High strength rivet

The high-strength rivet is a two-piece element that is used for joints subject to higher stresses. The rivet consists of a rivet sleeve with shank and rivet head and a mandrel. During the setting process, the mandrel head is pulled against the sleeve, which thus forms the closing head, and the mandrel is torn off at its predetermined breaking point. The mandrels are usually provided with grooves for a better transmission of the force. A pulling tool is required for the setting process.

The core piece of the processing is the setting unit

The setting tool for the processing of blind rivets 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. The extension of the piston rod is equipped with a clamping mechanism adapted to the blind rivet used. A vacuum generator is integrated in the setting unit to remove the mandrel after the setting process. Different pressure intensifiers with oil reservoir are used for the drive, which are equipped with the transmission ratios 9,7, 38 and 61, depending on the requirements of the setting forces. The setting tool is well suited for attachment to a linear unit, for extension with automatic feeding of the high-strength blind rivet and ideal for robot applications. A main focus during the design of the setting unit was the realization of the process monitoring.

Manual workstation as semi-automatic solution

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 tool stand with articulated arm. The mandrel container is arranged in such a way that the tube length is as short as possible without restricting the movement possibilities. The control is purely pneumatic and the release is done via the handle valve or optionally via a foot valve. The vacuum is then switched by a pneumatic timer to transport the mandrel into the mandrel container. If optional processing with process monitoring (pressure and travel) is required, a setting device with separate pressure intensifier is used. However, the measurement amplifier, the pressure sensor and the analogue displacement sensor must then be provided with a power supply. In this case, the indication of the process monitoring is shown on the display of the measurement amplifier.

Fully automatic and monitored processing

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 blind rivet 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 blind rivet is blown into the transfer with compressed air and is then inserted into the mouthpiece with a pick-and-place. In the case of a vertical arrangement, the blind rivet must be held in place by the vacuum or by a pre-pressure before positioning in the workpiece can take place. With the linear unit, the blind rivet is positioned in the bore of the workpiece and the setting process is triggered. After the mandrel is torn off, the setting unit moves back and the pressure intensifier is relieved, releasing the mandrel and allowing it to be sucked off.

The feeding system consists of a spiral conveyor, which can also be equipped with sound insulation and cover if required. The blind rivets are fed from the spiral conveyor in a hanging position into a non-driven accumulation section which is equipped with an accumulation monitoring system. After the accumulation line there is the separating device, from where the blind rivets are shot into the transfer.

The control unit is mounted on a base plate with the feeding equipment. If larger quantities of blind rivets are to be stored, a bunker in front of the spiral conveyor and a level monitoring system in the spiral conveyor can be provided.

The pressure intensifier and the mandrel container are arranged in the system according to the movements of the setting unit and the hose lengths selected to be as short as possible. The pressure sensor for process monitoring is located on the pressure intensifier. On a third console is the measurement 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.

Simplified, the first window shows whether the bore diameter was within the tolerance range. The second window shows whether the breaking load required for a completely finished setting process has been reached.

A hose sensor can be used to monitor the successful transport of the mandrel into the mandrel container.