Medical Investment Casting

Investment casting is a popular manufacturing process used to create high-quality medical equipment. The process involves pouring molten metal into a mold, allowing it to solidify, and removing the mold to reveal the finished product. Investment casting can produce complex shapes and intricate details that would be difficult or impossible to achieve using other methods. Investment casting is ideal for producing small to medium-sized medical equipment with complex shapes and high precision. Some examples of medical equipment that can be manufactured using investment casting include surgical instruments, dental implants, orthopedic implants, and prosthetic limbs.

We are a Chinese manufacturer of medical machinery products, committed to providing customized medical machinery casting and processing services for customers in various fields: diagnosis, health monitoring devices, research, beauty instruments, medical electronic devices, and many other medical equipment.

Investment casting medical equipment parts 02

Investment casting Medical equipment parts

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Medical scissors casting

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Medical equipment components

Medical investment casting roller

Medical investment casting roller

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Medical investment fittings casting

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Stainless steel Medical equipment casting

 
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Medical equipment investment casting Processes

Medical equipment investment casting involves several steps, including:

Pattern Creation:

The process begins with the creation of a pattern, which is a replica of the desired part. This pattern can be made from wax, plastic, or another material that can be easily melted or burned away. The pattern is typically created using a mold, CNC machining, or 3D printing.

2 Wax pattern creation

Assembly:

The assembly process involves multiple wax molds, which are commonly referred to as “trees”. This is because they are often connected to a central wax stick resembling a tree trunk. The assembled “tree” will be installed on the pouring system, its main function is to ensure that the molten metal can flow smoothly during the casting process and effectively remove gas. This design helps to improve the quality and production efficiency of castings.

Wax assembly module

Shell Making:

Subsequently, apply ceramic paste on the assembled wax mold. This slurry is composed of fine ceramic particles suspended in a liquid adhesive. After the coating is completed, the mold is often immersed in refractory materials such as sand or plaster to shape a thick shell. This process can be repeated multiple times to achieve the desired shell thickness.

faucet part shell making

Shell Drying:

Once the ceramic shell is formed, it can be thoroughly dried. This step plays a crucial role in ensuring the robustness of the mold and its ability to withstand high temperatures during the casting process.

Manufacturing shell

Wax Removal (Dewaxing):

Following drying, the ceramic molds are heated so as to melt and get rid of the wax patterns. This results in a cavity in the form of the desired part being left within the ceramic shell.

5 wax removal s 150x150 1

Preheated and Casting:

The ceramic molds are preheated to a relatively high temperature in order to ensure that they can bear the molten metal during the casting process without cracking or deforming. Afterwards, the molten metal is poured into the preheated ceramic molds. The metal fills the cavity that was left by the wax pattern and assumes its shape.

Melt And investment casting

Cooling and Shell Removal:

The filled molds are permitted to cool and the metal solidifies inside the ceramic shell, shaping the desired part. Once the metal has cooled and solidified completely, the ceramic shell is separated from the cast metal part. This can be accomplished by means of various approaches, like vibration, sandblasting, or chemical dissolution.

Faucet foundry shell removal

Finishing and Post Service:

The cast metal parts might go through additional finishing procedures, like grinding, machining, polishing, or heat treatment, in order to attain the wanted surface finish, dimensions, and mechanical characteristics. These additional processes can further refine and enhance the properties of the cast metal parts, ensuring they meet the specific requirements and standards for their intended applications. For example, grinding can be used to smooth out rough surfaces, machining can be employed to achieve precise dimensions, polishing can give a lustrous finish, and heat treatment can modify the mechanical properties for better performance.

investment casting Finishing and Subsequent processing

Advantages of investment casting in medical equipment manufacturing

– Investment casting is known as precision casting, so it has high precision and accuracy

– Ability to produce complex shapes and intricate details

– Consistency of part quality and dimensions

– Minimal machining required after casting

– Lower material waste compared to other manufacturing methods

Chapter 1

Circular Inner Runner in Fork shaped medical investment castings

Circular Inner Runner in Fork shaped medical investment castings

(1) The medical investment casting requirements: A fork shaped medical casting material of 45 steel, which is an export product. The customer requires a full silica sol shell with a diameter of D21mm, and the inner hole and bottom plane need to be machined, as shown in Figure as follows:

Process diagram of cross shaped casting group

1. Strengthening tendons; 2 circular runners; 3 inner runners

(2) Structural analysis of medical investment casting
The main body of this medical investment casting is a V-shaped arm with an inner hole at the lower part of the structural component. The internal opening distance of the fork is relatively wide, and ther…ding-relaxed break-words”>

(4) Analysis of Medical Investment Casting Products

Taking into account factors such as improving the one-time qualified rate of castings, increasing the output rate of the process, and the overall rationality of the process layout, it is still beneficial to adopt the process plan of “vertical mold head, dual sprue, and two-row tree”, as shown in the right Figure.

In order to overcome the negative impact caused by the installation of two inner runners, a circular ring with an outer diameter of 37mm, a thickness of 2.5mm, and a width of 2.5mm is added in the middle of the two inner runners. In other words, the circular ring is used to connect the two inner runners and make them form a whole.
Figure Cross shaped Casting Group Tree Diagram Batch Production Proof, achieving the expected process effect with a process yield rate of 70%,
The first pass rate of finished medical investment casting products is 99.7%.

Chapter 2

Production example of small and micro castings in medical investment casting

medical investment casting drawing of small and micro castings

Figure 6-63  medical investment casting drawing of small and micro castings

Producing small and miniature parts is an advantage of investment casting. So Medical parts usually choose this casting method. By using mid-temperature wax for molding and the all-silica sol process for shell making, it is possible to produce medical investment castings with precise dimensions and low surface roughness. Other representative products include sewing machine parts, instrument and meter components, and medical device parts. Typically, the weight of these castings is only a few grams or even less. Our precision casting company in China has accumulated rich experience in producing small and miniature parts.

As shown in Figure 6-63, the main body of this medical investment casting has a diameter of 4.7mm and a total length of 73mm. The bottom needle has a maximum diameter of 1mm and a length of 3mm. The main cylindrical body has barbs, with a row of 7 barbs and a total of 21 barbs in 3 rows. The top is sharp like a needle, and craftsmen figuratively call this piece a fish hook needle. The material of this medical investment casting is 304, and the weight of a single piece is 11g.

(1) For the first casting of this medical investment casting, a binary mold head was used for side pouring, as shown in Figure 6-64. The shell firing temperature was 1180℃ and the pouring temperature was 1680℃. As a result, the majority of the barbs were not filled during pouring, and all the casting parts were scrapped.

(2) For the production of small and miniature medical investment castings, it is generally not a problem to increase the shell firing temperature and pouring temperature of the steel. However, for the fish hook needle casting with its special small barbs, neglecting the element of rapid filling was the main reason for the failure of the first casting attempt using side pouring, which resulted in slow filling speeds and insufficient pressure causing all the castings to be scrapped.

For subsequent casting attempts, a top pouring method with a horizontal mold head was used, as shown in Figure 6-65. The firing and pouring temperatures remained the same. The situation for the second casting attempt was different: 56 pieces were assembled on one horizontal mold head, and only 7 medical investment castings were underfilled, all of which occurred at the gate position.

 

Side casting casting scheme

Figure 6-64 Side-casting casting scheme

Figure 6-65 Horizontal mold head group tree

(3) Why were there still underfilled defects at the gate position in the medical investment casting? Analysis suggests that it was mainly due to poor ventilation. Additionally, the rapid pouring speed may have caused air entrapment, resulting in insufficient filling of the small barbs.

The solution is to address the issue from the mold head perspective. Four 8mm diameter ventilation rods were added on the horizontal mold head of the medical investment casting, with their heights aligned with the plane of the pouring cup, as shown in Figure 6-66. To address the problem, the following measures were taken:

Figure 6-66 Medical investment casting

Firstly, the shell-making process was modified. Zircon slurry and zirconium sand were used for the surface layer, while the second layer utilized mullite powder slurry, sprinkled with 30-60 mesh mullite powder. The third layer used mullite powder slurry, sprinkled with 16-30 mesh mullite powder. A half layer of mullite powder slurry was used as the sealing layer, greatly improving the permeability of the mold shell.

Secondly, adding ventilation rods on the mold head had a significant effect. On one mold head with 56 assembled pieces, there were no underfilled defects, with a pass rate of 95%. The final medical investment casting product can be seen in Figure 6-67.

Figure 6-67 medical investment casting final appearance

Experience Summary:

The Medical investment casting fishbone products focus on two key aspects of the casting process: ensuring complete filling and smooth ventilation. This overcomes the underfilled defects in small barb pouring and once again proves that practice enriches theory.

Based on the characteristics of the product, taking targeted measures step by step will inevitably lead to success.

After practical application in our Medical investment casting factory, the best process is as follows: shell-making with three layers- surface layer, second layer, and third layer. Before applying the second and third layers, pre-wetting should be done instead of applying a sealing layer. During pouring, the filling should be done quickly, which will result in better ventilation performance of the mold shell and more complete filling of the Medical investment casting barbs. The pass rate of the final product can reach 98%.

FAQs

Medical equipment investment casting is a manufacturing process used to create complex and intricate metal parts for medical equipment with a high level of accuracy, repeatability, and quality.

Investment casting allows for the creation of intricate parts with tight tolerances, minimizing the need for secondary machining. It also provides high-quality surface finishes, which is critical in medical equipment applications.

Key considerations include the supplier’s experience and track record in producing high-quality medical equipment components, their capabilities and certifications specific to the medical industry, and their adherence to quality control and regulatory standards.

Lead times can vary depending on the complexity of the component and the supplier’s production schedule. It is important to communicate expectations and requirements with the supplier to ensure timely delivery.

Yes, medical equipment components typically require a high-quality surface finish to minimize the risk of contamination and improve the functionality of the component. This may include electropolishing or other specialized surface treatments.

Investment casting involves creating a wax model of the part to be cast, coating the model in a ceramic material, melting the wax away, and pouring molten metal into the cavity left by the wax. The metal cools and solidifies, and the ceramic material is removed, leaving behind a detailed metal part.

Common metals used in medical equipment investment casting include stainless steel, titanium, and cobalt-chromium alloys.

Quality can be ensured through rigorous process controls, inspection and testing at various stages of production, and adherence to industry standards and regulations.

Potential risks include defects in the casting that may compromise the durability or functionality of the component, as well as non-compliance with regulatory standards. It is important to work with a reputable and experienced supplier to minimize these risks.

Investment casting allows for the creation of complex and intricate parts that would be difficult or impossible to produce with other manufacturing methods, thereby enabling more innovative and sophisticated medical equipment designs.