Designing molds for unscrewing parts is a crucial skill in the realm of injection molding. Unscrewing molds are commonly used for producing threaded parts, such as caps, lids, and closures. Understanding the fundamentals of design for unscrewing molds is essential for beginners looking to venture into this area. In this guide, we’ll cover the basics of designing molds for unscrewing parts, including key considerations and best practices.

 

Understanding Unscrewing Molds

Unscrewing molds are a type of injection mold designed to produce threaded parts with helical features. Unlike standard molds, which rely on straight-pull actions to release parts from the mold cavity, unscrewing molds utilize rotational movements to release threaded parts from the mold core. This rotational action mimics the process of unscrewing a cap or lid from a bottle.

Key Components of Unscrewing Molds

Unscrewing molds consist of several key components, each playing a vital role in the molding process:

Core and cavity: The core and cavity form the mold cavity where the plastic part is formed. In unscrewing molds, the core typically contains the helical threads, while the cavity corresponds to the exterior shape of the part.
Threaded core: The threaded core is a specialized component that forms the internal threads of the molded part. It is designed to rotate within the mold to facilitate the unscrewing action.
Actuation mechanism: The actuation mechanism is responsible for rotating the threaded core to release the molded part. It can be driven by hydraulic, pneumatic, or mechanical means, depending on the specific design requirements.

Design Considerations for Unscrewing Molds

When designing molds for unscrewing parts, several factors must be taken into account to ensure successful molding operations:

Thread design: The design of the threads plays a crucial role in the functionality of the molded part. Threads must be properly sized and shaped to achieve a secure fit and proper sealing when the part is assembled.
Undercut features: Unscrewing molds often involve the presence of undercut features, which can complicate mold design and tooling. Careful consideration must be given to the location and geometry of undercut features to ensure they can be adequately released during the molding process.
Draft angles: Draft angles are essential for facilitating part ejection from the mold cavity. Adequate draft must be incorporated into the design of both the core and cavity to prevent friction and binding during the unscrewing process.

Best Practices for Designing Unscrewing Molds

To optimize the design of unscrewing molds and ensure efficient molding operations, consider the following best practices:

Simplify the design: Minimize the complexity of the mold design wherever possible to reduce costs and manufacturing time. Simplifying the design can also improve mold longevity and reliability.
Optimize cooling: Proper cooling is essential for maintaining consistent part quality and minimizing cycle times. Design the mold with adequate cooling channels to ensure efficient heat dissipation during the molding process.
Choose suitable materials: Select materials with the necessary strength, durability, and wear resistance for the components of the unscrewing mold. High-quality materials will contribute to the longevity and performance of the mold.

Conclusion

Designing molds for unscrewing parts requires careful consideration of various factors, including thread design, undercut features, and draft angles. By understanding the fundamentals of design for unscrewing molds and following best practices, beginners can create molds that produce high-quality threaded parts efficiently and reliably.

For further assistance or to explore our range of molding solutions, please don’t hesitate to contact us.

Many people are not aware of the advantages of thermoset materials. This guide describes the thermoset molding process and how it can benefit you.

 

Thermoset Molding

Thermoset molding is an irreversible molding process by which malleable forms of plastic are forced into a heated mold and formed into their final shape.

Thermoplastic molding is the reverse process where heated material is injected into a cool mold. The material is then cooled to maintain the final shape of the part.

Why Use Thermoset Molding?

Thermoset materials are generally stronger than thermoplastic materials due to the catalysts that are added to the base compound that cause chemical reactions at the molecular level, forming a harder, irreversible final form. Thermoset plastics cannot be re-melted, only ground and recycled as filler for different applications.

Thermoset molded products have electrical and thermal insulation properties, which make them ideal for electrical and electronic applications. They are resistant to corrosion and have high impact strength, depending on the resin, and are cost competitive with engineered thermoplastics. Using thermoset molding allows producers to maintain tighter tolerances during the molding process compared to similar thermoplastic materials.

 

Thermoset Injection Molding Process

The thermoset injection molding process involves several key steps:

1. Material Preparation: Thermoset compounds, such as BMC (Bulk Molding Compound) or SMC (Sheet Molding Compound), are prepared with fillers, resins, and additives to achieve the desired properties.

2. Heating & Injection: The material is heated and injected into the mold under high pressure, filling every cavity precisely.

3. Curing / Cross-Linking: Thermoset polymers undergo chemical cross-linking during heating, solidifying into a strong, heat-resistant part.

4. Demolding: Once fully cured, the part is removed from the mold. Unlike thermoplastics, it cannot be remelted or reshaped.

5. Finishing & Quality Control: Parts are trimmed, inspected, and tested to ensure dimensional accuracy and performance.

This process ensures precision and allows for complex geometries, making it suitable for high-performance industrial applications.

Applications of Thermoset Molding

Thermoset molding is widely used across multiple industries:

1. Automotive Components: Electrical connectors, insulators, engine parts, and high-heat-resistant components.

2. Electronics & Electrical Devices: Switches, connectors, insulating housings, and circuit components.

3. Industrial Equipment Parts: High-strength, heat- and chemical-resistant components for machinery.

4. Household Appliances: Oven handles, heating elements, and durable plastic housings.

Pros of Thermoset Injection Molding

Injection molded pieces may be the best fit for a piece for several reasons:

Many different types of materials may be used in injection molding, including thermoplastic and thermosetting resins, polymers, and elastomers. This offers the engineer a great deal of control over which blend of materials will yield the best outcome, especially when needing to meet specific property requirements.

Fantastic for high-volume runs.

Precision and low waste. Because of the specific tooling and material mix, there is less waste with injection-molded parts than with other processes.

Short cooling time – Injection molded pieces cool quickly, reducing the time required to release the injected piece from the mold.

Cons of Thermoset Injection Molding

While injection molding is a fantastic process for the reasons mentioned above, there are certain limitations and drawbacks. A few of these drawbacks include:

Tooling costs – These costs can be significant as precision crafted molds are required.

Flash – Flash is unavoidable when injection molding thermosets. Once the part has been created and ejected from the mold, an automated or manual next step is necessary to remove the flash (excess material). Flash isn’t an issue with thermoplastics due to the higher viscosity of the liquid plastic.

Part size – The size of the piece being created definitely matters when it comes to the molding process. Typically, smaller part sizes (0.1 lbs to 6 lbs) are injection molded, while larger parts are transfer or compression molded. The volume of the order will also dictate which molding process will be the best fit for the project. Compression molding would likely be used for larger parts with a low (or high) volume, while transfer molding would be used for medium to high volume projects. Injection molding would be ideal for high volume runs with smaller pieces.

 

WIT Mold offers Custom Plastic Molding and Tooling services, Contact us now for a competitive offer!

An injection mold is a tool for producing plastic products and for giving them a complete structure and precise dimensions. Read on for more information about common problems and solutions for injection molds.

 

 

A mismatch between mold and injection molding machine

Causes:

1. Positioning ring position is not correct, size is too big or too small.

2. Wrong position and size of the ejector hole of the mold; wrong position and size of the forced pull reset hole.

3. Mold width size is too big; mold height size is too small.

Solution:

1. Adjust the ejector hole position and size; adjust the reset hole position and size.

2. Replace the positioning ring; adjust the position and size of the positioning ring.

3. Change the tonnage of a large injection molding machine; increase the thickness of the mold.

 

Bad quality of parts

Causes:

1. The fit-gap is too large.

2. Poor glue walking, trapped air.

3. Ejector pin is too small, uneven ejection.

4. Too small bevel, burr, hardness is not enough.

5. Uneven injection pressure, insufficient strength of product form.

6. Processing error.

7. Far from the gate, low mold temperature.

Solution:

1. Trim the gate, pressure uniformity, strengthen the product strength.

2. Reasonable adjustment of clearance and grinding work part of the parting surface.

3. Improve the gate, increase the mold temperature.

4. Add local glue, add exhaust.

5. Re-processing.

6. Increase the ejector pin, evenly distributed.

7. Repair burr, increase slope, nitriding.

 

 

The parts are difficult to fill and difficult to take

Causes:

1. The pouring system is blocked, the runner cross-section size is too small, the gate arrangement is unreasonable, and the gate size is small.

2. The limit stroke of the mold is not enough, the extraction stroke of the mold is not enough, the ejecting stroke of the mold is not enough.

Solution:

1. Check whether the limit, core extraction, and ejection strokes meet the design requirements and adjust the strokes that do not meet the requirements.

2. Check the runner and gate of each section of the pouring system, and fix the parts concerned.

 

Mold opening and closing ejecting reset action is not smooth

Causes:

1. Slanting ejector, ejector pin sliding is not smooth.

2. Mold frame guide column, guide sleeve sliding is not smooth, with too tight

3. Reset spring elasticity or pre-pressure is not enough.

Solution:

1. Increase or replace the spring.

2. Repair or replace the guide pillar, guide bush.

3. Check and repair the slanting top, ejector pin.

 

Mold water transportation is not working or water leakage

Causes:

1. Water sealing rubber ring and water pipe joint are not sealed enough.

2. The mold water channel is blocked and the inlet and outlet water pipe joints are connected in the wrong way.

Solution:

1. Check the cooling system inlet and outlet water pipe joints connection and each section of the waterway, repair the relevant parts.

2. Check the water sealing rubber ring and water pipe joints, repair or replace the parts.

 

WIT MOLD is a very professional mold design and mold manufacturer located in southern China and has passed the ISO2009:2015 international quality Our injection molding process can be customized according to your unique project. If you are interested, please feel free to contact us.

Precision injection molding machine refers to the molding machinery and equipment suitable for the molding production of precision plastic products. For a precision injection molding machine, how should we measure or judge?

Many precision injection molding machines are also required

① High injection pressure and fast injection speed.

② The clamping system has enough rigidity and precision. The so-called precision of closing refers to the uniformity, adjustability, stability and repeatability of the closing force, as well as the high precision of the opening and closing position of the mold.

③ The pressure, flow rate, temperature and measurement can be accurately controlled to the corresponding accuracy, and the multi-stage injection can be used to ensure the reproducibility of the molding process and the repeated accuracy of the product.

Precision injection molding machines can achieve the benefits of high pressure molding

A, improve the precision and quality of precision products.

Injection pressure has the most obvious effect on molding shrinkage. When the injection pressure reaches 392MPa, the shrinkage rate of molding is almost zero. At this time, the accuracy of the product is only affected by the mold control or the environment. Experimental results show that the mechanical strength of the parts can be increased by 3 ~ 33% when the injection pressure is 98 ~ 392MPa.

 

B, can reduce the wall thickness of precision products, improve the molding length.

Taking PC as an example, the ordinary injection pressure of 177Mpa can form products with wall thickness of 0.8mm, while the precision injection pressure of 392MPa can form products with thickness of 0.45mm or more. Ultrahigh pressure injection machines can obtain products with higher flow ratio.

C. Increasing injection pressure can give full play to the efficacy of injection speed.

Injection molding machine performance to achieve precision injection

Injection molding products have been used in various fields, widely used to replace high-precision metal parts, so as to put forward strict requirements on dimensional accuracy, mass accuracy, apparent mass and mechanical properties of injection parts. At the same time, the technological factors affecting the quality of injection molding products also put forward higher requirements.

The ideal control state of injection molding machine is to directly control product size, mass, apparent mass, mechanical properties and other variables as feedback signals for feedback control. However, the method of direct measurement and conversion of these non-electric quantities into electrical signals has not been solved for the time being, and can only be solved by controlling the controllable variables of the injection molding machine that affect the quality of the above-mentioned products. .

We are a precision injection molding company, if you need please feel free to contact us.

 

In plastic injection molding, the cooling rate is the last section of the molding cycle.

The cooling rate is a decreasing rate from the time the plastic resin enters the mold until the last cavity of the mold is filled.

When the cooling process is complete, it is safe to remove the part from the mold.

Factors that affect the cooling rate and the final molded part

---

Mold Cavity Pressure

The cooling rate is monitored, measured, and displayed on a pressure curve. It is displayed this way because as the plastic resin cools, it shrinks, which reduces the mold cavity pressure.

Mold Temperature

In plastic injection molding, the temperature of the mold itself can be a factor in the cooling rate process. Aside from affecting mold cooling lines, mold temperature can affect part blemishes, like:

• Mold Warpage
• Sink Marks
• Jetting

Improper mold temperature can also impact properties, such as:

• Molded-in Stress
• Fatigue Resistance
• Wear Resistance
• Creep Resistance
• Molecular Weight
• Dimensional Stability

The cooling rate can also be affected by the use of metals that conduct heat away.

The cooling process is complete when the temperature is no longer reducing and any additional time spent to cool the part is useless.

When the cooling process is complete, it is safe to remove the part from the mold.

TIP: During the plastic mold design phase, you must consider the best possible cooling channels for the mold. Using a plastic molder with a deep knowledge of cooling rate process optimization will allow for better control over the mold temperature, and thus, the cooling rate. It will also provide the best cycle time and the best outcome for a good, stress-reduced molded part.

How to Calculate Cooling Time?

---

Cooling time in injection molding is a critical part of the production process. It is the amount of time the molten plastic takes to solidify. An adequate cooling system is required to transfer heat away from the mold and maintain a stable cooling rate, ensuring the highest quality final products.

One of the quickest methods for estimating the cooling time is using a formula that accounts for the thickness of the part in an equation based on the effective thermal diffusivity. The thermal diffusivity estimates the transfer of heat in and out of material.

 

Since its establishment, WIT MOLD has successfully exported more than 2000 sets of molds with different types of structures and designs, which are applied to a variety of industries.