Mold cleaning is a process where major maintenance bottlenecks often occur because molds are pulled faster than they can be cleaned and made production-ready. I have visited plants where molds waiting to be cleaned line hallways and toolrooms, taking up valuable bench space.

Many times, in order to meet production demands, molds get reset dirty or the cleaning process is rushed, which subjects tooling to more damage through hurried handling. The question is asked, “Can we run it the way it is, or does it really need to be cleaned?” In companies where firefighting is the accepted culture, the mold will be reset and started; if all the parts come out clean, it runs. Once this happens a few times, management comes to assume that molds need to be cleaned only when the residue level is bad enough to migrate out onto the part, or until the mold locks (galls) up.

Some shops handle cleaning chores by enlisting non-skilled employees or toolroom apprentices to wash tooling and plates as quickly as the repair technician can take them apart. This practice works, unless the product has critical flash, dimensional or aesthetic specifications, or the mold has a history of maintenance, reliability or quality issues. It is difficult for the repair technician to accurate troubleshoot mold and part defects when all the track marks are washed off from the tooling and plates.

Why clean injection molds?
Injection molding is a widely used process in mass production, therefore it is essential that the process is flawless in order to avoid unnecessary costs incurred from having to redo results or repair and or replace equipment and to ensure the quality of a large number of pieces.

Proper lubrication of the mold extraction mechanisms or mold cooling channels free from limescale and rust accumulations, are elements to pay attention to in the maintenance of injection molding machines. But the perfect cleanliness of the mould figures is perhaps the most important factor to ensure the highest quality of production.

It’s easy for a small imperfection in the surface of the mold, in contact with the molten polymer material, to create a defect in the final part once it has cooled. For this reason it is essential to rely on cleaning systems that not only carefully remove the residues that can be deposited on the mould figures (especially the smallest and richest ones), but also in order to prevent any damage to the mold.

The residues to be removed are usually deposits of release agents and lubricating oils – used to allow the detachment of the artifacts from the walls of the molds and the correct sliding of the mobile part of the mould. In addition, it is also possible that the molds must be cleaned of residues left by the gases that are created in the presence of pressure and high temperatures

How to clean injection molds
In order to avoid any damage to the surface of the mold, operations such as sandblasting, the small “clothespins” used to clean the surface of the mould or the use of aggressive and potentially corrosive substances are absolutely to be avoided as they could be counterproductive.

Even resorting to manual washing processes with rags and solvents may not be the best solution, as it could lead to unsatisfactory cleaning standards, especially in the case of moulds with complex geometries and small figures.

Finally, given the considerable impact of a mold on the quality of mass production, it would be advisable to proceed with a standardized washing process that always uses the same products: in this way it will be possible to minimize the possible variability of the production parts due to the level of cleanliness of the mold, eliminating the human factor from the equation.

Automatic parts washers that use gentle water-based detergents are almost always the best choice for washing injection molds.

In the case of complex moulds and with very small parts it may be necessary to resort to ultrasonic cleaning technology that allows you to reach every millimetre of the mold surface effectively. Ultrasonic cleaners have special features that generate micro-explosions in the washing fluid that the mold is immersed in. These in turn create friction that enhances the cleaning effect of the fluid, even when dealing with fine surface details.

For simpler moulds, however, a rotating basket parts washing machine can be sufficient to ensure standardization, effectiveness and delicacy of washing.

The only exceptions are hot chamber molds and mirror-polished molds.