EXPERT ADVICE ON TOOLING
Buildup on the cavity surface can cause gloss and sticking issues. This can be difficult to clean in the press with standard cleaners. I have developed a cleaner to address this issue, called Zap-Ox.
One issue that can frustrate toolmakers is damage from plastic flakes building up on the parting-line shutoffs. This is typically a result of bad gating, undercuts on sprue-puller pins, or stringers from the sprue or hot drop. The flaking or stringing issues should be resolved to prevent mold damage.
Different mold temperatures for the two mold halves can also contribute to wear, flash, galling, and contamination of the parts. Whenever mold temperatures differ between the two halves, the tool should be evaluated to see if this could cause any issues. The hotter half will thermally expand so it will be dimensionally larger. This can affect wear and galling on pins/bushings, lock angles/corner locks, and shutoffs, causing flash or galling, depending on which way the mold half is expanding. I have had cases where wear on the corner locks created contamination on the part from debris falling into the cavity.
Concerning pins and bushings, I prefer to use solid bronze bushings, especially on larger tools, to prevent gulling between the pin and bushing. Solid bronze will hold up better than bronze-plated bushings. Since implementing this standard in my shop years ago, galling of pins and bushings is no longer an issue.
One other area that is prone to wear if not maintained is slide-lock angles. This surface sees a lot of mechanical friction on mold closing. Many people focus on the horn/guide pin for the slide as what needs to be greased. It does need grease, but the lock angle is the surface that really deserves the attention. Once the lock-angle surface wears, it can contribute to flash from loss of preload.
When cleaning the parting lines or cavity surface, mold cleaner should never be sprayed directly on the components or cavity surface that has lifters or ejector pins. This can create bigger issues of bleeding onto the plastic part and loss of lubricant on the mold component. To remove excessive grease from a component, it should be cleaned with a rag sprayed with mold cleaner. Many mold makers apply more grease than necessary, and their grease of choice can contribute to the issue by not being optimal for the mold’s application.
Maintenance of the mold exterior varies among molders. This doesn’t take much effort and will also protect your platens. The outside of the tool, specifically the clamping surfaces, should be cleaned after pulling, and a rust preventative should be applied. This should also be performed on the platen surfaces. The other exterior surfaces of the mold should be examined for water leaks or rust and cleaned up or sent to the tool room to investigate the water leak. The mold-mounting surfaces should also be observed for burrs or dings at PM and when setting or pulling the tool.
The article comes from China injection mold manufacturer - Mold Best Assurance Company Limited, website is www.mbamoldanddesign.com
