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#047 Mold Welding Work

Category : Technical Information
June25, 2010

When a part of a component of a mold for plastic injection molding has become worn out or when a corner part has been chipped off due to hitting it against some hard object, etc., welding can be used as a method for repairing such parts. Although welding is not used in the case of precision molds because welding can result in big damage to the mold component due to high temperatures or formation of oxide layers during welding, welding is an important repairing technology in the case of large molds, or when the external appearance quality of molded products is not very severe, or for carrying out emergency repairs. In view of this, the outlines of welding are described below.

1. Types of welding

The following are the three major types of welding used for repairing molds.
(1)Brazing
(2)Gas welding
(3)Electrical arc welding

2. Features of the different welding methods

(1)Brazing
Brazing is that of affixing to the part to be repaired a material such as solder or silver by heating it in a flame and melting it. Since the repair will be made using a metallic material that is different from the base material which is carbon steel, the strength of the joint is not very good. However, since this type of welding work is simple, it is suitable for making emergency repairs.

(2)Gas welding
In general, this refers to oxy-acetylene welding. Oxygen and acetylene gases are supplied from two gas cylinders, the two are ignited and their flow rates are adjusted to obtain a very hot pointed jet of flame and the welding is carried out by feeding a welding rod between the part to be repaired and the flame. Although the strength of the welded joint is lower than that of electric arc welding, it can meet sufficiently the purpose of repairs. Compared to electric arc welding, since the thermal effect on the base material is small, this method is suitable for molds that are sensitive to deformations.

(3)Electric arc welding
This is the method of creating heat by causing an arc using an AC current or a DC current. The following three methods are used in this type of welding.

1)Coated electrode arc welding
 This arc welding is done using coated welding rods. This is used very frequently for ordinary mechanical parts.

2)Carbon dioxide gas arc welding
 In this method, the welding is done in a carbon dioxide gas shield. It is possible to prevent oxidization of the welding parts.

3)Inert gas arc welding
 In this method, the welding is done in an inert gas shield such as argon gas, etc. This is the most suitable method for repairing molds.

 Since it is possible to prevent definitely any oxidization of the welded parts and to suppress the generation of oxides, and generation of blow holes or air bubbles is difficult even if grinding is done. However, the cost of the work becomes high, and there is the limitation that this work cannot be made unless the company has the required equipment.

 

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