Share some manufacturing processes for screw molds

1、 Material pretreatment process
The initial state of mold materials directly affects the quality of subsequent processing, and pre-treatment is the basic step:
Material selection and cutting: Select materials based on the usage scenario of screw molds (such as forming material hardness, production batch), commonly using alloy structural steels such as 35CrMo and 40Cr (suitable for general requirements), or cold/hot work mold steels such as Cr12MoV and H13 (suitable for high wear resistance and high temperature scenarios). Cutting equipment such as sawing machines and plasma cutting is used to cut raw materials into billets that are close to the size of mold parts, reducing subsequent processing volume.
Forging: The billet is subjected to forging treatment, which involves pressure processing (forging, rolling) at high temperatures (such as 800-1200 ℃) to refine the material grains, eliminate internal defects such as porosity and looseness, and improve the material's density and mechanical properties (such as strength and wear resistance). For example, key components such as mold cores and cores usually require forging strengthening.
Annealing/Normalizing: After forging, annealing (slow cooling) or normalizing (air cooling) treatment is carried out to eliminate forging stress, reduce material hardness (such as controlling hardness at HB200-250), improve cutting performance, and avoid cracking or deformation during subsequent processing.
2、 Mechanical processing technology
The core step of mold forming is to process the shape and size of the pre processed billet through high-precision equipment
Rough machining: Remove most of the excess material and initially form the contour of the part.
Milling: Use a vertical/horizontal milling machine to machine the flat and stepped surfaces of the mold (such as the slide mounting surface of the mold), or rough mill the joint surface and cavity reserved area of the mold core through a CNC milling machine.
Turning: Turning the cylindrical structure of the core and mold core, processing the outer circle, end face, steps, etc., for example, the stem of the core needs to ensure basic cylindricity.
Drilling: Machining through holes or blind holes such as bolt holes, ejector pin holes, and cooling water holes in molds using bench drills or rocker drills to prepare for subsequent assembly and cooling systems.
Semi precision machining: further improve the accuracy of parts and reduce surface roughness.
Grinding: Use a surface grinder to machine the parting surface of the mold and the fitting surface of the upper and lower molds, ensuring flatness (usually ≤ 0.01mm/100mm); The outer circle of the core processed by the cylindrical grinder ensures cylindricity and dimensional accuracy (such as tolerance control within IT6-IT7 levels).
Numerical Control Milling (CNC): High precision machining is achieved through CNC milling for complex structures such as the joint surface of the mold cavity and the guiding slope. The tool radius compensation function is used to ensure dimensional consistency.
Precision machining: Achieving the final size and surface requirements of the mold directly affects the quality of screw molding.
Electric discharge machining (EDM): used for machining complex cavity structures in mold cores (such as threaded grooves and irregular cross-sections of screws), corroding materials through pulse discharge between electrodes and workpieces, with an accuracy of ± 0.005mm and a surface roughness of Ra0.8-1.6 μ m.
Wire cutting machining (WEDM): High precision cutting is performed on the splicing gaps of the mold core and the irregular cross-sections of the core, especially suitable for processing high hardness materials (such as quenched mold steel). The cutting accuracy can reach ± 0.003mm, and the surface roughness is Ra1.6-3.2 μ m.
Precision grinding: using coordinate grinding machines to process the positioning holes and guide holes of molds, ensuring the roundness and positional accuracy of the holes; The centerless grinder precision processes the outer circle of the core, ensuring its fit clearance with the cavity (usually controlled at 0.01-0.03mm).