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1、 Plastic mold materials

Plastic mold materials can be divided into molded parts materials and non molded parts materials according to their functions

The selection criteria for materials of formed parts are as follows:

1. Molding parts refer to mold parts that directly contact with plastic molding products, such as cavity, core, slider, insert, inclined top, side extraction, etc.

2. The material of molded parts is directly related to the quality and service life of the mold, which determines the appearance and internal quality of molded plastic products. It must be carefully selected according to the requirements and characteristics of products and molds on the basis of contract provisions and customer requirements.

3. The selection principle of molding parts and components materials is: according to the type of molding plastic, product shape, dimensional accuracy, product appearance quality, use requirements, production batch size, etc., consider various properties of materials, such as cutting, polishing, welding, etching, deformation, wear resistance, etc., and consider the economy of the mold, manufacturing conditions and processing methods, so as to select different types of steel.

4. For the mold used to form transparent plastic products, its cavity and core should adopt high-grade imported steel with high mirror polishing performance, such as 718 (P20 Ni), NAK80 (p21), S136 (420), H13 steel, etc. Among them, 718 and NAK80 are in the pre hardening state and do not need heat treatment; S136 and H13 steels are annealed, and the hardness is generally hb160-200. Vacuum quenching and tempering are required after rough machining. The hardness of S136 is HRC40-50, and the hardness of H13 steel is hrc45-55 (which can be determined according to the specific brand).

The material selection criteria for non formed parts are as follows:

1. The template material refers to the template standard. The template generally adopts imported S50C or domestic sm45, which requires hb160-200. The hardness of the template is uniform, the internal stress is small, and it is not easy to deform. The material of guide post is GCr15 or SUJ2, and the hardness is hrc56-62. The materials of guide sleeve, push plate guide post, push plate guide sleeve and reset rod can be made of GCr15 or SUJ2 with hardness of hrc56-62; T8A and T10A with hardness of hrc52-56 can also be used.

2. General structural parts in the mold, such as ejector locating ring, column, ejector limit block, limit pull rod, locking module, etc., have no special requirements for hardness and wear resistance. Domestic sm45 steel with hardness of hb160-200 can be used, which is normalized and does not need heat treatment.

3. Parts with high requirements for hardness, strength and wear resistance, such as sprue sleeve, wedge block, wear block, slider pressing plate, etc. in the mold, should adopt carbon tool steel or high-quality carbon tool steel, such as T8A, T10A, etc. This steel needs quenching to improve its hardness and wear resistance.

2、 Processing of plastic mold

Main processing equipment of plastic mold:

1. Ordinary milling machine (gong machine) can process structures with simple shape and low precision; For example, mold opening.

2. CNC milling machine (computer gong) can process structures with high precision and complex shape, such as mold cavity.

3. Lathe, processing round parts.

4. Drilling machine, drilling, tapping, drilling and transporting water holes, etc.

5. Grinding machine, steel die leveling or grinding datum.

6. Spark machine, processing parts with small structure that cannot be processed by CNC milling machine, such as deep stiffeners.

7. Wire cutting machine, mainly used for shape cutting.

Lathe: the machining accuracy is generally 0.02mm. Process guide posts, pins, round cores, punches, etc. on the mold.

Boring machine: the working principle is the same as that of the lathe. The lathe rotates the workpiece, while the boring machine rotates the cutter.

1. Machining accuracy of boring machine: 0.02mm

2. Process large through holes on the mold, such as guide post and guide sleeve holes.

Milling machine: the machining accuracy is generally 0.02mm.

Correct angle, rough machining, chamfer, etc. on the mold. It can also be used for cutting small parts.

Grinder: there are circular grinder and surface grinder. The general machining accuracy is 0.01 ~ 0.02 mm. The circular grinder can process guide posts, pins, thimbles, round cores, etc., and can also be used for blanking. Flatness of surface grinding machine, formwork and formwork core.

Drilling machine: generally, the machining accuracy of drilling machine is only 0.1mm, mainly processing water channel, thimble through hole, screw through hole, screw bottom hole, etc.

NC machining accuracy: 0.005 mm. CNC machining scope: Machining of parts with complex shapes, machining of high-order surfaces, machining of positioning blind holes, etc.

EDM: EDM is a special processing method that uses the electric erosion generated by the pulse discharge between the two poles immersed in the working fluid to etch away the conductive materials. It is also called EDM or electric discharge machining, and its English abbreviation is EDM.

EDM accuracy: it can be controlled within 0.005 mm.

Main processing areas: surface patterns, vertical corners that cannot be processed by CNC, special-shaped blind holes, etc.

Wire cutting: the principle is the same as EDM.

Wire cutting machine tools are generally divided into two types: slow wire walking and fast wire walking. Slow wire walking is mainly processed with copper wire, which is discarded after processing once. The wire walking speed is slow, the processing speed is slow, and the precision is high. Fast moving wire is mainly molybdenum wire, which is a domestic self-supporting product. Molybdenum wire has good corrosion resistance, can be reused, fast wire walking speed, fast processing speed and low precision. WEDM machining accuracy: slow wire walking can reach 0.002 mm. Scope of wire cutting: blanking of special-shaped parts. Special shaped through holes, conical through holes, through holes with high positioning requirements, etc. Generally speaking, the insert hole on the mold should be processed by wire cutting.