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Design Guide

From Coors Ceramics Company:

The single most important factor to consider when designing with ceramic materials is that they behave under stress as a brittle material. As such, a localized defect, flaw or other "stress riser" can be an initiation point for crack growth, fracture and potential catastrophic failure. Stress riser points can result from a design that incorporates sharp internal corners to undercuts in the material. When the part is mechanically stressed either by the application of a load or due to thermal loads, these points can end up in tension and may crack. To take full advantage of the properties of the ceramic materials the design should minimize tensile stresses in the part.

Avoid knife edge features. Because of the brittle nature of the ceramic, these types of features will be prone to chipping. Provide a 0.030" to 0.050" thick tip if knife edges are necessary.

Provide a 0.020" minimum radius on inside corners, whenever possible. The sharper this corner, the greater the possibility it can become a stress riser. Also, the sharper the corner the more expensive the part.

Provide a radius or chamfer on all edges to prevent chipping. Whenever possible specify a simple edge break with a minimum radius of 0.015" that can be applied by a simple hand operation. Tight tolerances on radii or chamfers require precise machine made features that are more costly.

Use standard fractional values for radii and angles to avoid special tooling. Try to use 30 or 45 degrees for angles and chamfers.

From Bralla's "Design for Manufacturability Handbook," McGraw-Hill, New York, 1999:

Since parts may sag or be distorted if not properly supported during firing, it is preferable to avoid large overhanging or unsupported sections. Otherwise, supporting fixture costs may be excessive.

Differential shrinkage of sections of non-uniform thickness during drying and firing causes stress, distortion, and cracking.

Gently curved surfaces without abrupt break lines or angularity are normally preferred with most ceramic-forming processes.

Molding of screw threads in ceramic parts is not very feasible.

Ribs and fins should be well rounded, wide, and well spaced and have normal draft.

Secondary grinding operations can be very expensive on ceramic parts. Limit high tolerance regions.