How to disable the title field on the node edit form?
You can use hook_form_alter() function to alter any form (including node edit form) and disable Title field. Check sample code below:

use Drupal\field_collection\Entity\FieldCollectionItem;

function [MODULE_NAME]_form_alter(&amp;$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  switch ($form_id) {
    case 'node_[CONTENT_TYPE]_edit_form':
      $form['title']['#disabled'] = 'disabled';
      break;
  }
}


If you're altering only one form you can check hook_form_FORM_ID_alter() function and change FORM_ID with node_[CONTENT_TYPE]_edit_form where CONTENT_TYPE is your node type form.

EDIT :

To automatically set node title without allowing user to see title field, you can use Automatic Entity Label Module. The module is in dev version for D8, but we can give it a try if functioning properly.

If don't want to use Automatic Entity Label module, you can try doing same with custom code, check sample code here