This is absolutely possible and, in fact, encouraged. It is somewhat of a twist on the BRRRR strategy, Buy/Renovate/Rent/Refinance/Repeat. It may be a little more difficult in execution though. I would develop a relationship with some lenders now in order to understand what their requirements are going to be and ensure you will be able to meet them. They likely will want to see some seasoning on the investment before they will lend so be prepared for that and there will be LTV, DSC, and personal credit requirements that you will have to meet.
@Brian Jones Buying with cash taking out via HELOC is the same as buying with Cash. You can do delayed financing on the purchase within 60 days at the purchase price/appraisal. If you are making improvements and want a new appraisal, then there will likely be a 3-6 month seasoning.
DO NOT go to the lender that you have the HELOC with. Most HELOC's have a clause that does not allow you to use the funds for investing, business, flips, etc. If they find out they can recall the loan.
Upen Patel, Mortgage Banker
VA, FHA, Investor Loan Specialist
National Lender, Federal NMLS# 1374243