Those of you in injection molding business have definitely encountered these frustrating situations: right after starting machine, material shortages, burrs, air bubbles, and burning all appear.
Customers are rushing to deliver, boss is watching, and you're constantly adjusting temperature, changing pressure, controlling speed, working up a sweat for three or four hours, only to find that one problem is solved while another arises, the more you adjust, the more chaotic it becomes, and scrap piles up, leaving you panicking: at best you'll get yelled at, at worst you'll be fired!
Today, we won't go into how to adjust individual parameters or fix specific defects, but rather share a practical strategy that will allow you to handle a host of problems like turning tide in a game, resolving them smoothly and effortlessly, saving you from endless busywork.

 

First, clarify: Are you dealing with a new mold or an old mold currently in mass production? Approaches to these two situations are completely different.

Many people, as soon as a new mold is installed, think about quickly producing a qualified product – this is a big mistake! I did this when I first entered industry. I spent most of day adjusting it, only to find out that mold's runner design was unbalanced. All that work wasted, and I had to stop machine for repairs, delaying project.
Core of new mold debugging is verifying mold's usability, not brute-forcing it with process. You need to focus on checking three things:
1. Is runner balanced? – Check if filling speed of each cavity is consistent;
2. Is cooling system adequate? – Feel temperature of different parts of mold; temperature difference shouldn't be too large;
3. Is venting sufficient? – Are there any dead spots where air can easily accumulate?
All your machine adjustments are tests to see if these problems can be compensated for by process. If they can't be compensated for (for example, some cavities just won't fill completely), don't hesitate, stop machine immediately and contact mold manufacturer! Bring machine adjustment records and explain situation clearly; we, machine adjusters, cannot be blamed for mold's problems.
Remember: If foundation isn't solid, all renovations will be in vain.

When an old mold suddenly malfunctions during mass production, the most frustrating thing is when boss says, "It was fine before," leaving you speechless. Don't panic. The key question is: What changed during production process?
Was it a new batch of materials? Or was machine's pressure inaccurate after last maintenance? Or was a screw not tightened after mold was disassembled? Finding this "variable" is half battle won.
Next, follow a three-step troubleshooting process, with clear logic: First, check materials and temperature → then check machine and mold → finally, adjust process parameters.

Many people spend a lot of time adjusting parameters, only to find out material wasn't dried properly, wasting valuable time.
1. Material drying is paramount.
Especially for absorbent materials like nylon with glass fiber, if not thoroughly dried before use, moisture in material will turn into bubbles, degrading material performance, causing product to yellow and become brittle.
Remember standard operating procedure: Use a dehumidifying dryer at 110℃ for 4 hours, ideally maintaining temperature in an insulated hopper. Proportion of recycled material should not exceed 30%, and it must be dried as thoroughly as virgin material.
Here's a simple method: inject a small amount of resin and check. If resin is foamy and lacks gloss, don't adjust the parameters. Either material wasn't dried properly, or it degraded after being burned for too long in nozzle. Address material issue first!
2. Hot runner temperature must be accurately measured, not just on screen!
In multi-cavity molds, uneven filling is often due to inconsistent hot runner temperatures. Don't rely on numbers on temperature control panel; use a thermometer to measure actual temperature of each hot runner. Temperature difference must be controlled within ±3℃.
Otherwise, some hot nozzles will discharge material quickly, while others will discharge slowly, naturally leading to material shortages in some cavities and burrs in others.

If material and temperature are fine, check hardware. Unstable hardware, no matter how fancy parameter settings, is useless; it's like building a house on sand—it will collapse in wind.
1. Check Machine: Is clamping force sufficient? Is mold closing level?
For large molds and multi-cavity production, first calculate if clamping force is sufficient. If it's insufficient, parting surface will leak glue, definitely resulting in burrs. Over time, mold-closing components will wear down, leading to loose mold closure.
Use a feeler gauge to check parting surface; if there's a gap, adjust it immediately. Don't force it to run!
2. Check Mold: Focus on venting and wear!
Air marks and burning are caused by poor venting! Venting channels are easily clogged by glue powder and oil; manually clean and remove them. Venting groove depth for nylon material is approximately two to three micrometers. If it's clogged, clean it; if it's insufficient, deepen it.
Additionally, check parting surface for wear and cavity for scratches. Apply red lead to mold and check contact marks after mold closing. Unevenness indicates a problem with mold closing.

 

Once materials, machine, and mold are all in order, adjust process. Core principle: solve critical problems first, address minor appearance issues!
1. First, address material shortages and burrs—don't get order wrong!
These are the most challenging issues; you must replenish material first, then control burrs!
Solving material shortages: Gradually increase injection speed, pressure, and material temperature until the most difficult-to-fill cavity is filled. For hot runner molds, you can separately heat the nozzle corresponding to cavity with material shortages.
Solving burrs: If burrs remain after filling cavity, first reduce holding pressure and time, not injection pressure! If reducing holding pressure doesn't work, then slightly reduce material temperature. If burrs still appear, check clamping force and mold parting surface again.
1. Address air bubbles and scorching – give gas an escape route!
Air bubbles and scorching occur because gas cannot escape, is trapped inside by high-pressure material.
The simplest solution: use multi-stage injection. When material fills 90%~95% of cavity, almost to venting groove, reduce injection speed to allow gas to escape slowly. Don't use high speed and high pressure to scorch gas.
Additionally, observe scorched areas and clean or deepen venting grooves there; this is 10 times more effective than adjusting parameters!
1. Finally, address weld line, loose fibers, and deformation – fine-tuning!
Wheel line: Increase material temperature and mold temperature slightly (engineering material mold temperature should ideally be above 100℃). Instantly accelerate at the point where material flows meet to ensure a stronger bond between two streams.
Fiber Explosion: Don't set screw speed too high, otherwise fiberglass will be sheared too finely; use high holding pressure and long holding time to ensure product surface adheres tightly to mold, preventing fiberglass from protruding.
Deformation: Use different temperatures for moving and fixed molds to guide product to shrink in correct direction; hold pressure longer for thicker areas to compensate for shrinkage differences.

1. Layered Troubleshooting: First check material and temperature, then hardware, and finally adjust process; don't haphazardly try to do everything at once.
2. Hardware First, Soft Second: Adjusting parameters is only effective once hardware, such as mold and machine, is sound.
3. Prioritize: First resolve major production-impacting issues like material shortages and burrs, then address minor appearance defects.
Following this approach, no matter how many problems you encounter, you can systematically clarify them, transforming yourself from a "firefighter" into a "machine adjustment expert"!