add_action('cred_save_data', 'my_save_data_action',10,2);
function my_save_data_action($post_id, $form_data)
{
    // Change your Form ID
    if ($form_data['id']==280)

    {
         //Declare the content of your variables
        $custom_title = get_post_meta( $post_id, 'wpcf-firstnamecpt' , true );
        $custom_title.= ' ';
        $custom_title.= get_post_meta($post_id, 'wpcf-last-namecpt', true) ;
//adding to post_meta because function only appears to take 1 value.
        //collect data and define new title
        $my_post = array(
            'ID'           => $post_id,
            'post_title'   => $custom_title,

        );

        // Update the post into the database
        wp_update_post( $my_post );

    }
}
//added cred hook to change post title for cred forms from now on.

add_action('cred_save_data','combined_title', 10, 2);
function combined_title($post_id, $form_data) {
// if a specific form
if ($form_data['id']==280) {
    $type = get_post_type($post_id, $form_data);
    if ($type == 'staff-member')
    {
        $wpt_intranet_smslug = get_post_meta($post_id, 'wpcf-firstnamecpt', true); //variable declared to hold post ID and fields
        $wpt_intranet_smslug .= get_post_meta($post_id, 'wpcf-last-namecpt', true) ;
        $key = $wpt_intranet_smslug . '-' . $post_id;
        $slug = sanitize_title($key);
        wp_update_post(array('ID' => $post_id, 'post_title' => $key, 'post_name' => $slug));
    }
}
}