The support article says that Apple adheres to just 400 micron of flatness tolerances and anything outside of that range will qualify for a warranty fix or replacement. The company says that the bend will not get progressively worse, which may offer a small consolation for consumers who have reported the issue.
The strips are added using a process called "co-molding" where "plastic is injected into precisely milled channels in the aluminum enclosure where it bonds to micro-pores in the aluminum surface". Under normal usage, an iPad with 400 microns of bend will make it hard to spot with the naked eye.
According to Apple, the new design and the presence of antenna modems on the new iPad versions might make it easier for the slight bend to be visible by the customer from certain angles.
Both the 2018 iPad Pros and the 2017 iPad Pros support keyboard attachments and the Apple Pencil - though you need a different Apple Pencil depending on the year of the iPad Pro. After the plastic cools, the enclosure is finished with precision CNC machining operation.
The latest generation iPad Pro has been causing some controversy as many users claimed that they had a bent iPad the moment they opened the box. Apple attempted to explain away any appearances of bending with the iPad Pro by claiming that it's normal for the iPad Pro to be bent from the factory. It seems it's the process of combining plastic with antenna "splits" for the cellular model using a new co-molding technique that may result in slight bends. The product specifications dictate that the flatness of finished models can not deviate more than 400 microns. The company wants customers to know that this amount of deviation is perfectly normal and does not compromise the strength or durability of the tablet, and the company encourages customers that feel their tablet has bent more than is acceptable to either return the tablet or send it in under warranty.
Apple has faced problems before with the iPhone 6 and iPod nano bending, as well as "antennagate" with the iPhone 4. The device is likely to be replaced by a new one.
First and foremost, Apple begins by emphasizing that the iPad Pro comes to be following a high-quality and high-precision manufacturing process that leaves little room for mistakes. But it is imperceptible during normal use - and I use this iPad every day.
What the heck is 400 microns?
The 2018 iPad Pros do have slightly larger rear camera lenses, and more obvious antenna lines, but they're only available in silver and space grey.