What Is The Press Mould Method?

Press molding, also known as compression molding, is a manufacturing process for producing parts from powdered or granular plastic material. The process involves placing a preheated molding compound into an open, heated mold cavity and applying pressure to shape and cure the material.

The origins of press molding date back to the late 1800s, when the process was first used to mold products from natural rubber. It became popular in the early 20th century for compression molding phenolic resins. When plastic polymers were developed in the 1940s, engineers adapted the press molding process to produce plastic parts.

The press molding process starts with plastic material, usually in powder or granule form, being placed into a mold cavity. The mold is heated as pressure is applied, which causes the plastic to soften and distribute uniformly within the mold. The pressure is held as the plastic cures, and then the mold is opened to eject the finished part. This gives press molding the benefits of high productivity and low waste compared to other molding processes.

Applications of Press Molding

Press molding is used across a wide range of industries to manufacture high-precision plastic parts. Some of the most common applications include:

Automotive Industry

The automotive industry uses press molding to produce many interior and exterior components such as bumpers, instrument panels, door panels, armrests, and grilles. Press molding allows these parts to be molded with tight tolerances, uniform wall thickness, and complex geometries. It is also a fast and cost-effective process suitable for automotive mass production.

Consumer Electronics

Press molding is commonly used to manufacture the plastic enclosures and cases for consumer electronics like phones, tablets, laptops, and game consoles. The process can mold detailed features and logos into the plastic with precision, and create the sleek and thin walls desired in these devices.

Medical Devices

Many plastic components in medical devices like inhalers, disposable syringes, test kits, and prosthetics are manufactured by press molding. The capability to mold complex internal channels and tight-tolerance parts makes press molding well-suited for medical applications. The process also allows medical devices to be cost-effectively mass-produced.

Materials Used

There are three main categories of materials used in press molding:

Thermoplastics

Thermoplastics are materials that become pliable or moldable above a specific temperature. Common thermoplastics used in press molding include polyethylene, polypropylene, polystyrene, polyvinyl chloride, and acrylonitrile butadiene styrene (ABS). Thermoplastics are popular because they can be repeatedly softened and hardened with temperature changes.

Thermosets

Thermosets are materials that permanently harden after being heated and formed for the first time. Common thermosets include epoxy, silicone, polyester, and phenolic resins. Thermosets cannot be remolded or reheated after they are cured initially.

Composites

Composites combine a plastic resin with strengtheners like glass or carbon fibers. The composite materials gain enhanced mechanical properties like high strength, rigidity, and resistance to heat and chemicals. Common composite materials used are glass fiber reinforced plastic, carbon fiber reinforced plastic, or glass-mat reinforced thermoplastics.

Press Molding Process Steps

The press molding process consists of four main steps:

Heating

The raw material, usually in the form of pellets or powder, is heated until it becomes soft and pliable. The material is heated to a temperature above its melting point, allowing it to be easily shaped.

Pressing

The heated material is then pressed between two mold halves that are the inverse of the desired shape. Pressure is applied to force the material to flow and take the shape of the mold cavity.

Cooling

Once the material has filled the mold, it is cooled either by ambient air or by circulating coolant through channels in the mold. Cooling allows the material to solidify in the desired shape.

Ejection

After adequate cooling, the mold opens and the finished molded part is ejected. The part will then undergo any additional finishing or post-molding operations.

Tooling

The mold design is a critical component in the press molding process. Some key considerations include:

• Number of cavities – Multiple cavities allow several parts to be molded at once but can increase tooling costs.
• Parting lines – Parting lines determine how the mold separates and must be properly designed to allow part ejection.
• Draft angles – Angled surfaces are required to allow part ejection from the mold.
• Ejection system – Ejector pins are needed to push finished parts out of the mold.
• Cooling system – Cooling channels circulate fluid to solidify molten material into finished parts.

Common mold materials used in press molding include:

• Aluminum – Lower cost but wears faster than steel.
• Stainless steel – More durable and better heat resistance than aluminum.
• P20 steel – Pre-hardened steel that is machinable and provides good durability.
• Beryllium copper – Excellent thermal conductivity to improve cooling.

Advantages of Press Molding

Press molding offers several key advantages that make it an attractive manufacturing process for many applications:

Low Cost

The press molding process is very economical compared to other manufacturing methods like injection molding. The molds are relatively simple and inexpensive to produce, especially for low to medium production runs. This helps keep per part costs low.

High Production Rates

Press molding is a fast production process capable of high output rates. Parts can be molded rapidly in a continuous automated process. Cycle times are short, often under one minute. This results in a high production volume able to meet demand.

Material Flexibility

Press molding can accommodate a wide range of materials including thermoset composites, thermoplastics, concrete, ceramics, and more. The process can handle materials ranging from powders to pelletized compounds. This flexibility allows manufacturers to optimize materials selection for their specific application and requirements.

Disadvantages

Press molding has some limitations and downsides that should be considered when determining if it is the right manufacturing process for a given application. Two of the main disadvantages of press molding are low dimensional accuracy and limitations with complex geometries.

The nature of pressing material into a mold cavity means that tolerances tend to be looser than with other processes like injection molding. There will inherently be some variability as material flows and takes shape within the mold. While processes can be optimized to minimize tolerance issues, press molded parts may require secondary machining if tighter tolerances are needed. The process is best suited for less complex, larger parts where precision is less critical.

Additionally, it can be challenging to press mold parts with intricate details, undercuts, or complex curved surfaces. As the material is physically pressed into shape, the mold and part design needs to facilitate removal once cured. This can limit geometric possibilities for press molded components compared to other processes. Significant undercuts and small details should be avoided if possible when designing parts for press molding.

By being aware of these limitations, designers and engineers can best determine if press molding is well suited for an application or if an alternative process would be recommended. The process remains ideal for high volume production of less complex but large-sized parts where achieving very tight tolerances is not critical.

Trends

The press molding industry is experiencing some key trends that are shaping the future of the process. Some major trends include:

Lightweighting

There is an increasing focus on lightweighting in press molding. Using lighter weight materials can reduce material costs and transportation costs, as well as reduce a product’s environmental impact. Press molders are exploring the use of materials like thermoplastics and organic fibers as a substitute for metals and other heavier materials.

Sustainable Materials

Sustainability is becoming increasingly important in manufacturing. Press molders are seeking ways to utilize more sustainable and renewable materials in their processes. Some options include plant-based resins, recycled plastics, and biodegradable materials. Using sustainable materials allows companies to reduce their environmental footprint.

Automation

Automation and Industry 4.0 innovations are being adopted by many press molding companies. Automated processes, robotics, and internet-connected systems allow for faster, more efficient production and lower labor costs. Smart factory technology provides press molders enhanced quality control, production monitoring, and data-driven decision making.

Notable Companies

Here are some notable companies that utilize press molding technology:

• Apple – Apple uses press molding to manufacture the polycarbonate bodies of many of its products like iPods and MacBooks.

• Samsung – Samsung uses press molding for smartphone and tablet cases and components.

• LG – LG manufactures press molded refrigerator liners, cell phone covers and TV components.

• Whirlpool – Whirlpool uses press molding for washer and dryer components as well as refrigerator parts.

• GE – GE utilizes press molding for appliance components including refrigerator liners and washer tubs.

• Sony – Sony press molds optoelectronic device housings, lenses and other electronic component enclosures.

• Panasonic – Panasonic manufactures press molded enclosures and cases for its electronic products.

• Toshiba – Toshiba uses press molding for laptop and television components.

The Future of Press Molding

Press molding is predicted to continue growing at a steady rate as manufacturers seek efficient and cost-effective production methods. Here are some of the innovations and trends expected in the future of press molding:

Growth in the automotive and aerospace industries will drive demand for press molded parts. Lightweight, high-strength press molded composites will replace metal components in vehicles and aircraft. The global press molded plastics market is projected to grow over 5% annually through 2025.

New press molding technologies will enable faster cycle times, more intricate part geometries, and multi-material molding. For example, gas-assisted injection molding injects gas into the mold cavity to push the material against the walls, reducing part thickness and material usage.

Automation and data-driven manufacturing will lead to “smart” press molds with sensors to monitor temperature, pressure, etc. This data allows for process optimization and quality control. More affordable and compact robots will automate post-molding secondary operations.

As sustainability becomes more important, press molding will adapt to utilize biodegradable and recycled materials. For instance, corn, hemp, and other natural fibers can reinforce plastic composites. Reprocessed scrap plastic can partially replace virgin resin.

In summary, press molding will continue evolving through innovation in materials, processes, automation, and data-driven technologies. The growth of press molded components, especially in the transportation sector, looks very promising.