May 19, 2021
How to deal with Mold repair in Injection Molding Service
Let us discuss the key factors in determining whether to repair a mold, create a new one, or do something in between during injection molding service.
Injection molds are designed to last a certain number of cycles depending on their mold class specification requirements. Once the mold has reached its usable life, there will be signs of wear, and replacement components will be required. When the mold is nearing the end of its functional life, it is essential to start looking at long-term repair costs, proactively sourcing back-up parts, and potentially complete mold replacement.
Let us discuss the key factors in determining whether to repair a mold, create a new one, or do something in between during injection molding service.
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Addressing the condition of the mold
The first step is to fix the state of the mold. This can be achieved by visual examination of the mold and its components. Dimensional inspections of parts over time are often necessary to account for possible wear areas, which also differ depending on the type of item being processed. Glass-filled components can wear tooling much earlier than other materials.
Unfortunately, the material flows will inevitably wear out everywhere. While it can often be challenging to see, tooling surface wear can show a thorough dimensional inspection in the assemblies’ fitting.
Long-term considerations
There’s a fair possibility that you initially created a mold that would last long enough to meet your manufacturing needs at injection molding companies. If your project is stuck in obsolescence, it may be best to make minor repairs to the mold. On the other hand, if the injection molding project is growing, this is a strong chance to reassess the project.
If your injection molding companies‘ project is rising, you might want to start developing higher cavitation tooling. If you were using a two-cavity mold, there might be considerable cost savings by switching to a four-cavity mold. In certain situations, the cost savings could yield a return on investment to your injection molding companies within a year.
Designing new tooling also allows your injection molding companies the ability to redesign or refine component designs in injection molding service. Style improvements, such as decreasing wall thickness, improving gate configurations, and increasing cooling capability, may also result in long-term cost savings for your injection molding companies.
Mold Complication
In the case of more complex molds using hydraulic systems, unscrewing cores, and other forms of operation, it is much more critical to fix possible failure points before the mold reaches the end of its functional existence. Your injection molding companies should be able to disassemble the mold, check the dimensions and examine the mold.
From there, they should be able to tell you any possible wear points and offer proactive maintenance guidance. More complex molds are less likely to replace them economically. However, with careful maintenance and some preparation, a well-built Class 101 or Class 102 mold will far exceed the cycle expectations in injection molding service.
When is a full replacement needed?
In injection molding service, at some point in the mold’s life, the time needed to rework the tooling, replace the parts, and fix the damage is just not worth the investment. In the end, the injection mold is an opportunity for your injection molding companies that produce the product you need to run your firm.
Ensuring that the mold is working correctly and does not achieve full failure is crucial to preventing downtime and maintaining the injection molding service’s supply chain.
Below are a few signs that a mold wants a great deal of care. If you discover some or more of these problems in the injection molding service at your injection molding companies, it might be time to start changing the mold entirely.
| Significant flash issues | The part flashes along with the ejector pins and the parting line (assuming acceptable processing practices), the tooling is worn out. |
| Dimensional changes over time | If you notice that any structural variations are increasingly occurring on your pieces in the plastic injection molding service, the tooling areas could be washed out of the material flow. |
| Issues of cooling | If the cooling lines are not properly maintained and cleaned, the injection molding process can slow down due to inefficient cooling. |
| Damaged tooling surfaces | Tooling surfaces are going to fade over time (especially textured surfaces). If the injection mold is not adequately handled, problems such as air traps will begin to pit the tooling surfaces. |
| Wear on Action | More complex injection molds with the operation have more moving components. These components are worn against each other over time and can need replacement. |
| Wear of the ejection system | Wearing of ejection devices over time. You will need to replace pins or bushings and redrill holes oversized to accommodate wear. |
| Lock damage | Tooling in the injection molding service can be designed to interlock so that the tooling does not move under injection pressure. Locks will wear over time, and they may need to be welded and reworked. |
If any of the above issues, it might be time to start preparing for a replacement mold. In any case, you don’t want to hesitate at the last minute. Early replacement planning will give you the space to learn about the project, look at long-term cost cuts and new projects, and hopefully fix any existing quality problems or design changes.
Mold Repair – Parting lines
The parting line is nothing but where the two halves of the mold intersect along with the part parameter. All parting lines need to be adequately sealed while the mold is clamped in a molding machine.
If the parting line is too loose or has undue wear, the mold will “leak” the plastic over the parting line during the process of injection molding service. This extra plastic is called flash and is a frequent obstacle to the injection molding service.
There should be no flickering on a new mold of sound engineering levels and quality tools. However, over time, tooling surface wear and parting lines also need to be reworked. Let us cover some of the usual parting line-related repairs in the plastic injection molding service.
Like for any repair, you need to find the root of the issue because you’re not only battling the symptoms. First, you want to look at the past of the mold and ask a few questions;
Have any parts of the molding process changed?
Changing materials, pressures, temperatures, and using a new molding machine will all produce a flash.
How did this issue develop?
A mold seldom begins to exhibit signs of wear “out of nowhere.” If the parting line is steadily being worn over time, you can see a poor edge starting to form. Sudden shifts are more likely to relate to processing conditions or damage.
How well is the mold maintained?
Maintaining a mold in the injection molding service is crucial to its survival. Allowing the molds to sit and make rust will cause problems with the parting line. It is necessary to keep the parting line surfaces clean and prevent any scenario in which residual plastic breaks through the parting line.
Where’s the flash?
The location of the flash is the first indication of possible places of wear. Flashing around the entire perimeter of the component may be a clamping force or a mold closure problem, whereas flashing at a particular small point could be due to mold damage. Flashing around ejector pins may be from a worn ejector pin/hole.
The injection molding technician will weld the damaged edges to repair the parting line, leaving the excess material. Using different CNC methods, technicians blend the new edge back into the mold with any existing surfaces.
If the component’s geometry allows, it is even possible to lower the whole shape enough to clean the damaged edges. Lowering the shape side involves the need to weld the tooling, but it also poses other difficulties, such as ensuring that all other components and structures are correctly aligned.
Mold Repair – Gates
Each part of the injection molding service has one or more gate locations. The gate is where the melted plastic comes into the portion of the runner device. Mold builders can take special steps to ensure that the gate’s portion is appropriately measured and built.
One significant concern, particularly for high-volume molding applications, is how the gate can be preserved over time. Now, we’re going to talk about why the gates are wearing and how this problem can be solved.
What makes Gates Wear Out?
Gate wear depends significantly on a few variables in the process of injection molding service. The type of material being handled is the primary concern. Glass-filled materials can wear gates (and all other tooling areas) much faster than other materials (like polypropylene, for example). Simply put, there’s no way around this fact.
Using hardened steel tooling to make the gate last as long as possible will help, but even then, the filling materials will still wear the gates.
What does it matter?
The indirect processing parameters of the injection molding system can alter as the gates wear. As the gate becomes more significant as it wears, the gate freeze time will be slower, and the gate shear will be smaller, the strain will be lower, etc. The part will change as either of these processes change.
A marginally larger gate and some changed processing parameters would not make any visible change in the portion for several plastic parts.
However, certain pieces can be severely impacted by minor modifications. It’s a good idea to review the scale of the gates annually and keep good process records. Seeing patterns over time can help you handle and even forecast problems with gate wear.
Fixing the Worn Gate
Except for a valve gate on a hot runner system, all gates are repaired in two ways. The gate is welded, or the gate is inserted. Welding a gate brings material back to the gate area to replace what has been worn. The technician then machines the added material back to the original form. If welding is not feasible or practical, the gate may be inserted.
To insert a gate, the engineer first designs a portion of the component that makes the whole gate area a removable insert. In high-volume applications (especially those using glass-filled materials), the engineer can insert the gates into a brand-new mold and make additional inserts.
In this case, once the gate has been worn, new gates can be easily added. Proactively inserting gates often saves on potential downtime, making routine repairs even more predictable. Instead of preparing repairs to inspect the gates, a mold maker may expect to change out the gates at a specified period.
Mold Repair – Ejection Systems
Ejector Pin & Hole Wear
Ejector pins (knockout pins) are placed around the surface of the element. During the injection molding service, the ejection assembly is retracted such that the ejector pins are flush with the tooling surface. Then, the ejection system and the pins are advanced, ejecting the component from the molding board.
Because the ejection systems cycle back and forth on each molding cycle, the guide hole in the tooling surface or the pin itself may be worn over time. That wear will display like flashing around a pin (since plastic can flow into the wear area).
Like much of the repair jobs, it’s essential to consider why anything happens first. This encourages you to solve the real problem, not just the symptom of the problem. The issue with worn ejector pins could be broader than mere wear.
You may have a misaligned ejection system, rust, or lack of clearance in the ejection system. That is why it is essential to resolve the problems as soon as possible. More wear needs more invasive and expensive maintenance work.
However, if there are no underlying problems, the fixing of the ejector pin and the hole wear is done in one of two ways-welding and reworking the area or increasing the pin’s size and the hole.
Wearing of a guided ejection system
Properly engineered and operated guided ejection systems are expected to last a long time in the injection molding service. Excessive wear can be caused by improper maintenance and lubrication of pins and bushings. Over time, the airborne grease absorbs dirt and dust from the shop, wearing the bushings and pins.
Grease can be washed and removed at regular intervals depending on the use of the mold. The directed ejection system is expected to run over a million cycles without replacement components with adequate servicing.
Lifter Mechanism Wear
Lifters have small guides to help them work properly. These components can also last a long time, provided they are well maintained. As for the driven ejection device, the assemblies should be disassembled, cleaned, and re-greased as much as required.
Compared to the ejector pin’s replacement, the replacement of lifters and lift components is much more intrusive and time-intensive and can require specially designed components. So, the components must be well treated to prevent costly maintenance.