Rubber mould is a single or assembled tooling system you can use to manipulate rubber into a desired shape.
Usually, the rubber mould design a replica of the final product. Therefore, the quality of rubber injection molding process will depend on the mold type.
Choosing Rubber Moulding Tooling Material
The quality of rubber injection molding tooling material is very critical. It determines the success of the entire process. When it comes to material type, you can choose any of these options:
Steel Rubber Mould
Steel remains a popular material for making mold for rubber. Usually, this is mainly attributed due to:
- Ease of fabrication – you can make molds with complex designs and shapes without compromising on quality.
- Strength and durability – steel is a strong material that can withstand rubber injection molding forces. Besides, it can withstand high injection molding temperatures while remaining dimensionally stable.
- Custom options available – For special finishes, steel can be coated for better quality. This produces injection molded rubber parts with superior surface finish.
The only downside with steel rubber mold is the high initial cost.
Aluminum Rubber Mould
Aluminum is a perfect alternative when making moulded rubber products. In fact, it is an affordable alternative compared to steel.
The best part, aluminum molds are lightweight, and offer good conductivity. However, they require regular maintenance.
Apart from steel and aluminum mold, copper alloys also make better molds for moulded rubber products. A good example is beryllium-copper alloy. Although the alloy is an expensive rubber mould, it offers perfect solution for rubber molding requiring superior thermal conductivity.
Rubber Mould Fabrication
In any rubber moulding process, the process starts by designing high quality tooling system that will ensure efficient and reliable manufacturing process.
Usually, the process involves the following key processes:
- Design the rubber parts you wish to make. This forms the fundamental design for your rubber mould.
- Choose suitable material for the mould. You can chose either steel or aluminum.
- Use electrical discharge machining or standard machining to fabricate the mold. You will cut the rubber moulding tooling system to suitable sections. By doing so, you will have a final product that meets you rubber fabrication specifications.
- Apply the necessary surface finishes on the mould
- Check for any defects on the mould system
Parts of Rubber Mould
Any tooling system for moulded rubber products is an assembly of different components carefully assembled to produce quality part. Usually, the number of parts will depending on the parts you wish to produce.
On average, the tooling systems for rubber mould have the following key parts:
There are 5 plates in most standard mould designs. Each plate perform a different function depending on the mold designs. These main functions include:
- Top plate – It clamps the upper section of the mold, which in most cases is movable.
- Bottom plate – It clamps the bottom section of the mold.
- Core plate – This section help reshape the injection molded rubber part. It is in the cavity section of the rubber mould.
- Cavity plate – Key component of the chamber that contain the molted rubber material ready for moulding process.
- Ejector plate – The section holds ejector pins. At the back section, there is an ejector back plate that keeps the pins in position.
The section helps to align rubber molding machine screws to the tooling system for an optimal output.
The section helps to remove rubber molded component from the mold cavity.
Molten rubber enters the mold through sprue bushing. It has a taper aperture that is about 3 to 5 degrees.
Usually, this section also consist of sprue puller pin, which helps remove the sprue from the sprue bush. Again, there is the sprue puller bushing that holds the pins in place.
Depending on the design of the tooling system for rubber moulding process, you may have about 5 ejector systems. Some of the most common design options include:
|Type of Ejector System||Function of the Ejector System|
|Sleeve Ejection||· Best for cylindrical core
· Has sleeve helping to remove rubber molded part
· Usually, it glide above the core system
|Core Rotation||· Uses rotating mechanism to discharge rubber moulded parts|
|Stripper Plate Ejection||· Suitable for rubber molded sections with broader sections where an extra stripper plate is necessary between the core plates and cavity|
|Air Ejection||· Compressed air actuates the ejector pins. The design is such that there are springs that retracts the ejector pins.|
|Blade Ejection||· It is a perfect choice when dealing with very thin rubber parts
· For seamless integration with the pin head, you may require counter bore
|Pin Ejection||· They are mostly cylindrical in shape and help remover molded rubber parts.
· The number of pins will depend on the mold design
Again, depending on your mold design for moulding rubber parts, your tooling system may have many gate systems. These gates may include sprue gate, winkle gate, edge gate, submarine gate, diaphragm gate, tab gate, ring gate or pin gate.
Note: These are some of the main components of rubber mould. The number of parts will vary depending on your design.
Types of Rubber Moulding Tooling Design
The tooling for rubber moulding design will depend on the specific parts you wish to make. For instance, a simple molded rubber parts require simple tooling design unlike complex parts.
When it comes to rubber molded tool analysis, there are certain variable you must consider. For a quick, reference, let’s summarize the design criteria as follows:
|Rubber Injection Mould Design||Remarks|
|Mould plates||· Available as two-plate, three-plate and stack injection mold for rubber
· Two-plate designs have single parting line while three-plate has two parting line
· Two-plate design is more expensive than three-plate options
· Stacked molds have more parallel plates
|Number of cavities||· Depends on the number of rubber molded parts you want to make in a single cycle
· Cavity range from single-cavity, multi-cavity to family molds
· Cost of mold design for rubber depends on the number of cavities
· For mass production of molded rubber parts, always choose multi cavity.
|Feeding system||· These are channels such as gates, rubbers, and spruces.
· You can choose hot rubber injection tooling, cold runner injection tooling or insulated rubber molds
Depending on your rubber molding process, you will configure all these parameters to suit you unique production needs. Remember, proper design will ensure zero rubber molding defects, which is a critical quality aspect.
In addition to these, other design considerations for rubber moulding tooling system include:
- Allow for sufficient draft. It will make removing moulded rubber parts easier.
- Sufficient cooling systems is critical for quality parts. Among the most common cooling systems are cooling circuit allowing for seamless flow of water.
- To prevent gases of air being trapped in the mold, ensure there is proper ventilation system. Remember, air may lead to rubber moulding parts defect such as flash.
- Always polish cavity core, runners and sprue. It will ensure easy flow of rubber material.
- Allow for ejection gap and shrinkage allowance.
Where to Use Rubber Moulding Tooling
Rubber products manufacturers use this tooling system to make various parts depending on their requirements. Depending on the tools, you can use it for small scale and large scale production processes.
Common rubber moulded products include:
- Grommets in compressor systems, panels, manifolds, etc.
- Anti-vibratory systems
- Rubber caps
- Bushing systems, etc.