A Complete Guide to Silicone Milling

Transforming silicone into finished products is an intricate process. This suggests that there are numerous steps and procedures that technicians follow strictly. Adhering to these guidelines ensures the final products are of high standards and quality. This article is an in-depth look into the silicone milling process. 

Overview of Silicone Milling

silicone rolling machine

Familiarizing yourself with the silicone milling process is beneficial in many ways. With an understanding of this process, you will be able to communicate with the manufacturer more efficiently about your needs. Let’s start by looking at what it entails.

What is Silicone Milling?

Silicone is a flexible material used across various industries. After being obtained from its raw materials—the silica stone—it is refined in multiple ways. The refining processes are essentially what defines silicone milling.

The milling process of silicone varies depending on diverse factors. Firstly, the specific product being manufactured is considered. Secondly, the specific type of silicone being used also influences the milling process utilized. Doing this is critical as it ensures not only compliance but also high production standards.

Silicone can be shaped, refined, or reduced in size during the milling process. Similarly, this depends on the products being manufactured. Silicone products are milled from a variety of forms of silicone materials. These forms of silicone are all derived from silicon, an element found in silica stones. 

The Benefits of Silicone Milling 

Did you know that silicone is among the most widely used materials in nearly every industry? Growing at a CAGR of 6.1%, according to Grand View Research, the demand for this material is a testament to its benefits. The following are some of them;

  • Silicone is a highly versatile material. The ability to be used to manufacture products for use in various sectors makes this material highly versatile. More so, due to its physical and chemical properties, it can be morphed into various shapes and sizes, thereby contributing to its widespread usage.
  • Silicone is cost-effective. Being a naturally occurring substance, the supply of silicone is plenty, which makes it affordable. Its production cost is also relatively low compared to other materials.
  • Efficient milling processes. The processes used to mill silicone are efficient ensuring a smooth handling process. Milling focuses on changing the mechanical and physical properties of this material. In return, the properties of this material are transferred to the final product without much alteration.
  • Better finishes. The milling processes used to manufacture products preserve the natural finish of silicone. This gives products a superior finish.

When you choose silicone as the material of your choice, you benefit immensely. If anything these are merely broad benefits. This implies that there are even major benefits that will be specific to the industry you are in. 

The Process of Milling Silicone Products

silicone rolling machine

Milling silicone products occurs in stages. These stages need to be followed precisely since each stage is a prerequisite for the subsequent step. Also, note that this process can be modified to suit the requirements of a certain product.

Here are the steps in the silicone milling process:

  • Step 1: Preparing the Material 

In the first step, the material needed for the milling is identified and prepared adequately for the milling process. 

Preparation involves selecting the appropriate form of silicone based on the products being manufactured. Additionally, initial tests are performed to ascertain the quality of the material to be used. If you are wondering what kinds of tests are carried out, keep reading because they are discussed in detail below.

In our milling process, we also perform Input Process Quality Control (IPQC) as an additional quality control procedure. The goal of IPQC is to pinpoint potential quality issues before production begins. IPQC is fundamentally a preventative measure.

  • Step 2: Setting Up the Milling Equipment

This is another key step in the process that is a huge determinant of success. There are different types of machines and equipment used to mill silicone. Each of these machines has a specific feature that makes them unique. 

When setting up the machine, the technicians will have to consider a number of factors. To start with, what type of silicone is being used? This is important since the machines or equipment are made to manufacture a particular type of silicone. A common machine is the injection molding machine used to transform LSR into various types of products.

Other equally important considerations made when setting up the equipment include production volume and level of precision needed. If you want to be involved in this step, a technician will help you make decisions by presenting the available options.

  • Step 3: Selection of Appropriate Tools 

Silicone milling machines can be fitted with a diverse set of cutting tools. These tools are categorized based on the nature of their cuts. To clarify, some cuts are rough while others are smooth. The desired type of cut will influence the cutting tool fitted.

Tooling is also dependent on other factors such as design complexity and desired surface finishing. However, this does not apply across the board since finishing is not a necessity in all industries. For instance, finishing is a vital consideration in the manufacture of medical products. 

  • Step 4: Beginning of the Actual Milling 

The technician starts the milling process after the materials have been selected and tested, and appropriate equipment is set up. The milling equipment is either manually controlled or programmed.

Before the miller starts functioning, it is fed the designs of the products. This design contains all the parameters required for the final product. Thereafter, the processor integrated with the machine interprets the designs and starts milling.

The time taken by the actual milling process depends on the volume required and the intricacy of the designs. Essentially, if the design is complex and your consignment is large, the process will take more time, and vice versa.

  • Step 5: Monitoring the Milling and Performing QC

While the machines are capable of milling the silicone without human intervention, carrying out monitoring is standard practice. 

Depending on a number of factors, monitoring may involve visual inspections, proportions, and sample quality checks. This is done to ensure the products meet requirements even before the process is over.

We go a step further to ship samples for you to inspect during this stage. A signed sample will be shipped to you before the mass production proceeds. This iterative approach ensures the product is as you envisioned it. Finally, corrections of issues to do with defects and imperfections are carried out in this step.

  • Step 6: Post-Milling Operations

Following a successful milling process, technicians perform a few activities before declaring the process complete. For instance, some milling machines or processes leave products with unwanted parts that need to be trimmed. 

Post-milling also includes polishing surfaces for desired looks. Cleaning products can also be undertaken as a post-milling activity. Post-milling operations are typically performed by support staff since they do not require technical knowledge. Technical knowledge is sought in the final step of this process.

  • Step 7: Final Inspections and Packaging

Experienced technicians use a set of guidelines to inspect the milled products as or before they are packaged. In this step, various tests are carried out and products are assigned a pass or fail based on the test.

Final inspection tests can be manual or automated. In this case, manual tests include visual inspections while automated could include automated optical inspections (AOI) and much more. Technicians also check whether the products are in line with your requirements and specifications. 

Products that pass the final inspection are packaged appropriately and delivered as agreed in the contract. Other final tasks might include payments, insurance, and other applicable operations. This step marks the end of a complete silicone milling process.

Common Silicone Milling Methods 

silicone molding machine

Silicone products can be milled in a variety of ways. As stated earlier, this depends on many factors. Most of these methods follow the above process of milling silicone we outlined. Let us look at some of the common methods used today.

Injection Molding

This is the most widely used method of milling silicone. It is commonly used due to its high level of precision. The injection machine uses molten silicone to mold products into desired shapes and sizes. The machine then kicks on and shapes the products. After the process is over, the machine cools the hot product, solidifies it, and ejects it.

Transfer Molding

Basically, this is a more advanced approach to injection molding. A new type of molding called compression molding is introduced. For this method, molten silicone is transferred to a closed mold cavity where a transfer pot applies pressure to the material and forces it into the mold cavity. This is where compression molding is being utilized.

Transfer molding is especially vital in specific industrial applications. The ability to control the flow of material and its positioning in the mold helps technicians have more precision control. This is helpful in the manufacture of products that have inserts.

Compression Molding

This technique is the ‘middle-ground’ molding method. Whereas transfer molding focuses on large-scale production and transfer on precision, compression is a much more flexible molding technique. It is ideal for situations where design flexibility is required. 

One of the key advantages of compression molding is the ability to control various physical properties of the final product. Properties like hardness, heat resistance, and flexibility are able to be controlled in various ways. These include adjusting the allowed curing time, pressure, and temperature inside the molding machine.

Extrusion

A special machine called an extruder is used in this method. It works by the use of force to direct silicone material through a die. The die has a specific shape and cross-section that the final product will emulate. The continuous nature of the extruder barrel makes this method quite suitable for large-scale productions.

Extrusion is widely used to manufacture silicone pipes, rods, and tubes. What’s more, this method can be applied to various forms of silicone material.

Calendering

This silicone milling method entails refining products using rollers. Calendering mostly works with sheets of silicone. 

In this method, a calendering machine with a series of rollers is used. Mainly, it contains rollers that continually adjust the thickness of the sheet as it passes from one roller to the other. The machine is calibrated using the desired thickness of the final product and it uses it as a reference when functioning.

Types of Silicone Used for Milling

silicone milling technician

Silicone is a type of rubber. Technically, it is a variety of polymers with the properties of rubber. That is why it is otherwise known as a synthetic elastomer.

The types of silicone used in milling processes include;

Liquid Silicone (LSR)

Maintaining silicone in a liquid state involves two major components. These are; a base polymer (highly-viscous silicone gum) and a crosslinking agent (low-viscosity liquid compound). 

This type of silicone is highly versatile. It is also the main ingredient used in the injection molding method. However, the material has to be converted to a solid elastomer before it is milled. In other words, liquid silicone cannot be processed since it has to undergo a solidification and curing process first.

Fluorosilicone

Silicone and Fluorosilicone are categorized under the same group of polymers called polysiloxanes. However, Fluorosilicone has a slightly unique chemical composition. The specific contrast between them is that instead of having exclusively methyl groups like silicone, Fluorosilicone has trifluoro-propyl groups.

It happens that this variation is beneficial. The trifluoro-propyl groups in the fluorosilicone’s polymer chain enhance its chemical resistance. As a result, Fluorosilicone is an excellent type of silicone useful in the manufacture of products for harsh environments.

High-Consistency Rubber (HCR)

This type of silicone is solid in nature. Chemically, it has a high molecular weight, a feature that contributes to its high heat resistance and hardness. Moreover, in the milling process, it can be cured with other additives to enhance these properties.

HCR is primarily used in compression molding and extrusion methods. Both of these methods are appropriate since they are highly likely to preserve HCR’s properties.

Room Temperature Vulcanized (RTV) Silicone

This represents silicones that do not require heat curing. Vulcanization is the curing process and it happens in room temperature conditions. This process requires two components—a base and a curing agent. The curing process transforms the silicone from a liquid to a solid elastomer that is ready for the silicone milling process.

Phenyl Silicone Rubber

This type of silicone has phenyl groups in the polymer chain. Its chemical structure puts it in the polydimethylsiloxane category of silicone polymers. Probably, the chemical elements might not be interesting to you. However, note that its chemical composition is what determines its properties. 

Phenyl groups contribute to several properties of this type of silicone. It has high resistance to oxidation, shearing, and heat. It also has a high optical clarity. These properties make it ideal for manufacturing products for use in extreme conditions.

How to Liquefy Silicone for Milling

grinding silicone

Liquefaction is the transformation of solid silicone to a liquid state. This is done to ensure the material is flowable and for it to be introduced in the various milling machines. 

Solid silicone manifests in either of two ways; rubber form or silicone compounds. These forms of silicone are liquified by heating them to a melting temperature. The temperature levels are decided by the level of flowability required. Also, the type of silicone being liquified is considered when calibrating the heating temperatures.

When the process is complete, the liquid/semi-liquid silicone is transferred to the suitable milling machine to commence the milling process.

Methods of liquefying Silicone

There are mainly three methods used for the large-scale liquefaction of silicone used for the milling process. Manufacturers decide on the method to use based on the type of silicone and the desired state. These methods are;

Heat Curing 

As the name suggests, this method uses heat to melt the solid silicone. This is done using special equipment such as kilns, pots, or hot plates. The equipment can be preheated to a certain temperature and then the solid material is charged. Alternatively, the material is added as the equipment is heated simultaneously. 

Solvent Dilution

Solvents made of chemical thinners can be used as a liquefaction method. These solvents break down the molecular structure of silicone. This method either disperses or dissolves the solid material to produce its liquid form.

The disadvantage of solvent dilution is that it can disorient the chemical structure of silicone. As a result, the properties of silicone are lowered as well. 

Two-Part Mixing

This silicone liquefaction method implies that the solid silicone undergoes two steps to turn it into a liquid. Two-part mixing entails mixing a curing agent and a base silicone under a reasonable temperature. RTV silicone is an example of a silicone that undergoes this method of liquefaction.

Conclusion

This was an in-depth look at the silicone milling process. We have looked at what happens from the moment a silicone product is commissioned to its final inspection after it has been produced. As you have seen, it is a lengthy process, but for good reasons. With this knowledge, you are sufficiently informed about everything involved in the process.

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