Surface Processing Method Selection

To correctly select processing methods, it is essential to understand the characteristics of various processing techniques and grasp the concepts of processing economic accuracy and economic surface roughness. This knowledge is particularly critical in shaping mould manufacturing, where precision directly impacts final product quality and production costs.

In any manufacturing process, numerous factors influence precision. Each processing method can achieve different levels of accuracy under varying working conditions. For example, a worker who operates meticulously and selects lower cutting parameters can achieve higher precision. However, this approach reduces productivity and increases costs. Conversely, increasing cutting parameters to improve production efficiency may lower costs but can increase processing errors, thereby reducing processing accuracy. This balance is especially important in shaping mould production, where both precision and efficiency are paramount.

Modern CNC machining centers can achieve remarkable precision in surface processing, essential for high-quality shaping mould production.

Economic Accuracy and Surface Roughness

Processing economic accuracy and economic surface roughness refer to the processing accuracy and surface roughness that can be achieved under normal processing conditions (using equipment, process equipment that meets quality standards, and workers of standard technical grades, without extending processing time). These parameters are crucial benchmarks in shaping mould manufacturing, as they represent the practical balance between precision and cost-effectiveness.

Various mechanical processing handbooks contain tables of economic accuracy and economic surface roughness levels that can be achieved by commonly used typical surface processing, as well as processing methods for various typical surfaces. For shaping mould manufacturers, these references serve as essential guides for selecting appropriate processing techniques based on specific part requirements.

Tables 2-7, 2-8, and 2-9 respectively extract the economic accuracy and economic surface roughness (economic accuracy expressed in tolerance grades) achievable by different processing schemes for typical surfaces such as outer circles, inner holes, and planes. Table 2-10 extracts the corresponding positional accuracy (expressed as errors) when processing axis-parallel hole systems with various processing schemes, for reference during selection. These tables are particularly valuable in shaping mould design and production, where precise hole positioning and surface finishes directly affect mould performance and longevity.

Table 2-7 specifically covers processing schemes for outer circular surfaces. When selecting processing methods, it is common to determine the initial approach based on experience or by consulting such tables, then modify it according to actual conditions or through process testing. This iterative approach is particularly valuable in shaping mould manufacturing, where unique part geometries often require customized processing strategies.

Key Considerations in Method Selection

From the data in Tables 2-7 to 2-10, it can be seen that there are several processing methods that can meet the same accuracy requirements. Therefore, when making a selection, the following issues should also be considered, especially in the context of shaping mould production where each decision impacts both performance and cost:

Material Properties & Heat Treatment

The nature of the workpiece material and heat treatment processes significantly influence processing method selection. For example, finish processing of hardened steel requires grinding, while finish processing of non-ferrous metals should use high-speed precision turning or precision boring to avoid clogging the grinding wheel – a critical distinction in shaping mould manufacturing where material diversity is common.

In shaping mould production, where materials range from tool steels to aluminum alloys, matching the processing method to material properties ensures both quality and efficiency. Heat-treated mould components often require specialized grinding processes to achieve the necessary surface finish and dimensional stability.

Workpiece Shape and Dimensions

The shape and size of the workpiece play a crucial role in determining the appropriate processing method. For example, holes in a multi-hole (circular hole) punching die would be complex and imprecise if processed using turning and internal grinding, and would fail to guarantee positional accuracy between holes. Instead, jig boring machines or jig grinding machines should be used – a standard practice in precision shaping mould manufacturing.

Large shaping mould components may require different processing strategies than small, intricate mould details. The accessibility of surfaces, aspect ratios of features, and overall part geometry must all be considered when selecting between conventional machining, CNC milling, EDM, or other specialized processes.

Production Type, Productivity & Economics

Processing methods must be compatible with production volume. For example, guide pillar and guide sleeve holes in die sets use drilling and matching boring processes in single-piece and small-batch production, while drilling and multi-axis boring processes are employed in mass production to ensure stable quality and high production efficiency – a distinction that directly applies to shaping mould manufacturing economics.

In shaping mould production, which often bridges low to medium volume manufacturing, the balance between setup time and production rate is critical. Investing in specialized tooling for a shaping mould production run must be justified by the number of moulds to be produced and their complexity.

Specific Production Conditions

Full use should be made of existing equipment and technological means, giving play to the creativity of technical personnel and tapping into enterprise potential. Sometimes, due to equipment load considerations, it is necessary to switch to other processing methods – a practical reality in many shaping mould workshops where equipment versatility is valued.

The skill level of available operators also influences processing method selection in shaping mould production. Complex CNC machining centers may offer superior precision but require more highly trained personnel than conventional milling machines, affecting both scheduling and quality in mould manufacturing operations.

Practical Application Examples

Automotive Shaping Mould Components

For critical automotive shaping mould components requiring IT6 tolerance and 0.4μm surface roughness, the optimal processing sequence typically involves: rough turning → heat treatment → grinding → superfinishing. This approach balances precision requirements with production economics for medium-volume mould production.

The selection of grinding wheels and coolants is particularly important in these applications to prevent thermal damage to the shaping mould surface while achieving the required finish. Statistical process control is often implemented to maintain consistent quality across production runs.

Precision Plastic Injection Moulds

High-gloss plastic parts require shaping mould surfaces with IT7 tolerance and 0.025μm roughness. These demanding specifications often necessitate: milling → EDM → polishing → diamond turning. Non-ferrous alloy inserts in these moulds are typically finished using high-speed precision turning rather than grinding to avoid surface contamination.

The polishing process for these shaping mould components requires specialized skills and may involve multiple stages using progressively finer abrasives. Automated polishing systems are increasingly being adopted to ensure consistency and reduce lead times in mould production.