Friction-rolling　additive　manufacturing　(FRAM)　is　a　solid-phase　additive　manufacturing　technology　that　relies　on　the　insertion　of　a　high-speed　rotating　toolhead　into　a　previous　layer　to　generate　heat　for　deposit　formation.　Press　depth　is　a　key　parameter　of　FRAM,　and　insufficient　press　depth　may　result　in　defects　that　affect　the　mechanical　properties　of　the　deposited　material.　In　this　study,　the　effect　of　press　depth　on　heat　generation　and　defect　formation　in　materials　was　revealed　for　the　first　time　using　the　Coupled　Eulerian-Lagrangian　method.　The　results　showed　that　at　a　small　press　depth,　the　temperature　and　stress　of　the　material　on　both　sides　of　the　interface　are　low,　and　the　plastic　deformation　produced　by　the　toolhead　does　not　affect　the　interface;　thus,　two　types　of　bonding　defects:　voids　and　tunnels,　appear　easily　at　the　interface　position.　With　an　increase　in　the　press　depth,　material　flow　along　the　travelling　direction　and　the　toolhead　direction　was　enhanced,　and　the　temperature,　stress,　and　plastic　deformation　at　the　interface　gradually　increased,　resulting　in　the　disappearance　of　the　defects,　and　the　order　of　disappearance　was　related　to　the　morphology　of　the　toolhead.　When　the　press　depth　was　1.90　mm,　the　materials　on　both　sides　of　the　bonding　interface　reached　70　%　of　the　melting　point,　resulting　in　an　almost　defect-free　interface.　The　simulation　results　were　consistent　with　the　experimental　results.　This　study　provides　a　better　understanding　of　the　defects　formation　during　FRAM　and　provides　guidance　for　regulating　the　defects　in　the　future.　©　2024　The　Society　of　Manufacturing　Engineers