In the field of die manufacturing, Wire Electrical Discharge Machining (WEDM) has become a widely adopted technique. However, during online cutting operations, molds are often prone to deformation and cracking, leading to part scrapping and increased production costs. As a result, the issue of mold deformation and cracking in wire-cutting machining is receiving growing attention from industry professionals. Despite years of practice, there remains a lack of comprehensive understanding regarding the causes of such defects, which often leads to conflicts between the WEDM department and incoming material processing teams. In reality, the factors contributing to deformation and cracking are numerous, including material properties, heat treatment processes, structural design, machining sequences, and issues related to workpiece clamping and electrode wire selection. The question is: can we identify patterns or laws governing these deformations and cracks? Through extensive research over the years, the author has developed several effective strategies to prevent such issues.
**1. Main Causes of Deformation and Cracks**
Through extensive analysis of real-world cases, the following factors have been identified as major contributors to deformation and cracking in wire-cutting processes:
**1.1 Part Structure-Related Issues**
1. Molds with long and narrow shapes are more likely to deform. The degree of deformation depends on the complexity of the shape, aspect ratio, and the width ratio between the cavity and frame. More complex shapes and higher aspect ratios lead to greater deformation. Typically, the cavity tends to sink inward, while the punch may warp.
2. Sharp corners in quenched cavities are prone to cracking, especially in complex shapes. The likelihood of this depends on the material composition and heat treatment process.
3. When cutting cylindrical walls, deformation is common, often causing the shape to shift from round to oval. If notches are cut, the part may even burst.
4. Deep notches on the outer surface of parts tend to cause deformation, typically resulting in the narrowing of the opening. The extent of deformation depends on the notch depth and material properties.
**1.2 Heat Treatment-Related Problems**
1. Improper forging temperatures, either too high or too low, can lead to internal stresses and deformation.
2. Excessive grain growth due to high final forging temperatures or slow cooling after forging can result in carbide precipitation and reduced material integrity.
3. Inadequate spheroidizing annealing can lead to excessive pearlite structure, increasing the risk of cracking.
4. Overheating during quenching can coarsen austenite grains, reducing toughness and increasing brittleness.
5. Failure to temper quenched parts in a timely manner can leave residual stresses that promote cracking.
**1.3 Machining Process-Related Factors**
1. Removing large areas of material without prior hollowing out can cause deformation due to stress release.
2. Lack of starting threading holes can force cutting from the outside, leading to deformation, especially in quenched parts.
3. Poor grinding parameters, such as incorrect wheel grit, feed rate, or cooling methods, can introduce micro-cracks and burns.
**1.4 Material-Related Issues**
1. Severe carbide segregation in raw materials increases the risk of cracking.
2. Materials with poor hardenability, like T10A and T8A, are more prone to deformation.
**1.5 Wire Cutting Process-Related Problems**
1. Incorrect cutting paths can lead to distortion.
2. Improper clamping methods or pressure points can cause deformation.
3. Inappropriate electrical parameters can result in cracking.
**2. Preventive Measures**
Understanding the root causes allows for targeted measures to prevent deformation and cracking. The following strategies are recommended:
**2.1 Select Appropriate Materials and Optimize Heat Treatment**
1. Thoroughly inspect raw materials for chemical composition, microstructure, and defects.
2. Use vacuum or electroslag remelting steels to improve quality.
3. Avoid materials with poor hardenability and high deformation tendencies.
4. Forge billets properly with appropriate forging ratios (preferably 2–3).
5. Improve heat treatment by using vacuum or protective atmosphere heating, graded quenching, and austempering.
6. Choose suitable cooling rates and media.
7. Temper quenched steel promptly to reduce residual stresses.
8. Perform long-term tempering to enhance fracture toughness.
9. Ensure full tempering to achieve stable microstructures.
10. Tempering multiple times to eliminate retained austenite and new stresses.
11. Address second-type temper brittleness in high-temperature quenched steels.
12. Apply diffusion or spheroidizing annealing before chemical treatments to refine the original structure.
**2.2 Optimize Mechanical Processing**
1. Ensure the workpiece blank size is adequate and avoid cutting near edges.
2. Hollow out large cavities or narrow punches during billet preparation to reduce stress.
3. Increase corner radii or drill relief holes to relieve stress concentration.
4. Drill threading holes in the billet before quenching to maintain internal stress balance.
**2.3 Optimize Wire Cutting Parameters**
**2.3.1 Cutting Method**
1. Use rough and finish cutting with adjustments based on deformation after the first pass.
2. Use single-point clamping to allow free deformation and avoid interference.
3. Arrange cutting paths based on part geometry to minimize deformation.
**2.3.2 Process Parameter Selection**
1. Use high peak, narrow pulse parameters to remove material efficiently and avoid overheating.
2. Monitor pulse discharge to control localized heating and prevent cracks.
3. Use low pulse energy for precision machining to reduce crack formation.
By implementing these strategies, manufacturers can significantly reduce the occurrence of deformation and cracking, improving both efficiency and product quality in wire-cutting operations.
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