CIM Design Guidelines

This CIM design guidelines is for technical ceramic products (such as alumina, zirconia, silicon nitride, silicon carbide) produced by “conventional” forming techniques, meaning ceramic powders that are pressed into a form, machined in a “green” or pre-fired state, fired, and then finished ground.

For successful ceramic injection molding, design guidelines prioritize uniform wall thicknesses, gradual transitions, and avoiding undercuts and sharp corners, while also considering materials and tolerances.

Ceramic Physical Properties

Ceramic’s set of physical properties differ greatly from those of metals and polymers. These differences should be considered when designing a ceramic part to replace a metallic or polymeric part to assure the design is both economical and fit for the intended purpose.

For example, when designing a metallic part, the average of measured mechanical strength properties is often used in design calculations, because the distribution of measured strengths is typically narrow. However, strength distributions of ceramics can be wide. If mechanical reliability of the part is critical, then understanding the ceramic’s Weibull modulus in combination with its measured average strength is important.

Here’s a more detailed breakdown of design considerations for ceramic injection molding:

1. Wall Thickness and Uniformity

Uniformity is Key

Aim for consistent wall thicknesses throughout the part to minimize stress concentrations and potential cracking during drying and firing.

Gradual Transitions

If uniform sections are not possible, ensure smooth and gradual transitions between different wall thicknesses.

Recommended Thickness

Generally, wall thicknesses between 1.2mm and 3mm are ideal, but this can vary based on the specific ceramic material and part geometry.

Avoid Thin Walls

Excessively thin walls can lead to issues like air entrapment and difficulties in filling the mold cavity.

Consider Material

The chosen ceramic material and its recommended wall thickness range should be considered.

Geometry and Features

Simple Shapes

Opt for designs that are as simple and regular as possible to reduce tooling costs and manufacturing complexities.

Round Parts

Round parts generally have lower tooling costs compared to other shapes, so consider their use where possible.

Avoid Undercuts

Undercuts can necessitate split molds, increasing costs and complexity.

Chamfers and Radii

Apply chamfers or radii to edges and corners to reduce stress concentrations and prevent chipping during handling or debinding.

Draft Angles

Consider draft angles, especially on vertical walls, to facilitate ejection from the mold.

Holes

Keep holes to a minimum diameter and consider draft angles for blind holes.

Parting Lines

Carefully consider the placement of parting lines to minimize flash and ensure easy removal of the part from the mold.

Materials and Tolerances

Material Selection

Choose a ceramic material appropriate for the intended application, considering factors like strength, temperature resistance, and wear resistance.

Tolerances

Set realistic tolerances, as tight tolerances can increase manufacturing costs and complexity.

Quality Assurance

Implement robust quality assurance protocols to ensure that the manufactured parts meet the specified tolerances and are free from defects.