Precision Turning Machining in Mold Component Manufacturing
Turning processes play a crucial role in the manufacturing of various mold components, especially those requiring cylindrical features and high-precision dimensions. This detailed guide explores practical turning applications for critical mold parts, highlighting techniques that ensure optimal performance in molded plastic production environments.
(1) Turning Process for Circular Punches
By analyzing the structure of various mold components, we can better understand the application of turning processes in mold manufacturing. Specific turning parameters will be discussed in subsequent chapters, but this section focuses on practical implementation for molded plastic production components.
Figure 1-5 shows a typical circular punch with an overall length of 70mm. The outer surface consists entirely of revolving surfaces, making its structure relatively simple and perfectly suited for turning operations. However, because this component functions as a punch, it requires specific hardness properties, necessitating heat treatment through quenching during the manufacturing process.
Both the fixing portion and working portion of the punch demand high dimensional accuracy and surface finish. This requires a strategic manufacturing sequence: after rough turning and semi-finish turning, the component undergoes hardening treatment, followed by grinding processes to achieve the required specifications. This approach ensures the punch can withstand the rigorous demands of molded plastic production cycles.
The punch is typically processed on a horizontal lathe for roughing and semi-finishing operations according to design specifications. During turning, except for the radial dimensions of the fixed台阶, which can be turned directly to final size, all other dimensions require machining allowances for subsequent grinding processes. This critical step ensures that after heat treatment hardening, precise grinding can achieve the exact dimensions needed for optimal performance in molded plastic applications.
Following heat treatment to harden the component, precision grinding on a cylindrical grinder achieves the final dimensions. Finally,钳工 perform polishing and edge grinding to create the ideal working profile and mating surfaces, ensuring the punch delivers consistent performance in molded plastic production environments.
Figure 1-5: Typical Circular Punch Structure
Precision-turned circular punch used in molded plastic manufacturing processes
Key Dimensions
Overall length: 70mm
Working diameter: 25-30mm (varies by application)
Material Requirements
High-carbon tool steel
Hardness: 58-62 HRC after heat treatment
Circular Punch Manufacturing Process Flow
Rough Turning
Initial shaping of the raw material to approximate dimensions, removing most excess material while establishing basic cylindrical form. This step creates the foundation for subsequent operations in the molded plastic component production process.
Semi-Finish Turning
Refines the component dimensions, bringing them closer to final specifications while maintaining appropriate allowances for subsequent grinding. Critical surfaces for molded plastic contact are carefully prepared at this stage.
Heat Treatment
Quenching and tempering processes to achieve the required hardness properties. This step is crucial for ensuring the punch can withstand repeated use in high-volume molded plastic production environments.
Precision Grinding
Final dimensional accuracy achieved through cylindrical grinding operations. This step ensures the tight tolerances required for proper function in molded plastic manufacturing equipment.
Finishing Operations
Polishing and edge preparation by skilled craftsmen to create the optimal working surface. These final touches ensure clean, precise cuts in molded plastic components during production.
(2) Turning Process for Circular Compound Dies
Figure 1-6 illustrates a circular blanking and punching compound die with an overall height of 50mm. Like the previously discussed punch, its surface consists entirely of revolving surfaces. While slightly more complex in structure than the circular punch shown in Figure 1-5, it is also well-suited for turning operations, particularly in the production of tools for molded plastic components.
As a compound die, this component also requires hardness, necessitating quench heat treatment. Both its outer diameter (functioning as a punch) and inner diameter (functioning as a die) require high dimensional accuracy and surface finish in the radial direction. These critical surfaces must be carefully prepared to ensure precise operation in molded plastic manufacturing processes.
Consequently, these two dimensions require grinding allowances after rough and semi-finish turning operations. The diameter of the material discharge hole and the diameter of the fixing stage can be turned directly to their final dimensions. This strategic approach ensures that after component hardening, precise grinding can achieve the exact specifications needed for reliable performance in molded plastic production.
Following hardening, the outer surface of the blanking punch portion, the inner surface of the punching die portion, and the cutting edge areas undergo grinding to meet final requirements. This multi-stage process ensures that all critical surfaces achieve the necessary precision for consistent operation in high-volume molded plastic manufacturing environments.
Therefore, the manufacturing process for this compound die follows this sequence: rough turning → semi-finish turning → heat treatment → external cylindrical grinding → internal cylindrical grinding →钳工 finishing. This comprehensive process ensures that the compound die meets all performance requirements for molded plastic production applications.
Figure 1-6: Circular Blanking and Punching Compound Die
Compound die with precision-turned inner and outer surfaces for molded plastic manufacturing
Critical Tolerances for Molded Plastic Applications
| Feature | Tolerance | Surface Finish |
|---|---|---|
| Outer Punch Diameter | ±0.002mm | Ra 0.4μm |
| Inner Die Diameter | ±0.001mm | Ra 0.2μm |
| Shoulder Perpendicularity | 0.003mm/100mm | - |
| Overall Height | ±0.01mm | - |
Turning Applications for Other Mold Components
In mold manufacturing, numerous components feature revolving surface configurations that rely heavily on turning processes. These include guide pillars, guide bushes, return pins, ejector pins, locating rings, sprue bushes, support pillars, and various other cylindrical components essential for precise mold operation in molded plastic production.
Standardized Components
It's important to note that many of these components have been standardized and are produced by specialized manufacturers. This standardization benefits the molded plastic industry by ensuring consistent quality and interchangeability across different mold systems. Most mold manufacturing companies no longer produce these standardized items in-house, instead sourcing them from specialized suppliers who maintain strict quality controls for molded plastic applications.
Custom Turning Applications
In modern mold manufacturing facilities, turning processes are primarily utilized for the roughing and semi-finishing of non-standard mold components such as circular compound dies and circular inserts. These custom components require tailored turning operations to meet specific molded plastic part requirements, often involving complex geometries and tight tolerances that cannot be achieved with standardized components.
Typical Turning Operations in Mold Manufacturing
Facing
Creating flat surfaces perpendicular to the component axis, essential for proper seating of parts in molded plastic molds.
Cylindrical Turning
Producing external cylindrical surfaces with precise diameters for critical functional features in molded plastic tooling.
Boring
Enlarging existing holes to create precise internal cylindrical surfaces for molded plastic flow channels and guide features.
Threading
Creating internal or external threads for assembly features in molded plastic mold components.
Grooving
Cutting narrow grooves for O-rings, snap rings, and other sealing or retaining features in molded plastic tooling.
Taper Turning
Producing conical surfaces for alignment features and self-locating components in molded plastic molds.
Surface Finish Requirements in Mold Turning
Surface finish is a critical consideration in turning operations for mold components, directly impacting both the performance of the mold and the quality of molded plastic parts. Different surfaces require different finishes based on their function within the mold system.
For example, guiding surfaces typically require smoother finishes to reduce friction and wear during repeated mold cycles, while non-functional surfaces can have coarser finishes. The contact surfaces that form the molded plastic part itself demand the highest quality finishes to ensure proper replication of surface details and easy part release.
Turning processes can achieve surface finishes ranging from approximately Ra 3.2μm for rough turning to Ra 0.8μm for fine turning operations. When higher finishes are required, subsequent grinding and polishing operations are employed to reach the Ra 0.025μm range necessary for critical molded plastic contact surfaces.
Summary of Turning Applications in Mold Manufacturing
Turning processes remain fundamental to mold component manufacturing, particularly for components with cylindrical features and rotational symmetry. From simple punches to more complex compound dies, turning provides the precision foundation necessary for creating high-quality mold components that produce consistent, accurate molded plastic parts.
The strategic combination of rough turning, semi-finish turning, heat treatment, and subsequent grinding operations ensures that mold components meet the strict dimensional, hardness, and surface finish requirements of modern molded plastic production. By understanding these processes and their applications, manufacturers can optimize their mold production workflows, resulting in higher quality molds and better final molded plastic products.