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Silicon nitride (Si₃N₄) is widely used for components that need a combination of strength, wear resistance, thermal stability, and electrical insulation. For a broader overview of silicon nitride ceramics, including their properties, applications, and material characteristics, see our [Silicon Nitride Ceramics] guide.It is found in semiconductor equipment, bearings, vacuum systems, aerospace components, and other demanding applications.
However, machining silicon nitride ceramics is by no means a simple task.
Unlike metals, silicon nitride cannot simply be milled with conventional carbide tools and treated like stainless steel or aluminum. Its hardness and brittle fracture behavior make tool selection, grinding parameters, cooling, geometry, and inspection closely connected.
For silicon nitride ceramic components, machining is not simply about removing material. It is about controlling edge chipping and other machining-induced damage throughout the process, because a defect introduced in one stage can compromise the entire part after several subsequent operations.
The first challenge is its high hardness combined with brittleness. Even with specialized diamond grinding tools, machining silicon nitride still involves significant risk.
This risk is particularly high around sharp edges, threads, grooves, and sharp internal corners, where edge chipping can occur easily. Once a critical edge is chipped, the part may no longer meet the drawing requirements and can become unusable—even after hours of machining have already been invested in it.So, this is obviously not what we want to see.
The process may include several operations rather than a single machining step. In many cases, the process starts with rough machining, followed by CNC machining of the required features. The parts may then return to the grinding department for precision surface grinding, followed by polishing, inspection, and cleaning.
However, this is not a fixed process sequence. For each component, we determine the machining sequence based on the drawing, geometry, dimensional tolerances, surface roughness requirements, and other critical features. Some parts may require additional grinding or inspection between machining operations, while others may follow a different sequence to minimize the risk of chipping, deformation, or dimensional deviation.
Diamond grinding is commonly used because conventional cutting tools are not suitable for efficiently machining fully sintered silicon nitride.
However, using a diamond wheel does not automatically produce the required surface finish. The grinding result depends on factors such as wheel specification, abrasive grain size, grinding depth, feed rate, wheel speed, cooling, and dressing condition.
We also use different abrasive grain sizes according to the machining stage and surface requirements. When a high surface finish is not required at the roughing stage, a coarser-grit wheel can be used to remove material more efficiently. Finer-grit wheels are then introduced for precision grinding when tighter surface roughness and dimensional requirements need to be achieved.
The choice is not simply “coarser for roughing and finer for finishing”; the wheel specification also needs to be matched to the material removal requirement, geometry, and final tolerance.
Small holes can be particularly challenging.
As the feature becomes smaller, there is less room for tool deflection, heat dissipation, and chip removal. The risk of edge damage also becomes more important.
The same principle applies to thin walls and narrow slots. A process that works well on a large, rigid block may not be suitable for a thin-walled component made from the same material.
This is why machining strategy should be developed from the actual geometry, rather than from material name alone.
The difference between machining a green body and machining fully sintered silicon nitride is significant.
In the green state, the material has not yet undergone final sintering. Because the material is much easier to shape at this stage, relatively complex features can be formed with less machining difficulty.
This can make green machining an attractive option for certain components, particularly when the dimensional requirements are not extremely demanding.
However, there is an important consideration: the part will shrink during sintering.
Once the green body has been formed and machined, it still needs to go through the sintering process. The resulting dimensional shrinkage must therefore be taken into account when designing the geometry and machining allowance.
For high-precision components, this can become a major challenge.
If the final dimensions and tolerances are extremely tight, relying on a dimensional state before sintering can make it difficult to consistently achieve the required final geometry. The shrinkage behavior of the material and manufacturing process must be carefully controlled.
For some applications, however, the requirements may not justify the additional cost of extensive hard machining after sintering.
In these cases, green machining can be a practical way to reduce machining difficulty and manufacturing cost, because the material is significantly easier to shape before it becomes fully dense.
The situation is very different for a fully sintered silicon nitride blank.
After sintering, the material has become dense and highly resistant to conventional machining. At this stage, achieving the required shape, dimensions, and tolerances requires specialized diamond tools and carefully controlled machining processes.
This additional machining is more demanding and generally requires more time and process control.
However, for applications such as semiconductor equipment, maintaining high dimensional accuracy and tight tolerances can be critical. In these cases, the additional machining required after sintering may be necessary to achieve the final requirements.
Therefore, there is no single answer to whether green machining or post-sintering machining is the right choice.
The appropriate approach depends on the part geometry, material grade, required tolerance, surface roughness, production quantity, and application requirements.
If you are unsure whether your component should be machined in the green state or after sintering, feel free to contact our experts. You can send us your drawing and requirements, and our engineers can help evaluate the suitable material and machining route for your application.
There is no single machining tolerance that applies to every silicon nitride component. A statement such as “±1 μm is possible” is incomplete without describing the part.
Achievable accuracy depends on factors including:Part size, Geometry, Material grade, Feature location, Wall thickness, etc.
For example, achieving a very tight tolerance on a small, simple ground surface is a different challenge from achieving the same tolerance across a large ceramic plate containing multiple holes, thin sections, and complex features.
The table below provides an overview of our silicon nitride machining capabilities. You can also send your drawings to our engineers by email for evaluation to ensure that we can meet your requirements.
| Capability | Silicon Nitride |
|---|---|
| Maximum Size | 400 × 400 mm |
| Flatness | 0.001 mm (Ø300) |
| Concentricity | 0.005 mm |
| Roundness | 0.001 mm |
| Parallelism | 0.001 mm |
| Minimum Wall Thickness | 0.4 mm |
| Minimum Hole Diameter | 0.3 mm |
| Minimum Slot Width | 1.0 mm |
| Minimum Internal Thread | M2.0 |
| Polishing | Ra 0.005 μm |
| Sandblasting / Roughening | 2 |
Several problems repeatedly require attention when machining silicon nitride.
Sharp edges and corners are particularly vulnerable. Excessive grinding force, unsuitable parameters, or insufficient support can cause localized chipping.
Damage may extend beneath the visible surface. A component can therefore appear acceptable visually while still requiring further evaluation depending on the application.
Diamond tools and grinding wheels also wear during machining. Changes in wheel condition can affect both dimensional accuracy and surface quality.
Grinding generates heat. Cooling conditions and grinding parameters need to be controlled to avoid unwanted thermal effects and maintain process stability.
These issues are interconnected. Changing one machining parameter can affect several aspects of the final result.
At Jundro, we treat silicon nitride machining as a process-development problem, rather than simply selecting a machine and starting production.
We begin with the drawing and evaluate:
Based on these factors, we determine the appropriate machining sequence and processing methods.
For some components, rough machining and CNC feature machining may come first. For others, grinding may need to be introduced earlier or between different machining operations.
The final process may include grinding, polishing, inspection, cleaning, or additional dimensional control depending on the component.
The goal is not simply to remove material as quickly as possible.
The goal is to reach the final geometry and tolerance while controlling the risk of chipping, deformation, surface damage, and dimensional deviation throughout the process.
Silicon nitride offers excellent performance in demanding applications, but its high hardness and brittle nature make precision machining significantly more challenging than machining conventional engineering materials.
The solution is not simply to use a harder tool.
Successful silicon nitride machining requires the right combination of material selection, machining strategy, tool selection, grinding parameters, process sequence, geometry control, and inspection.
For green machining, dimensional shrinkage during sintering must be considered.
For fully sintered material, specialized hard-machining processes are required to achieve the final geometry and tight tolerances.
Ultimately, the most suitable machining route depends on the actual component.
If you have a silicon nitride drawing and are unsure whether to use green machining or fully sintered material, or are uncertain about the appropriate machining process, you can send us the drawing and requirements. Our engineers can evaluate the geometry, tolerances, surface requirements, and manufacturing route before production.
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