What is two-color injection molding?
Two-color injection molding is two kinds of plastic materials injected into the same injection molding machine, and the products are molded twice, but the products only come out of the mold once. Generally, this two-color injection molding process is also called double-color injection molding, usually completed by a set of molds, and requires a special two-color injection molding machine.
Two-color injection molding is increasingly popular in the market because this process can make the appearance of the product more beautiful, easy to change the color without painting, but the cost is expensive and technical requirements are high.
What are the advantages of two-color injection molding?
The advantages of two-color injection molding are as follows.
- High precision and stable quality of products.
- Good structural strength and durability.
- Small mating gap and good appearance.
- Greatly reduce the cost.
30 experiences in two-color mold design and two-color injection molding
- The basic principles of two-color mold design.
(1) Hard rubber to do 1 time, soft rubber to do 2 times.
(2) Transparent to do 1 time, non-transparent to do 2 times.
(3) Do 1 time for plastics with high molding temperature and 2 times for plastics with low molding temperature.
The above is the basic principle of doing a two-color mold, otherwise, the mold will be done in vain.
In addition, when sealing the glue as far as possible with the broken sealer, do not use the broken sealer, even if it is suggested to the customer to modify the product must be as far as possible from the broken sealer.
- The mold embryo guide pillar guide pin must be symmetrical up and down, left and right, and front and rear mold symmetry.
- The back mold should be rotated 180 degrees, the front mold does not move.
- Product spacing must be based on the spacing of the injection molding machine nozzle, some foreign two-color injection molding machine nozzle spacing is adjustable, some are not adjustable, and the domestic non-adjustable.
- Two independent ejector systems, the top stick is also two. After the mold two products are the same, the ejector pin is the same, is a rotary relationship, do not make a translation relationship.
- The ejector plate can only be reset by spring, not by screw forced reset because the back mold rotates.
- The side lock must be in the center of the mold on all sides, and the front and back of the mold symmetry, otherwise when the back of the mold rotation 180 and the front of the mold can not be.
- If the spacing of the feeding point is different from the spacing of the gun nozzle of the injection molding machine, the hole of the top stick should be made waist-shaped because the spacing of the top stick of the two-color injection molding machine is not adjustable. Note that most domestic two-color injection molding machine injection nozzles are not adjustable.
- Pay attention to the direction of the parallel nozzle of the two-color injection molding machine provided by the customer, whether it is the x-axis or y-axis, so as to determine the layout of product placement.
- The direction of water in and out of the water must be on the heaven and earth side, and each cycle of water in and out must be on the same surface, not water in the sky, water on the ground side, because the rear mold to rotate 180 degrees, pay attention to the size of the mold embryo can not exceed the height of the injection molding machine water tank, otherwise it can not receive the water.
- The products of the first injection should be put on the non-operating side because the products should be rotated 180 degrees for the second injection after the first injection, which is just turned to the operating side so that it is convenient to take the products.
- The code mold position of the exit mold should be on the operation side and non-operation side, not on the heaven and earth side because their products have to be fully automatic.
- If it is the back mold rotation of the two colors, it is much simpler, the two front mold cores are the same, one side after injection of hard rubber. Rotate 180 degrees (note that the product can not fall when turning, the gate can be automatically separated), turn to the other side, and then injection soft rubber, injection hard rubber without the arrangement of the thimble, only the arrangement of the soft rubber side of the core can be, in addition to shrinkage should be noted, if the soft rubber completely wrapped around the hard rubber, only the hard rubber shrinkage, if the contour is connected, then both hard rubber and soft rubber to put shrinkage.
- Note on the parting surface: the parting surface of the rear mold should be obtained after the merger of two products for the rear mold; the parting surface of the front mold should be taken as a single product, and the parting surface of the combined products should not be taken.
- The tolerance of the front and the rear flange is minus 0.05mm, the tolerance of two flange spacing is plus or minus 0.02mm, the clearance between top stick and top stick hole is 0.1mm on one side, the tolerance of center distance of front and rear die guide sleeve and guide post is plus or minus 0.01, the tolerance of four sides and depth of die frame should be added, otherwise, when the rear die rotates 180 degrees, the height is inconsistent and the batch front is produced. The tolerance of frame depth is minus 0.02mm.
- If the mold embryo has been processed in the mold embryo factory, the factory should take the center of the spacing of the four guide pillars and guide bushing holes as the reference, otherwise, the deviation is too much and it is easy to jam the mold. When you order the mold embryo, you should specify that it is a two-color mold embryo, the four guide pillar guide bush and the frame is symmetrical, and the rear mold can match with the front mold after rotating 180 degrees.
- If it is a set of two-color mold, it is a straight barrel, a 90-degree barrel injection glue, no need to rotate, only a core, soft glue, and hard glue separation method rely on the line position seal glue.
- Cavity’s two shapes are different, respectively molding 1 kind of product. The two shapes of the core are the same.
- The front and back of the mold must match after rotating 180° from the center. It is necessary to do this check action when designing.
- The location of the ejector holes should be 210mm apart, and the number of ejector holes should be increased for large molds. And, because the ejector pin attached to the injection molding machine is not long enough, so we must design a longer ejector pin in the mold, the ejector pin is about 150mm long out of the mold base plate.
- 2 positioning rings must be designed on the back mold base plate.
- The total thickness of the front mold panel plus the a-plate should not be less than 170mm. please check the other reference data of this type of injection molding machine carefully, such as the maximum mold thickness, minimum mold thickness, and the interval of the top stick hole.
- The depth of the front side sprue should not exceed 65mm. the distance from the top of the upper side (big water outlet) sprue to the center of the mold embryo should not be less than 150mm.
- When designing the cavity of the second injection, in order to prevent the cavity from inserting (or rubbing) the glue position of the product that was molded for the first time, you can design a part to avoid the empty space. But it is necessary to carefully consider the strength of each cavity, that is, whether there will be a large injection pressure, or plastic deformation, resulting in the second injection may have the possibility of the batch front.
- When two-color injection molding, the size of the first injection molding product can be slightly larger, so that it can be pressed more tightly with another cavity in the second molding, in order to reach the role of sealing glue.
- Before the a and b plates are combined, pay attention to whether the front mold slider or lifter will be reset first and crush the product? In this case, we must find a way to make the slider or lifter of the front die reset only after the a and b boards are molded together first.
- The two cavities and core water transport arrangement as much as possible, and balance, the same.
- 99% of the time, the hard plastic part of the product is injected first, and then the soft plastic part of the product is injected. Because the soft plastic is easy to deform.
- Pay attention to the second injection, the plastic activity can be impulse the first time the product has been molded so that its plastic position deformation? If there is this possibility, you must find ways to improve.
- Two-color mold must be careful to choosing the gate position. It is better to choose submerged gluing for one product so that the product and the runner can be cut off automatically. When it is not possible to use submerged gluing, you can consider three board molds or hot runner molds. If the primary material is a pointed gate, make a wave boy avoid touching through the secondary material due to the residue of the primary feeding point.
Two-color injection molding vs traditional injection molding
The choice of a two-color mold is more than a single-color mold. Why?
Not only because of the single color or the price, the cost input fixed so that the two-color mold and single-color mold difference, but the most important thing is the technology above.
Two-color mold is generous and beautiful from the appearance of a lot, thus enhancing its own value, and shape value realized. And also conducive to better color, without too much to spray.
Of course, if the total, the cost is also high, then the market price will also be as high. In addition to these, there are technical aspects of two-color molds that are also much more demanding than single-color molds.
Two-color mold before and after the mold requirements to the same, and the mold frame processing requirements are high. According to the requirements of the product, there will be data control on the thickness of the panel of the mold, as well as the distance of the hole, and in the second injection, we should pay attention to the first time the product has been molded to glue bit, do not let part of the nostril. There is also the case of the strength of the glue bit in each place.
Two-color mold is two materials or a variety of materials mixed together into a color that is also very bright and beautiful. The choice of the two materials is also a matter of choice, requiring good bonding and strength requirements.
To ensure this, the bonding experiments can be carried out to ensure that there is no error before the mass production because it is also said that the technical requirements of the reason are relatively high. The monochrome molds are simpler and more homogeneous in terms of operation and technology.
The traditional mold industry is also used more, less cost investment, natural price and two-color will exist differences.
What are the causes of the need to use a hot runner in two-color mold manufacturing?
A hot runner is a mold that uses a heating device to keep the melt in the runner from solidifying. Because it is shorter than the traditional mold forming cycle and has more economical raw materials, the hot runner mold in today’s world industrial developed countries and regions is extremely widely used.
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