Small Module Gears, Titanium Alloy Lost-wax Casting

Small module gears typically refer to gears with a module less than 1 mm. They are small in size and require high precision. They are widely used in precision machinery, instrumentation, and aerospace fields, such as small transmission systems in aerospace equipment and precision transmission structures in instruments. Due to their small size, traditional machining methods may be insufficient to meet the manufacturing requirements of high precision and complex shapes.

Titanium alloys have advantages such as low density, high specific strength, and good corrosion resistance. They are widely used in aerospace, biomedical, and other fields. For small module gears, using titanium alloys can reduce weight while ensuring gear strength, thus improving the overall performance of the equipment. However, titanium alloys are difficult to machine; traditional machining methods are costly, inefficient, and prone to deformation.

Lost-waste casting, also known as investment casting, is a precision casting method. Its basic principle is to first create a wax model with the same shape as the desired part, and then coat the surface of the wax model with multiple layers of refractory material to form a shell. After the mold shell dries and hardens, the wax model is heated to melt and flow out, thus creating a cavity with the same shape as the part. Finally, the molten metal is poured into the cavity, and after cooling and solidification, the desired part is obtained.

1. Mold Design and Manufacturing

Design and manufacture the mold according to the size, shape, and precision requirements of the small module gear. High-precision machining methods, such as CNC machining, are typically used to ensure the dimensional accuracy and surface quality of the mold. The mold design must consider factors such as the shrinkage rate of the wax model and the demolding method.

2. Wax Material Selection and Treatment

Select a suitable wax material, generally requiring good fluidity, low shrinkage, and moderate strength. Commonly used wax materials include paraffin-stearic acid-based waxes. Before use, the wax material needs to be melted and filtered to remove impurities and air bubbles.

3. Wax Model Pressing

Inject the treated wax material into the mold, and under certain pressure and temperature, fill the mold cavity with the wax material. During the pressing process, pressure, temperature, and holding time must be carefully controlled to ensure the dimensional accuracy and surface quality of the wax model. After pressing, the wax model is cooled and demolded to obtain the final wax model.

1. Coating: Immerse the wax model in the coating, ensuring a uniform coating layer on its surface. The coating typically consists of refractory materials (such as silica sol, zircon powder, etc.), binders, and additives. The viscosity, density, and coating thickness of the coating must be carefully controlled during the coating process to guarantee the quality of the shell.

2. Sanding: Immediately after coating, place the wax model in a sand box and sprinkle a layer of refractory sand. The particle size and material of the sand must be selected according to the requirements of the shell. The purpose of sanding is to increase the strength and permeability of the shell.

3. Drying and Hardening: After coating and sanding, place the wax model in a drying chamber for drying and hardening. Temperature, humidity, and time must be carefully controlled during drying and hardening to ensure the strength and permeability of the shell. Generally, the steps of coating, sanding, drying, and hardening need to be repeated multiple times until the shell reaches the required thickness and strength.

4. Dewaxing: The mold shell is heated to a certain temperature, causing the wax model to melt and flow out. Dewaxing methods include hot water dewaxing and steam dewaxing. Temperature and time must be carefully controlled during dewaxing to ensure complete melting and flow of the wax model while preventing the mold shell from cracking.

1. Titanium Alloy Melting: Titanium alloy raw materials are melted using methods such as vacuum induction melting. Strict control of melting temperature, time, and atmosphere is crucial during melting to ensure the chemical composition and quality of the titanium alloy.

2. Casting: The molten titanium alloy is poured into the preheated mold shell. Pouring temperature, speed, and pressure must be carefully controlled during casting to ensure the molten titanium alloy fills the mold cavity and prevent defects such as porosity and inclusions.

1. Shell Removal: After casting, the titanium alloy is cooled and solidified, and the mold shell is removed. Shell removal methods include mechanical and chemical shell removal.

2. Heat Treatment: The small module gears after shell removal undergo heat treatment to improve their microstructure and properties. Common heat treatment methods include annealing, quenching, and tempering.

3. Machining and Surface Treatment

Based on the gear's precision requirements, the heat-treated gears undergo machining processes such as grinding and honing to improve dimensional accuracy and surface quality. Simultaneously, surface treatments such as nitriding and hard chrome plating are applied to enhance wear resistance and corrosion resistance.

1. High Precision: Lost-wafer casting can produce small-module gears with high dimensional accuracy and complex shapes, meeting the precision requirements of precision machinery and instrumentation.

2. High Material Utilization: Compared to traditional machining methods, lost-wafer casting reduces material waste and improves material utilization.

3. Suitable for Titanium Alloy Machining: Lost-wafer casting avoids machining deformation and surface damage that occur during titanium alloy processing, ensuring the quality of small-module titanium alloy gears.

1. High Process Control Difficulty: The lost-wafer casting process is complex, involving multiple stages, each affecting the quality of the final product. Therefore, process control is challenging, requiring strict control of all process parameters.

2. High Cost: Lost-wax casting involves significant equipment investment and complex processes, resulting in high production costs. This is particularly pronounced for small-batch production of small-module gears.

3. Environmental Issues: Lost-wax casting generates waste materials such as wax patterns and mold shells, which require proper disposal to avoid environmental pollution.