Custom solenoids are rarely complex products. They become slow projects because the specification arrives incomplete, the first sample is evaluated against criteria nobody wrote down, and the second sample fixes problems the first one introduced. This is the process that avoids those loops, described from the supplier side.
Stage 1: the specification sheet
A solenoid can be fully defined by nine parameters. If your RFQ covers all nine, feasibility can be answered in days rather than weeks.
| Parameter | What to state | Why it matters |
|---|---|---|
| Force | Required force at start and end of stroke, in N | Determines frame size and coil power |
| Stroke | Total travel in mm, plus any over-travel | Sets the air gap and therefore the force curve |
| Voltage / current | Nominal, minimum and maximum supply | Drives winding selection and force margin |
| Duty cycle | On-time, cycle time, ambient temperature | Sets the thermal design and insulation class |
| Envelope | Max length, diameter, mounting pattern | Constraints the magnetic circuit before design starts |
| Life | Cycles required, and acceptable force degradation | Determines bearing, plating and lubrication choices |
| Environment | IP rating, media, temperature range, vibration | Sealing, materials, potting and connector type |
| Connection | Lead wires, connector type, terminal orientation | Affects assembly tooling and unit cost |
| Noise / acoustics | Any impact-noise limit | May require end-stop damping or a bistable design |
The two parameters most often missing are minimum supply voltage and ambient temperature at the coil. Both directly reduce available force, and both are routinely discovered only at validation.
Stage 2: feasibility and design feedback (3–5 days)
A competent supplier returns more than a price. Expect:
- A proposed magnetic circuit and frame size, with the calculated force at start and end of stroke.
- A thermal estimate: coil power, expected temperature rise, insulation class.
- Design-for-manufacture comments — for example, that a 1.2 mm wall in the housing forces a more expensive machining route, or that the requested connector adds 3 mm to the envelope.
- Tooling and NRE costs, stated separately from unit price.
If the feedback contains no questions, be cautious. Every real solenoid project has at least one trade-off between force, envelope and heat.
Stage 3: prototype (7–15 days)
Prototypes are usually built from machined parts and hand-wound coils, so they represent the design intent rather than the production process. Two things to insist on:
- Measure the force-stroke curve, not just the holding force. Ask for the curve at rated voltage and at minimum voltage, cold and after 10 minutes at duty.
- Get the 2D drawing with tolerances at the same time as the sample, so that the mechanical interface can be checked before the second build.
Test the sample in the actual mechanism, at the actual ambient temperature, with the actual power supply. Roughly half of all “sample failures” are really integration failures: a return spring that was not in the calculation, a supply that sags, or a bracket that shorts the flux path.
Stage 4: validation and pilot run (2–4 weeks)
Validation should mirror the field, not the lab bench:
- Life test at rated duty and elevated ambient — typically 100k–500k cycles for an industrial actuator, 1M+ for a locking application.
- Thermal soak at maximum ambient with worst-case duty.
- Environmental — IP verification, salt spray for outdoor hardware, vibration sweep for transport.
- Electrical — insulation resistance, dielectric strength, and behaviour at minimum and maximum supply.
A pilot run of 100–500 pieces validates the production process: winding consistency, force spread, and the first real data on process capability.
Stage 5: production and quality control
For a mature solenoid line, the QC plan typically includes 100% force and current testing at a defined stroke, plus AQL sampling on dimensions, insulation resistance and appearance. Ask for the control plan and the last three months of force-distribution data — the spread tells you more about a supplier than the mean.
What drives unit cost
| Driver | Effect |
|---|---|
| Frame size and force class | Steel and copper content scale with force; a 2× force target is not a 2× cost, but it is close |
| Stroke length | Long stroke needs a longer magnetic circuit and more copper |
| Tolerance class | Precision bore and guided plunger add machining cost and reduce cycle time variability |
| Sealing / IP rating | Potting, O-rings and sealed connectors each add cost and assembly time |
| Connector and lead length | Often underestimated; can be 10–15% of unit price |
| Volume | Tooling amortisation dominates at low volume; material and labour dominate at high volume |
Realistic timeline
For a derivative of an existing platform: specification to first sample in 2–3 weeks. For a new magnetic circuit: 4–6 weeks to sample, 8–12 weeks to validated pilot. Anything promised materially faster usually means either an existing catalogue model is being adapted, or validation is being deferred to you.
Frequently asked questions
What is a typical MOQ for a custom solenoid?
For a modified catalogue design, 500–1,000 pieces is common. For a fully new design with new tooling, 2,000–5,000 pieces is typical so that NRE can be absorbed.
Can you work from a competitor sample?
Yes, and it is one of the fastest routes: reverse-engineering the envelope and force curve removes most of the specification risk. Expect the supplier to request the operating voltage and duty cycle, because those cannot be read from the part.
Do I own the tooling?
This should be agreed in writing before the first invoice. Standard practice is that dedicated tooling is charged to the customer and remains theirs, with the caveat that it stays at the supplier’s plant.
Cixin Industrial has manufactured custom solenoids and electromagnets since 2011, with in-house coil winding, machining, assembly and testing. If you are sizing a solenoid for a new design, send us your specification and we will return a feasibility assessment with a recommended model and sample lead time.