My problem is that I have used a 3D printing machine from the University and found out that the cover for the car was not smooth even after using sanding paper and painting it.
What material would work best to print the cover of the Cyber truck. I want it to be light and smooth.
I have to print it from any online companies that have this service here in Germany.
I have 3D printed models which were then sanded using progressively finer grades of sandpaper, terminating with wet sanding using micromesh to 12000 grit. The result was smooth and shining without any coating applied.
If your original results were not acceptable, the process may have been flawed and should be re-considered for technique.
For your purposes, as a body for a radio controlled vehicle, you'll want to consider something that can manage an impact reasonably well. ABS is going to be less expensive and provide some energy absorption but will have layer lines that require sanding and finishing. Layer thickness plays a substantial part in providing for good results and a smooth finish. I used 0.100 mm layers to get optimum smoothness.
You could request your model to be created in nylon using the SLS method, but the surface will be granular and would also require sanding to accomplish a smooth finish.
SLA or MSLA resin printed models will provide a very smooth surface, but the material is brittle and may crack during "on-road" use. You may find a printing service which offers to create using a more flexible resin, but you'd have to request that or confirm the selection when placing the order.
PLA is an obvious choice, but it has drawbacks compared with ABS.
I would consider ABS or ASA to be good choices for an RC-car body.
To get a really smooth surface, after printing with thin layers and good print settings to minimize strings and blobs, you will want to treat the surface. The two most common techniques are sanding and vapor smoothing.
Sanding is a great smoothing technique for PLA and even for ABS, but one must be careful. In addition to some of the sand paper grains being aligned as proper cutters to remove material, many grains are uselessly aligned and simply contribute to friction. The plastics used in FFF printing are, by definition, thermoplastics and will melt. One can easily soften and even melt plastic with dry sanding.
When the plastic softens, it can form little balls which dig into the surface, or stick to the surface. These hurt the surface finish like snowmen mar a field of freshly fallen snow.
Any sanding should be done wet, with wet-rated paper. Work up through the grits. Lower grit abrasive removes more material so that the surface can be "even". Lower grit lets you sand out the layer lines quickly.
Higher grit papers remove the scratch marks of the previous grit.
Generally, I go up by about 50% of grit number at each change.
When I am removing a lot of plastic and want to end with a glossy surface, I go through this sequence: 36->80->120->180->220->330->400->500->1000->1500->2500->3600->5000. Yes, I know that there are some big jumps there, but I haven't happened to stock papers at intermediate points, and it works for me. Depending on how smooth the surface already is, or how much material I must remove, I start further up the progressing. For 3D printed objects, I start at 220. The last three are critical.
Vapor finishing of ABS can give some very fine and glossy results. It is worth trying, although be aware that acetone mist is very flammable. If you are heating the acetone, treat it as life-threatening and possibly explosive.
If you use vapor finishing, consider that the acetone goes into the ABS. A warm soak or vacuum degassing could help remove it. You don't want the hood of your RC car to start bubbling in the sun as the acetone is motivated to escape.
You may consider PETG too. It's not as strong as ASA or ABS but it's much easier to print.
You can polish it by first sanding and then flame-smoothing.
See this video from CNC kitchen about comparing the different materials (ABS is not considered because similar to ASA in properties but more difficult to print) and see this video about flame-smoothing PETG.
