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CFRP Drilling and Trimming of Molded Parts
Holes, countersinks and edge trimming on cured carbon laminates, from flat panels to molded 3D shells. Reply within 24 business hours.
What good shops do differently
Drilling is where carbon parts most often fail inspection. As the drill pushes through, the last plies have nothing behind them and peel away from the laminate. On the entry side the cutting edges can lift the top ply. Both show as a fuzzy ring around the hole, and on a structural part both reduce strength around the fastener.
Shops that drill CFRP well use sharp carbide or diamond-coated drills with a point angle made for composites, back up the exit side, and drop the feed for the last fraction of a millimetre. For molded parts the outline and holes are trimmed on a fixture that supports the shell close to every cut, often on a 5-axis machine.
How the job runs
Fixture
A holding fixture or vacuum nest supports the part close to each cut and hole.
Drill with backing
Composite-geometry drills, backing on the exit face and a slower feed at breakthrough.
Trim
Edges trimmed with compression or diamond routers, on 5-axis for molded shapes.
Inspect
Hole size, position and the exit side checked for delamination before packing.
Typical capability
Planning values from shops that do this work. They are typical, not promised. The shop that quotes you confirms what it can hold on your part.
| Drilled holes | ±0.05 mm typical on diameter, with clean exit sides. |
| Reamed or interpolated holes | Tighter fits with PCD tools. Ask for the class you need, for example H8. |
| Countersinks | For flush fasteners. Keep about 1/3 of the thickness as straight hole. |
| Trim tolerance | ±0.1 to ±0.2 mm on molded parts, set mostly by how well the part sits in the fixture. |
| Stack drilling | Carbon with aluminium or titanium in one stack needs different feeds per layer. Say so on the RFQ. |
| Delamination check | Visual or by measuring the damage diameter against the hole. Agree the limit before the order. |
Put this on your drawing
A complete RFQ gets a firm quote the first time instead of a list of questions.
- STEP file of the molded part plus a PDF with every hole and trim line
- Hole sizes with tolerance class and fastener type
- Countersink angle and depth for flush fasteners
- Accepted delamination limit, if you have one
- How many parts and whether you send the parts or the shop molds them
- Datum surfaces the shop can fixture on
Mistakes that raise the price
- No exit supportA hole drilled through unsupported laminate almost always peels the back ply. Shops need a datum face to place backing.
- Trim lines without datumsA molded part is never exactly the CAD shape. Give the shop datum points so trimming follows the real part.
- Tapping carbonThreads cut into carbon strip under load. Use inserts or through bolts.
Send your part
We match it with up to 3 shops that do this work every day. Free for buyers. For full details, use the full RFQ form.
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Questions about cfrp drilling
Also see sheet and plate cutting and tube machining.
What causes delamination when drilling carbon fiber?
The thrust force of the drill. At breakthrough the last plies have no support and peel apart. Sharp tools, composite drill geometry, backing and a lower feed at exit keep it small.
Can you trim parts that we mold ourselves?
Yes. Send the STEP file and a few parts or photos of how they come out of the mold. Shops build a trim fixture and quote fixture and trimming separately.
Do I need 5-axis for trimming?
For flat or nearly flat parts a 3-axis router is enough. Shells with edges at several angles, like housings and fairings, need 5-axis or several fixtures.