[SOLVED]Why does this part detach when it is hit with an explosion?

1. It depends on the explosion's strength
2. It only welds this once. when the weld is removed, you cannot get it back, so i designed this piece of code

while true do
wait(0.0000001) -- if longer, once hit with explosion, weld will not be in same position
    if not workspace.Map.Crate.Core:FindFirstChild("Part_Weld") then
        function weld()
            local parts,last = {}
            local function scan(parent)
                for _,v in pairs(parent:GetChildren()) do
                    if (v:IsA("BasePart")) then
                        if (last) then
                            local w = Instance.new("Weld")
                            w.Name = ("%s_Weld"):format(v.Name)
                            w.Part0,w.Part1 = last,v
                            w.C0 = last.CFrame:inverse()
                            w.C1 = v.CFrame:inverse()
                            w.Parent = last
                        end
                        last = v
                        table.insert(parts,v)
                    end
                    scan(v)
                end
            end
            scan(script.Parent)
            for _,v in pairs(parts) do
                v.Anchored = false
            end
        end
        weld()
        print("welded!")
    end
end

--script:Remove()