Kovar is a nickel-cobalt-iron alloy. It is used in electronics and thermal expansion-compatible devices. Kovar CTE is the same as that of borosilicate glass and certain ceramics over a given temperature range. This makes it ideal for tight seals.
Although machining Kovar is difficult, it is highly strong and can be hardened if cut too swiftly. You must use sharp carbide tools, control heat, and take steady cuts to keep parts accurate.
Kovar is primarily used in semiconductors, vacuum tubes, and hermetic packages. It requires careful machining to allow parts to fit perfectly, last longer, and avoid production errors. Let's look into deeper about Kovar alloy properties, machining techniques, and industrial benefits.
What is Kovar Alloy?
Kovar is a silver-grey alloy made of nickel, iron, and cobalt. It was developed in the early 20th century for industrial use.
Kovar expands slightly under the influence of heat. Its thermal expansion is the same as that of glass and ceramics. So, it's perfect for strong, leak-proof seals.
Kovar maintains its shape and size during machining and over time. Many industries, including electronics, aerospace, and medical, use Kovar. It is often used in semiconductors, sensors, vacuum tubes, and other precision components. Kovar products last longer in critical applications.
In addition, Kovar is designated as ASTM F15 or NILO K. While related alloys include Alloy 42 (nickel-iron) and Invar 36 (nickel-iron with very low expansion), their thermal expansion behavior differs significantly from Kovar. These are nickel-iron-cobalt, with low thermal expansion and good glass-sealing ability. Minor changes in their composition give each one slightly different performance qualities.
Chemical Composition of Kovar and Similar Alloys
Kovar and related alloys have a mix of nickel, cobalt, and iron, with small amounts of other elements. The exact combination changes how each alloy works in sealing, heat control, and precision parts.
Machining Operations and Cutting Tools used with Kovar Alloy
Kovar metal is a highly strong material and must be machined cautiously to maintain the parts' integrity. You must control the heat and use sharp tools. Turning, drilling, tapping, EDM, and laser cutting are the common techniques to process Kovar.
Clear Knife and Square Edges
Kovar machining services require sharp tools to make clean cuts. Tools must be cleanly edged and angled correctly. Use sharp carbide tools with positive rake angles around 10°-20° to get clean cutting edges and minimize work hardening. Standard quality tools minimise damage and help you achieve the right dimensions.
CNC Turning and CNC Milling
Kovar can be precisely machined using high-speed tools, and sharp tools provide fine surfaces. Custom CNC machining can produce complicated forms by controlling work hardening. It is also time-saving and reduces material waste.
Electric Discharge Machining (EDM)
EDM is a non-contact way to machine Kovar. It imposes no strain on the material. You can achieve highly accurate details and tight tolerances using EDM machining. Usually, aerospace and electronics components are made with this technique.
Laser Cutting
Kovar Alloy Laser Cutting
Kovar can be precisely cut with a focused beam using laser cutting. It forms sharp lines and intricate forms. Heat-affected areas are not large, hence the alloy retains its strength. Laser cutting is a speedy process and produces repeatable outcomes.
Factors To Consider When Machining Kovar Alloy
Kovar doesn't machine like standard steels and aluminium alloys. It has a unique mix of toughness and low thermal expansion. This makes it valuable but complex for machines. Optimizing the process will save time, reduce waste, and give precise results.
Choose the Appropriate Cutting Tools
Kovar is rigid and likely to work harden. So you require tooling that can withstand continuous stress and not wear out fast. A solid carbide tool is better to use for Kovar. Keep the sharp edges sharp and the rake angle correct to avoid material waste. In such situations, chip breakers may assist in easier chip removal and surface finish.
Factors Affecting Work Hardening in Kovar
These are the common factors that can change how fast Kovar hardens.
* Cutting speed: Faster cutting makes it harder and quicker.
* Temperature: More heat can slow the hardening.
* Previous work: Metal that was shaped before may harden differently.
* Composition: Small changes in the alloy can affect hardening.
When making precision parts, these factors need to be controlled. If Kovar hardens too much, it may crack and change size. This causes the part to fail.
Manage your Speeds and Feeds
Avoid a high cutting speed for Kovar machining. High working speed produces excessive heat and causes the formation of dimensions and surface hardness. Using slowly and at an even pace with moderate feed is better. This will maintain lower temperatures and produce a cleaner, more precise finish.
Use the Right Coolants
Use coolants to protect the tool and workpiece. The friction can be lowered by water-soluble and light oil-based coolants that transport heat out of the cutting area. This makes the tool last longer, and the part does not overheat.
Stable Design in Mind
Consider how Kovar responds to cutting force. Avoid unnecessarily increasing the stress concentrations on the surface and permit good clamping conditions during machining.
Industries That Benefit from Kovar Alloy Machining
As mentioned before, Kovar has thermal expansion like glass and ceramics. So, it is commonly used for sealed, stable components.
Medical
Kovar is used to seal electronics safely in pacemakers and other implants. It is also used in imaging equipment, where it allows magnetic and radiation interference to be blocked.
Electronics
Kovar is used in diodes, transistors, terminal pins, crystal oscillators, microwave tubes, and X-ray housings to make parts secure and functional.
Aerospace and Defence
In aerospace, Kovar is used in satellites, avionics, and sensors. It can withstand severe heat, radiation, and pressure, and does not warp easily. Additionally, it guards lasers and instruments against an impaired environment.
Kovar Vs Invar: How They Differ
Both Kovar and Invar are nickel and iron-based alloys. They have low thermal expansion and different properties. Kovar has approximately;
* 29% Nickel
* 17% Cobalt
* The rest iron, mixed with trace elements
Its expansion rate is the same as that of glass and certain ceramics. Therefore, it can be used in glass-to-metal seals in electronics and hermetic packages.
On the other side, Invar contains about
* 36% Nickel,
* The remaining is chiefly Iron
Invar expansion rate is relatively low even within an extensive temperature range. So, it is applied in optical devices and measuring instruments.
Conclusion
Kovar is a nickel-cobalt alloy that is mostly used in glass-to-metal seals and vacuum systems. These parts must stay the same size even when temperatures vary. It is highly strong and steady. So, right tool selection, careful machining, and expertise are needed to avoid issues like hardening and shape variations.