I have an old thread that
@Martin Sweeney gave me this advice for ramifying crabapples, it worked well for me... You probably use this technique, but thought I'd copy and paste it here anyway.
For building ramification, you can cut back any time during the growing season. Just be aware that this can inhibit flowering on those branches for several years. The best practice for ramifying crabapples, and getting them to flower, is to nip the terminal buds early in spring when the new shoots are about an inch long. Then let them run for the remainder of the growing season, and in the fall, cut this year's shoots back to where you nipped them in the spring in. The next spring you should get 2 or 3 new shoots in those areas.
After you have nipped the early shoots, feel free to trim shoots that may be thickening too much and/or defoliate them to allow light to the inner parts of the plant. These branches are going to be cut off anyway.