possible without restricting the movement possibilities.

In the switch cabinet there is an electrical control unit with the Siemens logo and a controller for the gear motor. The pneumatic control is carried out via a solenoid valve for switching off the setting force when the specified value has been reached at the measurement amplifier. The Digiforce 9311 measurement amplifier provides a fully-fledged process monitoring system with pressure and displacement sensor. Alternatively, the force-controlled switch-off can also be performed with an intelligent pressure sensor.

Automatically process blind rivet nuts

With the fully automatic setting unit, the workpiece is automatically positioned and also transported further after the setting process. The setting unit is mounted on a linear unit with which the rivet nut can be positioned in the workpiece bore. The unit is mounted on a multi-axis handling system or on a robot. In another version, the robot takes over the positioning of the workpiece. The rivet nut is blown into the transfer with compressed air and positioned with a pick-and-place to the thread adapter in front of the mouthpiece. A brushless DC gear motor is used to wind up the rivet nut. With the linear unit the blind rivet nut is positioned in the bore of the workpiece and the setting process is triggered. After unscrewing the mandrel, the setting unit moves back and the pressure intensifier is relieved.

The feeding system consists of a spiral conveyor, which is also equipped with a sound insulation and cover if required. The rivet nuts are fed in a hanging position from the spiral conveyor into a linear conveyor, which is equipped with a jam control. After the linear conveyor is the separating device, from which the blind rivet nut is shot into the transfer.

The two control units of the feeding technology are mounted on a base plate. If larger quantities of rivet nuts are to be stocked, a bunker in front of the spiral conveyor and a level monitoring system in the spiral conveyor can be provided.

The pressure intensifier is arranged in the system according to the movements of the setting unit and the shortest possible hose length. The pressure sensor for process monitoring is located on the pressure intensifier. On a further console is the measured value amplifier for process monitoring, which is connected to the plant control system (PLC) via Profibus or Profinet.

In process monitoring, the pressure and the path of the setting process are recorded and the curve is monitored by means of defined windows. The entry and exit of the curve must take place at a specified position in the windows so that the setting process can be evaluated with IO.