Lost foam casting method for suspended male die insert type casting

Abstract

The invention relates to the technical field of full mold casting, and provides a lost foam casting method for a suspended male die insert type casting. The method comprises the following steps: firstly, in the process of manufacturing a foam model, releasing the bottom surface, a molded surface above a suspended part, a processing surface below the suspended part and a contour surface according to 15-20mm, and adding supports of 80 * 60mm on the processing surfaces at the two ends of the bottom surface of the suspended part and the middle part; then a bottom pouring type pouring system is arranged, sand isolation chilling blocks are arranged on the molded surface and the mounting surface, and cast iron rods, inner chilling blocks and step type inner chilling blocks are placed at the via hole positions; drying the shower coating; pretreatment is conducted before modeling; sand burying molding is carried out, pouring is carried out, and finally cooling and stress relief annealing machining are carried out; the problems of deformation of a suspended part, shrinkage cavity and shrinkage porosity of a thick and large position and slag inclusion during machining are solved, and the defects of shrinkage cavity and shrinkage porosity and inclusion of a machining surface are avoided through arrangement of a pouring system and matched use of inner chilling blocks and sand isolation chilling blocks.

Description

Technical Field

[0001] The invention relates to the technical field of full-mold casting, in particular to a lost foam casting method for suspended punch insert type castings. Background Art

[0002] The punch cover, also known as the punch pressure plate or upper die cover, is an important component of the stamping die. It is mainly used to fix and protect the punch. Through buffering and supporting effects, it reduces fatigue damage to the punch, extends the service life of the die, and ensures the stability and accuracy of the stamping process.

[0003] The punch cover plate serves as the "fixed base" and "protective shield" of the die, directly impacting stamping efficiency, product quality, and die life. Deformation control during the lost foam casting process requires a thorough solution. This type of punch cover plate features a unique "suspended" design, with a flange on one side and a suspended bottom on the other. Overall, it is thin and prone to deformation. The main function of the punch cover plate: The lower die punch cover plate is a crucial component of the die, primarily protecting and securing the punch, ensuring stability and precision during the stamping process. The cover plate securely secures the punch to the lower die, preventing loosening or displacement during the stamping process and ensuring dimensional accuracy and shape consistency of the stamped part. The punch cover plate is connected to the moving punch and other components, helping to reduce moving weight while aligning the striking force with the die centerline, improving stamping efficiency. To ensure dimensional accuracy and shape consistency of the stamped part, careful control of the punch cover plate's manufacturing dimensions is crucial. Controlling the dimensional accuracy of the punch cover requires a mature and effective process to control the entire lost foam casting process. This is essentially about controlling the deformation of the punch cover during production. Solving the deformation problem means solving the entire dimensional accuracy problem of the punch cover.

[0004] These structural castings are particularly thick and prone to defects such as slag inclusions, shrinkage cavities, and porosity. The safety features of these parts require extremely high machining quality, and multiple holes need to be drilled in these thick areas. Any slag inclusions, shrinkage cavities, or porosity defects that occur during drilling will render the casting scrapped. Lost foam casting (LSC) often uses multiple insulating risers for slag removal and shrinkage feeding, resulting in low process yields and significant cost. Therefore, addressing these issues is crucial. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for lost foam casting of suspended punch insert type castings, which solves the problems in the background technology.

[0006] Based on the above purpose, the present invention provides a method for lost foam casting of suspended punch insert type castings, comprising the following steps:

[0007] Step 1: Making a foam model: Use foam board, use the mold surface as the pouring bottom, the bottom surface as the slag discharge surface, and increase the bottom surface by 20mm. At the same time, increase the mold surface above the suspended part, the lower processing surface, and the contour surface by 15-20mm. Make a foam model through CNC machining, and process the holes to be processed; add 80*60mm supports on the processing surfaces at both ends of the bottom surface of the suspended part, and add 80*60mm supports every 250mm in the middle part. Keep the bottom surface of the support at the same height as the bottom surface of the model. The support and the model are processed together through CNC, and mark the side of the support.

[0008] Step 2: Setting up the pouring system:

[0009] A bottom pouring system was used, with six φ50 ingates placed, each avoiding the drilled holes. The sprue was set at the center of the model to ensure rapid and stable filling of the molten iron. Simulation was then performed using casting CAE software, with the sprue positions adjusted until all defects were eliminated.

[0010] Step 3: Chill position selection: Sand-insulating chillers are arranged on the mold surface and mounting surface. The positions of the machining holes of the casting are identified in advance according to the drawings. A 60mm diameter cast iron rod is placed at the safety bolt through-hole. A 20mm diameter inner chiller is placed at the mold through-hole. At the same time, a stepped inner chiller is placed at the tapping threaded hole position on the thick side surface.

[0011] Step 4: coating and drying:

[0012] First, seal the through holes on the model surface and the tapped threaded holes on the side with tape to prevent paint from entering the holes. Then, apply curtain coating to the product model and dry it after curtain coating.

[0013] Step 5: Model shaping: Before shaping, place the model on the shaping platform and measure its deformation. Place small counterweights around the model and on the overhanging parts. Then, mark the locations where sand-insulating chillers will be placed on the model surface. Remove the tape that sealed the machined holes before coating. Place cylindrical inner chillers on the surface through-holes and stepped inner chillers on the side tapped holes.

[0014] Molding, tamp the sand while burying it, place the sand separator chiller, and after the sand is buried in the lower box, wait for the sand to solidify and gain strength. Turn the box over after 5-6 hours, remove the reinforcing foam, and set up a slag discharge seat and slag discharge channel on the bottom. Finally, clean the surface of the bottom of the model with a vacuum cleaner and continue to bury the sand. After the molding is completed, fix the upper and lower molding sand boxes with clips, and hoist them to the pouring area after they are completely solidified.

[0015] Step 6: Model pouring: Place a weight on the surface of the sand box before pouring. The weight of the weight should be 7 times the weight of the pouring. Then pour at a temperature of 1365±5℃.

[0016] Step 7: Cooling: After pouring, cool the casting and remove the sand. Then, lift the casting out, remove the gating system and riser, polish them flat, and then perform stress relief annealing.

[0017] Step 8: Machining: After annealing, the casting is shot blasted and machined to remove the 80*60mm support.

[0018] Preferably, the density used in step 1 is less than 20KG / m 3 Low density copolymer foam board material.

[0019] Preferably, in step three, the inner chiller needs to be machined into shape with a smooth and rust-free surface, and the end of the inner chiller with a length of 300 mm and a diameter of 30 mm is machined into a diameter of 10 mm and a length of 60 mm to enhance the chilling effect and avoid shrinkage defects in the hole.

[0020] Preferably, the Baume degree of the water-based coating applied in step 4 is 55-65, and the minimum thickness of the model coating after two coats of coating is not less than 1.3 mm.

[0021] Preferably, a reinforcement model is also included between step four and step five: the model is reinforced after drying, and foam boards are filled between the supports below the suspended part and between the supports and the bottom flange surface, and fixed with bamboo sticks to prevent the reinforcement foam from moving when burying sand.

[0022] Preferably, in step five, the contact surface between the inner chill and the model is painted with alcohol-based paint with a coating thickness of 2 mm, and the modeling is performed after the paint is completely dried.

[0023] Preferably, the resin addition ratio of the molding sand in step 5 is 1.0%, ensuring that the strength of the molding sand is greater than 1.5 MPa.

[0024] Preferably, the pouring material in step six is: C 3.5-3.7%, Si 2.0-2.6%, Mn 0.4-0.7%, Cr0.1-0.3%, Cu 0.6-1.0%, Mg 0.04-0.06%, Re 0.02-0.04%, P≤0.05%, S≤0.012%, and the rest are Fe and impurity elements.

[0025] Preferably, the stress relief annealing in step seven is specifically as follows: firstly, the cast casting is heated to 540-560°C at a rate of ≤60°C / h, then kept at this temperature for 12 hours, and finally cooled to 200°C at a rate of ≤30°C / h, and then air-cooled to room temperature.

[0026] The beneficial effects of the present invention are as follows: first, in the process of making the foam model, the bottom surface, the molding surface above the suspended part, the lower processing surface and the contour surface are enlarged by 15-20mm, and then 80*60mm supports are added to the processing surfaces at both ends of the bottom surface of the suspended part and the middle part to prevent the suspended part from deforming during the coating and molding sand burying process; then a bottom pouring pouring system is set up, and CAE software is used for simulation to accurately locate the position where shrinkage cavities and shrinkage may occur in the casting; then sand isolation chillers are arranged on the molding surface and the installation surface, and the holes are placed on the bottom surface of the suspended part. Place cast iron rods, inner chillers and stepped inner chillers in the right position; then carry out coating and drying; carry out pretreatment before molding; then carry out sand embedding molding, then pouring, and finally cooling and stress relief annealing processing; this optimizes the model making process, and at the same time optimizes the lost foam casting process, solves the deformation problems of suspended parts, shrinkage holes and shrinkage problems in thick and large parts, and slag inclusion problems during processing, and avoids shrinkage holes and shrinkage defects and inclusion problems on the machined surface through the setting of the pouring system and the coordinated use of inner chillers and sand-insulating chillers, providing castings that meet the acceptance standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 is a schematic diagram of a casting of the present invention;

[0029] Figure 2 It is a schematic diagram of the model of the present invention with support;

[0030] Figure 3 It is a schematic diagram of the model of the present invention with an internal chiller;

[0031] Figure 4 It is a schematic diagram of the stepped inner chiller of the present invention;

[0032] Figure 5 is a temperature curve diagram of stress relief annealing of the present invention;

[0033] Figure 6 This is an electron microscope image of the casting of the present invention before corrosion;

[0034] Figure 7 It is an electron microscope picture of the casting of the present invention after corrosion. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0036] It should be noted that, unless otherwise defined, the technical or scientific terms used in the present invention should have the usual meanings understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0037] like Figures 1 to 5 As shown, a method for lost foam casting of suspended punch insert type castings includes the following steps:

[0038] S1, Foam model making: In order to reduce the probability of slag inclusion defects on the bottom surface of the casting during the later pouring process, a foam model with a density of less than 20KG / m 3 For low-density copolymer foam board, the key surface serves as the pouring bottom, and the bottom serves as the slag removal surface, with a 20mm overhang. The overhanging surface, the lower machined surface, and the contour surface are also oversized by 20mm. All other surfaces, except the upper overhanging surface, are oversized as normal to prevent casting deformation that could result in the overhanging surface, lower machined surface, and contour surface being lost. The model is directly machined using CNC machining, along with any holes to be machined, facilitating later measures to prevent shrinkage cavities and porosity within the holes. Furthermore, to prevent deformation of the overhanging area during the coating and sand embedding processes, 80*60mm supports are added to the machined surfaces at both ends of the underside of the overhanging area, and 80*60mm supports are added every 250mm in the middle. The bottom of the supports are maintained at the same height as the bottom of the model. The supports are CNC machined along with the model, and " / " marks are placed on the sides of the supports to facilitate their removal later.

[0039] S2, gating system settings:

[0040] First, the model is only 360mm tall. A bottom-injection pouring system is used, with six φ50 ingates placed, each positioned away from drilled holes. The sprue is positioned at the center of the model to ensure rapid and smooth filling of the molten iron. After the pouring system is set up, simulations are performed using casting CAE software. The gate positions are adjusted until all defects are eliminated. Through CAE casting simulations, potential shrinkage cavities and porosity are precisely located in the casting.

[0041] S3, chiller position selection: by arranging sand-insulating chillers on the molding surface and the mounting surface, the positions of the machining holes of the casting are identified in advance according to the drawings, and a 60mm diameter cast iron rod with sand-insulating is placed at the safety bolt through-hole position, and a 20mm diameter inner chiller is placed at the molding through-hole position. At the same time, a stepped inner chiller is placed at the tapped threaded hole position on the thick and large part of the side surface; the inner chiller needs to be machined into shape, and the surface must be smooth and rust-free. The end of the 300mm long and 30mm diameter inner chiller is machined to a diameter of 10mm and a length of 60mm to enhance the chilling effect and avoid shrinkage defects in the hole.

[0042] S4, coating and drying:

[0043] First, seal the mold surface through-holes and side tapped holes with tape to prevent paint from entering the holes. After the product model is processed, it is curtain coated with a water-based coating with a Baume degree of 60. After two coats of curtain coating, the minimum coating thickness of the model is controlled to be no less than 1.3mm. While the model is drying, the drying support frame is leveled to prevent deformation during drying.

[0044] S5, reinforcement model: After the model is dried, it is reinforced. Foam boards are filled between the 80*60mm supports below the suspended part and between the supports and the bottom flange surface, and fixed with bamboo sticks to prevent the reinforcement foam from moving when burying sand.

[0045] S6, model pre-processing: Place the model on the modeling platform and measure the deformation of the model, and place small counterweights around the model and above the surface of the suspended parts to ensure that the model is in close contact with the platform. At the same time, prevent the suspended parts from being lifted up during the molding sand burying process, which will result in a shortage of the processing surface below the suspended parts and a large surface processing allowance. Afterwards, the positions where sand-isolating chillers need to be placed will be marked on the model surface to facilitate identification by the modeling personnel. The tape used to seal the processing holes before coating will be removed, and a 300mm long and 20mm diameter internal chiller will be placed on the surface through-holes. Step-type internal chillers (30mm in diameter and 10mm in diameter, with lengths of 240mm and 60mm respectively) will be placed on the side tapped threaded holes. The contact surface between the internal chiller and the model will be painted with alcohol-based paint with a coating thickness of about 2mm, and the paint will be dried.

[0046] S7: Molding. Add 1.0% resin to the molding sand to ensure a strength greater than 1.5 MPa. Tamp the sand while burying it. Place the upper sand barrier chiller according to the process plan. After burying the sand in the lower box, wait for the sand to solidify and gain strength. After 6 hours, turn the box over. Remove the reinforcing foam after turning over, and install a slag discharge seat and slag channel on the bottom. Finally, vacuum the surface sand on the bottom of the model and continue burying the sand. After molding, secure the upper and lower sand boxes with clamps. Once fully solidified, hoist them to the pouring area.

[0047] S8, Model Pouring: Before pouring, place a weight on the flask surface. The weight of the weight should be seven times the pouring weight. This weight resists the pressure of the molten iron pouring, the pressure generated by the foam vaporization, and the expansion force of the ductile iron during graphitization, thereby preventing deformation of the casting during the pouring process. The pouring material is: C 3.6%, Si 2.3%, Mn 0.5%, Cr 0.2%, Cu 0.8%, Mg 0.08%, Re 0.03%, P 0.02%, S 0.010%, and the remainder is Fe and unavoidable impurities. By adjusting the chemical composition of the molten metal, increasing the carbon equivalent of the molten iron to a hypoeutectic composition, and appropriately controlling the composition ratio of the alloying elements, and setting the pouring temperature to 1365°C, the shrinkage tendency of the molten iron is reduced, which helps to improve the product quality of the punch insert casting.

[0048] S9, Cooling: After pouring, the casting is cooled and sanded. The casting is then hoisted out, the pouring system and riser are removed and polished, and then stress relief annealing is performed. If the residual stress in the casting is not eliminated, it will cause deformation or cracks in the casting after a certain period of time or during the subsequent cutting process. Through strict annealing process control, the molecular structure inside the casting can be effectively made more uniform and stable. Only by performing an effective annealing process can good machine tool parts be produced. The stress relief annealing of the movable table pad casting is to first heat the cast casting to 550℃ at a rate of 60℃ / h, then keep it warm for 12h, and finally cool it to 200℃ at a rate of 30℃ / h, and then air cool it to room temperature. The stress relief heating temperature is low, and there is no structural transformation during the annealing process. The main purpose is to eliminate the residual stress in the casting, stabilize the size and shape of the casting, and reduce the deformation and crack tendency of the movable table pad during cutting and use.

[0049] S10, after annealing, the casting is shot blasted and machined to remove the 80*60mm support.

[0050] This optimizes the model making process and the lost foam casting process at the same time, solves the deformation problems of suspended parts, shrinkage holes and porosity in thick parts, and slag inclusion problems during processing. By setting up the casting system and cooperating with the use of internal chiller and sand-insulating chiller, shrinkage holes and porosity defects and inclusion problems on the processed surface are avoided, providing castings that meet the acceptance standards.

[0051] The performance of the obtained castings was tested, as shown in the following table

[0052] Table 1 Material properties of punch insert castings

[0053]

[0054] Combined with the electron microscope image of the corrosion test on the casting Figure 6 and Figure 7 It can be seen that the castings prepared by this process have good strength, good elongation, high hardness, high pearlite content, and corrosion resistance.

[0055] Those skilled in the art will understand that the discussion of any of the above embodiments is merely illustrative and is not intended to limit the scope of the present invention to these examples. Within the spirit and principles of the present invention, the technical features of the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and many other variations exist in the various aspects of the present invention described above, which are not provided in detail for the sake of clarity. Any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for lost foam casting of suspended punch insert castings, characterized in that: The following steps are included: Step 1: Making a foam model: Use foam board, use the mold surface as the pouring bottom, the bottom surface as the slag discharge surface, and increase the bottom surface by 20mm. At the same time, increase the mold surface above the suspended part, the lower processing surface, and the contour surface by 15-20mm. Make a foam model through CNC machining, and process the holes to be processed; add 80*60mm supports on the processing surfaces at both ends of the bottom surface of the suspended part, and add 80*60mm supports every 250mm in the middle part. Keep the bottom surface of the support at the same height as the bottom surface of the model. The support and the model are processed together through CNC, and mark the side of the support. Step 2: Setting up the pouring system: A bottom pouring system was used, with six φ50 ingates placed, each avoiding the drilled holes. The sprue was set at the center of the model to ensure rapid and stable filling of the molten iron. Simulation was then performed using casting CAE software, with the sprue positions adjusted until all defects were eliminated. Step 3: Chill position selection: Sand-insulating chillers are arranged on the mold surface and mounting surface. The positions of the machining holes of the casting are identified in advance according to the drawings. A 60mm diameter cast iron rod is placed at the safety bolt through-hole. A 20mm diameter inner chiller is placed at the mold through-hole. At the same time, a stepped inner chiller is placed at the tapping threaded hole position on the thick side surface. Step 4: coating and drying: First, seal the through holes on the model surface and the tapped threaded holes on the side with tape to prevent paint from entering the holes. Then, apply curtain coating to the product model and dry it after curtain coating. Step 5: Model shaping: Before shaping, place the model on the shaping platform and measure its deformation. Place small counterweights around the model and on the overhanging parts. Then, mark the locations where sand-insulating chillers will be placed on the model surface. Remove the tape that sealed the machined holes before coating. Place cylindrical inner chillers on the surface through-holes and stepped inner chillers on the side tapped holes. Molding, tamp the sand while burying it, place the sand separator chiller, and after the sand is buried in the lower box, wait for the sand to solidify and gain strength. Turn the box over after 5-6 hours, remove the reinforcing foam, and set up a slag discharge seat and slag discharge channel on the bottom. Finally, clean the surface of the bottom of the model with a vacuum cleaner and continue to bury the sand. After the molding is completed, fix the upper and lower molding sand boxes with clips, and hoist them to the pouring area after they are completely solidified. Step 6: Model pouring: Place a weight on the surface of the sand box before pouring. The weight of the weight should be 7 times the weight of the pouring. Then pour at a temperature of 1365±5℃. Step 7: Cooling: After pouring, cool the casting and remove the sand. Then, lift the casting out, remove the gating system and riser, polish them flat, and then perform stress relief annealing. Step 8: Machining: After annealing, the casting is shot blasted and machined to remove the 80*60mm support.

2. A method for lost foam casting of suspended punch insert type castings according to claim 1, characterized in that: The density of step 1 is less than 20KG / m 3 Low density copolymer foam board material.

3. The lost foam casting method of suspended punch insert type casting according to claim 1, characterized in that: In step three, the inner chiller needs to be machined into shape with a smooth and rust-free surface. The end of the inner chiller with a length of 300 mm and a diameter of 30 mm is machined into a diameter of 10 mm and a length of 60 mm to enhance the chilling effect and avoid shrinkage defects in the hole.

4. The lost foam casting method of suspended punch insert type casting according to claim 1, characterized in that: The Baume degree of the water-based coating applied in step 4 is 55-65, and the minimum thickness of the model coating after two coats of coating is not less than 1.3 mm.

5. The lost foam casting method of suspended punch insert type casting according to claim 1, characterized in that: The reinforcement model is also included between step four and step five: the model is reinforced after drying, and foam boards are filled between the supports below the suspended part and between the supports and the bottom flange surface, and are fixed with bamboo sticks to prevent the reinforcement foam from moving when burying sand.

6. The lost foam casting method of suspended punch insert type casting according to claim 1, characterized in that: In the step 5, the contact surface between the inner chill and the model is painted with alcohol-based paint with a coating thickness of 2 mm, and the model is formed after the paint is completely dried.

7. A method for lost foam casting of suspended punch insert type castings according to claim 4, characterized in that: The resin addition ratio of the molding sand in step 5 is 1.0%, ensuring that the strength of the molding sand is greater than 1.5 MPa.

8. The lost foam casting method of suspended punch insert type casting according to claim 1, characterized in that: The pouring material in step six is: C 3.5-3.7%, Si 2.0-2.6%, Mn 0.4-0.7%, Cr 0.1-0.3%, Cu 0.6-1.0%, Mg 0.04-0.06%, Re 0.02-0.04%, P≤0.05%, S≤0.012%, and the rest are Fe and impurity elements.

9. The lost foam casting method of suspended punch insert type casting according to claim 1, characterized in that: The stress relief annealing step seven is specifically as follows: first, the cast casting is heated to 540-560°C at a rate of ≤60°C / h, then kept at this temperature for 12 hours, and finally cooled to 200°C at a rate of ≤30°C / h, and then air-cooled to room temperature.

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