Electric tools for assembly
Assembly production strives for high-quality and precise screw joints. We all want each of the screw joints to be sufficiently tightened. Of course, for the said repeatability, sometimes several conditions are necessary. The screw joint must be tightened with the correct force and to the proper depth. In production, we are faced with new materials. Due to the cheaper production process, self-tapping screws are used more and more, which requires even more attention to screwing itself. Precisely due to the mentioned problems, it is necessary to choose tools that can monitor several parameters during the screwing process itself and thus ensure that the screw connection is always tightened correctly.
We will briefly present the screwing equipment used in today's production. Technological progress has an impact practically everywhere; innovations enhance the development of tools and production. Air tools have been used in manufacturing plants for decades. The most accurate in the field of air screw-driving tools are certainly air screwdrivers with a shut-off clutch. Air screwdrivers are intended for critical screw-driving in metal, plastic, composites and wherever the torque control is required. The mentioned screwdrivers can work in the tolerance range of the tightening torque +/-10%. However, everything definitely depends on the screw joint itself - whether we are screwing a soft or hard screw joint. The speed of the air screwdriver is selected by the type of planetary gear in the screwdriver. The nominal rate of the screwdriver is the same throughout the entire area from the beginning to the end of the screwing process. Air screwdrivers are sometimes used for self-tapping screws, but only under the condition that the tapping torque does not exceed the final prescribed target torque of the screw joint. Suppliers of screws usually prescribe a reduction in screw speed during the final tightening of the screw. Considering that air screwdrivers cannot reduce the rate of the screwing itself, they are not the best solution for screwing self-tapping screws.
Around 1990, the first power tools appeared in assembly productions, offering greater precision and accuracy and having more options in one tool. Cordless tools have become a standard on the production line because they allow freedom from hoses and cables: This has improved safety and ergonomics at the workplace. Production takes advantage of electric and battery-powered tools in all newly established factories. Even in existing factories, air tools are being replaced by electric and battery-powered ones due to the high costs of producing compressed air to drive pneumatic motors.
Electric screwdrivers allow greater control over the work process. The most basic screwdrivers from the group of electric screwdrivers are certainly screwdrivers with a cut-off clutch. They differ from air screwdrivers primarily in the possibility of setting the optimal speed in the entire screwing range. Electric screwdrivers can set a soft start at the beginning of the screwing process. They are equipped with non-contact sensors in the screwdriver, which detect the state of the screwdriver during the working process. The information about the state of the screwdriver can be monitored on the outputs of the control unit of the screwdriver.
Already, with the previously described tools that detect only the final cut-off torque, we can conclude with a reflection that the often-mentioned condition of monitoring the final torque itself is insufficient. However, the joint itself can also cause an improperly tightened screw. There can be several reasons for the mentioned cause:
- A missing part in the screw joint, such as a gasket or a washer, changes the entire characteristic of the screw joint.
- The quality of the screw can be poor, which leads to the deformation of the screw in the plastic zone of the screw.
- Damaged threads or impurities in the screw joint itself lead to an improperly tightened joint.
Tools with a shut-off mechanism will reach the target torque significantly earlier than a screw would normally have to be screwed. In order to control the problems mentioned above in screw joints, we monitor the turn of the screw during the entire screwing process. It is the next step to ensure accurate assembly production. Missing washers, missing threads, impurities in the joint, screws that are too short or the wrong screws lead to an incorrectly achieved tightening torque that will be outside the previously set tolerances of the screwing process.
To solve the mentioned problem, we have to use the screwdrivers that measure the desired tightening torque based on the consumed current of the screwdriver motor according to the previously calculated algorithm. These are screwdrivers with the current control. The mentioned tools enable regulation of the screwing speed itself, depending on the tightening torque in the screw joint. Tools with torque measurement depending on the electric current are an excellent choice for screw joints, where we do not have extremely fast changes in the screw joint. Given that the entire screw affects the final result of the tightening, the mentioned tools are not the most desirable for safety-critical joints, where we need to attach a report and traceability of the calibrated torque value of each tightening.
Safety-critical screwing is screwing in which there is a risk in the use of the final product if the screwing is not performed correctly. An example of a critical screw joint is screw joints that are critical in a passenger car for personal safety. To minimize the number of recalls, manufacturers must demonstrate that critical joints are tightened correctly. The evidence mentioned above of the tightening of screw joints is only possible with advanced controlled screw tools with a built-in calibrated measuring probe. The mentioned tools enable torque and angle control with a built-in measuring probe located at the end of the output of the screw tool. They also allow us to regulate the speed at any time during the screwing process and to store the parameters of each screwing. This is the only way to prove or find an error in a particular part of the screwing process. The measuring probe in the screwdriver is calibrated according to the prescribed protocol. The mentioned tools with a measuring probe (»DC tools«) allow the most comprehensive view into the assembly process.
The screw system with a measuring probe also enables multi-stage screwing in several steps. The mentioned advantage allows us to optimally set the speed, torque, and turn at any moment during the tightening process.
We will briefly present the screwing equipment used in today's production. Technological progress has an impact practically everywhere; innovations enhance the development of tools and production. Air tools have been used in manufacturing plants for decades. The most accurate in the field of air screw-driving tools are certainly air screwdrivers with a shut-off clutch. Air screwdrivers are intended for critical screw-driving in metal, plastic, composites and wherever the torque control is required. The mentioned screwdrivers can work in the tolerance range of the tightening torque +/-10%. However, everything definitely depends on the screw joint itself - whether we are screwing a soft or hard screw joint. The speed of the air screwdriver is selected by the type of planetary gear in the screwdriver. The nominal rate of the screwdriver is the same throughout the entire area from the beginning to the end of the screwing process. Air screwdrivers are sometimes used for self-tapping screws, but only under the condition that the tapping torque does not exceed the final prescribed target torque of the screw joint. Suppliers of screws usually prescribe a reduction in screw speed during the final tightening of the screw. Considering that air screwdrivers cannot reduce the rate of the screwing itself, they are not the best solution for screwing self-tapping screws.
Electric screwdrivers allow greater control over the work process. The most basic screwdrivers from the group of electric screwdrivers are certainly screwdrivers with a cut-off clutch. They differ from air screwdrivers primarily in the possibility of setting the optimal speed in the entire screwing range. Electric screwdrivers can set a soft start at the beginning of the screwing process. They are equipped with non-contact sensors in the screwdriver, which detect the state of the screwdriver during the working process. The information about the state of the screwdriver can be monitored on the outputs of the control unit of the screwdriver.
Already, with the previously described tools that detect only the final cut-off torque, we can conclude with a reflection that the often-mentioned condition of monitoring the final torque itself is insufficient. However, the joint itself can also cause an improperly tightened screw. There can be several reasons for the mentioned cause:
- A missing part in the screw joint, such as a gasket or a washer, changes the entire characteristic of the screw joint.
- The quality of the screw can be poor, which leads to the deformation of the screw in the plastic zone of the screw.
- Damaged threads or impurities in the screw joint itself lead to an improperly tightened joint.
Tools with a shut-off mechanism will reach the target torque significantly earlier than a screw would normally have to be screwed. In order to control the problems mentioned above in screw joints, we monitor the turn of the screw during the entire screwing process. It is the next step to ensure accurate assembly production. Missing washers, missing threads, impurities in the joint, screws that are too short or the wrong screws lead to an incorrectly achieved tightening torque that will be outside the previously set tolerances of the screwing process.
To solve the mentioned problem, we have to use the screwdrivers that measure the desired tightening torque based on the consumed current of the screwdriver motor according to the previously calculated algorithm. These are screwdrivers with the current control. The mentioned tools enable regulation of the screwing speed itself, depending on the tightening torque in the screw joint. Tools with torque measurement depending on the electric current are an excellent choice for screw joints, where we do not have extremely fast changes in the screw joint. Given that the entire screw affects the final result of the tightening, the mentioned tools are not the most desirable for safety-critical joints, where we need to attach a report and traceability of the calibrated torque value of each tightening.
Safety-critical screwing is screwing in which there is a risk in the use of the final product if the screwing is not performed correctly. An example of a critical screw joint is screw joints that are critical in a passenger car for personal safety. To minimize the number of recalls, manufacturers must demonstrate that critical joints are tightened correctly. The evidence mentioned above of the tightening of screw joints is only possible with advanced controlled screw tools with a built-in calibrated measuring probe. The mentioned tools enable torque and angle control with a built-in measuring probe located at the end of the output of the screw tool. They also allow us to regulate the speed at any time during the screwing process and to store the parameters of each screwing. This is the only way to prove or find an error in a particular part of the screwing process. The measuring probe in the screwdriver is calibrated according to the prescribed protocol. The mentioned tools with a measuring probe (»DC tools«) allow the most comprehensive view into the assembly process.
The screw system with a measuring probe also enables multi-stage screwing in several steps. The mentioned advantage allows us to optimally set the speed, torque, and turn at any moment during the tightening process.