A preparation method of a drawing die for red copper rectangular tube production

Abstract

A kind of preparation method of drawing die for red copper rectangular tube production, specific preparation method is as follows: using the designed die parameter to prepare die blank, line cutting cavity sizing band and deformation zone, after line cutting, stress annealing is carried out by electric furnace, annealing temperature is 380 DEG C-390 DEG C, the furnace temperature holding time of die is not less than 3-3.5 hours, after annealing to room temperature, grind inner and outer R angle, adopt multiple finished product trial drawing, the inner size of die is ground and shaped according to the outer size of trial drawing pipe, after polishing, the finished product is obtained.The die form used in the application is innovative in material selection and die structure, compared with the die used in traditional process, the core head is saved, the die manufacturing cost is reduced by 50%, the die manufacturing time and product delivery period are greatly shortened, and the inner surface defects of rectangular pipe are obviously reduced.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal smelting and processing, and specifically relates to a method for preparing a stretching die for the production of rectangular copper tubes. Background Technology

[0002] High-precision rectangular copper tubes for industrial use are in high demand in metallurgy, power transmission, and motor manufacturing due to their excellent electrical and thermal conductivity, and are highly favored in the market. The precision and manufacturing cycle of the drawing die directly affect the precision and delivery time of the rectangular copper tube.

[0003] The traditional production process for rectangular copper tubes is as follows: Based on the length-to-width ratio of the rectangular tube product, calculate the die allowance, design the final drawing die and mandrel process route → mold manufacturing → electroplating and polishing of the drawing die and mandrel → drawing into a round tube according to the process → mandrel shaping and drawing within the drawing die. Problems include: the drawing die and mandrel manufacturing process is time-consuming, requiring more than two months, affecting delivery time; the mandrel manufacturing process has high requirements and is difficult to process, making it impossible to guarantee the surface finish of the mandrel, resulting in scratches on the inner wall of the rectangular tube. Summary of the Invention

[0004] To overcome the above shortcomings, the present invention provides a method for preparing a stretching die for the production of rectangular copper tubes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a drawing die for producing rectangular copper tubes includes the following steps: preparing a die blank using pre-designed die parameters; wire-cutting the cavity sizing zone and deformation zone; stress-relief annealing in an electric furnace at 380℃-390℃; holding the die at the furnace temperature for 3-3.5 hours; grinding the inner and outer radius angles after annealing; performing multiple trial drawing operations on the finished product; refining and shaping the die's inner dimensions according to the outer dimensions of the trial-drawn tube; and polishing to obtain the finished product.

[0007] Further optimization involves the design of the mold blank and the mold structure. The mold blank is designed such that its outer diameter is 20-40mm larger than the diagonal of the smallest rectangular tube, and its outer thickness and angle match the thickness and inner hole angle of the mold sleeve.

[0008] The mold structure design includes the design of the mold hole allowance and the design of the mold hole inlet angle. The mold hole allowance is designed based on the length and width of the pipe cross-section, and is specifically divided into the following three types:

[0009] a. When the length-to-width ratio is 1-1.2, the margin is 0.4-0.8%;

[0010] b. When the length-to-width ratio is 1.2-1.5, the margin is 0.8-1%.

[0011] c. When the length-to-width ratio is 1.5-2, the margin is 1-1.3%;

[0012] The center width of the die hole is the sum of the cross-sectional width of the pipe and the die hole allowance;

[0013] The die inlet angles β, β1, and α are set according to the transition circle size, and the die inlet diagonal is 1.1-1.2 times the outer diameter of the transition circle.

[0014] Further optimization involves leaving a 0.05mm grinding allowance when machining the wire-cut die cavity.

[0015] To further optimize, during the trial drawing of the finished product, the amount of grinding each time should not exceed 70% of the difference between the lower tolerance limit and the actual size.

[0016] Further optimization involves first manually grinding the mold to achieve a cavity roughness of 0.7-0.9, and then polishing with a tapered cloth abrasive wheel to achieve an inner hole roughness of 0.4. The manual grinding uses a mixture of borax and polishing paste with a mass ratio of 1:2-1:2.5.

[0017] Beneficial effects of the present invention

[0018] 1. In terms of material selection, the mold material used in traditional processes is T8A chrome-plated material. During use, when copper sticks to the surface of the mold cavity or defects occur, polishing and repair will cause the chrome plating layer to fall off, and the wear resistance of the mold will be greatly reduced. However, Cr12MoV material is used, which has better overall hardness and wear resistance and does not affect grinding.

[0019] 2. In terms of mold structure, after the die hole allowance is optimized, the tube is drawn to the required wall thickness in the transition round pass. No rod (core head) is used during the drawing process. The outer dimension of the tube in the finished pass is directly determined, which avoids the risk of scratches on the inner surface of rectangular tubes.

[0020] The mold design used in this invention innovates in material selection and mold structure. Compared with the molds used in traditional processes, it eliminates the core head, reduces mold manufacturing costs by 50%, significantly shortens mold manufacturing time and product delivery time, and significantly reduces defects on the inner surface of rectangular tubes. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the tube mold blank;

[0022] Figure 2 This is a schematic diagram of the die angle β for drawing rectangular tubing;

[0023] Figure 3 This is a schematic diagram showing the angle α of the die for drawing rectangular tubing.

[0024] Figure 4 This is a schematic diagram of the die angle β1 for drawing rectangular tubing.

[0025] Figure 5 This is a schematic diagram of a rectangular tube forming process.

[0026] Figure 6 This is a schematic diagram of a rectangular tube forming structure.

[0027] Figure 7 This is a side view of the rectangular tube forming process.

[0028] Figure 8 This is a top view of the rectangular tube forming process. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings.

[0030] A method for preparing a stretching die for the production of rectangular copper tubes, the specific steps of which are as follows:

[0031] Step 1: The material for the stretching die is cold work die steel. Based on the company's product structure and scale, relevant specifications of tube die blanks can be pre-stocked. The design of the tube die blank is as follows: the outer diameter φ is greater than the diagonal of the minimum specification rectangular tube +20mm-40mm; the outer thickness and angle match the die sleeve thickness and inner hole angle; to facilitate wire cutting and wire threading, the inner hole of the blank φ1=10mm.

[0032] Step 2, Mold Design:

[0033] a. Mold cavity allowance k design: The mold cavity length, shoulder width, and center width are labeled A, B1, and B respectively, where the center width is calculated as follows:

[0034] B = B1 + B1 × margin k;

[0035] When the ratio of length A to width B1 is 1-1.2, the margin k is 0.4-0.8%.

[0036] When the ratio of length A to width B1 is 1.2-1.5, the margin k is 0.8-1%.

[0037] When the ratio of length A to width B1 is 1.5-2, the margin k is 1-1.3%.

[0038] The above three standard aspect ratios apply to all rectangular tubes in the national standard;

[0039] b. Design of the die inlet angle:

[0040] The mold angles β, β1, and α are designed based on the transition circle dimensions to ensure that the diagonal of the mold inlet is 1.1-1.2 times the outer diameter of the transition circle;

[0041] The inner radius of the mold (R) is equal to the outer radius of the rectangular tube minus 1mm.

[0042] Step 3: Use a large taper wire cutter to cut the cavity sizing zone and deformation zone, leaving a 0.05mm grinding allowance;

[0043] Step 4: After wire cutting, use a regular electric furnace for stress-relief annealing. Set the temperature to 380℃-390℃. After the mold is heated to the set temperature with the furnace, hold it at that temperature for 3-3.5 hours. Then turn off the power and let it cool naturally to room temperature before removing it from the furnace.

[0044] Step 5: Grind the inner and outer radius angles to meet the requirements of the drawing;

[0045] Step 6: The finished product drawing no longer uses the mandrel rod for shaping. Multiple trial drawing is adopted. The inner dimension of the mold is ground and shaped according to the outer dimension of the tube in the trial drawing. The amount of grinding each time is ≤ (lower tolerance limit size - actual size) × 70%. The grinding must ensure the arc transition of the inner dimension and the perpendicularity of the sizing zone. Steps and misalignments are not allowed until the grinding and trial drawing enter the tolerance range, that is, within the range of the outer diameter size and the waist size.

[0046] Step 7: Polishing. First, use a mixture of borax and polishing paste at a mass ratio of 1:2 to 1:2.5 for manual polishing to achieve a roughness of about 0.8 for the mold cavity. Then, use a tapered cloth abrasive wheel of #240 or higher for polishing. The roughness of the inner hole should reach 0.4 to be considered qualified and ready for use.

[0047] Example 1

[0048] A rectangular copper tube with a wall thickness of 86×60×7mm, a transition circle of φ94, an allowable deviation of ±0.5mm for inner and outer dimensions, a waist sag of ≤0.5mm, and an outer fillet radius of R=4.

[0049] Drawing: The die blank is made of Cr12MoV material, with specifications of φ250 (outer diameter) / φ20 (inner diameter) × 70 (thickness). The die angles are β=4°, β1=2°, α=16°, with a margin of 2.3%, B1=60.6, and the die inner radius R=3. A chain-type drawing machine is used for multi-pass drawing. Round drawing ensures uniform pipe wall thickness; the transition to rectangular drawing achieves a smooth transition from round to rectangular. Its advantages include: die preparation completed in 7 days, no mandrel insertion, cost savings, and the pipe's internal and external dimensions, central waist collapse, and radius R all meet requirements, with a smooth inner wall.

[0050] Example 2

[0051] A rectangular copper tube with dimensions of 60×33×5 (wall thickness) mm, a transition circle of φ60, an allowable deviation of ±0.35 mm for inner and outer dimensions, a waist diameter of ≤0.35 mm, and an outer fillet radius of R=4.

[0052] Drawing: The die blank is made of Cr12MoV material, with specifications of φ150 (outer diameter) / φ10 (inner hole) × 50 (thickness). The die angles are β=3°, β1=2°, α=18°30′, with a margin of 3%, B1=33.33, and the inner radius of the die is R=3. A chain-type drawing machine is used for multi-pass drawing. Round drawing ensures uniform pipe wall thickness; the transition to rectangular drawing achieves the transition from round to rectangular. Its characteristics include: die preparation completed in 5 days, no mandrel not used, cost savings, and product inspection showing that the internal and external dimensions, center waist size, and radius of curvature all meet requirements, with a smooth inner wall.

[0053] The foregoing has shown and described the main features, usage methods, basic principles, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention based on actual circumstances without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a stretching die for producing rectangular copper tubes, characterized in that, The specific preparation method is as follows: A mold blank is prepared using pre-designed mold parameters. The cavity sizing zone and deformation zone are then wire-cut. After wire cutting, the mold undergoes stress-relief annealing in an electric furnace at 380℃-390℃. The mold is heated in the furnace and held for 3-3.5 hours. After power is cut off and the mold cools to room temperature, it is removed from the furnace. The inner and outer radius angles are ground. Multiple trial pulls are performed, and the inner dimensions of the mold are ground and shaped according to the outer dimensions of the test-pulled tube. The finished product is obtained after polishing. The mold parameters include the design of the mold blank and the mold structure. The mold blank is designed as follows: the outer diameter of the blank is 20-40mm larger than the diagonal of the smallest rectangular tube, and the outer thickness and angle match the thickness and inner hole angle of the mold sleeve. The mold structure design includes the design of the mold hole allowance and the design of the mold hole inlet angle. The mold hole allowance is designed based on the length and width of the pipe cross-section, and is specifically divided into the following three types: a. When the length-to-width ratio is 1-1.2, the margin is 0.4-0.8%; b. When the length-to-width ratio is 1.2-1.5, the margin is 0.8-1%. c. When the length-to-width ratio is 1.5-2, the margin is 1-1.3%; The center width of the die hole is the sum of the cross-sectional width of the pipe and the die hole allowance; The die inlet angles β, β1, and α are set according to the transition circle size, and the die inlet diagonal is 1.1-1.2 times the outer diameter of the transition circle.

2. The method for preparing a stretching die for producing rectangular copper tubes as described in claim 1, characterized in that, Leave a 0.05mm grinding allowance when wire cutting the mold cavity.

3. The method for preparing a stretching die for producing rectangular copper tubes as described in claim 1, characterized in that, When drawing finished products, the amount of grinding done each time should not exceed 70% of the difference between the lower tolerance limit and the actual size.

4. The method for preparing a stretching die for producing rectangular copper tubes as described in claim 1, characterized in that, The mold is first manually ground to achieve a roughness of 0.7-0.9 in the mold cavity, and then polished with a conical cloth abrasive wheel. After polishing, the roughness of the inner hole reaches 0.

4. The manual grinding uses a mixture of borax and polishing paste with a mass ratio of 1:2-1:2.5.

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