(Song Pingping, mid/topcoat engineer at the Paint Shop of SAIC Passenger Vehicle Lingang Base, recipient of the Rationalization Suggestion Second Prize, Advanced Individual, and Seven-Color Pioneer awards.)
0. Introduction
Painted body surfaces after coating are typically brilliant and vividly colored. The gloss of the paint film surface generally exceeds 90% (slightly lower for metallic paint), approaching a mirror-like finish. On such a glossy surface, any defect becomes clearly visible, especially dust particles, which are extremely conspicuous. Currently, the main issue affecting the first-pass yield rate in our workshop is dust particles on body surfaces, accounting for 30% to 40% of defective vehicles off the line.
This article combines on-site experience to analyze the current state of dust particle control and prevention in the workshop.
1. Main Types and Sources of Dust Particles in the Workshop
1) Atmospheric dust, including various impurities (airborne dust and suspended particles).
2) Metal debris, originating from iron filings and zinc powder generated during body sanding.
3) Welding slag (beads), originating from electric welding which can produce large amounts of welding slag, some of which adheres to body surfaces and cannot be removed during pre-treatment.
4) Adhesive, originating from weld seam adhesive in body structural gaps.
5) Residual PVC sealant, originating from splatter during robotic or manual PVC sealant application that is not completely wiped off and remains on body surfaces.
6) Damping pad particles, originating from surface particle residue during damping pad installation at the sealing line, transferring to body surfaces or interiors.
7) Overspray agglomerates, originating from spray equipment such as spray gun nozzles, spray cups, or clothing, dripping onto the wet paint film.
8) Sanding particles, originating from electrodeposition and mid-coat sanding, including paint particles and sandpaper grit.
9) Fibers, originating from work clothing, gloves, air filtration materials, and spray robot protective suits.
10) Fixture and skid particles, originating from fixture collisions during door opening/closing and paint chip detachment; and particles from skid friction with roller beds during movement.
2. Workshop Dust Particle Process Control and Prevention Measures
2.1 For Atmospheric Dust Defects
1) While the workshop ADT cleaning company carries out daily cleaning plans, the workshop assigns dedicated personnel to track and evaluate the cleaning company's work (areas difficult to inspect during daily production, such as pre-treatment, electrophoresis tank cleaning, spray booth interiors, flash-off ovens, topcoat elevators, and mid/topcoat ovens in core areas), and develops relevant cleaning measures together with ADT based on changes in vehicle surface dust particle conditions.
2) The workshop establishes a 5S status maintenance system for work areas, with each section continuously monitoring its designated area and promptly reporting any cleaning-related anomalies to cleaning personnel for rectification.
3) The workshop divides cleaning zones by grade, with weekly dust particle monitoring for high-grade cleaning areas (such as spray booth interiors and flash-off ovens) to track the cleanliness status of high-grade cleaning zones.
2.2 For Welding Slag and Metal Debris Control
1) First, control source particles by urging the body shop to control particles on both the interior and exterior of the body-in-white, while pre-treatment electrophoresis engineers regularly confirm the particle status of incoming body-in-white at the workshop entrance.
2) Install high-power vacuum devices in the pre-treatment incoming pre-cleaning chamber to reduce welding slag and metal debris entering the pre-treatment electrophoresis system and contaminating the tanks.
3) Add deslagging and de-chipping process equipment during pre-treatment electrophoresis (such as combined filters, hot water wash buffer tanks, magnetic filters, paper band filters, and phosphating deslagging machines) to improve the efficiency of capturing welding slag and metal debris.
4) Pre-treatment electrophoresis engineers perform planned tank updates, maintenance, and cleaning while closely monitoring the status of deslagging and de-chipping equipment and filter bag replacement frequency. If abnormalities occur, they sample and analyze the relevant tank solution to identify the root cause.
2.3 For Electrophoresis Body Surface Adhesive Control
1) Pre-treatment electrophoresis engineers regularly inspect the body structural adhesive at sheet metal seams of the body-in-white to prevent adhesive overflow from contaminating the tank solution and affecting electrophoresis body surface quality.
2) Engineers perform daily inspections of high-flow spray and flood conditions in pre-treatment to prevent the spray and flood from washing off body seam adhesive and contaminating the tanks, which would affect pre-treatment electrophoresis body surface quality.
3) Conduct 5x5x5 surface quality sampling inspections at pre-treatment and electrophoresis exits; if surface quality abnormalities are found, promptly trace back to preceding processes for inspection.
2.4 For Underbody PVC Adhesive and Damping Pad Particle Control
First, the underbody adhesive booth must activate its supply and exhaust air system; a certain downward vertical air velocity prevents bottom PVC adhesive mist from splashing onto body surfaces. Second, both sides of the UBS hanger should be equipped with protective measures to prevent adhesive splatter.
(Note: This article is reproduced from industry publications for technical reference. The original author is Song Pingping from SAIC Motor.)
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