Extend Tool Life - Design Operation and Maintenance

It is one thing to have an amazing die casting project and design, but another thing is to extend its life cycle. This boils down to the maintenance and operational model of the entire process.

This blog will help put in place all that is needed to enhance the product’s life. As a result, we will consider the following aspects;

  • Points for attention in die casting design
  • Points for attention in die-casting mold design
  • Points for attention in the operation of the die casting process
  • Mold maintenance

1.Points for attention in die casting design

Under this aspect, we will explore areas that should be avoided in Die Casting Designs

Sharp corners

Reflecting on the following questions is of utmost importance

When you design your product, what’s the minimum radius that you specify for die features?

Why avoid sharp corners?

Because the sharp corners can cause thermal junctions on the mold, thermal fatigue cracks develop on the mold surface in advance, resulting in premature mold failure. Sharp corners can also cause stress concentrations that can lead to die cracks or direct cracking. So the product should have certain rounded corners.

Usually, the R corner radius of die casting alloy is

Moreover, it can be measured through experiments that the larger the R angle, the better the impact toughness.

Thick walls/Heavy walls

Why avoid thick/heavy walls?
  • If the wall thickness of the casting is very thick, it will cause heat concentration or large heat conduction, resulting in thermal fatigue of the mold.
  • The special geometry of some castings, such as closely spaced fins or ribs, will make it difficult to dissipate heat in the thinner part of the mold.

Little or no draft angle

If the product has no draft angle or the draft angle is very small, it will cause a sticking phenomenon, or the product will be mechanically strained during demolding.

Therefore, when designing products, there must be a suitable draft angle.

2.Points for attention in die-casting mold design

A. The die-casting mold must have enough strength to match the die-casting machine’s injection capacity and clamping force. Die-casting molds that are too small will cause the mold to deform and collapse, causing premature failure of the mold.

The wall thickness of the mold should be sufficient, as shown in the picture.

B. The die-casting mold cannot determine the inner gate area solely by feeling or experience. If the inner gate area is too small, it will cause the mold temperature to be too high. Therefore, the product should be designed based on the data from the flow channel to the inner gate, slag discharge, exhaust, etc.

C. In the design of the runner system, it is also necessary to master the flow state control. For example, the molten metal should try to avoid the direct punch of the core and reduce the turbulent flow.

D. Design a reasonable mold temperature field, plan the transfer of mold heat, and reduce mold thermal fatigue and adhesion.

E. Make sure the mold is large enough so that the four tie bars can distribute the clamping force as evenly as possible when the mold is closed on the die casting machine. Avoid deflection and deformation of molds and equipment under load.

F. Make good use of the support column of the mold to disperse the injection strength. Disperses the impact of the shot onto the Green column. The figure below shows the amount of deformation of the mold during the die-casting process for different forms of support columns: the more support columns, the better. Reasonably arranging the positions of the support columns will have a multiplier effect. Case “d” in the figure works best.

3.Points for attention in the operation of the die casting process

In the process of die casting production, the most important thing is to control the temperature field of the mold. Control the following factors:

  • Mold preheat temperature and working temperature
  • Cooling water
  • Spray
  • Die casting cycle
  • Alloy liquid temperature

Preheat the mold:

Heating can usually be done by flame, infrared, or a mold temperature machine. It is also possible to increase the temperature of the mold by slowly injecting the aluminum liquid into the mold at the beginning, using low-speed injection without pressure.

The generally recommended mold operating temperature is as follows

Minimize the temperature difference of the mold and make the mold reach thermal equilibrium within a certain temperature range.

Four factors that must be paid attention to in cooling water circuit design

  • Suitable location
  • The right size
  • Suitable length
  • Appropriate flow

The mold should regularly maintain the cooling water pipeline, check whether it is blocked, and remove rust.

The main functions of spraying release agent are:

  • Release casting
  • Protect the mold
  • Lubricate
  • Temperature control (auxiliary function)

Do not overspray; if the mold surface temperature is lowered too much, the mold life will be reduced, and the residual spray will cause porosity.

Die casting cycle time

Extending the cycle time does not increase the life of the mold often. Instead, the extension of the cycle time will reduce the temperature of the mold, thereby increasing the temperature difference that the mold is subjected to and causing the mold to prematurely thermally fatigue.

Alloy liquid temperature

The temperature of the molten metal directly impacts the life of the mold. When the temperature of the alloy liquid increases, the mold’s corrosion will rapidly increase, and the mold will soon generate thermal fatigue cracks.

On the premise of ensuring the quality of die casting, the molten metal temperature should be reduced as much as possible. Therefore, common alloy liquid temperatures are shown in the table below.

4.Mold Maintenance

Mold maintenance is very important, and the mold should be checked and maintained regularly. When a mold problem is found, it needs to be dealt with as soon as possible.

Mold inspection

The inspection work includes appearance inspection and hardness inspection. Check the appearance of the mold for hot cracks, erosion, and aluminum sticking. The hardness of the mold is tested, and the hardness of the mold core should be greater than 38HRC.

The hardness of the new mold should be tested during the first maintenance. After that, test every 10,000 to 20,000 molds.

Stress relief

It should be ensured that the mold is subjected to a stress relief treatment after each period of use. It is recommended that the new mold can be used for 5,000 to 10,000 mold times to relieve stress. After that, a stress relief treatment is performed every 15,000-25,000 mold times.

The surface of the mold can be subjected to Micro-Precision Shot Peening to remove stress. In the following cases, micro-dense shot peening can be used to remove stress:

  • For new molds.
  • Stress Relief Use shot blasting every two times to relieve stress;
  • Molds that are more than half their lifespan

Remove surface impurities

If it is found that there is adhesion, flash, carbon deposition, rust, or corrosion on the surface of the mold, it should be removed in time.

Possible ways include:

  • Grinding technology
  • Chemical cleaning
  • Machining
  • Water based technology

Weld repair

Sometimes the mold must be repaired by welding, so several key points must be paid attention to minimize the risk of welding.

A. Preparation before welding

Remove oil stains and cracks on the surface of the mold, and machine a U-shaped pit in the area that needs to be welded. Avoid sharp V-shaped corners

B. Mold preheating

Preheat the mold to a suitable temperature, generally 538° for annealed materials and 75% tempering temperature for quenched materials

C. Heat treatment after welding

Heat treatment must be performed after welding to minimize mold stress and reduce the risk of mold cracking.

Mold storage

The mold should exist in a clean, dry place. The necessary mold parts should be sprayed with anti-rust oil.