01How the process works
Surfaces are cleaned and pretreated, adhesive is applied as a bead or film, parts are fixtured and the adhesive cures by heat, moisture or mixing. Bond strength depends far more on surface preparation and cure than on the adhesive itself.
Because a bonded joint cannot be inspected for strength without breaking it, process control is everything: surface energy checks, bead monitoring, cure schedules and witness coupons tested in each batch.
- Surface preparation. Cleaning, abrading, primers.
- Application. Bead or film applied, often by robot.
- Joining and fixturing. Parts positioned and held.
- Curing. Time and temperature controlled.
- Testing. Witness coupons, visual, NDT.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Adhesive failure (no adhesion) | Contaminated surface | Peel and shear tests on coupons |
| Voids in bond line | Application, air entrapment | Ultrasonic, tap test |
| Incomplete cure | Temperature, mix ratio | Hardness, cure records |
| Bead missing or broken | Dispensing fault | Vision systems, visual |
| Squeeze out | Excess adhesive | Visual |
| Expired material | Shelf life | Batch records |
03Where an inspector should look
01
Before production
- Bonding procedure and qualification
- Adhesive batch and shelf life
- Operator training
02
During production
- Surface energy or water break test
- Mix ratio and bead check
- Cure oven charts
03
After production
- Witness coupon tests
- Visual and tap test
- Records per batch
04Standards and references
ISO 4587 (lap shear), DIN 6701 (adhesive bonding of rail vehicles), DIN 2304 (quality requirements for adhesive bonding).
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.
05How we support buyers of adhesive bonding parts
Manufacturing and Special Process AuditsProcess audits of casting, machining, welding, heat treatment, plating and moulding, with VDA 6.3 style evaluation.
Third-Party Quality AssuranceReview of the supplier's quality plan, procedures, records, competence and controls to ensure conformity is repeatable.