When parts are produced in an injection-molding operation, the work product is continually checked for conformance to specifications. When part non-conformance is detected, experienced operators inspect their molds to determine issues that may be contributing to the problem. Following inspection, a detailed action plan must be established to correct these non-conformances.
Corrective actions for problematic molds may include:
- Refurbish: Such action can consist of a major overhaul of all mold systems and restoration of molding surfaces to production-worthy condition.
- Repair: This is limited to correcting specific failures, which can include one or multiple mold systems.
- Upgrade: Implementing improvements to the tool. This may consist of system upgrades to improve productivity and reduce instances of common component failures, or replacement of commercial components that are no longer available.
- Replace: This most often occurs at the end of a mold’s life cycle, or when there is a change in volume requirements that the existing tool can no longer meet. Mold replacement offers the opportunity to incorporate upgrades for productivity improvements.
Corrective actions for molds that are producing non-conforming parts
|Option||Drivers/reasons||Cost||Time||Extent of qualification required|
|Refurbish||Use||One-third the cost of new||Medium||Dependent upon components that are refurbished|
|Repair||• Catastrophic event|
• Normal wear and tear or damage to specific components
|Upgrade||• The need to integrate new technology|
• Parts are no longer available
• Change in design or utilization
|Medium||Medium||Limited to full|
|Replace||The mold is worn and refurbishing or repair is not practical||High||High||Full|
What is the extent of mold qualification necessary after refurbishment to guarantee that the mold once again can produce conforming parts?
First, let’s look at when mold refurbishment should be considered:
- The tooling is no longer capable of producing conforming parts, or efficiencies drop due to downtime and reduced quality.
- A tool has reached a designated or recommended number of cycles that require the components to be refreshed to ensure that the mold will continue to be viable for an extended period of time. Operators should not wait until components are worn out because the parts can no longer be refurbished; they can only be replaced.
- Whereas the option of repairing is localized to just mold components, refurbishment is a holistic approach to maintaining the mold. Refurbishment is not the same as an upgrade.
- Refurbishment does not include modifications that happen within the mold.
A mold refurbishment is approximately 30 percent of the cost of purchasing a new mold. So it makes good practical sense for operators to keep a close eye on the condition of their molds. COAST Systems can be of assistance in this regard by implementing a regular inspection schedule for a given mold—or molds—based on usage or number of shots. Such a schedule will aid in determining whether to refurbish, repair, upgrade, or replace a mold.
How will you know whether your refurbished mold will require qualification?
The short answer is…it depends. And it depends mostly on whether the refurbishment affected the molding surfaces. If the molding surfaces have been affected, then a mold qualification is advised since finished part geometry could be impacted by the refurbishment.
However, if the refurbishment did not affect the molding surfaces, then qualification is unnecessary. In a mold refurbishment, all components–including worn-out items–are refurbished or replaced to OEM specifications, which enables the mold to again deliver conforming parts. Mold refurbishment offers cost and time advantages over mold replacement and enables the tool to again deliver conforming parts.
If a mold requires qualification, what should that include?
Using an agreed-upon validation process, assess the components for:
- First article inspection (FAI):
- Define cavity-to-cavity variations in dimensional stability, typically validating all product drawing variable attributes, for three to five shots of product. Process capability metrics (Cpk) and process performance metrics (Ppk) are beneficial to define stability.
- Process development study:
- Qualified process review–As molds wear and degrade over time, it is not uncommon for the master process to be modified slightly to overcome deficiencies in the mold, such as cooling efficiency. Refurbished molds should always be requalified against the original master process parameters.
- Weight variations–Measuring part weight by cavity, using an electronic scale to three decimal place resolution, can be valuable as a process control.
- Flow of materials–Short shot studies help define flow balance conditions that may occur due to change/repair of hot manifold systems, runners, or gate geometry.
- Part functionality–First-shot samples may require assembly functionality testing before a refurbished mold is approved.
The bottom line: Make sure your molds are delivering conforming parts
When an injection molding operation identifies non-conforming production parts, experienced operators inspect their molds to help determine the problem. Following inspection and upon identification of specific issues, corrective actions for problematic molds may include a repair, refurbishment, upgrade, or replacement. A mold refurbishment can be a cost effective way of returning a mold to its original performance specifications, but a refurbished mold may need to be qualified, depending on whether the mold surfaces were affected by the refurbishment.
Contributing author: Iynesh Kumar – Senior Qualification Analyst
In addition to leading the maintenance management market with a highly rated CMMS software solution, COAST Systems offers global mold asset management to assist manufacturers in the maintenance planning and tracking of their critical mold assets. Partner with COAST Systems to optimize the value of your investments in mold tooling.