Machining Examples of Rotational Parts
A comprehensive guide to the precision machining processes for guide pillars and bushings, essential components in plastic molds and various industrial applications.
Advanced CNC machining ensures tight tolerances for critical components in plastic molds and machinery
1. Part Analysis
Guide Pillar
As shown in Figure 3-12(a), the part is a stamping die guide pillar, consisting of coaxial outer circles of different diameters, chamfers, and tool withdrawal grooves. The structure is simple and has good structural processability, making it suitable for use in plastic molds and various precision machinery.
Guide Bushing
Figure 3-12(b) shows a stamping die guide bushing, which works in conjunction with the guide pillar to ensure precise alignment in plastic molds and other precision equipment. The interaction between these components is critical for maintaining dimensional accuracy in manufacturing processes.
Technical Requirements Analysis for Guide Pillars
① Dimensional and Geometric Accuracy
The mating surface 32 of the guide pillar is an important surface with a diameter accuracy requirement of IT6 and a cylindricity of 0.006mm. These tight tolerances are essential for ensuring proper functionality in high-precision applications such as plastic molds, where even minor deviations can affect product quality.
② Position Accuracy
The coaxiality tolerance between the mating surfaces 32h6 and 32r6 on the guide pillar is 0.008mm, representing a high precision requirement. This level of accuracy ensures smooth operation and extended service life in demanding applications, including plastic molds that require thousands of production cycles.
③ Surface Roughness
All surfaces of the guide pillar are machined surfaces with specified surface roughness requirements. The 32h6 outer circle has the highest requirement with Ra 0.1μm, followed by the 32r6 outer circle with Ra 0.4μm. The remaining surfaces have a surface roughness of Ra 3.2μm. These specifications ensure proper lubrication retention and minimize wear, particularly important in plastic molds where consistent performance is critical.
From the above analysis, it is evident that the main machining surfaces of the guide pillar are the φ32h6 outer circle and φ32r6 outer circle. Due to their high precision requirements, grinding and fine polishing must be employed to meet the specified accuracy levels. These processes are similar to those used in manufacturing high-precision components for plastic molds, where surface finish and dimensional accuracy directly impact performance and longevity.
2. Turning Process for Guide Pillars
(1) Machine Selection
In this case, the guide pillar has a diameter of 32mm and features a stepped shaft shape with minimal differences between segment dimensions. The blank is made of hot-rolled round steel, resulting in a cylindrical毛坯 shape. Therefore, an ordinary lathe meets the processing requirements, and the CA6140 lathe is selected for this purpose. This versatile machine is commonly used in producing components for plastic molds and various mechanical applications.
The CA6140 lathe offers sufficient precision and rigidity for machining the guide pillar's initial dimensions before finishing operations. Its reliability makes it a staple in workshops producing parts for plastic molds and other precision equipment.
CA6140 lathe setup for preliminary turning operations on guide pillars, commonly used in plastic molds manufacturing
(2) Determining Blank Dimensions
To ensure sufficient allowance for each processing step, the dimensions of the round steel are set to 38mm × 215mm. This provides adequate material for all machining operations while minimizing waste, an important consideration in cost-effective production of components for plastic molds and other industrial applications.
The selection of proper blank dimensions is crucial for maintaining dimensional accuracy throughout the manufacturing process. This is especially true for components used in plastic molds, where consistent quality directly affects the final product's integrity.
Hot-rolled round steel bars prepared as blanks for guide pillar production, suitable for plastic molds components
(3) Workpiece Clamping
In this case, the guide pillar blank is a 38mm diameter bar. A standard self-centering chuck is sufficient for clamping. This type of chuck provides reliable gripping while ensuring concentricity, which is essential for maintaining the dimensional accuracy required in components for plastic molds.
Proper clamping is critical to prevent workpiece movement during machining, which could result in dimensional inaccuracies or surface finish defects. The self-centering chuck offers a good balance between clamping force and precision, making it suitable for this application as well as many other components used in plastic molds.
Self-centering chuck properly clamping a round bar for precise turning operations, a common setup in plastic molds manufacturing
3. Guide Bushing Processing
(1) Analysis of Guide Bushing Processing Measures
Guide bushing components require machining of both inner and outer surfaces. The inner cylindrical surface has straightness requirements, and the outer cylindrical surface has coaxiality requirements with the axis. These precision requirements are similar to those found in many components used in plastic molds, where accurate mating of parts is essential.
One-piece Machining Advantages
During the turning process, completing all inner and outer surface machining in a single setup minimizes clamping errors and achieves high positional accuracy. This technique is widely used in manufacturing components for plastic molds where precision is paramount.
It is advisable to machine the outer circle first, then use the outer circle as a precision reference for machining the inner hole. This approach minimizes straightness, coaxiality, and runout errors. For this purpose, fixtures with high centering accuracy should be used, such as elastic sheet chucks, liquid plastic collets, specially ground self-centering chucks, and soft jaws—all common in the production of precision parts for plastic molds.
Deformation Considerations
Guide bushing components typically have thin walls, making them prone to deformation during processing. Therefore, attention must be paid to factors such as clamping force, cutting force, internal stress, and cutting heat during machining. These considerations are particularly important in plastic molds production, where dimensional stability is critical.
Batch Processing Strategies
For batch processing, it is advisable to separate roughing and finishing operations. This helps minimize processing allowances, allows for increased number of passes, and reduces clamping force—all important factors in maintaining dimensional accuracy in components for plastic molds and other precision applications.
Grinding Operations
To ensure the dimensional and form accuracy of guide bushings, grinding processes are necessary. Proper selection of positioning datums during guide bushing grinding is crucial for ensuring coaxiality between inner and outer cylindrical surfaces. This level of precision is essential in plastic molds, where even minor misalignments can cause premature wear or product defects.
Single Piece Production Method
The guide bushing processing route can be performed on a universal cylindrical grinder using a self-centering chuck to clamp the φ48mm outer cylindrical surface. This method can ensure coaxiality requirements but requires frequent machine adjustments, making it suitable only for single piece production. This approach is sometimes used for custom components in specialized plastic molds.
Batch Production Method
For batch processing, the outer cylindrical surface can be ground using a specially designed tapered mandrel, with positioning on the center holes at both ends of the mandrel. This method achieves high coaxiality requirements and is ideal for producing components for plastic molds in medium to large production runs.
Mandrel Specifications
Such mandrels should have high manufacturing accuracy, with a taper in the range of 1/5000 to 1/1000 and a hardness of over 60HRC. These precision tools ensure consistent results, which is essential for maintaining quality standards in the production of components for plastic molds and other high-precision applications.
Lapping Processes
To further improve guide bushing accuracy, lapping can be employed. Lapping guide bushings is similar to lapping guide pillars. During the grinding and lapping processes, attention must be paid to the selection of lapping tool materials, abrasives, and grinding fluids. Additionally, precautions should be taken to prevent the formation of bell-mouthed openings during grinding—an important consideration in ensuring proper fit and function in plastic molds and other precision assemblies.
(2) Machine Selection
In this case, the guide bushing has an outer diameter of φ48mm and features a stepped shaft shape with minimal differences between segment dimensions. The blank is made of hot-rolled round steel, resulting in a cylindrical shape. Therefore, ordinary machine tools can meet the processing requirements.
CA6140 Lathe
Used for turning operations to achieve initial dimensions and surface finishes, suitable for plastic molds components.
M1432A Universal Cylindrical Grinder
Provides precise grinding operations to achieve final dimensions and surface finishes required for plastic molds.
ZQ3040 Drilling Machine
Used for hole drilling operations, ensuring accurate positioning and dimensions critical for plastic molds.
T68 Horizontal Boring Machine
Provides precise boring operations for achieving tight tolerances in components for plastic molds.
The combination of these machines allows for the complete manufacturing process of guide bushings from raw material to finished component, ensuring all dimensional and surface finish requirements are met. This comprehensive approach to machining is essential for producing high-quality components not only for the guide bushings described here but also for various other precision parts used in plastic molds and industrial machinery.