What is Investment Casting

The investment casting process refers to making a model with wax, wrapping a layer of refractory materials such as clay on its surface, heating the wax to melt and flow out, thereby obtaining an empty shell formed by refractory materials, and then pouring the melted metal into the empty shell. After the metal cools, the refractory material is broken to obtain a metal mold. This 3d printing investment casting process of processing metal is called precision casting, also known as investment casting or lost wax casting.

Advantages and disadvantages of investment casting process

Precision casting is also called investment casting. Compared with other casting methods and part forming methods, investment casting has the following advantages:

• 1. The casting has high dimensional accuracy and fine surface roughness. The dimensional accuracy of the casting can reach 4-6 levels, and the surface roughness can reach 0.4-3.2μm, which can greatly reduce the machining allowance of the casting, and can achieve no-allowance manufacturing, reducing production costs.
• 2. It can cast castings with complex shapes that are difficult to process by other methods. The outline size of the casting ranges from a few millimeters to thousands of millimeters, with the thinnest wall thickness of 0.5mm and the minimum hole diameter of less than 1.0mm.
• 3. Alloy materials are not restricted: materials such as carbon steel, stainless steel, alloy steel, copper alloy, aluminum alloy, high-temperature alloy, titanium alloy and precious metal can all be produced by precision casting. For alloy materials that are difficult to forge, weld and cut, precision casting is particularly suitable for production.
• 4. High production flexibility and strong adaptability. It can be used for mass production, small batch production or even single-piece production.

In summary, precision investment casting has the advantages of small investment scale, large production capacity, low production cost, simplified process of complex products and quick investment effect. Thus, it is in a favorable position in the competition with other processes and production methods.

However, the following defects are prone to occur during the production of wax molds

• 1. Wax mold deformation. After the wax mold is taken out of the mold, in addition to the size reduction, it is sometimes artificially deformed due to incorrect removal techniques; since it is common for the wax mold to bend and deform during cooling, the wax mold just taken out of the die should still be carefully placed, usually with a larger plane as the reference surface. In addition, it may also be caused by factors such as too soft wax material and unreasonable die design.
• 2. The wax mold is not fully filled. The main reason is that the temperature of the wax material is too low, the injection speed is slow, and the molding temperature is low, causing the wax material to cool quickly during the flow process. This is manifested in the corners and edges or the thin-walled parts of the wax mold are not fully filled, and the corners appear rounded. This situation is very similar to the insufficient pouring of metal castings.
• 3. Wrinkles on the surface of the wax mold are due to the low temperature of the wax material, the low injection speed, the improper coordination of the movement of the lost wax casting material and the molding temperature; or due to the damage or uncleanness of the inner surface of the molding; improper placement of the chilled metal block, etc., leaving traces of movement on the surface of the wax mold. Deeper lines are similar to the cold shut defects of metal castings; and sometimes seams can be seen around the core and around the holes, which are slightly concave. In fact, the junction of the two wax streams failed to fuse well. This is the result of insufficient temperature and pressure of the wax material.
• 4. The surface of the wax mold is concave, mainly because the injection pressure and time are not enough, or the temperature of the wax material is high, the cooling time is insufficient, and sometimes too much release agent is used. The surface concave involves a large area, which is difficult to repair and easily causes waste.
• 5. The wax mold has seams, which is the most common defect, that is, there are thin wax flakes escaping at the joints of the press mold, the joints of the press mold assembly blocks, and the joints between the core and the core seat. The main reasons for this are insufficient press mold accuracy, damage to the press mold parting surface or the joint surface of the inner part of the mold, or insufficient mold force, and too high injection pressure. Or the temperature of the wax is too high. The hair wings must be completely removed before the wax mold can be used.
• 6. The wax mold is adhered to the press mold, which is caused by not using a release agent, or the temperature of the wax and the press mold is too high, or the inner surface of the press mold is not clean enough.
• 7. The surface of the wax mold is rough. Due to the low injection pressure or low injection speed, the contact density between the wax material and the inner surface of the press mold is not enough, and serious wrinkles will appear.
• 8. There are bubbles in the wax mold. One is the surface bubbles visible to the naked eye, and the other is the bubbles inside the wax mold. They are usually larger and cannot be seen with the naked eye, but can be found through the local bulging of the wax mold. This is caused by the expansion of gas in the wax mold.

Key points of investment casting process

• 1. Do not spray too much parting agent in the mold cavity.
• 2. After the cycle parameters of the pressing melt (wax) mold are established, do not change them easily.
• 3. The wax molds should be placed in the storage tray and isolated from each other to avoid damage. If necessary, clamps can be used to avoid deformation of the wax mold.
• 4. Be careful not to damage the mold surface during the correction process.

Application scope of investment casting process

Precision casting is used in almost all industrial sectors, especially electronics, petroleum, chemical etching equipment parts, energy, transportation, light industry, textiles, pharmaceuticals, medical equipment, pumps and valves.