Method for free forging of large crankshaft forgings

Abstract

The application discloses a free forging method for large crank shaft forgings, and particularly relates to the following steps: first fire: chamfering and cutting water riser of a steel ingot, upsetting and elongating to a flat steel ingot, clamping the flat steel ingot to obtain a blank including I, II and III parts; second fire: placing the blank on an upsetting table, elongating the II part in the middle of the blank by using an upper anvil, clamping the I and II parts to obtain a rough forging including I, II, III, IV and V parts; third fire: cooling the end face of the II part of the rough forging and in contact with the upper anvil in step 2, elongating the IV and V parts of the rough forging to obtain a semi-finished forging; fourth fire: elongating and rounding the II, IV and V parts of the semi-finished forging by using the upper anvil and a lower anvil to obtain a finished forging. The forging obtained by the method has a small weight and a long service life.

Description

Technical Field

[0001] This invention belongs to the field of free forging technology, specifically relating to a free forging method for large crankshaft forgings. Background Technology

[0002] In free forging production, there are many large crankshafts that are forged. However, due to the eccentricity during the free forging process of large crankshafts, the forging shrinkage phenomenon is relatively serious, which makes it difficult to control the size of the central concave part. Often, the shape of the forging blank does not meet the requirements of the drawing and is scrapped. Therefore, when using the free forging process, the central concave part is often not forged, which requires more forging allowance, resulting in an increase in the weight of the forging. Moreover, due to the limitation of the shape of the forging, the flow line of the forging is easily cut off during processing, which leads to a reduction in the service life of the parts. Summary of the Invention

[0003] The purpose of this invention is to provide a free forging method for large crankshaft forgings, which solves the problems of existing large crankshaft forgings requiring additional forging allowances and the easy cutting off of the forging flow lines during processing.

[0004] The technical solution adopted in this invention is a free forging method for large crankshaft forgings, which is implemented according to the following steps:

[0005] Step 1, First Fire: Beveling the steel ingot, cutting off the water riser, upsetting and drawing it into a flat square steel ingot, and then stamping the flat square steel ingot to obtain a billet including parts I, II and III;

[0006] Step 2, Second Fire: Place the billet on the upsetting table, use the upper flat anvil to draw out part II in the middle of the billet, and mark parts I and II to obtain a prototype forging including parts I, II, III, IV and V.

[0007] Step 3, Third heat: Cool part II of the prototype forging and the end face that contacted the upper anvil in step 2, and draw out parts IV and V of the prototype forging to obtain a semi-finished forging;

[0008] Step 4, Fourth Fire: Use the upper and lower flat anvils to elongate and round the II, IV, and V parts of the semi-finished forging to obtain the finished forging.

[0009] The invention is further characterized in that,

[0010] In step 1, the upsetting ratio is 2 to 2.2, and the drawing ratio is 3 to 3.5.

[0011] In step 1, the stamping process is as follows: using triangular engraving, two opposite and largest surfaces of the flat square steel ingot and the top surface are stamped, with two parallel stamps on each surface. The stamps on the two largest surfaces are symmetrically arranged, and each set of stamps on the three surfaces is arranged in an n-shape.

[0012] In step 2, the forging ratio for drawing is 3 to 3.5.

[0013] In step 2, the stamping process is as follows: the elongated blank is turned upside down and the two sides and top surface of part I and part III are stamped using a triangular engraving tool. Thus, there are three stamps on part I and part II. The stamps on the sides of part I and part III are set on the same side as the stamp on the surface with the largest area in step 1. The stamps on part I and part II are both set in an n-shape.

[0014] In step 3, cooling is achieved by spraying or water spraying, with a target temperature of 850℃~900℃.

[0015] In step 3, the specific process of drawing is as follows: the cooled end face is placed on the pad, the pad is placed on the upsetting table, and the IV and V parts are drawn in sequence using the upper flat anvil. The drawing ratio is 3 to 3.5.

[0016] The pad is a right quadrangular prism with an isosceles trapezoidal base. The side of the quadrangular prism, which is coplanar with the upper base of the isosceles trapezoid, contacts the cooling end face. The side edges connecting to the two ends of the upper base of the isosceles trapezoid are rounded.

[0017] In step 4, the forging ratio for drawing is 3 to 3.5.

[0018] The beneficial effects of this invention are: the free forging method for large crankshaft forgings of this invention enables the forging of large crankshaft forgings that meet the part contour requirements on a free forging equipment, ensuring the internal flow lines of the forgings and increasing the service life of the forgings; and it eliminates the need for additional forging allowances, reducing the weight of the forgings and lowering the cost of the forgings. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the billet obtained in step 1 of the free forging method of the present invention;

[0020] Figure 2 This is a schematic diagram of the elongation of part II in step 2 of the free forging method of the present invention;

[0021] Figure 3 This is a schematic diagram of the prototype forging obtained in step 2 of the free forging method of the present invention;

[0022] Figure 4 This is a schematic diagram of step 3 in the free forging method of the present invention;

[0023] Figure 5 This is a schematic diagram of step 4 in the free forging method of the present invention.

[0024] In the figure, 1. billet, 2. prototype forging, 3. upper anvil, 4. upsetting platform, 5. spacer block, 6. semi-finished forging, 7. lower anvil, 8. finished forging. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] The free forging method for large crankshaft forgings of the present invention is implemented according to the following steps:

[0028] Step 1, First Fire: Beveling the steel ingot, removing the riser, upsetting, and drawing it into a flat square steel ingot. The upsetting ratio is 2-2.2, and the drawing forging ratio is 3-3.5. The flat square steel ingot is then marked to divide it into parts I, II, and III. Specifically, parts I, II, and III are arranged sequentially from one end of billet 1 to the other, with part II located in the middle and parts I and III located at both ends. This yields billet 1 containing parts I, II, and III.

[0029] The process of card printing is as follows: using triangular engraving to press two opposite and largest surfaces of the flat square steel ingot and the top surface, pressing two parallel imprints on each surface, with the imprints on the two largest surfaces symmetrically arranged, and each set of imprints on the three surfaces arranged in an n-shape.

[0030] The allowance for the flat section is as follows: thickness allowance is 20mm to 30mm, height allowance is 60mm to 80mm, and the width dimension has a large step difference, so the allowance needs to be increased to avoid the width dimension not meeting the forging process requirements due to stretching and shrinkage.

[0031] The size of the card is calculated based on the size of the middle II part of the large crankshaft forging, that is, by adding the heat loss to the weight and then dividing by the density to convert it into volume, which is the existing technology.

[0032] Step 2, Second Fire: Place the billet on the upsetting table 4, and use the upper flat anvil 3 to draw out part II in the middle of the billet 1. The forging ratio is 3 to 3.5. Mark parts I and III. Divide part IV on part I by marking. Part IV is located on the side of part I away from part II. Divide part V on part III by marking. Part V is located on the side of part III away from part II. The prototype forging 2 including parts I, II, III, IV and V is obtained.

[0033] The process of stamping is as follows: the drawn blank 1 is inverted and placed, that is, the surface that contacts the roughing platform 4 during the drawing process is on the top, as the top surface. Triangular engraving is used to stamp the two sides and the top surface of part I and part III respectively, so that three stamps are stamped on part I and part II. The stamps on the sides of part I and part III are set on the same side as the stamp on the surface with the largest area in step 1. The stamps of part I and part II are both set in an n-shape.

[0034] Because part II in large crankshaft forgings has an asymmetrical structure, the upper flat anvil 3 and upsetting table 4 are selected for forging to reduce the width shrinkage while ensuring part II in the forged crankshaft forging.

[0035] Step 3, Third heat: Cool the II part of the prototype forging 2, the end face that was in contact with the upper anvil 3 in step 2, to 850℃~900℃ by spraying or water spraying. Place the cooled end face on the pad 5, and place the pad 5 on the upsetting 4. Use the upper anvil 3 to draw the IV part and V part in sequence, with a forging ratio of 3~3.5, to obtain the semi-finished forging 6;

[0036] Among them, the pad 5 is a right quadrangular prism with an isosceles trapezoidal base. The side of the quadrangular prism, which is coplanar with the upper base of the isosceles trapezoid, contacts the cooling end face. The side edges connected to the two ends of the upper base of the isosceles trapezoid are rounded to facilitate the removal of the pad. The rounded shape can also prevent the forging billet from being forged and broken. The lower base angle of the isosceles trapezoid is 10° to 15°. The length of the lower base of the isosceles trapezoid is 20mm to 30mm shorter than part II of the billet 1. The height of the isosceles trapezoid is equal to the depth of the concave platform corresponding to part II of the prototype forging 2.

[0037] The pad 5 has two functions: (1) When obtaining the prototype forging 2 in step 2, part II needs to be elongated, and a concave platform is formed at the corresponding position of part II. This causes the tops of parts I and III located at the concave platform to shrink into the concave platform. Therefore, the pad 5 is placed in the concave platform (i.e., the cooled end face contacts the pad 5). The wider bottom of the pad 5 can straighten parts I and III. (2) Since part II has been forged in step 2 during the process of obtaining the semi-finished forging 6, when elongating parts IV and V, the prototype forging 2 is elongated. The small contact area between the forging 2 and the upsetting platform 4 leads to increased pressure and severe shrinkage of the forging, resulting in dimensions that do not meet process requirements and potentially causing the forging to be scrapped. Therefore, cooling treatment is performed to increase the deformation resistance of this part through rapid cooling, thereby reducing deformation in this part when drawing parts IV and V. In addition, the contact area between the forging and the upsetting platform 4 is increased by the pad block 5, which supports part II, thus minimizing the shrinkage of the forging and ensuring that the dimensions of the forging meet process requirements.

[0038] When elongating parts IV and V, the lower flat anvil 7 should be used to press down on these parts repeatedly. The initial pressing amount should be 20% of the size of the part to be pressed, and the subsequent pressing amount should not exceed 20%.

[0039] Step 4, Fourth Heat: Using the upper flat anvil 3 and the lower flat anvil 7, the II, IV, and V parts of the semi-finished forging 6 are drawn and rounded, with a forging ratio of 3 to 3.5, to obtain the finished forging 8; after obtaining the finished forging 8, it is necessary to perform a normal tempering treatment.

[0040] The temperatures and holding times for the first, second, third, and fourth tempering processes, as well as the positive tempering, involved in the method of this invention are determined based on the material and the cross-section or ingot shape of the raw material, and belong to the prior art.

[0041] Example 2

[0042] The present invention discloses a free forging method for large crankshaft forgings, which uses 5.2t steel ingots and is made of 42CrMo. The method is implemented according to the following steps:

[0043] Step 1: Heat the billet to 1200±10℃ (bill temperature) and hold for 5 hours. Then, bevel the steel ingot, remove the riser, upset, and draw it into a flat square steel ingot. The upsetting ratio is 2, and the drawing ratio is 3. Mark the flat square steel ingot with the markings to divide it into parts I, II, and III. Specifically, parts I, II, and III are set sequentially from one end of billet 1 to the other end, with part II located in the middle and parts I and III located at both ends. This yields billet 1, which includes parts I, II, and III.

[0044] The process of card printing is as follows: using triangular engraving to press two opposite and largest surfaces of the flat square steel ingot and the top surface, pressing two parallel imprints on each surface, with the imprints on the two largest surfaces symmetrically arranged, and each set of imprints on the three surfaces arranged in an n-shape.

[0045] The allowance for the flat section is as follows: 20mm for thickness and 60mm for height.

[0046] Step 2, heating the billet to 1200±10℃ (bill temperature) and holding for 3 hours: Place the billet on the upsetting table 4, and use the upper flat anvil 3 to draw out part II in the middle of the billet 1. The forging ratio is 3. Mark parts I and III. Divide part IV on part I by marking. Part IV is located on the side of part I away from part II. Divide part V on part III by marking. Part V is located on the side of part III away from part II. The prototype forging 2 including parts I, II, III, IV and V is obtained.

[0047] The process of stamping is as follows: the drawn blank 1 is inverted and placed, that is, the surface that contacts the roughing platform 4 during the drawing process is on the top, as the top surface. Triangular engraving is used to stamp the two sides and the top surface of part I and part III respectively, so that three stamps are stamped on part I and part II. The stamps on the sides of part I and part III are set on the same side as the stamp on the surface with the largest area in step 1. The stamps of part I and part II are both set in an n-shape.

[0048] Step 3, heating to 1200±10℃ (ingot temperature) and holding for 3 hours: Cool the II part of the prototype forging 2 and the end face that contacts the upper anvil 3 in step 2 to 850℃ by spraying or water spraying. Place the cooled end face on the pad 5, and place the pad 5 on the upsetting 4. Use the upper anvil 3 to draw the IV part and V part in sequence. The forging ratio is 3, and the semi-finished forging 6 is obtained.

[0049] Among them, the pad block 5 is a right quadrangular prism with an isosceles trapezoidal base. The side of the quadrangular prism, which is coplanar with the upper base of the isosceles trapezoid, contacts the cooling end face. The side edges connected to the two ends of the upper base of the isosceles trapezoid are rounded. The lower base angle of the isosceles trapezoid is 10°. The length of the lower base of the isosceles trapezoid is 20mm shorter than part II of the billet 1. The height of the isosceles trapezoid is equal to the depth of the concave platform corresponding to part II of the prototype forging 2.

[0050] When elongating parts IV and V, the lower flat anvil 7 should be used to press down on these parts repeatedly. The initial pressing amount should be 20% of the size of the part to be pressed, and the subsequent pressing amount should not exceed 10%.

[0051] Step 4, fourth heating to 1100±10℃ (ingot temperature) and holding for 2 hours: Using upper flat anvil 3 and lower flat anvil 7, elongate and round parts II, IV, and V of the semi-finished forging 6, with a forging ratio of 3, to obtain the finished forging 8; after obtaining the finished forging 8, it is necessary to perform normalizing and tempering treatment. The specific operation of normalizing and tempering is: normalizing at 880±10℃ and holding for 4 hours, tempering at 650±10℃ and holding for 10 hours. The normalizing and tempering process can effectively refine the grains and provide a good microstructure for subsequent heat treatment.

[0052] The performance requirements (i.e., standard requirements) for this component after quenching and tempering are: tensile strength: 690-840 MPa, yield strength ≥460 MPa, elongation ≥15%, reduction of area ≥50%, and impact energy (AKv) ≥35 J. The actual performance test values ​​for this component after quenching and tempering are: tensile strength: 810 MPa, yield strength: 580 MPa, elongation: 22%, reduction of area: 61%, and impact energy (AKv) of 88 / 93 / 89, far exceeding the performance requirements.

[0053] Example 3

[0054] The present invention discloses a free forging method for large crankshaft forgings, which uses 7.5t steel ingots and is made of 34CrNi3Mo. The method is implemented according to the following steps:

[0055] Step 1: Heat the billet to 1220±10℃ (bill temperature) and hold for 6.5 hours. Then, bevel the steel ingot, remove the riser, upset and draw it into a flat square steel ingot. The upsetting ratio is 2.2, and the drawing forging ratio is 3.5. Mark the flat square steel ingot with the markings to divide it into parts I, II, and III. Specifically, parts I, II, and III are set sequentially from one end of billet 1 to the other end, with part II located in the middle and parts I and III located at both ends. This yields billet 1 including parts I, II, and III.

[0056] The process of card printing is as follows: using triangular engraving to press two opposite and largest surfaces of the flat square steel ingot and the top surface, pressing two parallel imprints on each surface, with the imprints on the two largest surfaces symmetrically arranged, and each set of imprints on the three surfaces arranged in an n-shape.

[0057] The allowance for the flat section is as follows: 30mm for thickness and 80mm for height.

[0058] Step 2, heating the billet to 1220±10℃ (bill temperature) and holding for 4.5h: Place the billet on the upsetting table 4, and use the upper flat anvil 3 to draw out part II in the middle of the billet 1. The forging ratio is 3.5. Mark parts I and III. Divide part IV on part I by marking. Part IV is located on the side of part I away from part II. Divide part V on part III by marking. Part V is located on the side of part III away from part II. The prototype forging 2 including parts I, II, III, IV and V is obtained.

[0059] The process of stamping is as follows: the drawn blank 1 is inverted and placed, that is, the surface that contacts the roughing platform 4 during the drawing process is on the top, as the top surface. Triangular engraving is used to stamp the two sides and the top surface of part I and part III respectively, so that three stamps are stamped on part I and part II. The stamps on the sides of part I and part III are set on the same side as the stamp on the surface with the largest area in step 1. The stamps of part I and part II are both set in an n-shape.

[0060] Step 3, heating to 1220±10℃ (ingot temperature) in the third heat and holding for 4.5h: Cooling part II of the prototype forging 2 and the end face that contacted the upper anvil 3 in step 2 to 900℃ by spraying or water spraying. Place the cooled end face on the pad 5, and place the pad 5 on the upsetting 4. Use the upper anvil 3 to draw part IV and part V in sequence. The forging ratio is 3.5 to obtain the semi-finished forging 6.

[0061] Among them, the pad 5 is a right quadrangular prism with an isosceles trapezoidal base. The side of the quadrangular prism, which is coplanar with the upper base of the isosceles trapezoid, contacts the cooling end face. The side edges connected to the two ends of the upper base of the isosceles trapezoid are rounded. The lower base angle of the isosceles trapezoid is 15°. The length of the lower base of the isosceles trapezoid is 30mm shorter than part II of the billet 1. The height of the isosceles trapezoid is equal to the depth of the concave platform corresponding to part II of the prototype forging 2.

[0062] When elongating parts IV and V, the lower flat anvil 7 should be used to press down on these parts repeatedly. The initial pressing amount is 20% of the size of the part to be pressed, and the subsequent pressing amount should not exceed 8%.

[0063] Step 4, fourth heating to 1150±10℃ (ingot temperature) and holding for 3 hours: Using upper flat anvil 3 and lower flat anvil 7, elongate and round parts II, IV, and V of the semi-finished forging 6, with a forging ratio of 3.5, to obtain the finished forging 8; after obtaining the finished forging 8, it is necessary to perform normalizing and tempering treatment. The specific operation of normalizing and tempering is: normalizing at 880±10℃ and holding for 5.5 hours, and tempering at 650±10℃ and holding for 15 hours. The normalizing and tempering process can effectively refine the grains and provide a good microstructure for subsequent heat treatment.

[0064] The performance requirements (i.e., standard requirements) for this component after quenching and tempering are: tensile strength ≥ 805 MPa, yield strength ≥ 685 MPa, elongation ≥ 13%, reduction of area ≥ 35%, and impact energy (AKv) ≥ 31 J. The actual performance test values ​​for this component after quenching and tempering are: tensile strength: 1125 MPa, yield strength: 830 MPa, elongation: 20%, reduction of area: 48%, and impact energy (AKv) of 10⁴ / 10⁸ / 11³, far exceeding the performance requirements.

[0065] This invention, through the design of the pad and the process, not only meets the drawing requirements in terms of external dimensions, but also meets the standard requirements in terms of performance. It also greatly saves material and machining costs, ensures that the internal flow lines of the forging are not interrupted, increases the service life of the forging, and enhances the market competitiveness of this type of forging.

Claims

1. A free forging method for large crankshaft forgings, characterized in that, The specific steps are as follows: Step 1, First fire: Beveling the steel ingot, cutting the water riser, upsetting and drawing it into a flat square steel ingot, and stamping the flat square steel ingot to obtain a billet (1) including parts I, II and III. Parts I, II and III are set sequentially from one end of the billet (1) to the other end. In step 1, the process of card printing is as follows: use triangular engraving to press two opposite and largest surfaces of the flat square steel ingot and the top surface, press two parallel imprints on each surface, the imprints on the two largest surfaces are symmetrically arranged, and each set of imprints on the three surfaces is arranged in an n-shape. Step 2, Second Fire: Place the billet on the upsetting table (4), use the upper flat anvil (3) to draw out part II in the middle of the billet (1), mark parts I and III, divide part IV on part I by marking, part IV is located on the side of part I away from part II, divide part V on part III by marking, part V is located on the side of part III away from part II, and obtain a prototype forging (2) including parts I, II, III, IV and V. In step 2, the process of card printing is as follows: the elongated blank (1) is placed upside down, and the two sides and the top surface of part I and part III are pressed with triangular engraving respectively. Then there are three marks on part I and part II. The marks on the sides of part I and part III are set on the same side as the mark on the surface with the largest area in step 1. The marks on part I and part II are set in an n-shape. Step 3, Third fire: Cool the II part of the prototype forging (2) and the end face that contacts the upper anvil (3) in step 2, and draw out the IV and V parts of the prototype forging (2) to obtain the semi-finished forging (6). In step 3, the specific process of stretching is as follows: the cooled end face is placed on the pad (5), the pad (5) is placed on the upsetting table (4), and the IV and V parts are stretched in sequence using the upper flat anvil (3); Step 4, Fourth Fire: Use the upper flat anvil (3) and the lower flat anvil (7) to draw and roll the II, IV and V parts of the semi-finished forging (6) to obtain the finished forging (8).

2. The free forging method for large crankshaft forgings according to claim 1, characterized in that, In step 1, the upsetting ratio is 2~2.2, and the drawing ratio is 3~3.

5.

3. The free forging method for large crankshaft forgings according to claim 1, characterized in that, In step 2, the forging ratio for drawing is 3~3.

5.

4. The free forging method for large crankshaft forgings according to claim 1, characterized in that, In step 3, cooling is achieved by spraying or water spraying, with a target cooling temperature of 850℃~900℃.

5. The free forging method for large crankshaft forgings according to claim 1, characterized in that, In step 3, the forging ratio for drawing is 3~3.

5.

6. The free forging method for large crankshaft forgings according to claim 5, characterized in that, The pad (5) is a straight quadrangular prism with an isosceles trapezoidal base. The side of the quadrangular prism, which is coplanar with the upper base of the isosceles trapezoid, contacts the cooling end face. The side edges connected to the two ends of the upper base of the isosceles trapezoid are set as arcs.

7. The free forging method for large crankshaft forgings according to claim 1, characterized in that, In step 4, the forging ratio for drawing is 3 to 3.5.

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