Processing Technology Routes for Injected Molded Plastic Components
Methods for Formulating Processing Technology Routes for Mold Components
The formulation of processing technology routes for mold components is the foundation for developing processing technology procedures for mold parts. The main tasks in formulating processing technology routes include selecting processing methods for component surfaces, determining processing sequences, and dividing operations. Based on the technology route, process benchmarks for each operation can be selected, and specific operational dimensions, equipment, tooling, cutting parameters, and time quotas can be determined.
When formulating technology routes, special attention should be paid to the characteristics of mold manufacturing, which involves single-piece or small-batch production with high precision requirements. Starting from the actual conditions of the factory, emphasis should be placed on the feasibility and economy of new processes and technologies. Multiple schemes should be proposed, analyzed, and compared to determine an optimal technology route that suits the actual factory conditions.
Selection of Surface Processing Methods
To correctly select processing methods, it is essential to understand the characteristics of various processing methods and master the concepts of economic processing accuracy and economic surface roughness. During processing, many factors affect accuracy. Each processing method can achieve different levels of accuracy under different working conditions.
For instance, when workers operate carefully and select lower cutting parameters, higher accuracy can be achieved. However, this reduces productivity and increases costs. Conversely, increasing cutting parameters to improve production efficiency can reduce costs but may increase processing errors, thereby reducing processing accuracy.
Economic processing accuracy and economic surface roughness refer to the processing accuracy and surface roughness that can be achieved under normal processing conditions, using equipment that meets quality standards, process equipment, and workers of standard technical grades without extending processing time.
External Cylindrical Surface Processing Schemes
Multiple processing schemes exist for external cylindrical surfaces of injected molded plastic mold components:
Rough Turning: Achieves IT11-IT13 accuracy grades with surface roughness Ra of 12.5-50 μm. Suitable for all metals except hardened steel.
Rough Turning → Semi-finish Turning: Achieves IT8-IT10 accuracy grades with surface roughness Ra of 3.2-6.3 μm.
Rough Turning → Semi-finish Turning → Finish Turning: Achieves IT7-IT8 accuracy grades with surface roughness Ra of 0.8-1.6 μm.
Rough Turning → Semi-finish Turning → Finish Turning → Rolling or Polishing: Achieves IT6-IT7 accuracy grades with surface roughness Ra of 0.06-0.20 μm.
Rough Turning → Semi-finish Turning → Grinding: Achieves IT6-IT7 accuracy grades with surface roughness Ra of 0.4-0.8 μm.
Internal Hole Processing Schemes
Internal hole processing for injected molded plastic molds requires specific approaches:
Drilling: Basic drilling achieves IT11-IT13 accuracy grades with surface roughness Ra of 12.5-50 μm.
Drilling → Reaming: Achieves IT8-IT9 accuracy grades with surface roughness Ra of 1.6-3.2 μm.
Drilling → Rough Reaming → Finish Reaming: Achieves IT7-IT8 accuracy grades with surface roughness Ra of 0.8-1.6 μm.
Drilling → Expanding: Achieves IT10-IT11 accuracy grades with surface roughness Ra of 6.3-12.5 μm.
Rough Boring → Semi-finish Boring → Finish Boring: Achieves IT7-IT8 accuracy grades with surface roughness Ra of 0.8-1.6 μm.
Planar Surface Processing Schemes
Planar surface processing is crucial for injected molded plastic mold manufacturing:
Rough Turning: For rotational body end faces, achieves IT11-IT13 accuracy grades with surface roughness Ra of 12.5-50 μm.
Rough Turning → Semi-finish Turning: Achieves IT8-IT10 accuracy grades with surface roughness Ra of 3.2-6.3 μm.
Rough Planing or Milling: Achieves IT11-IT13 accuracy grades with surface roughness Ra of 12.5-50 μm for general non-hardened planes.
Rough Planing or Milling → Finish Planing or Milling: Achieves IT8-IT10 accuracy grades with surface roughness Ra of 1.6-6.3 μm.
Rough Milling → Finish Milling → Grinding → Lapping → Polishing: Achieves accuracy above IT5 with surface roughness Ra of 0.025-0.1 μm.
Hole System Processing with Positional Accuracy Requirements
For hole systems requiring positional accuracy in injected molded plastic mold manufacturing:
Drilling on Vertical or Radial Drilling Machines: Using drill jigs achieves distance errors of 0.05-0.2mm.
CNC Milling or Machining Center Processing: Achieves distance errors of 0.005-0.05mm.
Coordinate Boring Machine Processing: Using optical instruments achieves distance errors of 0.004-0.015mm.
Diamond Boring Machine Processing: Coordinate measuring devices achieve distance errors of 0.008-0.02mm.
Horizontal Boring and Milling Machine Processing: Various positioning methods achieve different accuracies from 0.005-1.0mm.
Advanced Processing Methods for Complex Surfaces
For complex surface processing in injected molded plastic mold manufacturing, beyond conventional turning, grinding, planing, and milling on ordinary machine tools, CNC machine processing, EDM processing, and form grinding are primarily employed. For hole systems requiring high positional and dimensional accuracy, coordinate boring, coordinate grinding, and CNC milling methods are generally used.
CNC Machine Processing
Can process various formed surfaces and complex surfaces, particularly suitable for processing cavities, cores, and various complex curved surfaces in injected molded plastic mold manufacturing.
EDM Processing
One of the commonly used processing methods in mold manufacturing, with EDM forming processing particularly widely applied in hardened mold cavity processing for injected molded plastic production.
Precision Coordinate Methods
Coordinate boring and coordinate grinding are mainly used for precision processing of hole systems requiring high positional accuracy in injected molded plastic molds.
Form grinding processing includes form grinding wheel grinding and form fixture grinding methods, mainly used for precision processing of punches and die inserts. Optical curve grinding machines are suitable for precision processing of special-shaped working surfaces of small injected molded plastic molds.
When selecting processing methods, attention should be paid to the fact that when mold part surface processing accuracy requirements are high, the final processing method for the processed surface should first be determined based on factors such as economic processing accuracy and surface roughness achievable by different process methods. Then, a series of preparatory operation processing methods and sequences before the final processing method should be selected to achieve design requirements through successive processing.
Processing method selection often relies on experience or reference tables, then modifications are made based on actual conditions or through process testing. From the data in the referenced tables, it can be seen that several processing methods can satisfy the same accuracy requirements, so the following issues should also be considered during selection:
Workpiece Material Properties and Heat Treatment Processes
For example, precision processing of hardened steel requires grinding, while precision processing of non-ferrous metals should use high-speed finish turning or fine boring to avoid wheel clogging during grinding.
Production Type, Productivity, and Economic Issues
Processing method selection should adapt to production type. For example, for guide post and guide sleeve holes in die seats, single-piece small-batch production uses drilling and matching boring processes, while high-volume production uses drilling and multi-spindle boring processes.
Workpiece Shape and Dimensions
For example, holes in multi-hole punching dies adopting turning and internal grinding not only complicate the process but also cannot ensure positional accuracy between holes. Coordinate boring machines or coordinate grinding machines should be used.
Specific Production Conditions
Existing equipment and process means should be fully utilized, technical personnel creativity should be leveraged, and enterprise potential should be explored. Sometimes, due to equipment load reasons, other processing methods need to be adopted.
Additionally, when selecting processing methods, the possibility of utilizing new processes and technologies should be fully considered to improve process levels.
Division of Processing Stages
Technology routes are generally divided into rough processing, semi-finish processing, and finish processing stages according to operation nature. For surfaces requiring particularly high processing accuracy and surface quality, a finishing processing stage should be arranged at the end of the process.
Main Tasks of Each Processing Stage
Rough Processing Stage
The main task of rough processing is to remove most of the processing allowance from processed surfaces, making blank shapes and dimensions as close as possible to finished products. During rough processing, accuracy requirements are not high, and cutting parameters and cutting forces are relatively large. Therefore, rough processing should mainly consider how to improve labor productivity.
Finish Processing Stage
Finish processing makes high-accuracy surfaces meet design quality requirements. Required processing accuracy is high, and processing allowances and cutting parameters for all surfaces are relatively small.
Semi-finish Processing Stage
Semi-finish processing prepares necessary accuracy and allowance for precision processing of main surfaces and completes processing of some secondary surfaces such as drilling, tapping, and grooving. For surfaces or parts with low accuracy requirements, semi-finish processing can meet design requirements.
Finishing Processing Stage
The main task of finishing processing is to improve dimensional accuracy of processed surfaces and reduce surface roughness. Generally, it cannot correct shape and position errors. Finishing processing is arranged only for surfaces requiring particularly high dimensional accuracy and surface roughness, such as some injected molded plastic mold cavity surface processing.
Functions of Dividing Processing Stages
| Function | Description |
|---|---|
| Ensuring Product Quality | Rough processing removes large allowances, generating large cutting forces and heat. Staged processing gradually reduces these factors, eliminating previous errors and meeting design requirements. |
| Rational Equipment Use | Rough processing uses high-power, low-precision machines for productivity, while finish processing uses high-precision equipment, extending their service life. |
| Facilitating Heat Treatment | Staged processing allows proper placement of heat treatment operations, utilizing their effects while enabling correction of any resulting deformation. |
| Defect Discovery & Surface Protection | Rough processing reveals blank defects early, preventing wasted effort on unsalvageable parts and protecting finished surfaces from damage during subsequent operations. |
Therefore, when formulating mold part processing technology routes, the principle of dividing processing stages should generally be followed, but it cannot be absolute in specific applications. Technology route processing stage division applies to the entire workpiece processing process, not to processing of a particular surface or operation. For example, some positioning reference surfaces need precise processing in semi-finish or even rough processing stages, while rough processing of some small holes is often arranged in finish processing stages.
Operation Division and Processing Sequence Arrangement
Principles of Operation Division
Based on design requirements for processed surfaces in each processing stage of parts, combined with selected surface processing methods, processing of surfaces in the same stage can be combined into different operations. When dividing operations, principles of operation concentration or operation dispersion can be adopted.
Operation Concentration Principle
If each operation includes much processing content, part processing can be concentrated in few operations, called operation concentration.
Better ensures mutual positional accuracy between surfaces
Reduces workpiece clamping times and auxiliary time
Reduces machine tool and operator numbers
Equipment and tooling have complex structures with large investments
Difficult adjustment and maintenance, high technical requirements
Operation Dispersion Principle
If each operation includes little processing content, part processing is dispersed among many operations, called operation dispersion.
Machine equipment and tooling are relatively simple
Convenient to adjust, easy for workers to master
Can adopt optimal cutting parameters, reducing machining time
Requires large equipment quantities and many operators
Needs large production areas
Since injected molded plastic mold processing requires high accuracy and mostly involves single-piece or small-batch production, it is more suitable for dividing operations according to operation concentration principles. Professional production enterprises for mold standard parts combine both operation concentration and dispersion, requiring technical economic analysis based on specific conditions.
Processing Sequence Arrangement
Workpiece mechanical processing involves cutting processing, heat treatment, and auxiliary operations. Therefore, when formulating technology routes, cutting processing, heat treatment, and auxiliary operation sequences should be reasonably and comprehensively arranged.
Cutting Processing Operation Arrangement
Processed surfaces of injected molded plastic mold parts have not only individual accuracy requirements but also certain positional accuracy requirements between surfaces. During part processing, attention should be paid to reference selection and conversion. Processing sequence arrangement should follow these principles:
Rough First, Then Precision
Rough processing first, then semi-finish, finally finish processing
Reference First, Then Others
Process reference surfaces first for subsequent operations
Main First, Then Secondary
Process main surfaces first, then secondary surfaces
Planes First, Then Holes
Process planes first as references, then internal holes
Heat Treatment Operation Arrangement
Heat treatment operation arrangement in technology routes mainly depends on part heat treatment purposes. According to heat treatment purposes, heat treatment processes can be roughly divided into two categories: preparatory heat treatment and final heat treatment.
Preparatory Heat Treatment
Preparatory heat treatment aims to improve workpiece processing performance, eliminate internal stress, improve metallographic structure, and prepare for final heat treatment.
Annealing and normalizing: Generally arranged after blank manufacturing and before mechanical processing.
Tempering treatment: Generally arranged between rough and semi-finish processing.
Aging treatment: Eliminates internal stress. Arranged based on precision requirements, sometimes multiple times.
Final Heat Treatment
Final heat treatment aims to improve part performance such as strength, hardness, and wear resistance.
Quenching: Improves hardness. Must be followed by tempering to reduce internal stress.
Carburizing and quenching: Improves surface hardness while maintaining core toughness.
Nitriding: Improves surface properties with minimal deformation, arranged as late as possible.
Hard compound coating: Applied after precision processing to improve mold life.
Auxiliary Operation Arrangement
Auxiliary operations mainly include inspection, deburring, rust prevention, and cleaning. Among these, inspection is the main content of auxiliary operations and plays an extremely important role in ensuring part processing quality.
| Auxiliary Operation | Arrangement |
|---|---|
| Inspection Operations | After rough or semi-finish processing, before and after important operations, before sending to external workshops, and after all processing completion. |
| Deburring Operations | Often arranged after operations prone to burr formation and before inspection and heat treatment. In single-piece production, often done after processing completion. |
| Rust Prevention Operations | Includes inter-operation rust prevention (for parts with long transfer times) and product warehousing rust prevention. |
| Cleaning Operations | Arranged before surface magnetic particle inspection and before oil sealing, packaging, and assembly. |
The comprehensive approach to processing technology routes for injected molded plastic components requires careful consideration of all these factors to achieve optimal results in mold manufacturing. The integration of traditional machining methods with modern CNC technology and advanced surface treatment processes ensures that injected molded plastic molds meet the stringent requirements of contemporary manufacturing while maintaining economic viability and production efficiency.