There are many uses for molded rubber in industries all over the world. Some of these uses include rubber vibration isolation, rubber injection molding, extruded rubber, and rubber-to-metal bonding. These small products are essential for vehicles and machinery and can mean the difference between success and failure for standard operations.
On the other hand, molding is a type of manufacturing process where the liquid material is added to a mold so that it takes on the desired shape. The raw material is heated before being added to the mold, and as it cools and hardens, it takes on the shape of the mold.
Rubber injection molding and compression molding are both processes that involve the use of heat and pressure. The difference is that injection molding moves the material through a screw and a hopper, whereas compression molding does not. However, the debate over compression molding vs injection molding is still ongoing among top manufacturers. But who is correct?
Rubber Injection Molding
Injection molding of rubber is a process that alters the plastic molding process by heating the rubber and placing it under significantly more pressure per square inch of cavity surface in molding. This is different from the plastic injection molding process where the materials are cooled under less pressure. Through various innovations, injection molding has become one of the most efficient ways to create molded rubber products in many cases.
Material preparation is key to efficient injection molding. To begin, the material is mixed in bulk and then stripped into continuous strips that are approximately 1.25″ wide and .375″ thick. These strips are then fed into a screw, which fills a barrel with the appropriate amount of rubber material.
The process is quick with cycle times as fast as 10 seconds. It is best for medium to high-volume production runs of 10,000 to 100,000 parts, depending on the molds used. You can increase production by using a multi-cavity or family mold. This way, you can produce several parts from one press, which will help you increase your manufacturing rate.
Rubber Injection molding is a process that allows for the creation of large volumes of uniform, complex parts. However, there are a number of factors that must be taken into account to ensure the success of the process, such as vent and gate placements, weld lines, corner transitions, wall thickness, rib and boss design, and more. Paying attention to these factors will help to ease ejection and achieve precise parts.
Another key benefit of rubber injection molding is its repeatability. With just one mold, you can produce thousands of identical parts. Plus, an aluminum mold will generally last between 5,000 and 10,000 cycles, while a full-scale steel production mold can last upwards of 100,000 cycles.
Initial start-up costs for creating custom tooling for injection molded parts are high, and not economical for low-volume production runs. Tooling for a simple design and small production run can be between $2,000-$5,000, but tooling for large, complex molds ready for full-scale production can cost several times more.
Depending on the size and complexity of the mold, as well as the number of parts you need, the cost of the mold can vary significantly. However, keep in mind that you can often reuse molds multiple times, which can save on tooling costs in the long run. It’s important to partner with an injection molding manufacturer who can help you refine your mold design and get the most out of your money.
Rubber Compression Molding
Compression molding is a process where rubber compounds or raw materials are turned into “pre-forms” that resemble the final product. These pre-forms have extra material to account for any empty spaces in the mold so that the final product will be free of defects.
The mold is then closed and placed under heat and pressure until the pre-form fills the mold. Once the mold is full, any excess material is pushed into overflow grooves. After the rubber has cooled and hardened, it is removed from the mold, usually by hand.
Compression molding is a type of rubber molding that is often chosen for medium hardness compounds. It is used in low-volume production or in applications that require expensive materials. This process helps to minimize the amount of overflow or flash created during the rubber molding process.
Compression molding is advantageous when it comes to manufacturing larger parts and components. The material can be loaded directly into the mold cavity without any restrictions, which means that there are no weight limits for the finished product. Injection molding has a barrel that can only be filled to a certain volume, which limits the weight of the part or component that can be manufactured.
The low cost of tooling is one of the advantages of compressed molding. Without a transfer cycle or injection process, there is not much infrastructure involved. Therefore, tooling costs are significantly less compared to other rubber manufacturing methods.
Rubber compression molding did not require any tooling features that would waste material, like runners, gates, or sprues. This means that less material is wasted overall, there are fewer cosmetic distractions, and the cost is reduced.
Cost of labor is a key differentiating factor between compression molding and injection molding. Compression molding is a relatively simple process, however, it is not semi-automatic like injection molding. As a result, compression molding generally requires more manpower, which leads to increased labor costs.
Excess waste is the biggest issue associated with molding rubber using the compressed method. This method can result in overfilling the mold cavity, which is sometimes necessary to achieve the correct pressure for curving a part or component.
The decision of whether to use rubber injection molding or compression molding comes down to cost, volume, and time constraints. Neither method is innately better than the other, it all depends on the specifics of your product and application – both are great innovations in technology, after all.