Precision casting using gasified models: advantages 

Why gasification casting is chosen for complex parts

Precision casting using gasified models: the advantages of this technology lie in the possibility of producing metal products of the most complex geometry with minimal allowances for machining and the absence of mold parting lines. Unlike traditional sand casting or even classic lost wax casting, the use of polystyrene foam models allows the creation of monolithic structures where previously welding of several components was required. We are seeing this technology become the standard for pump housings, exhaust manifolds and turbine components where sealing and aerodynamics are critical.

Our team of process engineers, over 15 years of working with this method, has identified a key success factor: controlling the density of the sand around the model. An error at this stage leads to surface defects that cannot be corrected without rejecting the entire batch. This is not a theoretical warning - one of our clients experienced a 40% loss of production due to unstable mold filling pressure, which resulted in thin-walled parts warping. That is why in this article we will analyze in detail the technical nuances, economic benefits and real limitations of the method, based on production test data and GOST R 53463-2009 standards.

Technological essence of the process and difference from analogues

The essence of the method is that the model made of expanded polystyrene (EPS) or styrene copolymer (STMMA) remains in the mold while molten metal is poured. Under the influence of high temperature, the model instantly gasifies, making room for liquid metal, which occupies its exact shape. The molding mixture, usually consisting of quartz sand with the addition of binders, is held in a vacuum, which prevents the walls of the cavity from collapsing after the model disappears. This process eliminates the need to remove the model before pouring, which is a major limitation in other types of casting.

The main difference from lost wax casting is the absence of the stage of removing wax and drying the ceramic shell. Lost wax casting technology requires a lot of time to deposit multiple layers of ceramic and then fire them to create a durable mold. Here, the shape is formed directly around the model in a matter of minutes. This reduces the production preparation cycle from several days to several hours. However, it is important to understand that the quality of the casting surface directly depends on the quality of coating the model with a refractory composition before installation in the mold.

In our practice, we often compare this method with sand casting using cold-hardening mixtures (CMC). If CTS gives good dimensional accuracy (up to IT14), then casting using gasified models stably provides quality IT12-IT13 without the need to use rods for internal cavities. Cores in traditional casting always carry the risk of displacement, seams and additional costs for their production and removal. Here, the internal configuration of the casting is formed by the model itself, which eliminates these risks completely.

However, the technology has its own specifics, which marketing brochures are silent about. The gas permeability of the molding sand plays a decisive role. If the sand is too fine or poorly prepared, the decomposition products of polystyrene do not have time to evacuate through the walls of the mold. This leads to the formation of gas pockets and carbon inclusions in the metal. We have seen cases where attempts to save on the sand fraction led to the rejection of critical stainless steel parts, where the requirements for the purity of the alloy are maximum. Therefore, the choice of sand is not a question of price, but a question of the physics of the process.

To make the right technological decision, it is necessary to take into account the chemical activity of the metal. Aluminum alloys are less sensitive to carburization than steels, but require more careful control of pouring temperature to avoid underfilling of thin sections. Steel, in turn, can absorb carbon from the decomposing model, changing its mechanical properties in the surface layer. The solution to this problem lies in the use of special coatings for models and optimization of pouring speed.Recommendation:Before starting the series, be sure to carry out a test casting with an analysis of the chemical composition of the surface layer of the casting.

Key benefits for designers and buyers

When designers evaluate the possibility of switching to a new technology, they look at the freedom of geometric creativity. Casting using gasified models removes the restrictions imposed by the need to remove the model from the mold. You can design parts with undercuts, complex internal channels, and variable cross-sections that previously required multi-part assembly. This opens the way to optimizing the weight of structures without losing strength, which is especially important for the automotive and aviation industries.

Economic efficiency is manifested in reduced metal consumption. Due to the high precision of shape reproduction, machining allowances are reduced to 1-2 mm, and in some places can be eliminated completely. For large-sized castings made of expensive alloys, such as heat-resistant steels or titanium, savings on metal and machining time cover the cost of manufacturing tooling already in the first batch. Our calculations show that for series of 50 pieces and above, this method becomes more profitable than traditional earth casting.

Simplification of technological equipment is another compelling argument. Instead of using complex metal molds to make cores and half-moulds, aluminum or even wood models are used to produce polystyrene foam blanks. The production time for such equipment is 3-4 times less than that of a metal injection mold. This allows you to quickly enter the market with a new product and quickly make changes to the design of a part without huge financial losses.

The absence of mold parting lines improves not only the appearance, but also the performance characteristics of the product. Parting lines in traditional casting often become stress raisers and initiation points for corrosion. The monolithic structure of the casting, obtained from gasified models, ensures uniform distribution of loads. This is critical for parts that operate under high pressure or cyclic load conditions, such as gear housings or vehicle suspension components.

However, it is important to be honest about the limitation: the method is not suitable for one-off production of unique large parts if the cost of manufacturing the foam model itself is high. Although the model is cheaper than a metal mold, it still requires manufacturing. For prototyping single items, it is sometimes more profitable to use 3D printing of sand molds. But as soon as it comes to small and medium-sized series, the advantages of scalability come to the fore.Action:analyze your annual parts consumption; if it exceeds 100 units per year, the transition to this technology is justified.

Application in various industries

The automotive industry is one of the main drivers of development in this area. Engine manufacturers are actively using the technology to manufacture intake and exhaust manifolds. The complex shape of the channels required to optimize the gas flow is ideally realized by the gasification model method. We worked with a customer who replaced a four-piece welded manifold with a cast monoblock design. The result was a reduction in unit weight by 18% and an increase in throughput by 12%, which directly affected engine power. Exhaust gas temperatures reached 850°C, and the monolithic structure provided the necessary heat resistance without the risk of weld failure.

In power engineering, the method is indispensable for the production of turbine and pump casings. The requirements for the tightness of such products are extremely high. Traditional casting often requires lengthy flaw detection and welding of pores, which increases the cost of the process. The use of this technology allowed one of our partners to reduce the percentage of defects due to gas porosity from 7% to 0.5% through the introduction of a mold evacuation system with a pressure of 0.04 MPa. The cooled surface area of ​​such housings can reach 15 m², and the absence of core seams guarantees reliability when operating under pressure up to 25 MPa.

The agricultural machinery industry also benefits from the adoption of this process. Transmission housings, differential housings and attachment components are often ribbed to increase rigidity while minimizing weight. Gasification casting makes it possible to accurately reproduce these ribs without thickening at the joints characteristic of sand casting. Metal savings on one tractor part can be up to 3 kg, which on a plant scale results in a significant reduction in the cost of the final product.

A special place is occupied by the production of artistic castings and architectural elements. The ability to convey the smallest details of the relief makes this method ideal for restoring historical objects or creating modern sculptures. Unlike wax casting, where large models can deform under their own weight, polystyrene foam models are sufficiently rigid and can be easily reinforced if necessary. We carried out orders for the casting of decorative elements of facades up to 2 meters high, where the accuracy of the texture was a critical requirement of the customer.

However, not all materials are equally suitable for different industries. For the food industry, where high corrosion resistance and surface cleanliness are required, it is necessary to carefully select the composition of the molding sand and the coating of the model to prevent contamination of the alloy. In one case, the wrong choice of binder led to the appearance of inclusions in food-grade stainless steel castings, which required a complete rework of the batch.Advice:When ordering castings for the food industry, request a certificate of compliance of the mold materials with sanitary standards.

Quality control and the influence of parameters on the result

The quality of castings directly depends on the stability of the gasification process. The rate of filling the mold with metal must be synchronized with the rate of evaporation of the model. If the metal flows too slowly, the model has time to cool down and stops gasifying, which leads to underfilling. If it is too fast, turbulence occurs, trapping decomposition products into the casting body. In our laboratory, we use high-speed cameras to analyze mold filling, which allows us to adjust the filling mode with millisecond precision.

Vibration of the mold during pouring is another critical parameter. It is necessary to compact the sand around the model and ensure the release of gases. However, excessive vibration can lead to the destruction of the fragile foam model or its displacement relative to the flask. We encountered a situation where the vibration frequency on new equipment was set incorrectly, which caused microcracks in models with complex configurations. These cracks were filled with metal, forming thin “whiskers” on the finished casting, which were extremely difficult to remove mechanically.

The chemical composition of the molding sand must be strictly controlled. The content of coal dust (to create a reducing environment) and binders affects gas permeability and mold strength. According to the GOST 2138-91 standard, casting sand must have a certain fire resistance and a clay fraction content of no more than 0.5%. Exceeding this indicator by even 0.2% can lead to metal burning and deterioration in surface quality. Regular granulometric analysis of sand is a mandatory procedure for any foundry working using this technology.

Model coatings perform a dual function: they create a barrier between the metal and the foam, improving the surface of the casting, and regulate the rate of heat transfer. The thickness of the coating layer must be uniform. Dip application is preferable to spraying for complex parts as it ensures coverage of all hard-to-reach areas. We recommend using water-based zircon coatings for steel castings as they provide better heat resistance than quartz compounds.

It is important to note that visual inspection does not always reveal internal defects. X-ray inspection or ultrasonic flaw detection is necessary for critical parts. In one of the projects, we discovered a hidden gas pore in the body of a gear wheel only after taking an x-ray, although the outer surface was ideal. This time could cause the wheel to break under load.Requirement:include a clause on non-destructive testing in the terms of reference for the supply of critical components.

Economic justification and payback periods

Calculation of the economic efficiency of technology implementation should take into account not only the cost of one casting, but also the full life cycle of the product. The reduction in machining labor is often up to 40% of the total cost of the part. For complex surfaces such as pump impellers, this means eliminating the use of 5-axis machines for roughing operations, freeing up expensive equipment for more precise work.

The production time for a pilot batch is much shorter. The absence of the need for complex metal equipment allows us to obtain the first samples 2-3 weeks after the approval of the drawings. For traditional injection molding this period is 2-3 months. In a fast-to-market environment, this advantage can be a critical success factor. We helped a startup bring a new engine to market 2 months ahead of competitors precisely thanks to the use of fast aluminum foam models.

Waste disposal also has an economic aspect. Expanded polystyrene, when properly burned in special installations, does not harm the environment, and waste sand can be regenerated and reused up to 90%. This reduces the cost of purchasing new sand and waste disposal. However, the initial investment in a sand recovery system can be high, so for small industries it makes more sense to enter into contracts for removal and processing with specialized companies.

When calculating the cost, it is necessary to take into account the consumption of the model material. The metal utilization coefficient (the ratio of the weight of the casting to the weight of the poured metal) in this method is higher than in sand casting, since there are no gating systems of large mass. However, the foam itself is a consumable material, and its cost is included in the price of each casting. As prices for petrochemical raw materials rise, production costs may fluctuate, which requires a flexible pricing policy for long-term contracts.

The payback for switching to a new technology for existing production usually occurs in 6-8 months when the line load is at least 60%. The main source of savings is a reduction in scrap and a reduction in the wage fund due to the elimination of operations for the manufacture and installation of rods.Solution:Conduct an audit of ongoing scrap and post-processing costs; if they exceed 15% of the cost, modernization of the technological process is inevitable.

Frequently Asked Questions

What metals can be used for gasification casting?

The technology is universal and allows the casting of almost all industrial alloys: gray and high-strength cast irons, carbon and alloy steels, aluminum, magnesium and copper alloys. However, each metal has its own nuances. For example, when casting manganese steels, special attention must be paid to the pouring temperature to avoid excessive decomposition of the model. Aluminum alloys require lower temperatures, which makes the task easier, but increases the risk of underfilling thin walls. The choice of a specific alloy should be based on the requirements for the mechanical properties of the finished product.

What is the maximum weight of the casting that can be obtained using this method?

There are no theoretical restrictions on weight; practice shows the successful production of castings weighing up to 5 tons or more. Limitations are dictated by the capabilities of the workshop's lifting equipment and the size of the vibrating platforms. Large castings require special filling technology to avoid erosion of the mold by the metal flow. We have successfully cast hydraulic turbine casings weighing 3.5 tons with a wall thickness of 20 mm. The main condition is to ensure uniform filling of the mold and effective removal of gases from large volumes.

How environmentally friendly is the foam gasification process?

The process is accompanied by the release of thermal decomposition products of polystyrene, which can be harmful if not disposed of correctly. Modern foundries are equipped with aspiration and thermal gas neutralization systems, which reduce emissions to a safe level. In addition, the use of sand that does not contain chemical binders (dry sand) makes it easier to reuse and reduces the environmental burden compared to chemically hardening mixtures. Compliance with ISO 14001 standards is achieved through the installation of filters and air monitoring systems.

Is it possible to produce castings with threads or small diameter holes?

Yes, it is possible, but with reservations. The thread can be cast directly, but its accuracy will be lower than that of a mechanically cut one. Usually, allowance is left for threading. Holes with a diameter of less than 4 mm are recommended to be machined, since foam rods of this size are too fragile and may break when filled with sand. For holes of medium diameter (from 6 mm), the use of removable foam rods is quite effective and economically justified.

Conclusion and recommendations for choosing a supplier

Precision gasification casting: The benefits of this technology are obvious to manufacturers seeking to optimize costs and improve product quality. The ability to create complex geometric shapes without parting lines, reducing processing allowances and speeding up the introduction of new products to the market make this method one of the most promising in modern mechanical engineering. However, success depends on strict adherence to technological discipline and the quality of raw materials.

When choosing a partner for ordering castings, pay attention not only to the price, but also to the availability of its own quality control laboratory and a fleet of sand recovery equipment. A supplier's experience with your type of alloy is critical, especially when dealing with specialty materials such as titanium, nickel alloys or marine grade brass, which are widely used in harsh refining and energy environments. Feel free to request flaw detection reports from previous batches and certificates for molding materials. A reliable supplier is always open to dialogue and is ready to provide samples for testing.

In this context, it is worth mentioning the company's experienceWuxi Kaisheng Electric Power and Petrochemical Equipment Co., Ltd.. Specializing in the design and production of heat transfer equipment, as well as components for the energy and petrochemical industries, the company has accumulated deep expertise in working with complex alloys. Their products, which include titanium shell-and-tube heat exchangers, ASME-standard high-pressure units, corrugated tube bundles in 316 stainless steel, C46400 marine brass, and nickel alloys (such as N06625), require impeccable casting and finishing quality. Tube sheets and other components made from carbon, alloy steels and copper alloys must have high corrosion resistance and resistance to extreme pressures and temperatures. This PED and ASME certified manufacturing approach demonstrates the importance of selecting a supplier that can provide customized solutions and consistent quality to global customers in demanding applications such as shipbuilding, desalination and chemicals.

We are ready to offer comprehensive solutions for the production of castings of any complexity, using advanced methods for modeling mold filling processes. Our expertise allows us to minimize the risks of defects and guarantee that products comply with the most stringent international standards. If you are planning to modernize your production or search for a reliable source of components, contact our technical specialists to discuss the details of your project.

Find out more about gasified casting technologyand you can receive a commercial offer by leaving a request on our website. We will conduct a free analysis of your drawings and offer the best implementation option.

Contact us today for a consultation with a leading process engineer.