When customizing precision ceramic structural parts, what are the common design techniques to prevent cracking and deformation?

In advanced manufacturing and industrial applications, precision ceramics (such as alumina, zirconia, silicon nitride, silicon carbide) have become indispensable core materials due to their high hardness, wear resistance, high temperature resistance and corrosion resistance. However, due to the inherent high brittleness of ceramic materials and the severe volume shrinkage faced during high-temperature sintering (the shrinkage rate is usually within 15% to 25% ), the design and manufacturing of its structural parts are extremely challenging. Irrational structural design often leads to cracking, warping and deformation of products during sintering, machining or actual service.

This guide systematically summarizes the core design anti-cracking techniques, anti-deformation strategies and process matching specifications in the customization process of precision ceramic structural parts, aiming to help design engineers optimize product structure, improve yield and reduce production costs.

1. Three key points of ceramic material properties and customization

Before starting any ceramic customization project, the following three mutually restricting core elements must be examined from a global perspective.

1. Material selection

The physical and chemical properties of materials determine the upper performance limit of structural parts. The following table lists the core characteristics and typical application scenarios of four mainstream precision ceramic materials.

2. Dimensional accuracy and machining allowance

• Sintering tolerance: Directly sintered " green body " becoming " Ripe billet " Finally, due to uneven shrinkage, the tolerance can usually only be controlled within ±1% or ±0.1mm Around.
• Finishing allowance: For extremely high matching accuracy requirements (such as micron level μm ) interface must be set aside during design 15mm-0.3mm diamond grinding wheel grinding allowance.

3. Molding process matching

Select the process according to the production batch and structural complexity: dry pressing is suitable for large quantities of simple flat parts; cold isostatic pressing (CIP) Suitable for large size, bar or tube blanks; ceramic injection molding (CIM) It is suitable for three-dimensional small parts with extremely complex structures, but the mold opening cost is high.

2. Core design skills for anti-cracking and anti-deformation

1. Wall Thickness Design: Pursuit " absolutely uniform "

Uneven wall thickness is the number one cause of cracking in ceramic parts during sintering and cooling. The thermal expansion and contraction rates of thick parts and thin parts are different, which will generate huge internal stress.

• Avoid disparities in thickness: Try to keep the overall wall thickness consistent. If there must be thickness changes in the structure, gentle slope transitions should be used and absolutely avoided 90° of sudden changes.
• Process weight reduction holes: For heavy solid parts, blind holes, through holes or back hollowing (grooving) should be designed to reduce local thickness while ensuring mechanical strength.

2. Corner design: full acute angle circle ( R angle specification)

Ceramics produced at sharp corners " stress concentration " Extremely sensitive. Sharp internal or external corners can easily become the source of cracks when subjected to thermal shock or mechanical stress.

• within / External corner radius: All corners and step transitions must be rounded. Recommend internal R angle is at least greater than 5mm (recommended R≥1.0mm ). Space permitting, R The larger the angle, the more rigid the structure.
• Assembling the corner clearing slot: If it must be retained due to the need to match metal parts 90° For external right angles, one should be designed inward at the internal corner. " Undercut " or " blind hole " , move the stress relief area away from the right angle vertex.

3. Hole and edge design: Prevent sintering cracking and edge chipping

When opening holes (such as screw holes and weight-reducing holes) in ceramic parts, the position and shape of the holes have a great influence on the molding quality.

• Critical edge distance: The distance from the hole wall to the outer edge of the ceramic piece, as well as the net distance between the two holes, must be greater than the hole diameter. 5 times. Too close a distance will cause the weak area to be pulled apart at both ends during sintering shrinkage.
• Orifice chamfer: The opening edges of all through and blind vias should be designed 45°×0.3mm-0.5mm Chamfer to prevent edge chipping during subsequent grinding or actual assembly.
• Avoid shaped holes: Try to use standard round holes. Try to avoid designing long holes, square holes or special holes with sharp corners. Such holes have obvious anisotropy when shrinking and are prone to micro-cracks around them.

4. Eliminate large flat surfaces: fight warping deformation

Due to the influence of gravity, friction and small differences in furnace temperature during sintering, large and thin flat parts are easily prone to warping deformation (commonly known as " Banana Bend " ).

• Set stiffeners: Designing cross-shaped, tic-shaped or radial reinforcing ribs on the back of the flat piece can significantly improve the rigidity and lock the shrinkage direction.
• Local boss design: If a certain plane needs to be used as an assembly contact surface, do not make the entire large plane into a high-precision precision contact surface. Tiny local bosses should be designed around screw holes or key fitting points, and only the surface of the bosses should be ground during subsequent finishing. This not only saves processing costs, but also effectively avoids the impact of overall plane warpage.

5. Symmetrical design: balanced sintering tension

When ceramic parts are sintered in the furnace, the shrinkage force is relatively balanced in all directions. If the structure is severely asymmetrical, it will lead to unbalanced tension and overall distortion.

• Geometric symmetry: Try to make the structural parts maintain central symmetry, axis symmetry or shape symmetry on a two-dimensional or three-dimensional level.
• Craft tie (craft support beam): For asymmetric opening shapes (such as C shape, U (shaped structure), one should be artificially added to the opening during design. " Temporary process connection beam " , so that it maintains a closed-loop symmetric structure during sintering. After sintering and grinding, the temporary beam is cut off with a diamond slice.

Three. Cheat Sheet for Design Specifications of Precision Ceramic Structural Parts

The following table summarizes the wrong practices and correct specifications when designing precision ceramic structural parts for quick reference by engineers.

Note: During the actual project development process, it is strongly recommended to conduct manufacturing-oriented design with the ceramic forward process engineer as soon as possible after the first draft of the structural design is completed ( DFM ) review to further optimize dimensions based on the mechanical properties of the specific material.