What quality of materials do they use?
Good quality materials, just like any manufacturer.
For example, their direct drive motors, valves, pumps, outer tubs etc. As any other factory in the world (including the USA, of course) They have dozens of suppliers for parts because it simply doesn`t make any sense to make 100% of the parts for a washing machine. Some suppliers can even be the same suppliers as other famous brands.
How big are their direct drive motors in terms of size and thickness? Does it matter A bigger motor doesn't exactly mean it is better or stronger or will last longer.
As for their matching dryers, what type of belts and blower motors do they use? They use the type specified by the engineers for each specific model, just like any other manufacturer.
What is the quality of their materials? Good and Excellent. All washers have pros and cons. Even the best washer in the world has it's weak points and the worst washer in the world has it's good points.
How big is their appliance manufacturing plant? VERY big. They make not only for the USA, but for many other countries and also OEM for other companies.
This is specifically for their washers and dryers. Do lg washers and dryers use some sort of grease to keep them running smoothly? It is very difficult, if not impossible, to find a modern washer that uses grease.
Both LG and Samsung know how to make washers and they know it very well. Even the BOL models have more technology than traditional American brands like Whirlpool, specially on bells and whistles.
Both Samsung and LG invest a lot of money in new technologies and quality.
And just like any other washing machine in the world, someday they will break. What doesn't exist is a washing machine that will last 100 years without any failure.
