Injection molding is a common process that is common to most industries, but the catch here is that not all injection moldings are equal. There are two distinct processes, i.e., plastic injection molding (PIM) and metal injection molding (MIM), which are used to process different materials, industries, and applications.
It is only after discovering the most applicable differences between plastic and metal injection molding that one selects the most suitable process for your product needs. It is on what differences in their material, process, application, cost, and performance characteristics shall here be discussed.
1. What Is Plastic Injection Molding?
Plastic injection molding is the most common type of injection molding used by China plastic molding manufacturers and even all over the world. To better understand its purposes, let’s first figure out what it is and why it is used so aggressively.
Definition and Properties
Plastic injection moulding is a process where molten thermosetting or thermoplastic polymer is injected into the specially designed mould cavity. It opens the mould after it has cooled and hardened, and the plastic part that is formed is pushed out.
The process enables cost-effective production of complex and high-precision parts at low cost in large quantities. Material used tends to be most often ABS, polycarbonate, polypropylene, nylon, and other engineered resins.
2. What Is Metal Injection Molding?
Metal injection molding is different from plastics since powder metallurgy is entering the injection molding process. Let us learn about how MIM is done and how it is utilized for precision metal components.
Definition and Key Features
Metal injection molding (MIM) is a combination of plastic injection molding technology and metallurgy. It is a procedure that involves compounding very fine powders of metals with a binder to create feedstock, injection into a mold, and debinding and sintering treatments thereafter.
MIM is highly appropriate for the manufacturing of small, intricate metal pieces with greater mechanical properties similar to those of conventionally forged or machined pieces.
3. Differences in Process Flow
Although both plastic injection molding and metal injection molding are the injection of material into a mold, the latter process subsequent to molding, is quite different. Because of this, a difference is observed subsequent to molding.
Step-by-Step Comparison
Cooling and ejection are the processes that produce the final product subsequent to plastic injection molding. Other processes like trimming or surface decoration can be feasible, but no change in material is inherent to the process.
The “green component” ejected in metal injection molding must undergo a debinding operation for binder elimination and a high-temperature sintering operation for metal densification. These ancillary processes, however, add complexity, time, and cost to the MIM process relative to plastics.
4. Materials Used in Each Process
It is one of its strong points, where it varies a lot from plastic injection molding regarding using distinct materials for distinct functional requirements.
1) Plastic Materials
The following are the thermoplastics such as ABS, polypropylene, polycarbonate, nylon, and PEEK, common in plastic injection molding as sources of strength, flexibility, heat resistance, and beauty.
2) Metal Materials
Stainless steels, tool steels, titanium, cobalt-chrome, tungsten, and other metal alloys are used in metal injection molding processes to produce more strength, harder, wear and chemically resistant parts.
5. Comparison of Applications
Aside from process and material, metal and plastic injection molding diverge significantly in application markets. Let’s briefly discuss where each technology excels.
1) Plastic injection molding: typical applications
Plastic injection molding is traditionally performed on car parts, medical device packaging, home appliances, electronics, toys, and packaging because it can be designer-friendly and/or cost-effective.
2) Common Metal Injection Molding Applications
MIM deals with producing very fine, very small but strength-intensive parts such as surgical devices, fire arm components, microscopic aircraft components, gearings, and watch parts that require accuracy.
6. Cost Considerations Between Plastic and Metal Injection Molding
Cost thus becomes the determining factor in choosing plastic or metal injection molding, though they both involve investment in initial tooling, their production cost economics in the long term are vastly different.
1) Tooling and Initial Investment
Injection molds of plastic are cheaper to produce, especially for relatively low-precision components. Family molds, aluminum molds, or standard steel molds may be used through additional initial cost saving.
Conversely, metal injection molds will most probably require to be designed with higher precision and more complex gating geometries in order to hold up against close feedstock and with allowance for shrinkage after sintering. That is, higher initial mold cost than plastic injection molding.
2) Per-Part Production Cost
Plastic molding is less material and cycle time intensive, and unit cost thus is comparatively low in the event of medium and large lot sizes. Because of this, plastics’ usage is replacing buyer’s product, automotive trim, and packaging.
For MIM, the components see further debinding and sintering that require further production time and cost of operation. But for very intricate very small parts where CNC machining will inevitably prove too expensive or too extravagant, MIM can be even more economical per-part at mid-to-high rates of production.
3) General Cost-Efficiency Thresholds
Plastic injection molding still has the lowest cost for large parts and very high-volume production runs. Metal injection molding would only be cost-effective if small complex parts were manufactured in volumes large enough to justify the extra tooling and secondary processing expense.
7. Advantages and Limitations of Each Process
Both plastic and metal injection moldings possess their own strengths and weaknesses. Get to know them in order to choose the most appropriate process for your application.
1) Advantages of Plastic Injection Molding
Plastic injection molding enjoys unparalleled design flexibility. One can utilize it to produce a very wide range of part sizes, from very small clips to very large car panels, and with many surface textures and colors available directly from the mold. The quick production cycle and lower cost of resin are considerations which enable one to have very economically quantity production. Plastics are extremely light in weight and non-corrosive and therefore especially well-suited for application where weight saving is most critical.
2) Advantages of Metal Injection Molding
Metal injection molding is optimal when mechanical strength, thermal stability, and wear resistance are the primary concerns. MIM parts can be on par with wrought metal in property, with improved performance in intricate, small geometries impossible or expensive to achieve otherwise by traditional machining, casting, or forging processes. MIM is of crucial importance in medical, aerospace, and firearms manufacturing applications.
3) Weak points of Plastic Injection Molding
Although there are some advantages of plastic injection molding, this technique is not appropriate if there is a need for the parts to sustain extremely high mechanical stress, wear, and heat for a large period of time. The electricity and hardness of metal cannot be discovered in the plastic parts.
4) Weak points of Metal Injection Molding
Metal injection molding is harder for longer lead times from post-processing operations and is uneconomical for very small batch sizes. The component size is also limited; very large components cannot be manufactured using MIM due to sintering and warping limitations.
8. How to Decide Between Plastic and Metal Injection Molding?
Plastic or metal injection moulding is a compromise of your project’s special needs. Let us quickly describe the most critical factors so a decision can be made.
When deciding between the technologies, the following must be considered:
- Mechanical and environmental specifications
- Requirements for part size, weight, and complexity
- Anticipated production rate
- Surface finish and aesthetics needed
- Overall lifecycle cost considerations
Proper selection of process ensures the finished product is technically specification compliant, within delivery and cost constraints.
9. Conclusion
Metal injection molding and plastic injection molding are robust yet dissimilar manufacturing processes. Though they share the same general idea of producing intricate parts through molding processes, they differ considerably in material capability, processing routes, applications, and cost profiles.
With this type of information, product engineers, designers, and buyers are now able to make informed decisions, ensuring optimum performance, cost-saving, and trouble-free production in today’s risk-intensive business.
The best type of injection molding technology to use is not a technical choice but a business strategic choice that determines your success and also the success of your business.