Many beginners want to quickly understand insert molding. As an industry leader, we have involved insert molding product engineers and wrote this latest ultimate guide in 2023, which can guide everyone to quickly understand insert molding products.
Insert molding is one of the many techniques of injection molding. It is a single-step process in which the metallic parts are placed inside a mold opening before placing the plastic injection. The insert is very carefully placed in the mold cavity by hand or by a machine. After that, the molten plastic is injected and the mold gets closed. In simple words, insert molding is a process of molding thermoplastic materials in inserts to create final products that are used in several materials. As compared to other molding techniques, insert molding eradicates the requirement of the further installation process and hence the cost is reduced in insert molding. Insert molding is used in a huge range of applications including electronics, the consumer industry, medicine and the engineering sector. Due to the vast range of applications, one must comprehend the process accurately, the design procedure of insert molding and the working principle as well.
Insert molding technique with metallic inserts is used to amplify the mechanical strength of the plastics. The process of insert molding needs experience and specific design considerations. Insert molding produces durable bonds between plastic parts and metallic inserts. Since it is a complicated molding procedure therefore only experts who are aware of the design parameters and its working principle should use it to save their time and cost.
Many different types of materials are used as inserts. These materials include metals, pieces of cloth, papers, aluminium, thread, pins, coils, ceramics, magnets, stainless steel, wood, brass, needles, pins, bushings and even PCB (printed circuit board) sheets. The selection of the material that can be used for insert molding is dependent upon the application of the product. The inserts used for insert molding must have a firm tolerance otherwise any misalignment might cause failures. Apart from these materials, any material that can bear the heat and pressure requirements of the molding procedures can be used as inserts.
One way of insert molding makes use of a metal which is placed in the molding cavity and molded with plastic. The resultant component has better mechanical properties. Common type of insert is brass thread. The brass thread inserts not only increase the mechanical strength of the plastic but also improves its capability to be joined together.
Any kind of plastic material can be used in insert molding including both general-purpose and engineering-graded materials. A range of these materials is given below:
● PP (Polypropylene)
● ABS (Acrylonitrile Butadiene Styrene)
● Nylon (Polyamide 6/66)
● PC (Polycarbonate)
● HDPE (High-density Polyethylene)
● PEEK (Polyether Ether Ketone)
● PE (Polyethylene)
● PEI (Polyetherimide)
● PBT (Polybutylene Terephthalate)
● PMMA (Acrylic)
● POM (Polyoxymethylene)
● TPE (Thermoplastic Elastomers)
● TPU (Thermoplastic Polyurethane)
Any material that has a small shrink ratio works best. Especially hardened grade resins that have greater protraction and also have large resistance against cracking.
Insert molding is one of the techniques of injection molding procedures employed to enclose a part in a plastic component. The procedure comprises two main parts: Initially, the part is placed into the mold cavity before the molding procedure gets started. Secondly, as liquid plastic is inserted into the mold cavity, it acquires the figure of the part and seals the part into the plastic.
Insert molding is different from other traditional injection molding techniques. In the insert molding technique, the insert is fixed in the molding opening before injecting the molding material. The process of insert molding is comparable to the overmolding technique. Inserts should be in their fixed positions before injecting the material to make sure that the mold is closed and would not be destroyed by the misplacement of inserts. The inserts are placed in their positions either manually or by an automated process. The process of insert molding consists of the following steps:
Step 1: The Inserts must be placed in the accurate position in the mold cavity.
Step 2: The melted plastic material is injected into the mold and it flows around the metal or plastic insert.
Step 3: When the plastic gets cooled and hardened, the product is ejected out of the mold cavity, and the next molding cycle starts.
1) Manual loading of inserts
Manual loading is suitable for a small level of production or a product having a complex structure. The manual loading of inserts enhances the cycle of injection molding. In manual loading, a worker can check if the insert is in the accurate position or not to avoid any mold damage due to the misplacement of the insert. Moreover, in manual loading, the operator can also check the quality of the product which is useful for quality control of the product and thus protects the mold.
On the other hand, manual loading is not as efficacious as automated loading since it cannot offer the reliability, accuracy and uniformity provided by automated or robotic loading. Another problem faced in manual loading is the requirement of high temperatures to warm up the inserts or to provide heat to the molding. This heat or high temperature impacts the handiness of the workers as they have to wear gloves to avoid contact with heat.
2) Automated or robotic loading of inserts
Automated loading of inserts is useful for production on a large scale. Automated loading eliminates the possibility of human error thus it enhances the efficiency of the system, shortens the molding cycles and also enhances the product authenticity. Automated systems or robots have several features that make them better than manual loading. For example, they can tolerate high temperatures or heat, and perform chores with high accuracy without any possibility of human errors repetitively. But the primary cost linked with automated loading is very high and production must be on a large level to compensate for the cost.
Automated and manual loading have their pros and cons and should be selected according to the prevailing situation.
5. Applications of insert molding
Insert molding is used in almost all industries these days. The industries that are getting full benefits from the techniques of insert molding include medicine, automation, cosmetics, consumer industry, electronics and manufacturing industry. Insert molding gives the best results for molding metallic components with plastic parts as compared to other molding technologies. The applications of insert molding in various industries are given below:
● Consumer Goods such as screwdrivers, washing machine filters, water pipe connectors and several other things.
● Medical devices for example defibrillators, pacemakers, and many other medical device components.
● Automotive parts include gears, knobs, electrical sensors, handles, fasteners, and other automotive parts.
● Electrical and electronics such as encapsulated PCB boards, spring contacts, pins, etc.
● Mechanical equipment parts
● Aerospace technology especially special threaded components.
● Office accessories especially magnetic office accessories.
One of the most useful benefits of insert molding is that it amplifies the mechanical strength of the plastic components. The metallic inserts amplify the strength and firmness of the plastic parts which turns out to be extremely beneficial for device covers and electronics casings. Coupling parts can also be fitted with metallic sleeves and bushings to enhance the wearing resistance and thus increases the life span of the components. Some of the most useful benefits of insert molding are described below:
1) Increasing plastic durability
Plastic parts with components integrated through the insert molding technique are durable and more authentic. Since no connectors are used for integration, thus there is no possibility of inadequate tightening of the components. Plastic parts molded through insert molding have strong resistance against vibration and shocks. A plastic part integrated with a metallic insert through an insert molding procedure produces a unified plastic component.
2) Improves component reliability
The insert molding technique enhances the authenticity and reliability of the molding components since there is no chance of misalignment or failure of any kind. As compared to other molding methods, insert molding does not have any separate assembly requirement. Thus the possibility of manufacturing faults is reduced in insert molding. The other molding methods issues such as alignment problems or loosening of parts are not present in insert molding.
3) Cost-Efficiency
One of the great benefits offered by insert molding is its cost-efficiency as compared to other molding methods. As no separate assembly is required in insert molding, this technique reduces both time and labor expenses as well. The metal is integrated with the plastic component in a single step eliminating the extra costs for time, workforce and special equipment.
4) Flexible part design
The process of insert molding allows engineers to create a variety of designs and shapes thus increasing the design and manufacturing opportunities in a variety of fields. Insert molding is flexible not only for insert materials but also for a range of configurations, designs and shapes. The infinite number of designs and alignments provided by insert molding has opened doors to new possibilities in different industries all over the world.
5) Light in weight
Plastic components are less bulky than metals but metals are durable and strong as compared to plastics. By the use of the insert molding technique, metal inserts are integrated into plastic parts without any connectors and fasteners and the resultant product is one unified product. Thus insert molding technique, manufacturers and engineers can take the advantage of lighter plastics with integrated metal inserts that provide firmness and durability.
6) Quality Assurance
The insert molding method with the use of servo motors and robots has made the industrial manufacturing processes highly automated. There is no need for quality controls as the risks of spatial errors are largely reduced and thus the quality is assured.
7) Elimination of assembly
The best thing about the insert molding technique is that it reduces the requirement of assembly which makes the process simpler, shorter, more reliable and cost-effective.
7. Drawbacks of insert molding
Although there are several benefits of insert molding, but still there are a few possible disadvantages that engineers must be alert of.
There are given below:
1) Insert fixing problem
The accurate positioning of inserts in the mold cavity makes the structure of the mold complex and the cycle of the insert molding gets elongated. In this way, the cost of production cost is enlarged and the automation of the process becomes difficult.
2) Cracking risk - Residual Stress
The coefficient of thermal expansion of inserts and plastics is not constant and produces internal stresses in the products ensuing in the product falling out. This is most obvious in the injection molding processes of nut inserts. The especial molding material is polycarbonate(PC).
3) Insert warpage
The residual stresses produced due to the thermal expansion of metals also result in the deformation of the products. Inserts (particularly nut inserts) frequently need preheating and dehydrating, to decrease internal stress or force that reduces manufacturing risk.
4) Faulty parts
Once faulty parts are created in the injection molding process like defective molding procedure, inappropriate dimension of the insert, poor look, etc., the entire product would be damaged, and the plastic can"t be reused.
5) Labor charges are greater in manual insertion.
So for low-volume insert molding, manual loading inserts lead to high costs that won’t avoid. But the labor cost of manufacturing with insert molding is much lower than the cost required by other processes. The most important thing is that the quality of the product produced by the insert molding process is reliable.
6) The adjustment costs for damaged molds are high and a longer time is required to repair them.
7) Resins may be compelled inside the inserts due to molding pressure.
When this occurs, the additional flash should be washed out in another move.
8) The equipment design should be well-suited to the insert.
If they are not suitable with each other properly when the mold is shut and during injection compression, the mold could be impaired or ruined.
8. Insert Molding Design Considerations
A common Insert molding example is the usage of a threaded insert to produce a firm thread in a plastic component. Nevertheless, just like several other plastic molding procedures, insert molding usage opportunities are never-ending. Any kind of inserts could be used from compound threads to electrical links. Due to the extensive range of possible uses, it is essential to comprehend the insert molding procedure, design the component properly, and evaluate the working of the making procedure.
To design products through the insert molding process, their characteristic features and design for manufacturability must be considered. The design parameters for the insert molding technique are almost similar to traditional injection molding techniques. Preserving uniformity in the thickness of the wall, the addition of a mechanical interlock and the addition of a draft for part ejection are commonly used parameters.
Along with the design considerations for traditional molding, the additional considerations for insert molding are described below:
1) Proper material selection
Any common thermoplastic can be used for the insert molding process. It usually depends on the product surroundings which include the required temperature, mechanical properties, period, and other factors to select the precise material.
2) The position of the gate should be considered when design the product
The gate position must be considered when designing a product through the insert molding procedure. The direction of injecting pressure as well as the direction of the insert should be the same otherwise the design would fail.
3) Utilize a Stress Chain Chart
When selecting materials, a stress chain chart can help you to understand the advantages and disadvantages of different plastic raw materials. It can be used to avoid many design flaws when you design. Allowing you to design the most appropriate sharp of the insert molding product.
4) Selection of insert materials
The selection of the insert material is also an important choice when considering design parameters for insert molding. The materials suitable for inserts include: Copper, aluminum, steel, magnets, ceramics, etc. amongst these materials brass is the best since it has the most useful features for example brass is unable to oxidize, is erosion resistant, and is economical.
5) Inserts shapes
Along with insert material, insert shape is also another important parameter to consider. Mostly circular-shaped or axisymmetric-shaped inserts are employed in insert molding procedures. To assist even tightening and avert local strain sharp angles are not used.
6) The hygiene of the inserts should be ensured
Metallic inserts are manufactured by the process of cutting and stamping. Therefore, the shapes of the inserts should be of excellent handling technology which means that no burrs should be present. Even a minor burr can destroy the mold.
7) The insert must assist with location and placement in the molds
The bulging portion of the insert (the portion that is positioned inside the mold) must be designed in a cylinder shape as the mold is at ease when processing round holes. The simplest method to create molds is around holes.
8) It is very important to carefully consider the position and fixing of the insert.
The position of the insert is a very important design consideration in insert molding. If the insert is misplaced, misalignment will be produced and the design will be affected. For precise placement inserts, inserts are positioned on metal positioning pins at the bottom of the mold. Support pins typically leave small holes. There should be space or structure to fix the insert, such as posts or holes to fix the insert, or posts to fix the insert around. You can see below reference structure.
9) Inserts must be strong
The inserts must be selected with caution so that offer adequate mechanical durability. Moreover, the inserts must be capable to bear injecting pressure without any distortion or twisting.
10) Mechanical interlock
The inserts must be interlocked to increase the mechanical strength and durability of the parts.
11) Inserts must maintain tight tolerance
The insert molding technique requires exceptionally tight tolerance since the slightest misalignment will destroy the whole insert molding procedure. Thus to maintain a tight tolerance is an important design consideration in insert molding.
9. Insert Molding Mold Design and Making Considerations
The technique of insert molding is an injection molding procedure that could be easily regulated and also deliver improved outcomes as compared to other techniques for molding metal inserts to plastic parts. Different industries such as manufacturing goods, fitness and health, cosmetics, electronics and automotive sectors are making the most out of the insert molding technique. Nonetheless, to get the best out of the insert molding, product crews must consider the specific design and procedure parameters.
A mold for insert molding is entirely different from a traditional molding process and the following parameters must be considered when creating molds for the insert molding process:
1) Design molds to fix inserts correctly is critical
The inserts must be carefully placed in the correct position and direction. Throughout the molding process, the inserts must be kept in their precise locations.
2) The ejector mechanism should consider the inserts.
When expelling the finished product from the molds, the inserts must not be disturbed or affected. If the insert gets affected in the ejection of the final product, the next insert molding procedure will be failed. The best solution is to add a pin or ejector system to help strip the whole part. For some complex parts, an auxiliary pin is required during ejection.
3) Maintaining insert enough stability during injection is a very important consideration.
Under high injection molding pressure, even minor deviance can cause the molding process to fail. It can destroy the mold or the final products. There is a risk of misalignment or misplacement of inserts in the insert molding procedure. Thus the engineers and manufacturers must take into account the structure of the mold for the stability of the insert. For some products where the shape of the insert can’t be changed, pre-testing the insert strength is essential.
4) Inserts can be placed easily
The engineers must consider the position of the insert at the mold design phase to make sure that the inserts could be placed at the required places without any problem.
5) Shut-off or sealing of inserts
Inserts must fit flawlessly in the mold cavities specifically for products with touched exteriors. Inserts must be placed well into mold openings to ensure the shutting. The closed surfaces must be in accurate positions. If the inserts are not coupled perfectly with the mold cavities or the sealing is not well, the molten plastic will easy to come out and occur flash. The tolerance level for insert molding varies from material to material. For example, the tolerance tightening should be +/- 0.05 mm for ABS material and for pp material, it is +/- 0.02 mm.
6) Sealing insert avoids complex curved surfaces.
Try to avoid complicated and curvy surfaces between mold and sealing surfaces of inserts. Moreover, the area of the sealing surfaces as big as possible. If the mold gets impaired it can be fixed quickly at a low cost if the sealing surface is simple. But for complex and curvy surface areas, the molds cannot be repaired easily at low costs.
7) Consider using spring loading area sealing insert
If the insert is of metal or some other non-compressible substance, a spring loading area must be provided.
8) Mold tolerance
A very important parameter to consider in mold creation and designing is mold tolerance. The molds must be kept to tight tolerances so that the insert can be placed in the correct position when the molding material enters the insert. If there is no tight tolerance, the inserts might get misplaced and will damage the mold.
10. Insert Molding Production Considerations
The process of insert molding is a highly technical procedure and it requires important mold design, mold creation, material and inserts design and many other parameters to be considered to accomplish it successfully. Apart from product and mold design parameters, the important process design parameters are given below:
1) Prototype manufacturing
Creating a prototype before starting the actual manufacturing process is a smart idea. It is important to detect any design or operational problems in the production process. Moreover, with the help of a prototype, engineers can assess any future problems that may arise during the process. Thus creating a prototype in insert molding helps engineers to minimize errors and issues in the production process.
2) Inserts should be preheated before molding
The inserts must be heated before molding to avoid any shrinking afterward. Moreover, the pre-heating also enhances the weld line's durability. Since metal inserts are used in insert molding and metals could be thermally expanded or contracted in cold, so to avoid any failures in the molding process, the metal inserts must be preheated and dried. Moreover, the preheating of metallic inserts also reduces the quenching effect of thermally conductive metals. The metallic inserts are expanded on pre-heating and shrink on cooling with the molds. In this manner, the molded-in stress level decreases.
3) As far as possible choose vertical rotary injection molding machine production
In a vertical insert molding machine, the mold opens and shuts vertically (y-axis), thus letting gravity hold inserts inside the molds. In vertical injection molding, it is quite easy to load the hard and prevent it from falling out. A vertical injection loading machine not only saves time but also improves production efficiency.
4) Automated insert molding if available
Although automated insert loading is suitable for mass production, if it is available and is cost-effective for the manufacturing process, it is a good choice to have. The automated insert loading reduces the chances of manual faults and provides reliability and consistency to the molding process. And the use of rotary injection molding machine production, when a "half mold" in the molding production, can be placed another "half mold" insert, which saves time, and greatly increased production efficiency.
5) Pay attention to the stresses in production
We know that residual stresses are produced in the molding process. Engineers must consider these stresses during the process of insert molding.
11. Differences between Insert Molding and Conventional Injection Molding
Insert molding is a type of injection molding technique in which the insert is placed in the molding cavity before adding the molten plastic. Insert molding technique differs from traditional injection molding in several ways.
For example, the materials used in the traditional molding process are plastics whereas in insert molding both metals and plastic materials can be used as inserts. The tolerance in the traditional molding process is not very strict whereas in the insert molding technique tight tolerance is maintained to avoid any misalignment. For the design process of conventional injection molding, the components and the assembly gap must be considered.
In the insert molding technique, no further assembly is required, thus for insert molding combined features must be considered. The time period for design a traditional molding process is longer compared to that of insert molding. For mold design and creating in traditional molding low precision is needed thus it produces low cost. In insert molding, the designing and creation of the molds need high accuracy and precision and higher costs are required for it. In the conventional molding process, a subsequent manual assembly is required whereas in insert molding no subsequent assembly is required. Look at the below table will help you.
12. Rotary Vertical Insert Molding
Horizontal and vertical injection machines work in almost the same manner except for the fact that in vertical insert molding, the molds get open and closed along the vertical axis. In this way, gravity keeps the inserts in their accurate positions and no misalignment is caused. Thus better results are produced with insert molding machines working in vertical manners as compared to horizontal insert molding machines.
In insert molding, inserts are placed in the molds before the molding process gets started. The further procedure is not at all different from the regular injection molding process. The metallic or plastic inserts are carefully positioned in the mold cavities and molten plastic is injected. The mold cavity is shut, and the fillings are cooled and then expelled out of the molds, and are prepared for the subsequent phase in the manufacturing procedure.
Mostly, the process of insert molding is performed vertically since it is easier to load and hold the insert to avoid falling out. Automated insert loading is suitable and economical if the production or manufacturing is taking place on a large level. But for a small to medium level of production, manual insert loading suits the most. Although manual loading amplifies the labor costs and time but still manual loading is better option for small to medium manufacturing levels. The process of insert molding can be carried out in the traditional horizontal injection molding machine but the insert loading and hold will be problematic and therefore it will add limitations to the designing of the component. The rotary vertical injection machine is best suited for insert molding since this allows the workers to load the inserts in the lower half of the mold whereas the molding process takes place in the other half. vertical machines can also be used in the automated load and unloading of inserts.
13. How to Avoid Stress in Insert Molding?
Residual stress is difficult to avoid in injection molding of various materials and shapes. This residual stress must be assessed during the design stage, molding process, fixturing process and molded parts performance. The residual stresses might be substantial and frequently appears as parts fail to perform after the parts have been dispatched, assembled and in usage for a time.
In insert molding, the molten plastic encapsulating a metal insert contracts as it cools, thus creating hoop stress in the plastic mold. This hoop stress is persistent stress on the plastic component all through the lifetime of the component and probably ends in a fracture if the stress is not reduced in the manufacturing procedure. This constant residual stress or force in the plastic molded components might create an expanse with the passage of time. The larger the force or the stress, the quicker the stretch will take place. For an extended time period, the plastic particles just cannot bear the load and will break.
One of the largest distress in insert molding is the contraction of the resin. This generates hoop stress or force in the plastic mold that may get ruptured with the passage of time, particularly if the plastic component is under mechanical pressure.
To deal with this problem, the engineers must follow the below points:
● Using a resin material that has a comparatively small contraction level
● Using filler raw materials reduces shrinkage.
● Surrounding the inserts with a greater region of plastic
● Supporting the inserts with bosses and beams
● Preheating the insert before the molding process. It permits the resin and the insert to cool down and contract in tandem, therefore releasing a few of the strains among the materials.
● Using already-created inserts that have rough exteriors to keep them locked in their places.
● Try to avoid sharp corners and utilize round shapes instead to decrease the residue strain.
● Inserts should be designed in a way that they are lowered a little to avoid any damage to the equipment.
● Addition of trenches and outlines. Numerous trenches and knobby designs are usually employed to increase the evacuation or turning opposition, but these must not have sharp angles, or they would perform as strain creators in the plastic components. Similarly, the inserts must be well-created without machining labels or burrs that can act as stress risers.
● The speed and pressure for injecting molten plastic must be low.
● Higher temperatures for molding are also beneficial for reduction.
14. Insert molding vs overmolding
1) What is overmolding?
Overmolding is a distinct type of injection molding process. Contrasting to the traditional molding process, in which a final product is created in a single cycle, the overmolding technique needs an extra injection cycle at least by means of a different material. This technique is also recognized as 2K overmolding, multi-shot molding, and also multiple materials molding techniques.
The process of overmolding begins with a base substance. On its top, a comparatively soft TPE or TPU substance is fused. Overmolding utilizes a distinctive kind of plastic injecting molding device that has an opening for the substrate part and an isolated opening demonstrating the overmolded segment.
2) Difference between insert molding and over molding
Even though overmolding and insert molding are confused with one another, these two techniques are completely different from one another. In overmolding technique, the substrate part is molded first, then molding the second layer of soft plastic is above the substrate. Thus we can say that overmolding is a two-step molding technique. The procedure of over-molding is a high-tech engineering process and needs highly competent operators, outstanding mold creation and tight tolerances. The process of insert molding, on the other hand, is quite simple. In the insert molding technique, a finished metallic part is placed in the mold cavity and then the plastic part is molded around it. To demonstrate the process of insert molding let's take the example of a screwdriver. A metal insert is covered with fine and flexible molding and a single product is produced. Although both processes have different molding techniques, these can be used together to achieve various manufacturing benefits.
Once the plastic injection molding process is selected for explicit use, the following stage is usually to decide between insert molding and overmolding. When we try to assess the benefits of the procedures, it is significant to precisely outline the product use. Both of these procedures have particular applications that are suitable for diverse product kinds.
15. Conclusion
To conclude, the process of insert molding is a better choice as compared to other molding techniques in encapsulation metal using plastic. The majority of designers and engineers approve that the insert molding technique is one of the best and most effective injection molding techniques. Although, the insert molding technique has some drawbacks too, its benefits are far more than its disadvantage. It provides the facility to work with an extensive variety of materials and produce complicated shapes of parts. The cost reductions and the enhanced schemes provide competent manufacturability and client contentment also.
