Choosing the right method for silicone part molding will define the success of your entire project. The two most common processes are Compression Molding and Liquid Injection Molding. However, the question remains: which one fits your project more?
In this guide, we will break down the differences between the two so you can select the approach that best fulfills your requirements while maintaining splendid accuracy. So, keep reading!
Understanding the basics of processes: Compression molding vs liquid injection molding
You may be aware that compression molding and liquid injection molding are two methods used for producing silicone parts. Let us first get familiar with the basic methods involved in each one of them!
What is Compression Molding?
Compression molding is the earliest shaping technique whereby the silicone rubber is applied and placed as a preform into an open mold. The open mold has to be set at the required temperature and dimension. Once the required mechanical force is applied, the mold gets filled with solid rubber.
Filling is followed by the application of heat, which can reach 150-200 °C. Such temperatures activate the internal curing agent, which causes vulcanization. This is the process in which a polymer undergoes a chemical transformation.
Thus, resulting in an elastomeric solid that is stable dimensionally and possesses favorable mechanical characteristics.
What is Liquid Injection Molding (LIM)?
Liquid Injection molding is an advanced shaping method that utilizes a two-part Liquid Silicone Rubber (LSR) system, which includes:
- Part A: A composition of polydimethylsiloxane (PDMS) with specific fillers and reinforcing agents.
- Part B: A platinum catalyst system
Those two components are injected separately, then mixed in a 1:1 ratio just before injection. The mixture is then delivered to a sealed mold via a cold-runner injection system to prevent any pre-curing.
The blend is pumped into a closed mold that is preheated to between 120 °C to 150 °C. The curing reaction begins during this process and turns the blend into solid rubber. Since LSR has a low viscosity, the fill time is very rapid. Thus, the chances of defects are minimized.
Key Differences Between Compression and Liquid Injection Molding
Each silicone part needs a specific molding process, but there are clear differences between compression molding and Liquid Injection Molding (LIM). While both methods use heat to cure silicone, the differences in approach, outcomes, and prospective benefits differ.
Let us analyze the difference for your convenience.
Precision and Accuracy: Compression molding vs Liquid injection molding
- Compression Molding: With compression molding, solid silicone is filled manually into the mold. Since the solid does not flow, it fails to fill all the voids and thus results in the silicone part’s shape being poorly yielded in detail.
- Liquid Injection Molding: With LIM, liquid silicone flows smoothly into all details, holes, and crevices. Because injection molding machines control both the volume delivered and the speed, every component is expertly crafted to be a mirror image of each other in size and detail.
- Outcome:
For projects that require attention to detail and tighter tolerances, the choice is clear and overwhelming: LIM wins.
Curing and Temperature Management: Liquid Injection molding vs Compression molding
- Compression Molding: In compression molding, silicone is heated externally, which can cause uneven curing, especially in thicker sections. Softer centers tend to be over-cured, leading to weaker, defective edges.
- Liquid Injection Molding: Unlike most other processes, addition curing LIM uses a platinum catalyst with heat. This helps process every part in parallel, resulting in the best strength and stability.
- Outcome:
Once again, we see that LIM is optimal because uniform heating, along with catalyst addition, leads to balanced curing.
Speed and Cycle Time: Compression molding vs Liquid injection molding
- Compression molding: Compression molded silicone parts take several minutes to complete. They require additional finishing processes, such as trimming away flash and their post-curing, which extends the labor time.
- Liquid Injection Molding: In contrast, parts made through LIM achieve curing within seconds. Every piece is perfectly shaped and does not require trimming or any other additional processes.
- Outcome:
Hence, high-speed cycles coupled with a minimal workforce ensure amplified productivity from LIM processes.
Safety and Purity: Compression molding vs Liquid injection molding
- Compression molding: Peroxide curing used in squeeze mold machining generates hazardous by-products that require additional heating to eliminate. This is not suitable for medical or baby-safe products.
- Liquid Injection Molding: Platinum curing does not generate any harmful wastes, making LIM safe for food, surfaces, and even for internal human body parts.
- Outcome:
Again, proceeding with chronological reasoning, LIM appears to be the clear winner, boasting safe, process-free by-product hazards.
Equipment and Cost: Liquid injection molding vs Compression molding
- Compression molding: A starter compression molder will incur low costs from single basic tools and presses, which is advantageous for testers and those needing low part volumes.
- Liquid Injection Molding: Automation in mass production helps offset the cost of expensive mixers and injection units for liquid injection molding, resulting in lower costs over time due to significant savings from rapid cycle times and automation.
- Outcome:
With compression, small runs are more efficient; liquid injection molding shines in high-volume production.
Summary Table
| Compression molding | Liquid injection molding | Winner | |
| Precision | Manual, less accurate | Automated, highly accurate | LIM |
| Curing Consistency | Slower, uneven in thick parts | Fast and even curing | LIM |
| Cycle Time | Long | Short | LIM |
| Waste/Flash | More waste needs trimming | Clean, minimal flash | LIM |
| Material Safety | Not safe for baby products | Very clean and safe | LIM |
| Cost Efficiency | Low upfront cost | Better for large-scale production | Depends on volume |
Applications of Compression Molding vs. Liquid Injection Molding (LIM)
i) Applications of Compression Molding
In compression molding, simpler, thicker parts requiring lower precision can be made. Also, the technique is suitable for mid-volume production due to low tooling cost as well as complexity. This method is best for:
- Keypads and buttons with a basic structure.
- Custom parts for prototypes or testing purposes.
- Thick shock-absorbing and vibration-isolating pads and bumpers.
- Electrical insulators and protective boots for various components.
- Seals and gaskets for plumbing, industrial equipment, and vehicles.
ii) Applications of Liquid Injection Molding (LIM)
Because material flows into the mold as a liquid, LIM lends itself to more intricate, delicate, and larger-scale portions to be manufactured with greater precision. Its common uses include:
- Seal, switch covers, and other electronics peripherals like keypads.
- Lenses and other optical plastic components that need precision and clarity.
- Grommets, connectors, sensor housings, O-rings, and other automotive component parts.
- Phone case, fitness tracker bands, wearable technology, kitchenware, and other consumer goods.
- Medical plastic components, for example, baby bottle nipples and hearing aids, catheters, syringe seals, and hearing aid parts.
Final Words
In short, both compression and liquid injection molding are used for shaping silicone parts. However, the way they produce silicone parts is quite different, which I have discussed throughout the article. So, if your projects are small and don’t require high precision, then compression molding would be the most cost-effective choice.
However, if you are working on large, complex, and precision-requiring projects, then go for Liquid injection molding to get outstanding results. Looking for a custom silicone products manufacturer? Then look no further, as we have what you need.
At LanXin, we focus on OEM/ODM silicone rubber and die-cut products along with LSR injection molding. Reach out to us today!
