Plastic moulding dies modification

Time:2019-06-19 16:00:01 / Popularity: / Source:

mold repair 
Mold has an extremely important role in modern industry, and its quality directly determines quality of product. Improve life and accuracy of mold, shortening manufacturing cycle of mold is a technical problem that many plastic mold factory urgently need to solve. However, in process of using mold, failure forms such as sag, deformation, wear and even breakage often occur.

Production of plastic moulding dies defects

Thermoplastic injection molding is process of melting a plastic material and then injecting it into membrane cavity. Once molten plastic enters plastic moulding dies, it is shaped into a shape by cold cavity. Resulting shape is often final product and no further processing is required prior to installation or use as a final product. Many details, such as bosses, ribs, threads, can be formed in injection molding operation.
Injection molding machines have two basic components: an injection device and a clamping device for melting and feeding plastic into plastic moulding dies. Function of mold device is: 1. Mold is closed while receiving injection pressure; 2. Product is taken out of injection device and melted before plastic is injected into mold, and then pressure and speed are controlled to inject melt into mold. There are two types of injection devices currently in use: a screw pre-plasticizer or a two-stage device, and a reciprocating screw. Screw pre-plasticizer uses a pre-plasticized screw (first stage) to inject molten plastic into shot bar (second stage). Advantages of screw pre-plasticizer are constant melt mass, high pressure and high speed, and precise injection volume control (using mechanical thrust stops at both ends of the piston stroke).
These strengths are required for transparent, thin-walled products and high production rates. Disadvantages include uneven residence time (resulting in material degradation), higher equipment costs, and maintenance costs. Although mold design is carried out under expected process conditions when selecting molding materials and equipment, people's understanding is often imperfect. Therefore, after mold processing is completed, mold test must be carried out to see molded parts and perform error correction.
There are many types of defects in plastic parts, and reasons are also very complicated. There are mold reasons and process conditions, these two tend to be together. Before plastic moulding dies is repaired, it should be carefully analyzed according to actual situation of defective parts of plastic parts, and remedy method should be proposed after finding out cause of defects of plastic parts. Since molding conditions are easy to change, it is common practice to change molding conditions first, and when molding conditions cannot be solved, mold is considered to be repaired by plastic mold factory.
Process of mold repair generally includes following aspects:
1. Analyze reasons for mold repair and prepare for repairs
2. Familiar with structural characteristics and operating principle of plastic moulding dies to be repaired.
3. Understand quality of products manufactured before mold repair, and analyze causes of mold failure.
4. Determine part of mold repair and carefully observe damage of plastic moulding dies.
5. Develop a repair process plan.
6. Prepare necessary repair tools and spare parts according to repair plan.
Repairing mold should be more cautious, suggest not to act rashly if not sure. Reason is that once mold conditions are changed, it is impossible to make major modifications and restore original condition. Therefore, repair of plastic moulding dies is also necessary. There are many ways to repair molds, such as EDM, argon arc welding, laser surfacing, and brush plating.
mold repair 

Argon arc welding

Arc that burned between continuously fed wire and workpiece is used as a heat source, and gas ejected from torch nozzle protects arc for welding. At present, argon arc welding is a commonly used method and can be applied to most major metals, including carbon steel and alloy steel. Melting inert gas shielded welding is suitable for stainless steel, aluminum, magnesium, copper, titanium, zirconium and nickel alloys. Due to its low price, it is widely used in mold repair welding by plastic mold factory, but welding heat has large area and large solder joints. At present, argon arc welding repair has been gradually replaced by laser welding in precision plastic moulding dies repair.

Brush plating repair

Brush plating technology uses a special DC power supply device. Positive electrode of power supply is connected with a pen as anode during brush plating. Negative electrode of power supply is connected to workpiece as cathode during brush plating. Plated pen is usually made of high-purity fine graphite block as anode material, graphite block is covered with cotton and a wear-resistant polyester cotton sleeve. During operation, power component is adjusted to a suitable voltage, plated pen impregnated with plating solution moves at a relative relative movement speed corresponding to surface of workpiece to be repaired, metal ions in plating solution are diffused to workpiece under action of electric field force. and electrons are reduced to metal atoms on the surface, so that these metal atoms are deposited and crystallized to form a coating, that is a uniform deposited layer is obtained on working face of plastic mold cavity to be repaired.

Laser surfacing repair

Laser welding is a process in which a laser beam is used as a heat source by focusing with a high-power coherent monochromatic photon stream. This welding method usually has continuous power laser welding and pulse power laser welding. Advantage of laser welding is that it does not need to be carried out in a vacuum. Disadvantage is that penetration force is not as strong as that of electron beam welding. Accurate energy control during laser welding enables precision soldering of devices. It can be applied to many metals, especially to weld some difficult-to-weld metals and dissimilar metals. It has been widely used in the repair of injection molding by plastic mold factory.

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