Invar and Kovar machining is a specialist job because these low-expansion nickel alloys are sticky, gummy, and prone to warping if you treat them like steel and hope the program saves you. Invar barely changes size with temperature; Kovar matches the expansion of glass and ceramics for hermetic seals that survive solder without cracking the glass. Both are vital in semiconductors, aerospace, and electronics, where a micron of drift is a failed device and a leaked seal is a scrapped batch. This guide explains the process and what to brief your shop so the part holds size from lab cold to operating heat.
What Invar and Kovar Are
Invar (nickel-iron) has a near-zero thermal expansion; Kovar (nickel-cobalt-iron) expands like glass, so it seals metal to ceramic. They appear in semiconductor parts, sensor packages, and precision machined parts where drift is failure and a loose seal is a returned lot. Machining them is closer to Inconel than to aluminium, and the shops that quote them cheapest are usually the ones that skip the stress relief and ship you a part that looks perfect and moves a micron after you unclamp it.
Where Low-Expansion Alloys Are Used
Optical mounts, laser and microwave packages, hermetic connectors, and aerospace molds all rely on dimensional stability across a wide temperature band. The part must hold size from lab cold to operating heat, so process control beats hourly rate every time, and we quote on control, not on a race to the bottom that the customer pays for later in scrap and field returns.
Machining Challenges
Invar is gummy and builds up edge on a dull tool; Kovar work-hardens if the tool hesitates for a microsecond at the bottom of a hole. The fix is sharp solid-carbide tooling, trochoidal paths, constant feed, and high-pressure coolant that clears the chip before it welds itself back. CNC milling and CNC turning run on rigid 5-axis machines with disciplined parameters so the chip loads stay consistent through corners where lesser shops let the spindle slow.
Stress Relief and Thermal Cycling
Heavy cuts leave residual stress that warps the part when released from the vise. We insert intermediate stress-relief cycles and gentle thermal cycling so the finished part stays stable instead of relaxing into a new shape on your shelf. Skipping this is the usual cause of field failure, and it is invisible until the part is out of the vise, which is the worst time to find out that your seal no longer seats.
Grinding and EDM Finish
Flat seats and fine features get surface grinding; intricate internal forms use wire EDM that leaves no burr to later break loose in a sealed package. Polishing improves sealing faces and removes the micro-roughness that a leak path loves. We verify flatness and parallelism to microns, because a seal that is a fraction off is a leak no amount of torque fixes once the lid is on.
How to Request a Quote
Send the alloy (Invar 36, Kovar, or Super Invar), the drawing with tolerance and flatness, quantity, and any thermal-cycle requirement. The more we know about the operating range, the better we control warp and the tighter the price, since scrap on a precision package is pure loss and a re-run costs more than the first part did.
Inspection and Quality Control
Low-expansion parts are inspected for stability first, because a part that measures perfect in the vise and drifts on the shelf is worse than one that was wrong from the start. We verify flatness and parallelism to microns on sealing faces, check critical dimensions on a CMM after the final stress-relief so the number you see is the number you get, and confirm the seal seat is free of burrs that a later break-loose could drop into a hermetic package. For semiconductor and aerospace work we tie every measurement to the thermal cycle the part actually saw, not a generic assumption, so the report proves the part holds size across the band it will live in. Every lot ships with the inspection record so your assembly team can trust the part without a teardown, which is what lets a sealed device leave the line instead of circling back for a leak that a micron of warp caused.
Lead Time, Volume, and How to Start
Low-expansion work is usually low volume and high consequence, so we quote within 24 hours and treat the prototype as the qualification, not a throwaway. First articles are measured after final stress-relief so the number you approve is the number you receive, and production lots repeat the same thermal cycle so drift stays bounded across the whole order. Minimum quantities are flexible because a sealed package may need ten parts while a sensor program needs ten thousand, and we would rather support the program than force a volume that ages in storage. Engage us during design and we can often relax a tolerance that machining cannot hold economically or add a stress-relief step that saves the part from warping, which protects both your yield and your schedule when the device has to leave the line right the first time.
Frequently Asked Questions
Why does Invar gum up the tool?
Its high nickel content is gummy and builds edge. Sharp carbide and high-pressure coolant stop it; dull tools make bird nests around the shank.
How do you stop Kovar warping?
Constant feed and intermediate stress-relief cycles. We never let the tool dwell and we cycle thermally before finish.
Can you hold micron flatness?
Yes. Grinding and inspection hold flatness and parallelism to microns on sealing faces.
Do you machine Super Invar?
Yes. Super Invar needs even tighter thermal control; we set the process to the stability spec you require.
Which industries use these parts?
Semiconductor, aerospace, medical, and electronics, anywhere drift with temperature is failure.
How fast can you quote?
Send the drawing with alloy and tolerance and we return a build-ready quote within 24 hours.
Ready to Start Your Project?
Get a build-ready quote on your custom metal parts within 24 hours. Share your drawing and our engineers will respond with process, lead time, and pricing.
