Packaging Machined Parts: Protecting Precision Surfaces in Transit

A machined part that survives 6,000 km of ocean and arrives with a scuffed cosmetic face, a spot of white corrosion in a bore, or a bent mounting ear is not a shipping problem. It is a total loss with extra steps: the part is unusable, the freight was paid, and the replacement takes another five weeks.

Packaging is 1-4% of the piece price and it protects the other 96%. The mistake buyers make is not under-spending; it is specifying the wrong protection for the failure mode they actually have.

The five ways a machined part gets damaged

Impact. A 4 kg aluminum housing dropped 40 cm onto concrete generates a deceleration of 30-50 g, more than enough to deform a thin flange or crack a casting. Cartons fall off pallets in every warehouse between here and your dock.

Abrasion. Parts rubbing against each other in a carton polish away an anodized film, or worse, wear a machined face out of tolerance. This is why bulk-packed parts often fail cosmetic inspection even when they left the shop perfect.

Corrosion. Bare aluminum, steel, and brass oxidize in a container that sees 65-90% relative humidity and 15-30°C temperature swings over 30 days. Condensation forms on the parts when the container cools overnight — the phenomenon usually called container rain — and a machined bore can show white rust within two weeks.

Distortion. Long, thin parts packed flat in the middle of a heavy crate bend under load. A 600 mm rail with a 0.1 mm straightness callout can sag 0.3 mm if it is supported only at the ends with weight on top.

Contamination. Chips and cutting fluid left in blind holes or internal passages look like debris to your assembly line and like a warranty claim six months later.

Protection levels and what they cost

The jump from USD 0.40 to USD 1.60 per part looks like a 300% increase. On a 500-piece order it is USD 600 against a part value of perhaps USD 25,000 — 2.4% of the order to remove a 5% loss risk and a five-week replacement cycle.

See also: Air vs Sea Freight Cost for Machined Parts: When Air Actually Wins and The Real Cost of Holding Machined Parts in Inventory.

Corrosion protection for a month at sea

Three tools, used together, handle almost every case.

VCI — vapor corrosion inhibitor — emits molecules that form a passive layer on metal surfaces. A VCI bag at USD 0.35-0.90 per part covers a machined component for 12-24 months of closed storage. For anything ferrous or uncoated aluminum going by sea, this is the default.

Desiccant controls the moisture inside a sealed barrier. The working figure is one 33 g unit per 30 liters of enclosed volume, more if the cargo has wood or cardboard inside, both of which release moisture. Do not skip the desiccant because the bag is sealed — sealing traps the water that was already in the air.

Barrier bags and vacuum. A vacuum bag pulls the film against the part and removes most of the air. It protects precision surfaces from abrasion as well as moisture, and it lets your receiving inspector see at a glance whether the seal held. Cost is USD 0.60-1.80 per part plus 20-40 seconds of labor.

For uncoated aluminum, add one more step: wrap in VCI paper or use a VCI-emitting film rather than plain polyethylene. Plain PE film against a bare aluminum surface in a humid container can trap condensation and accelerate the staining you were trying to prevent.

Heavy parts, crates, and dunnage

Above roughly 25 kg, cartons stop being appropriate. A wooden crate is the standard, and for export it must be ISPM 15 compliant — heat-treated or fumigated, with the stamp visible on at least two sides. Heat treatment adds USD 8-15 per crate and 1-2 days if your supplier does not hold stamped stock.

Inside the crate, the part must be blocked, not just cushioned. Foam that compresses under load is useless for a 90 kg housing: at 0.15 kg/cm² bearing capacity, a 90 kg part needs at least 600 cm² of contact area, which is why heavy parts are bolted to a plywood base or blocked with timber battens rather than nested in foam.

Three details that prevent most heavy-part claims: bolt the part to the crate floor through existing mounting holes when possible; add a diagonal brace against the top so the crate cannot rack; and stencil the gross weight and a "this side up" arrow on two faces, not one.

Kitting for the line

If your assembly line takes the parts straight to a station, packaging becomes a production tool. A kit is a box or tote containing one assembly's worth of parts — bracket, fasteners, gasket, label — in the sequence the operator uses them.

Kitting costs money at the supplier: USD 0.60-2.50 per kit in labor, plus the tote. It saves more at your end: no line-side sorting, no wrong-part errors, less floor space, and a clean count at receiving. For a program running 200 assemblies a week, the labor saved on your side usually exceeds the kit charge by a factor of two.

Two rules make kits work. Standardize the tote so it fits your racking, and print the part number, revision, and quantity on the outside in large type. A kit that requires opening to identify defeats the purpose.

Writing packaging into the PO

Specify packaging as a line item with a part number, not as an instruction in an email. Say the method (VCI bag, foam insert, carton), the carton dimensions, the units per carton, the pallet configuration, and the labeling format — barcode symbology, label position, and whether labels go on the carton or the part.

State the acceptance test too: no visible corrosion at receiving, no abrasion on cosmetic faces, dimensional check on a sample of 5% after unpacking. That last one matters because damage that occurs in transit and damage that occurred before packing look identical three weeks later.

Our capabilities page lists the finishing and packing options we run in-house, and packaging specifications can be quoted as a separate line so you can see exactly what protection costs on your part.

Frequently asked questions

How much should packaging cost as a share of the part price?

Between 1% and 4% for most machined parts in cartons, and 3-6% for heavy parts in crates. If a supplier quotes under 0.5%, either the parts are simple or the protection is a poly bag.

Is a VCI bag necessary if the parts are anodized?

For anodized parts, VCI is optional; the coating already passivates the surface. For bare aluminum, steel, or brass, it is close to essential on any sea shipment longer than three weeks, and it costs under USD 1 per part.

What is the right desiccant quantity?

One 33 g unit per 30 liters of sealed volume, increased by 50% if the packaging contains cardboard or wood. Sealing without desiccant traps ambient moisture and can make condensation worse than an open carton.

Do wooden crates need ISPM 15 treatment for export?

Yes, for solid wood packaging entering the US, EU, UK, and most other markets. Heat treatment adds USD 8-15 per crate. Plywood and processed board are exempt in most jurisdictions because they carry no bark or live pests.

Related reading

• What Drives CNC Prototype Cost, Line by Line2026-10-10
• How CNC Machining Price Per Part Falls From 1 to 1,0002026-10-11
• Machining Cycle Time Calculation: A Worked Example on an Aluminum Bracket2026-10-22