Double shot injection molding are popular currently in the market. This process can make appearance of product more beautiful, easy to change colors and can be sprayed, but it is expensive on the plastic molding cost and technically demanding. Plastic overmolding can also have similar effects. Design of plastic overmolding should pay attention to positioning of hard rubber parts. It is necessary to achieve a reliable sealing and a reverse-sloping hole on the rubber parts to prevent deformation of rubber. So what is difference between a double shot injection molding and a plastic overmolding?

Overview of double shot injection molding

1, What is a double shot injection molding?

Two plastic materials are injected on the same injection molding machine and molded in two parts, but product is only molded once. Generally, this double shot mould manufacturing is also called double-material injection molding, usually completed by a set of molds, and requires a special two-color injection molding machine. Double shot injection molding are popular currently in the market. This double shot mould manufacturing can make appearance of product more beautiful, easy to change colors and can be sprayed, but it is expensive and technically demanding.

2, Application fields of double shot injection molding:

  • Product function requirements: power switch, mobile phone button
  • Improve feel: some handheld products, such as power tools, toothbrush handles, vacuum flasks
  • Increase beauty, such as LOGO for viewing, that is, beautiful and will not be rubbed off

3, Remarks of double shot injection molding design

  • Two materials should be compatible. If two materials are incompatible, first cavity must be reversed to hold the second material, otherwise it will fall off automatically. In order to make two plastics “stick” tighter, some ribs are needed to enhance adhesion. Surface roughness of mold: the smoother the surface, the more “sticky”.
  • Melting point of first injection material must be higher than melting point of the second material.
  • Note that in the second injection, whether flow of plastic will impinge on product that has been formed for the first time, so that glue position is deformed.
  • Selection of water location. For products with LOGO, side of LOGO opening should be selected for water inlet to facilitate the filling of the secondary material; if primary material is a point gate, wave should be made to avoid the secondary material being broken due to residual glue point; For the first time, latent glue should be selected to ensure that product and flow channel can be cut off automatically. When latent type cannot be used, a three-plate mold or a hot runner mold can be considered.
  • Preloading. Because primary mold is pressed once, if there is LOGO on the surface of molding, this will have a very sensitive influence on the shape of LOGO. Generally, height of LOGO is 0.02-0.05 larger than theoretical value. If it is too small, the secondary material will run in, making outline of text unclear. If preload is too large, it will cause LOGO preload deformation.

Overview of plastic overmolding

1, What is plastic overmolding?

Overmolding: Two kinds of plastic materials are not necessarily injection molded on the same injection molding machine, and are molded in two parts; after product is taken out from a set of molds, it is placed in another set of molds for the second Injection. Therefore, this mould manufacturing is generally completed by two sets of molds, without need for a special double shot injection molding machine.

2, Notes of plastic overmolding

  • Plastic overmolding should pay attention to strength of skeleton to prevent deformation after rubber coating.
  • Injection mould maker should pay attention to problem of shrinkage. External parts are not shrinking. Then there is a design problem: empty space is as empty as possible to facilitate placement of external parts and plastic molding cost. In principle, it does not affect the sealing!
  • Reliable sealing and anti-slanting holes on rubber parts to prevent deformation of rubber.
  • Softening temperature of bottom piece and rubber compound should be at least 20, otherwise rubber material will be melted.
  • Hard rubber should be supported by steel material, especially back side of soft rubber. Clearance should not exceed 0.3S.
  • Leave 0.07~0.13 as preload in sealant position of soft rubber
  • Runner should not be lighted, and pattern can help mold. Front mold should be sun-dried, otherwise front mold will stick.
  • TPE material, it should not be used as a thimble in water. It can be changed to a straight top. Glue is made on a straight top. It is best to use a square shape. Straight top and hole should be smooth, gap should be within 0.02MM, otherwise it will easily produce rubber powder. .

Sum up

Difficulty of double shot injection molding is that two identical molds have to be produced. To achieve this result, the key is to rely on the mold and equipment to ensure that intermediate does not participate in the artificial factors, and processing needs and processing precision of mold are required. Glue mold is higher grade, and when one of places needs to be modified, both molds must be modified at the same time. Plastic overmolding does not have this problem. Plastic overmolding first makes a color plastic part on the first monochrome injection molding machine, and then manually puts product into second mold for molding, because it is manually placed, so lack of accuracy is likely to cause surface quality problems such as snagging, strain, and breakage after product comes out, so amount of scrapping will be very large. Therefore, you can choose to use double shot injection molding to create high-quality products. If you want to save plastic molding cost and requirements of the products are not too demanding, you can choose to use plastic overmolding for production.