Weld marks of forming defects

Weld mark

The fusion joint melt plastic in the cavity is confluent in multiple strands due to the penetration hole, the flow rate is not consistent, and the area where the filling material flow is interrupted. This kind of fusion of low temperature molten material can not fully fuse and produce linear fusion joint. In addition, the injection filling of the gate will also produce the fusion joint. This kind of weld mark only occurs at the fusion part of the molten material (the product with one gate and does not make the material flow from two directions generally has no fusion mark), that is, it only occurs in the products formed with holes or multiple gates, where the strength is lower than that of other parts. The weld marks of grid and other parts appear in the center, which have an influence on the strength and appearance.

The distinction between the weld mark and the crack can be distinguished by applying ink on the product; With this phenomenon, the flying edge is also easily produced in the place where the weld mark is found. This means that the pressure of the material is at a higher level where the weld marks are located. Because of this, there are few dents in the fusion mark.

If you want to avoid the weld mark, only change the position of the gate so that the weld mark occurs in a position that is not visible or looks smooth. The pin on the mold (the hole in the work in process) will generally have a weld mark.

It can also be used to make the weld mark happen on the excess sheet of the product, and then cut the sheet off

The details of weld marks are as follows:

1. Mold: the welding mark is related to the gate and the shape of the parts. When it cannot be eliminated, it should be moved to a position that does not affect the appearance quality. Therefore, if there are too many gates in the same cavity, the gate or symmetrical setting should be reduced or the setting should be as close as possible to the fusion joint; Exhaust system should be set up for poor exhaust at the fusion joint; The gate is too large and the pouring system is not in proper size. The gate shall be set to avoid the flow of melt around the hole of the insert or to use the insert as little as possible; If the wall thickness changes too much or the wall thickness is too thin, the wall thickness of the parts shall be uniform; If necessary, overflow chute shall be set at the weld joint, and cut off after forming or designed as an automatic off potential.

2. Process: injection pressure and speed are too low, and the temperature of the barrel and mold are too low, which causes the melt into the mold to cool early and the fusion joint appears; When the injection pressure and speed are too high, the injection will appear and the fusion joint will appear; The viscosity of plastics and density should be increased by increasing the speed and back pressure; Plastic should be dry well, recycled materials should be used less, too much release agent or poor quality will also appear weld joints; Reduce the locking force, and facilitate exhaust.

3. Plastic: if the fluidity of the molten material is insufficient, the temperature of the melt will be lower and the pressure loss is also large, which will make the weld mark obvious and the strength will decrease; The measure is to raise the temperature of the molten material to improve the fluidity; Accelerate the injection speed to make the fusion point without cooling, raise the mold temperature and reduce the temperature of the molten material; To reduce the flow resistance, the thickness of the parts on the path of gate or thickened to the junction is expanded. It is helpful to use plastic with good fluidity to reduce weld mark. When multiple gates are used, the weld marks will be produced, while when single gate can be formed, there may be no weld marks. Lubricants and stabilizers shall be added to plastics with poor fluidity or heat sensitivity; Plastic contains many impurities, if necessary, to replace the plastic with good quality.

4. Although the welding marks of air or volatile components are unavoidable as mentioned above, the air or volatile components should be removed first when the molten material flows. If the exhaust is not smooth, the weld marks will certainly become obvious. In this case, it may cause insufficient filling or burn (refer to insufficient filling and burn); Considering this possibility, it is necessary to exhaust or set exhaust channels by using the gap of inserts. The welding marks caused by air are exactly the opposite of the usual methods to eliminate the weld marks. Sometimes, the injection speed can be reduced to make the weld marks not obvious.

5. When the mold cavity surface is coated with release agent, once the molten material is transported to the fusion joint, the weld mark will be caused by the non fusion between the release agent and the molten material. This phenomenon is more serious when using silicon containing release agent. If the weld mark is heavy, the parts are often fragile and easy to crack (refer to fragile).

6. The color additive causes that if aluminum foil or particle colorant is added to form the round plate, the weld mark obviously changes with the properties of the colorant. It is difficult to eliminate this weld mark (refer to uneven color).



About JasonMould Industrial Company Limited

Jasonmould is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.

Person: James Yuan
Company: JasonMould Industrial Company Limited
Add:  LongGang Village,LongXi Town,BoLuo County,HuiZhou City,GuangDong Province, China
Tel: 86-752-6682869
Email: [email protected]

Site: https://www.jasonmolding.com/custom-injection-molding/

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