Key takeaways
- A busbar FAI pack proves three things: the geometry, the material and the finished current path.
- Balloon the drawing before the first part is measured, and link every balloon to a recorded result.
- Material certificates, temper, section and plating thickness belong in the pack, not in an email folder.
- PPAP adds process evidence and commitment to the FAI; a dimensional report on its own is neither.
What a busbar first article has to prove
A first article inspection is a full, independent check of the first production part against the drawing and the specification. On a busbar, that means more than measuring length, width and hole positions. The part also has to show that the correct material was used, that the temper suits the forming route, that the plating is the right thickness on the right surfaces and that the finished bar conducts as the design intended.
That combination is why busbar first articles go wrong. A fabricator measures the outline, records the plating thickness on a flat face and signs the pack. Nothing in the pack shows the temper of the bar, the conductivity of the lot or the condition of a bent edge. Months later a joint runs hot and the paperwork cannot answer the first question an engineer will ask.
Balloon the drawing before anything is measured
Ballooning means numbering every dimension, note, tolerance and symbol on the drawing and carrying those numbers into the inspection record. Do it before the first part arrives, because the exercise exposes gaps in the drawing while there is still time to fix them.
A busbar drawing often has a general tolerance in the title block, a tighter tolerance on hole positions, a bend angle callout, a flatness note and a plating specification. Each of those needs its own balloon. A note such as plating to a named standard with a minimum thickness is a characteristic, not background text, and the pack must show a measured value against it.
A note without a balloon is a note nobody checks
If the plating callout, the material grade or the edge condition is not ballooned, it will not appear in the inspection record. Treat every note as a characteristic with a result and an acceptance rule.
Material, temper and section
Start with the certificate and then verify it. The mill certificate should name the grade, the temper, the heat or lot number and the mechanical properties. For copper busbars that usually means conductivity or resistivity, tensile strength and hardness. For aluminium it means alloy, temper and conductivity.
The certificate alone is not enough. Measure the section at several points along the bar, because thickness and width tolerances sit at the mill and a bar at the low end of both has less copper than the drawing assumes. Record the measurements by position so a tapered or cambered bar is visible in the data. Check the temper indirectly through hardness or a bend result if the drawing does not call for a tensile test.
The dimensional layout
Measure the part after forming, never on the flat pattern. Bend allowance and springback move hole positions and terminal faces, and a flat measurement tells you what the blank was, not what the assembly will receive. The layout should record overall length and width, thickness at the ends and the middle, hole diameter and position, bend angles, the distance between terminal faces and flatness across the mounting face.
Busbars are often long and slender, so the measurement setup matters as much as the instrument. Support the bar at the same points the assembly will support it. A bar measured hanging over the edge of a surface plate will show a bow that disappears once it is bolted down, or hide one that appears under load. State the support condition on the record.
Finish, edges and joint faces
Plating is a functional coating on a busbar. It lowers contact resistance at the joint, protects the bar from corrosion and, in silver, provides a surface that survives repeated mating. The pack should record the plating type, the measured thickness at defined points and an adhesion result. Measure on a flat face, on a bent face and near a cut edge, because thickness varies with geometry and current density.
Cut edges and punched holes are part of the current path and part of the corrosion surface. Record burr height and edge condition against the drawing note, and note any discolouration or exposed base metal. On a silver-plated bar, a thin or missing deposit at a hole is a joint risk, not a cosmetic defect.
Electrical and functional evidence
A busbar FAI should include at least one check that current can pass. Conductivity or resistivity on a sample from the lot is the cheapest evidence and it catches grade and temper mistakes. A millivolt drop test across a representative joint goes further: it measures the finished interface, including plating, flatness and bolt tension, under a known current.
Record the test current, the probe positions, the length of the measured span and the ambient temperature. A millivolt drop number without those conditions cannot be compared with a later reading. If the drawing or the customer standard gives a limit, state it next to the result. If there is no limit, agree one before the first shipment rather than after the first hot joint.
Where PPAP adds to the FAI
FAI proves the part. PPAP proves the process that will make the part repeatedly. A production part approval file usually includes the design record, engineering change documents, a process flow diagram, a control plan, measurement system analysis, dimensional results, material and performance test results, a sample part and a part submission warrant. The exact set depends on the customer and the level requested.
For a busbar programme, the control plan is the document that earns its keep. It should name the operations, the characteristics checked at each one, the frequency and the reaction plan. If plating is subcontracted, the control plan must show how that supplier is monitored and how its certificates reach the pack. If bending is the risk, the plan needs a first-off and a periodic angle check, not a final dimensional audit.
What a reviewer should send back
Reject a pack that reports results without acceptance limits. Reject one that measures the flat pattern rather than the formed part, or that lists plating thickness without saying where it was measured. Reject a certificate that names a grade but not a temper, and reject a dimensional report that has no balloon map behind it.
The strongest packs are short and complete. A clear ballooned drawing, a results table with limits and pass or fail, certificates tied to the lot, a plating record, one electrical result and a signed warrant will clear most reviews in a single pass. Length is not evidence.
| Evidence | What it must show |
|---|---|
| Ballooned drawing | Revision stated on the warrant, every note included |
| Results table | Nominal, tolerance, measured value and pass or fail |
| Material certificate | Grade, temper, lot, conductivity and mechanical properties |
| Section record | Measurements at defined positions along the bar |
| Plating record | Type, thickness at defined points and adhesion |
| Joint and edge | Face flatness, hole pattern and burr condition |
| Electrical result | Conductivity or millivolt drop with test conditions |
| Process pack | Control plan and flow diagram that match the route |
Frequently asked questions
Is a busbar FAI the same as a PPAP?
No. The FAI is the full dimensional and material check of the first production part. PPAP is a wider submission that includes the FAI plus process evidence such as the flow diagram, control plan, measurement system analysis and a part submission warrant. Many customers ask for both, with the FAI results forming the dimensional section of the PPAP.
How many busbars should be in a first article sample?
The customer standard decides. A common approach is one part from each cavity, tool or line, taken from a production run rather than a hand-built sample. For a long bar with several bends, take parts from the start, middle and end of the run so that wear and setup drift are visible.
Should conductivity be tested on every busbar lot?
Not necessarily on every part, but a lot level check is worth having, especially where the grade or temper is critical. Conductivity on a coupon or a sample from the lot catches material substitution that dimensional checks cannot. Frequency belongs in the control plan.
What plating evidence should the FAI include?
The plating type and standard, measured thickness at stated positions including a bend and a cut edge, an adhesion result and a note on coverage of holes and masked areas. If the joint is critical, add a contact resistance or millivolt drop result on the plated surface.
Sources and further reading
- AIAG, Production Part Approval Process (PPAP), 4th edition
- AS9102 Rev C, Aerospace first article inspection requirement
- IEC 61439-1, Low-voltage switchgear and controlgear assemblies, general rules
Qumek Engineering Desk
Engineering team
The engineering team behind Qumek drawings, DFM notes, tolerances and inspection standards. Every guide is reviewed against the drawings and processes used on live programmes.
Need a busbar first article pack reviewed?
Send the drawing, the current revision and the inspection record. The engineering desk will reply with the gaps that would stop an approval.
Send a drawing