Voids

Voids are caused by various physical and chemical processes that occur during manufacture:

• Shrinkage: when materials change from the liquid to the solid phase as they cool, they shrink. This can create cavities if the volume is not fully compensated.

• Gas formation: trapped gases or released chemical substances can cause bubbles in the material.

• Uneven cooling: different cooling rates within a workpiece lead to internal stresses and voids.

• Material composition: materials with insufficient viscosity or poor flow properties are more prone to void formation.

There are different types of voids, which differ in size, shape and cause:

Casting voids

• Description: form when molten metals or plastics cool.

• Typical cause: shrinkage and insufficient feeding of material.

Gas porosity

• Description: small, distributed pores caused by trapped gases.

• Typical cause: release of gases during processing.

Shrinkage cavities

• Description: large, irregular cavities, often located inside components.

• Typical cause: uneven cooling or lack of material.

Voids can significantly affect the quality and function of a workpiece:

• Mechanical weakening: cavities reduce the strength and load-bearing capacity of the material.

• Surface defects: visible voids impair appearance and can be a problem in sensitive applications, for example in the medical or automotive industry.

• Leaks: in seals or containers, voids can cause leakage.

• Quality problems: products with voids may not meet the required specifications.

Void formation can be minimised by various measures during the manufacturing process:

Optimising the manufacturing process

• Process parameters: optimisation of temperature, pressure and cooling rate.

• Choice of material: use of materials with a low shrinkage rate and good flow properties.

• Venting: use of venting systems to remove trapped gases.

Design measures

• Gating systems: use of feeders and risers to compensate for lack of material.

• Design adjustments: avoiding thick wall sections that lead to uneven cooling.

Post-processing

• Grinding: removal of surface voids.

• Filling: use of filler materials to repair cavities.

Voids are a common problem in various industries and require specific solutions:

Automotive industry

• Castings: optimisation of engine blocks and gearbox housings to avoid voids.

• Seals: ensuring material integrity in elastomer components.

Medical technology

• Implants: avoiding pores and voids for maximum stability.

• Instruments: high-precision processing to ensure functionality.

Construction industry

• Concrete components: minimising voids to improve load-bearing capacity.

• Facades: avoiding visible surface voids for an attractive appearance.

Minimising voids offers the following advantages:

• Higher quality: products with a homogeneous structure meet higher standards.

• Reliability: fewer material defects increase service life.

• Cost efficiency: less scrap and lower rework costs.

Despite modern technology, avoiding voids remains demanding:

• Material costs: high-quality materials with better properties are often more expensive.

• Complex geometries: components with complex shapes require elaborate manufacturing strategies.

• Process monitoring: precise control of temperature, pressure and time is necessary.

• How are voids detected? By visual inspection, ultrasonic testing or X-ray examination.

• Can voids be repaired? Yes, by grinding, filling or other post-processing methods.

• Which materials are particularly prone to voids? Materials with a high shrinkage rate, such as aluminium or certain plastics.

• How can voids in castings be avoided? Through optimal process parameters, feeding systems and good venting.

Voids are a common problem in manufacturing that can impair both the quality and the function of components. With optimised processes, suitable materials and targeted post-processing, however, many void problems can be avoided or remedied. Reducing voids contributes significantly to better product quality and cost efficiency.