On 2018-08-08 14:48:54
Code for straightening process of heat-treated parts
(1) general provisions
1. After the heat treatment of the workpiece, due to the thermal stress and tissue stress will cause bending or warping deformation, the deformation will often exceed the tolerance range, therefore, it is necessary to use the straightening method to make up for this change in shape, so as to make the size and shape of the workpiece conform to the specified range.
2. The straightening methods used by the factory are: cold pressure straightening, heat straightening, hot spot straightening, temper straightening and cold shock straightening. The straightening process should be selected correctly according to the material, shape and mechanical properties of the workpiece.
3. The straightening of the workpiece should generally include the straightening before heat treatment (in the machining workshop) and after heat treatment. For slender and thin plate shaped parts, more attention should be paid to the deformation before quenching, which should be controlled within the scope specified in the process.
4. Our factory generally quench parts, after straightening should keep its vibration pendulum less than 1/2 of grinding allowance, quench parts should be less than 1-1.5mm.
5. All straightening parts should go through stress removal treatment to eliminate the straightening stress. Generally, parts can be carried out in the well tempering furnace, and the tempering parts should be carried out within 50-100℃ below the tempering temperature.
(2) preparation of the university ahead
1. The straightening parts must be cleaned first to remove the oxide skin and grease on the surface.
2. Check whether the measuring part is flat and the center hole at both ends is blocked with dirt or other filth.
3. Check the accuracy of measuring tools such as dial gauge, plate, triangle iron and center frame.
4. Understand the material, hardness and heat treatment process of the workpiece.
(3) measurement method of parts:
1. Stick parts: fasten the parts with the top, then measure the outer circle with the dial meter, find the highest point, and mark it with chalk.
2. Thin-plate parts: place the parts on the flat plate and measure the clearance with a feeler to check the warping degree of the workpiece.
3. For parts with irregular shape, the parallelism can be measured by dial meter.
4. For parts without a center, use triangle iron to use its two ends, and then use the dial meter to measure.
(4) principle of process selection
1. Cold pressure straightening method can be used for parts that have not been quenched, or whose shape is simple and hardness is lower than HRC38. (on 60 ton hydraulic press)
2. Carburized or surface quenched parts, whose single-side hardening layer is less than 1/5 of the diameter or thickness, can be used cold pressure straightening method, more than 1/5 in the process allows the use of hot spot straightening method.
3. Alloy steel and alloy tool steel with high hardness shall be straightened by hot spot method.
4. Carbon steel and alloy steel parts, after quenching and tempering, whose hardness is above HRC38, where local soft spots are allowed, can be straightened by hot-spot method.
5. Thin section parts can be clamped by fixture and straightened by "tempering process straightening method" in tempering.
6. For parts with less bending, cold shock straightening method can be used.
1. Cold pressure straightening method:
A) will measure the good parts, with the Angle iron put aside into a level, and then to the workpiece bending side pressure high up, make its produce plastic deformation, the size of the pressure, according to the part shape and bend degree to decide, can generally be weighed more than a few horizontal line, a pressure cannot fully straightening can be repeated.
B) for parts with pin grooves, threads and sharp angles protruding, copper sheet must be used as a liner at the pressing and supporting points to prevent damage to the surface of the workpiece.
C) parts after quenching and tempering, especially alloy steel, have good toughness. In order to achieve good results, it is necessary to press more than the horizontal line during cold pressing.
D) carburizing and quenching parts can be straightened immediately before cooling to room temperature after quenching, which can improve efficiency.
2. Hot correction method
A) after quenching, the workpiece shall be cooled to about 200℃, that is, within the temperature range where the austenite has not undergone complete transformation, and straightening shall be carried out immediately. At this time, the plasticity is better and the pressure need not be too large.
B) the operation must be rapid. During the cooling process, the alignment shall be measured continuously until the final alignment temperature.
C) the final setting temperature should be well controlled and should not be too low, otherwise it will be easy to break. Generally, it can be decided according to practical experience, which is about 60℃. When it is close to the final calibration temperature, the pressure will be small and the time will be long.
3. Hot method
A) in the middle of the high bending side of the part, use neutral oxyacetylene flame to conduct hot spot, the hot spot temperature is about 800℃, and then quickly cover it with wet cotton yarn for cooling.
B) the alloy steel parts should be preheated around the hot spot at a temperature of about 150℃, and then hot spots should be conducted. The hot spot temperature should not exceed 700℃.
C) the hot spot should be carried out in the scapula or other less important positions as far as possible. The faster the heating speed is, the better. Generally, it should not be carried out within 20 seconds.
D) in places where hot spots have been burned, it can only be repeated once in general, otherwise the effect is not big and it is easy to cause cracks.
4. Alignment during tempering
A) place the parts in the fixture, press them slightly with the pressing plate screws, and then place them in the furnace for tempering. After about ten minutes, take out the fixture from the furnace and put it into the furnace for tempering.
B) alignment must be carried out in the first tempering, if it is the second tempering, the effect will be insignificant.
C) parts with severe warping deformation must be pre-calibrated several times below the tempering temperature before clamping, so as to avoid brittle fracturing.
5. Cold strike alignment
A) place the measured part on the flat plate and hit the protruding part with the hammer.
B) a special hammer head shall be used, and the hardness of the hammer head shall not exceed HRC25, or the hammer head shall be made of copper.
C) before and after hammering, the parts must undergo stress removal treatment.
6. Safety precautions during operation
A) in cold pressing, the support of the parts must be stabilized before the pressure can be applied.
B) all padding iron and triangular iron used on the press shall not be made of pig iron.
C) when under pressure, prevent parts from breaking and causing injuries.
7. Technical inspection
A) all parts that have been straightened must be inspected to meet the requirements of process vibration or warping.
B) if there is no straightening procedure for parts with vibration or warping requirements specified in the process, the inspector shall conduct inspection. If the requirements are exceeded, the straightening procedure shall be added by the technologist.
For parts with sharp corners, pin grooves or fine lines, check their appearance for dents, cracks and other damage.