Precision parts ruined on the way to your dock
A buyer in Michigan once sent me photos of a batch of precision stainless shafts that arrived at their assembly plant with dented ends, corrosion spots, and embedded cardboard fibers on critical sealing surfaces. The parts were machined to within 0.01 mm of nominal - and they were scrap because they had been tossed loose in a cardboard box with no rust protection and no individual wrapping. The machine shop did great work; the packaging team destroyed it. Shipping damage is preventable, but only if you specify packaging requirements up front.
How precision CNC parts get damaged in transit
Understanding the failure modes helps you specify the right packaging:
- Impact damage: parts thrown loose in a box dent each other, especially threads, sealing surfaces, and sharp edges
- Abrasion: parts rubbing together during transit cause cosmetic scratches and can damage tight-tolerance surfaces
- Corrosion: unprotected steel and stainless steel parts rust in ocean freight containers due to condensation (container rain) and humidity over multi-week voyages
- Deformation: long slender shafts and thin-walled parts bend under their own weight or from stacking weight if not properly supported
- Contamination: packing material fibers, dust, or oil residue on critical surfaces causes problems in cleanroom, medical, or sealing applications
Minimum packaging standards for machined parts
These are the packaging requirements I put on every PO for precision CNC parts going overseas:
- Individual wrapping: each part in a sealed poly bag or VCI (volatile corrosion inhibitor) paper/bag for steel and stainless parts
- Thread protection: all external threaded sections capped with plastic thread protectors; internal threaded holes plugged
- Separation: parts in individual compartments within corrugated dividers, or separated by foam sheets - no part-to-part contact
- Rust prevention: VCI bags, desiccant packs, or anti-corrosion oil on uncoated steel parts for ocean freight
- Sturdy outer carton: double-wall corrugated with sufficient fill to prevent shifting; heavy parts in plywood crates
- Sealing surface protection: critical ground or polished surfaces covered with peel-off protective film or soft caps
Ocean freight vs air freight: different risks
Ocean freight subjects parts to weeks of humidity, temperature cycling, and rough handling at ports. VCI packaging is not optional for ocean shipments of steel parts - the humidity inside a shipping container during a Pacific crossing reaches levels that cause flash rust on unprotected steel within days. Use desiccant and VCI film, and consider vacuum packing for critical parts.
Air freight is faster and less humid but involves more loading and unloading events, which means more opportunities for impact damage. Stacking strength of cartons matters on air pallets, where boxes are stacked several layers deep. Foam-in-place or custom-molded foam inserts pay for themselves in reduced scrap rates for fragile or high-value parts.
Specifying packaging in the purchase order
Do not leave packaging to the supplier's judgment. Add a packaging clause to your PO that specifies:
- Individual part wrapping method (poly bag, VCI, foam, etc.)
- Thread and sealing surface protection requirements
- Carton specifications (double-wall, maximum weight per carton)
- Outer packing (pallet, crate, carton) and stacking constraints
- Labeling requirements (part number, quantity, PO number)
- Desiccant and VCI requirements for sea freight; specify minimum VCI protection period (e.g., 6 months)
For your first order with a new supplier, ask them to photograph the packed cartons before shipment. This gives you visibility into their actual packaging practice without waiting for the parts to arrive.
What to do at receiving: open and inspect immediately
When parts arrive, open and inspect within the first few days. Document any damage with photos showing the outer carton condition, inner packaging, and the damaged parts themselves. Report shipping damage to the freight forwarder and the supplier promptly. Claims for transit damage are much harder to file weeks after delivery, and most freight carriers have strict reporting windows.
Frequently Asked Questions
Is VCI packaging necessary for stainless steel parts?
For short air shipments, standard poly bags with desiccant are usually sufficient. For ocean freight or long-term storage, VCI packaging is recommended even for stainless - while stainless resists corrosion better than carbon steel, 303 and 304 can develop surface rust in prolonged high-humidity environments, especially if free iron from machining is on the surface.
Who is responsible for shipping damage?
Depends on incoterms. Under FOB terms, risk transfers when goods pass the ship's rail (for sea freight) or are loaded on the carrier. Under DDP, the supplier is responsible until delivery to your door. Specify packaging requirements in the PO regardless of incoterm; good packaging prevents damage no matter who is liable.
How much extra does proper packaging cost?
Basic protective packaging (individual bags, dividers, desiccant) adds modestly to per-part cost. Custom foam inserts or vacuum-sealed VCI add more but are still cheap compared to scrapping a full production lot. The cost of damaged parts always exceeds the cost of good packaging.
Should I ask for photos before shipment?
Yes, especially for first orders and production runs. Request photos of the parts, the inner packaging, the sealed cartons, and the pallet. A supplier who takes packaging seriously will not object; a supplier who cuts corners on packaging will resist or send low-quality photos.