In aluminum alloy die casting, the draft angle is a slight taper applied to the vertical surface of the part to ensure smooth demolding from the die casting mold. It can reduce friction, prevent sticking, and avoid surface defects such as scratches or warping. A reasonable draft angle design can improve dimensional accuracy, extend mold life, and improve production efficiency in the die casting process.
This article will explore the importance of draft angle, influencing factors, design standards, common design errors, and best practices. Read on to learn how to improve the quality and efficiency of die casting aluminum through scientific draft design.
Importance of Draft Angle in Die Casting
Smooth Demolding
Draft angle can effectively reduce the contact friction between the part and the mold, and reduce the risk of sticking and jamming.
This not only allows the part to be ejected from the mold smoothly and steadily, but also avoids structural damage or deformation caused by forced ejection.
Extend Mold Life
The cavity and core of the die casting mold are subjected to huge mechanical stress during repeated use.
Designing a reasonable draft angle can significantly reduce friction and wear in these areas, reduce the frequency of loss, and thus extend the service life of the mold.
Protect Surface Quality
When the draft angle is insufficient, parts are prone to scratches, pull marks, or even tears on the surface during demolding.
A reasonable draft angle can achieve clean demolding, effectively protect the surface quality of parts, and avoid additional repairs and rework in the later stage.
Reduce Costs and Increase Efficiency
Scientific draft design can not only shorten the demolding time of each production cycle, but also improve the fluency and capacity of the entire production line.
At the same time, it reduces the scrap rate and rework frequency, helping companies save raw materials and labor costs.
Improve Dimensional Accuracy
Uneven pulling force during demolding can cause dimensional deformation of thin-walled or detailed aluminium die casting components.
By setting a reasonable draft angle, this deformation can be avoided, ensuring that each product has consistent dimensions in high-pressure die casting.
Factors Affecting Draft Angle Design
Part Geometry
Narrow, deep cavities or vertical high walls increase the contact area between the mold and the part, resulting in increased friction and increased demolding difficulty.
Sharp corners and geometric mutation areas are also more prone to mold jams, which puts higher requirements on the draft angle.
Aluminum Alloy Material Characteristics
Different aluminum alloys have different cooling shrinkage rates.
The greater the shrinkage rate, the stronger the grip on the mold wall, and the larger the draft angle is required to ensure smooth demolding during the die casting process.
In addition, some materials are more prone to cracking or adhesion under stress, which also affects the draft angle design.
Surface Texture
Rough or textured surfaces have greater friction. The deeper the texture, the larger the draft angle is required to avoid scratches during demolding.
Demolding Mechanism Design
Structures such as ejectors, sliders, and cores in the mold require a sufficient draft angle to cooperate when performing demolding.
An insufficient draft angle will limit the operation of these mechanisms and even cause uneven force on parts.
The more complex the mechanism, the greater the dependence on draft angle.
Post-Processing Process
If a certain surface needs CNC machining or removal of the casting layer, theoretically, no draft angle can be set.
However, in the early stage of casting, demolding requirements must still be considered, so the processing technology will affect the initial draft design.
In addition, the thickness changes of surface treatments such as anodizing and spraying also require space to be reserved when designing the draft angle.
Recommended Draft Angle Standards
For General Surfaces
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For polished or smooth surfaces, a draft angle of 0.5° to 1° is generally sufficient for smooth demolding and maintaining appearance.
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Lightly textured surfaces require 1.5° to 2° to prevent surface tearing.
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Medium to heavy textures recommend at least 3° to avoid surface defects.
Adjustment of Structural Details
Structures such as thin ribs, deep grooves, and narrow columns are difficult to demold, and it is recommended to increase the draft angle by 1° to 2° more than the main wall.
High-wall structures have a large contact area with the mold, and it is recommended to use a draft angle of 2° to 3° to prevent deformation.
Inner walls require a larger draft angle than outer walls due to high friction and difficulty in applying demolding force.
Adjustment Methods for Complex Structures
Parts with complex geometries or concave features should be adjusted locally and cannot be generalized.
Areas with high surface roughness, deep cavities, and thin walls require additional draft angles to ensure smooth production.
Special Case: Zero Draft Angle
Applicable Scenarios
Zero draft angle design can be used on parts with extremely high precision requirements, such as vertical walls that must be kept at right angles, or certain areas that need to be machined later.
Zero draft angle is also allowed for certain aesthetic or space-constrained structures (such as shells), provided that the production volume is low and the mold wear is controllable.
Risks and Challenges
Zero draft angle design is prone to cause part sticking, requiring higher demolding force, and easily causing surface damage or part deformation.
High-frequency use accelerates mold wear, greatly shortens maintenance and replacement cycles, and increases production costs.
Design Alternatives
Minimum draft angles (such as 0.5°) can be used as a compromise to provide demolding support while maintaining almost unchanged appearance.
Using high-performance mold coatings or lubricants to reduce friction makes zero draft areas easier to demold, but it will increase costs.
The draft angle can be designed on hidden or secondary surfaces, which does not affect appearance and ensures manufacturability.
Common Design Errors and Solutions
Ignored During the Design Phase
Error: Not setting the draft angle during the modeling phase is one of the most expensive errors. Modification after mold manufacturing will cost a lot of time and money.
Solution: Be sure to design the draft angle during the 3D modeling phase before submitting the mold.
Uniform Draft Angle for All Surfaces
Error: Different structures require different draft angles, and a one-size-fits-all uniform design often leads to demolding difficulties or product defects.
Solution: The draft angle needs to be customized according to the part position, function, and degree of contact with the mold.
Ignored Surface Finish
Error: The rougher the surface of the casting, the more difficult it is to release from the mold. If the draft design is not coordinated, it is very easy to cause tearing or warping during demolding.
Solution: During the design review, both the surface treatment method and the draft angle must be considered to ensure that the matching of the two will not affect demolding and dimensional accuracy.
Believe the Zero Draft Is Always Feasible
Even if machining is to be performed later, if there is no draft angle during early demolding, the part may be deformed or scratched and cannot be used.
It is recommended to use simulation software analysis or consult a professional mold engineer to determine whether a zero draft design can be adopted.
Practical Suggestions for Draft Angle Design
Think Ahead
Draft angles should be considered in the early design stage rather than as a remedy later. Planning can reduce rework and speed up mold making.
Verify with Simulation Software
Use CAD draft analysis tools and mold flow software to simulate actual demolding forces and mold performance, predict potential demolding risks in advance, and optimize the design.
Apply DFM Concepts
Design needs to take into account formability, demoldability, and cost-effectiveness, and draft angle is the core of DFM.
It is necessary to ensure that the draft direction is consistent with the opening and closing direction of the mold to avoid design errors that hinder normal demolding.
Collaborate with Suppliers Early
Die casting plants have rich experience and can provide advice on mold behavior and material properties.
Early cooperation helps improve design accuracy. CEX Casting can provide DFM reports and mold recommendations to help customers optimize the draft strategy.
CEX Casting’s Draft Advantage
CEX Casting focuses on high-precision aluminum alloy die casting and mold design, ensuring that the draft angle is reasonable and feasible from the early stage of product development.
We help customers develop the best draft solution for complex die casting parts through internal mold flow analysis and DFM reports.
The integrated production process from mold manufacturing to automatic high-pressure die casting and post-processing ensures smooth part demolding and stable surface quality.
Conclusion
A reasonable draft angle design is essential for efficient, low-cost, and high-quality aluminum die casting components.
It helps reduce friction, improve mold life, and ensure smooth part ejection.
As a leading die casting manufacturer, CEX Casting tailors end-to-end die casting solutions for you.
Contact us today to get our professional draft design suggestions to improve the performance of your next die casting project.