Coating & Painting

Application

What is robot painting?

In robot painting, an industrial robot guides an applicator (spray gun, rotary atomizer or powder gun) precisely along the workpiece surface. Result: consistent film thicknesses, defined path spacing, documentable application parameters — identical across shifts and batches.

Manual painting has three systemic problems: high material loss (overspray of up to 60 % is normal for hand application), inconsistent films and colour tones, and heavy exposure of the specialist (solvent vapours, monotonous posture). Skilled painters are becoming increasingly scarce — automated cells free up the remaining workforce for preparation and quality tasks.

The economic lever is often not staff saving but material saving: 30-50 % less paint through better atomization, precise application path and electrostatic attraction dramatically reduce material consumption. For high-value effect or 2K paints, the cell often pays back on this alone in 12-24 months.

Processes at a glance

• Wet painting — liquid paint, mostly solvent- or water-based. Application via airless (high pressure without air), airmix (combination) or HVLP (high volume low pressure, for fine surfaces).
• Electrostatic wet painting — paint droplets are charged and attracted to the grounded workpiece. Significantly less overspray, but the workpiece must be conductive and grounded.
• Powder coating — dry powder is electrostatically charged, adheres to the workpiece, is cured in an oven. No solvent, hardly any waste, robust surface. Standard process for metal parts.
• UV coating — liquid paint cured in seconds by UV light. For furniture, plastics, packaging — very fast drying, energy-efficient.
• Rotary atomizer (bell atomizer) — standard for automotive bodies and add-on parts. Rotating bell atomizes paint finely, electrostatically charged. Highest transfer efficiency (up to 90 %).

Pre- and post-treatment

Painting is only one of several process steps. For lasting quality, surface pre-treatment is decisive:

• Cleaning and degreasing — washing line, ultrasound or plasma cleaning removes oil, grease, silicones.
• Plasma activation — for plastic and hard-to-wet surfaces. Atmospheric-pressure plasma systems can be operated by the same robot with a tool changer.
• Primer — for adhesion and corrosion protection. Usually applied by the same or a second robot.
• Drying / curing — convection oven, infrared or UV. Robot hangs the workpiece into the oven and picks it up after the process.
• Post-inspection — visual inspection or vision system for film-thickness measurement, colour accuracy, defect detection.

Explosion protection (ATEX) is mandatory

In wet and powder painting an explosive atmosphere is created in the booth (solvent vapours or combustible powder clouds). Legal basis in the EU: ATEX Directive 2014/34/EU. The cell must be classified and equipped:

• Zone 1 (wet-paint booth, direct application area) — only explosion-protected equipment may be operated there.
• Zone 21 (powder booth, direct powder area) — analogous for combustible dusts.
• Ex-protected robots (FANUC P series, ABB IRB 5500, Kawasaki KJ, Kuka KR Agilus WP) are available in Ex design — with encapsulated electrics and pressurisation.
• Grounding of all conductive parts — workpiece, booth walls, robot, operator during set-up/rework. Electrostatic discharges are the most common ignition source.
• Emergency shutdowns and explosion pressure relief — booths need pressure relief areas (rupture discs) or active explosion suppression (Fike, Rembe).

Alternative: robot outside the Ex zone, applicator in the zone. The robot stands in the safe zone, only the applicator and material lines extend into the booth. Reduces cost significantly, but path flexibility is limited.

Typical applications

• Automotive — body (primer, base coat, clear coat), add-on parts (bumpers, mirrors, wheel arches), plastic interior parts.
• Mechanical and plant engineering — plant components, frames, housings powder-coated or painted with high-quality 2K paint.
• Furniture and wood industry — UV paint on furniture surfaces for fast drying and robust finishes. Kitchen and bathroom furniture production.
• Consumer goods and white goods — refrigerators, washing machines, appliances: powder-coated sheet-metal parts.
• Electronics — housing coating for EMC shielding, protective coating of PCBs (conformal coating).
• Construction industry — window frames, doors, structural steel with powder or wet paint.

Common challenges

• Programming effort — each new workpiece needs paths with application parameters (spray distance, speed, overlap). Offline programming with NEXOS.XR or the robot manufacturers' programming aids (FANUC PaintPro, ABB RobView, Dürr EcoRP series) reduce set-up time significantly.
• Colour change time — in small batches with multi-colour applications, circuit cleaning often dominates cycle time. Block changers or colour change stacks reduce purge losses and change time.
• In-line film-thickness measurement — useful for quality control but expensive. Alternative: statistical sample checks offline with magnetic induction or eddy current gauges.
• Maintenance and wear — nozzles, filters, paint circuits need regular maintenance. Neglected maintenance is the number-one cause of scrap.
• Isocyanates (2K PU) — avoid skin contact, extraction per TRGS 430. Only with appropriate PPE for set-up and maintenance.
• Booth climate — temperature and humidity control are not a nice-to-have but a prerequisite for consistent results. Too high humidity → condensation, too low → static charging.