Screwdriving

Application

What is robot screwdriving?

Screwdriving is one of the most common joining tasks in industrial assembly. Cars, home appliances, consumer electronics, furniture — everywhere multiple components are joined releasably. A robot with a servo-driven nutrunner sets every screw with the exact same torque, the exact same rotation angle, at the exact same position — shift after shift, millions of times without fatigue.

The economic and quality lever is particularly clear for safety-relevant joints: in automotive, medical technology and aerospace, complete screwdriving documentation is now mandatory. For traceability, liability, recalls — every single screw must be stored with values and time stamp. That is practically impossible to do manually anymore.

Principle of the screwdriving cell

An automated screwdriving cell consists of three core components working synchronously:

1. Robot — moves the nutrunner precisely to each screw position
2. Nutrunner — performs the screwdriving operation with torque and/or angle control
3. Screw feeding — supplies the next screw into the nutrunner so no manual loading is needed

Complemented by workpiece fixture, safety enclosure and control with logging. Via the cell control, all process data flow into the documentation in real time.

Nutrunner types

• Servo-driven DC nutrunners — the standard for controlled screwdriving. Torque, angle and speed freely programmable, values documented in real time. For critical joints.
• Electronic pulse nutrunners — high torque in a compact design (chassis, engine, gearbox screwdriving in automotive).
• Pneumatic pulse tools — high speeds, lower purchase cost, but less precise. Only recommended for uncritical joints.
• Common brands: Atlas Copco, Desoutter, Bosch Rexroth, Deprag, Ingersoll Rand, Cleco. For cobot integration: Spin Robotics, Kolver.

Screw feeding — critical for cycle time

Feeding often determines the cycle time of the entire cell. Four common principles:

• Vibratory feeder (bowl feeder) — the classic. Screws are lined up in the bowl and transferred to the nutrunner via a guide rail. For high throughput and standard screws. Downside: noisy, large, each screw type needs its own tooling.
• Blow feeding — screws are blown through a hose with compressed air directly into the nutrunner head. Very compact, flexible when changing screw types. For smaller screws and high flexibility.
• Strip feeding — screws on plastic strips (as with drywall screwdrivers). For very high quantities of a single screw.
• Bin picking — reaching into an unordered bin with vision. Highest flexibility but lowest cycle-time efficiency. For small and special series.

Cobot or industrial robot — two variants

Typical applications

• Automotive interior — cockpit assembly, door trim, seat screwdriving
• Automotive powertrain — gearbox, engine, axle screwdriving (high torques 100+ Nm)
• Consumer electronics — laptop, smartphone, home-appliance assembly
• White goods — washing machines, refrigerators, dryers
• Furniture assembly — cabinet cases, bed frames, office chairs
• Solar and battery manufacturing — module and cell screwdriving
• Safety technology — control cabinet assembly, electrical subassemblies

The NEXOS configuration

• Robot — cobot or industrial robot depending on the variant (see above).
• Nutrunner — servo-driven DC nutrunner depending on torque range. Market-open selection: Atlas Copco, Desoutter, Bosch Rexroth, Deprag, Spin Robotics.
• Screw feeding — vibratory feeder, blow feeding or strip feeding. For multi-screw-type: several parallel feeders or a bit change station.
• Workpiece fixture — with clamping, position indexing, workpiece positioner for two-station operation if needed.
• Vision system (optional) — for exact detection of screw points on tolerance-affected parts. Adjusts the path dynamically.
• NEXOS.Cube as the assembly cell. For cleanroom applications as a stainless-steel variant.
• Integration with NEXOS.DSP — for full screwdriving logging, batch traceability, MES/QMS integration.

Sequence of a typical cell

1. Load and fixture workpiece (operator or upstream cell)
2. Cycle start — position check via sensor or vision
3. Robot moves to the first screw position, nutrunner program is selected (for multi-screw-type)
4. Screw separation — feeder delivers a screw into the nutrunner head
5. Screwdriving — robot applies light down-force, nutrunner runs the program (pre-tighten, joining, final torque, re-tighten if needed)
6. Check — torque, angle, thread depth if applicable. NOK detected immediately.
7. Proceed to the next screw position until all positions are done
8. Remove or transfer workpiece
9. Log to DSP/MES/QMS with time stamp, values per screw, batch and tool ID

Why it pays off

• Cobot cell: investment 50,000-120,000 € (robot + nutrunner + feeder + cell). Typical payback 12-24 months in two-shift operation.
• Industrial-robot cell: investment 120,000-300,000 €. Payback 1.5-3 years in series operation.
• Quality improvement: screwdriving NOK rate typically from 0.5-2 % (manual) to <0.05 % (automated). Reduced rework, fewer field failures, fewer complaints.
• Traceability: legally required in automotive (VDA), aerospace (AS9100), medical (ISO 13485). Hardly economical to fulfil without automation.
• Ergonomics: repetitive screwdriving motions lead to RSI and tendonitis. Staff freed up for higher-value joining tasks.

Scalability

• Stage 1 — single cobot screwdriving cell with one screw type and vibratory feeder
• Stage 2 — multi-screw-type with two parallel feeders or bit change
• Stage 3 — two-workpiece operation with positioner/rotary table for continuous cell utilisation
• Stage 4 — vision-based position correction for workpieces with high production tolerance
• Stage 5 — connected assembly line with multiple screwdriving cells, material supply via HERROX.250, central MES

Expansion options

• Automatic bit change — for applications with >2 different screw types
• Vision positioning — dynamic path correction when workpiece position varies
• Force-torque sensor on the robot flange for haptic thread search on stripped or misaligned openings
• Screw presence sensor in the nutrunner — detects a missing screw before the screwdriving operation
• Digital twin via NEXOS.XR — virtual programming of new workpieces, collision check

Key sizing parameters

• Screw: type (head shape, drive), length, diameter, material, coating if any
• Torque range: nominal and maximum torque, tolerance
• Number of screws per part and number of different screw types
• Accessibility of the screw position — open, countersunk, in a blind hole, requiring on-site feeding?
• Reachability: which axis must the nutrunner approach? Angle adapters or gear heads may be needed
• Cycle rate in parts/hour and screws/part — determines cell design
• Traceability requirement (VDA, AS9100, ISO 13485, individual) — determines data scope and retention

Safety & traceability

• Collaborative operation possible at low torques, if necessary with a safety cover around the nutrunner head. From higher torques onwards, a closed cell.
• Emergency stop and two-hand control when loading — standard safety requirement.
• Traceability record per screw: workpiece ID, position, time stamp, actual torque, actual angle, result (OK/NOK), tool ID. Retention typically 10 years after subassembly delivery.
• Tool calibration — regular, in some cases required daily. Calibration result is logged as well.