During injection moulding, plastic pellets are melted. Once they are sufficiently malleable, the pellets are injected using a high pressure into a mould cavity. When the cavity is full, the plastic is left to dry and solidify, which is when the final product is ready.
How does plastic injection moulding work?
The thermoplastic injection moulding process involves heating and using pressure to inject plastic material into a closed metal mould tool. A barrel is filled with resin pellets, which are melted, compressed, and injected into the mould’s runner system. The mould cavity is shot with hot resin and the part is moulded. Ejector pins are used to help remove the part from the mould and are then placed into a loading bin.
Once the plastic cools, it hardens and takes the shape of the mould tool. When this is opened, the mouldings can be removed for inspection, delivery, or secondary operations, and time can be spent on cosmetic issues.
Injection moulding tools
There are two main types of injection moulding tools: soft tooling and hard tooling. While hard tooling is mainly used in high-volume production, soft tooling is employed for prototyping or small production. What material you select depends on several factors, including how big your budget is and your volume requirements.
Soft tooling is a cost-effective tooling method that is popular for use with cast urethane moulding. It permits manufacturers to quickly produce relatively low volumes of parts. Silicone is the most commonly used soft tool material for cast urethane, and it is an ideal manufacturing process for low-volume production and prototyping.
Key characteristics of soft tooling:
- The tool inserts are made of P20 or 718
- Drill, mill and grind inserts can be used with the normal machining process
- The tool life is guaranteed up to 100 K shot
- The manufacture lead-time is shorter than with hard tools
Soft tooling has several advantages:
- Its material requirements are flexible, which means manufacturers can use materials without having to worry about compatibility.
- It is a good choice for prototyping as well as projects that demand a simple and functional product that has a smooth finish.
- It is the method generally used for creating complex mould patterns that would be too time-consuming made any other way.
- It is used to make test units for rapid customer evaluation, thanks to its quick turnaround time.
However, soft tooling does have certain limitations. Since soft tool materials are soft they do not have the durability or wear-resistance of tools produced using the hard tooling method. Tools made of silicone, on average, only make up to 25 parts before they need to be replaced by new tools. Additionally, once tooling is complete, it is difficult to make changes to soft tools.
Hard tooling is commonly used for injection moulding. Hard tools are made of durable and long-lasting metals, including steel or nickel alloys, that can be used in multiple production cycles, allowing manufacturers to quickly produce high volumes of parts. This tooling type is ideal for producing durable high-precision parts.
Key characteristics of hard tooling:
- Drill and mill inserts can be used
- Tool life is up to 1 million shots
- The manufacture lead-time is longer than with soft tool because of the heat treatment process
- Tool inserts are made using H13 or Stavax
Hard tooling has several advantages:
- It is used when manufacturers must adhere to strict tolerances, testing requirements, and function standards.
- A single hard tooling mould can have multiple cavities, meaning multiple pieces of the same part can be created at the same time.
- Hard moulds allow for high-volume production.
- Hard tooling moulds can tolerate higher temperatures than soft tooling moulds.
- Parts with simple designs can be used straight away.
However, hard tooling is more expensive and more time-consuming than soft tooling. For short production runs or when you want to get products to market as quickly as possible, hard tooling is not very cost-effective. Additionally, hard tools take longer to make due to the heat treatments needed to produce them and post-processing. Extra machining is also needed to give hard tools a smooth finish, which guarantees they have one critical component—a seamless layup.
Soft Tooling vs Hard Tooling
Key factors to help manufacturers, engineers, and designers choose between soft tooling and hard tooling for their next project include considering the time available for developing the project. Here are the variable pros and cons of hard tooling vs soft tooling.
First, soft tooling will probably be the best option if speed, flexibility, and affordability are the most important project characteristics. Second, soft tooling is useful in prototyping and making a small number of parts. Finally, soft tooling moulds can be made quickly and cheaply. They do, however, wear out rapidly, but their low price means multiple soft tooling moulds can be made at a lower cost than a single hard tooling mould.
First, hard tooling is a better option if a manufacturer has an exact design with which to build a highly precise product. Second, hard tooling is preferable if you want to manufacture a large number of parts (thousands or even millions) resulting in a lower 'piece part' unit cost. Despite hard tooling moulds taking longer to make and being more expensive, they are much more durable and long-lasting, which counters the higher costs during long production runs. Finally, hard tooling allows for better features for part designs and more challenging surface/texture requirements.
There are pros and cons of hard tooling vs soft tooling. A decision should be made based on the needs of the project and specific company requirements. An expert manufacturing partner will be able to provide helpful advice that will allow all companies to make the right decision.