Technical Cutting for Aerospace: Waterjet, Fiber Laser and Plasma
Use abrasive waterjet when the edge must have no heat affected zone or the material is titanium, a nickel alloy or a composite; use fiber laser for fast, accurate sheet profiles where a small heat affected zone is acceptable; use plasma to rough out thick plate blanks. On flight hardware, treat any thermally cut edge as needing removal by machining unless the drawing says otherwise.
Updated
The three processes side by side
The choice comes down to heat, accuracy and thickness. Waterjet puts no heat into the part, laser puts in a little in a narrow band, and plasma puts in the most and holds the loosest tolerance, but cuts thick steel and aluminum plate quickly and cheaply.
| Item | Abrasive waterjet | Fiber laser | Plasma |
|---|---|---|---|
| Heat affected zone | None; no heat input | Small | Relatively large |
| Published accuracy | Average about ±0.003 in (±0.08 mm), down to about 0.001 in with advanced controls | About ±0.001 in (±25 micrometers), better on thin material | About ±0.030 to ±0.060 in (±0.75 to ±1.5 mm) |
| Kerf | About 1.0 to 1.3 mm (0.04 to 0.05 in) abrasive | As small as 0.004 in (0.10 mm), depending on thickness | Wider at the top than the bottom; edges often asymmetric |
| Thickness | Metals to about 6 in in general references; one maker publishes up to 24 in | Industrial 1 kW and up lasers cut carbon steel from about 0.51 to 13 mm; higher power machines go thicker | CNC torches to about 6 in (150 mm) of steel |
| Materials | Nearly anything, including composites, glass and stone | Metals; fiber lasers handle reflective copper and brass | Conductive metals: steel, stainless, aluminum, brass, copper |
| Typical aerospace use | Titanium and nickel blanks, CFRP trim, thick aluminum, near net shapes before machining | Sheet metal details, brackets, flat patterns, GSE panels | Thick plate blanks for GSE frames and tooling, weld preps |
The accuracy row comes from a waterjet manufacturer's comparison page (OMAX), and the kerf and thickness rows from general published references. Machine condition, part size, thickness and the shop's process control all move these numbers, so quote tolerances from the supplier's own capability for your material and thickness rather than from a generic table. Wire EDM, which holds far tighter tolerances on conductive material, is covered on the EDM and precision grinding page.
Abrasive waterjet: cold cutting with taper to manage
Abrasive waterjet is the default for aerospace materials that must not see heat. The jet cuts without changing temper or microstructure, so a waterjet blank of 7075-T7351, Ti-6Al-4V or 718 arrives at the machine shop with the properties on the mill cert.
- Pressure and abrasive. Ultra high pressure pumps run from about 40,000 psi (280 MPa) up to 100,000 psi (690 MPa). Garnet is the common abrasive, fed into a mixing chamber behind the nozzle.
- Taper and jet lag. The jet spreads and trails as it cuts, so walls are not perfectly square. General references put taper on most cuts under 1 degree. Modern controllers model taper and jet lag and compensate, which is why shop capability varies so much between machines.
- Edge quality numbers. Waterjet software commonly uses quality settings Q1 (roughest, fastest) to Q5 (smoothest, slowest). One published example for 4 in aluminum gives 4.2 in/min at Q1 against 0.72 in/min at Q5, a factor of almost six. Ask for the quality level on the quote, because it drives both price and edge finish.
- Combined with EDM. Waterjet can rough out a profile and pierce start holes for wire EDM, leaving EDM to finish only the features that need its accuracy.
Waterjet edge finish depends on the quality setting, from rough at Q1 to smooth at Q5. For many brackets and blanks that is acceptable as is; for fatigue critical edges and fastener holes it is a starting point for machining.
Have a part like this?Send it in under a minute. A person replies within 1 business day.Fiber laser: speed and accuracy with a narrow heat band
Fiber lasers dominate sheet metal profile work because they are fast, accurate and cheap to run on thin material. Published references credit the small spot size that comes with the fiber laser 1064 nm wavelength for its ability to cut reflective metals such as copper and brass, which older CO2 lasers handle poorly.
What the buyer gets from a laser:
- Kerfs as narrow as 0.004 in (0.10 mm) on thin stock, which allows small features and tight nesting.
- Published surface finish of roughly 125 to 250 microinch on the cut face, rougher as thickness increases.
- A small heat affected zone and a thin resolidified layer on the cut face. The assist gas matters: gases such as oxygen or argon clear molten metal from the cut, and an inert gas shield reduces oxidation on the edge. State on the PO if an oxide free edge is needed for welding or bonding.
The heat affected zone is the reason a laser edge is treated differently on flight hardware. A waterjet maker's comparison notes that the laser's heat affected zone can be a problem for titanium and tool steel. On precipitation hardened aluminum and steels, the narrow zone near the cut has seen a thermal cycle the rest of the part has not, and a resolidified edge raises the same questions as the EDM recast layer. Whether that matters depends on the edge: a nonstructural cover panel edge rarely does, a fatigue loaded flange edge or a fastener hole usually does.
Plasma: thick plate blanks and weld preps
Plasma is the fast, low cost way to cut thick conductive plate into blanks. CNC torches cut steel up to about 6 in (150 mm), and tilting heads cut bevels at constant angle through the thickness, which can supply a weld preparation without secondary grinding. Newer fine nozzle torches narrow the arc and improve edge precision considerably compared with older plasma.
The tradeoffs are a relatively large heat affected zone, a kerf that is wider at the top surface than the bottom, cut edges that are often asymmetrical left to right, and the loosest tolerance of the three processes. For thin material, plasma is steadily being replaced by laser, mainly because laser cuts much better holes. In aerospace work, plasma belongs on ground support equipment frames, fixtures, tooling bases and blanks that will be machined all over. It does not belong on a finished flight edge.
Heat affected zone and recast limits on aerospace drawings
Requirements for thermally cut edges come from the drawing, the prime's process specifications or the structural analysis, not from the cutting process. If the drawing is silent, a supplier may reasonably deliver a laser or plasma edge. That is why the drawing or PO should state one of the following for each class of edge:
| Edge type | Typical drawing intent | How to state it |
|---|---|---|
| Nonstructural sheet edges, covers, GSE panels | Any process acceptable | No note, or state that thermal cutting is permitted |
| Structural edges in sheet and plate | Thermal cutting allowed if the affected layer is removed | Note requiring removal of a stated minimum depth by machining, routing or grinding after thermal cutting |
| Fatigue critical edges, lugs, fastener holes | No thermal cut on the final edge | Note prohibiting thermal cutting on the finished surface, or requiring the final contour by machining |
| Titanium, precipitation hardened steels, heat treated aluminum | Avoid thermal cutting or remove the affected layer | Specify waterjet or machining, or state the removal depth and how it is verified |
The removal depth is an engineering decision for the design authority, and it is verified on a coupon cut under the same settings by metallographic section and etch, the same way EDM recast is checked. If a supplier proposes laser cutting where your drawing assumes waterjet or machining, the change belongs in front of engineering before the first article, not at receiving inspection. The EDM and precision grinding page covers recast layers in more depth.
When to follow the cut with machining
Profile cutting is usually the first operation, not the last. Plan for machining after the cut when any of these apply:
- Fastener holes and bearing bores. Holes for structural fasteners need size, roundness, perpendicularity and surface finish that profile cutting does not reliably deliver. Cut undersize or not at all, then drill and ream.
- Datum features. Edges used as datums for later operations or assembly should be machined so they are square and repeatable.
- Profile tolerance tighter than the process. If the drawing holds a profile tighter than the supplier's demonstrated capability for that thickness, leave stock and finish the edge on a mill or router.
- Taper on thick sections. Waterjet taper and plasma bevel on thick plate can exceed the perpendicularity on the drawing.
- Heat affected or resolidified edges on structural or fatigue loaded features, per the previous section.
Leave a consistent cleanup allowance and tell the cutting supplier which edges are finished as cut and which are stock. Mixing the two on one drawing without a note causes the most rework.
Cutting titanium and composites
Titanium. Waterjet is the safe default. A waterjet manufacturer states that titanium cuts without thermal distortion or surface embrittlement, and the tooling problems of machining titanium do not apply. A laser or plasma edge on titanium has been melted, which raises the oxygen pickup and alpha case concerns explained on the titanium alloys page. If a titanium part must be laser cut for cost reasons, require removal of the edge layer by machining and verification on a coupon.
Carbon fiber and other laminates. Waterjet makers promote it for carbon fiber because there is no melting, no tool clogging or wear and no hazardous fumes. The risk is delamination, especially at the pierce point where the jet first enters the laminate. Waterjet makers address this with low pressure piercing for layered materials, and many shops drill a start hole instead of piercing. Delamination at high cutting speed was one of the problems when waterjets were first used to cut honeycomb laminate for the XB-70 program. Ask engineering before allowing any thermal process on a composite edge, since heat affects the resin matrix differently from metal. Moisture from the jet is another consideration on composites and honeycomb, so ask how the supplier dries parts before bonding or inspection. The composites fabrication page covers trim and drill in the wider process.
Nesting, material traceability and edge witness marks
Nesting software places parts on a sheet or plate to minimize scrap, and it can quietly break three aerospace requirements if nobody checks the nest.
- Grain direction. Parts that are formed after cutting, or that have properties called out by direction, must be nested in the right orientation to the rolling direction. Mark the grain direction on the drawing, and make sure the nest respects it. The sheet metal and aerospace welding page explains why bend radius depends on grain.
- Heat lot traceability. Every part cut from a sheet inherits that sheet's heat or lot. Nests that pull parts from several sheets, or from remnants, need the heat number transferred to each part or its bag. Remnants returned to stock should be marked with the heat number and spec before they leave the cutting table.
- Tabs and microjoints. Parts held in the skeleton by small tabs leave witness marks when broken out. Say whether those marks must be dressed flush and to what finish.
- Lead ins and pierce points. Pierce points leave a local defect. Ask the programmer to keep pierces and lead ins in scrap or on edges that will be machined.
For certs and how traceability is kept from mill to part, see material certs and traceability.
What to call out on the drawing or PO
- Material, temper and procurement spec, with grain direction where it matters
- Permitted cutting processes, or prohibited ones, by edge or zone
- Required removal depth after thermal cutting and how it is verified
- Edges finished as cut versus edges with machining stock
- Waterjet quality level or edge finish requirement where appearance or fatigue matters
- Hole callouts: cut, cut undersize, or drill and ream
- Assist gas or oxide free edge requirement for parts that are welded or bonded
- Heat lot traceability on every nested part and on returned remnants
- For composites, delamination limits at edges and pierce points, and drying before bonding
Get cut and machined parts sourced
Profile cut blanks and sheet parts often need a cutting source, a machine shop or fabricator and a finisher. Send the drawings and flat patterns with your edge requirements, and we source qualified suppliers, flow down the permitted processes, removal depth and traceability requirements, check certs against the PO, and deliver with a certificate package on one PO. A person replies within one business day, and a mutual NDA comes before files. Related reading: forging, casting and the processes hub.
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Questions
Does abrasive waterjet leave a heat affected zone?
No. Waterjet cutting adds no heat to the material, so it does not change temper, microstructure or hardness at the edge, and it does not warp the part through heat. That is why it is preferred for titanium, nickel alloys, heat treated aluminum and composites. The edge does have taper and a matte, striated finish, so fatigue critical edges and holes may still need machining for dimensional and finish reasons.
How accurate is waterjet compared with laser and plasma?
One waterjet maker publishes an average of about ±0.003 in for waterjet, about ±0.001 in for laser on thin material, and about ±0.030 to ±0.060 in for plasma. Real capability depends on the machine, material, thickness and part size. Ask the supplier for demonstrated capability on your material and thickness, and leave machining stock on any edge tighter than that.
Can flight hardware be laser cut?
Often, if the drawing permits it. The question is the edge: laser leaves a small heat affected zone and a resolidified layer, which may be unacceptable on fatigue loaded edges, fastener holes, titanium and some heat treated alloys. Put the permitted processes and any required removal depth on the drawing so the supplier does not have to guess.
Is waterjet good for cutting carbon fiber?
Usually. Waterjet makers point to no melting, no tool clogging or wear and no hazardous fumes when cutting carbon fiber, and it avoids the heat that thermal processes put into the resin. The main risk is delamination, especially at the pierce point, so suppliers use low pressure piercing or drilled start holes. State edge delamination limits on the drawing and ask how parts are dried before bonding or inspection, particularly with honeycomb cores.
When is plasma acceptable for aerospace work?
Plasma is suited to thick plate blanks for ground support equipment, fixtures and tooling, and to blanks that will be machined all over. It is fast and cuts steel up to about 6 in thick, but it has a relatively large heat affected zone, a beveled and often asymmetric kerf and the loosest tolerance of the common processes. It should not be used for finished flight hardware edges.
How do I keep heat lot traceability on nested parts?
Require the supplier to transfer the heat or lot number from the sheet to every part cut from it, by marking or by bagging and tagging, and to mark remnants with heat number and spec before they return to stock. When a nest draws parts from more than one sheet, the traveler should record which parts came from which heat. Check this at receiving against the mill cert.
Related
Sources
- OMAX: waterjet cutting compared with laser, plasma and EDM
- OMAX: what materials can a waterjet cut
- Water jet cutter: pressures, kerf, taper, quality levels
- Laser cutting: fiber lasers, kerf, finish, thickness
- Plasma cutting: thickness, bevel heads, kerf behavior
- Heat-affected zone: definition and heat input effects
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