What is Low pressure overmolding？
Difference between low-pressure injection molding (low-pressure overmolding) process and conventional injection molding process.
Low Pressure Plastic Injection Molding (LPM) is an injection molding method in which low pressure injection materials are injected into the mold at a very low injection pressure (0.15-4MPa) and cured quickly (5-50 seconds).
Low-pressure injection molding is generally not a separate injection molded product, but another part as an embedded part, and then injection molding, the final embedded part is wrapped in plastic or is combined to form a combination of parts with integrated.
Low-pressure injection molding and traditional injection molding is the most obvious difference between the injection pressure is low, low injection pressure is not easy to damage is wrapped or combined parts, the main applications are the following two categories:
1, electrical and electronic fields, focusing on containing PCBA, very fine conductor welding, low strength connector molding, as well as precision, sensitive electronic components encapsulation and protection, including: Printed Circuit Board (PCB), automotive electronics, cell phone batteries, wiring harnesses, waterproof connectors, sensors, microswitches, inductors, antennae, ring rope and so on.
Most of the electronic components are relatively fragile, easy due to external factors (force, humidity, temperature, dust, chemical solvents, etc.) and cause damage to the components, in some products or use of scenarios, the need to encapsulate and protect the electronic components, so that they play a sealed, moisture-proof, waterproof, dustproof, chemical corrosion-resistant, in addition to taking into account, including high- and low-temperature resistance, impact resistance, insulating and flame-retardant properties. Performance.
2, the automotive industry, need to cover the skin (fabric, PVC fabric, etc.) of the car door guards, pillar guards and parcel shelf guards and other auto parts.
①. low-pressure injection molding (low-pressure overmolding) process and the traditional high-pressure injection molding process comparison:
low-pressure injection molding (low-pressure overmolding) process is a new process between potting and traditional high-pressure injection molding, low-pressure injection molding (low-pressure overmolding) process is very similar to the traditional high-pressure injection molding process, but used in the packaging of electronic components has the following advantages:
1, with excellent performance, low defect rate
(1) in the injection molding materials, low-pressure injection molding (low-pressure overmolding) process uses a special hot melt adhesive (polyurethane resin), this hot melt adhesive in the molten state of the viscosity is very low, good fluidity, only a small amount of pressure to fill the mold cavity.
At the same time, hot melt adhesives have excellent flexibility and good adhesion to polar materials, which can produce functional protection, waterproof/environmental resistance properties/electrical insulation, etc., which can protect and seal electronic components. Engineering plastics, on the other hand, have excellent mechanical strength and low adhesion and are mainly used for injection molding housings.
2) In terms of injection pressure, low-pressure injection hot melt adhesive: low viscosity, low injection pressure required: 1.5~40bar, will not damage sensitive electronic components; injection pressure of engineering injection molding: generally more than 400bar, may damage electronic components.
(3) In terms of injection temperature, the injection temperature of low-pressure molding process (190~230℃) is also lower than the traditional high-pressure injection temperature (230~300℃), thus reducing the chance of damaging sensitive and precise components due to the high temperature.
2、Saving production costs
(1) low cost of equipment, traditional injection molding process equipment systems, generally speaking, higher costs, including the purchase of high-pressure injection molding machine, in addition to water-cooling systems and expensive steel mold. low-pressure injection molding (low-pressure overmolding) process equipment system is generally relatively simple, only by the hot melt adhesive machine, work console and mold three parts.
(2) low mold cost, short cycle, due to the injection pressure is very low, the mold can be cast aluminum mold, easy to mold design, development and processing and manufacturing, can save material costs and development cycle.
②. low-pressure injection molding (low-pressure overmolding) process and the traditional potting process comparison:
low-pressure injection molding (low-pressure overmolding) process and the traditional potting process can be used to encapsulate electronic components, but compared with the traditional potting process, low-pressure injection molding (low-pressure overmolding) process is not only environmentally friendly, while greatly improving the production efficiency can help reduce the total cost of production.
Low pressure injection molding process:
1, add low-pressure injection molding materials, and components into the mold;
2, set the hot melt adhesive machine and injection of hot melt adhesive to the mold;
3、After 1 minute or so, you can open the mold and take the parts.
low-pressure injection molding (low-pressure overmolding) process has the following advantages compared with the traditional potting process:
1, the traditional potting process curing mechanism for the chemical reaction, low-pressure injection molding (low-pressure overmolding) process curing mechanism for the physical reaction, excess material and waste can be recycled.
2, the traditional potting process requires about 24 hours of process cycle, low-pressure injection molding (low-pressure overmolding) process cycle can be reduced to a few seconds to dozens of seconds, greatly promoting the production efficiency.
3, the traditional potting process requires engineering plastic preparation of the shell, while the low-pressure injection molding (low-pressure overmolding) process does not require pre-preparation of the plastic shell, but in the injection molding process of the encapsulation of the shell, the volume is small, low cost.
4, the traditional potting process requires precise control of the proportion of 2K components, the entire process is cumbersome, while the low-pressure injection molding (low-pressure overmolding) process uses only one kind of adhesive, and the process is less, the process is simple, and can be mass-produced.
5, the traditional potting process curing time is long, thus requiring more stents to store samples, occupying more production space, while the low-pressure injection molding (low-pressure overmolding) process does not require additional curing after molding products can go into the packaging process, do not need to be used for the curing of the stents, occupying less production space.
6, the traditional potting process requires more encapsulation materials, and low-pressure injection molding (low-pressure overmolding) process can be designed to reduce the amount of encapsulation materials through the cavity design, and can even achieve partial encapsulation.
③. low-pressure injection molding (low-pressure overmolding) process in the field of electrical and electronic typical applications:
1, the packaging of electronic components
Such as electronic products with PCBs, PCBs with connectors, PCBs with wire harnesses, etc., the use of low-pressure in the injection molding process can prevent damage to sensitive electronic components. This material can protect electronic devices from the external environment (such as water vapor, mechanical stress, etc.), and can act as a shell.
2, connector waterproof sealing
The use of low-pressure injection molding hot melt adhesive sealing plugs as well as cable clamps, the flexibility of low-pressure injection molding materials so that the connector can be better eliminated after the package sealing stress, and its adhesive properties play a water sealing, and even reach the IP67 level of waterproof requirements.
3、On-site injection molding to make the cable ring
This low-pressure injection molding (low-pressure overmolding) process can be used for on-site production of rings. Rapid molding, tension cushioning, protection of the wire harness. Overcome the time consumed in the process of shuttle ring and improve the production process.
4、Molded with the function of structural parts
Low-pressure injection molding after molding has an integrated shell, through the flexible structural design, can realize diversified assembly requirements, can be directly to the next step of assembly.
④. low-pressure injection molding (low-pressure overmolding) process in the automotive industry in the field of typical applications:
Low-pressure injection molding in the automotive field in addition to the application of electronic devices, PCB boards, wiring harness connector encapsulation, electric vehicle battery packages and other packaging protection. There are also applications in automotive interior parts.
With the rapid development of the automotive industry and the continuous improvement of the material needs of drivers and passengers, users of automotive interior aesthetics and comfort put forward higher requirements; more and more automotive products through the use of fabric fabric cladding pillar trim to increase the aesthetics and comfort of automotive interiors, to enhance the sensory quality of the interior.
The process of fabric fabric wrapping pillar trim mainly includes traditional hand wrapping and low-pressure injection molding; low-pressure injection molding has the advantages of high production efficiency, environmental protection and good consistency compared with traditional hand wrapping, and has a better application prospect.
low-pressure injection molding (low-pressure overmolding) process: the PVC skin or knitted fabrics are put into the mold in advance, and then with the help of screw thrust, the molten state of the plastic has been plasticized plastic (generally for the better fluidity of modified PP and PC/ABS, etc.) is injected into the closed cavity, and then after curing and shaping to obtain the products, the whole process to complete the surface layer of the material and the skeleton of the material between the composite injection molding.
At present, this process has been widely used in the production of automobile door guards, pillar guards and parcel shelf guards and other products.
Advantages of low-pressure injection molding (low-pressure overmolding) process compared with traditional wrapping process:
(1) Low-pressure injection molding is the skin material and plastic substrate into one, the combination of high strength, low risk of falling off;
(2) As there is no coating process necessary for the wrapping process, the low-pressure injection molding (low-pressure overmolding) process is more environmentally friendly, and can effectively improve the VOC volatility of parts and odor, and improve the air quality in the car;
(3) The internal structure of low-pressure double-layer injection-molded parts can be designed arbitrarily, and the degree of freedom of surface modeling is greater than that of the overmolding process, as well as the modeling features are clearer and stiffer, with a good feel and appearance;
(4) Low-pressure injection molding does not require additional secondary cladding, fewer processes, improve production efficiency and yield rate;
2, at the same time, low-pressure injection molding (low-pressure overmolding) process also has the following disadvantages:
1) the process is more complex, susceptible to molds as well as fabric/PVC skin ductility, scrap rate is relatively high;
(2) Pattern retention, in the high stretch, pattern three-dimensional sense of some poor;
(3) Higher mold tooling costs, process fabrics are also more expensive;
(4) low-pressure injection molding (low-pressure overmolding) process due to low injection pressure, not suitable for injection molding more complex structure of the product.
⑤. Summary:
1, the design of low-pressure injection molding is not intended to be used as a direct replacement for traditional engineering plastics, for example: a component (such as connectors) can be successfully molded in PVC, there is no need to consider the use of low-pressure injection molding. If PVC injection molding due to high pressure and lead to high scrap rate, low pressure injection molding may be more economical, because it produces less scrap.
2, low-pressure injection molding is generally used to replace multi-step production operations, such as plastic shell molding with epoxy potting. Simple steps can usually be achieved using low pressure injection molding. When a component is molded using low-pressure injection molding, an additional plastic shell is usually not required.
3, the limitations of low-pressure injection molding (low-pressure overmolding) process: due to the high cost of hot melt adhesive used in low-pressure injection molding, so the low-pressure injection molding (low-pressure overmolding) process is mainly used in the smaller volume of precision components encapsulation and protection, for the larger volume of components, it can not reflect its economy.
