The correct screwdriver as a guarantor for high quality

Process reliability starts with the selection of tools / Basic information regarding screw assembly technology

The correct screwdriver as a guarantor for high quality
(PresseBox) ( Amberg, )
In the domain of technology, screw joints are the most frequently used method for joining components and, in many cases, to separate them again.

Screws can be tightened and loosened again without damaging the connected components in most applications. In today's environmentally aware times, people have come to understand the value of the materials contained in defunct consumer goods. The edict is "prudent reuse of resources". If we consider recycling demands alone, it can be argued that screwed connections have their undeniable place in modern assembly processes. One can only effectively disassemble an item for targeted re-use if it was screwed together.

The screw assembly process gives the impression of being a very simple task, but in the assembly process it is encumbered with many potential pitfalls. From the moment the screw is seated, the assembled components behave like a single part. It is the task of the screw to clamp the components together with sufficient force so that normal use will not influence the integrity of the assembled joint. Achievement of this force - called pre-tension force - is defined by the designer, but can only be measured with great difficulty and effort during factory assembly. This poses a huge problem for the goal of zero-defects . Since "Pretension" cannot be measured using practical methods during assembly, the "Torque" value is used. The Torque value can be derived from the required pre-tension force and has therefore become the process-control measurement in screw assembly.

Every manufacturer strives to aviod quality issues as a result of faulty screw joints. They can result in product recall campaigns or the return of an entire batch of product from the end user, The economic and market image damage can be significant. Besides training of staff and the use of high quality materials, selection of the correct screwdriver for the application plays the main role in order to ensure reliability in the assembly process.

DEPRAG screwdriving expert, Rudolf Schmidbauer, relates from experience: "A screw task can only be performed with process reliability, when the work is performed by high precision screwdriver spindles". In the screw assembly case study laboratory at the Head Office of DEPRAG SCHULZ GMBH & CO. in Amberg/Bavaria, Mr. Schmidbauer assembles and loosens screws on a daily basis, measures the quality of the screw joints and analyses product design and materials. "It is important that the screwdriver spindle is optimized for the application".

In his laboratory he works with screwdriver spindles produced by Deprag. And he loves working with them: "Our screwdriver spindles are not only reliable and have an extremely long service life. But the drives are very quiet and the ergonomic design is well-thought-out. They are light and fit the hand comfortably. These factors help to protect the worker from fatigue, even when involved in industrial mass production".

The DEPRAG product range is very broad. Besides screwdriver spindles, designed for automated machinery, the focus is also on manual screwdrivers for industrial mass production. The full service provider DEPRAG has developed a competency in the field of screw assembly technology over decades of first hand experience. The screwdriver spindles can be combined with DEPRAG measurement technology or with the proven DEPRAG screw feeder systems. Sales Manager Jürgen Hierold is confident: "We can offer the suitable screwdriver spindle for every screw assembly application at an attractive cost-performance ratio.

The industry wide spectrum of demanding screw assembly tasks are addressed by the MINIMAT/MICROMAT manual screwdriver series. With torque a range from 0.02 to 80Nm, configurations for every application and the most modern motor7drive technology, they achieve maximum process reliability at every step. Depending on the application, the user can select between a straight design for vertical screw insertions, pistol grip design for horizontal screwing and angle head design for confined spaces and higher torque requirements. Besides the proven pneumatic screw spindles with which DEPRAG made their mark, the extensive portfolio comprises a series of distinguished electronically driven screwdrivers. But which screwdriver spindle is best suited for which screwing task?

The MINIMAT-EC servo screwdriver spindle with a reliable and low maintenance brushless EC motor, offers a high degree of process reliability for industrial production Maximum flexibility is achieved with this drive technology and the associated AST30 control system, which is suitable for manual or automated assembly process. All essential process parameters are set in the control system. an Integrated torque transducer and an angle encoder measure the torque and angular displacemrnt actually applied by the tool. These values can then be documented and evaluated for purposes of quality control.

The MICROMAT-EC for smaller torques from 3 to 80Ncm as well as its big brother MINIMAT-EC have a brushless electronic drive and the associated AST10 motor control system combined with angle measurement. The process parameters for the screw assembly task are stored, processed, documented and evaluated by the screwdriver controller.

Both screwdriver spindle families, with EC and EC servo design, allow interface to a higher level control system, e.g. for controlling statistic process data.

The digital electronic screwdriver spindle MINIMAT-ED, recently developed by DEPRAG, has proven to be a flexible all-rounder. When the adjustable screwdriver torque is reached, it switches off reliably and very precisely via an electro-magnetic clutch mechanism. The required torque is conveniently entered by the worker via on board controller and user interface directly on the screwdriver spindle, where the entered value is displayed on an easy to read LED display. The MINIMAT-ED is especially suited for workplace benches with variable assembly tasks and torque requirements. Therefore it is ideally suited for serial manufacturing re-work, and in the volume recycling or repair industry.

The DEPRAG pneumatic screwdriver spindle MINIMAT/MICROMAT with pneumatic drive is suitable as a basic solution for any screwing task where documentation is not required. Its specially designed, high precision shut off clutch allows torque repeatability of less than +/- 3% standard deviation. This level of repeatbility can be relied upon for millions of cycles. The DEPRAG shut off clutch reliably prevents "over torque", as is bemoaned for conventional stall type screwdriver spindles. The design of the shut off clutch system also insures that the DEPRAG screwdriver spindle repeatability is assured regardless of compressed air fluctuations. The Screwdriver performance can be verified by means of relevant torque measuring devices.

The manual screwdriver spindle MICROMAT-F/MINIMAT-F is equipped with additional functional control for error proofing of a manual work station. The associated fc 20 control system is designed to oversee and control screw assembly processes. In case of faulty or incomplete assembly sequences, the FC20 control system blocks the connected F screwdriver spindle from further operation and can control the release of subject parts for the next process. The subsequent assembly process can only be started if the previous task was completed properly. The correct number of tightened screws per assembly can also be controlled. The screwdriver spindle therefore checks its own performance (and that of its operator).

The DEPRAG SENSOMAT is design specifically for self-tapping, thread cutting or self drilling screws. For many of these types of screw assemblies, the torque required to form the screw threads is close to the torque required for final screw seating or potentially even higher, due to high friction during the thread forming process.

The DEPRAG engineers have adapted the SENSOMAT for this problem. It first screws in the screw at full power and only enables the shut off clutch shortly before the screw head is seated. In this way the required final torque can be achieved accurately without damage to the screw joint.

There are numerous manual screwdriver spindles for special applications in the product range of the screwdriving specialist in the Upper Palatinate in Bavaria. DEPRAG pulse screwdrivers - straight and in pistol grip form - are available with and without an auto shut-off clutch. These are impact screwdrivers, however, with a hydraulic impulse mechanism. The pulse screwdrivers are characterised by high torque, high repeatability of torque and minimal torque reaction. In addition they operate at a very low noise level when compared to a traditional non hydraulic impact driver.

DEPRAG impact drivers are furnished with a pistol grip or fist grip. For impact screwdrivers without a gearbox, the hammer is connected directly to the rotor. Energy is "accumulated" with every rotation, which is then transmitted via movable clutch dogs as a powerful impact onto the drive shaft. Impact drivers are suitable for torques between 90 and 2,100Nm.

The MINIMAT-T depth shut-off screwdriver spindle is designed specifically for applications where the screw must be stopped at depth only, not torque. For example, when fastening wood screws or plasterboard to a frame, where a consistent torque value cannot be relied upon. A sensor sleeve, which is set to a defined screw depth/travel value, captures the screw depth and precisely triggers the shut-off clutch of the screwdriver. In this way every screw is seated to the specified depth. The VARIOMAT on the other hand was developed specifically for the wood industry. The user can employ it for both drilling and screw assembly in one step. Its extensive accessories present a magnitude of application options.

The RECYCLING screwdriver is a special version for the recycling industry. Before chemical or thermal treatment of electronic scrap, the parts must first be disassembled. The DEPRAG special application screwdriver spindle aids the bit to screw head engagement by ramping up the screwdriver speed and applies the necessary end-load pressure onto the screwdriver bit right from the start, in order to prevent camb-out or stripping of the screw drive. Increased loosening or reverse torque due to corrosion or deformation is compensated through the ergonomic pistol grip of the screwdriver spindle in horizontal applications, or limited by an adjustable safety clutch (LH operation) for vertical applications.

The DEPRAG pneumatic screwdriver with slip clutch is suited for screw assembly applications where torque accuracy is not ciritical. It is available in straight design, pistol grip or angle head design. If screws have to be assembled with limited vertical access , the flathead screwdriver can be applied. It is designed to assemble screws from M3 to M18 and is furnished with interchangeable tool adapters - square drive and hexagon socket. An open head is available for over pipe nut assembly. When the air supply to the flathead screwdriver spindle is turned off, the worker can also use the wrench to tighten the fasteners manually in the same fashion as a manual tool.

Ergonomic design of the tools has always been an edict of DEPRAG product development.. "We have therefore designed the grips according to latest medical insights" is how Sales Manager Jürgen Hierold explains the advantages of the MICROMAT/MINIMAT screwdriver spindle family. The high power density of the motors allows a very slender construction and a convenient light tool weight. "The MICROMAT screwdriver spindle for the lowest torque values, is approximately the size of a ballpoint pen. With its slender form it is designed with special recessed grips, helping to prevent strenuous postures".

Strenuous posture or forearm fatigue as a result of gripping, are addressed in the MINIMAT screwdrivers by a well thought-through design. DEPRAG Development Manager for serial devices, Gerd Zinn, explains: "The design of the hand grip as a modified square grip complies with the natural anatomy of the hand and allows friction-and form-fit force transmission. Less worker fatigue promises higher quality in industrial applications of the screwdriver spindles".
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