Adverse factors of plastic material and injection mold are in the following:
- The plastic melt is provided with high flow viscosity, resulting in poor flow and filling capacity.
- The plastic melt has poor plasticity, excessively low temperature for plastication and unbalanced melt temperature, which altogether result in the poor melt fluidity.
- Mold temperature is overlow or unbalanced, temperature of some parts is too low and temperature of melt injected into the cavity drops too fast.
- The flow of melt in the mold is too long or too complicated, the resistance against filling is large and the filling is not smooth, even resulting instagnation.
- Temperature of nozzle is too low and the cold-slug well of feed system is improperly set, resulting in jam and stagnation when the front cold material of melt enters the cavity.
- During the filling, molds are not sufficiently aired and the gas has not been discharged in time, thereby resulting in the expansion of filling resistance.
Solutions:
- Use plastics with low viscosity and sound fluidity or adjust prescription of plastics and reduce viscosity of melt.
- Improve barrel temperature, increase injection pressure, raise melt temperature to reduce viscosity, and improve plastication quality
- Improve mold temperature, and uniformity thereof, raise nozzle temperature and properly set cold-slug well.
- Increase dimension of the runner and gate and properly set gate position to avoid overlong flow during filling and overlarge loss of pressure when the melt enters cavity.
- Properly design mold exhausting scheme and change number of position of gate as well as position of parting line when necessary to achieve sound exhausting effect.
Before you endeavor to produce a part via injection molding consider a few of the following things.
Start with Financial Considerations
You’ll want to determine the number of parts produced at which injection molding becomes the most cost effective method of manufacturing.
From there, you’ll want to determine the number of parts produced at which you expect to break even on your investment (consider the costs of design, testing, production, assembly, marketing, and distribution as well as the expected price point for sales). Build in a conservative margin.
And don’t forget about entry costs. Preparing a product for injection molded manufacturing requires a large initial investment. Make sure you understand this crucial point up front.
Let’s Talk Design Considerations
When it comes to part design, you want to design the part from day one with injection molding in mind. Simplifying geometry and minimizing the number of parts early on will pay dividends down the road.
When designing the mold tool, the top priority is to prevent defects during production. For a list of 10 common injection molding defects and how to fix or prevent them read here. Consider gate locations and run simulations using moldflow software like Solidworks Plastics.
Getting Production Right for Injection Molding
Cycle time is crucial here. Minimize cycle time as much as possible. Using machines with hot runner technology will help as will well-thought-out tooling. Small changes can make a big difference and cutting a few seconds from your cycle time can translate into big savings when you’re producing millions of parts.
Tied to production is the assembly process. You’ll want to design your part to minimize assembly. Much of the reason injection molding is done in southeast Asia is the cost of assembling simple parts during an injection molding run. To the extent that you can design assembly out of the process you will save significant money on the cost of labor.
Injection Molding: The Bottom Line
Injection molding is a great technology for finished production on a massive scale. It is also useful for finalized prototypes that are used for consumer and/or product testing. Prior to this late stage in production, however, 3D printing is much more affordable and flexible for products in the early stages of design.
It is not easy to master injection molding technology.
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A qualified injection mold engineer must have sufficient knowledge in polymer materials and practical experience in mold making and molding
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