1. Introduction
As a core component of diving equipment, the diving mask operates under harsh conditions including high pressure, seawater corrosion, and temperature variations over extended service periods. This places extremely high demands on its structural strength, sealing performance, corrosion resistance, and lightweight characteristics. Traditional diving masks are mostly manufactured using a split construction process—the frame, window, breathing valve seat, and other parts are fabricated separately and then assembled into a whole through welding or bolting. This process route has inherent drawbacks such as accumulated assembly errors, numerous sealing interfaces, and excessive structural weight. The emergence of integrated die casting technology offers a completely new technical pathway for manufacturing diving masks: the main mask structure is formed in a single die-casting operation, substantially reducing the number of components and assembly steps while simultaneously improving the overall mechanical properties and dimensional accuracy of the product.
2. Process Overview and Technical Principles
Integrated die casting is a technology that consolidates multiple components originally manufactured independently into a single cast part, formed in one step via high-pressure die casting. Its core principle is: molten metal is injected into a precision mold cavity under high speed and high pressure, completing filling and solidification within an extremely short time to obtain a near-net-shape casting.
For diving masks, the goal of integrated die casting is to integrate functional units such as the mask frame, window mounting grooves, breathing valve interfaces, and head strap fixing structures into a complete aluminum alloy casting. This process route not only eliminates stress concentrations and sealing risks associated with traditional welding or assembly, but also significantly reduces the overall weight of the product—which is crucial for diving equipment, directly affecting the diver's wearing comfort and underwater maneuverability.
3. Material Selection
The material selection for integrated die-cast diving masks requires a balanced consideration of the following performance indicators: seawater corrosion resistance, mechanical strength, casting fluidity, heat treatment strengthening potential, and cost. At present, the following categories of aluminum alloys are primarily used in engineering practice:
The AlSi10MgMn series alloy is one of the preferred materials for this application. This alloy offers excellent casting fluidity and mold-filling capability, meeting the forming requirements of the mask's complex thin-walled structures; at the same time, its corrosion resistance ranks among the best in aluminum alloys, allowing long-term service in seawater environments after appropriate surface treatment. The AlSi9Cu3 series alloy is suitable for scenarios with higher strength requirements, but it should be noted that the addition of copper moderately reduces corrosion resistance, necessitating supplementary anodizing or coating protection.
In terms of material condition, the as-cast mask blank typically requires T6 heat treatment (solution treatment + artificial aging) to significantly enhance the material's tensile strength and yield strength, meeting the water pressure bearing requirements imposed by diving depth.
4. Mold Design and Manufacturing
The mold design for the integrated die-cast diving mask represents the most technically challenging link in the entire process chain.
Parting surface design must fully consider the three-dimensional curved surface characteristics of the mask. To fit the contours of the human face, the diving mask typically features complex free-form surfaces. The selection of the parting surface directly affects demolding feasibility and the surface quality of the casting. Generally, the parting surface is positioned at the maximum cross-sectional contour of the mask to ensure that the casting can be smoothly ejected when the moving and fixed mold halves separate.
Gating system design is the key to ensuring filling quality. Given the relatively thin wall thickness of the mask (typically 2–4 mm) and its complex structure, the molten metal travels a long flow path. Therefore, a fan shaped runner or multi point ingate design is required to ensure rapid and stable filling of all areas of the cavity, avoiding defects such as cold shuts and flow marks.
Overflow and venting systems are indispensable. During the integrated die casting process, gases trapped in the cavity—if not expelled in time—will cause porosity in the casting, severely compromising the mask's airtightness and mechanical properties. Accordingly, overflow slots and venting grooves must be rationally arranged in the areas where the metal fills last.
Temperature control system has a marked influence on casting quality. Wall thickness varies considerably across different parts of the mask—thicker at the window edges and thinner in the facial contact zones. This non uniformity tends to cause inconsistent solidification shrinkage, leading to shrinkage porosity. By arranging appropriate cooling channels within the mold, the cooling rate in different regions can be precisely controlled, thereby reducing casting defects.
5. Die Casting Process Flow
5.1 Melting and Refining
Aluminum alloy ingots are melted in an electric resistance furnace or gas fired furnace, with the melting temperature generally controlled at 680–720°C. During melting, refining treatment is required—nitrogen or argon gas is purged through the melt together with the addition of a flux—to remove dissolved gases and non metallic inclusions. For products such as diving masks that demand extremely high airtightness, melt cleanliness directly determines the soundness of the casting, so the refining step cannot be overlooked.
5.2 Die Casting Forming
The selection of die casting process parameters directly affects the forming quality of the mask. The core parameters include:
Injection speed : A three stage injection process is typically adopted. The low speed stage (0.1–0.3 m/s) is used to smoothly deliver the molten metal to the ingate; the high speed stage (2–5 m/s) achieves rapid cavity filling to ensure complete replication of thin walled areas; and the intensification stage is applied to compact the solidification shrinkage.
Injection pressure : Intensification pressure is generally set between 80 and 120 MPa to ensure a dense casting structure.
Mold temperature : Controlled at 180–250°C. Too low a mold temperature causes cold shuts, while too high a temperature prolongs solidification time and reduces production efficiency.
Pouring temperature : 680–700°C, kept as low as possible while ensuring sufficient fluidity to minimise shrinkage porosity tendency.
The die casting cycle time is typically controlled within 60–120 seconds, depending on the casting size and wall thickness.
5.3 Vacuum Assisted Die Casting
Given the stringent airtightness requirements of diving masks, conventional die casting often falls short—gases trapped in the cavity are entrained by the high speed molten metal and form pores, which may become leakage paths during subsequent machining or in service. Vacuum die casting technology, by evacuating the mold cavity during the casting process (vacuum level generally controlled at 50–80 mbar), substantially reduces the gas content in the cavity and yields dense castings nearly free of porosity. For professional grade diving masks rated for working depths exceeding 50 metres, vacuum die casting has become a standard process configuration.
5.4 Demolding and Cleaning
After the mold opens, the mask casting is ejected by the ejector mechanism. Subsequently, the runners and overflow slots are removed (typically by sawing or punching), and flash is ground and cleaned. At this stage, care must be taken to avoid damaging the critical sealing surfaces and mounting surfaces of the casting.
6. Heat Treatment
The heat treatment of aluminum alloy integrated die-cast diving masks typically employs the T6 process:
1. Solution treatment: The casting is heated to 490–530°C and held for 4–8 hours to fully dissolve the alloying elements into solid solution.
2. Quenching: The casting is rapidly immersed in hot water at 60–80°C to obtain a supersaturated solid solution.
3. Artificial aging: The casting is held at 150–180°C for 4–10 hours to precipitate strengthening phases, significantly enhancing the strength and hardness of the component.
After T6 heat treatment, the AlSi10MgMn series alloy can achieve a tensile strength of over 300 MPa and a yield strength of over 240 MPa, fully meeting the load bearing requirements of deep water pressure.
7. Quality Control and Inspection
Quality control for integrated die cast diving masks runs throughout the entire process flow. The key inspection items include:
Dimensional accuracy inspection: Critical dimensions such as the window mounting groove dimensions, sealing surface contours, and interface threads are measured using a coordinate measuring machine (CMM) to ensure they meet assembly and sealing requirements.
Non destructive testing: X ray inspection or industrial computed tomography (CT) is used to identify internal defects such as porosity and shrinkage porosity in the casting. For vacuum die cast products, the internal porosity rate should be controlled below 1%.
Airtightness test: This is the most critical performance indicator for diving masks. After the window is installed on the finished mask, a specified air pressure (typically 1.5 times the working pressure) is applied on a dedicated airtightness test bench. The pressure is held for a set period, and the pressure drop is checked to see if it remains within the allowable range.
Pressure resistance test: To simulate the water pressure corresponding to actual diving depths, the mask is placed in a hydrostatic pressure chamber for a hydrostatic pressure test, verifying the structural integrity of the mask under extreme conditions.
Surface treatment quality inspection: The thickness, uniformity, and corrosion resistance of anodized or micro arc oxidation coatings are verified using a coating thickness gauge and salt spray testing.
8. Process Advantages and Technical Challenges
8.1 Advantages
Compared with traditional split manufacturing, the integrated die-cast diving mask offers significant advantages: the number of components is reduced by more than 50%, welding and bolted connections are eliminated, and multiple potential leakage paths are removed; product weight is reduced by 20–30%, improving wearing comfort for divers; high dimensional accuracy and good consistency make it suitable for mass production.
8.2 Challenges
This process also faces numerous technical challenges: the mold design and manufacturing cycle is long and costly, making it unsuitable for small batch, multi variety production; filling the thin walled, complex structure of the mask is difficult, imposing stringent requirements on the die casting machine and process parameter control; thin walled areas are prone to deformation during heat treatment, necessitating dedicated heat treatment fixtures; and residual internal stresses in the casting may affect subsequent machining accuracy and service stability, which must be mitigated through aging treatment.
9. Conclusion
Integrated die casting technology has brought revolutionary changes to the manufacture of diving masks—from multi component assembly to one shot forming, from welded connections to an integral structure. This not only enhances product reliability and safety but also opens up new possibilities for lightweighting and high performance design of diving equipment. With continued advances in vacuum die casting technology, high strength and high toughness aluminum alloys, and intelligent process control for die casting, the overall performance of integrated die cast diving masks will be further improved, promising broad application prospects in professional diving, emergency rescue, and underwater operations.
WAVE China is a diving mask manufacturer. If you are interested in diving masks, please contact us.
