How to submit angular reactive form by appending it to Formdata in easiest way?

onSubmit() 
{
const formData = new FormData();
formData.append('auth_sign', this.invoice_form.get('auth_sign').value);
}

The above method is working fine but is there any alternative way to append the reactive form to FormData because i have 31 fileds to post. so, if i append in this method my lines of code will get increased.