THE PAINTING OF HEAT SENSITIVE

Transcription

1 THE PAINTING OF HEAT SENSITIVE Finishing '93 Conference October 25, 1993 Cincinnati, Ohio Society of Manufacturing Engineers Sponsored by the Society of Manufacturing Engineers and the Association for Finishing Processes of SME

2 Table of Contents The Painting of Heat Sensitive Plastics The New Dodge Viper Viper History Selection of Substrate Selection of Coating Material Standard Preparation of Panels + Maximum Preparation + Minimum Preparation Topcoat Repair Finessing

3 Viper History The Dodge Viper RTI10 is the latest attention grabber in the U.S. car industry. This high-performance sports car is the result of a bold experiment at Chrysler Corporation. Objective A concept Viper sports car was first shown at the Detroit International Auto Show in January The customer response was so overwhelming that in March 1989 Chrysler formed a small group called "Team Viper" to investigate feasibility and develop a plan. There were several program objectives but the key ones pertinent to the body panels are: low investment, accelerated development (3 years) minimum weight, and economy of scale even at low annual volume (3,000-5,000). Several molding processes were reviewed but the one that met key objectives was RTM. As there was limited knowledge and experience available in RTM body panels in the U.S. for Class A applications. Chrysler organized a team of experts from Chrysler and the supplier base to develop the technology. Material and Process Development Early prototypes of the body were made from room temperature cure epoxy tools and polyester/glass composites for design verification and development. The ability to build tools in a short 2-3 week period and also modify, if necessary, were key factors at these early stages of development. A prototype heated door tool was built to evaluate resins/filler/glass and gel coats to optimize the base composite. Several factors including paintability were considered in the selection of the materials. The quality and performance of RTM composite depends primarily on the resin system and also on the reinforcements. Several resin systems were evaluated and the one that met Chrysler's requirements was ICl's Modar. Since start-up, Ashland has also become a supplier. The next focus of attention was the Class "A" surface optimization. Chrysler formed an RTM task force consisting of material and process specialists from Chrysler, material suppliers and molders. A similar group, the Paint Task Force, consisting of Chrysler specialists, material suppliers and paint applicators also met weekly to develop the paint materials application and testing.

4 Painting The primer and the paint system used is based on a two-component urethane with a bake temperature of 180 F instead of conventional 250 F bake system. Lower bake temperatures improve the dimensional stability and surface quality. The Akzo Coatings primer and paint system was selected, as the primer system is sandable, and the topcoat system, a basecoatklearcoat, has superior gloss and distinctiveness of image (DOI). The urethane system also met a wide range of impact, chip and etch resistance requirements. The body panels are primed by the molders, painted by ASC, and shipped to New Mack Viper assembly plant on a specially designed shipping rack. Profiling Surface quality requirements have been defined through benchmarking the current European RTM body cars. Additionally several measuring instruments were evaluated to determine their effectiveness. The surface waviness and the paint requirements were developed and are shown in the following table. Surface Quality Requirements Viper Body Panels Panel Paint 1. Surface waviness index Avg. Mav 150 (Diffract0 D-Sight) 2. Distinctiveness of Image DO1 80 (Auto Specification) 3. Orange Peel 70 (Auto Specification) 4. Gloss 60 (Auto Specification) Diffracto's D-Sight audit station and a portable system have been extensively used for the measurement of the surface waviness of the molded parts at various stages including: as molded, post cured, primed and painted. D-Sight is a full field imaging technique that produces detailed images of surface variations of a panel or a tool surface. The images are then processed on a computer data base to quantify the surface waviness. The ability to measure defective areas in a tool prior to completion has been extremely helpful in developing and maintaining high quality tools. D-Sight is now being used as a quality assurance tool in the Viper assembly plant. Chrysler is well into production of the Dodge Viper RT/10. Actions are underway to increase production from 300 units the first year to over 3,000 units for Acknowledgment I would like to thank Nippani Rao of Chrysler Corporation for supplying information on the history of Viper.

5 Selection of Substrate The exterior appearance of the Viper was designed to recall the muscle sports cars of the 1960's and 1970's. The body is a product of some of the automotive industry's most advanced technology. It is the first car on the U.S. market with a majority of its body panels, both outer and inner, made from composite material formed by (RTM) a resin-transfer-molding process. It represents a 40% weightsavings over sheet metal. These panels include the car's inner and outer assemblies for the rear quarter panels, rear deck lid doors and the massive, single-piece hood and front fender combination (to date the largest individual plastics part on any U.S. built car). In addition, two of the parts, namely the sport cap and the windshield surround panel contain a metal reinforcement and a foam core under the RTM skin. The RTM process was selected because the process can be controlled more closely, stronger panels can be made, and tooling can be produced faster and lower cost. RTM is a very suitable process for a low volume, low investment and short development lead-time vehicle.

6 Selection of Coatings Obviously, a car of this standard required a perfect finish. Chrysler has achieved this with a paint system which was specially designed for the Dodge Viper. The system consists of a low-bake two-component primer surfacer, a two-pack basecoat system and a low bake, two-component clearcoat. All products can be baked at 150 F or above.

7 Material Standard Exterior Coating System for Resin Transfer Molded (RTM) Glass Fiber Reinforced Thermoset Composite. This standard presents the requirements of an exterior body color coating system for gel coated RTM conforming to MS-DBS65, and other substrates as specified. There are two coating systems covered in this standard. One coating system consists of a two-component acrylic urethane primer, and a two-component urethane baseklear topcoat. The second coating system is a black twocomponent urethane coating which can be applied directly to gel coated RTM and other substrates as specified. Primer, Basecoat, Clearcoat System Acceptable Performance Resistance Test (Chrysler Laboratory (MS-PP 1-1 Procedure) Test Duration) hours Pencil Hardness 463PB Fluid Resistance 463PB Cas, Oil, Anti- Freeze, Windshield Solvent DOI, Gloss, Orange Peel Autospect Tukon Hardness Salt Spray* 463PB hours *Applies to metallic substrates only.

8 Preparation of Panels A. Maximum Preparation Cleaning + Hand TSP followed by fresh water rinse and dry off + Power Wash System Chemical clean Tap water rinse Conditioner rinse water spot eliminator DI rinse Final DI rinse Dry off Degrease DA with 240 grit paper until surface is smooth. Do not break through gel coat Write up areas of porosity and fill Grind cracks, chips, etc. and fill with a glass reinforced filler similar to Duraglass Body finish seams, porosity and imperfections on top surface with a good grade of polyester body filler Block sand with 150 grit paper, followed by 240 grit paper on repaired areas only Apply up to 20 mils wet of a leading polyester based primer-surfacer Bake at 150 F part temperature for 30 minutes Block sand part with 240 grit paper and finish with 240 grit DA Tack off/vertical blow-off Apply 3 coats (1.3 mils per coat) of a good two-component acrylic urethane primer surfacer Flash for 15 minutes

9 Bake at 180 F for 30 minutes, can be baked at 140 F for 60 minutes Guide coat and wet sand using grit wet. Remove guide coat only Check for 100% coverage of two-component acrylic urethane primer surfacer. Re-prime if burned through Wipe down complete part with wax and grease remover to remove sludge, fingerprints, etc. Move to topcoat area Application Characteristics for Polyester Filler Spray Gun and Pressure B. Minimum Preparation Cleaning + Hand TSP followed by fresh water rinse and dry off + Power Wash System Chemical clean Tap water rinse Conditioner rinse water spot eliminator DI rinse Final DI rinse Dry off Degrease DA with 240 grit paper until surface is smooth. Do not break through gel coat Tack-offhertical blow-off

10 Degrease Apply 3 coats (1.3 mils per coat) of a good two-component acrylic urethane primer surfacer Flash for 15 minutes Bake at 180 F for 30 minutes, can be baked at 140 F for 60 minutes Guide coat and wet sand using grit wet. Remove guide coat only Wipe down complete part with wax and grease remover to remove sludge, fingerprints, etc. Move to topcoat area

11 Topcoat Paint Process Description 0 All parts will be received totally ready for final topcoat application, with primer coat applied. The surface shall be smooth, free of pits, dirt or any other type of inclusion Parts will be inspected, and if acceptable, will be loaded onto the paint dolly. The parts will be supported in a convenient spray position, essentially in car position, on a dolly designed to properly support the parts. Two separate and different dollies will be used to carry all of the above parts. If sanding is required on the parts before topcoating, all sanding or dirt producing operations will be performed in a separate area away from and separated from the clean room and spray area. Parts will be solvent wiped, using clean lint-free rags, with M-600 degreaser. Parts will be tacked-off immediately before entering the clean room for coating. Deionized air will be introduced to the body as it enters the clean room to remove any static electricity which may have been built-up on the parts. All parts will be sprayed manually, using the spray variables as shown on the attached spray information chart, with the following process steps: 1. Spray first coat of basecoat 2. Allow 5 minute flash 3. Spray second coat of basecoat 4. Allow 10 minutes of flash 5. Spray first coat of clearcoat 6. Allow 5 minutes of flash 7. Spray second coat of clearcoat 8. Allow minutes of ambient flash 9. Push dolly into oven for heat cure. Provide 15 minute heat-up followed by a 60 minute bake at 160 F or a 30 minute bake at 180" F 10. After cool down following bake, all parts will go to a well lighted inspection area. 0 0 Any panels showing dust or dirt in the clearcoat will be finessed and polished to remove any surface defect and produce a good part. (3M Finesses Repair System, attached) Any panel which cannot be finessed and polished to produce a perfect part would be resanded and reorocessed through the entire towoating mocess. v v 1

12 All finished parts will be placed in specially designed racks to properly protect the parts from any damage during transportation to the assembly point. Any panels damaged during transportation, or during assembly would be replaced with another good panel, and the damaged panel returned to the paint shop for repair. Application Characteristics Basecoat Applied Viscosity seconds #4 Ford Cup seconds #2 Zahn Clearcoat Applied Viscosity seconds #2 Zahn Spray Gun and Pressure

13 Area larger than repair 2. Mix color to recommendation a. Apply first coat or until covered b. Reduce 100% - fade out Viper Spot Repair Procedures 3. Mix clear 100:50:30 - Hardener and Fast Reducer a. Apply 1st coat b. Add 50 parts reducer; apply 2nd coat c. Add 50 parts reducer; apply 3rd coat 4. Empty gun cap leaving a small amount of clear in the bottom. Add fast reducer (approximately 1/2 cup). Apply light coats to blend edge until edge is dissolved. 5. Rebake in oven for one (1) hour at regular temperature or use heat lamp for one (1 ) hour on small areas. Materials Nikon 1200 & 2000 DeVilbiss Spray Gun & 30 air cap Compound 3M Microfinishing or Finesseit 3M Microfinishing Machine Glaze

14 Finessing Light Sanding - minimal 1500 grit. Preferred 9 micron film disc's Always sand in a circular motion Use a flat pad - small 1-3 inch pads are specifically made for this Water/soap to keep surface wet so not to create deep scratches Wipe with 75/25 water/lpa blend to remove sludge Compound Buffing - 2,400-3,300 RPM Polishing Wheel Air drive motor Use good quality wool pad Use specified products for initial polishing and scratch removing Keep surface wet with compound Use a flat movement with light pressure over the affected area Check and reapply more compound if necessary Polish to uniform good surface one that is scratch free Polishing - 7,000-10,000 OPM Orbital Wheel Diameter Can use cloth bonnet or foam pad Use specified finishing compound Use light back and forth motion over area to remove swirl marks Clean up - 50/50 IPA/Water Inspection - Mercury Vapor Lights

15 NOTES