Causes analysis and improvement methods of poor cold shut in die casting products

Posted on : March 22, 2022 By  GREFEE

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What is die casting cold shut?

The “cold shut” is a common problem in die casting production. Because several strands of liquid material are over-cooled during the flowing process but cannot be fused thoroughly, the liquid in the cold shut is not fused evenly and firmly. There would have micro-cracks during heat treatment, which affect the product quality. Generally, when the liquid temperature reaching to a level, the mold temp will be lower, and the quality of the products is higher.

There are evident, irregular, narrow, and small dented linear grains (penetrating and non-penetrating), some have smooth connection edges, which are likely to develop by the external force.

Two strands of liquid aluminum connect but do not fuse thoroughly and without things in between. The binding force of the two strands of liquid aluminum is weak; an irregular crevice at the joint of liquid aluminum without fusion.

What are the causes of cold shut in die casting products?

1.too low liquid metal pouring temp or too low mold temp

2.Substandard die casting material composition, poor flowability

3.Liquid metal filling by strands, poor fusion

4.Improper gate, too long flow path

5.Low filling speed or insufficient venting

6.Low pressure to injection ratio

How to improve the cold shut problem of castings?

1. The product is black accompanied by flow marks increase the pouring temp and mold temp appropriately

2. Poor flowability – adjust the alloy contents, enhances the flowability

3. Poor fusion – observes the flow direction of liquid aluminum, impacts between liquid metal generate cold shut which is usually vortex with flow marks. Improves the pouring system and the filling direction of the in-gate. In addition, adds slag traps on the edges of casting to enhance the filling conditions.

4. Insufficient compressing at the fore-end – change the gate position and cross-area, improve the exhaust conditions, and increase the overflow volume.

5. Gloomy product with bubbles on surface – increase the injection speed

6.whole casting has insufficient compressing – increase the ratio pressure (is not preferred)

Key inspection areas of castings:Based on our experience, areas that are likely to have poor cold shut problems are the casting surface areas, which are away from the gate and thin areas.

How does cold shut influence the products?

Cold shut affects the airtightness of products, and the appearance requirements will affect the aesthetic value of product surface, especially ones that need baking paint on surfaces.

How to assess whether a casting with poor cold shut is qualified or not?

Generally, the checking method for cold shut is by eyes after the polishing and grind finishes. Besides, we need to cut the areas that have cold shut for the convenience of the depth measurement of cold shut.

1. It is unqualified if it has the surface of re-product or surface to be painted.

2. It is unqualified if there is re-product cavity with width ≤1/50 wall thickness and length/ outline dimension ≤ 1/100

3. you cannot have the opposite side of the same area in the meantime, for the cold shut may penetrate the whole product wall.

4. Follows customers’ standards if customers specified.

Improves the quality of your die casting parts

GREFEE believes that finding out whether there are any undercasting issues in the stage of design and CAE analysis or not is essential. In addition to other factors, like the influence of die casting technology and mold. Eliminates the risks before initiating the project.

If you also got undercasting problems, contact GREFE for free technical support.

For aluminum alloy die-casting and zinc alloy die casting, the cold shut problems have been plagued many operators for a long time. With a deep understanding of die-casting material, pouring system, product features, mold structure, parameters of die casting machines, etc. Putting the ideas into practice, we can make a reliable plan to produce qualified products. Through almost 20 years of die casting experience, GREFEE has obtained a mature operation system for any die casting problems.

If you also got cold shut problems, contact GREFE for free technical support. We can help you with that!

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