Delamination
What is the mechanical threshold that causes delamination?
Delamination begins when local cutting thrust or interlaminar stress exceeds the laminate’s interlayer bond strength or fracture toughness. For aerospace CFRP, failure may start when thrust force exceeds roughly 100–150 N, but actual limits vary with layup, thickness, fiber orientation, and tooling.
Why does delamination happen more at the exit side?
At breakthrough, the remaining unsupported plies lose backing, so the drill’s axial force converts into a peeling load that opens the laminate instead of cleanly severing it. This makes exit push-out a common defect.
Why do compression cutters reduce delamination?
Compression geometry applies opposing up-cut and down-cut forces so the laminate is pushed toward the neutral axis, reducing both top-surface lifting (peel-up) and bottom-surface blowout (push-out).
Delamination is the separation of bonded layers in laminated materials when cutting thrust force exceeds interlaminar fracture toughness. In CNC machining of composites like CFRP and FR4, it manifests as peel-up at tool entry and push-out at tool exit, directly reducing structural integrity, hole quality, and fastener performance.
On a CNC router, drill, or trim cell, delamination is a process-control defect that compromises structural integrity, hole quality, fatigue life, and fastener performance. In CFRP or FR4 machining, operators reduce thrust force through sharp tooling, compression cutters, proper helix geometry, shallow depth of cut, correct feed per tooth, and solid backing support at the exit side. For laminated wood panels, the same failure occurs when an up-cut tool lifts the top veneer or tears the core. The shop floor response involves inspecting cut edges for edge lift, ply breakout, fraying, void-like gaps, and layered separation, then adjusting tooling and parameters. Delamination risk peaks at entry and exit transitions, so step drilling, backer boards, sacrificial skins, and reduced exit feed are common countermeasures.
Excessive thrust force at hole exit: This push-out delamination occurs when feed is too aggressive or tool is blunt, causing unsupported plies to separate at breakthrough.
Wrong cutter geometry for layered stock: An up-cut spiral lifts top layers, initiating peel-up delamination, especially when a standard metal-cutting tool is used on laminate requiring compression.
Heat softening the matrix or adhesive bond: High friction from dull tools or poor chip evacuation weakens the resin, lowering interlaminar strength and triggering layer separation.