What is punch and die clearance？
Die clearance refers to the distance between the punch and the die in a mold, which significantly influences mold performance and part quality. Adjusting and controlling die clearance is a critical aspect of mold manufacturing and maintenance.
Firstly, there are several methods to adjust the die gap, including the light transmission method and the shim method. The light transmission method is suitable for small molds, where the size and uniformity of the gap between the punch and the die are adjusted by shining light and observing through the material pouring hole at the bottom base of the die.
The shim method involves placing metal shims appropriately around the edge of the die and adjusting the gap by observing whether the punch enters the edge of the die smoothly while closing the mold.
Secondly, the size of the die gap directly affects the quality of the stamped parts. Too large and too small gaps can adversely affect stamped parts. For example, when the gap is too large, it can lead to increased burrs and a greater cross-section collapse angle, affecting dimensional accuracy.
On the other hand, when the gap is very small, it can lead to an increase in the material's resistance to deformation, requiring greater shear force. Therefore, reasonably selecting and adjusting the die gap is very important.
Furthermore, measuring the die clearance is essential to ensure the normal operation of the mold and improve product quality. Special tools for measuring die clearance can be used for accurate measurement.
Optimal clearance between punch and die
CNC punching machine and CNC turret punching machine can produce shear crack joint, maintain balanced cutting force, ensure good punching quality and extend mold life.
It is recommended to consult the punch and die clearance table (as shown in Table 1) for best results.
Table 1. Punch and clearance chart
Unit: mm
| Thickness | mild steel | Stainless | Aluminum* |
| 0.8 | 0.15-0.20 | 0.20-0.24 | 0.15-0.16 |
| 1.0 | 0.20-0.25 | 0.25-0.30 | 0.15-0.20 |
| 1.5 | 0.30-0.38 | 0.37-0.45 | 0.22-0.30 |
| 2.0 | 0.40-0.50 | 0.50-0.60 | 0.30-0.40 |
| 2.5 | 0.50-0.63 | 0.62-0.75 | 0.37-0.50 |
| 3.0 | 0.60-0.75 | 0.75-0.90 | 0.45-0.60 |
| 3.2 | 0.64-0.80 | 0.80-0.96 | 0.48-0.64 |
| 3.5 | 0.70-0.88 | 0.88-1.05 | 0.53-0.70 |
| 4.0 | 0.80-1.00 | 1h00-1h20 | 0.60-0.80 |
| 4.5 | 0.90-1.13 | 1.13-1.35 | 0.68-0.90 |
| 5.0 | 1:00-1:25 | – | 0.75-1.00 |
| 5.5 | 1.10-1.38 | – | 0.83-1.10 |
| 6.0 | 1.20-1.50 | – | 0.90-1.20 |
* Also applicable to copper and brass
How to choose the right clearance for punch and die ?
Choosing the die clearance value for a CNC punching machine or a CNC turret punching machine is usually done using empirical formulas and graphs.
An experienced stamping die designer and installer with a good knowledge of different products including their material, size and precision requirements will know how to design the mold to produce qualified products and reduce repair times.
The gap between the punch and the die has a significant impact on the quality of the stamped part and the service life of the stamping die.
Therefore, when designing the stamping die, a reasonable clearance should be chosen to ensure the quality and precision of the stamped parts.
A smaller clearance value should be used for parts with high dimensional accuracy and perpendicularity requirements, while larger clearance values can be used for parts with lower accuracy requirements to reduce punching force and improve die life of stamping.
There are two methods for determining punch and die clearance, by experiment and formula.
The reasonable minimum clearance value should be used when designing and manufacturing a new stamping die, taking into account deviation in production and wear during use.
In the production process, the stamping die will continually wear out, increasing the gap, so it is essential to keep the gap within a reasonable range.
(1) From experience
The percentage of die gap to material thickness:
◆ Minimum useful life of matrices: 15%
◆ Ideal clearance: 20~25%
◆ Long die life: 30%
◆ Heavy-duty die clearance: 30%
(Table 1) Recommended die clearance table
|
Thickness (mm) |
Aluminum (mm) |
mild steel (mm) |
Stainless steel (mm) |
|---|---|---|---|
| 1.00 | 0.15 | 0.20 | 0.20 |
| 1.50 | 0.23 | 0:30 | 0.40 |
| 2:00 | 0:30 | 0.40 | 0.50 |
| 3:00 | 0.60 | 0.75 | 0.90 |
| 4:00 | 0.80 | 1.00 | 1.20 |
| 5:00 | 1.00 | 1.25 | 1.75 |
| 6:35 am | 1.60 | 2:00 | 2.22 |
(2) By punch and die clearance Formula
Its value can be calculated according to the following punch and die clearance formula:
Soft Materials:
- Material thickness t < 1 mm, cutting gap c = (3% ~ 4%)t
- t = 1 ~ 3 mm, c = (5% ~ 8%) t
- t = 3 ~ 5 mm, c = (8% ~ 10%) t
Hard materials:
- t < 1mm,c = (4% ~5%)t
- t = 1 ~ 3 mm, c = (6% ~ 8%) t
- t = 3 ~ 8 mm, c = (8% ~ 13%) t
Why use correct die clearance?
◆ Extend mold life
◆ Good material return effect
◆ The burr generated is small
◆ Get a cleaner and tidier hole
◆ Reduce the possibility of sticking
◆ Part leveling
◆ The hole position is more accurate
◆ Minimum punching force is required for cutting
Impacts of excessively large or small die gaps
The effects of excessively large or small gaps on the quality of stamped parts are mainly reflected in the following aspects:
When the die backlash is too large:
- It can easily cause deformation of the workpiece or significant size deviations.
- It reduces friction between the sides of the punch and die and the material, but also mitigates the impact of uneven clearances.
- The quality of the stamped cutting surface is characterized by “large burrs, serious corner collapses, enlarged fracture zones and smaller shiny zones”.
When the die gap is too small:
- A very small gap is extremely detrimental to the useful life of the die, as there is friction between the die and the droplet material, and the smaller the gap, the more severe the friction will be.
- If the clearance of the punch and die is too small or uneven, it may scratch the surface of the part during deep drawing.
- Reducing the clearance of the punch and die can effectively reduce the deburring of stamped parts, but it also means that the die needs to undergo hardening treatment to adapt to such adjustments.
Adequacy of die clearance is crucial to ensure the quality of stamped parts. Excessive and insufficient clearances can negatively impact the quality of these parts, including but not limited to workpiece deformation, dimensional deviations, surface damage, and reduced die life.
Therefore, when designing and adjusting dies, specific stamping requirements and material characteristics must be taken into consideration to accurately control die clearance, thereby ensuring the quality of stamped parts and long-term use of dies.
What are the latest technologies and methods for adjusting mold gaps?
The latest technologies and methods for adjusting mold gaps include a variety of ways, the main purpose of which is to ensure reasonable mold gaps, improve product quality, and extend mold life. Here are some specific methods and technologies:
Adjusting screw method: This is a common way of adjusting the opening of the mold edge, utilizing the elasticity of the mold steel, in conjunction with conveniently force-applied screws, to cause a change in the opening clearance.
Upper and lower plate distance adjustment: In the segment difference mold adjustment of the press brake machine, the required segment difference gap is achieved by first adjusting the distance between the upper and lower plates, then the mold is placed in the press for pressing , observing and checking whether the quality and size of the product meets the requirements.
Concave-convex mold gap adjustment: By adjusting the gap between concave and convex molds, the production of defective products can be effectively reduced. In addition, mold performance can be further optimized by adjusting the air cushion pressure of the concave mold, trimming the R-convex mold, or reducing rebound by adjusting the negative angle of the convex mold.
Use of professional design tools: SolidWorks input diagnostic tools, for example, can help identify defects in the model, such as face-to-face gap issues, thus avoiding these problems in the design phase.
Unguided Punch Installation and Adjustment: Installation and adjustment of an unguided punch is relatively complex, requiring the punch to be placed in the center of the press and supported on blocks, while adjusting the nuts on the press slider to complete the adjustment.
Readjusting mold gaps: When the mold gap is too large or uneven, the mold gap needs to be readjusted to ensure the normal operation of the mold and product quality.
How can mold gap measurement accuracy be improved?
To increase the accuracy of mold gap measurement, current advanced measurement techniques include:
1. 3D Scanning Technology:
This non-contact measurement method uses optical principles or laser interference principles to perform a full-scale scan of the casting mold, obtaining high-precision three-dimensional data. Compared with traditional contact measurement methods, 3D scanning technology can provide faster and more accurate results.
Furthermore, optical and non-contact three-dimensional laser scanning techniques can quickly and accurately measure against original CAD to determine geometric sizing and tolerance (GD&T), thus helping manufacturers regularly monitor mold quality and identify and correct problems.
2. Coordinate measuring machine:
With advanced sensor technology and measurement algorithms, it provides a high level of measurement accuracy, usually at the micron level. This device is particularly suitable for high-precision product measurement requirements in SMC molds, accurately controlling quality and optimizing the production process.
3. Real-time measurement mechanisms:
This specifically involves a mechanism for real-time measurement of glass mold clearance. This technology changes the way mold clearance is measured in existing technology, improving production efficiency and the quality of the entire casting system.
4. Stamping mold closing gap monitoring method:
Through specific experimental verification, this method can accurately measure the mold closing gap, with an accuracy of up to 0.01 mm. This indicates its applicability to a variety of stamping mold closing gap monitoring, reducing mold installation and debugging time, improving the quality of stamped parts and saving costs.
During the mold manufacturing process, how can we effectively prevent and control mold clearance problems?
Effectively preventing and controlling mold clearance problems during the mold manufacturing process is a complex but crucial task. Here are some methods that can be applied:
Considerations during the design phase:
When designing and manufacturing stamping molds, it is important to ensure adequate space between the male and female dies. This not only helps maintain consistency in clearance, but also simplifies the manufacturing process. In addition, for irregularly shaped parts, it is necessary to accurately determine the dimensions and tolerances of the workpieces of the male and female dies.
Machining Precision Control:
To ensure a minimum stamping gap (such as 1 μm), strict control of the workshop temperature is necessary, as the part accuracy is significantly related to the ambient temperature. This means that temperature control is one of the key factors during precision machining.
Application of mold fitting techniques:
Problems with mold surface clearance can be solved through deformation processing adjustment methods. This includes discussion of mold surface processing adjustments and obtaining adjusted mold surfaces. In addition, methods such as local pressure compensation of the pressing plane and other viable mold surface gap adjustment solutions can be used.
Techniques to avoid burrs:
During double-sided negative clearance stamping without burrs, if burr problems are found that are difficult to eliminate, a deburring process can be carried out on the mold to eliminate these burrs.
Mold clearance design:
When designing mold gap, a calculation method can be used to determine the amount of gap change caused by thermal deformation, reducing mold machining and assembly time.
Wire breakage prevention:
When using electrical discharge machining with rapid wire cutting, attention must be paid to the contact between the conductive block and the electrode wire to avoid wire breakage caused by poor contact, which is crucial to maintain continuity and stability of the machining process.
