Lost-wax Casting Of Titanium Alloy For Automotive Oil Pipes

o. Mold Design and Manufacturing: Based on the design drawings of the automotive fuel pipes, the mold is designed using Computer-Aided Design (CAD) software. Then, the mold is manufactured using methods such as machining and electrical discharge machining. The precision of the mold directly affects the quality of the wax model; therefore, dimensional accuracy and surface roughness must be strictly controlled during the manufacturing process.

o. Wax Injection: The wax is heated to a suitable temperature to achieve good fluidity. Then, the wax is injected into the mold using an injection molding machine and maintained at a certain pressure and temperature for a period of time to allow the wax to fill the mold cavity. After the wax cools and solidifies, the mold is opened, and the wax model is removed.

o. Wax Model Finishing and Assembly: The removed wax model is inspected, and burrs, flash, and other defects are removed from the surface. If the automotive fuel pipe consists of multiple parts, the individual wax models need to be assembled to form a complete wax model assembly. During assembly, it is essential to ensure that the connections between the individual wax models are secure and their positions are accurate.

o. Coating: The wax model assembly is immersed in a specially formulated refractory coating, ensuring a uniform coating layer on its surface. The coating typically includes refractory materials (such as zircon sand and corundum powder), binders (such as water glass and silica sol), and additives. The purpose of the coating is to ensure the smoothness and dimensional accuracy of the casting surface.

o. Sand Spreading: Immediately after coating, the wax model assembly is placed in a sand spreading machine to evenly adhere sand particles to the coating layer. The sand particle size is selected based on the casting requirements and process characteristics; generally, the surface layer sand has a finer particle size.

o. Drying and Hardening: The sand-coated wax model assembly is placed in a drying chamber to allow the coating layer to dry and harden. Temperature, humidity, and ventilation must be carefully controlled during the drying process to ensure the quality of the coating layer.

o. Repeated Coating and Sand Spreading: To increase the strength and thickness of the shell, the coating and sand spreading operations need to be repeated. Multiple coatings are generally required, and the coating and sand particle size may vary in each layer.

o. Dewaxing: The prepared mold shell is placed in a dewaxing device, where heating melts the wax model, causing it to flow out. Various dewaxing methods exist, such as hot water dewaxing, steam dewaxing, and microwave dewaxing. The dewaxing process must ensure the wax model completely melts and is removed from the mold shell to prevent residual wax from affecting the casting quality.

o. Titanium Alloy Melting: Suitable titanium alloy raw materials are selected and batched according to alloy composition requirements. The batched materials are placed in a vacuum induction melting furnace and heated to melt under vacuum. During melting, temperature, time, and furnace atmosphere must be strictly controlled to ensure uniform chemical composition and low impurity content of the titanium alloy.

o. Casting: Once the titanium alloy melt reaches the appropriate temperature and fluidity, it is poured into the preheated mold shell. The casting process must be rapid and stable to avoid splashing and oxidation of the molten metal. Simultaneously, the casting speed and volume must be controlled to ensure the molten metal fills the mold shell cavity.

o. Sand Removal and Cutting: After the casting has cooled and solidified, remove excess parts such as the mold shell and gating gates. Methods such as vibration sand removal and shot blasting can be used to remove the mold shell, followed by cutting off the gating gates using cutting equipment.

o. Heat Treatment: The casting undergoes heat treatment to improve its microstructure and properties. Common heat treatment processes include annealing, quenching, and tempering. Appropriate process parameters should be selected based on the type of titanium alloy and the intended use of the casting.

o. Machining and Surface Treatment: According to the design requirements of the automotive oil pipes, the castings are machined using techniques such as turning, milling, and drilling to achieve precise dimensions and surface roughness. Finally, the oil pipe surface is treated, such as polishing and passivation, to improve its corrosion resistance and appearance quality.

Strict quality inspection is conducted on titanium alloy raw materials and auxiliary materials such as wax and refractory materials. The chemical composition and physical properties of the raw materials are checked to ensure they meet requirements and that the quality of the raw materials is stable and reliable.

Real-time monitoring of each stage of the casting process. For example, during wax pattern making, the temperature, injection pressure, and time of the wax are monitored; during shell fabrication, the viscosity, drying time, and temperature of the coating are monitored; and during melting and casting, parameters such as melting temperature and casting speed are monitored. Through process monitoring, problems can be identified and adjusted promptly, ensuring the stability and consistency of the casting process.

Comprehensive inspection is performed on the cast automotive fuel lines. This includes dimensional accuracy inspection, surface quality inspection, and internal defect detection. Dimensional accuracy inspection can be performed using measuring tools; surface quality inspection can be conducted through visual inspection and metallographic microscopy; and internal defect detection can employ non-destructive testing techniques such as ultrasonic testing and X-ray inspection. Only products that pass inspection can proceed to the next process or be delivered for use.