Achieving the required accuracy in bolt tightening is critical. If torque or angle falls short of specification, the constantly varying loads encountered while the vehicle is in motion can cause bolts to loosen or even fall out—potentially endangering lives. Take the driveshaft as an example: its tightening specification is 15 Nm ± 1.2 Nm followed by an additional 95° ± 7′ 2″. Both torque and angle must be kept within ±10 %. Any significant deviation risks either shearing the driveshaft bolt or leaving it loose. Because the consequences of improper fastening are so severe, operators must achieve absolute reliability during tightening. Relying solely on operator attentiveness or personal habit is clearly inadequate, and the results of manual work lack traceability, making it impossible to verify whether each bolt has actually been tightened to the specified torque range.

In earlier plants—and still in some lines today—workers tighten bolts with conventional pneumatic drivers and then check torque with a manual torque wrench, sometimes adding a prescribed angle after the torque is reached. This approach only solves part of the problem; many issues remain:

1. Missed bolts
   Purely manual tightening cannot prevent operators from inadvertently skipping one or more bolts.

2. Incorrect torque
   Ordinary tools cannot guarantee the required accuracy, especially for angle control, which is almost impossible to measure reliably on the shop floor.

3. Double tightening
   Conversely, operators may skip a bolt, then mistakenly re-tighten one that has already been finished.

4. Defective threads or bolts
   If a tapped hole is obstructed or partially stripped, the bolt may reach a high peak torque after only a small rotation (as if jammed), or it may spin several turns without achieving the required torque (as if freewheeling).

5. Discontinuous tightening or premature shut-off
   Manual operation is inherently inconsistent; the timing of each phase, pauses, and the constantly changing torque and speed cannot be guaranteed. Complex tightening strategies are impossible to execute manually.

6. Wrong torque values for the vehicle
   Most plants run multiple models on the same line to save cost and boost efficiency, so a single tool must handle several torque specifications. Relying on operators to select the correct value in a busy mixed-model environment inevitably leads to errors.

7. Lack of traceability
   Because high-precision bolts have a major impact on vehicle life and safety, automakers must be able to demonstrate compliance to customers for the entire service life of the vehicle. Conventional tightening leaves no verifiable record, undermining quality assurance.

Clearly, reliable threaded joints are essential in automotive assembly. Drawing on years of intelligent-tightening experience in the automotive industry, Danikor has independently developed the DK electric screwdriver to raise tightening quality in Chinese automotive plants and help the industry advance faster and better.

The tool typically consists of a brushless DC motor equipped with torque and angle sensors, connected by cable to an electronic control unit (ECU). The ECU contains a motor-servo drive and microprocessor-based control electronics that acquire, process, and report tightening status. Recorded data can include final torque and angle for each cycle, parameter sets, date/time stamps, and statistical values based on predetermined sample sizes or all data, as required. All data can be uploaded to the EMS system on demand. In addition, the ECU accepts external commands from intelligent devices such as PLCs and provides external outputs to line controllers or data-collection networks.

When production tightening begins, the operator simply presses the start button; the electric screwdriver executes the programmed tightening sequence, monitoring both torque and angle simultaneously.

After tightening, the screwdriver’s ECU transmits the results to the EMS host database, including both pass and fail outcomes. Failures are flagged as single-bolt or multiple-bolt rejects. In either case, the control panel displays the name of the failed bolt, and the database records each bolt’s torque, angle, and pass/fail status.

When a failure occurs, the operator switches the ECU to manual mode and re-tightens the bolt by hand. After completion, the operator stamps the contingency form. Later—either a few stations downstream or at final line-off—quality-control personnel verify the torque of every bolt flagged as failed in the EMS system.

The screwdriver’s ECU can store 2,000 tightening records and upload them to the EMS, ensuring that the tightening data of every bolt on every vehicle can be retrieved. Each year the EMS performs statistical analysis on all tightening results for a given bolt, using the findings to assess the screwdriver’s accuracy and to guide calibration.

Today, Danikor electric screwdrivers are widely used by major automakers, enabling fully automatic tightening, improving assembly quality, increasing customer satisfaction, and delivering cost savings and efficiency gains.