Why is the injection mold thimble always easy to break? (2)

Update:24-05-2022
Summary:

2. The principle of thimble selection (1) Use a thimble […]

2. The principle of thimble selection
(1) Use a thimble with a larger diameter. That is, when there is enough ejection position, the ejector pin with larger diameter and size should be selected.

(2) The specifications of the thimble should be selected as little as possible. When choosing a thimble, the size of the thimble should be adjusted to minimize the size specifications, and at the same time, try to choose the preferred size series.

(3) The selected thimble should meet the ejection strength requirements. When ejecting, the thimble should bear a large pressure. In order to avoid the bending deformation of the small thimble, when the diameter of the thimble is less than 2.5mm, a supporting thimble should be used.
Difficulty in demolding the mold, easy to break the thimble can be reduced by various means, but it cannot be eliminated, and the maintenance cost is high in the later period

Some of the reasons and suggestions are as follows:

1. The production environment temperature is high, causing fatigue, thimble material annealing and failure

2. Whether the dimensional accuracy meets the requirements for use

3. Stress concentration.

When machining steps, the shaft is prone to form stress concentration at the parts where the diameter changes suddenly (other workpieces are at the parts where the shape changes abruptly), thus cracking or breaking when external forces (especially radial forces) are encountered in the use project.

4. Heat treatment

Most thimbles require heat treatment during the manufacturing process. Products that are not tempered after quenching or have insufficient tempering time are prone to quality problems such as excessive residual stress;

5. Surface treatment, in order to improve wear resistance, nitriding treatment is often used to check whether the nitriding process is standardized. The higher nitriding temperature causes the material to be tempered or even annealed and fail.

6. Try to avoid radial force on the ejector pin during use.

7. When designing the mold, consider the use of rounded transitions or increase of stress relief grooves in the diameter-reducing part of the hole.

8. Check the size and roughness of the aperture before installing the thimble. If the thimble is loose after the thimble hole is reamed, the thimble hole is easy to feed, and the thimble is easy to break. If it is very tight, it is easy to burn at high temperature. Die, so the fit between the thimble and the hole must be mastered.

9. Mould daily maintenance and process debugging

It is better to apply anti-seize oil every time the mold is installed. The daily maintenance is mainly to apply lubricating oil or thimble oil regularly. The thimble of the mold has a gap of 3-5μ, and the general lubricating oil can last up to 3 to 5 days after being applied. With the accumulation of dust and metal powder formed by the friction of the mold, it enters the gap between the thimble, the slider and the inclined roof tunnel. The gap of the mating surface is getting smaller and smaller, the finish is getting lower and lower, and finally it is completely ablated and stuck until it breaks.

Therefore, it is necessary to wipe the dirt on the thimble and the die surface and apply a clean lubricant. During maintenance, pay attention to applying high temperature-resistant lubricating paste to the inclined top and thimble as much as possible to form a thin film. Do not apply force with a brush, otherwise it will easily cause oil pollution to contaminate the injection molded parts.

10. In pursuit of a shorter cycle, the ejection and ejection speeds are set too fast for the mold to bear.

11. If the demoulding is too fast, the air intake at the bottom of the product is insufficient, which will form a damping state of negative pressure and increase the resistance of demoulding. The top rod will be subject to great resistance

12. If the ejector rod is relatively thin, it is also easy to be damaged.

13. The resistance is too large during ejection. Check whether the beer is strained or deformed, and appropriately improve the mold ejection slope. For the first few molds, shorten the mold opening time, just one or two seconds. It is not a system problem, but a product. The reason for too much buckling force.

14. After the shutdown, the cooling water is not turned off, and the mold temperature drops. When pressing the first mold, the cooling time is long, the tightening force is large, and the mold opening time is shortened.

15. For the material problem of the thimble, the new material Toolox44 Tuoda steel can be selected to solve the problem of material and heat treatment. Toolox is the hardest pre-hardened steel in the world. It is pre-hardened to 45-48HRC at the time of delivery, which reduces the risk and cycle of heat treatment. Nitriding Excellent performance, almost no stress, no deformation, 2-3 times higher toughness than traditional materials, can resist high temperature below 640 ° C, can completely solve the problem of fracture or deformation, is currently the best choice for high temperature stability.

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