Analysis of Common Issues in Die Cutting and Creasing Process

Die cutting is a forming process in which a cutting die is created based on the required design pattern of the product. Under pressure, the printed material or other sheet-like materials are cut into the desired shape. Creasing is the process of creating line marks on the sheet material using a scoring knife or scoring die, or by rolling a scoring wheel on the sheet material, allowing for folding and forming at designated positions.

Generally, die cutting machines can be categorized into three basic types: flatbed die cutting, rotary die cutting, and combination die cutting, based on the shape of the die and the cutting structure.

Key Process Parameters in Die Cutting and Creasing

The main process parameters in die cutting and creasing include die cutting pressure and die cutting speed. The theoretical calculation formula for die cutting pressure is: P=KσA, where P is the required cutting force, σ is the shear stress value per unit area in the cutting process, A is the actual area of separation in the die cutting process, and K is a coefficient that takes into account practical conditions and various technical factors influencing the die cutting process. The value of K ranges between 0.76 and 1.34.

In practical production, the value of cutting force F per unit length is often determined through experiments, and then the die cutting pressure can be calculated. This can be done by setting a certain length of steel blade and steel wire on a testing machine and applying pressure to the material until the desired line mark is achieved. The pressure value P1 at this moment is recorded. Repeat this process 10 times, take the average value, and then divide the measured pressure value P1 by the total length (l) of the cut and scored lines. This will give the average die cutting force per unit length, F=P1/l.

The required die cutting pressure can be calculated using the following formula: P=K1*L*F, where P is the die cutting pressure, L is the total circumference of the die cutting area (including cut and scored lines), F is the die cutting force per unit length, and K1 is a coefficient that considers various unfavorable factors in actual production. Typically, K1 is taken as 1.3.

Die cutting speed is related to the machine's working frequency and directly affects the productivity of die cutting and creasing. Generally, an increase in die cutting speed leads to an increase in die cutting pressure.

Common Technical Issues in Die Cutting and Creasing

1. Misalignment between die cutting lines and product position

(1) Errors in the manufacturing process of the cutting die. Manual die making may not achieve the desired precision due to limitations in the skills of technicians and equipment. For products that require high die cutting accuracy, laser die making can be used as an alternative.

(2) Product specifications are inconsistent. If the product has large dimensional errors, it may be due to insufficient movement of the secondary positioning mechanism of the die cutting machine. This can be resolved by adjusting the secondary positioning mechanism to increase its movement distance.

(3) Misalignment between die cutting lines and product grids. The solution is to recalibrate the cutting die based on the product requirements and align the product with the die cutting lines.

(4) Differential deformation or elongation of materials caused by different working environments can also lead to misalignment of die cutting lines. To solve this issue, efforts should be made to ensure that die cutting takes place in the same working environment as the production process or that the working environments have consistent conditions (e.g., temperature and humidity).

2. Unclear crease lines

Unclear crease lines typically fall into two categories: dark lines, which refer to undesired crease lines, and burst lines, which occur when the die cutting pressure is too high and exceeds the material's withstand pressure, resulting in product breakage. The main causes are as follows:

(1) Inappropriate selection of creasing lines and creasing dies. It is important to choose the correct creasing die model and creasing line height. When selecting the die cutting material, the depth of the creasing die should be equal to the thickness of the material, and the width should be 1.5 times the thickness of the paper plus the height of the creasing line, ensuring the same height as the cutting blade.

(2) Inaccurate pressure from the die cutting machine. Adjustments should be made to the pressure control mechanism of the die cutting machine to ensure that the pressure meets the appropriate standards.

3. Excessive burrs and debris during die cutting

(1) Insufficient sharpness of the cutting edge. If the cutting edge of the die cutting blade is not sharp enough, or if the quality of the blade is substandard, it can result in an uneven and rough cutting edge. To ensure product quality, it is necessary to select high-quality steel blades that are suitable for die cutting.

(2) Severe wear of the die cutting blade. Die cutting blades are subject to wear during regular use. If the wear is severe and not replaced in a timely manner, the blade will lose its effectiveness. Therefore, regular inspections of the blade edge should be conducted and replacements should be made when necessary.

(3) Inappropriate selection of the die cutting blade and rubber pad. The rubber pad must have a certain hardness to allow for smooth cutting of the paper. Accordingly, different rubber pads should be selected based on the characteristics of the paper. Additionally, the rubber pad should be installed at a distance from both ends of the die cutting blade, typically with a minimum distance of 2mm. Improper distance can result in uneven force on the rubber pad, causing the pad to break before the product is completely cut, thereby generating a large amount of paper dust and debris. Furthermore, it is important to ensure that the number, hardness, and height of the rubber pads are evenly distributed on the entire template to ensure a standardized operating process.

4. Adhesion between the product and the cutting die

In actual production, it is common for the product to become stuck to the cutting die. This is mainly due to the low hardness of the rubber pad, which prevents the paper from bouncing back. To address this, rubber pads with different hardness levels can be used according to the specific situation, or additional rubber pads can be applied in local areas. Another possibility is that the cutting edge of the die cutting blade is not sharp enough while the thickness of the product is too large, leading to adhesion between the product and the die. In such cases, the condition of the cutting die should be regularly checked, and replacements should be made in a timely manner. The angle of the blade edge may also contribute to the adhesion issue. Different types of cutting edges, such as double-edge, inner-edge, and outer-edge blades, should be selected appropriately to avoid adhesion issues.