injection molding thick wall

Injection molding is a general method that is typically used in the manufacturing industry. Here, the material is pushed under high pressure into a die cavity. Typically, during the designing stage, the wall thickness of a part is one of the most important considerations. So, in this article, we will discuss wall thickness, its relationship with injection molding, and its insight into how it affects part quality and manufacturing capability.

How would you define injection molding wall thickness?

Injection molding Wall thickness is a measure of the thickness of the walls of the molded part produced with the help of an injection molding process. It is the quantity, in millimeters, from one of the outermost surfaces of the part to the other outermost surface. Moreover, wall thickness is perhaps the most important, as it determines the ability of the molded part to resist failure mechanisms. These may include yielding, buckling, warping, and cosmetic defects. Wall thickness must always be designed to suit certain conditions, i.e., the material, the functioning of the part, the design, and the molding equipment used. So, selecting the appropriate thickness for the walls is pivotal to delivering the desired parts.

injection molding wall thickness

What is the importance of uniform wall thickness?

Uniform wall thickness is very important when it comes to high quality. It helps provide defect-free and structurally sound injection-molded parts and also increases structural integrity. Besides this, it helps improve efficiency and optimize material use. So. Let’s discuss more about the importance of uniform wall thickness.

1. Impact on Part Quality

So, first of all, uniform wall thickness gives consistent cooling and also prevents internal stresses and deformations. Besides this, it helps maintain precise dimensions so it can avoid surface imperfections, i.e., sink marks and warping. Additionally, it increases both the functionality and aesthetics of the final part.

2. Reduction of Defects

Secondly, if the wall’s thickness is uniform, it ultimately reduces warping and sink marks. It promotes even cooling and reduces internal stresses, so it eventually gives us stronger and more durable parts with fewer weak spots.

3. Structural Integrity

The uniform wall thickness provides a balanced load distribution to improve strength and durability. Moreover, it improves the mechanical properties of the products, i.e., tensile strength and impact resistance, to provide reliable performance.

4. Better Manufacturing Efficiency

It also facilitates the mold design and injection molding processes. It reduces cycle times and production costs. Additionally, it also promotes faster and better cooling and optimizes the production process.

Material Considerations in Injection Molding

The following are the material considerations for injection molting wall thickness.

  1. Type: Examples: thermoplastics, including ABS and PC; thermosets like epoxy resins; elastomers such as silicone rubber; and TPE.
  2. Flow: Mold filling depends on viscosity, where the product is to be thin. It requires high-flow material, and where the thickness is required, low-flow material is most appropriate.
  3. Shrinkage: With metals, they reduce in size from a molten state and exhibit a solid state or a cast state; this is considered in the design of a mold to make the correct size of a part.
  4. Strength and Flexibility: Additional factors include stiffness and strength, as these dictate the thickness of the wall during construction for a reliable structural outlook.
  5. Resistance: resistance to heat and chemicals to promote long life in any type of operating condition.
  6. Surface Finish: A molding material’s characteristics impose on the surface finish and look of the molded part to increase its aesthetics and smoothness.
  7. Cost and Environmental Impact: These include the unit cost of the material, recycling ability, and its conformity to sustainable standards.

So, the following table describes the suitable ranges that the respective material can support; below is a thick wall injection molding part we made in PC material, lear more about PC injection molding.

Thick wall injection molding

 

Material Typical Wall Thickness Range:
ABS 1.0–3.0 mm
Polycarbonate (PC) 1.0–3.0 mm
Polypropylene (PP) 0.8 – 2.5 mm
Polyethylene (PE) 1.0–3.0 mm
Nylon (PA) 1.0–3.0 mm
Acetal (POM) 0.8–3.0 mm
Polyethylene Terephthalate (PET) 1.0–3.0 mm
Polyvinyl Chloride (PVC) 1.0–3.0 mm
Acrylic (PMMA) 1.0–3.0 mm
Polyethylene Vinyl Acetate (EVA) 1.0–3.0 mm
Thermoplastic Elastomers (TPE) 1.0–3.0 mm
Epoxy Resin 1.0 – 5.0 mm
Silicone 1.5 – 6.0 mm

Guidelines for Designing Wall Thickness in Injection Molding

Here is a brief table that will help us design an optimal wall thickness in injection molding.

 

Guideline Description
General Rules of Thumb ●       Maintain uniform thickness to prevent defects.

●       Guarantee smooth and thick transitions.

Minimum Wall Thickness ●       It depends on material flow; high-flow materials can be 0.5–1.5 mm thick.

●       Make sure the minimum thickness is for strength.

●       Allow for complete mold filling.

Maximum Wall Thickness ●       Thicker walls (>4 mm) increase cooling and cycle time.

●       Optimize to reduce costs and weight.

●       Thicker walls risk sink marks and voids.

Structural/Functional Requirements ●       Thicker walls for high-stress parts.

●       Specific thickness for thermal and electrical insulation

●       Balance thickness for flexibility and strength.

Design for Manufacturability ●       Make sure of design compatibility and material flow.

●       Include 1-2-degree drafts for easy ejection.

●       Reinforce thin walls without adding bulk.

Simulation and Testing ●       Use CAE to predict and fix issues.

●       Test prototypes to validate the design.

Tools and Resources for Wall Thickness Optimization

Here are some tools and resources that can help you increase the effectiveness of injection molding wall thickness.

Software Tools for Simulation

It is used effectively in injection molding to determine a suitable wall thickness. It plays a very vital role in the determination of the wall thickness. These tools give information on how the material is going to be transported and its behavior in the injection molding process. So,  designers can be able to prevent or solve some of the challenges that may arise during the actual process of molding. Key benefits and features include:

  1. Flow Analysis: It imitates the process of the molten material getting into the mold. Then it shows the parts where the material might end up not flowing properly or where the creation of air traps is happening.
  2. Cooling Analysis: Uses computer modeling to forecast cooling patterns to enable the cooling to occur at an even rate. So, it helps eliminate problems such as warping and sink marks.
  3. Stress Analysis: Check the stresses in the part to confirm the thickness of the wall. It checks if it is optimal and if the stress level is sufficient for the intended application but not too high.
  4. Optimization Algorithms: Propose changes that should be made to wall thickness and any other design characteristics. Because it can affect the ability to produce the part and the efficiency of its operation.

Some of the well-known simulation software programs for injection molding are Auto Desk Mold Flow, Solid Work Plastics, and Moldex3D. They all assist designers in designing sections to optimize solutions without defects.

2. Prototyping Options

There are several possible types of prototyping. This means that designers can make important physical and real-formative adjustments as compared to the simulated models. Besides this, these options aim to manufacture the part, so these prototyping methods include:

  • 3D Printing (Additive Manufacturing): Enables the development of prototypes at a higher speed while maintaining different thicknesses of side walls. The most apparent advantage is that it is inexpensive to quickly test various designs. Besides this, it can either be form or function prototypes.
  • CNC Machining: Offers contemplative prototypes that have used production materials so that the outcome is nearly perfect. This method allows for the identification of the mechanical part’s characteristics and its behavior under actual operating conditions.
  • Soft Tooling: This is characterized by the use of low-strength and brief-forming dies to produce few parts by comparison with die casting. So, this approach is advantageous in the assessment of the molding process as well as the identification of the wall thickness. It also helps with the standardization of the entire mold type.

What Factors Affect Injection Molding Wall Thickness?

Multiple factors can affect the wall thickness in injection molding. Let’s discuss these factors in detail:

1. Material Properties

These properties may include:

  • Viscosity: If we talk about low-viscosity materials, they flow easily into thin sections and allow for thinner walls. While the high-viscosity materials may need thicker walls to perform complete mold filling,
  • Shrinkage: Material with a high-shrinkage value might need thicker walls. So, they can account for dimensional changes during cooling.
  • Strength and Flexibility: Mechanical properties, i.e., tensile strength and flexibility, determine the wall thickness for optimal performance.

2. Design Requirements

The following design requirements may affect the wall thickness.

  • Functional Requirements: It all depends on the part you need to manufacture. If it is a structural part, then the walls must be thicker so they can be rigid. On the other hand, the cosmetics part will need thinner walls so they can achieve the best look.
  • Aesthetic Considerations: Thin walls can provide a smart appearance. On the other hand, the thicker walls are strong enough, and they can avoid defects, i.e., sink marks or warping.
  • The complexity of design: The complex geometries may require varying wall thicknesses. So, they can guarantee all features are formed correctly, and the part can be easily removed from the mold.

3. Manufacturing Capabilities

  • Mold Design and Construction: Molds with high precision can handle thinner walls easily, and simpler molds need thicker walls for proper filling. So, they can guarantee the part quality.
  • Injection Pressure and Speed: Machines with high capability can achieve thinner walls, and they deliver higher pressure and speed.
  • Cooling Rates: Uniform cooling is quite important, as thicker walls need longer cooling times. It directly impacts their cycle time and production efficiency. So, the advanced cooling systems help create thinner walls and will also maintain quality.

Conclusion

In summary, injection molding wall thickness gives high-quality, well-shaped, and cost-effective parts. So, it is essential to carefully consider material properties and design requirements to help designers maintain a balance. This balance will increase the part’s performance and manufacturability. Moreover, you can use different advanced simulation software and prototyping options to refine the whole process. These tools will also produce designs with minimal defects. Additionally, advancements in materials, simulation technology, real-time monitoring, and sustainable practices will make improvements in injection molding. So, it can optimize wall thickness more precisely and efficiently.

high volume injection molding

Frequently Asked Questions

What factors influence the choice of material in injection molding?

The type of material is decided based on properties like tensile strength and elasticities, electron microscopy, heat, and chemical resistance. Besides this, it also depends on the appearance and smoothness of the material, its cost, and its recycling ability.

What are some common defects in injection molding and how can they be prevented?

Some of the most frequent defaults are sink marks, which originate from different cooling rates; warping, resulting from internal stress; and flash, which is an excessive building up of material at injection molding parting lines. These problems can normally be avoided by compliance with best design procedures and regulation of degrees of heat, pressure, and other conditions that might affect the product.

How can simulation software benefit injection molding processes?

Computer-aided simulation enables designers and engineers to model and analyze the mold designs, material choice, and process factors in a virtual environment. With the help of this software, one can predict the patterns of material movement, cooling rates, and other things before physical molds are designed for use. So, this helps in upgrading the quality and manufacturability of the part.

What are the advantages of using additives or fillers in injection molding materials?

Additives and fillers can improve characteristic features of materials including strength, stiffness, flame resistance, and impact strength. It can also enhance processability and decrease material cost by adding a greater volume of another more affordable material to resin. However, much effort should be made to have compatibility, equal dispersal, and minimal interferences on the other components.

hdpe injection molding

Thermoplastic injection molding has become the most applicable plastic manufacturing process. It is renowned for producing products of high standard quality in minimal turnaround and large quantities. The increasing need for high quality plastic products in different sectors has boosted the application of thermoplastic materials.

These materials are based on polymer resins, and when heated, they turn into a homogeneous liquid that becomes solid when cooled. Injection molding employs thermoplastics and thermosetting plastics or even elastomeric materials to form high-performance moldable parts or products. Newer technologies in injection molding thermoplastic and better molds have enabled the reduction of costs, better looks, and better manufacturing prospects.

Why Are Thermoplastics Materials Used in Injection Molding?

 

Thermoplastics are used in injection molding since they melt at high temperatures and crystallize at low temperatures. This property makes them ideal for being recycled and formed into different forms and structures. They are the most preferred materials in industries due to their flexibility and versatility of use.

thermoplastic injection molding

How To Produce Injection Molded Thermoplastic Products?

Thermoplastic injection molding is one of the most fundamental processes in contemporary production. It entails the creation of a variety of plastic products through the employment of thermoplastic polymers.

Step 1. Appropriate Material Selection

The material type used determines the final product’s functionality, appearance, and durability. Select materials by considering their mechanical properties, heat stability, and specific use.

Step 2. Material Preparation

This process entails drying raw plastic pellets to eliminate moisture. Because moisture content significantly impacts and is destructive to the melting process and the molded part. These prepared pellets are then fed into the hopper of the injection molding thermoplastic machine through a conveyor belt.

Step 3. Melting

The plastic pellets are melted in a barrel which entails a reciprocating screw. These pellets then take the form of molten lava or red hot liquid. During this phase, temperature controls are crucial to obtain the right consistency and the flow of the molten plastic to the required standard.

Step 4. Injection

As the name suggests, the molten plastic is injected into the mold cavity by applying highly controlled injection pressure. The precise control over this process determines the part’s exact specifications and finishes. The resulting parts are then cooled down and solidified at optimal conditions.

Step 5. Ejection

The required part is then taken out from the mold by using ejector pins after the solidification. This process must be timed and controlled so that it does not harm the part and that it is released properly.

Step 5. Post-Processing

This phase is typically used to cut to shape parts into desired shapes. The parts can be painted, anodized, trimmed, polished, etc, depending on the required functionality and aesthetics.

What are the Critical Parts of a Thermoplastic Injection Molding Machine?

A thermoplastic injection molding machine is made of several parts. Some commonest parts include;

Clamping Unit

The clamping unit tightly holds the two parts of the mold to ensure that they do not open during the injection. It has to apply enough force to resist the force exerted by the molten plastic being injected to ensure that the mold does not open and the part is well formed.

Injection Unit

The injection unit, which is said to be the heart of the machine, is in charge of heating the plastic material and injecting it into the mold cavity. It has a heated barrel with a screw that moves back and forth to force the plastic through a nozzle into the mold and maintain a steady supply of material.

Dwelling and Cooling System

Once the molten plastic has been injected into the mold, the dwelling and cooling system keeps pressure to guarantee that the plastic occupies all the mold cavities and solidifies into the right shape. Cooling is a very important process in the reduction of the cycle time as well as enhancing the quality of the final product.

Ejection Process

After the plastic has been set, the ejection process starts. The mold is opened, and the ejector pins, which are provided on the side of the mold, throw out the finished part from the mold cavity. This process must be done carefully and at the right time so that the part is not damaged and the removal is done well.

Mold Tool

The mold tool is a negative one and is made from steel or aluminum and forms the final product. It defines the surface finish and size of the product. The tool has two halves that are connected at the center and which are injected apart from each other.

injection molded thermoplastic

Material Types Are Used in Thermoplastic Injection Molding?

The are many type of thermoplastic injection molding materials used to create molding products include;

ABS (Acrylonitrile Butadiene Styrene) is characterized by high impact strength, high rigidity, and low shrinkage. This makes it ideal for automotive components, consumer electronics, and toys where durability and mechanical stress resistance are of paramount importance. Read more about ABS injection molding.

Polyamide (Nylon) has high strength, thermal stability, and wear resistance. These attributes make it ideal for use in automotive parts, mechanical products, and other consumer products that require strength and performance. Read more about nylon injection molding.

Polyvinyl Chloride (PVC) has the advantages of high strength, good chemical resistance, and fire resistance. Some of the uses are plumbing pipes, medical tubing, and outdoor furniture, which makes it a material that can be used in many fields.

Polyethylene Terephthalate (PET) is valued for its transparency, mechanical properties and food contact approval. This material is used in beverage bottles, packaging materials, and synthetic fabrics because of its strength and clarity.

PMMA or Acrylic offers sound light transmission and is not affected by weathering or UV radiation. These features make it suitable for signs, lamps, and windows where transparency and strength are desirable. Read more about PMMA injection molding.

Polystyrene (PS) is a lightweight material, relatively cheap, and often used in disposable cutlery, CD cases, and insulating materials because it is easy to shape and relatively cheap. Read more about PS injection molding.

Thermoplastic Polyurethane (TPU) is characterized by high elasticity, oil resistance, and abrasion resistance. It is applied in the production of soles and insoles of shoes, flexible medical tubes, seals and gaskets of automobiles, etc. Read more about TPU injection molding.

Polyoxymethylene (POM) has high rigidity, low wear rate, and good resistance to shrinkage and swelling. It is suitable for applications that call for strength and accuracy, like gears and bearings, electrical parts, and consumer products. Read more about POM injection molding.

Polybutylene Terephthalate (PBT) has good electrical properties, heat and chemical resistance. It is widely applied in electrical parts, automotive parts, and under-hood parts because of its high strength and heat resistance.

High Impact Polystyrene (HIPS) is characterized by high impact strength and good processability. It is used in model making, sign writing, and in the housing of consumer electronic products where strength and stability are required.

Thermoplastic elastomers or TPE are materials that have characteristics of both thermoplastics and rubber and are flexible and elastic. They are applied to sealing and gasket applications, soft feel parts in household goods, and handles. Read  more about TPE injection molding.

Polyphenylene Oxide (PPO) is well known for its heat resistance, low thermal expansion coefficient and electrical insulation. It is applied in automotive parts, electrical parts, and appliances that need to be hard-wearing and heat-resistant.

LCP is characterized by high mechanical strength, high-temperature stability, and good chemical resistance. It is applied in high-voltage electrical contacts, microwave oven parts, and other critical uses.

Polyetherimide (PEI) has high heat, strength, and flame resistance. It is used in aerospace parts, medical equipment, and other places where high stress is experienced.

Polyether ether ketone (PEEK) is characterized by high-temperature stability, chemical inactivity, and mechanical characteristics. It is applied in aerospace parts, automotive applications, and medical applications where strength and toughness are needed. Read more about PEEK injection molding.

Polyphenylene Sulfide (PPS) has high heat resistance, chemical resistance, and low thermal shrinkage. It is used in automotive, electrical and electronics and in coatings that require chemical and heat stability. Read more about PPS injection molding.

Styrene Acrylonitrile (SAN) is preferred for its clarity, stiffness and resistance to chemicals. These properties make it suitable for use in food containers since fats and oils are some of the things that the containers should be able to withstand. SAN is also often applied in kitchenware because of its high heat resistance and in bathroom fittings because of chemical resistance.

Acetal (Polyoxymethylene, POM) is highly stiff, self-lubricating, and has good dimensional stability. Acetal is also used in electrical insulators and consumer goods. Some common examples include; zippers and window latches, where strength and wear resistance are required.

Ethylene Vinyl Acetate (EVA) is known for its flexibility, high-impact strength, and clarity. It is a rubber like material that can be molded and recycled and is used in foam products used in sports equipment padding, footwear such as soles and insoles, and flexible packaging films.

Polyurethane (PU) is a flexible polymer that is applied to foam furniture and car seats because of its comfort and sturdiness. Also, PU is used in wheels and tires of industrial and recreational vehicles and automotive interior parts such as dashboards.

PPSU is highly heat resistant, very tough, and can withstand steam sterilization, which makes it suitable for challenging conditions. PPSU is widely used in medical instruments that are often sterilized, aircraft interiors that are exposed to high temperatures and stress, and plumbing where heat and mechanical stress are essential. Read more about PPSU injection molding.

Polyethylene Naphthalate (PEN) is a variant of PET but has better barrier properties, heat and chemical resistance. PEN is applied in packaging materials that need to be very strong and have good barrier properties and in electronics where parts need to be dimensionally stable and electrical insulating.

Polybutylene’s peculiar characteristics, like heat and pressure resistance, make it ideal for use in piping systems in hot and cold water distribution and under-floor heating systems where high temperature and pressure are required.

Polymethylpentene (PMP) is a rather special type of thermoplastic due to its transparency and heat resistance. PMP is used in laboratory equipment where chemical resistance and clarity are required and in microwave cookware because of its heat resistance and quality food preparation.

Polysulfone (PSU) is characterized by high heat resistance, strength, and transparency. These characteristics make it ideal for use in medical devices, especially those that are reusable and need to be sterilized, water filtration systems because of their stability and strength, and electrical parts where insulation and heat resistance are important.

Injection Molding Nylon

Thermoset Vs Thermoplastic Injection Molding: Key Differences

Thermoplastic Injection Molding

This thermoplastic molding technique uses materials such as; polyethylene and nylon that can be reheated and recycled for second use. It is perfect for producing numerous components that require flexibility, impact strength, or clarity.

Thermoset Injection Molding

This method uses materials such as epoxy and polyester, which undergo a chemical reaction when exposed to heat and harden to a specific form. They cannot be reshaped once they have cooled down. It is used where high strength, heat or chemical resistance is required, but unlike thermoplastics, they cannot be recycled

Therefore, the major distinction is that thermoplastics can be recycled through melting and thermosets are permanently molded and cannot be remolded, providing different strength as per the requirement.

Industrial Applications of Thermoplastic Injection molding

Automotive Industry: Thermoplastic injection molding is widely applied for fabricating interior to exterior components of automobiles like dashboard parts, bumpers, and door panels of cars. It is also useful for creating under-the-hood parts such as fluid reservoirs and housings because of its strength and accuracy.

Medical Industry: In the medicare sector, thermoplastic injection molding is very significant in the manufacturing of disposable syringes, surgical instruments, and enclosures for medical devices. Due to its precision in developing complex patterns, it is essential to develop parts utilized in diagnostic tools and prosthetics.

Consumer Electronics: In electronics, this molding process is used in the production of enclosures of smart phones, remote controls, and computer parts, among others. It is also used in the fabrication of battery casings and connectors because of its strength and versatility of shape.

Construction Industry: In construction, thermoplastic injection molding is applied in the production of pipe fittings, plumbing parts, and electrical enclosures because of the strength and durability of the material. It is also applied in the production of insulating materials and window frames due to its strength and heat resistance.

Toys and Recreation: This molding process is used in creating action figures, puzzles, and boards games that have designs that are complex. It is also used in the manufacture of outdoor items such as garden implements and children’s play equipment since it can yield strong and safe products.

Household Products: Thermoplastic injection molding is vital in the production of kitchen appliances, containers, and utensils because of the heat and chemical resistance. It is also used in making storage bins and cleaning tools due to its strength and simplicity.

Thermoplastic Injection Molding: Common Defects & Remedies

Below are typical challenges encountered during the process and strategies to address them effectively:

Insufficient Filling: This is so when the mold is not fully filled. To address this, one may increase injection speed or pressure, check the temperature of the material, or increase the size of the gate.

Flash Formation: This is a condition where there is the formation of a thin layer of plastic on the edge of the part after it has been molded. This can be solved by either lowering the injection pressure or clamping force or by checking the mold for any damages.

Warping: If the part distorts during cooling, then consider uniform cooling temperature, cycle time to optimal state.

Sink Marks: These are small contours on the part’s surface and normally occur in varying sizes. To prevent these, increase the cooling time or reduce the holding pressure.

Burn Marks: These occur when a material is overheated or air is trapped and may cause black or brown discoloration on the part surface. This can be overcome by reducing the melt and mold temperature and, at the same time, increasing the injection speed so as to avoid overheating or the formation of air pockets.

Such changes should enhance the quality and productivity of the injection molding process.

Summing Up

Thermoplastic injection molding remains one of the most significant pillars of innovation that offers flexibility and effectiveness in developing quality products. It is used in automotive and medical industries, consumer electronics and many more industries proving its versatility and efficiency.

Companies like Sincer Tech are the best examples of plastic injection molding services that provide full-service solutions with a focus on quality and accuracy. Our company specializes in overmolding and insert molding and uses a variety of materials to guarantee that each product is of the highest quality.

They offer a wide range of thermoplastics, and their experience in prototype molding and mass production makes them among the best. Whether it is a prototype or a mass production project, Sincere Techs’ dedication to the advancement of technology and the production of high-quality products is evident in all of their work.