Plastic injection molding is a method of producing custom plastic parts. In this advanced technique, plastic is melted then injected into a custom mold. The plastic cools and hardens until it takes on the shape of the mold. The plastic molding company then uses various types of plastics to produce parts in multiple sizes, shapes, and quantities.
Manufacturers and suppliers of plastic injection molding such as MSI can offer a variety of services:
- Plastic part design
- Injection mold design and construction
- Custom injection molding
- Injection molding of prototypes
What Is Plastic Injection Molding?
Plastic injection molding is a process that uses thermoplastic and thermosetting polymers to create large volumes of parts. It is ideal for the rapid mass production of complex parts ranging from precision components to disposable goods.
This highly repeatable process can handle high volumes, anywhere from a few thousand to millions of identical parts. Waste rates from plastic injection molding are very low and with the reuse of excess plastic, it can achieve almost zero wasted materials.
The plastic molding company is responsible for designing and creating a plastic injection mold for the client. Molds must conform to specifications, be constructed with the proper materials, and be robust enough to handle the expected volume. The plastic mold manufacturer can give clients expert guidance in selecting the best plastic material for the requested part. An experienced, high-quality plastic molding company can also help their customers with long term target cost planning.
Plastic Molding Process
Plastic injection molds are the largest up front cost for customers in the injection molding process. Though some plastic injection molding suppliers outsource the construction of their molds, others like MSI have in-house mold manufacturing facilities.
Though the production injection molding process is very fast, most of the lead time required for producing parts comes from building the molds. This requires the expertise of engineers, machinists, and skilled technicians using precision machinery and tooling to ensure mold quality and conformance to product specifications.
The plastic molding process consists of four primary steps:
- Clamping – The mold is made of two halves that are closed by the injection molding machine before the molten plastic is injected. Clamping ensures the mold does not open under the force of the injection step.
- Injection & Plastification – After the mold is closed the molten plastic gets injected into the clamped mold under high pressure and is held under pressure for some time. After injection hold time, the plastification step starts with feeding small pellets of raw plastic into the machine. As the reciprocating screw moves the pellets through the heated zones, compression and temperature heat the plastic to its melting point. Once melted, the plastic is transferred to the front of the screw in a controlled dosage, where it becomes the plastic to be used in the next production cycle.
- Cooling –The cooling step also begins after the injection hold time. When the melted plastic touches the inner mold surface the part takes on the shape of the interior mold Cooling time depends on several characteristics of the part, such as wall thickness and the thermodynamic properties of the particular plastic used.
- Ejection – Once the part has cooled, the machine un-clamps and opens the mold. After the mold is fully open the machine then pushes out the custom molded part with the mold ejector system.
How To Choose a Plastic Molding Company
There are many plastic molding suppliers. However, it is crucial that you choose carefully, as the expertise and experience of the supplier have a material impact on the quality of your final product. Several critical factors differentiate good plastic injection molding companies from bad ones, including but not limited to the following:
- Superior customer service
- In-house facilities for building injection molds
- Expertise in thermoplastics and their recommended applications
- Advanced quality planning as a primary focus
- Modern machinery and quality staff
When plastic injection molding companies and suppliers outsource parts of their injection mold building process, there are more opportunities for miscommunication, delays, and quality issues. MSI Mold’s lean manufacturing facility with in-house capabilities carried out by their coordinated and collaborative team simplifies the end-to-end process, improves communication, and increases the quality and consistency of your parts.
Understanding whether your supplier has what it takes to be a reliable plastic molding company requires asking the right questions. Before deciding on your molding supplier, ask the following:
- Is your manufacturing facility in the United States?
- Are the injection molds built in-house?
- Will my mold and parts be produced in the USA?
- How many years have you been in business?
- May I do a walkthrough of your manufacturing site?
- What is your advanced quality assurance and resolution processes?
Costs Associated with Plastic Molding
The total investment for plastic molding consists of a one-time tooling cost and the actual production costs. Plastic injection molding costs vary depending upon several factors. The price of the raw materials along with the time it takes to create a part are the most significant determinants of cost.
Extra add-ons, such as special packaging or secondary operations like additional machining and pad printing, can contribute to increased costs, particularly in smaller orders. These additional factors also can impact the final cost:
The more complex the part, the more precision processes are required. The more procedures are required, the higher the cost of the component. Details like undercut features, sharp corners, or thin ribs may require mold side actions or EDM machining, adding more mold construction time and increasing costs.
Molds fall into two categories: free standing or insert molds. There can be multiple variations in style, size, and complexity within these groups, including those that must accommodate side actions or moving parts. In general, insert molds are significantly less expensive than free-standing injection molds.
Number of Cavities
The number of part cavities will depends on how many of parts are needed. High volumes require multiple cavities to produce numerous parts per machine cycle, while a smaller quantity order typically only requires one cavity. The more cavities required, the higher the cost.
Part size is a significant determinant of the total cost. A large mold requires more metal, space, and costly CNC machinery and equipment to construct. Large parts not only require large molds, but they are heavier and require a lot more plastic. However, in some cases a small highly complex mold could cost more to build than a larger mold with a simple design.
Custom Plastic Injection Molding
Custom injection molding is a service offered by experienced plastic molding companies like MSI. Our capabilities extend to a vast array of industries, types of plastics, and add-ons for custom parts. Industry leading custom plastic injection molding companies have a history of on-time deliveries, high-quality custom molds and parts.
Customers benefit from fast quotes, knowledgeable and friendly customer service, advanced quality planning, and clear and frequent communication. These qualities ensure a streamlined process, attention to quality, and adherence to specifications.
Prototype Plastic Molding
Plastic molding companies like MSI also offer prototype injection molding services. Creating and testing a prototype of a design can bring design issues to light before introducing them into mass production and causing costly delays and rework.
An injection molding prototype can uncover mistakes or design flaws such as surface defects or aesthetic problems. It can also pinpoint issues with wall thickness, wrong gate type or location, and ensure compliance to critical dimensions. Prototyping is a great solution for properly identifying warp and material shrink on highly precise parts. The cost for prototyping is nominal compared to the increased production costs for an overlooked design issue introduced into mass production.