What is an Injection Mold? An injection mold is a custom machined piece of tooling that encapsulates the geometric shape of a product intended to be manufactured by plastic injection molding. After molten plastic is injected into the mold, the product goes through a cooling process, then the product is de-molded for its intended use.
How is a Plastic Injection Mold Made?
Most of the machining for making a plastic injection mold is done using CNC machines and electrical discharge machines (EDM). Today’s CNC machining and EDM machining are highly automated. The mold design is captured in a 3D computer model and it is imported into computer-aided manufacturing (CAM) software.
A skilled CNC programmer uses the CAM software to create machining operations with cutting tools to cut the product shape into the metal. After all the cutter operations are programmed and double checked they are saved as a “cutter path program” and sent directly to the CNC machine.
For features in the injection mold that cannot be cut with cutting tools electrical discharge machining is used. EDM machining adds an extra step in the machining process for mold makers. With EDM machining, a graphite or copper electrode must be made in the form of the feature to be made, then it is submerged in a dielectric fluid with an electrical charge to burn the metal away. The most common plastic product features that require EDM machining are sharp corners and deep thin ribs.
Injection Mold Manufacturers
When you partner with an injection mold maker like MSI, you are trusting that the quality of your final product will be dimensionally and geometrically correct. For this to happen, MSI uses both software technology, high performance machining technology, and skilled injection mold makers to build plastic injection molds that produce parts to your exact specifications.
After your custom injection mold is fully completed, it will typically go through a series of production trials to test the mold is functioning correctly and to produce some initial samples for customer review and approval before mass production will begin. The number of production trials that molds require will depend on how complex the mold and parts are and how critical the part dimensions are.
Oftentimes complex molds or parts requiring very close tolerances will have a trial run, then adjusted, then another trial again to confirm the mold adjustments. We call these three steps a “tuning cycle” for your mold. At the end of the required tuning cycles the mold is ready for mass production.
To receive high quality molded plastic parts it requires choosing the best injection molding manufacturers with expert knowledge in the injection molding process, modern injection molding machines, and in-house making of injection molds.
Components of an Injection Mold
Plastic injection molds are constructed from blocks of metal and other sub components for it to function properly. Molds can be made with a single cavity to produce one part per molding cycle or they can have multiple cavities that can process up to hundreds of parts per molding cycle.
All molds have two halves, a cavity side and a core side. Each half is made up of multiple components which are all precisely machined for fit and function on creating the custom molded parts.
The mold’s inner area or mold cavity is custom shaped and machined to precisely recreate the shape of the finished product. When molten plastic is injected into the cavity it will form the finished product. If a mold has multiple cavities, the feed system must be properly balanced to avoid manufacturing defects. The feed system is a series of channels machined into the mold to distribute the molten polymer into each of the mold cavities during the injection molding cycle.
A short list of common mold components or features include:
- Sprue bushing
- Core block
- Cavity block
- Clamp plates
- Support pillars
- Ejector pins
These are just several basic components that are used for building the mold used in the plastic injection molding process. The complete mold assembly provides for proper distribution of the plastic into the mold cavity, proper cooling of the plastic part, and trouble free ejection of the custom molded part when it is ready for demolding.
Distribution occurs when the heated plastic is injected down through the sprue bushing. Then runners and gates direct the molten plastic into the mold cavity.
After the cavity is full of plastic, the plastic must be held under high pressures to fully cool and harden into the finished shape. The mold will then open up and ejector pins or other specialty components will push the finished product out of the mold.
Common Types of Injection Molds
Plastic injection molding companies, like MSI Mold, classify molds based on a number of design features. There are dozens of common mold design categories and skilled injection mold makers will use years of experience to determine which mold design is right for specific custom plastic parts.
Insert molds feature cavity and core sides that will fit inside of a custom mold base. These molds are economical for small order quantities and can produce small to medium-sized components with very fast lead times. Insert molds are a low-cost solution, because the mold design is very basic and allows us to avoid all the material and machining costs that come with making a complete mold base.
Free standing Molds
Free standing molds or stand-alone molds are an all-in-one design with the mold base, and inserts. While free-standing molds cost more, they are the best choice for multi-cavity production of medium and large parts that will not fit into insert molds.
Here are just a few examples of different mold design categories:
Hot Runner Molds vs. Cold Runner Molds
Runner distribution can be hot or cold, depending on your custom plastic part needs.
Hot runners are heated internally by precision heating elements. Typically heating elements are usually permanently held within a stationary manifold plate. Hot runner molds are a popular option for high-volume production of custom plastic parts and yield the least scrap plastic from the molding process.
Cold runners are cut into the mold and are unheated. This is the most common runner system and the most economical. The plastic produced in this runner system is usually recycled as part of the production process.
Two Plate vs. Multi-Plate Molds
Most custom plastic part designs allow for the injection mold makers to build a two plate injection mold. Even plastic parts with undercuts that require side actions in the mold can utilize a two plate mold design.
However, some parts require gate fill locations that force mold makers in the plastic molding company to add a third or fourth plate to the mold design. Three plate molds are often used in place of hot runner molds because they are often more economical to build.
How To Choose Injection Mold Makers
You need to work closely with your plastic mold manufacturer to create high quality custom plastic components to fit your industrial specifications. Choosing a poor supplier can result in lost time, reduced plastic part quality and a lot of unexpected costs.
Compare injection mold makers using these key features:
- In-house injection molding and mold making capabilities
- Customer service reputation
- State-of-the-art machinery and equipment
- Expert knowledge of thermoplastic options and applications
What Are the Key Questions to ask an Injection Mold Company?
Verify you’re working with a global leader in the industry by asking injection mold makers these key questions:
- How many years have you been in operation?
- Are your injection molds built in-house?
- Where is your manufacturing site located?
- Do you have the resources to predict and resolve part quality issues?
In-House Injection Mold Makers vs Outsourced or Offshore Makers
Injection molders take one of two basic approaches to help you to create custom plastic parts for your industry: Create injection molds in-house or outsource the service to an injection mold maker.
At MSI Mold we manufacture both your injection molds and custom plastic parts in-house. Before you source an injection molding supplier without in-house mold making, consider sourcing us your molding project and enjoy:
- Fast communication and timing flexibility during design and production stages
- Reliable and honest quoted lead times
- Single source responsibility of quality and delivery
- American made quality
Plastic Molding Companies
Not all plastic molding companies are the same. Consider using injection molding manufacturers that offer plastic part design services and in-house injection mold making. Contact us today to discuss your custom plastic part design specifications with a single, experienced team of sales engineers for a streamlined sourcing process.
At MSI Mold, we’re confident our team and cutting-edge technology can create the high quality molds and plastic parts your company needs.