Method for machining a cast lower nozzle of a nuclear fuel assembly

Abstract

The application relates to the technical field of nuclear fuel element manufacturing, and particularly discloses a mechanical processing method for a cast lower tube support of a nuclear fuel assembly, which comprises the following steps: step 1, fixing a tube support blank; step 2, fine milling an inner cavity; step 3, processing S holes and chamfering each skirt edge; and step 4, processing a welding position. The processing method can meet the continuous and rapid processing requirement of the cast lower tube support of the fuel assembly, and can ensure that the structural features and overall shape size of each part of the cast lower tube support meet the drawing and technical requirements.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel element manufacturing technology, specifically relating to a method for machining a casting molded lower tube seat for nuclear fuel assemblies. Background Technology

[0002] Cast lower tube seats are thin-walled, multi-cavity components, and the sequence of machining steps directly affects the final deformation of the seat. The machining datum for cast lower tube seats is difficult to determine. During machining, the positioning datum from the casting process must be considered, and before machining, each key positioning surface needs to be milled and measured to compensate for any offsets in the machining coordinate system to ensure the product's structural dimensions. The machining process for cast lower tube seats is complex, and currently, it is still in the initial development stage in China.

[0003] In order to ensure the manufacturing technology requirements of the cast lower tube seat and fill the gap in the existing machining of cast tube seats for nuclear fuel elements, it is urgent to design a machining method for the cast lower tube seat of nuclear fuel assembly. Summary of the Invention

[0004] The purpose of this invention is to provide a machining method for the casting lower tube seat of nuclear fuel assemblies, so as to meet the requirements of continuous and rapid machining of the casting lower tube seat of fuel assemblies.

[0005] The technical solution of the present invention is as follows:

[0006] A method for machining a cast lower tube seat for nuclear fuel assemblies includes the following steps:

[0007] Step 1: Fix the tube seat blank;

[0008] Step 2: Precision milling of the inner cavity;

[0009] Step 3: Machining the S-holes and chamfering each skirt edge;

[0010] Step 4: Process the weld joint.

[0011] Specifically, the following steps are included:

[0012] Step 1: Fix the tube seat blank

[0013] Clamp the blank material with flat-nose pliers, use a dial indicator to initially align the pipe seat using the casting reference surface, and then machine the process hole.

[0014] The tube seat is positioned through the process hole, and the tube seat is clamped by a fixture and fixed on the machining center.

[0015] Step 2: Precision milling of the inner cavity

[0016] Measure the machining allowance of the inner cavity, and add the machining allowance values ​​of each side into the workpiece coordinate system through coordinate system compensation;

[0017] Set the machining parameters of the tool, use an end mill for roughing, after roughing, leave a margin of more than 0.4mm on all four sides of the inner cavity, initially level the inner cavity surface, use an infrared probe to measure the finishing margin, and finally finish to the required dimensions.

[0018] Step 3: Machining S-holes and chamfering of each skirt edge

[0019] When machining the S-hole, the upper surface water flow hole is used for positioning, and the tube seat is positioned on the fixture by using a fixing pin; the position of the water flow hole is located by using an infrared probe, and the workpiece coordinate system is established based on the spatial position relationship of the water flow hole. The position of the S-hole is found in the workpiece coordinate system by calculation, and the allowance is measured to see if it meets the machining requirements.

[0020] If the requirements are met, use a forming reamer to process the S-hole to the qualified size in one go, and use a chamfering cutter to process the chamfers of each skirt edge to ensure that the chamfer size and its positional relationship with the S-hole meet the requirements.

[0021] Step 4: Process the weld joint

[0022] When machining the weld joint, S-holes are used for positioning, infrared probes are used to measure the remaining machining allowance of the weld joint on all four sides, the workpiece coordinate system is established with the spatial position of the S-holes as the reference, and carbide end mills are used for rough machining to initially level the weld surface.

[0023] The remaining allowance on all four sides is checked again using an infrared probe to avoid the shape being unable to be machined to the required dimensions due to welding deformation and uneven casting wall thickness.

[0024] If the allowance is sufficient, perform a final finishing process to the median dimension required by the technical specifications; if the allowance is insufficient, calculate reasonable machining dimensions within the tolerance zone to ensure that the overall dimensions and the dimensions of the S-hole and the four-sided positions meet the requirements.

[0025] In step 1, the process hole is rough-machined using a drill bit and finished using a reamer.

[0026] In step 1, the machining process holes are made to ensure that the dimensional tolerance of the process holes is less than 0.02 mm and the form and position tolerance is less than 0.02 mm.

[0027] In step 1, a clamping fixture is used to hold the pipe seat.

[0028] In step 2, the cutting speed of the tool is set to 60-80 m / min.

[0029] In step 2, the feed rate is set to 0.1-0.5 mm / r during tool finishing.

[0030] In step 2, the cutting depth ap is set to 2-5 mm during rough machining.

[0031] In step 2, the cutting depth ap is set to 0.2-0.5 mm for finishing.

[0032] In step 4, the roughing speed is 1000 rpm, the feed F = 100, and the allowance on all four sides is greater than 0.4 mm.

[0033] The significant advantages of this invention are:

[0034] (1) The processing method of the present invention can meet the continuous and rapid processing requirements of the casting lower tube seat of the fuel assembly, and ensure that the structural features and overall dimensions of each part of the casting lower tube seat meet the drawings and technical requirements.

[0035] (2) The processing method of the present invention can be applied to the machining of various fuel assembly casting lower tube seats. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the cast lower tube seat for nuclear fuel assemblies. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] A method for machining a cast lower tube seat for nuclear fuel assemblies includes the following steps:

[0039] Step 1: Fix the tube seat blank

[0040] Clamp the blank material with flat-nose pliers, use a dial indicator to initially align the pipe seat using the pre-reserved datum surface in the casting, use a drill bit to rough machine the process hole, and use a reamer to finish machine the process hole, ensuring that the dimensional tolerance of the process hole is less than 0.02mm and the form and position tolerance is less than 0.02mm, and ensuring positioning accuracy.

[0041] The tube seat is positioned through the process hole, and a clamping fixture is used to hold the tube seat and fix it on the machining center.

[0042] Step 2: Precision milling of the inner cavity

[0043] The machining allowance of the inner cavity is measured. Since the inner cavity is cast, the allowances on each side are inconsistent. After the measurement is completed, the machining allowance values ​​of each side are added into the workpiece coordinate system through coordinate system compensation.

[0044] Set the cutting speed, feed rate, depth of cut, and other machining parameters for the tool;

[0045] Next, use an end mill for rough machining. After rough machining, leave a margin of more than 0.4mm on all four sides of the inner cavity. Initially level the inner cavity surface, use an infrared probe to measure the finishing margin, and finally finish machine to the required dimensions.

[0046] Cutting speed: To ensure reasonable tool durability, the cutting speed should be reduced. Generally, it should be selected as 40-60% of the cutting speed for ordinary carbon steel, usually 60-80 m / min. If it is a small diameter tool or a special tool, the cutting speed should be reduced by 5% due to the poor tool rigidity, heat dissipation, cooling and lubrication effect and chip removal.

[0047] Feed rate: To improve the surface quality of the machined surface, a smaller feed rate should be used during finishing. At the same time, it should be noted that the feed rate should not be less than 0.1 mm / r, and micro-feeding should be avoided to prevent cutting in the work-hardened zone. Also, care should be taken to ensure that the cutting edge does not linger on the cutting surface. The feed rate is generally selected from 0.1 to 0.5 mm / r.

[0048] Depth of cut ap: When roughing, the allowance is large, so a larger depth of cut should be selected to reduce the number of passes and avoid the tool tip from contacting the workpiece surface, thus reducing tool wear. However, when increasing the depth of cut, care should be taken not to cause vibration due to excessive cutting force. An ap of 2 to 5 mm can be selected. When finishing, a smaller depth of cut can be selected, and the hardened layer should be avoided. Generally, an ap of 0.2 to 0.5 mm is used.

[0049] Step 3: Machining S-holes and chamfering of each skirt edge

[0050] When machining the S-hole, the upper surface water flow hole is used for positioning, and the tube seat is positioned on the fixture by using a fixing pin; the position of the water flow hole is located by using an infrared probe, and the workpiece coordinate system is established based on the spatial position relationship of the water flow hole. The position of the S-hole is found in the workpiece coordinate system by calculation, and the allowance is measured to see if it meets the machining requirements.

[0051] If the requirements are met, use a forming reamer to process the S-hole to the qualified size in one go, and use a chamfering cutter to process the chamfers of each skirt edge to ensure that the chamfer size and its positional relationship with the S-hole meet the requirements.

[0052] Step 4: Process the weld joint

[0053] When machining the weld joint, S-holes are used for positioning. Infrared probes are used to measure the remaining machining allowance on all four sides of the weld joint. The workpiece coordinate system is established with the spatial position of the S-holes as the reference. Carbide end mills are used for rough machining at a speed of 1000 rpm and a feed rate of F=100. The allowance on all four sides is greater than 0.4 mm. The weld surface is initially leveled.

[0054] The remaining allowance on all four sides is checked again using an infrared probe to avoid the shape being unable to be machined to the required dimensions due to welding deformation and uneven casting wall thickness.

[0055] If the allowance is sufficient, perform a final finishing process to the median dimension required by the technical specifications; if the allowance is insufficient, calculate reasonable machining dimensions within the tolerance zone to ensure that the overall dimensions and the dimensions of the S-hole and the four-sided positions meet the requirements.

[0056] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0057] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for machining a casting molded lower tube seat for nuclear fuel assemblies, characterized in that: The steps include: Step 1: Fixing the tube seat blank; Step 2: Precision milling of the inner cavity; Step 3: Machining the S-holes and chamfering all skirt edges; Step 4: Process the weld joint; Specifically, the following steps are included: Step 1: Fix the tube seat blank Clamp the blank material with flat-nose pliers, use a dial indicator to initially align the pipe seat using the casting reference surface, and then machine the process hole. Position the tube seat through the process hole, clamp the tube seat with a fixture, and fix the tube seat on the machining center; Step 2: Precision mill the inner cavity. Measure the machining allowance of the inner cavity, and add the machining allowance values ​​of each side into the workpiece coordinate system through coordinate system compensation; Set the machining parameters of the tool, use an end mill for roughing, after roughing, leave a margin of more than 0.4mm on all four sides of the inner cavity, initially level the inner cavity surface, use an infrared probe to measure the finishing margin, and finally finish to the required dimensions. Step 3: Machining the S-holes and chamfering each skirt edge. When machining the S-hole, the upper surface drainage hole is used for positioning. The tube seat is positioned on the fixture by using a fixing pin. An infrared probe is used to locate the position of the drainage hole. The workpiece coordinate system is established based on the spatial position relationship of the drainage hole. The position of the S-hole is found in the workpiece coordinate system by calculation, and the allowance is measured to see if it meets the machining requirements. If the requirements are met, use a forming reamer to process the S-hole to the qualified size in one go, and use a chamfering cutter to process the chamfers of each skirt edge to ensure that the chamfer size and the positional relationship with the S-hole meet the requirements; Step 4: Process the weld joint When machining the weld joint, S-holes are used for positioning, infrared probes are used to measure the remaining machining allowance on all four sides of the weld joint, the workpiece coordinate system is established with the spatial position of the S-holes as the reference, and carbide end mills are used for rough machining to initially level the weld surface. The remaining allowance on all four sides is checked again using an infrared probe to avoid the shape being unable to be machined to the required dimensions due to welding deformation and uneven casting wall thickness. If the allowance is sufficient, perform a final finishing process to the median dimension required by the technical specifications; if the allowance is insufficient, calculate reasonable machining dimensions within the tolerance zone to ensure that the overall dimensions and the dimensions of the S-hole and the four-sided positions meet the requirements.

2. The machining method for the lower tube seat of a nuclear fuel assembly casting as described in claim 1, characterized in that: In step 1, the process hole is rough-machined using a drill bit and finished using a reamer.

3. The machining method for the lower tube seat of a nuclear fuel assembly casting as described in claim 1, characterized in that: In step 1, the machining process holes are made to ensure that the dimensional tolerance of the process holes is less than 0.02mm and the form and position tolerance is less than 0.02mm.

4. The machining method for the lower tube seat of a nuclear fuel assembly casting as described in claim 1, characterized in that: In step 1, a clamping fixture is used to hold the pipe seat.

5. The machining method for the lower tube seat of a nuclear fuel assembly casting as described in claim 1, characterized in that: In step 2, the cutting speed of the tool is set to 60-80 m / min.

6. The machining method for the lower tube seat of a nuclear fuel assembly casting as described in claim 1, characterized in that: In step 2, the feed rate for finishing is set to 0.1–0.5 mm / r.

7. The machining method for the lower tube seat of a nuclear fuel assembly casting as described in claim 1, characterized in that: In step 2, the cutting depth ap is set to 2-5 mm during rough machining.

8. The machining method for the lower tube seat of a nuclear fuel assembly casting as described in claim 1, characterized in that: In step 2, the cutting depth ap is set to 0.2-0.5 mm for tool finishing.

9. A method for machining the lower tube seat of a nuclear fuel assembly casting as described in claim 1, characterized in that: In step 4, the roughing speed is 1000 rpm and the feed rate is F = 100 mm / min, with a allowance of more than 0.4 mm on all four sides.

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