Large Injection Molding

Inox Cast Large Injection Molding

Inox Cast is a trusted manufacturer and supplier of large injection molding services for more than 20 years. We provide excellent large injection molding services to different industries like automotive, medical, electrical, and more.

Here in Inox Cast, we are committed to bringing the best products to our customers. We are an OEM manufacturer that offers full customization of your orders. We manufacture products based on your exact specification to meet your application requirements.

At Inox Cast, we also have expert engineers to manufacture your orders. Our R&D team focuses on prototyping, designing, development, production, and services of large injection molding. Therefore, you can assure that Inox Cast can surely provide your needs.

Advantages of Inox Cast Large Injection Molding

• Provides unique capabilities with 31lb shot sizes
• Our large injection molding capacities include structural foam, injection, and more
• Full finishing capacity like assembly, shielding, decorating, painting
• Competitive cycle times
• Supports large part applications ranging from 450 tons to 1574 tons with 26 presses

At Inox Cast, you can find the right infrastructure of large injection molding. We are driven by expertise innovation to manufacture cost-effective and high-quality parts. We have meet customer’s requirements by ensuring fit, function, and form. All our products and services are offered at a competitive price.

Choose Inox Cast as your no.1 large injection molding services provider. Inquire now!

Large Injection Molding: The Ultimate Guide

I know you are probably wondering what large injection molding plastic parts entail.

A reason this guide takes you through critical aspects such as tonnage, injection molding techniques, prototyping to part sizes.

So, if you want to learn more, read this guide.

1.  What Is Large Tonnage Injection Molding?

Large tonnage injection molding is a process that requires the use of machines that are rated 500 or more tons of clamping force.

Large tonnage injection molding refers to a method of getting molded products through the injection of plastic materials that are molten by heat.

In the end, it forms a mold and then cools and solidifies

large injection molding guide

tonnage injection molding

It is suited for the production of products in large quantities, and which have complicated shapes.

2.  How Do You Choose Large Tonnage Injection Molding Machine?

Some of the features to choose a large tonnage injection molding machine include:

• Faster cycle performance: the large tonnage injection molding machine chosen should be able to reduce the dry cycle time by enhancing the speed.
• Phenomenal energy savings: it should reduce the consumption of power by more than half and also reduce CO2.
• Reduced cycle time and energy savings: should be able to increase the number of products manufactured per hour and also reduce the mold close or open time and power consumption.

tonnage injection molding machine

3.  Clamp Force Vs Injection Pressure in Large Injection Molding

Clamp force refers to the way a clamp found on an injection molding holds the two halves of the mold together during the injection process.

clamp force

 Injection pressure on the other hand refers to the measure of pounds per square (PSI) which is needed to inject the plastic resin that is melted.

This is to remove the air and fill up the cavity by use of sufficient pressure to make a quality part.

The greater the injection pressure is will enable the pushing of the plastic to melt thus resulting in the greater clamping force needed in ensuring the mold holds together.

pressure injection molding overview

4.  Determining Size Of Machine For Large Injection Molding

The size of the machine for large injection molding is determined by the use of the general rule of thumb which is 2-8 tons per square inch.

When a part is large, it will need more clamp force in holding the two halves of the mold in place during the process of injection.

Some of the factors which determine the amount of clamping force that is needed include:

• Wall thickness: thick walls provide more volume for the flow of the plastic melt.

They also offer insulation to the melt and enable it to move further using little pressure.

When the walls are thinner, heat will be transferred faster from the plastic melts.

You will require a lot of pressure in moving the melt to thin segments.

• Geometry: when the part is more tortuous, and the distance for the plastic melt to move is long;

then the volume of the melt and the transfer of the heat to the cooling zone will be greater.

• Gating of part
• Viscosity of resin
• The temperature of injection mold: increasing the injection mold’s temperature helps in better flow of the plastic materials and needs little pressure.

Thus, closing the clamping force for holding the mold closed during the filling process.

5.  Advantages Of Large Injection Molding

Some of the advantages of large injection molding include:

• Fast production: large injection molding can manufacture a high number of parts per hour averagely between 15 to 20 seconds per cycle time.
• Low labor costs: large injection molding tends to be an automated process and thus many of the processes are carried out using machines.

This assists in the reduction of the manufacturing costs as there is a reduction in overheads.

• Design flexibility: large injection molding makes it possible for the production of intricate shapes and manufacturing designs that seem complicated.
• High production output: it makes it possible to produce thousands of parts before the large injection molding machine is maintained.
• Large material choice: it makes it possible to select a wide range of polymer resins and even simultaneously incorporate multiple plastic materials.
• Ability to include inserts: large injection molding makes it possible to insert molded metal or plastic.
• Good color control: it makes it possible to produce plastic parts in any colors needed by the use of compounding or masterbatches.
• Product consistency: large injection molding tends to be a repetitive process thus one will be able to manufacture identical products in high volume.
• Reduced finishing requirements: large injection molding eliminates the need for post-production work as parts tend to have a good finished look in the end.

6.  Applications Of Large Part Injection Molding

Some of the applications of large part injection molding include:

• Aviation
• Electronics industry: examples of electronics include:
  • Electronic components for use in bigger machines
  • Electrical switches.
  • Computer housings
  • TV housings
  • Compressors
• Machinery: used in making large medical equipment, various consumer products, and furniture.
• Marine industry
• Aerospace and automotive industry: given aerospace and automotive industries need larger plastic components which are manufactured using large molds such as:
  • automotive dashboard components
  • Door liners or handles
  • Seat belt components
  • Instrument panels
  • Fenders
  • Grilles
  • Bumpers
  • Door panels
  • Floor rails
  • Light housings
  • Splash guards
  • Glove compartments
  • Air vents

7.  Choosing Materials for Large Injection Molding

Plastic resins are available in different grades and they tend to be specified using physical, chemical, and environmental resistance properties needed for the finished parts.

Each resin grade tends to have an ideal processing temperature range.

It does not have degrading properties in the production process. Each different grade of material tends to have a different rate within which the plastic melt flows.

The melt flow index (MFI) refers to a measure of the ease of flow of the melt of a thermoplastic polymer.

The material chosen for large injection molding should be able to flow in about ten minutes via a capillary of a given diameter and length.

The pressure used should be imposed via alternative gravimetric weights for temperatures specified.

It should also have a wide range of MFI within a given material grade.

It is important to note that the higher the MFI, the easier the melt will flow and the less the injection pressure will be required in filling the cavity.

This will also ensure that less clamp tonnage is needed by the large injection molding machine.

Some of the materials which are used for large injection molding include:

Nylon Polyamide (PA)

It tends to be extremely tough, has a high melting point, and can accommodate significant wear and tear.

Nylon is also relatively light in weight and has a high chemical resistance.

It is often used in strong mechanical parts like bearings, gears, bushings, slides, electrical connectors, threaded inserts, and medical implants.

Polycarbonate (PC)

These are materials that are strong, tough, naturally transparent, and able to maintain their temperature range over a wider period.

Polycarbonate can maintain its color over time and retains its strength thus ensuring durability.

Some of the uses of polycarbonate include machinery guards, diffusers, and light pipes.

Polyethylene (PE)

It is categorized into three main types namely; high density (HDPE, PEHD), low density (LDPE), and polyethylene terephthalate (PET, PETE).

HDPE and LDPE are chemical resistant, flexible, have optical transparency, and have a high melting point.

PET on the other hand is not defined by density and can be as clear as glass. LDPE tends to be more flexible as compared to opaque HDPE.

Examples of uses of PE include electronic wires, cable insulators, and medical device components.

Polyoxymethylene (POM)

It is used on molding parts that need low friction, excellent dimensional stability, and high stiffness.

It also has excellent stability, low water absorption, and great chemical resistance.

The main types of polyoxymethylene include homopolymers and copolymers and manufacturers should select based on required properties.

Polypropylene (PP)

It is very hard and resistant to heat and its density tends to change with fillers.

Polypropylene also has good chemical resistance and can retain its shape after bending.

Examples of applications of polypropylene include sporting goods, power tool bodies, storage containers, and packaging appliances.

Polystyrene (PS)

It has less dimensional stability, is brittle, light in weight, and resistant to the growth of bacteria and moisture.

Polystyrene is used in optical, medical, electrical, and electronic applications.

Thermoplastic Elastomer (TPE)

This material is a blend of rubber and plastic thus it is elastic and recyclable.

Some of the uses of TPE include medical devices, auto parts, weather seals, footwear, breathing tubes, ventilation masks, and shock dust boots.

Thermoplastic Polyurethane (TPU)

It is suited for extreme temperatures and chemical resistance. It is used in gaskets, caster wheels, and sporting wheels

Selecting Mold For Large Size Injection Molding

Mold refers to a metal block that is hollow and molten plastic tends to be injected into it to make a shape that is fixed.

Several holes tend to be drilled into the mold to ensure temperature control using hot water, heaters, or oil.

Molten plastic normally enters a mold via fill cavities and a sprue by use of gates and runners.

Once this is done, the mold is opened once cooling is done and the ejector rod of the machine moves the ejector plate to further eject moldings.

Some of the mold materials used for large injection molding include:

• Steel molds: they are suited in cases where detailed features are required and are great for advanced resins.

Steel molds tend to have better durability and thus are worth selection for high volume production.

• Aluminum molds: are relatively cost-effective and require a lower production time as compared to steel molds.

It is also easy to modify and repair aluminum molds and they do not need cooling or heating lines like steel.

Why Clamp Tonnage Is Critical On Large Size Injection Molding

Choosing the right clamp tonnage tends to be the basis of commencing your large-size injection molding process.

When there is excessive or insufficient clamp tonnage, the clamping pressure may result in damages, flash, and problems to the mold, machine, and parts.

When there is insufficient clamp tonnage, it results in short moldings.

This results in the inconsistent flash, weights, poor surface finish, wall selection variation, and size variation.

In case the clamp tonnage force is very low, it will be hard to manufacture quality parts and will result in excessive mold wear.

When excessive clamp tonnage is used in large size injection molding, some of the moldings defects that can be immediately seen on parts include:

• Short shots
• Burns
• Gloss level changes

This will not only affect the quality of the part but also the large injection molding machine and mold will be destroyed from excessive clamping.

Some of the long terms side effects which might be imposed in the mold include:

• Broken inserts
• Crushed vents
• Cracked core or cavity block
• Rolled parting line

Some of the potential failures on the large injection molding machine when excessive clamping pressure is applied include:

• Deformed platens
• Fractured machine frame
• Cracked hydraulic-cylinder mounting plates

From the analysis above, it is vivid that insufficient or excessive clamp tonnage does no good to the purpose of large size injection molding.

Therefore, it is important to choose an injection molding machine that offers good clamp force and avoid choosing one that gives too much or less pressure for the job.

Why Is injection Molding Prototyping Critical For Large Parts?

Injection molding prototyping is critical for large parts because of the following reasons:

• It automates the process of mass production.
• Depending on your molding design, injection molding prototyping ensures that a single shot may lead to the production of many parts.
• Injection molding prototyping is critical for large parts as it ensures efficiency, predictability, and less troubleshooting.
• It brings the design to life so that you can see it before the production process begins.

Large Injection Molding Process

The process of large injection molding entails the following steps:

Filling Stage

The first step in large injection molding entails filling the melt flow into the cavities of the mold up to about 95 percent of their capacity.

Note that the shorter the time used in the filling, the higher the molding efficiency.

Some of the factors which affect the filling of the mold in the filling stage include:

• The viscosity of the material
• Venting
• Injection pressure
• Mold temperature setting
• Setting the injection speed to a faster rate
• Mold structure
• Gate friction loss

Packing Stage

In this stage, there is the constant application of holding pressure and compacting of the melt to add the material’s density.

The pressure in the process of packing is high it is almost full filled.

Also, the screws of large injection molding machines will continue to slightly move forward as the rate of flow gradually reduces.

Plastic mold wall is then cooled down and allowed to solidify until the gate closes.

The holding pressure in this stage tends to range between 50 percent to 65 percent of the speed of filling and maximum pressure.

This ensures that the holding pressure ranges between 0.6 to 0.8 MPa lower than the injection pressure.

Cooling Stage

It is important to ensure that the cooling system of the large injection mold is well designed.

This is because the molded material requires to be solidified and cooled to avoid damage or deformation.

The time for cooling ranges between 70 percent to 80 percent of the total cycle of injection molding.

Therefore, a cooling system that is well designed will reduce the molding time and greatly increase productivity.

When the cooling system is not well designed, the molding time will take long thus increasing costs and resulting in uneven cooling.

Releasing Stage

Finally, at this stage, the large injection molding releases parts from the mold cavities. Manufacturers need to exercise caution and ensure the products are released properly.

This is because improper release may result in deformation and damage.

There are two main ways of releasing and these include stripper plate and injector.

The most appropriate method to use is determined by the structure of the end product.

It is important to ensure that the layout of the ejector is uniform to ensure that there is stable releasing.

large injection molding

Defects In Large Injection Molding

Some of the defects in large injection molding include:

Burn Marks

Tend to be caused by overheating of resins or air trapped bubbles during the injection molding process.

This defect occurs due to either high rates of injection or excessive heating of the material used.

It can mainly be prevented by reducing the melt and mold temperature and the speed of injection in the molding tool.

Additionally, manufacturers can avoid burn marks by adding exhaust systems and expanding the gas vents to ensure that trapped air escapes with ease during the low-pressure injection.

Surface Delamination

It refers to a surface layer flaking defect.

Which happens when thin layers which are on the molded component’s surface separate readily or peel away from the underlying material.

It is mainly caused by foreign material contamination of the resin pellets or any other materials for the base.

It can be prevented by appropriately storing and handling resin pellets.

Additionally, manufacturers should attempt to the reliance on these components by redesigning the mold and ensuring the injection nozzle is okay.

Vacuum Voids

They usually happen when an insufficient amount of plastic material is injected into the mold.

This is mainly caused by a short shot or vacuum voids in forming gas pockets in the plastic material within the mold.

Some of how gas bubbles may form include:

• Poor venting may cause air to remain in the mold rather than being placed entirely by the plastic.
• Volatile compounds which are part of the resin mixture may mix into a gas as the plastic resin is heated.
• Water in the mold tends to vaporize within the mold and cause the formation of pockets.

Troubleshooting vacuum voids should adhere to determining the main cause of the void and then fixing the process.

This is done by altering injection pressure, runner size, cooling rate, or design changes.

Discoloration

It occurs when a molded part has a different color than expected and is often restricted to a small region or a few streaks of different colors.

To solve this defect, ensure that ingredients or residual resins are eliminated.

This is done by ensuring that every part of the machine is clean between each manufacturing cycle.

The color agents which are used should also have excellent heat conductivity and be able to withstand high temperatures.

Warping

It occurs when sections of the molded part do not shrink properly and are mainly caused by rapid or premature cooling.

To prevent warping, ensure that the cooling process is gradual and long enough to enable the material slowly cool without warping.

Flash

This is an excess mold material that appears as a protrusion at the edge of the component.

It happens when the material flows outside the given flow channel to the gap between the tooling plates or the injector pin.

It can be prevented by increasing the clamping force on the plate to ensure that the material stays in the channel.

Additionally, flash can be troubleshot by increasing the material flow and adjusting the mold temperature, ventilation, and injection pressure.

Sink Marks

These are small depressions or craters that occur on the thicker parts and they mostly happen when the interior of the molded part shrinks.

This pulls the material inwards. Sink marks can be prevented by increasing the cooling time to reduce shrinkage.

Additionally, reduction of the thickness of the thickest wall parts needs to be reduced to provide shorter times for cooling.

Conditions Affecting Quality of Large Injection Molded Parts

Some of the conditions which affect the quality of large injection molded parts include:

• Requirements for injection molding materials: it is important to note that plastics tend to use different steels which require special care like corrosion resistance and polishing.
• Surface finish: the surface treatment of large injection molded parts is very important as it tends to enhance their hardness and increase their lifespan.
• Structural design: reasonable mold structure helps in increasing the life of the life injection mold.

It also makes sure that the production process is smooth thus enhancing efficiency and reducing costs.

• Mold processing: the organization of the molding process is very important as it fastens the production cycle, saves costs, and shortens the processing time.

Mold processing also helps in ensuring longevity and stability of the mold thus ensuring the quality of the finished product is great.

In case you have any questions or inquiry about large injection molding, Inox team is here to help – contact us now.