What is compression molding and die casting process?

Compression molding

The compression molding thermosetting materials obvious advantage is the system simple. Heating the material into a cavity, pressure to the required group of the time. Due process is simple, costs less. Additives and enhancers without rules, and can get a better strength. Since no gate and runner, do not waste materials, mold is almost no maintenance. Parts of unity, and no casting port and flow marks, reducing the cost of modification. According to product structure and the characteristics used in plastic applications, can be used full pressure type mold, semi-pressure type mold and closed modules (see, for compression molds in the article).

Equipment: a simple compression molding equipment is the main feature. Two and a half plate together, heating, pressure, shape of the material intended. Most of the process of compression molding hydraulic operation; also pneumatic operation. Upper and lower platen under pressure in the four corner posts on the up and down. Compression molding equipment according to the size, the pressure is generally 20-1000 tons. Plate size is generally 8 inches 2-5 feet 2.

After feeding and curing in the mold there different levels of automation, the most commonly used in modern hydraulic machine. The previous simple system with temperature control, pressure control, pressure control and stop time control. Modern equipment uses more advanced microprocessor control. For thinner products, available in sheet or tube with the heater heating. On the deeper parts, need to use cylindrical electric heater, steam heating or hot oil heating system. There are several types of plastic used in pressure in the heating system: steam heated mold temperature uniformity, but the heating temperature limit at 350 กใ F below; sleeve heating or other heating (heating coil, plus tropical, etc.) relatively clean, easy maintenance, with was more popular; hot oil heating, as heating medium loop stability, the heat evenly. Now there are many new methods of heating, hot water heating, similar to the hot oil heating, water heating medium a continuous cycle of a gas burner, which provides higher compression molding temperatures.

Modification of polymer materials to enhance the rapid industrial development, requires a new and improved compression molding industry. Reinforced plastic molding mold with two: male mold (mold plug) and female mold (cavity). When the mold is filled with reinforcing material, the two halves of the mold is closed hot mold, then heated, pressurized curing to get products. Match the complexity of the mold vary widely, the available aluminum, plastic or steel to do.

Lightweight materials making up relatively cheap, generally used for short-term production, such as "cold molding." Cold molding room temperature curing resin used, but still use the molds and compression molding hydraulic press. Long-term production more cost-effective use of hardened steel mold, the mouth of the cut blanks can be cut to provide better performance and excellent finish. The pressure on the steel mold using mechanical adaptation of the cut blank mouth, usually the face of the mold area. This kind of model with the metal mold, the product surface uniformity, good finish. Closed mold for compression molding, die casting, injection molding and some can be punched reinforced composites.

Some plastics can be compression molded thermoplastic molding material, but in general, or pre-blended with the thermosetting resin such as BMC (total pre-molding), SMC (sheet molding plastic material), TMC (thick molding compound), Mat forming, etc. .

Mat forming sometimes called wet molding composite materials under the action of the hydraulic machine will enhance the material and resin together. Often placed in the mold carpet pieces, dumped in strengthening the resin material. Pressure during the resin filled in the cavity, strengthening of material stationary.

If the parts are shaped or severe slope, there is a need for pre-forming. Most felt pieces and pre-forming system in the projection area of ​​the state need to add 150-200 lb / inch 2-mode pressure.

Pre-compounding, such as SMC, prepreg resins, fillers, catalysts and enhance the team sheet material cut to size, then add the hot mold (usually 300-400 กใ F), in the 1000 to 2000 lb / inch 2 pressure under the molding.

For the newer SMC compression molding equipment, the total cycle may be less than one minute (from start to finish). Has developed a special hydraulic equipment to push back pressure in the cylinder presses, automatic level control plate degree.

Reinforced plastics, such as SMC, molded plastic with a metal finish for good, which parts of the surface is very important. Sometimes occur in the processing of fibrous contraction.

Coating method using internal model can improve surface finish. The BMC compression molding process is the oldest pre-mixing one after the molding process.

Filler (sawdust, mineral materials, cellulose, etc.) mixed in the mixing blade-shaped mixer carried out. A batch of material into 300 ~ 400 กใ F the mold. 500 lb / inch 2 pressure molding. Due to cheap materials, so the raw materials and low cost. However, as in the molding process of the orientation of the fiber reduces the mechanical strength.

High-speed compression molding, which reinforced thermoplastic sheet stamping, and versatile. Film and polypropylene glass mat can match for stamping plastic, its cycle less than 40 seconds. Green sent to the convection oven. After heating, the rough into the compression molds, this process speeds with the new pressure presses up to 1400 inches / minute. 75 inches / minute (the SMC compression molding process than about 3 times faster) pressurized feed. According to market requirements, some new to stamping plastic, surface finish, and can be coated with nature. Molding pressure is generally 1 ton / inch 2. Traditional compression molding process in recent years has shown a growth trend. In space technology and defense applications are difficult to make this process to its impact.

In the SMC, BMC, TMC, thermoplastic sheet stamping, reinforcement of mechanical mixing and compression molding, rapid growth in development to meet the industry's new requirements.

Some advanced plastic compounding the pressure mainly in the application of space technology and the rapid development of national defense. Tool and mold a new concept and high temperature (up to 1200 กใ F) molding machine, so that a carbon-graphite fiber composite materials can be developed to replace the existing metal casting.

High-pressure high-temperature silicone is used as a medium. Composite material made of layers used for modeling the pressure. Now, materials and production costs have made the process more suitable for space technology market, these silicone soon turned to the automotive sector.

Die-casting

In the casting process, the thermosetting resin material is expected to join a separate chamber, often called the trough, and then forced into one or more closed mold for polymerization (curing).

Materials Road, also known as sprue and runners, so that material flows from the trough cavity, before entering the cavity through the limiter or gate. Many cavity with a single trough. Material in the cavity air is replaced by the incoming materials, and placed through a special exhaust port.

When the material into the trough, in a compact measuring device measured quantity, and then warm up to near the polymerization temperature. Added only once a sufficient amount of injection.

Preheat the raw materials will be sent trough the power feeder and then sent to a Note, the Note feeder trough mounted on immediately to prevent the trough from the side of the piston and the gap between the drain material. Usually sealed Taoka further leakage into the Note feeder.

Trough, note feeder, gate, runner and cavities of the surface material can maintain a certain temperature fast curing, according to the material properties, mold design and the geometry of the workpiece temperature is 280 ~ 380 กใ F.

In the casting material to reach the end of curing period when the second material to a complete mold casting, including the removal of the gate, runner, sprue and solidified material formed in the trough pad (called residual material).

In casting, the material is Aluminum castings  very important to warm up. Slow-moving cold material, the first material into the mold cavity to its end yet, which may be aggregated. If that happens, poor product quality, not only appearance, but also reflected in the mechanical properties. Some exceptions, such as a small injection volume, or some low-viscosity materials. Available heating lamp or stove heating, but effective and commonly used method is to use for making plastic molded dielectric heater.

Now commonly used thermosetting plastics heating screw-type material.

This device can be combined with molding equipment, it can be independent, with reduced volume and accurate determination of the advantages of fluxes in other systems must be combined with the pre-forming.

The type of die-casting mold

"Overall trough casting" is the first to be used, because the trough and the injection mold material rod as a whole to do together. The most commonly used is the circular trough, other shapes may also be used to meet the special requirements of the gate in order to produce less waste.

A simple pressure plastic presses and die-casting machine can be used together. The whole trough is the trough in the middle mold frame plate of the three. Note rod installed in the feed box at the top of mold, the mold cavity at the bottom.

Trough than the total area of ​​at least the cavity mold segment in the total area (in contact with the plastic material level) is 10%. This prevents the excess caused by the mold clamping force flash.

Material after curing, stripping pole by moving parts of the pressure stripping, but the residual waste and sprue molding material is still one or more of the "dove tail" remained at the bottom of the rod material injection.

With wood or soft hammer to remove the waste and the clean mode.

In the single-trough have a big waste, sometimes used to multi-cavity double trough feeding. At this time, although the weight of two to make a little trough range, still with a horizontal plate to balance the pressure in each trough.

Pressure die-casting mold material rod rod material, also known as injection mold, it uses an auxiliary pressure plunger rod into the trough forced injection material (or barrel), will feed from the trough to move out of the mold cavity. Pressure die casting and casting speed is easy to control, nothing to do with the clamping pressure.

Plug binder in the trough of the size of the die casting (deciding the size of waste) only large and deep enough to meet just feeding quantity can be.

Maximum trough area of ​​the die-casting machine to give the auxiliary plunger force (in tonnes) and divisible by 3.5 to determine. This guarantees that 3.5 tons / inch 2 pressure for molding pressure Sand castings  level for the most die-casting material formulation, the pressure is sufficient.

Auxiliary plunger is usually mounted on the upper fixed plate over the top, down the role. Pressing the plunger to move up the closed mold under the template. When the mold clamping after the raw material into the trough, the auxiliary column Se Shijia force. Mold plunger and auxiliary column Se Shijia force ratio, usually 3:1 or 4:1.

After curing materials, auxiliary plunger back, die-casting machine to open. Molded parts, scrap, material flow cold stripping pole while being sent.

This casting mold of a three-plate injection material is deformed rod casting mold, which has a floating plate will flow directly to the material assigned to the material feeding cavity Road.

The Act applies to the mold line where the runner can not be opened, or parting line plane moving core, and ten parts very irregular set of ground disturbance McCain Maibu million.

Specially designed die-casting machine has the following types:

1) at the end of squeeze casting mold material rod installed in the die casting machine, in which auxiliary plunger mold plunger installed in the main, if one or more die there is enough space between units, the installation of auxiliary plunger on the next plate. The advantages of this method, the mold can be opened to the trough in the loading. This design than in the trough to wait before loading slightly faster closed mold design. And auxiliary piston stroke can be reduced, saving a few seconds for each cycle time. The die-casting machine can be used with the top plunger rod casting material injection mold, but the pre-binder tablet to align in order to ensure the material well into the trough, or closed mold problems.
2) with a trough to feed more than one auxiliary plunger multi-casting machine, with more than one cavity can be filled, no waste and no inefficiencies long, curved flow channel.
3) with a small powder die casting machine automatically, the level of operation can also be vertical operation, there are vertical with the auxiliary mold plunger plunger for raw material injection mold line.
4) the overall model of prefabricated plastic (BMC), usually glass-filled polyester, with horizontal die casting machine, with attachments can be expected for material compacted and then sent to the casting barrel.
5) die-casting machine is a thermosetting resin injection molding machine prototype. This machine will screw plasticizing and preheat the mold together.
After preheating the material sent to the molding mold line or at tight frame with die-cast barrel County in the following celebration.