One of the main influences to a good / bad part is the gating system. Commonly there are cold runner or hot runners be used. We focus in a high level of detail in a very early beginning of the project to balance the gating system to have a uniform filling in all cavities.
To get a first estimation what happens in the cavities we make a simple filling study. At this stage with no cooling implemented we get a larger understanding of the "problem" areas from your part.
The possibility to create in our simulation software helps us to get a understanding which influence the cooling have to your part. We create the optimal cooling and start the next step of simulation to understand the thermal influences.
We send our cooling proposal to the toolmaker, the toolmaker try to implement the optimal cooling in the tool. For sure this is in most of the cases not possible because of ejectors, inserts etc.
After we get the real cooling back from the toolmaker we start to analyze this cooling. Flow length, and flow rate of each cooling channel will be checked. After an positive result we start the "real" simulation. Therefore we include the mold materials (Moldmax inserts, steel types with different thermal conductivity etc.) to get the real wall temperatures in each step of injection.
A very clear report will be generated as PDF, pptx or a web based file. You will get an easy to understand result and a large understanding of your part.
Plastic components are in use by every industry and manufacturing these components through injection molding has come a long way. A wide range of equipment options exist depending on your application and capabilities. Generally speaking you have a choice between traditional cold runners or the more advanced hot runners. Each option comes with its own unique sets of pros and cons and so understanding the differences and how they relate to your application could have a big impact on your productivity and overall profitability.
In a cold runner mold, the molten thermoplastic is injected into the mold which fills the runners that distribute the molten plastic to the individual mold cavities. The cold runner mold then cools the sprue, runner, and gate along with the molded part.
Cold runner molds are certainly more economical to manufacture and can be easier to maintain, however they have several major limitations compared to molds with hot runner systems:
Longer cycle time
Creates waste (sub-runners)
Require additional auxiliary processing equipment (robotics, re-grinding machines/employee labor to remove runners, etc.)
Secondary operations (degating, removal of cold runners, re-grinding etc.)
Why Choose Hot Runners
While hot runners often come with a higher upfront cost and require some additional maintenance, their more efficient design can often easily provide a valuable return on this investment. Hot runners significantly overcome the inefficiencies of its cold runner counterpart.
Hot runner systems produce less wasted plastic, have shorter cycle times, use less energy, improve gate quality, use fewer auxiliaries and require less manual labor for runner handling, trimming and regrinding.
Wasted Plastic & Energy
Depending on the part design, the cold runner can equal 50% to 250% of the mold part weight with regrind typically limited to 15% at most, so the remaining 85% is waste or has minimal salvage value. Re-grinding also adds a step in the manufacturing process and could decrease the plastic’s mechanical properties
For some markets, this waste could be much higher. The medical market requires 100% virgin resin, so all of the runner would be scrap. The energy consumption of a cold runner can double due to extra heat, cool and regrind wasted.
For many applications, the wasted runner can double the part cost.
Cycle time is typically dominated by part cooling, with cooling time being dictated by part wall thickness or cold runner thickness. Even optimized cold runners cause typically 50% to 100% longer cycle times than hot runners.
Hot runners offer higher productivity yields due to significantly reduced process cycle times.
Cold runners mold with 3 plate design, trimming equipment, regrinding equipment, added chilling/cooling capacity and metering blender. Hot runners only require a manifold, nozzles and plates as well as a temperature controller, which is reusable.
Managing additional overhead and operational factors such as added chilling capacity and the noise and dust related to grinding scrap runners.
Cold runner costs include runner handling, trimming, re-blending and scrap. They are prone to occasional stick in molds interrupting overall operation. Maintenance is also required on numerous auxiliaries.
Hot runners are highly automated and are ideally suited to scheduled preventative maintenance. Interruptions are possible with failed heaters or thermocouples but depending on the hot runner manufacturer, these interruptions can be minimal.
Eliminating the cold runner saves the added labor from runner handling, gate trimming and regrinding.
For years, natural balance has been the cornerstone of a successful hot runner balance. This means that the melt experiences the same flow length and the same diameter melt channels from when it leaves the machine nozzle until it enters each cavity within the mold. This approach has served the industry well.
In recent years, much attention has been paid to the effects that shear has on the melt as it flows through a cold runner system. Of specific interest is how shear heated melt is distributed by the cold runner geometry. Research in this field has led to a greater understanding of shear-induced variances as they apply to cold runner systems and led to the introduction of technologies that are aimed to help address molding issues which have irritated molders for years.
It has also led to a greater awareness of the topic by the general injection molding community. While the majority of published research on this phenomenon has been based on cold runner systems, it has naturally called into question the validity of natural balance principles as applied to hot runner systems.
Balance Sensitive Applications
Uniform balance is always desirable. If a mold is significantly imbalanced, it will be difficult to start up and may have a narrow process window. The balance that can be achieved between cavities on a multi-cavity mold will have a bearing on the part to part consistency. That being said, there are some applications that will require a higher degree of balance than others. These will include parts that have a demanding dimensional requirement or parts that will be difficult to eject if they are over packed. Here uniform balance is important to ensure that all cavities are uniformly filled. It is important to recognize applications where balance will be critical.
However, it’s important to recognize that there are some fundamental differences between hot runner system and cold runner system designs. Cold runner systems are more prone to the effects of shear due to their inherent design.