Casting White Pattern Process: The Key to Improving Casting Quality and Production Efficiency

In the current foundry industry, the casting white pattern process holds a pivotal position. It plays a crucial role in enabling enterprises to produce high-quality castings and is one of the important means for achieving precision casting and producing castings with complex shapes.

On the one hand, the white pattern process can accurately replicate the shape of the required casting. Its high-precision feature enables the final produced casting to better meet various complex design requirements. Whether in the field of casting high-end artworks or manufacturing precision mechanical parts, high-standard products can be created by relying on this process. For example, some artistic sculptures with fine textures and complex structures, or aerospace components with extremely high requirements for dimensional accuracy, can all be presented with high quality through the white pattern process.

On the other hand, judging from the application situations of numerous foundry enterprises, the application range of the white pattern process is constantly expanding. More and more enterprises have realized its advantages in improving product quality, reducing production costs, and increasing production efficiency. Especially in the casting of single-piece products or trial-produced products, its characteristics of low cost and convenient processing are even more prominent. Many small and medium-sized foundry enterprises have also introduced the white pattern process one after another to enhance their competitiveness in the market and meet the diverse and high-quality needs of different customers for castings.

In short, the casting white pattern process has already become an indispensable production process for foundry enterprises. Next, we will introduce its specific process contents in detail so that everyone can have a deeper understanding of its application in actual production.

II. Mold Making Method of the Casting White Pattern Process

Determine Dimensions and Select Materials

In the mold making method of the casting white pattern process, the first step is crucial, which is to determine the dimensions and select materials. First of all, it is necessary to accurately determine the respective shape and size of the regular parts and curved surface parts of the white pattern mold according to the specific shape and size requirements of the casting. This step is like the cornerstone of a building, laying the foundation for the subsequent production process.

In terms of material selection, we usually choose foam blocks with a foaming specific gravity of not less than 30g/ml and uniform beads as the white pattern materials. This material has many advantages. On the one hand, it is very convenient to process, enabling subsequent operations such as cutting, assembling, and carving to be carried out more smoothly. On the other hand, it is low in cost and is especially suitable for the casting scenarios of single-piece products or trial-produced products. For those casting tasks with a small output and the need to control costs, such a material selection is undoubtedly a cost-effective decision, which can meet the production needs and reasonably control the cost expenditure.

Cutting and Assembly

After completing the determination of dimensions and the selection of materials, we enter the cutting and assembly stage. In this process, we will use a wire cutting machine with an electrically heated resistance wire to cut the selected foam block materials according to the previously determined shape and size of the regular parts of the casting mold, so as to obtain the corresponding white pattern parts.

After the cutting is completed, the next step is to assemble these cut white patterns so that the overall shape and size after assembly are completely consistent with the requirements of the regular parts of the casting mold. Moreover, during the assembly process, special attention should be paid to ensuring the straightness of the surface. This point has a crucial impact on whether the subsequent white pattern can be conveniently cut during processing. If the surface straightness is poor, it may lead to deviations during cutting, affecting the accuracy and quality of the mold, and then having an adverse impact on the forming effect of the final casting.

Carving and Machining

After the cutting and assembly of the white pattern are completed, the treatment of the curved surface parts of the mold relies on the carving and machining stage. We will use a milling cutter CNC engraving machine to carefully carve out the corresponding curved surface shapes on the already assembled white pattern according to the size requirements of the curved surface parts of the casting mold.

In this process, the selection of cutting tools is a crucial link. It is necessary to select appropriate cutting tools according to the specific processing requirements and the characteristics of the white pattern materials to ensure that the cutting marks are as small as possible. Because the size of the cutting marks is directly related to the quality of the finally cut mold. If the marks are too large, flaws may be left on the surface of the mold, affecting its flatness and accuracy, and then causing defects in the casting in the subsequent casting process. Therefore, ensuring small cutting marks is one of the key points for ensuring the high quality of the mold.

Welding and Grinding

After the previous cutting, assembly, carving, and machining, the next step is to perform the welding operation on the cut and assembled white pattern and the carved white pattern to make them into a complete casting mold through welding. The welding work needs to be meticulous to ensure that all parts can be firmly connected together to form an integral structure, laying a solid foundation for subsequent use.

After the welding is completed, grinding the surface of the mold to make it smooth is an essential step. The purpose of grinding is to facilitate the subsequent mold removal operation. A smooth-surfaced mold can be separated from the casting more smoothly during mold removal, avoiding situations such as the mold adhering to the casting, ensuring the efficient progress of the casting process and the integrity and surface quality of the casting.

Sand Filling and Molding

After the casting mold is made, the key step of sand filling and molding should be carried out. First, the made casting mold needs to be accurately placed in the casting position, and then molding sand should be filled into the mold. When filling the molding sand, it is necessary to ensure that the sand is placed and rammed evenly. Only by ensuring that the strength of the molding sand in all parts is consistent can the stability and quality of the entire sand mold be ensured.

For white patterns with different degrees of complexity, the subsequent treatment methods are also different. For relatively simple white patterns, after the molding sand hardens, the mold can be opened and removed, and such white patterns can also be reused, further saving costs. For complex parts, it is necessary to pour out and remove the white pattern to form a cavity to meet the requirements of subsequent casting processes such as pouring metal liquid, and finally achieve the production of high-quality castings.

III. Foaming Molding Method of the Casting White Pattern Process

Pre-foaming of Beads

In the foaming molding method of the casting white pattern process, the pre-foaming of beads is a crucial starting step. We usually choose beads of materials such as expandable polystyrene (EPS) and put them into a pre-foaming machine to make the beads expand by means of heating, steam, etc. For example, in the common steam pre-foaming method, the expandable polystyrene beads will gradually soften and expand under the heat in the barrel of the pre-foaming machine. At the same time, under the stirring action of the stirrer, according to the difference in the density of the pre-foaming beads, the lighter beads will float on the top, and the heavier ones will sink to the bottom. Moreover, due to the continuous feeding of the screw feeder, the expanded beads at the bottom will exert a thrust on the foaming particles at the top, making them continuously rise along the barrel wall, finally reach the discharge port, and be pushed out outward under the action of centrifugal force, fall into the air duct, and then be sent to the dryer to dry the surface moisture.

During this process, the degree of pre-foaming needs to be strictly controlled, as it has a significant impact on the quality of subsequent molding. The degree of pre-foaming will be affected by the cooperation of conditions such as the temperature in the barrel, the height of the discharge port, and the amount of feeding. If the temperature is high, the position of the discharge port is high, and the amount of feeding is small, the beads will receive a large amount of heat, and the density of the pre-foaming beads will be correspondingly reduced, thereby affecting the quality of the subsequently formed white pattern. Therefore, it is necessary to accurately adjust various parameters according to the actual production needs and product requirements to ensure that the pre-foaming reaches an ideal state and lays a good foundation for the subsequent molding process.

Molding

After completing the pre-foaming of beads, we enter the molding stage. Fill the pre-foamed beads into the mold and heat them again. At this time, the beads will further expand and fuse with each other. After cooling, a white pattern is formed. For example, in the production of large quantities of large and medium-sized foam patterns, molding machines are often used to carry out this operation. The molding machine uniformly heats the beads in the mold to make them fully expand and fill all the gaps, and finally fuse into a whole.

In this process, it is crucial to ensure that the beads are evenly filled in the mold. Because once the beads are filled unevenly, it is easy to have situations such as uneven local density or defects. For example, it may lead to loose structures and insufficient strength in some parts of the white pattern, which are easily damaged in the subsequent casting process, affecting the quality and accuracy of the final casting. Therefore, whether using a molding machine or other methods for the molding operation, corresponding measures should be taken, such as reasonably designing the layout of the vent holes of the mold and controlling the feeding method, to ensure that the beads can be evenly filled in the mold, so as to produce high-quality white patterns.

IV. 3D Printing Method of the Casting White Pattern Process

Model Design

When using the 3D printing method for the casting white pattern process, model design is the first and crucial step. First, it is necessary to use computer-aided design (CAD) software to design the three-dimensional model of the casting. Designers should accurately construct the corresponding three-dimensional solid graphics in the software according to the actual use requirements, structural characteristics, and size requirements of the casting. For example, when designing the casting model of a mechanical part with a complex internal structure, every detail part such as holes, grooves, and bosses should be carefully outlined to ensure that the model can completely and accurately reflect the appearance of the final casting.

After completing the preliminary design of the three-dimensional model, it is also necessary to convert it into a file format suitable for 3D printing, such as the common STL format. During this conversion process, it is necessary to reasonably set some parameters of the model. For example, the size of the model should take into account the printing space size of the 3D printer to avoid the situation that the model is too large to be printed at one time. If the size is close to the limit of the printer, the cutting and splicing process can be used to reduce the risk and also appropriately control the printing cost. In addition, to ensure the structural strength of the model, an appropriate wall thickness should be set. Different 3D printing processes and materials have different minimum wall thicknesses. Generally, the wall thickness can be appropriately adjusted within the allowable range according to the functional requirements of the model. For example, the minimum wall thickness of LCD printing is usually about 0.5mm. The larger the model size, the corresponding increase in the required minimum wall thickness. Moreover, the surface of the model should be ensured to be closely connected without gaps to prevent situations such as water flowing out during the water injection test, ensuring the integrity and sealing of the model, so as to lay a good foundation for the subsequent printing work and ensure that the quality of the finally printed white pattern meets the requirements.

Printing

The next step is the printing stage. In this process, materials such as foamed plastics are used as raw materials, and a 3D printer is used to print according to the previously designed model, thus directly generating a white pattern. Nowadays, there are various types of 3D printers suitable for casting on the market. For example, industrial-grade 3D printers developed by manufacturers such as Harbin Institute of Technology 3D can have characteristics such as high precision, high stability, and high efficiency, which can well meet the requirements of the foundry industry.

When printing, the operating technicians should reasonably set printing parameters, such as printing speed, temperature, and layer thickness, according to the type of the selected 3D printer and the characteristics of the materials. The accurate setting of these parameters will directly affect the quality and accuracy of the white pattern. This method of generating a white pattern by 3D printing is especially suitable for the production of single-piece or small-batch products, as well as casting scenarios where the shape is complex and difficult to manufacture by traditional processes. For example, some artistic sculpture castings have fine textures and unique shapes, and it is extremely difficult to make them by traditional processes. However, through the 3D printing method, the white pattern that meets the requirements can be quickly and accurately manufactured. Another example is that some parts castings in the aerospace field with extremely high requirements for shape and accuracy can also use 3D printing technology to realize the production of the white pattern, thereby providing a powerful guarantee for the subsequent casting of high-quality final products. At the same time, 3D printing technology can also achieve rapid customized production, which can be customized according to the personalized needs of different customers, greatly improving production efficiency and production quality, reducing material waste, reducing production costs, and bringing more development opportunities and competitive advantages to foundry enterprises.

V. Bonding and Assembly Method of the Casting White Pattern Process

White Pattern Preparation

When preparing the white pattern for the bonding and assembly method, first, it is necessary to ensure that the existing individual white pattern parts are from reliable sources. These individual white pattern parts can be obtained through the processes such as the mold making method, the foaming molding method, or the 3D printing method introduced before. For example, for the white pattern obtained through the mold making method, after completing the processes such as cutting, assembly, carving, and welding and grinding, it is necessary to ensure that its size meets the design requirements and there are no obvious flaws and damages on the surface. If it is a white pattern made by the foaming molding method, attention should be paid to the quality control in the processes of bead pre-foaming and molding, such as whether the bead filling is even, whether there are problems such as uneven local density or defects, to ensure that the overall quality of the white pattern meets the standards. For the white pattern obtained by the 3D printing method, it is necessary to check whether the various parameters set during the model design are accurate and whether there are deformations, unclear patterns, and other situations during the printing process.

At the same time, for the prepared white pattern parts, it is necessary to check whether the bonding surfaces are flat. The flatness of the bonding surfaces directly affects the firmness of the subsequent bonding. Generally, the unevenness is required to be no greater than 1mm. Especially for the straight pipe modules with a diameter larger than DN300, it is also necessary to measure the circumference and pay attention to relevant information such as the production date of the module. In addition, it is not allowed to use modules that have not been cured and are not dry for mold assembly. Before the modules are bonded, the misalignment, flash, and burrs on the surface must be removed. However, it should be noted that when removing these flaws, the surface and contour of the model should not be damaged. Only in this way can a good foundation be laid for the subsequent bonding work and the quality of the final white pattern combination be ensured.

Bonding

After completing the white pattern preparation, we enter the bonding stage. In this process, we usually use bonding agents such as cold glue or hot-melt glue to bond and assemble the various white pattern parts together according to the requirements of the casting. For example, for small-area bonding parts, hot glue can play a better bonding role. While for large-area bonding, cold glue is more suitable. However, no matter which bonding agent is used, the key is to apply the glue evenly to fill the gaps between the components without leaving any gaps, ensuring that the bonding agent can fully fill the gaps and achieve a good bonding effect.

During the specific operation, first, apply the corresponding bonding agent to the bonding surface of the module, such as the common 851 cold glue. After the cold glue on the bonding surface is dry on the surface, then perform the joining, and at the same time, use hidden force to squeeze so that the two bonding surfaces can be closely attached. Moreover, scrape off the excess glue extruded inside and outside the model to avoid the influence of the excess glue on the subsequent processes or the casting quality. In addition, during the bonding process, attention should also be paid to the concentricity between the modules and the alignment requirements of other relevant model shape and position tolerances to ensure that the overall position accuracy of the bonded white pattern parts meets the design standards of the casting. Because once there is a deviation in the bonding, it may lead to the situation that the shape and size of the final casting do not meet the requirements, affecting the product qualification rate. Therefore, firm bonding and accurate positioning are the key points that need to be focused on in this stage.

Repairing

After the bonding is completed, the next step is to carefully check the bonded white pattern to see if there are any gaps or other defects. Because even if the bonding operation is carried out in accordance with the specifications, due to some slight differences in the white pattern itself or uncontrollable factors in the bonding process, some gaps or small surface defects may still occur. For these problems, we can use lost foam repair paste for repair.

For example, when a small gap is found on the surface of the white pattern, apply an appropriate amount of lost foam repair paste evenly on the gap to fill the gap and achieve a sealing effect. For some small surface defects, such as slight scratches and pits, they can also be filled and repaired with the repair paste, and then the repaired parts are trimmed. If there are protruding parts, use fine sandpaper to gently grind them until the surface is smooth and flat, ensuring the integrity and sealing of the white pattern. When bonding or repairing, it is necessary to strictly control the amount of glue used to avoid situations such as excessive water molecules generated in the subsequent casting process due to excessive glue, which will then affect the casting quality. Through these repair operations, the white pattern can enter the subsequent casting process in the best state.

VI. Advantages of the Casting White Pattern Process in Enterprise Applications

Cost Advantage

The casting white pattern process has significant cost advantages in enterprise applications. First, in terms of materials, for example, the foam blocks with a foaming specific gravity of not less than 30g/ml and uniform beads selected in the mold making method are low in cost themselves and are especially suitable for the casting of single-piece products or trial-produced products, which can control the material cost expenditure at the source. The bead materials such as expandable polystyrene (EPS) commonly used in the foaming molding method are also relatively affordable in price, and material waste can be further reduced by reasonably controlling the pre-foaming and other links.

Furthermore, from the production perspective, the white pattern process can reduce mold maintenance costs. For example, some traditional molds may be prone to wear, deformation, and other situations due to frequent opening, closing