Die casting molds are one of the four essential elements in die casting production (alongside casting materials, equipment, and processes). Cracking in the die casting mold cavity is a common and severe failure mode, directly impacting production scheduling. The primary causes of mold cavity cracking include direct contact with high-temperature metal liquids, erosion during the filling stage by high-speed flowing metal, and the impact of high pressure during the pressurization stage. Additionally, the severe fluctuation of mold steel temperature in each casting cycle contributes to this issue.

A proficient die casting company embraces the challenges in various processes. Addressing and resolving different process issues enriches manufacturing experience, enabling the production of satisfactory parts for diverse clients.

Factors Related to Die Casting Mold Cracking

1.1 Mold Design

1.1.1 Material Selection

For the forming parts of die casting molds, specific hot work mold steels are commonly chosen. Grades like 1.2343 and 1.2344 are suitable for large molds, while 1.2367 is preferred for parts where erosion is severe. However, due to processing difficulty and hardenability issues, 1.2367 is not ideal for very large forming parts. It’s recommended to use high-grade varieties processed with electroslag remelting technology, as they have lower impurity content and less variation between core and surface, reducing the risk of cracking.

Model	High-Temperature Strength	High-temperature toughness	High-temperature wear resistance	Machinability
1.2343/8402/H11/SKD6
1.2344/8407/H13/SKD61
1.2367/8418

1.1.2 Product Geometric Shape

Common risks include:

• a. Deep groove structures with small draft angles or excessive length-to-diameter ratios;
• b. Insufficient local radii causing stress concentration;
• c. Inadequate draft angles in areas eroded by molten aluminum;

All of these common risks need to be improved from a product design perspective, as follows

1.1.3 Mold Geometric Shape

Common risks include:

• a. Insufficient local radii leading to stress concentration;
• b. Sharp angles and knife edges caused by insert structures;
• c. Weak structures in mold filling channels;

All of these common risks need to be avoided from a parting design perspective.

1.1.4 Gating System Design

Common risks include:

• a. Insufficient radii in gate design;
• b. Gates facing weak structural areas;

These common risks need to be avoided from the gating system design point of view, see the following figure:

1.1.5 Cooling System Design

Common risks include:

• a. Excessively deep cooling holes leading to insufficient local strength;
• b. Poor cooling layout causing significant temperature distribution differences and stress;

These common risks need to be balanced from a cooling system design perspective, as below:

1.2 Mold Manufacturing

1.2.1 Material Control

As per the North American Die Casting Association (NADCA) standards, high-quality materials from mainstream suppliers typically meet or exceed these standards, reducing the likelihood of defects.

1.2.2 Machining Methods

Electrical Discharge Machining (EDM) can affect the surface composition and structure of the mold, leading to micro-cracks and stress concentration. Minimizing the use of EDM can significantly reduce the risk of mold cracking.

1.2.3 Machining Parameters

Adhering to the recommended machining parameters for the selected material, such as cutting speed, feed per revolution, cutting depth, and tool type, is essential. Deviating from these guidelines can result in residual stress and potential stress cracks.

1.2.4 Stress Relief Grinding

EDM is often unavoidable in large die casting mold processing. Post-EDM, it’s crucial to grind and polish the affected areas as per the material guidelines to remove harmful structures and alleviate stress.

1.2.5 Heat Treatment Process

The heat treatment of mold materials includes softening, stress relieving, and hardening. Following the detailed requirements for quenching media, cooling rate, and tempering intervals in the material guidelines ensures the internal and external structure of the material meets expectations.

1.2.6 Nitriding Control

Nitriding enhances the mold’s surface wear resistance, delaying the erosion caused by molten aluminum. However, it also makes the surface more brittle and increases the risk of cracking. The depth and conditions of nitriding must be strictly controlled, especially for large parts (0.03-0.07 depth).

Process Design and Its Impact

1.3.1 Hot Mold Process

The method of starting production with a cold mold greatly affects the life of the mold, especially due to thermal stress caused by alternating cold and hot impacts. It’s recommended to preheat the mold using a mold temperature machine rather than starting directly with a low-pressure hot mold. During a cold mold start, typically 5-10 low-pressure, low-speed injection cycles are needed to raise the mold temperature. Therefore, it’s crucial to avoid initiating high-speed, high-pressure injection cycles too early.

1.3.2 Cooling Techniques

The chosen cooling process in production significantly impacts the thermal stress on the mold surface. This is evident in the maximum and minimum temperature differences during the die casting cycle and on the mold surface. The former often leads to cracking and crack development, while the latter can cause stress cracks.

A good cooling process should consider controlling the cooling water time, cooling during the solidification stage, and avoiding constant cooling throughout the cycle. It’s also important to control the temperature drop from spraying and rely less on spraying for cooling. Ensuring a compact cycle time is crucial to avoid large fluctuations in mold temperature differences within the cycle.

1.3.3 Injection Speed

Erosion from molten aluminum significantly damages the mold. A lower gate speed is more beneficial for mold life. To balance filling quality, it’s advised to keep the gate filling speed within 30-50m/s. If possible, try to control the filling speed of each branch gate below 45m/s.

1.3.4 Boost Pressure

Reducing casting pressure is beneficial for extending mold life. The recommended injection pressure should be below 100MPa. Choosing the right timing for boosting pressure is also crucial for mold longevity, so avoid boosting too early or too late.

Maintenance and Care for Prolonging Mold Life

1.4.1 Production Scheduling Habits

Production scheduling habits significantly affect mold life, mainly due to temperature fluctuations caused by intermittent production. Continuous 24-hour production leads to a dynamic equilibrium in mold temperature, reducing the temperature difference in each cycle and across different mold areas. Intermittent production, leading to frequent cold mold startups, increases thermal stress, causing cracks and crazing, negatively impacting mold life.

1.4.2 Mold Spot Checks

Timely removal of aluminum adhesion on the mold surface can reduce demolding resistance and delay crack development. For areas severely eroded by molten aluminum, electro-discharge coating is recommended to enhance local wear resistance and delay the onset and development of crazing.

1.4.3 Mold Maintenance

Periodic stress-relief annealing can eliminate thermal stress to some extent. Cleaning the mold surface of aluminum adhesion and dirt reduces erosion. Regular checks for proper mold closing can prevent excessive squeezing and damage during operation.

Conclusion and Preventative Measures

To prevent die casting mold cracking, it’s essential to:

1. Minimize occurrences of sharp angles, insufficient fillets, and inadequate draft angles in mold design. Collaborate with product design early to mitigate risks.
2. Be cautious in selecting steel materials with poor through-hardening properties for large molded parts. Avoid excessively high hardness and deep nitriding layers to prevent significant hardness differences within the workpiece.
3. Opt for lower gate speeds, reduced boost pressures, and appropriate boosting timing in the process design. Shorten the die casting cycle to minimize temperature variations.
4. Reduce downtime and strictly control the cold mold startup process. Preheating molds with a mold temperature machine can help stabilize temperature fluctuations during startup.

The post Analysis of Cracking Factors in Large Die Casting Molds appeared first on Prototool written by Prototool.

Die casting stands out as a prominent metal casting technique, characterized by the application of high pressure to molten metal within a mold cavity, drawing parallels to the injection molding of plastics. This method is especially favored for producing a vast number of small to medium-sized castings, making it the most widely used among various casting processes. Compared to other casting techniques, die casting boasts a smoother surface finish and superior dimensional consistency. However, it’s crucial to note that improper operations and parameters can lead to a myriad of die casting defects.

Flow Marks and Patterns in Die Casting

When examining the surface of die-cast parts, one might notice streaks that align with the direction of the molten metal flow. These streaks, distinct from the base metal color, exhibit non-directional patterns and do not show signs of progression.

Understanding the root causes of these flow marks is essential to mitigate such die-casting anomalies. Here are some primary reasons behind their formation:

Key Causes of Flow Marks

1. Low Mold Temperature: An insufficiently heated mold can lead to premature solidification of the molten metal, resulting in these streaks.
2. Poor Gating Design and Inadequate Sprue Positioning: The channels guiding the molten metal into the mold, if not designed optimally, can disrupt the flow, leading to these defects.
3. Low Material Temperature: If the molten metal isn’t hot enough, it might not flow smoothly, causing irregularities on the surface.
4. Slow Filling Speed and Short Filling Time: A slow or inconsistent pour can result in uneven cooling and solidification, leading to visible flow marks.
5. Inefficient Pouring System: An improperly designed system can hinder the smooth flow of molten metal, causing these patterns.
6. Inadequate Venting: Without proper venting, trapped air can disrupt the flow of the molten metal, leading to surface imperfections.
7. Improper Spraying: Inconsistent or improper spraying can affect the temperature and flow of the molten metal, leading to these defects.

Dendritic Cracking in Die Casting

Upon inspecting die-cast parts, one might notice a network or tree-like pattern of cracks on the surface. These dendritic cracks can become more pronounced and widespread with an increasing number of casting cycles.

Understanding the root causes of dendritic cracking is essential for producing high-quality die-cast parts. Here are the primary reasons for the emergence of this defect:

Main Causes of Dendritic Cracking

1. Cracks on the Die Casting Mold Surface: The presence of even minor cracks on the mold surface can lead to the formation of dendritic patterns on the cast part.
2. Uneven Preheating of the Die Casting Mold: If a mold isn’t heated uniformly, it can cause the molten metal to solidify unevenly, leading to dendritic cracks. Ensuring consistent and proper preheating is crucial to prevent such defects in die-cast parts.

Cold Shuts in Die Casting

Cold shuts are one of the common imperfections in the die-casting process. When inspecting die-cast parts, you might notice distinct, irregular, and linear indentations on the surface. These indentations can either be penetrating or non-penetrating. They are typically narrow and elongated, and sometimes, their adjoining edges appear smooth. Under external forces, there’s a possibility that these areas might break or separate.

Understanding the root causes of cold shuts can help in mitigating this die casting anomaly. Here are the primary reasons for the emergence of this defect:

Main Causes of Cold Shuts

1. Incomplete Metal Fusion: When two streams of molten metal meet but don’t fully merge, and there are no impurities between them, the resulting bond can be weak. This scenario often leads to the formation of cold shuts.
2. Low Pouring or Mold Temperature: If the temperature of the molten metal or the die casting mold is too low, it can prevent the metal streams from merging properly, resulting in cold shuts.
3. Improper Gate Location or Extended Flow Path: The position of the gate or an overly long flow path can hinder the smooth flow of molten metal, increasing the chances of cold shuts.
4. Slow Filling Speed: A slow pouring speed can make the hot metal harden too soon and not completely fill the mold, which can result in cold gaps or defects. Ensuring an optimal filling speed is crucial to prevent such casting imperfections.

Shrinkage Defects (Sink Marks)

Visual Inspection:

Upon examining the surface of thicker sections of die-cast parts, one can observe smooth indentations that resemble the shape of a saucer.

Causes of Shrinkage Defects:

1. Contraction-Induced Issues:

• Improper design of the die-cast part leads to significant thickness variations.
• Incorrect positioning of the gating system.

• Insufficient pressure during the casting process and short holding time.
• Overheating in certain areas of the die-casting mold.

2. Inadequate Cooling System Design:

The design of the cooling system plays a pivotal role in the solidification of the molten metal. An inefficient design can lead to uneven cooling, which in turn can cause shrinkage defects.

3. Premature Mold Opening:

Opening the mold too early, before the metal has solidified completely, can lead to sink marks on the part’s surface.

4. Excessive Pouring Temperature:

Using a molten metal temperature that’s too high can exacerbate the shrinkage issue. It’s crucial to maintain an optimal temperature to ensure uniform solidification and minimize casting anomalies.

Recommendations for Avoiding Shrinkage Defects:

To mitigate the risk of shrinkage defects, it’s essential to focus on the design phase. Ensuring uniform wall thickness, optimizing the gating system, and maintaining the right casting parameters can go a long way in producing high-quality die-cast parts. Regularly monitoring and adjusting the process variables, coupled with routine mold maintenance, can further enhance the casting quality and reduce the occurrence of such flaws.

Die Marks

Visual Inspection:

On the surface of the castings, there are traces left from contact with the die casting mold cavity or step-like marks appearing on the surface of the castings.

Causes of Die Marks:

Ejection Component-Related Causes

1. Wear on the end face of the ejector pin.
2. Inconsistent adjustment lengths of ejector pins.
3. Poor alignment between parts of the die-casting mold cavity.

Assembly or Moving Part-Related Causes

1. Loosening of the inserted parts.
2. Wear or loosening of moving parts.
3. The side surface of the casting is formed by the interlocking inserts of the moving and fixed molds.

Soldering Marks in Die Casting

Visual Inspection:

Upon examination, one can observe small patches on the die-cast surface where the casting metal has unintentionally fused with the die. These patches, which can be either metallic or non-metallic, can peel off under external forces. Once they detach, the affected areas on the casting surface can appear either shiny or have a dark gray hue.

Causes of Soldering Marks:

1. Presence of Residual Material: The die cavity surface may have remnants of metal or non-metallic substances.
2. Impurities Introduced During Casting: During the casting process, impurities can be introduced and adhere to the die surface.

Lamination Defects

Visual or Destructive Inspection:

Upon inspection, certain areas of the die-cast part display evident metallic layers.

Causes of Lamination Defects:

1. Insufficient Mold Rigidity: During the metal filling process, the mold may vibrate if it lacks the necessary rigidity.
2. Plunger Movement Issues: Inconsistencies or crawling phenomena in the plunger’s movement during the shot phase can lead to these defects.
3. Improper Gating System Design: The design of the gating system plays a crucial role in ensuring a defect-free casting. An improper design can lead to laminar defects.

Metal Erosion in Die Casting

Visual Inspection:

Upon examination, certain areas of the die-cast part’s surface display a noticeable rough texture.

Causes of Metal Erosion:

1. Gating System Issues: The improper positioning, direction, and shape of the internal gating system in the die-cast mold can lead to turbulent flow of the molten metal, increasing the risk of erosion.
2. Inadequate Cooling: If the turbulent areas of the molten metal within the gating system are not cooled sufficiently due to casting conditions, it can exacerbate the erosion effect on the mold’s surface.

Cracking in Die-Cast Parts

Visual Inspection:

When the die-cast component is immersed in an alkaline solution, the areas with cracks appear in a dark gray hue. The damage to the metal matrix and the opening of the cracks can be linear or wavy in nature. These cracks are narrow and elongated, and they tend to propagate or grow when subjected to external forces.

Causes of Cracking:

1. Alloy Composition Issues:

1. Excessive iron content or insufficient silicon content in the alloy.
2. Harmful impurities in the alloy at high levels can reduce the alloy’s ductility.
3. Aluminum-silicon alloys or aluminum-silicon-copper alloys with high zinc or copper content.
4. Aluminum-magnesium alloys with an overly high magnesium content.

2. Casting Process Issues:

2. Short mold retention time and brief pressure maintenance time.
3. Parts of the casting with significant wall thickness variations.

3. Force Imbalance:

3. Excessive localized clamping force, leading to uneven forces during ejection.

Navigating the Complexities of Die Casting

There are many other types of die-casting defects, and we will have the opportunity to explain each of them carefully in the future. At Prototool, we pride ourselves on our expertise in die casting services. Our skilled team can fix various defects to ensure the end product is top-notch in quality and durability. We’re dedicated to being excellent and always getting better, making Prototool a dependable partner for your die-casting requirements. Trust us to navigate the complexities of this process and deliver exceptional results every time.

The post Common Die Casting Defects: A Brief Overview of Causes and Solutions appeared first on Prototool written by Prototool.

Die casting, and injection Molding is probably naming you’ve heard of, but you may not fully understand either method or its differences. Depending on the specifics of your application or components, you may be able to choose between die casting and injection Molding, two of the most frequent manufacturing processes. Which one is the best: Die casting vs Injection Molding?

Each method of manufacturing has its advantages and disadvantages. Due to the similarities between the methods, designers and engineers may have difficulty selecting which manufacturing method is best for satisfying the demands imposed on the component manufacturer over which they are responsible.

Both die casting and injection Molding are widely used in the industry. Many materials used in homes, offices, and other locations were likely created using one of these two methods.

A clear vision of the final project can help you choose the proper materials. If, on the other hand, you’re not sure which technique is best for you, this guide tends to portray a thorough comparison that will choose you between Die casting vs Injection Molding; keep reading!

Die Casting

Die casting is a high-pressure metal casting process used in industry. All the while, the metals are heated to the melting point. The liquid metal is then subjected to tremendous pressure, where it is reshaped. The efficacy of this strategy has been recognized from the beginning of time. In fact, it dates back to the 1850s.

Die casting is an excellent method for making geometrically complicated components since the metals are kept in a liquid state throughout the operation. This method requires using die-casting equipment with either a built-in or separate furnace.

At this point, the metal used as the raw material has been heated to the point where it is liquid. Aluminum, zinc, and coppers are nonferrous metals and the most common choices.

Pros Of Die Casting

Die casting is a very efficient method for producing large quantities in rapid succession since it is a highly repeatable process. These are some additional benefits of die casting:

• Precision and dimensional stability
• Reducing or doing away with secondary, tertiary, or final production steps
• Possibility of producing complex geometries
• Standardized subassemblies

Injection Molding

Generally, this is one of the most productive modern production methods. Many companies that make custom belt buckles rely on it. Raw materials may be created from a wide variety of resources, including metal, glass, confections, and elastomers.

Yet, plastic is used more often than any other basic material. Many polymers, such as polyethene, ABS, nylon, polypropylene, and thermoplastic polyurethane, are often used.

Injection Molding of plastics and other polymers may produce almost any shape or form desired. In addition, it may be used to make plastic components with thin walls, which can be used for various uses. Plastic housing is the most popular, and it’s utilized to make all sorts of things, from electrical components’ insulation to car dashboards. A further case in point is home appliances.

Pros of Injection Molding

The following are most common benefits of opting for injection moulding:

• The price of plastic-moulded parts may be lower than that of metal ones depending on their volume.
• Parts manufactured using plastic injection Molding are insulators of the highest grade.
• Greater malleability during the casting process
• Accommodates a wide range of plastic and polymer types
• It’s not uncommon for plastic moulds to have fillers added to them to increase the material’s strength.

Differences: Die Casting vs Injection Molding

Moulding and casting are, unsurprisingly, very comparable procedures. However, there are a few key distinctions, most notably the materials used in production. 

Possibilities of the Method

If you go back and read how to implement each tactic, you’ll see that they’re quite similar. However, not every process makes use of the same components or is conducted under identical environmental circumstances.

In plastic injection Molding, controlling the temperature is essential. Temperatures vary between the barrel, the nozzle, and the mould. Both low temperatures and high ones will induce flaws in the product.

Differences in precision and accuracy in measurements

Each metal alloy has its own tolerance requirements that determine how close together a component may be cast during the die-casting process. A uniform tolerance grade is assigned to each metal. Size and storage capacity are other important considerations. On the other hand, die-casting usually results in high accuracy and tolerance.

In general, products with tighter tolerances are more accurate. However, it’s crucial to adhere to the industrial tolerance rules while making products using the die-casting method. Die casting often results in more precise and acceptable products than injection Molding, which is why it’s so popular.

Usage of Materials Varies

Die casting often makes use of metals and alloys for its base materials. In contrast, to blow Molding, injection Molding is applicable to a wider variety of materials. Metals such as steel, Aluminum, and brass may be used as raw materials for injection Molding, which is similar to plastic injection Molding but uses metals rather than polymers.

Injection Molding is a common manufacturing method, and steel and Aluminum are two common metals and alloys utilized as raw materials. This proves that injection Molding is a more flexible and comprehensive manufacturing method.

A Wide Range of Surface Finishing Choices

It’s common knowledge that production isn’t done until it’s finished. In contrast, the die-casting process often results in a highly polished final product. It’s a plus to have this operation done. Extra polishing is for show only. Injection Molding is a one-step procedure; thus, no further finishing steps are required. Even more common than die-casting is this practice.

Surface finishing techniques such as anodizing, powder coating, chem film, gold plating, impregnation, and others are all accessible for die casting. The primary goals of these coatings are to improve the product’s appearance while also enhancing its longevity, thickness, mechanical resistance, and chemical resistance. De-gating, de-flashing, cleaning, and decorating are the four primary sub-categories that fall under the overarching term “finishes” when discussing injection Molding.

Costs associated with production, such as tooling

The bulk of a die-casting operation’s budget goes toward labour and machinery. There is less manual labour required. Hence the price is mostly determined by the equipment needed to complete the process. Costs associated with creating specialized dies for precise die casting might be considerable. They are excellent examples of any kind of high-quality production method.

But injection Molding may be done at a lower cost. The price of injection Molding may be affected by a number of factors, such as the complexity of the product and the kind of raw material used. On the other hand, you may reduce the overall price by employing finishes just where they are needed and keeping the design as simple as possible.

Plastic injection manufacturing is substantially more cost-effective than die casting for the mass production of a single item. In particular, it is one of the least expensive production methods.

Moulds Comparing

Although the end products of injection Molding and die casting are similar, the two processes are vastly different in a number of critical ways.

Die casting requires a high injection pressure. Thus the casting’s mould should be rather thick to prevent deformation and breakage during heat treatment. A diversion cone is utilized to break up the high pressure caused by the flow of material since the gate of a die-casting mould is different from that of an injection mould.

Because of the high temperature (over 700 degrees) reached in the mould cavity during die casting, quenching the cavity is unnecessary. On the other hand, injection moulds need a quenching step. Die casting tooling is very corrosive. Thus it has to be cleaned and protected before it can be used.

The exhaust slot and slag collecting bag must be opened for a die-casting mould to vent gas. In contrast, ejector pins and a parting surface are all needed for injection Molding.

How to choose: Die Casting Vs Injection Molding

Plastic injection Molding is an alternative when choosing between die casting and plastic injection Molding. The first step in building any component is understanding how it currently operates. This facilitates the decision-making process. The next stage analyses the pros and cons of die casting and injection moulding for how the component works. It will then be clear to your which approach is best.

Die casting is not the optimum technique for materials that expand or contract under pressure, such as fluids. The injection moulding process is ideal for making huge quantities of identical products. However, an exceptionally high precision and accuracy standard is required to manufacture very complex components.

In certain cases, the output of one of these techniques could be up to snuff. After that, we can talk about the constraints of our budget, which is critical when looking for places to save money.

Conclusion

Numerous analyses of Die casting vs Injection Molding reveal that both processes are excellent methods for high-quality manufacturing products. Since die casting and injection moulding are two of the most widespread techniques used in production, they are naturally of interest to many businesses throughout the globe. There are advantages and disadvantages to each approach. Knowing the procedures involved and the benefits and drawbacks of each method makes it much simpler to decide which ways to apply.

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