Thank you for your question about whether you can use "create" instead" of "generate" in the following sentence:
"General speaking, some reject products will be created at the beginning, in the middle or in the end of producing proceess."
Your suggested usage is correct. You can also use"made" or "produced".
Please note that we use the preposition "at" when talking about the beginning or end of something and we use production process (a noun-noun combination) to describe how somthing is made.
Therefore, the final part of the sentences should be:
"or AT the end of the producTION process"