Kovar Machining: The Complete Guide
Kovar is an excellent precision alloy used where dimensional stability and reliable sealing are required.
It has essential use in electronics, semiconductors, and high-reliability devices due to its unique thermal and mechanical characteristics.
- Specialized in tight-tolerance Kovar machining for precision parts.
- Advanced finishing and stress-relief processes ensure reliable sealing.
- Capable of producing complex Kovar geometries with minimal distortion.
What is Kovar?
Kovar is a nickel–cobalt–iron alloy designed to closely match the thermal expansion of borosilicate glass and alumina ceramics. This will eliminate stress and failure in delicate assemblies.
Understanding Kovar Alloy
Kovar is designed to expand in a controlled way so that glass and ceramic components remain tightly sealed as temperatures change. Its engineered thermal behavior ensures that sensitive assemblies stay stable even under significant temperature fluctuations. This predictable expansion makes Kovar a trusted material for hermetic packaging, optical devices, and high-reliability electronic components where seal integrity and dimensional accuracy are critical.
Physical and Mechanical Properties
| Property | Description |
|---|---|
| Coefficient of Thermal Expansion (CTE) | Expands at a similar rate to glass and ceramics, helping to prevent cracks and sealing failures. |
| Density | 8.36 g/cm³ (0.302 lb/in³); dense yet workable for precision components. |
| Melting Point | It has a very high melting temperature of 1450°C (2640°F), and is used in high-heat conditions. |
| Tensile Strength | 517–700 MPa, where it exhibits greater resistance to breaking when under stress. |
| Hardness | 80–90 HRB (annealed), has a high degree of strength with machinability. |
| Magnetic Properties | Turns magnetic at temperatures below 435°C (815°F), applicable to some electronic designs. |
| Thermal & Electric Conductivity | Delivers constant heat and current to sensitive equipment. |
Essential Thermal Expansion Properties
- A small thermal expansion coefficient (5 × 10⁻⁶/K) reduces dimensional change in precision assemblies.
- Nonlinear expansion curve: Expansion varies across different temperature ranges, which should be considered in sealing and machining.
- Compatibility: Compatible with borosilicate glass and alumina ceramics for hermetic sealing.
- Temperature stability range: Kovar works well between -80°F and 450°F (-62°C and 232°C).
Why Kovar Is Difficult to Machine?
Several factors make Kovar difficult to machine. Its low thermal expansion, hardness, and glass compatibility introduce unique challenges.
Work Hardening Tendency
Kovar is generally hard to cut, and can severely shorten the life of a tool, as well as compromise surface quality. Hardness may increase from 80–90 HRB to 25–30 HRC under machining stress, where further cuts become harder. Speed, feed, and temperature control are essential to ensure cutting efficiency and dimensional accuracy.
Heat Management and Heat Generation
Machining generates significant heat due to friction and Kovar’s thermal properties. Overheating may bend tools, change tolerances, and even cause micro-cracking. It is necessary to ensure stability and part integrity through proper cooling, lubrication, and the management of cutting parameters.
Tool Wear Challenges
The hardness of Kovar makes the tools wear out faster, reducing the life of cutters and inserts. Quality tools that are durable and wear-free are required, and the cutting performance must be closely observed by the operators to reduce frequent tool replacement.
Surface Oxidation Issues
The oxidation of Kovar can occur when exposed to heat and air, reducing surface quality and seal integrity. Constant lubrication, heat reduction, and post-machining cleaning are also necessary to maintain the integrity of the surface and functional performance.
Types of Kovar Machining
Machining Kovar requires specialized techniques to achieve dimensional stability, minimize thermal distortion, and ensure compatibility with delicate materials such as glass and ceramics.
CNC Turning of Kovar
One of the best process methods of making cylindrical or rotational symmetrical Kovar pieces is CNC turning. The approach provides smooth and stable surfaces, and it regulates distortion in the process of machining. In turning Kovar, low cutting speeds, constant feed rates, and hard tooling commonly are used by operators to provide the tight tolerances needed in electronic and micro-mechanical products.
CNC Milling Kovar
CNC milling has made the production of fine detail (micro-features), complex shapes, and 3D detail on Kovar. Due to its ability to work-harden and its moderate hardness, milling is done at low cutting speeds, using carbide tools with special coatings, and in climb milling. It is best suited for frames, housings, precision covers, and components with strong, high-precision geometries.
Drilling, Reaming, and Tapping
To avoid edge chipping or hole deformation, drilling, reaming, and Kovar tapping require high tool stability. To reduce friction, sharp cutting tools are needed, along with good lubrication, to ensure precision. The manufacturers can obtain high-precision holes with controlled feed rates and correct threading features that meet hermetic sealing requirements with proper drilling parameters.
Wire EDM of Complex Geometries
The wire EDM is recommended for machining complex Kovar geometries. Since the process uses electrical discharge rather than mechanical force, it reduces cutting stress and minimizes thermal distortion to a great extent. Wire EDM applications are typically on micro-parts, fine slots, complex contours, and components that cannot be made by conventional CNC machining.
Laser Cutting of Kovar
Kovar thin sheets are best cut with a laser to create fine profiles. High-energy laser beams enable fast cutting speeds, clean cuts, and minimal burr. The process is widely used on lead frames, precision-cutouts, and other small parts that require precise shapes and no mechanical strain.
Grinding and Precision Finishing
Final surface quality and very tight tolerances on Kovar parts require grinding and precision finishing. Surface grinding, lapping, and polishing are some of the processes that aid in removing slight deviations, resulting in smooth and uniform surfaces. These finishing steps help ensure performance and reliability.
Common Machining Challenges and Solutions
Kovar machining challenges can be controlled with careful planning and process optimization.
- Preventing Work Hardening
To avoid work hardening, tools should be kept sharp, constant feed rates should be maintained, and cutting passes should maintain proper engagement to avoid rubbing. The process of continuous chip removal and dwell-mark avoidance also contributes to keeping the conditions of the materials softer.
- Managing Heat Generation
Reduction of heat is necessitated by effective cooling, low cutting speeds, and constant tool engagement. Optimized toolpaths, such as reduced radial depths of cut, also reduce temperature peaks and assist in dimensional control.
- Minimizing Tool Wear
Gear fixturing with coated carbide tools, stable fixturing, and conservative parameters minimizes wear significantly. Frequent checks of the tools and their timely replacement eliminate low-quality surfaces and keep the process stable.
- Management of Surface Oxidation
Oxidation is minimized by flood coolant, minimized exposure to heat, followed by post-process cleaning. In the case of critical surfaces, polishing or slight grinding could be required to refinish the surface.
- Getting Rid of Residual Stress
Residual stress may result from heat or aggressive cutting conditions. Shallow passes, correct tool geometry, and temperatures minimize stress formation. Finally, stress-relieving heat treatments can be introduced in cases where ultra-high precision is required.
Critical Machining Parameters
Kovar requires specific machining parameters to maintain accuracy, control heat, and prolong tool life.
Cutting Tool Selection
- AlCrN or TiAlN-coated carbide tools: Strength and heat.
- High-speed steel (HSS): Suitable for interrupted cuts.
- Diamond tools: Provide long tool life for milling or finishing operations.
- Cubic boron nitride (CBN): Ideal for finishing hardened surfaces.
- Tool geometry: Positive rake angles of 10–20° minimize cutting forces and work hardening.
Reduction of Speeds and Feed Rates
Machining Kovar must be done at low speeds and feeds to avoid heat accumulation and surface hardening. Reduced cutting speeds prevent temperature spikes, and constant feed rates keep the tool continuously engaged with the material. These balanced parameters help achieve a smoother surface, longer tool life, and improved dimensional control.
Coolant and Lubrication Requirement
Coolant is essential for machining Kovar due to the alloy’s tendency to accumulate heat. Flood-type coolant delivery at high pressure assists in heat removal, chip flushing, and maintaining surface integrity. High-lubricity coolant also reduces friction, eliminates microhardening, and reduces the risk of tool edge breakdowns.
Tool Geometry and Edge Preparation
- Nose radius: 0.005 inches, smooth turning finishes.
- Side cutting edge angle: 15° to enhance the flow of chips.
- Turning back and side rake angles: 8° reduces cutting stress.
- End mill specifications: 0.005-inch corner radius, 30–45° angle of helix.
- Edge sharpness: Maintaining sharp edges reduces work hardening and improves dimensional control.
Surface Treatments and Post-Machining Processes
Post-machining treatments ensure Kovar maintains stability, corrosion resistance, and reliable bonding performance.
Annealing and Heat Treatment
The annealing work is critical to de-stress machining work and impart the controlled-expansion characteristic once again in the alloy. Correct heat cycles bring Kovar back to a consistent microstructure, enhancing dimensional accuracy and long-term operation. Heat treatment is also used to prepare surfaces that are to be sealed, plated, or welded.
Surface Finishing Options Guide
Surface finishing improves part quality, enhances sealing performance, and increases corrosion resistance. Methods include grinding, polishing, lapping, or micro-finishing, based on the tolerance and smoothness level specifications. Finishing of interfaces, optical components, and assemblies is essential to ensure proper sealing.
Sealing of Glass with Oxide Layer
The formation of a controlled oxide layer is unequivocal for robust, trustworthy glass-to-metal seals. The optimal oxide thickness provides good wetting and mechanical bonding. Good seals are generally grey, grey-blue, or grey-brown, indicating a well-developed oxide structure.
Quality Control and Inspection
Control of quality assures accuracy, consistency, and integrity of sealing. Defect detection before final assembly is conducted through dimensional checks, surface analysis, hardness testing, and oxide-layer inspections. High-technology instruments like CMMs, optical microscopes, and XRF plating analyzers are used to ensure that all Kovar components meet high-reliability standards.
Machined Kovar Components Applications
Due to its special thermal expansion and sealing properties, Kovar is necessary in high-precision and high-reliability industries.
Electronics and Semiconductor Packaging
Kovar is commonly found in semiconductor headers, hermetic packages, transistor housings, RF housings, and microelectronic connectors. It matches thermal expansion with glass and ceramics, preventing sealing failures and providing long-term stability in sensitive devices.
Medical Equipment Production
Medical imaging, diagnostic instruments, implantable electronics, and sealed sensor housings are also valued by Kovar. Its stability makes it accurate and long-term reliable in mission-critical devices.
Telecommunications Industry
Hermetic RF housings, fiber-optic, and microwave packages use Kovar due to its predictable behavior and long-lasting glass-to-metal seals.
Aerospace and Defense Applications
The use of Kovar components is essential in systems that require them to maintain durability, controlled expansion, and reliability under extreme conditions.
Radiofrequency Devices and Structures
Kovar maintains thermal stability under vacuum conditions and rapid temperature changes, such as those encountered in satellites.
Missile Guidance Systems
Kovar sensors, electronic housings, and stable mounting structures in guidance units are all supported using precision-machined Kovar.
High-Performance Sensors
Its stable growth helps to avoid drift and distortion of sensors subjected to vibration, heat, and atmospheric variations.
Radar System Components
Waveguides, RF housings, and sealed radar electronics applications require dimensional integrity to minimize signal error.
Laser and Optical Assemblies
Controlled expansion also allows easy alignment of optical paths and laser systems to avoid distortion at changing temperatures.
Critical Connectors and Thermal Expansion
Kovar connectors ensure alignment and structural integrity of the systems in which any slight expansion or disintegration can lead to failure.
Kovar Supplier Selection Requirement
Precision manufacturing, control of material, and sophisticated finishing are the key elements of Kovar machining that need a supplier with precision capabilities. In high-tolerance components constructed to the standards of the aerospace and semiconductor industries, collaborate with HRCCNC.
Material Quality Standards
An effective supplier delivers Kovar that is ASTM F-15 compliant, has very strict compositional control, and exhibits consistent thermal expansion, which is of great concern in hermeticity and precision assemblies.
Assessment of Machining Capabilities
Test the supplier's ability to machine Kovar without stress or work hardening, including experience in turning, milling, EDM, plating prep, and tight-tolerance finishing.
Certifications and Standards
The essential ones are ISO 9001, AS9100 aerospace, and written traceability of materials. The certifications indicate the supplier's capability to meet performance requirements as required periodically.
Experience and Expertise
Select suppliers with a strong reliability track record, e.g., aerospace, semiconductors, optics, and medical equipment. The experience will be used over the long term to avoid machining defects and rework, which are expensive.
Additional Services
Value-added services, such as plating, heat treating, oxide finishing, hermetic sealing preparation, and full inspection, facilitate production and enhance the consistency of the final parts.
FAQs About Kovar Machining Services
Can Kovar rust?
Kovar is an oxidizing material with a lower tendency to rust than carbon steel. It has a nickel and cobalt content that offers partial corrosion resistance, albeit not as good as stainless steel. It is advisable to use protective plating or store it properly.
Is Kovar a steel?
Yes, technically Kovar is an iron-nickel-cobalt alloy and therefore belongs to the specialty steel group. Kovar is designed to expand predictably under temperature changes, rather than to maximize structural strength like conventional steels.
How strong is Kovar?
The common annealed or cold-worked tensile strength of Kovar normally ranges from 70 to 80 ksi. Kovar’s primary advantage is thermal stability, rather than raw strength, making it suitable for housings, seals, and mechanical frames.
Can Kovar be welded?
Yes, Kovar is weldable, but only by TIG, which is best controlled. Nevertheless, the heat input should be controlled so that its thermal expansion properties are not affected. It is advisable to post-weld anneal.
Is Kovar hard to machine?
Yes, Kovar is said to be hard to machine. It is highly work-hardening, prone to rapid heating, and tools wear out faster than with most steels. Speed, feed, and tooling must be carefully controlled.
What is the speed and feed of Kovar?
Kovar must be cut with extremely slow parameters, since it hardens very quickly. Normal speeds are 35–70 FPM, with feeds of 0.10 ipr for turning and 0.002–0.005 ipm for milling. The conservative cuts can contain heat and preserve the tool’s duration.We work with a wide range of materials for custom CNC machining, including metals like aluminum, steel, titanium, brass, and plastics like ABS, Nylon, and PEEK. Our aluminum CNC machining service is highly popular for lightweight and strong components.
What is the distinction between Kovar and Invar?
Although both are Fe-Ni alloys, Kovar and Invar serve different engineering applications. Kovar is engineered with a regulated thermal expansion coefficient identical to that of glass and ceramics, and is suited to hermetic sealing. Invar, in turn, has an ultra-low coefficient of thermal expansion, which is used in precision tools.
Request a Free Quote
Upload your CAD files or part drawings and receive an accurate quotation within 24 hours. Our experts will analyze your design and provide cost-effective suggestions to enhance manufacturability and reduce lead time.
Design Consultation Services
Need help refining your design? Our experienced engineers offer DFM (Design for Manufacturing) support to ensure your parts are optimized for CNC machining, reducing unnecessary costs and avoiding machining challenges.
Lead Time & Shipping Information
We guarantee fast turnaround times for prototypes (as quick as 3 days) and reliable shipping worldwide. All parts are securely packaged and tracked to ensure safe delivery to your location.
Email: Info@hrccnc.com
Phone: +86 17318068324
Our support team is available to assist you with material selection, tolerance requirements, and finishing options.