Whenever any weekly payment has been continued for not less than six weeks, the liability therefor may, when the employee so requests and the commission deems it not to be contrary to the best interest of the employee or his dependents, or when it will prevent undue hardship on the employer or his insurance carrier, without prejudicing the interest of the employee or his dependents, be redeemed, in whole or in part, by the payment by the employer of a lump sum which shall be fixed by the commission, but in no case to be less than ninety percent of, nor to exceed, the commutable value of the future installments commuted so as not to exceed six percent nor to be less than two percent. The commission, however, in its discretion, may at any time in the case of a minor who has received permanently disabling injuries, either partial or total, provide that he be compensated, in whole or in part, by the payment of a lump sum, the amount of which shall be fixed by the commission but in no case to be less than ninety percent of, nor to exceed, the commutable value of the future installments which may be due under this title. Upon a finding by the commission that a lump sum payment should be made, the burden of proof as to the abuse of discretion in such finding shall be upon the employer or carrier in any appeal proceedings.