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.
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.
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.
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:
Improper mold temperature can also impact properties, such as:
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.
There are a variety of manufacturing methods used to create products using plastic polymers, including two-shot injection molding, compression thermoset molding and extrusion. While all of these are viable manufacturing processes, there are several advantages to this process that make it the top choice for many plastics manufacturers. The process is relatively simple; one material is injected into a mold in order to make the initial section of the product, followed by a second injection of a secondary material that is compatible with the original material. There are three good reasons many manufacturers use this method of manufacturing plastics or polymers.
Advantages of two-shot injection molding
Two-shot injection molding is cost-effective
The two-step process needs only one machine cycle, rotating the initial mold out of the way and putting the secondary mold around the product so that the second, compatible thermoplastic can be inserted into the second mold. Because the technique uses only one cycle instead of separate machine cycles, it costs less for any production run and requires fewer employees to make the finished product while delivering more items per run. It also ensures a strong bond between the materials without the need for further assembly down the line.
Enhanced product quality
Two-shot injection molding enhances the quality of most thermoplastic items in several ways:
ㆍImproved esthetics. Items look better and are more appealing to the consumer when they are crafted of different colored plastics or polymers. The merchandise looks more expensive if it utilizes more than one color or texture
ㆍImproved ergonomics. Because the process allows for the use of soft-touch surfaces, the resulting items can have ergonomically designed handles or other parts. This is particularly important for tools, medical devices, and other hand-held items.
ㆍIt provides for a better seal when silicone plastics and other rubbery materials are used for gaskets and other parts that require a strong seal.
ㆍIt lets you combine both hard and soft polymers for outstanding comfort and utility for even the smallest of products.
ㆍIt can greatly reduce the number of misalignments when compared to over-molding or more traditional insert processes.
ㆍIt enables manufacturers to create more complex mold designs using multiple materials that can’t be effectively bonded using other processes.
ㆍThe bond created is exceptionally strong, creating a product that is more durable, more reliable, and with longer life.
Product manufacturers favor a wide range of applications for two-shot injection molding, including automotive interior parts, medical equipment, tools, and toys. It allows manufacturers to combine various materials and colors to create a strong and attractive final product. Some materials can be effectively combined with this process, including silicone and thermoplastics, nylon and thermoplastic elastomers, or hard nylon and soft-touch materials.
Two-shot injection molding can solve your company’s product production difficulties. An experienced plastic manufacturer can guide you from concept to finished product and ensure a cost-effective solution.
Producing an assembly with multiple components
Compared to other methods of plastic molding, two-shot is ultimately a more cost-efficient way of producing an assembly with multiple components. Here’s why:
Part Consolidation: Two-shot injection molding reduces the number of components in a finished assembly, eliminating an average of $40K in development, engineering, and validation costs associated with each additional part number.
Improved Efficiency: Two-shot molding allows multiple components to be molded with a single tool, reducing the amount of labor needed to run your parts and eliminating the need to weld or join components after the molding process.
Improved Quality: Two-shot is carried out within a single tool, allowing for lower tolerances than other molding processes, a high level of accuracy and repeat-ability, and reduced scrap rates.
Complex Moldings: Two-shot injection molding allows for the creation of complex mold designs that incorporate multiple materials for functionality that cannot be achieved through other molding processes.
Disadvantages of two-shot injection molding
1) High tooling costs and long setup lead times. Up-front costs are high due to the design, testing, and tooling required. There is the initial design and prototyping (probably via CNC or 3D printing), then the design of a prototype mold tool to produce replicas of the part in volume. Lastly, and only after extensive testing during both stages, you can finally inject mold apart.
2) Part design restrictions. Plastic parts must be designed with injection molding consideration and must follow the basic rules of injection molding, for example:
Avoid undercuts and sharp edges as much as possible
Use uniform wall thicknesses to prevent inconsistencies in the cooling process resulting in defects like sink marks.
Draft angles are encouraged for better de-molding.
Don’t forget, because tools are typically made from steel or aluminum, it can be difficult to make design changes. If you need to add plastic to the part, you can make the tool cavity larger by cutting away steel or aluminum. But in order to take away plastic, you need to decrease the size of the tool cavity by adding aluminum or metal to it. This is extremely difficult and in many cases might mean scrapping the tool (or part of it) and starting over.
Also, the weight and size of the part will determine the tool size and necessary press size. The larger the part, the more difficult and expensive it will be.
3) Small runs of parts can be costly. Due to the complexity of tooling, and the necessity to rid the machine of all previous material before the next product can be made, the setup time can be quite lengthy. Therefore small runs of parts have traditionally always been thought of as too expensive to injection mold.
Precision injection molding machine refers to the molding machinery and equipment that is suitable for molding and producing precision plastic products. For a precision injection molding machine, how should we measure or judge it?
Many precision injection molding also requires injection molding machines with
① High injection pressure and high injection speed.
②Mold clamping system with sufficient rigidity and clamping accuracy. The so-called clamping accuracy refers to the uniformity, adjustability, stability and repeatability of the clamping force, and high accuracy of the opening and closing position of the mold.
③The pressure, flow, temperature and metering can be controlled precisely to the corresponding accuracy, and multi-stage injection can be used to ensure the reproduction of the molding process and the repetition accuracy of the products, etc.
The benefits of high-pressure molding that can be realized by precision injection molding machine
A. Improve the precision and quality of precision products.
The injection pressure has the most obvious effect on the shrinkage rate of the product molding. When the injection pressure reaches 392 MPa, the shrinkage rate of the product molding is almost zero. And the precision of the products at this time is only affected by the mold control or environment. Experimental evidence: injection pressure from 98 to 392 MPa, the mechanical strength of the parts can be increased by 3 to 33%.
B. The wall thickness of precision products can be reduced and the molding length can be improved.
Take PC as an example, ordinary machine injection pressure of 177 Mpa can mold 0.8mm wall thickness products, while precision machine injection pressure of 392 MPa can mold products with thickness of 0.45mm or more. Ultra-high pressure injection machine can obtain products with greater flow length ratio.
C. Increase the injection pressure can fully develop the efficacy of injection rate.
The performance of injection molding machine to achieve precision injection molding
Injection molded products have been applied to various fields and widely used to replace metal parts with high precision, thus putting forward strict requirements on the dimensional accuracy, quality accuracy, apparent quality and mechanical properties of injection molded parts. At the same time, the process factors affecting the quality of injection molded products have also put forward higher requirements.
The ideal state of injection molding machine control is to directly control the product size, quality, apparent quality, mechanical properties of the variables as feedback signals for feedback control. However, for the time being, direct measurement and conversion of these non-electrical quantities into electrical signals has not been solved, so it can only be solved by controlling the controllable variables of the injection molding machine that affect the quality of the above mentioned products.
Injection molding is a popular manufacturing process, which can quickly produce complex-shaped precise parts without wasting a lot of materials.
Many different processes belong to the category of injection molding, including over-molding and two-shot molding. The two processes are similar, but there are some key differences-here are what engineers and designers need to know:
What is two-shot molding?
Two Shot Injection Molds, also known as dual-molds, double-shot molds, or multi-shot molds, are a subcategory of injection molding that allows engineers to create multi-material or multi-colored parts without adding additional assembly steps.
Through the different layers of materials or colors created by the injection molding machine, the two-shot injection molding process is best understood. The first material is injected into the mold to create the substrate, and other materials or materials will be molded around the substrate. After the substrate solidifies and cools, it is transferred by hand, robotic arm, or rotating plane to another cavity of the mold.
From there, the mold opens and rotates 180° with one side of the substrate to meet the other mold chamber and injection molding nozzle. Once the substrate is in place, the second material is injected and combined with the substrate to form a firm hold. Once the second layer has cooled, the last part will be sprayed out.
Engineers should know that Two Shot Mold can be accelerated or slowed down, depending on how the substrate is transferred to another cavity of the mold. Hand and robot arm transfer takes longer than the rotating plane, but the rotating platen molding is more expensive, usually, there are only high-efficiency options, mass production runs.
In addition, it is very important that the material of the mold is easy to bond, and the mold must be aligned to prevent deformation of the parts.
Advantages and disadvantages of two-shot molding
Two-shot injection molding is efficient and economical manufacturing technology. This process also produces highly durable terminal parts and assemblies.
From a design point of view, two-shot molding provides designers with a lot of flexibility, because this process can create complex geometric shapes and adapt to multiple colors to produce more beautiful parts.
In addition, because one machine manufactures the entire part, no post-processing is required, and engineers can greatly reduce manufacturing time, thereby reducing costs. However, it is worth noting that the initial two-shot injection molding machine may be costly, and the two-shot injection molding machine is more expensive than the standard injection molding machine. Fortunately, these costs are usually offset by labor savings and assembly costs for large-scale production runs.
What is over-molding?
Overmolding, like Two Shot Moulding, is a multi-shot injection molding process that produces a single final product from two or more different thermoplastics. This process is ideal for engineers who want to build components that are powerful, functional, beautiful, and that will not separate over time.
At the beginning of the over-molding process, engineers inject the substrate with a harder over-molding material. Then, the substrate is placed in an over-mold tool or an over-mold cavity within the same mold. The molten-over mold material is then sprayed into, onto, or around the substrate. After the molten material is cooled, the substrate and the over-mold are chemically or mechanically combined. The entire over-molding process only takes 30 seconds.
The product team must remember that all thermoplastics used in the over-molding process must be chemically or thermally compatible with each other. Compatibility with metal substrates is usually not a problem, because they can be used with any plastic over mold, but the product team may encounter compatibility issues when using plastic over molds. If the substrate and mold are not compatible, the final product may be deformed or poorly bound.
However, if two less compatible plastics must be used, the team can design mechanical bonding properties for the part after the fact, although this may result in higher costs.
Advantages and disadvantages of over-molding
Overmolding and two-shot injection molding have many of the same advantages. They are ideal for quickly creating durable, reliable, and vibration-resistant parts with complex geometries, but over-molding is best suited for low-volume production runs.
Compared with two-shot molding, over-mold design is also easier, because engineers can use any standard injection molding machine to carry out this process.
In terms of disadvantages, the tolerances of over-molded parts are often lower than those of two-shot injection molding. It is also important to remember that plastic compatibility requirements may constrain designers.
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
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.
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
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.
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.
6. Increase the ejector pin, evenly distributed.
7. Repair burr, increase slope, nitriding.
The parts are difficult to fill and difficult to take
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.
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
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.
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
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.
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.
One of the most unique types of injection molds is unscrewing molds. Unscrewing molding is a unique injection molding process with mold technology that includes movement and rotation to produce threaded components. Some plastic parts such as caps and closures with detailed threads cannot be removed using standard knock-off methods. After they are molded, parts need to be carefully unscrewed from mold to avoid damaging the threads.
The unscrewing molds are part of everyday use, which may cause you to think that you won’t need to spend much time considering the required design. To demonstrate the wide use of this particular mold type, the following is a shortlist of the types of products that use unscrewing molds in the design:
• Bottle and milk caps
• Condition and shampoo lids
• Prescription medication bottles
• Medical supplies
• Sprinkler and showerheads
• Screws, nuts, and bolts
Here’s How It Works:
• First, the plastic is injected into the tool. After the plastic has cooled, the threaded core starts to unscrew. The unscrewing mechanism works off of a rack and pinion and is powered by a hydraulic cylinder.
• The rack turns three sets of gears which then retracts the threaded core into the ejector box.
• Once the threaded core is fully unscrewed, the mold opens and the ejector system pushes a stripper plate forward to eject the part.
• After the part is fully ejected, the hydraulic cylinder reverses, screwing the threaded core back into the molding position, and the process repeats.
What factors need to be considered?
When you need one of these types of plastic molds, there are several things you have to determine to make sure you get the right fit for your product and budget.
The volume of the product will probably determine many different aspects of the final product, including the thread count, the size of the part, and the type of material that will be used during production. While other factors are important, the design of the various unscrewing molds is more complex and costly than many of the other types of molds.
Ease of Removal
The ease by which an unscrewing mold should be removed from the final product is an important factor to consider in the design. Water bottles have only a few threads, sometimes only two or three because they need to be easy to remove. To ensure that the tops do not fall off easily, the threads are spaced out a bit more. An unscrewing mold on a medical device will likely need a lot of threads that are evenly spaced and very difficult to pull off of the device. The material required for these two vastly different uses is affected by how easily the part should be removed from the product.
The number of threads is going to vary based on the final product. Water bottles do not require a high thread count because they are relatively light and should be easily removed. If the unscrewing mold is for a plastic part under the hood of a car, it needs to have a higher thread count to be more durable. The number of threads required plays a large role in the final cost of production, so it needs to be tested to ensure it meets the needs of the final product.
Applications and Maintenance
High volume, reliable unscrewing plastic injection molds are some of the more complex plastic injection molds that can be manufactured. Unscrewing plastic injection molds are typically utilized for high volume applications where threaded plastic parts are needed for items such as:
ㆍNuts and bolts
ㆍSprinkler heads, lawn & garden parts
Most threaded plastic parts on standard plastic injection molds are not easy to remove using standard knock-off techniques. Therefore more complex unscrewing plastic injection molds must be utilized to prevent the threads on threaded plastic parts from being damaged while the parts are coming off of the plastic injection mold.
Because these threaded plastic parts are typically needed in high volume applications for items such as bottle caps or cosmetics packaging, the unscrewing plastic injection mold most operate at a high speed to reduce cycle times thus reducing part costs. The unscrewing plastic injection molds must also be high quality and reliable to operate for a large number of cycles while only needing routine preventative maintenance.
WIT MOLD is a very professional mold design and mold maker located South of China, certified ISO2009:2015 international quality standard. Reach out to us for a Rapid Quote to take advantage of this new offering for your internally threaded plastic parts.
Two-shot injection molding is a multi-material injection molding process. The molded plastic part can be a combination of two different materials or a combination of different colors of the same material.
Two-shot molding can also be called 2k injection molding, double shot molding, multiple injection molding (sequential injection molding).
When Is The Use of Two-shot Molding?
ㆍProduct function requirements
For example, power switches, phone buttons, keyboard indicators, car switches, etc. Portion with an LED capable of transmitting light.
ㆍImprove the handle feeling
Some handheld products require the use of rubber in hand-held parts, which makes the hand feel more comfortable. For example, walkie-talkie housing, power tool handle, wrench, screwdriver handle, toothbrush handle, thermos, etc.
For example, some plastic parts have a logo. If you use two-shot injection molding, you don’t have to worry about it being erased.
ㆍA localized area of the product that needs to be plated
In the plastic range, only ABS and PSUsurfaces can be plated. If it is necessary to plate a part or a single side of the product, the plating area should be injected into the ABS. Areas that do not require plating are injected with other materials such as PC.
7 Suggestions for Product Design
Two-shot molding frees the designer’s creativity. However, the following factors should also be noted in the product design process.
Choose the right material. The figure below shows the compatibility of different plastics.
1 ) The core material can use low viscosity materials to reduce the injection pressure.
2) Consider from the perspective of environmental protection. The recycled material can be used as a core material.
3) Optimize the product according to the characteristics of different materials. For thick parts, the finished skin layer uses soft materials. The core material uses hard or foamed plastic to reduce weight.
If the material is not chemically compatible, the two materials can be integrated by mechanical interlocking.
The hard plastic is molded for the first time, and the soft plastic is molded for the second time. Transparent for the first time, non-transparent for the second time. The plastic with high molding temperature is molded for the first time, and the plastic with low molding temperature is used for the second molding.
Before the official production, test the mold to produce a complete product.
Identify all possible defects in the process and eliminate them before the mold is manufactured.
Consider the shrinkage of the two materials.In general, shrinkage is determined by the material that is first formed.
A second injection can only be made after the first injection has been completely completed.
Consider the molded position, to prevent damage in the process.
Allow the edge of the first injection molded part to be too large. This ensures a higher pressure during the second injection.
Ensure that the parameters of the injection unit provide the required pressure, flow rate and cooling capacity.
Ensure that the structural strength of the first molded part can withstand the injection pressure of the second molding.
Check for loose or damaged fastening parts of the double shot mold. The solution is to find parts of the same specification for replacement.
After the mold has been used for a long time, the cutting edge must be cleaned and ground. After grinding, the surface of the cutting edge must be demagnetized, otherwise it will easily block the material.
Elastic parts such as springs of the two-shot mold are most susceptible to damage during use. Breakage and deformation usually occur.
The method adopted is to replace, and the specifications and model of the spring must be paid attention to during the replacement process.
Two-shotmold punch during use prone to breakage or bending. Damage to the punch and the sleeve is generally replaced with parts of the same specification. The parameters of the punch mainly include the working part size, the mounting part size, and the length size.
Check the pressure plate, top plate and other parts of the double shot mold. During maintenance, check the accessories of each part and whether there is any damage, and repair the damaged parts. Pneumatic ejector check for air leaks, and specific measures taken.
Two-shot molding increases the added value and productivity of the product. At the same time, plastics are becoming more and more colorful.
Correspondingly, the cost of two-shot molding is higher. Master the design points and avoid risks in advance. Avoid cost waste.
If you have any questions about two-shot injection molds, please contact us directly. Get a free quote.
The tolerance stated in the plastic injection mold is an engineering requirement. In basic terms, they are allowable variants to the initial dimensions of the parts or the base dimension. As it is impossible to generate a product that purely abides by the base measurements, some leeway obtains factored into the design of items.
This margin ensures that all measurements for molded products fit the setting up demands. For example, you may wish to produce products with a size of 2.8 mm. Nevertheless, attempting to produce them might end up with some of them gauging 2.6 mm.
What tolerances do is to establish minimum as well as optimum values for the production process in a way that ensures the product fits. In this case, the reduced limit can be evaluated 0mm while the ceiling is readied to 0.3 mm. By doing this, you are assured products whose diameters range between 2.8 mm and also 3.1 mm.
The important of tolerances
Generating plastic parts for your products calls for that their measurements fit perfectly. It’s very easy to offer dimensions for the type of components you want; obtaining them to have similar measurements to your requirements is a virtually impossible venture to achieve.
The type of making procedure you go for also has a terrific bearing on the high quality of completion product. Injection molding is among the most effective processes you can experience with standards like hubbub 16901 to name a few, but it’s still unable to produce parts with the right fit.
The only escape of such a scenario where it’s impossible to get an exact suit is to leave area for some distinctions in dimension. They don’t need to be major; they simply require not interfere with the item style. This is where tolerances are available in.
What Influences Tolerance?
The kind of polymer utilized throughout the creation of your items substantially identifies whether the tolerances are within acceptable limitations. As distinct polymers obtain injected into the plastic mold, they cool as well as shrink at different prices.
Despite the fact that these shrinkage rates can be quickly represented, completion product will certainly have different tolerance ranges and also discrepancies from the acceptable varieties. The array is a dimension of the difference between the biggest as well as tiniest measurements of measurements in the created batch.
Various other aspects that figure out tolerance consist of the style of the product, the intricacy of the style along with the atmosphere the injection molded parts will certainly be running in.
Minimum/Good Tolerances for Plastic molds
The great, or rather, minimal tolerances are established by the plastic polymer you choose to use for your products. These tolerances also can be found in various forms. For one, there are dimensional, straightness/flatness, and also hole diameter tolerances. They are also divided right into business tolerances and precision tolerances, which are greater in price.
Considered that an injection-molded physical tightening is a result of the cooling, the facet of temperature level decrease is influenced by various other aspects as well. They include the thaw thermal reading, the cooling price, the thickness of the part, the dimensions of eviction, as well as much more.
Furthermore, a section of the molded product that is thicker than an additional will certainly experience even more shrinking. All these variables are since even though it is possible to forecast the behavior of the plastic polymer you wish to be molded; the material will never ever act as anticipated 100% of the time.
The polymer concerned might likewise experience warpage. This is particularly real with parts that are non-uniform as they shrink at various rates in comparison to components that have uniform wall surface thickness. These non-uniform components can happen whenever the part’s design has a concern.
The final words
WIT MOLD has become one of the best molds in the industry because we combine the essence of the latest technology with proven traditional methods.
With an expert team composed of experienced and knowledgeable experts, we are able to complete custom orders for Custom Plastic Molds and parts that may exceed the capabilities of our competitors. We are also unremittingly committed to improving customer satisfaction, which includes providing comprehensive end-to-end quality assurance for every product we produce.
Weighing the pros and cons of the molding process for your composites can help you determine whether it is the right choice for your project needs. Manufacturing plastic or composite parts requires heating and pouring the raw materials into a mold that has been specially made for the part. The four most common molding processes are:
Different molding processes are used to create different works. In this article, we will weigh the pros and cons of the injection molding process for thermoset composites.
Injection-molded parts may be the most suitable one for several reasons:
ㆍMany different types of materials can be used for injection molding, including thermoplastics and thermosetting resins, polymers, and elastomers. This provides engineers with a lot of control over which hybrid material will produce the best results, especially when it is necessary to meet specific performance requirements.
ㆍVery suitable for high-volume operation.
ㆍPrecision and low waste. Due to the specific mold and material combination, compared with other processes, there is less waste of injection molded parts.
ㆍShort cooling time-the injection molded parts cool quickly, reducing the time required for the injection molded parts to be released from the mold.
Thermoset Injection Molding
Disadvantages of thermoset injection molding
For the above reasons, injection molding is an excellent process, but it also has certain limitations and defects. These disadvantages include:
ㆍMold costs – these costs can be very important because precision-made molds are required.
ㆍFlash – Flash is inevitable when injection molding thermoset plastics. Once the part is created and ejected from the mold, the next step is to automatically or manually remove the flash (excess material). Due to the high viscosity of liquid plastics, a flash of thermoplastics is not a problem.
ㆍPart size – The size of the part being created is very important in the molding process. Typically, smaller part sizes (0.1 lb to 6 lb) are injection molded, while larger parts are transfer or compression molded. The number of orders will also determine which molding process is best for the project. Compression molding may be used for smaller parts with a low (or high) volume, while transfer molding may be used for medium to high volume projects. Injection molding will be ideal for large-volume running smaller pieces.
Finally, when choosing a molding process for your part, it is always recommended to talk to a thermoset composite or thermoplastic engineer. After assessing your needs, they will be the most capable and able to make suggestions for your work and provide the highest quality products at the most reasonable cost.
There are various sub-processes within injection molding that add further capabilities to this already versatile technology. This article will explore insert molding vs overmolding and the advantages of each.
Injection molding is a broad term used to describe one of the most important processes in the manufacturing industry. It’s a process that requires a mold, typically made of metal with a cavity in the shape of the desired part. Molten plastic is injected into the mold and ejected. The process repeats to produce thousands of identical parts. It’s safe to assume that every large-volume plastic part on the market has come from an injection molding machine because the benefits of using injection molding for production are numerous. These benefits include low cost per part, short cycle times, extensive materials, and compatible, in-tolerance parts.
Various sub-processes add further capabilities to this already versatile technology. This article will specifically explore insert molding vs. overmolding and the advantages of each.
What is Insert Molding?
Insert molding is a subset of injection molding techniques similar to overmolding where metal components are placed into a mold cavity before the actual plastic injection. The insert is precisely positioned inside the mold either manually or by a robotic arm. The mold then closes, and plastic is molded over the insert, creating a single part.
One of the most common applications for insert molding is the creation of metal attachment features for fasteners. Fasteners enable assemblies to be securely assembled and disassembled without product damage. Heat-set threaded inserts are molded into plastic to reduce the risks of thread damage during installation.
Insert molding can also eliminate the need for fasteners by including the necessary metal parts in the mold, thus firmly securing the parts into a single bonded component.
Why Choose Insert Molding?
Insert molding is a versatile process that has numerous benefits, some of which are listed below.
Reduced Assembly Cost – An injection molding machine can create thousands of parts per day. Such economies of scale can significantly reduce the cost of the individual parts. In a typical CNC machining, sheet metal, or additive manufactured part, any required assembly can be a major bottleneck. Insert molding can be used to eliminate assembly and thus maximize cost savings.
Part Performance – In general, plastic parts are less robust than their metal counterparts. However, plastic offers other benefits such as reduced cost, superior design flexibility, and lighter weight. Combining both metal and plastic materials into one part can capitalize on the benefits of both. Metal inserts can be used where strength and stiffness are required and the remainder of the part can be made of plastic to reduce weight. Moreover, plastic parts do not fare well against wear and tear and metal inserts add an element of durability to parts to withstand any kind of cyclical loading.
What are the Disadvantages of Insert Molding?
Despite the many benefits of insert molding, a few disadvantages need to be considered before choosing to use this sub-process.
Multiple Manufacturing Technologies – Insert molding can involve a 2-step manufacturing process. If the inserts are a custom design and not off-the-shelf parts, they will need to be manufactured using a metal forming process like CNC machining. These metal forming techniques are often significantly more expensive per part than similar, fully injection-molded processes. In some cases, the metal parts can be manufactured via die casting or MIM (metal injection molding). This can reduce the overall cost of the metal inserts but cannot eliminate the insert molded unit’s increased cost because parts with metal inserts will typically cost more than a part that is only plastic.
Increased Part Complexity – If a custom-made metal insert is required, the designer must be aware of both technologies’ design for manufacturability (DFM) principles and understand how best to integrate these technologies into a single practical part.
What is Overmolding?
Overmolding is essentially a type of insert molding. However, overmolding vs. insert molding is, as the name suggests, plastic is molded over another molded part. The first component is made inside an injection mold, and it is then placed into a second mold to add the over-molded material. This technique combines multiple plastics for either practical or aesthetic purposes. For example, one might use different durometer plastics to mold a softer plastic over a more rigid one to make a part easier to grip. Using multiple colored plastics in an over molded part can also distinguish the product from other brands. Overmolding is regularly used on the handles of tools like screwdrivers, power drills, or toothbrushes.
Why Choose Overmolding?
Overmolding is a versatile process that has numerous benefits:
Increased Material Flexibility – Overmolding allows designers to leverage the benefits of multiple types of materials to create complex parts with different properties, add visual complexity, or add haptics.
No Adhesives Required – Overmolding allows different materials to be fused in the mold, thus eliminating the need for glues or other permanent bonding methods. This increases the part’s overall durability and reduces assembly costs.
Embedded Seals – Overmolding offers the option of molding soft seals into parts. An example would be an electronics enclosure that needs to be IP rated. Usually, the part will have a groove into which an o-ring can be installed later. However, it is far more cost-efficient and robust to permanently mold the seal as an integral component.
What are the Disadvantages of Overmolding
Despite the many benefits of overmolding, a few disadvantages need to be considered before deciding to use this process.
Multi-Step Process – Overmolded parts are made in a two-step process. This increases part cycle time and is thus more expensive than molding a single part with no overmolding. This also requires two tools or a complex two-shot mold with increased upfront costs. However, when the alternative is to create two separate injection-molded parts and then assemble them after the fact, overmolding becomes a value-added solution.
Debonding – Bonding two different materials together in an injection mold runs the risk of delamination. This typically happens if the temperatures are not in the optimal range for the specific material combination. In some cases, mechanical interlocks may be required when materials cannot be reliably bonded together using heat.
Conclusion: Choosing Between Insert Molding, Overmolding, or Injection Molding
Injection molding, which includes the sub-processes of insert molding and overmolding, is a versatile and low-cost manufacturing production process that is used in the large majority of consumer products. Injection molding often results in the lowest cost per part when compared to other manufacturing techniques like CNC machining and even 3D printing.
Once injection molding is chosen for a specific application, the next step is often whether to use insert molding, overmolding, or just stick with plain injection molding. When trying to weigh the advantages of the processes, it is important to accurately define the product application. Each of these processes has specific use cases that are suited to different product types. It can be difficult to gauge which process will best suit your particular product, so it’s good to get expert advice early on. Contact WIT and We will help steer your design decisions in the right direction so that you can choose between insert molding vs. overmolding or just injection molding.
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