Every manufacturer fears errors in assembly. If defective screw connections result in product recall, the economic damage can be massive. Along with the training of staff, the use of high quality materials and the determination of processing parameters, it is the selection of the optimum screwdriving tool which plays a decisive role in guaranteeing the processing reliability of assembly procedures. Legal requirements and internal guidelines which must be adhered to can make the search for the right screwdriving tool a difficult one.
DEPRAG SCHULZ GMBH u. CO. has made a name for itself in the field of screwdriving both for handheld and stationary usage. Jürgen Hierold, Sales Manager at DEPRAG: “We support our clients in the selection of appropriate screwdriving systems and tools, thereby preventing product recall caused by faulty screw connections.”
One approach to fulfilling safety requirements is the selection of suitable screwdriving technology. Intelligent screwdriving systems based on EC-Servo technology allow the recording, evaluation and documentation of individual assembly steps. In combination with the screwdriving controller AST, the MINIMAT-EC-Servo screwdriver with highly dynamic drive technology enables free programming of screw tightening and offers maximum flexibility and processing reliability. The complete system consists of EC-Servo screwdriver, sequence controller and cable set.
The flexible system is suited to applications with high safety requirements, and those which require the direct measurement of control and regulating parameters. “In the automobile industry our EC-Servo screwdriving technology is the ideal partner for requirements of the risk class A: Danger to life and limb”, explains Hierold. This comes into effect when the failure of the screw connection could indirectly cause danger to life and limb.
DEPRAG screwdrivers, based on EC-Servo technology enable torque precision of <1% standard deviation which is maintained over millions of cycles. The machine capability index of ≥1.67 is thereby attainable with a tolerance value of ±5% relating to 6 sigma. A CMK value of 1.67 means that the fault rate is under 0.6 per million screw assemblies.
The use of brushless EC motors is a prerequisite for maintenance free operation without wear parts. They provide outstanding dynamics and high peak torques with the lowest space requirements – ideal for the tightening of screws. The sensor technology for the torque and angle measurement is directly integrated into the screwdriver. It enables precise control of screw tightening and as well as top precision, it guarantees reliable documentation of important processing parameters.
MINIMAT-EC-Servo screwdrivers are available for operator held as well as stationary use. The MINIMAT-EC-Servo screwdriver can reach high precision torques of 0.01 to 500 Nm.
A sequence controller AST with integrated power electronic is required for the operation of the MINIMAT-EC-Servo screwdriver. In the sequence controller standard screwdriving procedures are provided as complete basic programs. Amongst others, the available screwdriving procedures include tightening and loosening to torque, angle or an external stop signal.
Torque, speed, waiting time and rotational direction can all be individually adapted to the screwdriving task within the power range of each screwdriver. The parameters can be adjusted to the screw assembly task via web browser or touch screen. Through a combination of different screwdriving procedures with flexible tightening parameters, multi-level sequences can be complied quickly and conveniently and therefore realised within one assembly transaction.
Through this method, up to 120 screwdriving programs can be programmed. The sequence controller AST records the screw assembly results of the last seven production days.
The sequence controller AST5-S is required for the operation of the handheld screwdriver. The controller is particularly suitable for manual work stations with limited space because of its small size. The stationary screwdriver is operated together with the sequence controller AST40. If no touch display is required because e.g. the controller is being built into a control cabinet, an ASTi40 can be used. The software module required allows simple integration into a higher lever system controller.
System commissioning is carried out in very few steps. All the necessary functions are available in the web interface and touch display so no additional software need be installed. Comprehensive software add-on modules enable data recording and graphic display for statistical evaluations and screw joint analysis.
Varying tightening torques e.g. for direct screw assemblies in plastics or metal result in fluctuating pre-load forces. The tightening procedure DEPRAG Clamp Force Control (CFC) was developed as a new screwdriving procedure for EC-Servo screwdrivers in combination with the sequence controller AST40. Final tightening is carried out to difference torque or difference angle based on seating point detection. This results in a considerable improvement in constancy of pre-load force in comparison to purely torque guided tightening procedures.