What is overmolding?Everything You Need to Know

Overmolding is the making of a product by joining two or more materials into one product. It is also applied in most industries, such as electronics, medical equipment, automotive, and consumer products. It is done by molding over a base material known as an overmold, over a base material known as a substrate.

Overmolding is done to enhance the aesthetic, longevity, and functionality of products. It enables manufacturers to incorporate the power of one material with the flexibility or softness of the other. This makes products more comfortable, easier to deal with, and durable.

Overmolding appears in items that we use on a daily basis. This has been applied to toothbrush handles and phone cases as well as power tools and surgical instruments, among other items in contemporary manufacturing. Knowing about overmolding will make it easy to see how convenient and safe objects in everyday life are.

What is Overmolding?

Overstøping is a procedure through which one product is formed out of two materials. The initial material is known as the substrate and typically is a hard plastic such as ABS, PC, or PP. It has a tensile strength of 30-50 Mpa tensile strength and a melting temperature of 200- 250 °C. The other material, which is the overmold, is soft, e.g., TPE or silicone, with a Shore A hardness of 40-80.

The substrate is allowed to cool down to 50-70 °C. The pressure injected into the overmold is 50-120Mpa. This forms a strong bond. Overmolding enhances the holding power, strength, and durability of products.

One such typical object is a toothbrush. The handle is of hard plastic to ensure strength. The grip itself is of soft rubber and, therefore, is comfortable to hold. This basic application demonstrates the real-life uses of overmolding.

Overmolding does not apply only to soft grips. It is also applied in covering electronic products, giving an object a colorful decoration, and extending the life of a product. This flexibility enables it to be one of the most applicable manufacturing methods in contemporary days.

Full Process

Valg av materiale

The procedure of overmolding starts with the choice of the materials. The substrate normally is a hard plastic like ABS, PC, or PP. They contain tensile strength of 30-50 Mpa and a melting point of 200- 250 °C. The molded material is usually a soft one, such as TPE or silicone, and has a Shore A hardness of 40-80. It is necessary to select the materials that are compatible. Failure of the final product to withstand stress can be caused by failure of the bonding of the materials.

Substrate Molding

The substrate was poured into the mold at a pressure of 40-80 Mpa after heating to 220-250 °C. Once injected, it is allowed to solidify to 50-70 °C to render it dimensionally stable. The time taken in this process is usually 30-60 seconds in relation to the size and the thickness of the part. There are extremely high tolerances, and deviation is typically not more than +-0.05 mm. Deviation will result in the product being affected in regard to overmold fit and product quality.

Preparation of the mold to be overmolded

Following the cooling, the substrate is then carefully transferred to a second mold, during which the overmold injection is done. The mold is preheated to 60-80 °C. Preheating eliminates the effect of thermal shock and also allows the overmold material to flow smoothly over the substrate. Mold preparation is needed to prevent any voids, warping, or poor bonding in the final product.

Overmold Injection

The pressure is injected into the substrate using 50-120 Mpa of the overmold material. The temperature of the injection is conditional upon the material: TPE 200-230 °C, silicone 180-210 °C. This step must be precise. Improper temperature or pressure may result in defects of bubbles, separation, or insufficient coverage.

Avkjøling og størkning

Following injection, the part is cooled to enable solidification of the overmold and its strong bond to the substrate to take place. The cooling time ranges from 30 to 90 seconds based on the thickness of the parts. The thin regions cool more quickly, whereas the thicker ones are slower to cool. Adequate cooling is needed to guarantee even bonding as well as minimize internal stress that may cause cracks or deformation.

Ejection and Finishing

The part is forced out of the mold after being cooled down. Any surplus, referred to as flash, is excised. The component is checked in terms of surface finish and dimensional accuracy. This will make sure that the product is of the required quality and is compatible with the other parts in case of need.

Testing and Inspection

The final step is testing. Test types: Tensile or peel tests determine the strength of the bond, which is usually 1-5 MPa. Shore A tests would be used to check overmold hardness. The defects, such as bubbles, cracks, or misalignment, can be visually detected. Only components that are tested are shipped or put together into finished products.

Types of Overmolding

Two-Shot Molding

Two-shot molding involves one machine molding two materials. The molding is done at a temperature of 220-250 °C and pressure of 40-80 MPa, followed by the second material injection, which is at 50-120 MPa. The technique is quick and accurate and is suitable when a large number of products, such as rubber grips and soft-touch buttons, are involved.

Innsatsstøping

During insert molding, the substrate is already prepared and inserted into the mold. It is covered with an overmold, either TPE or silicone, which is injected at 50-120 MPa. Bond strength is usually 1-5 MPa. This approach is typical of the tools, toothbrushes, and healthcare devices.

Multi-Material Overmolding

Multi-material overmolding is an overmolding where there is more than 2 materials in a single part. The injection duration of every material is in sequence 200-250 °C, 50-120 MPa. It permits complicated structures with hard, delicate, and covering sections.

Overmolding has been used in applications

The applications of overmolding are very diverse. The following are the typical examples:

Elektronikk

Telephone cases usually have hard plastic with soft rubber edges. The buttons of remote controls are constructed of rubber as they provide better touch. Electronic components are safeguarded with overmolding, and enhanced usability is provided.

Medisinsk utstyr

Protective seals, surgical instruments, and syringes are usually overmolded. Soft products facilitate easier handling of the devices and also make them safer. This is essential in the medical applications where comfort and precision are important.

Bilindustrien

 Overmolding is used to make soft-touch buttons, grips, and seals used in car interiors. Seals of rubber are used to block water or dust from entering parts. This enhances comfort as well as durability.

Forbrukerprodukter

Overmolding is commonly used in toothbrush handles, kitchen utensils, power tools, and sports equipment. The process is used to add grips, protect surfaces, and add design.

Industrial Tools

Overmolding is used in tools such as screwdrivers, hammers, and pliers, which are used to make soft handles. This limits the fatigue of the hands and enhances the safety of use.

Emballasje

Overmolding of some part of the packaging (e.g., bottle tops or safeguarding seals) is used to enhance handling and functionality.

Overmolding enables the manufacturer to produce products that are functional, safe, and also appealing.

Benefits of Overmolding

There are numerous benefits of over-molding.

Improved Grip and Comfort

Products are made easier to handle by the use of soft materials. This applies to tools, household products, and medical devices.

Increased Durability

Attachment of several materials enhances the strength of products. The hard and soft materials guarantee the safety of the product.

Better Protection

Cover or seals of electronics, machinery, or delicate instruments can be added through overmolding.

Attractive Design

The products are designed in various colors and textures. This enhances image and branding.

Ergonomics

Soft grips minimize fatigue in the hand and make objects or devices more comfortable to work with for longer.

Allsidighet

Overmolding uses a wide variety of materials and can be used to form intricate forms. This enables manufacturers to come up with products that are innovative.

Challenges of Overmolding

There are also some challenges of overmolding, which should be taken into consideration by the manufacturers:

Materialkompatibilitet

Not all materials bond well. Certain combinations might need to be adhesive-bonded or surfaced.

Higher Cost

Because it involves additional materials, molds, and steps of production, overmolding may raise production costs.

Complex Process

Mold design, pressure, and temperature have to be strictly regulated. Defects can be brought about by the slightest of errors.

Production Time

Molding Two-stage molding may require more time than single-material molding. New technologies, such as two-shot molding, can, however, cut this time.

Design Limitations

Complex shapes can need custom molds, and this can be costly to make.

Nonetheless, these discouraging issues have not stopped overmolding since it enhances the quality of products and performance.

Overmolding Design Principles

Overmolding is a design where the base is made of a material, and the mold is made out of a different material.

Materialkompatibilitet

Select the materials that are bonded. Overmold and substrate should be compatible with each other in terms of their chemical and thermal characteristics. Similar materials that have close melting points minimize the chances of weak bonding or delamination.

Veggtykkelse

Keep the thickness of the wall constant so that there is consistency in the flow of the material. Lack of uniformity of the walls may lead to faults such as sink marks, voids, or warping. Walls are usually between 1.2 and 3.0 mm of various materials.

Utkast til vinkler

Emboss angles on vertical surfaces to facilitate ejection. An angle of 1- 3 degrees assists in avoiding damage to the substrate or overmold during demolding.

Rounded Corners

Avoid sharp corners. Rounded edges enhance the flow of materials during injection, and stress concentration is decreased. The recommended corner radii are 0.5-2mm.

Bonding Features

Pits or grooves are made, or interlocked structures are made to grow mechanical bonding between the substrate and the overmold. The features add peel and shear strength.

Venting and Gate Placement

Install vents that will enable the escape of air and gases. Position injection gates in locations other than the sensitive areas in order to achieve a homogeneous flow that avoids cosmetic faults.

Shrinkage Consideration

Consider variation in the shrinkage of materials. The shrinkage of thermoplastics can be as little as 0.4-1.2 or elastomers can be 1-3%. The correct design will avoid distortion and dimensional errors.

Technical Decision Table: Is Overmolding Right for Your Project?

Parts Made by Overmolding

Tool Handles

Overmolding is used to create a hard core and soft rubber grip in many hand tools. This enhances comfort and minimizes fatigue of hand usage and offers greater control of usage.

Forbrukerprodukter

Most common products, such as toothbrushes, kitchenware, and tools that require electricity, usually utilize overmolding. Soft grips or cushions help to improve ergonomics and lifespan.

Elektronikk

In the phone case, remote control, and protective housings, common applications of overmolding include these. It also provides shock absorption, insulation, and a soft touch surface.

Bilkomponenter

Overmolded buttons, seals, gaskets, and grips are a common feature in the interior of cars. Soft-touch systems enhance the comfort, noise, and vibrations.

Medisinsk utstyr

Overmolding is used in medical devices such as syringes, surgical instruments, handheld objects, and the like. The process will guarantee thorough-going safety, accuracy, and firm hold.

Raw Materials in Overmolding

Material selection is of importance. Common substrates include:

Hard plastics such as polypropylene (PP), polycarbonate (PC), and ABS.

Metals in fields of application

The overmold materials usually are:

• Soft plastics
• Rubber
• Nylon thermoplastic elastomers (TPE)
• Silicone

The choice of the material is based on the use of the product. As an illustration, biocompatible materials are needed in medical gadgets. Electronic requires materials that are insulative and protective.

Best Practices in the Design of Overmolding Parts

The design of parts to be overmolded must be well considered in order to attain high levels of bonding, attractive outlook, and quality performance. Adhering to established design guidelines contributes to minimizing the error rate, and the quality of the products becomes consistent.

Select Materials which are compatible

The overmolding depends on the choice of material. The overmold and the underlying material have to have a good connection. Commodities that melt at similar rates and have the same chemical properties have more powerful and dependable bonds.

Design for Strong Bonding

Good mechanical bonding between the part design and the design itself should be supported. Undercuts, grooves, and interlocking shapes are some of the features that enable the overmolded material to hold the base part firmly. This minimizes the chances of separation when in use.

Keep the wall thickness in the right way

A uniform thickness in the walls enables the flow of materials in the molding process. Lack of uniformity in the thickness may lead to sink marks, voids, or weak sections in the component. A symmetric design enhances strength as well as its looks.

Use Adequate Draft Angles

Draft angles simplify the process of extracting the part from the mold. Friction and damage can be minimized in ejection through proper draft, and this is particularly useful in complex overmolded parts.

Avoid Sharp Corners

Acute edges have the potential to cause stress points and limit the flow of material. Rounded edges and flowing results enhance strength and make the overmolded compound flow evenly around the component.

Include Venting Features

During injection, good venting enables the trapped air and gases to escape. Good vents allow avoiding air pockets and surface flaws, as well as filling the mold halfway.

Plan Overmold Material Positioning

The injection points are not to be placed near important features and edges. This eliminates the accumulation of materials, rupture of flow, and aesthetic defects in the exposed parts.

Optimize Tool Design

The successful overmolding requires well-designed molds. Proper placement of the gate, balanced runners, and effective cooling channels contribute to ensuring that there is even flow and stable production.

Take into consideration Material Shrinkage

Various substances have different rate in cooling down. These differences should be taken into account by designers so that no warping, misalignment, or dimensional problems can be observed in the final part.

What are some of the materials used to overmold?

Overmolding gives the manufacturers the chance to mix dissimilar materials to accomplish certain mechanical, operational, and aesthetic traits. The choice of the material is determined by its strength, flexibility, comfort, and environmental resistance.

Thermoplastic, not Thermoplastic.

It is one of the most widespread overmolding combinations. The base material is a thermoplastic polymer, which is a polycarbonate (PC). It is then covered with a softer thermoplastic such as TPU. This composite enhances grip, comfort, and surface feel, and structural strength is not sacrificed.

Thermoplastic over Metal

This technique uses a thermoplastic material that is molded on top of a metal part. Metals like steel or aluminum are usually coated with plastics like polypropylene (PP). This assists in guarding against corrosion of the metal, reducing vibration, and decreasing noise during usage.

TPE over Elastomer.

This system employs a hard plastic recycled substrate like ABS with the addition of a flexible elastomer on the top. It is normally applied in products that require durability and flexibility, such as tool handles and medical equipment.

Silicone over Plastic

Silicone is also overmolded over plastic materials such as polycarbonate. This offers a high level of water resistance, sealing capability, and low tactile feel. It is commonly applied in medical and electronic devices.

TPE over TPE

Overmolding of different grades of thermoplastic elastomers can also be performed. This enables the manufacturers to produce products that have different textures, colors, or functional areas, within one part.

Is Overmolding the Right Choice?

When your product requires strength, comfort, and durability at the same time, overstøping is the appropriate decision to make. It is particularly suitable when used with components that need a soft handle, impact resistance, or additional protection without adding more assembly processes. Overmolding can be used on products that are frequently touched, like tools, medical equipment, or even electronic cases.

Nevertheless, overmolding does not apply to all projects. It is normally associated with increased tooling expenses and intricate mold pattern design as opposed to single-material molding. When production quantities are small or product design is basic, then the traditional molding processes could work out to be less expensive.

Assessing the material compatibility, volume of production, requirement of functionality, and budget with consideration at the initial design stage will help in deciding whether an overmolding solution is the most effective in addressing your project.

Examples of overmolding in the real-life

Toothbrushes

The handle is hard plastic. The grip is soft rubber. This eases the task of cleaning the teeth.

Phone Cases

The device is covered with hard plastic. Drop shock is absorbed on soft rubber edges.

Power Tools

The rubber is overmolded on handles to minimize vibration and enhance safety.

Car Interiors

Control knobs and buttons are usually soft in their feel, which makes the user experience better.

The following examples demonstrate the enhancement of usability, safety, and design of overmolding.

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Konklusjon

Overmolding is a flexible and useful technique of manufacturing. It is a process that involves a combination of two or more materials to make products stronger, safer, and more comfortable. It is broadly applied in electronics, medical devices, automotive components, domestic appliances, and industrial tools.

This is done by a careful choice of the material, accurate shape of the molds, and by ensuring that the temperature and the pressure are kept in check. Overmolding has considerable benefits, even though it is faced with some challenges, such as increased cost and increased production time.

Overmolded products are more durable, ergonomic, appealing to the eye, and functional. One of the areas where overmolding has become an inseparable component of modern manufacturing is the case of everyday products, such as toothbrushes and phone cases, to more serious items such as medical equipment and automobile interiors.

Knowing about overmolding, we may feel grateful to the fact that it is due to simple decisions in the design that help to make the products more convenient to use and longer-lasting. Such a little yet significant process goes on to enhance the quality and functionality of the goods that we use in our daily lives.