A processing method for repairing gas shrinkage holes of a die casting
By using X-ray flaw detection and high-speed friction extrusion repair, the problems of surface quality and airtightness of the die casting caused by gas shrinkage cavities were solved, achieving efficient and stable repair results and improving the overall performance of the die casting.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHANJIANG DENI VEHICLE PARTS
- Filing Date
- 2026-03-27
- Publication Date
- 2026-06-02
AI Technical Summary
After machining, die-cast parts suffer from substandard surface quality and airtightness leakage due to shrinkage cavities. Existing repair methods are inefficient and prone to secondary defects, making it difficult to meet high-precision requirements.
X-ray flaw detection and trial cutting were used to identify gas shrinkage cavities. Combined with high-speed friction extrusion repair, the defects in the cavity wall were filled by the high-speed rotation and axial feeding of the extrusion sleeve. Ultrasonic flaw detection and dimensional inspection were then performed to verify the repair effect.
It effectively eliminates air shrinkage cavities, improves the density and performance of the pore wall, avoids secondary defects such as hot cracks, and significantly improves the microhardness and fatigue resistance of the repaired pore wall, meeting high precision requirements.
Smart Images
Figure CN122125442A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of metal processing technology, specifically a processing method for repairing gas shrinkage cavities in die-cast parts. Background Technology
[0002] During the production of high-pressure aluminum and zinc alloy die-castings, porosity and shrinkage cavities (collectively referred to as gas shrinkage cavities) are easily formed inside the castings due to factors such as gas evolution and solidification shrinkage within the molten metal. When these defects are located in the periphery of holes to be machined (such as mounting holes, oil passages, etc.), these defects will be exposed on the inner wall of the hole after the remaining material is removed by subsequent mechanical cutting. This will lead to substandard surface quality and excessive porosity within the hole, and leakage will occur during airtightness testing, causing the entire part to be scrapped because it cannot meet performance requirements.
[0003] The problem of shrinkage cavities has long existed in the die-casting industry, seriously affecting the yield rate of castings, increasing the workload of die-casting and machining processes, and also causing a large waste of raw materials and energy, thus increasing overall production costs. Traditionally, for parts with exposed shrinkage cavities, scrapping or attempted repair welding are often adopted. However, the repair welding process has problems such as a large heat-affected zone, easy generation of new stresses and defects, unstable repair results, low efficiency, and high skill requirements for operators, making it difficult to meet the needs of large-volume, high-quality repair of high-precision, high-performance die-cast parts. Summary of the Invention
[0004] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide a processing method for repairing gas shrinkage cavities in die castings.
[0005] The technical solution adopted by this invention to solve its technical problem is: a processing method for repairing gas shrinkage cavities in die-cast parts, comprising the following steps: S1. X-ray flaw detection: X-ray flaw detection is used to detect the hole positions of die casting blanks to identify internal gas shrinkage defects. S2. Trial cutting and cross-section verification: Trial cutting and cross-sectioning are performed at the defect locations found by X-ray flaw detection. The morphology and distribution of gas shrinkage cavities are confirmed by electron microscopy to determine whether they meet the product technical requirements. If they meet the requirements, the product passes inspection; if they do not meet the requirements, repair processing is carried out. S3. High-speed friction extrusion repair processing: An extrusion sleeve is fitted onto the spindle, and the spindle is started until the extrusion sleeve reaches the preset speed and stabilizes; then the extrusion sleeve is controlled to move near the hole opening, and the extrusion feed speed is switched when it is a set distance away from the hole opening; after the extrusion sleeve enters the hole, it maintains rotation and axial feed, and moves at a constant speed along the hole axis to perform friction extrusion on the hole wall; after the extrusion processing is completed, the extrusion sleeve is withdrawn, and the hole is cooled and cleaned; S4. Samples of the extruded holes are subjected to ultrasonic flaw detection and dimensional inspection to verify the filling effect and dimensional accuracy of the gas shrinkage cavities; if the verification meets the requirements, fine machining is carried out; if the verification does not meet the requirements, the samples are discarded. S5. Perform finishing on the holes and conduct a full inspection on the finished holes to check the condition of the shrinkage holes and the air tightness. If the verification meets the requirements, all verifications are passed; if the verification does not meet the requirements, the holes are rejected.
[0006] Preferably, in step S3, the spindle speed is 1000-5000 rpm and the linear speed is 15-30 m / s.
[0007] Preferably, in step S3, the extrusion feed speed of the extrusion sleeve is 20-100 mm / min, and the machining allowance is 0.2-1 mm.
[0008] Preferably, the extrusion sleeve is made of cemented carbide material.
[0009] Preferably, the extrusion sleeve switches to extrusion feed speed 3-5 mm before entering the orifice.
[0010] As a preferred option, in step S3, when the hole depth is greater than 5 times the hole diameter, a reciprocating extrusion method is adopted, that is, after feeding a section, the hole retracts a small section, and repeats this process multiple times until the bottom of the hole is reached.
[0011] Preferably, in step S4, the sampling inspection ratio is not less than 5%, and the defect elimination rate of ultrasonic flaw detection verification is not less than 99%.
[0012] Preferably, in step S5, the machining allowance on one side is controlled at 0.2-0.6mm.
[0013] Preferably, in step S5, the verification standard for the airtightness test using gas detection is an inflation pressure of not less than 0.2 MPa and a leakage rate of not more than 1.5 mL / min; or the verification standard for the water test using gas detection is a pressure of 0.5 MPa and no leakage after holding the pressure for 30 seconds.
[0014] Preferably, the die-casting material is an aluminum-silicon alloy or a zinc alloy.
[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention solves the technical problem of exposed shrinkage cavities after hole machining in die-cast parts, leading to part scrapping, through a process of detection-verification-extrusion repair-re-verification. The combination of X-ray flaw detection (S1) and trial cutting verification (S2) first non-destructively screens out batches of parts with internal shrinkage cavities. Further microscopic analysis precisely confirms the nature and extent of the defects, providing a clear decision-making basis and target area for subsequent repair. In step S3, high-speed friction extrusion repair utilizes the localized heat generated by the friction between the high-speed rotating extrusion sleeve and the hole wall to rapidly bring the surface metal of the hole wall to its optimal plastic state. Simultaneously, under controllable axial extrusion pressure, the metal undergoes plastic flow, thereby "squeezing in" and densifying the metal in the pre-reserved machining allowance to fill the original shrinkage cavity defects. This avoids secondary defects such as hot cracks, porosity, and stress concentration that may occur with welding repair. The repaired part and the substrate are metallurgically bonded, resulting in high bonding strength and an extremely high defect elimination rate. The high-speed friction extrusion process not only fills the defects, but the accompanying thermo-mechanical coupling also causes dynamic recrystallization of the surface metal of the hole wall, resulting in refined grains and a denser microstructure. This leads to a significant improvement in the microhardness, wear resistance, and fatigue resistance of the repaired hole wall area, thereby extending the service life of the parts. Attached Figure Description
[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 This is a schematic diagram of the high-speed friction extrusion repair process in step S3. Detailed Implementation
[0018] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0020] Example 1 This embodiment discloses a machining method for repairing gas shrinkage cavities in die-cast parts, including the following steps: S1. X-ray flaw detection: X-ray flaw detection was performed on the unfinished mounting holes on a batch of engine bracket castings. The testing equipment and methods were performed in accordance with DIN EN 12681.
[0021] S2. Three parts suspected of having defects were randomly selected, and wire cutting was performed at the defect locations marked on X-rays to cut open the hole wall area. After preparing metallographic samples, they were observed under a scanning electron microscope. Electron microscopy confirmed the presence of dispersed shrinkage cavities, which did not meet the Class I internal quality standard ASTM E505-15. Therefore, it was determined that all holes at this location in this batch required repair.
[0022] S3. High-speed friction extrusion repair processing, such as... Figure 1 As shown, a vertical machining center with a spindle speed adjustable range of ≥5000rpm is selected. The spindle is equipped with a hydraulic tool holder, with a clamping accuracy of ≤0.01mm, and clamps a carbide round bar as an extrusion sleeve. The spindle is started, causing the carbide extrusion sleeve to rotate at a high speed of 1000-5000rpm and run stably. The machine tool is controlled to quickly move the rotating extrusion sleeve above the hole to be repaired. When 3-5mm away from the hole opening, the feed mode is switched from rapid traverse to the preset 20-100 mm / min. The extrusion sleeve enters the hole at a stable speed and a feed rate of 40 mm / min, advancing along the hole axis. This process applies frictional extrusion to the hole wall, with a machining allowance of 0.2-1mm. Frictional heat raises the temperature of the ADC12 aluminum alloy surface layer of the hole wall to approximately 250℃, placing it in a good plastic state. Under the extrusion force, the metal undergoes plastic flow, filling and compacting the gas shrinkage cavities. After completing the extrusion stroke for the entire hole depth, the extrusion sleeve quickly withdraws from the hole opening. Subsequently, compressed air is used to blow away the repaired holes to achieve cooling and cleaning.
[0023] S4. Intermediate verification inspection: Samples are drawn from the repaired parts at a sampling rate of no less than 5%. Ultrasonic testing is performed on the sample holes to verify the filling effect of the shrinkage cavities. The inspection shows that the original defect signals have basically disappeared, and the defect elimination rate is estimated to be no less than 99%. Simultaneously, a pneumatic plug gauge is used to check the hole diameter, and the results are all within ±0.1mm of the deviation. Verification is passed, and the entire batch of parts proceeds to the finishing process.
[0024] S5. Finishing: Using a precision reamer, the repaired hole is precision reamed with a single-sided machining allowance of 0.2-0.6mm to achieve the final dimensions and surface finish requirements. A gas detection method is used: compressed air at a pressure not less than 0.2MPa is introduced and held for 1 minute; the leakage rate is measured to be less than or greater than 1.5mL / min. The condition of the gas shrinkage cavities is re-inspected; randomly selected samples are cut and examined under an electron microscope. If the results show a porosity of less than 0.1%, a dense structure, and compliance with product technical requirements, then all inspection items are qualified, and the part is allowed to be released.
[0025] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A machining method for repairing gas shrinkage cavities in die-cast parts, characterized in that, Includes the following steps: S1. X-ray flaw detection: X-ray flaw detection is used to detect the hole positions of die casting blanks to identify internal gas shrinkage defects. S2. Trial cutting and cross-section verification: Trial cutting and cross-sectioning are performed at the defect locations found by X-ray flaw detection. The morphology and distribution of gas shrinkage cavities are confirmed by electron microscopy to determine whether they meet the product technical requirements. If they meet the requirements, the product passes inspection; if they do not meet the requirements, repair processing is carried out. S3. High-speed friction extrusion repair processing: An extrusion sleeve is fitted onto the spindle, and the spindle is started until the extrusion sleeve reaches the preset speed and stabilizes; then the extrusion sleeve is controlled to move near the hole opening, and the extrusion feed speed is switched when it is a set distance away from the hole opening; after the extrusion sleeve enters the hole, it maintains rotation and axial feed, and moves at a constant speed along the hole axis to perform friction extrusion on the hole wall; after the extrusion processing is completed, the extrusion sleeve is withdrawn, and the hole is cooled and cleaned; S4. Samples of the extruded holes are subjected to ultrasonic flaw detection and dimensional inspection to verify the filling effect and dimensional accuracy of the gas shrinkage cavities; if the verification meets the requirements, fine machining is carried out; if the verification does not meet the requirements, the samples are discarded. S5. Perform finishing on the holes and conduct a full inspection on the finished holes to check the condition of the shrinkage holes and the air tightness. If the verification meets the requirements, all verifications are passed; if the verification does not meet the requirements, the holes are rejected.
2. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, In step S3, the spindle speed is 1000-5000 rpm and the linear speed is 15-30 m / s.
3. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, In step S3, the extrusion feed speed of the extrusion sleeve is 20-100 mm / min, and the machining allowance is 0.2-1 mm.
4. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, The extrusion sleeve is made of cemented carbide material.
5. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, The extrusion sleeve switches to extrusion feed speed 3-5mm before entering the orifice.
6. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, In step S3, when the hole depth is greater than 5 times the hole diameter, a reciprocating extrusion method is adopted, that is, after feeding a section, the hole retracts a small section, and repeats this process multiple times until the bottom of the hole is reached.
7. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, In step S4, the sampling inspection ratio shall not be less than 5%, and the defect elimination rate of ultrasonic flaw detection verification shall not be less than 99%.
8. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, In step S5, the machining allowance on one side is controlled between 0.2 and 0.6 mm.
9. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, In step S5, the verification standard for the airtightness test using gas detection is that the inflation pressure is not less than 0.2 MPa and the leakage is not greater than 1.5 mL / min; or the verification standard for the water test using gas detection is that the pressure is 0.5 MPa and there is no leakage after holding the pressure for 30 seconds.
10. The processing method for repairing gas shrinkage cavities in die-cast parts according to claim 1, characterized in that, The die-casting material is an aluminum-silicon alloy or a zinc alloy.