Currently (All the Mods 9 version 0.2.46), it is not possible to make Sky Steel from scratch except by submerging ingredients in lava. However, all of its ingredients (iron ingot, charged certus quartz, and sky stone) are not immune to lava and will burn up after 10 seconds, regardless of if the recipe is successful.

If attempting to make more than 64 at a time, some of the ingredients will be voided, such that dumping 4 stacks worth of each ingredient in the same block of lava may only yield 150-400 sky steel instead of 512.

To alleviate this, a recipe using the Create mixer can be added, which takes the above-mentioned ingredients plus 250 mB of lava to make Sky Steel in an easier-to-automate way.

For reference, the Create mixer recipe for the Fluix Crystal can be found at: https://github.com/Creators-of-Create/Create/blob/mc1.20.1/dev/src/main/resources/data/create/recipes/compat/ae2/mixing/fluix_crystal.json
The recipe for the Sky Steel can be found at: https://github.com/62832/MEGACells/blob/64a144a15d1f04f29f7ff10ff8fe44aed859cf19/common/src/data/java/gripe/_90/megacells/datagen/CommonRecipeProvider.java#L178