Thanks very much,it indeed can solve the problem for some of my parts. I have a project with may parts like this,but most of the parts still can not be unfold,it reminds the following information when i try to convert to sheet metal part,because the part itself is a solid,i don't know what do do about this,i also try to create a midleface,sew them together, trying to unfold using one-step analysis,but still no luck...it would be apprecaite if you could take more time to check this part for me.
Can I ask how these parts were created? For a valid sheet metal part, the material must be a constant thickness. Convert to Sheet Metal can convert most things and in some cases cleanup and/or optimize face are needed before converting. Take a look through the part and see if it can even be manufactured. for example, this area would be a challenge and may be the cause of Convert not allowing flattening.
See if you can adjust the geometry to get the following profile before trying to convert
Have a look at the attached. You'll note some areas have been removed - they would need 'fixing' too.