Machinability test of metal

Metal bending test

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Metal bending test is a test that the bending center of the specified size is used to bend the specimen to the specified degree, and to test the metal’s ability to withstand bending plastic deformation and show its defects.
Metal bending tests can be performed at room temperature (cold bending test) or hot state (hot bending test). The size and shape of the specimen shall be determined according to the type of metal material according to the relevant standards. Bending test can be carried out on press, special testing machine, universal testing machine or round mouth vice and other equipment. If there is no suitable equipment, the bending shall be carried out with a hammer, mechanical hammer or hook bending machine approved by both parties. When metal bending test is conducted, the bending degree under force can be divided into three types:
① Bending to a specified angle a;
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② Bend around the center of the bend to two parallel bends;

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③ Bend to a coincident bend where both sides are in contact.
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Metal cupping test

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The metal cupping test is a test to measure the cupping depth by pressing the clamped metal plate or strip sample into the die with specified size until there is a through crack.
The metal cupping test should be carried out at 10-35 ℃. When strictly required, the test temperature should be 23 ℃± 5 ℃. It is suitable for metal plates and strips with thickness of 0.2-2mm and width of 90mm or more. The edge width or diameter of the sample is 90-95mm. The metal cup test is carried out on a testing machine equipped with a die, a cushion die and a punch (see the figure below). During the metal cupping test, both sides of the sample and the punch should be lightly coated with graphite grease. After zeroing, the sample should be clamped between the die and the cushion die. The constant clamping force is about 10kN. The cupping test was carried out without impact, and the speed of the punch was 5-20 mm · min-1. At the end of the test, the speed is reduced to near the lower limit, so as to correctly determine the moment of crack occurrence.
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Fig. schematic diagram of metal cupping test
1 – Test thickness, denoted by a; 2 – width or diameter of specimen;
3-die diameter; 4-pad die diameter; 5-die outer diameter; 6-pad die outer diameter;
7 – Inner fillet radius of die hole; 8 – outer fillet radius of die;
9-outside fillet radius of cushion die; 10-hole depth of die; 11 die thickness;
12 – cushion die thickness; 13 – punch spherical part diameter, expressed by D; 14 – Cupping depth
After the metal cupping test, the cupping depth should be measured with an accuracy of 0.1 mm when there is a through crack, expressed as ie, which is called cupping value.

Repeated bending test of metals

The metal repeated bending test is to clamp one end of the sample and conduct 90 times of repeated reverse bending on the cylindrical surface of the specified radius to test the resistance of the metal and its coating to repeated bending and show its defects.
The metal repeated bending test is only carried out at room temperature. It is suitable for wire (and strip) with cross section less than or equal to 120mm2 and strip and plate with thickness less than or equal to 5mm. In the repeated bending test of metal, the sample is clamped vertically in the clamping mouth of the testing machine to ensure that the sample does not move during the test. Make 90 ° repeated bending along the left and right direction in the plane at right angles to the contact line of the test machine’s clamp mouth (as shown in the figure below), bend 90 ° to the left and then return to the right as a repeated bending. The bending speed shall not exceed 60 times per minute until the number of repeated bending specified in relevant standards is reached or the specimen breaks.

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Figure diagram of repeated bending
In the repeated bending test, the bending parts of the sample and its covering layer shall be inspected after reaching the specified number of times. In the absence of specific provisions in relevant standards or technical agreements, the sample shall be considered qualified if there is no crack, crack, fracture, peeling or peeling.

Experiment on winding looseness of wire rod

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The winding looseness test of metal wire rod is a test to test the ability of coated and uncoated metal wire rod to bear winding and looseness deformation, and to show its defects and coating bonding fastness by winding the sample on the core rod with specified diameter in a tight spiral direction.
The loose winding of metal wire is carried out at room temperature, which is suitable for round coated and uncoated metal wire with diameter equal to or less than 10 mm. The length of the sample shall meet the requirements of the testing machine.
When the winding of the metal wire is loose, the sample shall be put on the wooden mat and straightened gently with a soft hammer (the coated wire shall be straightened gently with a wooden hammer or a rubber hammer) or with a stable pressure. Then fix one end of the sample on the core rod with diameter D of the testing machine (see the figure below), pull the other end B by hand or by mechanical method, and rotate the core rod for winding. The spiral coils shall be arranged close to the core rod and shall not overlap. According to the regulations, it can be wound at the speed of 15, 20 or 60 laps per minute to the specified number of laps, and then the laps are broken at a uniform speed, and at least one laps are retained at the end of the laps. For double winding test, bend the sample into a U shape, and then wind one end around the other end to form a closely arranged spiral circle (see the figure below).

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Figure diagram of wire winding looseness

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Figure diagram of double winding test
After the winding relaxation test of metal wire, the surface of the sample shall be inspected. If there is no crack, coating crack, swelling and falling, etc. in the absence of specific provisions in relevant standards or technical agreements, the test shall be considered as qualified.

Torsion test of metal wire

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The torsion test of metal wire is to clamp the two ends of the sample and rotate the chuck around the axis of the sample to test the ability of the metal wire to bear plastic deformation when it is twisted in one direction or alternating direction, and to show the uniformity, surface and internal defects of the material.
Torsion test of metal wire is carried out at room temperature, which is generally suitable for cold drawn and hot rolled wire with diameter of 0.3 ~ 10.0 mm.
During the torsion test of metal wire, one end of the sample clamped on the testing machine shall not move, and its longitudinal axis shall coincide with the axis of the chuck, and a tension force shall be applied.

Torsion can be divided into fixed direction torsion, alternating direction torsion and double torsion. Torsion in the fixed direction takes one full turn (360 °) of the rotating end of the specimen as one torsion, while torsion in the alternating direction takes one full turn (360 °) of the rotating end of the specimen in either direction as one torsion, and the torsion times in different directions shall be recorded separately; the double torsion of two specimens twisted in the same direction side by side, The rotating chuck rotates a whole circle (360 °) as a torsion. If the specimen splits seriously during the test, the last torsion number is invalid.
After torsion, the torsion uniformity, crack layer, fracture shape and defect of the whole length of the specimen (or magnifying glass can be used if there are special regulations) shall be visually inspected, and the crack performance when the specimen is damaged by hammering shall be judged according to relevant standards and technical agreement.

Experimental study on double bite bending of sheet metal

The double bite bending test of metal sheet is to bite and bend the metal sheet and its cladding according to the specified size and shape to test its plastic deformation ability and show its defects.
The double bite bending test of sheet metal is carried out at room temperature. It is suitable for sheet metal with thickness less than 0.8 mm. The sample size is about 100 mm × 150 mm, but the occlusal line should not be less than 150 mm. In the double-layer occlusal bending test of metal sheet, the two sheet specimens are occluded tightly in the order shown in the figure below, and then bent around the direction perpendicular to the occlusal joint to an angle of about 45 °. Flattening (including the number of times of flattening) or non flattening shall be in accordance with relevant standards. The bending is carried out with a wooden hammer on a flat plate. When bending, the flat side serves as the outside of the bend. Reverse bending is not allowed during the test.

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Fig. double tight occlusal sequence
After the test, the bending surface of the sample metal and its covering layer shall be inspected. Generally, if there is no crack, fracture or peeling, the sample shall be considered as qualified.

Bending test of metal without hardening

The non hardening bending test of metal is a test to test the ability of metal to bear the bending plastic deformation of the specified bending degree after quenching close to the quenching temperature, and to show its defects.
The non hardening bending test of metal was carried out at room temperature. The size and shape of the sample shall be determined according to the type of metal material and relevant standards. The bending test can be carried out on press, special testing machine, universal testing machine or round mouth vice. If there is no proper equipment, the bending shall be carried out by hand hammer, mechanical hammer or hook bending machine as agreed by both parties.
In the non hardening bending test of metal, the bending degree under the force can be divided into the following three types:

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① Bending up to the specified angle α;

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② Bend around the center of the bend to two parallel bends;

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③ Bend to a coincident bend where both sides are in contact.
After the bending test, check the outside and side of the bending part of the sample. If there is no specific provision in the relevant standard or technical agreement, the sample is generally considered qualified if there is no crack, fracture or delamination.

Metal forging test

Metal forging test is a kind of test to test the ability of metal to bear the specified degree of forging deformation and show its defects by forging the sample to the specified size at room temperature or hot state.
The metal forging test can be carried out at room temperature or hot state. Samples can be cut from metal strips, strips, plates and rivets. The size and shape of the sample shall be determined according to the material type and relevant standards. Metal forging test can be carried out on press, mechanical hammer or forging hammer, or hand hammer or sledge hammer. When the metal forging test is carried out, the head diameter of the sample cut from the strip or rivet material shall be 1.5-1.6 times of the leg diameter, and the height shall be 0.4-0.5 times of the leg diameter. Before the test, the height of the part exposed from the die hole to withstand the forging shall be 1.2 times of the leg diameter. For the strip and plate samples, the width of the sample shall be increased to the specified value in the relevant standards, In this case, the ratio of the diameter of the rivet leg to the diameter of the rivet leg should be equal to 2 times of the length of the rivet leg. After the forging test, the surface of the deformed part of the sample shall be inspected. If there is no crack or crack, the sample shall be regarded as qualified.

Strain aging sensitivity test of steel

The strain aging sensitivity test of steel is a test to determine the corresponding aging sensitivity of steel by comparing the impact absorption energy of samples without strain aging and those with strain aging.
The impact test in the strain aging sensitivity test of steel is generally carried out at 20 ℃± 5 ℃. It is suitable for steel plates, steel strips, section steels and special-shaped steels with thickness greater than or equal to 6 mm and whose size and shape can ensure that the required size of one side of the rolled sample billet can be cut. The impact specimens are 10 mm × 10 mm × 55 mm, 7.5 mm × 10 mm × 55 mm and 5 mm × 10 mm × 55 mm with notch. It is suggested that V-notch impact specimens should be used as far as possible. In the strain aging sensitivity test of steel, the specimens prepared from the billets subjected to tensile strain (residual strain: 10% for low carbon steel and 5% for low alloy steel) are uniformly heated at 250 ℃± 10 ℃ and artificially aged for 1 h, and then cooled to room temperature in air. The impact test is carried out at 20 ℃± 5 ℃ according to the standard of metal impact test method. The measured strain aging impact absorption function is expressed by Akus or akvs, and then the strain aging sensitivity coefficient C is determined according to the following formula:
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In the formula, AK is the average value of the impact absorption energy of the impact specimen without strain aging; AKS is the average value of the impact absorption energy of the impact specimen with strain aging. Generally, the sensitivity coefficient of the u-notch specimen is expressed by Cu, and the sensitivity coefficient of the V-notch specimen is expressed by CV. When measuring the value of C, it should not be less than 6 specimens, 3 specimens without strain aging, and 3 specimens with strain aging.

Repeated bending test of metal wire

The repeated bending test of metal wire rod is to clamp the sample in the clamping mouth through the pulling hole, and conduct 90 ° repeated reverse bending in the bending arc plane of the specified radius, so as to test the repeated bending resistance of metal wire rod and show defects.
The repeated bending test of metal wire is only carried out at room temperature, which is generally applicable to diameter. 0.3 ~ 10 mm cold drawn and hot rolled wire rod. The length of the sample is 100 ~ 150 mm, which can be cut from any part of the wire. According to the wire diameter, the radius of bending arc and the diameter of rod drawing hole on the testing machine are selected. During the repeated bending test of metal wire, the sample shall be clamped in the clamp (or pad) through the pull-out hole, but the clamping deviation is not allowed. At the same time, the wire shall be perpendicular to the plane passing through the center line of the bending arc, and be repeatedly bent 90 ° to the left and right in turn (as shown in the figure below). The first bending is 90 ° to the right from the starting position, the second bending is 90 ° to the left, and the third bending is 90 ° to the right. Bend repeatedly until the bending times specified in relevant standards or the specimen breaks. When the bending times are recorded, the last bending at the time of specimen fracture is not counted. When recording the test results, the wire diameter, bending arc radius, bending times and standard number must be indicated.
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Figure schematic diagram of repeated bending of wire rod

Flattening test of metal tube


The flattening test of metal tube is to flatten the metal tube to the specified size, check its plastic deformation ability and show its defects.
Flattening test of metal tube is usually carried out at room temperature, which is suitable for seamless and welded metal tube. The range of outer diameter and wall thickness of the tested metal pipe shall be specified in relevant standards and agreements between both parties. The length of the sample is approximately equal to the outer diameter of the metal tube. If the outer diameter is less than 20 mm, it shall be 20 mm, and the maximum length shall not exceed 100 mm. During flattening test of metal pipe, place the sample between two parallel plates, and press it evenly to the pressing plate distance h or inner wall distance h (see the figure below) specified in relevant standards or agreement of both parties by press or other methods. The distance shall be measured under load. When testing the welded pipe, the position of the weld should be 90 ° with the direction of force application (see the figure below). The flattening speed should be 20 ~ 50 mm · min-1. After the flattening test, check the bending deformation of the sample. If there is no crack, crack or welding crack in the relevant standard or technical agreement, the sample is considered qualified.

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Figure diagram of flattening test

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Fig. weld position during flattening test of welded pipe

Expanding test of metal pipe

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The expanding test of metal tube is to press the top center with specified taper into one end of the metal tube to make its diameter expand evenly to the specified size, to test the ability of the metal tube to bear the radial expansion plastic deformation and to show its defects.
Metal tube flaring test can be carried out at room temperature or hot state, it is suitable for seamless and welded metal tube. The length of the sample is about 2 times of the outer diameter of the tube when the flaring taper is less than or equal to 30 ° and 1.5 times of the outer diameter of the tube when the cone head is more than 30 ° but not less than 50 mm. During the metal tube expanding test, a specified taper of the top center is pressed into one end of the sample with a press or other methods (see the figure below), so as to evenly expand to the expanding rate X specified in the relevant standards. X is calculated according to the following formula:

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In the formula, D is the outer diameter of the tube end of the original sample, mm; DU is the outer diameter of the tube end after flaring, mm; the taper of the top center can be 6 °, 20 °, 30 °, 45 °, 60 °, 90 ° or 120 ° according to relevant standards. The recommended top core angles are 30 °, 45 ° and 60 °. In case of dispute, the jacking speed should be 20 ~ 50 mm · min-1. After the flaring test, the flaring position of the sample shall be inspected. If there is no specific provision in the relevant standard or technical agreement, the sample is generally considered qualified if there is no crack, crack or weld crack.

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Figure diagram of flaring test

Metal necking test

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Metal necking test is to press the metal pipe into the seat sleeve with specified taper to make its diameter uniformly shrink to the specified size, to test the ability of the metal pipe to bear the radial compression plastic deformation and to show its defects.
Metal tube necking test can be carried out at room temperature or hot state. The length of the sample is about 2.sd + 50mm (D is the outer diameter of the metal tube). During the necking test of metal pipe, punch or press the metal pipe into the seat sleeve with specified taper by hand hammer or press machine (see the figure below) to make it uniformly reduce to the necking rate X specified in relevant standards. X is calculated as follows:

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Where D is the outer diameter of the tube end of the original sample, mm; DU is the outer diameter of the tube end after necking. The taper of seat cover is generally 1:10, and 1:5 or other taper can also be used according to regulations. After the necking test, check the necking of the sample. If there is no specific provision in the relevant standard or technical agreement, the sample is generally considered qualified if there is no crack or crack. If there is fracture, the sample must be taken and tried again.
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Figure schematic diagram of metal pipe necking test

Curling test of metal tube

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The curling test of metal tube is to press the top center of the specified shape into one end of the metal tube to make the tube wall curl evenly to the specified size, to test the ability of the tube wall to bear the plastic deformation of the outer coil and to show its defects.
Metal tube curling test can be carried out at room temperature or hot state, generally at room temperature. It is suitable for seamless and welded metal tube. If the length of the sample is 100 mm, short sample can also be used, but the height of the cylindrical part after the test should be more than half of the outer diameter. During the metal tube curling test, press the top center of a certain shape into one end of the sample with a press or other methods to make the tube wall curl uniformly to the specified requirements (as shown in the figure below). The hemming width 1 and hemming angle A shall be specified in relevant standards. When crimping, it is allowed to use the appropriate angle of the top center in advance (90 ° in case of objection) for flaring (as shown in the figure below). The crimp rate X is calculated according to the following formula:

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Where, D is the outer diameter of the tube end of the original sample, mm; DU is the outer diameter of the tube end after crimping, mm. In case of any objection, the pressing speed of the top center in the sample shall not exceed 50 mm · min-1. After the edge curling test, check the edge curling of the sample. If there is no crack, crack or welding crack in the relevant standard or technical agreement, it is considered that the sample is qualified.

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Figure schematic diagram of metal tube curling test

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Figure diagram of expanding with top center before edge rolling

Bending test of metal tube

The bending test of metal tube refers to the test of bending the sample to the specified degree at the grooved bending center to test the ability of metal tube to bear bending plastic deformation and show its defects.
The bending test of metal pipe is usually carried out at room temperature, and it is suitable for the pipe with the outer diameter less than 65mm. For the metal tube with outer diameter greater than 60mm, if cold bending is not specified, it shall be bent in hot state (700 ~ 750 ℃), or it can be made into strip sample according to regulations, and bending test shall be carried out according to “metal bending test method”. The sample can be cut from any part of the metal tube which has passed the appearance inspection. The length of the specimen shall be such that it can be bent at the specified bending angle and radius. During the bending test of metal pipe, according to the methods specified in relevant standards (mechanical or manual, with or without filler, with or without bending center), the bending center of a certain length of metal pipe around the groove shall be continuously and slowly bent to the specified bending angle α (see the figure below). During the experiment, the bending section of the metal tube should be avoided to become a significant ellipse. The bending angle and bending center radius of the specimen are specified in relevant standards or technical agreements. When testing the welded pipe, the position of the weld should be specified in the relevant standards. If not specified, the weld can be placed in any position.
The bending test of metal tube refers to the test of bending the sample to the specified degree at the grooved bending center to test the ability of metal tube to bear bending plastic deformation and show its defects.
The bending test of metal pipe is usually carried out at room temperature, and it is suitable for the pipe with the outer diameter less than 65mm. For the metal tube with outer diameter greater than 60mm, if cold bending is not specified, it shall be bent in hot state (700 ~ 750 ℃), or it can be made into strip sample according to regulations, and bending test shall be carried out according to “metal bending test method”. The sample can be cut from any part of the metal tube which has passed the appearance inspection. The length of the specimen shall be such that it can be bent at the specified bending angle and radius. During the bending test of metal pipe, according to the methods specified in relevant standards (mechanical or manual, with or without filler, with or without bending center), the bending center of a certain length of metal pipe around the groove shall be continuously and slowly bent to the specified bending angle α (see the figure below). During the experiment, the bending section of the metal tube should be avoided to become a significant ellipse. The bending angle and bending center radius of the specimen are specified in relevant standards or technical agreements. When testing the welded pipe, the position of the weld should be specified in the relevant standards. If not specified, the weld can be placed in any position.

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Figure diagram of metal tube bending test
After the bending test, check the bending area of the sample. If there is no specific provision in the relevant standard or technical agreement, the sample is generally considered qualified if there is no crack, crack, delamination or welding crack.

Hydraulic test of metal pipe

The hydraulic test of metal pipe is to fill the metal pipe with water or specified liquid, make it bear the specified pressure within a certain period of time, check the quality and strength of the metal pipe and show its defects. Metal pipe hydraulic test is usually carried out at room temperature, which is suitable for steel pipe, cast iron pipe and non-ferrous metal pipe. The whole tube can be randomly selected from a batch of metal tubes which have passed the appearance inspection as the sample. Any type of liquid press, connecting parts and pressure gauge with accuracy no less than 1.5 can be selected as the experimental device to meet the requirements of this test. Both ends of the sample shall be closely connected with the relevant connecting parts of the press. During the hydraulic test of metal pipe, fill the pipe sample with water or specified liquid and pressurize it evenly until the specified maximum test pressure. There shall be no impact in the middle. The maximum test pressure and test duration shall be specified in relevant product standards or technical agreements; if not specified, the maximum test pressure P can be calculated as follows:
Where, σ is the filling stress, MPa; s is the wall thickness of metal tube, mm; D is the outer diameter of metal tube. The maximum test pressure shall not cause permanent deformation of metal pipe, and the test duration shall not be less than 5S generally. If there is no leakage and the metal tube does not produce permanent deformation (expansion) after the test, it is considered that the hydraulic test of the metal tube is qualified.

Source: China Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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