Injection Molding – Design tips and Design Rules – Preventing Flaws

Injection Molding – Design tips and Design Rules – Preventing Flaws makenica.com/injection-molding-design-tips-and-design-rules-preventing-flaws April 3, 2021

Injection molding service is a well-known industrial technique that is mainly used to produce high-volume plastic components. With the Plastic Injection molding service, we can make components and products out of various materials, but it is most widely used to make thermoplastic polymers and thermosetting polymers.

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What is the function of injection molding?

Injection-molded components are used in nearly every industry and consumer plastic goods. Injection molding service is often used for the following purposes: Packaging Toys Medical equipment Electrical appliances Agricultural items Automotive parts Lighting components Telecom equipment Injection molding companies use this process for the production of a high number of items with limited customization.

Advantages of injection molding service: -High output rates.

- Inserts and fillers can be used - completely automated process - little downtime for running - Scrap can be ground and reused - Economical way to mold Small, complex parts Disadvantages of injection molding service: -Not cost-effective for short runs.

-Large capital investment in equipment More overhead required.

-Molds can be costly, requiring large runs to justify the ROI of tooling.

-Requires a high degree of design and process expertise and experience to produce good parts and have low scrap rates.

-Thick cross-sections cannot be easily or reliably produced.

Tips and Considerations for the Best Plastic Injection Molded Design for injection molding companies

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Molding and design. These two endeavors must be seen together when it comes to custom plastic injection molded components by injection molding companies. This post will go over the best plastic injection molded design tips and rules for plastic injection molding companies. Here's what you should remember.

Tip #1 for Plastic Injection Molding: Begin with the End in Mind For plastics, this means beginning with the environment, where the plastic injection molded component would end up.

You may also be aware that plastic's material properties are influenced by temperature, chemicals, stress, and time. And you may be mindful of the importance of addressing these stressors concerning one another and the environment when it comes to optimum plastic design and molding.

Remember that when coping with these stressors, they cannot be considered separately.

Take, for example, Nylon. Nylon can survive high temperatures and, aside from being hygro scopic, does not mind being hot. As Nylon is immersed in hot water, say -95°C, it resembles dense mucus.

Creep, or the deformation of a rigid material, happens due to time and stress, and high temperatures intensify the rate at which a material creeps. This scratches the surface with the many factors to remember when it comes to design and molding.

Bear in mind the consequences for finite element analysis when designing the projects (FEA). The properties described in material data sheets are obtained from samples with specific sizes and shapes, samples with typical mold filling directions, and samples subjected to a particular load rate at a particular temperature and humidity.

As a consequence, some of the properties described on material data sheets could be inapplicable.

Typically, design guides provide material that will assist you in "knocking down" properties. The process of injection molding service itself may have a significant effect on the efficiency of a part. Processing parameters such as gate orientation, regrind usage, and even storage may all impact strength.

Look at Nylon once more: when immersed in water, it becomes thicker. Water soaking is an essential way to condition components before adding assembly pressures when pressing together parts in an assembly.

Tip #2 for Plastic Injection Molding: Design for Uniform Wall Thickness It is critical to design for standardized wall thicknesses when making custom molded plastic pieces.

Tip #3 for Plastic Injection Molding: Design Ribbed Walls

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To avoid sink at the intersection, support ribs should be roughly half the primary wall thickness, except for thin-walled sections. Radii at the intersection can be 1/4 the width of the main wall.

Beyond Plastic Injection Molded Parts Tips Aside from the tips we've already discussed, there are also structural requirements for compression limiters, adhesive joints, labels, cavities, and thin-walled plastic components followed by plastic injection molding companies. Let's take a closer look at this.

Custom Molded Plastic Parts and Compression Limiters What to do when we need to connect a plastic fragment to another? Compression limiters come into play in this situation. We also used compression limiters in a wide range of designs at Makenica.

Our experience with custom molded plastic components and compression limiters spans the gamut, from grooved compression limiters to knurling and inserting other retaining features directly into parts. In reality, to keep the component in place, we built assemblies with retention features and a groove in the limiter.

Adhesive Joints These can be very strong when designed correctly. We prefer to use the adhesive just for structural purposes. If a pressure-tight seal is required, it may be advisable to incorporate a seal in the joint.

Design Rules Injection molding service is a flexible method that can be used to produce almost any component. While injection molding is the industry standard for manufacturing product pieces, it is not without its disadvantages.

There are a few basic restrictions that must be addressed. Here are eight guidelines to consider when developing a product to ensure consistency and longevity by injection molding companies: Maximum thickness of the wall. Your part's wall thickness is equal to both the overall materials used to produce the part and the required cooling time. By lowering the full thickness of your part's wall, you minimize all of these causes, resulting in a shorter cycle time and, as a result, lower manufacturing costs.

If your component's wall is too dense or inconsistent, shrinkage and warpage will occur, resulting in rejects and expensive redesigns. Ensure the wall thickness is sufficient for the machine's capability.

The corners. They will trigger problems in a mold and may not always come out flush. It is almost impossible to push the plastic into a precise corner, and the effect would look sloppy and amateurish, not to mention that the part's strength could be jeopardized. To 4/8

improve aesthetics and reliability, round all corners as far as possible.

Using a draft. A draft is a small angle, typically one or two degrees applied to the face of the mold perpendicular to the parting axis. This would make it easier to remove the piece from the mold. If you do not have a draft in your design, the injection molding machine's automatic ejection mechanism will not work.

Ribs. Ribs are structural elements for your component that are used to manage overall stability. They are perpendicularly projecting thin wall protrusions from a wall or plane.

Adding ribs instead of thicker walls would have more structural strength.

The bosses. Bosses are hollow, cylindrical protrusions typically used in a design to accommodate screws or other mating components. If they are protected by connecting them to a wall or inserting ribs, the bosses would stay straight and embrace their intended role without issue.

External Undercuts. When attempting to remove sections from the mold, a protrusion or depression on the mold's exterior — the cavity half — will cause issues. To satisfy this, change the parting line.

Internal Undercuts. These protrusions or depressions, similar to external undercuts, are on the interior of the mold — on the core half. To satisfy this, change the parting line.

Threads. If your mold has a thread, make sure it's perpendicular to the parting line. This guarantees that the delicate thread is not affected. It is preferable if at all practicable, to avoid using thread in your design. Simplifying the design decreases the risk of anything going wrong.

Injection molding design guarantees a high-quality output, and the endless possibilities well outnumber the constraints. The design process's core is designing for a high-quality injection-molded component, and these constraints serve as instructions for producing a flexible final product for injection molding companies.

Preventing Flaws Contamination To put it simply, contamination happens when a foreign substance becomes stuck in molten plastic during the injection molding service. These contaminants can vary from excess moisture to dirt. Also from flecks of paint from the inside of the machines, and even bugs.

There are typically four sources of contamination: machinery, mold, material, and operator.

Contamination of Machinery Oil spills, debris, and other matter will get into the plastics if the injection molding equipment is in disrepair or is not being used properly.

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Find the following solutions: Repairing any oil spills as soon as possible and wiping up any grease drips as quickly as possible Use the hopper lid at all times. Make no effort to improvise by using cardboard boxes or other items.

Between material changes, properly clean the hopper. Wipe the interior of the hopper with a soft cloth dampened with denatured alcohol if necessary.

Mold Contamination Moving parts in a mold, such as slides, lifters, or other mechanical behavior, need regular lubrication to maintain them in good working order. However, if too much lubricant is used, the excess will penetrate the mold.

The only way to avoid corrosion that can affect the plastics' quality and consistency is to optimize the use of lubricants.

Contamination of Materials Often the raw materials used in the injection molding process get infected, which has a detrimental effect on the final product.

Materials contamination may occur due to regrinding or material that has already been through the process and has become dirty from machinery. This exposure can be avoided by keeping machines cleaner and thoroughly inspecting any regrind that could be used.

Excess moisture from steam can also contaminate the injection molding process. To prevent water leakage, thoroughly dry all raw materials before sending them into the molding process.

Contamination of the Operator: Not all injection mold operators and injection molding companies are as cautious as they can be about their operations. Food and drink stored near the machinery, incorrect cleaning practices, or even incompetence and carelessness may result in costly defects in molded items.

Evaluate all sweeping and housekeeping practices for the staff daily, and spot check the floor to ensure that the rules are being enforced.

Splay Splay is off-colored streaking in a finished product created by moisture trapped in the material during the injection or material deterioration.

What Causes Splay?

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Excess moisture in the molten material when it is injected into the mold causes splay in many situations. During the injection process, this moisture turns into steam, compromising and discoloring the final product.

Moisture is most likely to be the splay source if the flaw does not appear in the same part of the finished product each time.

Excessive heat may also generate a look similar to moisture splay. Heat-related splay can be identified by looking for signs of stickiness or burning on the finished product, as well as an odor of overheated products.

Splay may also be triggered by shear during the injection process, and this form of splay is also repeatable on other molded parts since the problem happens at the same stage in the injection process each time.

How to Stop Splay The underlying cause would heavily influence the solution to your splay dilemma.

Here are some typical injection molding splay fixes: Moisture-related: It is essential to ensure that all material is completely dry before starting the injection mold process. Mold leaks may also cause moisture-related splay, so closely examine the mold for any signs of degradation or leakage.

Heat-related: To avoid overheating, ensure that the melting temperature is within the temperature range indicated by the material's manufacturer. Too much back pressure will also cause the material to overheat and splay, so the amount of backpressure used in the process must be carefully dialed in.

Shear-related: If your piece has smaller gate sizes, reduce the beginning-of-fill pressure to avoid overfilling the mold. Significant temperature differences between when the material exits the nozzle and when it reaches the mold may also induce shear-related splay. Both temperatures should be tested and appropriately calibrated.

Delamination Delamination is an injection molding fault marked by a flaking surface coating, which means your finished piece's layers aren't adhering properly. This is often viewed as a dangerous weakness because delamination directly affects the final product's integrity and power.

What Are the Causes of Delamination?

The most frequent delamination source is the contamination of the raw material pellets, which can be caused by either a foreign material or moisture. Where the material is infected, the layers are prevented from correctly adhering together, resulting in layer separation.

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Delamination can also occur where two incompatible material types are used in the same piece.

How to Prevent Delamination Delamination can be avoided in many ways, including: Being sure that the components used are compliant with one another.

If moisture is the culprit, increase the mold temperature or pre-dry the stuff.

Assuring that all products are treated and handled correctly to avoid contamination.

Consider redesigning the mold to minimize the use of release agents, leading to corrosion and delamination.

Read More : PLA Vs ABS – The Difference

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