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Machining parts processing: three factors to be considered i
By: www.plusminusthree.com  Time2018-01-17
     Plusminusthree CNC Machining: three elements to be considered in the design of injection molding for precision parts. Injection molding is a common and economical method for manufacturing parts. It is widely used in various fields, such as medical devices, children toys, household appliances, auto parts and other fields, and produces high strength and light weight parts. In many cases, it can replace machined or cast metal products.
Sometimes, however, the plastic parts of the injection molding need a little help. Low impact or anti vibration, smooth surface, poor ergonomics and cosmetic problem is just why some second moulded parts are usually added to handle, handle, cover or sleeve.
Some manufacturers choose to use glue, screw or interference fit to assemble these two different moulded components, but this will take time and cost, and may lead to less desirable results. Fortunately, the process of plastic injection molding provides another solution.
This design technique explores three important elements of rapid coating molding:
What is the rapid overlap injection?
The process uses a mechanical or chemical bond (usually both) to permanently combine the two parts. This avoids the trouble of assembly, simplifies the design of the product, and improves the characteristics of many injection molded parts.
In Proto Labs, its working principle is to put a pre molded part substrate back into the press, and injecting second plastic or liquid silicone rubber (LSR) to the surrounding part of the original part. The two process requires a pair of moulds - one for the base material and the other for a complete coating. It also requires a person to manipulate the machine, load the substrate and uninstall the finished product, the process is called "pick up" coating molding.
What is the next step? A few design considerations should be taken into consideration before starting any supermodel design project:
Combination。 The strong bonding between the two materials is essential for overlapping molding.
Material Science。 The substrate and the coated material should be compatible in physical, chemical and thermal.
Principle。 The principle of injection molding is also suitable for coating molding, and there are some additional considerations to be paid attention to.

Let's start with the glue. In the perfect covering part, the overlay can not be removed, and it will tear before it is separated from the base, or even take away some of the following materials. For example, thermoplastic TPU and TPC and ABS, polycarbonate and PBT Valox (a polybutene) form a strong chemical bond. Santoprene thermoplastic vulcanizate (TPV) is a tough but flexible rubber vulcanizate. It is widely used in sealing strip, food service and wire and cable applications.
It is not always possible to achieve a high level of chemical bonds, but in many cases it is not even necessary. A coated gasket made of a soft sealing material is considered in the case of the cover of a molded electronic device. Once the lid is locked in place, the gasket is nowhere to go. The pad can be fixed to the substrate with sufficient adhesives so that it will not fall off or dislocation during the assembly process. By the way, this is an excellent coating application because it eliminates the need for manually bonded punching paper or rubber washer.
In most cases, we recommend using mechanical interlocking to enhance or even replace chemical bonds. This can be achieved by placing a bottom cut or a series of reverse cone or countersink holes that can be poured into the base components, so as to ensure the non failure mechanism in all applications except the most demanding applications.

Material compatibility chart
The substrate material package of plastic injection molding material in ABS LUSTRANABS / PC CYCOLO C2950-111PC LEXAN 940-701PBT VALOX 357-1001PP PROFAX 6323 ZYTEL 103 HSL nylon 66 NC010TPU - Texin 983-000000CCCC - AOC m m Santoprene 101-87 m m m m C m TPE m 101-64 m - Santoprene m m C m LSR - Elastosil 3003/30 A / B-- - TPC - medium medium medium Hytrel 3078CCCC TPE-Versaflex OM 1060X-1CCC m m m m m TPE-Versaflex OM 6240-1 / td> m m m m m m m m m CTPE-Versaflex OM 6258-1 CTPE-Versaflex OM 1040X-1CCC medium medium medium medium
M = mechanical key (recommended) C = chemical bond

Maximum material selection
There are a lot of reasons for the model. The most common way is to maintain the physical strength while improving the grip strength of the product, such as the handle for electric tools, or the anti-skid handle for surgical instruments. In this case, TPU on ABS is a good choice. Aesthetics and product brand is also very easy to achieve by molding - sports franchise stores can use two piece molding protective masks for the players and the team colors, a famous tractor manufacturer can decorate the green and yellow coating fairing riding mower.
LSR is another popular injection molding material. It has excellent tensile and tear strength, hydrophobicity (repulsive water), flexibility, antibacterial and UV resistance, and biocompatibility. The only drawback of LSR -- at least in the case of clad molding, is that its relatively high molding temperature is 350 degrees Fahrenheit (177 degrees Celsius), and heat is enough to soften materials such as ABS, polyethylene and so on. Fortunately, polybutylene terephthalate (PBT) and glass fiber nylon are well maintained. In the atomic laboratory, we provide over 100 engineering grade thermoplastic and liquid silicone rubber materials, as well as dozens of coloring agents.
If bonding is critical to your application, it is strongly recommended to use mechanical interlocking (such a place). This can increase or even replace chemical bonds.
Abide by the rules (Principles)
Compared with the traditional injection molding process, overlapping injection can be read from the same tool book and have some additional features:
The two part must maintain an appropriate draft angle, transition line uniform thickness and smooth. The thickness of the coated material shall be less than or equal to the thickness of the underneath. The melting temperature of the coated material should be lower than the melting temperature of the substrate (for example, our LSR example). If the chemical keys are not practical, do not despair. Mechanical interlocking is a good way to "put them together" and should be used as much as possible. The texture of the substrate workpieces may contribute to the bonding. The texturing of the coated parts provides a better grip and more attractive surface. The surface of the coated part should be flat or slightly below the surface of any adjacent substrate.
Plastic injection molding is a good way to improve the physical properties of the product or to enhance its appearance. As with our other injection services, we produce cost - efficient moulds within 15 days, with a production number of 25 to 10000 or more. If you want to manufacture millions of parts, quick investment coating is also a good way to test the bonding and material compatibility prototypes before investing in the two production of molds, or as a bridging tool before the mold is ready.
Because the rapid injection molding is more complex than the standard injection molding, the cost of the prophase mold may be slightly higher than the sum of the two mold and assembly components. However, we will be able to take back the cost soon after mass production and production sharing.



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