Quality control in hydraulic forged cylinder barrel machining process
Introduced several kinds of hydraulic forged cylinder barrel machining processes, and the main factors affecting the quality of each machining process were analyzed and put forward to improve the quality of the processing of specific measures. At the same time, the forged cylinder bore of several commonly used machining processes for comparison pointed out the advantages and disadvantages of each and the scope of application.
The hydraulic forged cylinder is one of the important parts commonly used in modern engineering machinery and other equipment, the processing of the production process of the forged cylinder is an important component of the forged cylinder barrel of the high rate of scrap; the main reasons are:
- 1) The toolpost is long and thin with small rigidity, which can easily cause tool deflection and vibration.
- 2) The rigidity of the forged cylinder blank itself is poor, which can easily cause straightness and roundness.
- 3) Cooling and chip removal is difficult, and iron chips easily scratch the machining surface.
- 4) Difficulty in guiding the cutter head, resulting in wear of the guiding strip, destroying the guiding effect.
Therefore, it is necessary to take corresponding measures to ensure the reliability of guidance, cutting, chip removal, lubrication, and cooling to reduce the forged cylinder scrap rate effectively.
1. Forged cylinder barrel processing technology program development
Most hydraulic forged cylinders are round bar as raw materials, low-pressure forged cylinders with 20# steel and 25# steel, without heat treatment. Medium and high-pressure forged cylinder or important forged cylinder barrels of more than 35# steel, 45# steel, 27SiMn, 25CrMo, and other materials, tempering treatment. The forged cylinder barrel machining process of different material blanks is similar. Still, according to the blanks of raw materials and heat treatment state, the process parameters differ in developing their technology programs and parameters.
The hydraulic forged cylinder structure shown in Figure 1, the structure of the forged cylinder can be developed for the following types of processing technology routes.
- Program 1: metal material → → → heat treatment → → straightening → → → car boring machine with positioning stop → → → rough boring → → → semi-finish boring → → → fine boring (floating boring) → → → rolling.
- Option 2:Unloading → → Heat Treatment → → Straightening → → Positioning Stop for Turning and Honing Machine → → Rough Boring → → Semi-fine Boring → → Honing.
- Option 3:Unloading→→Heat treatment→→Straightening→→Positioning stop for turning and boring machine→→Combined boring.
- Option 4: Cold-drawn precision seamless steel tube unloading → → → car honing machine with positioning stop → → → honing.
2. Problems to be noted in forged cylinder barrel processing
When the material should be considered when the size of the process chuck, the size is too small may make both ends of the processing of the positioning stop length too short, resulting in the boring of the workpiece in the boring machine positioning inaccurate, resulting in the processing of the finished forged cylinder wall thickness is not uniform.
Figure.1 Schematic diagram of forged cylinder barrel structure
2.2 Heat treatment
The forged cylinder’s size and uniformity of hardness after heat treatment not only affects the forged cylinder’s quality but also greatly influences subsequent processing procedures. The uneven hardness of the forged cylinder, in the subsequent boring bore, tool wear will be increased and may even “hit the knife,” resulting in workpiece scrap. Especially in the use of floating boring tool finishing, the quality of the finished bore will also decline. For this kind of blank tube, it is best to use honing in the boring processing.
Cylinder barrel blanks use the most heat treatment in a box furnace or pit-type furnace heating, vertical quenching; this way is likely to cause the forged cylinder barrel’s local hardness is not uniform. Seamless steel pipe quenching treatment in the medium frequency quenching line, due to the uniform contact between the cooling medium and the workpiece, the forged cylinder blank hardness is uniform, and the consistency of the hardness of the workpiece is also good for the subsequent process is very favorable. However, due to the induction heating coil size limitations, this quenching method in a single piece, small batch, and special forged cylinder production is more difficult to apply.
2.3 Boring machine adjustment and workpiece clamping
In the entire boring process, ensure that the boring machine spindle, fixture, workpiece, boring tool, boring bar, oil receiver, and boring bar seat centerline are consistent to ensure the quality of the inner hole of the processing procedures. In the boring machine adjustment, you can use the magnetic table seat attached to the boring machine spindle, check the boring tool bar and oil receiver, and the concentricity of the spindle. The boring machine oil receiver tail vibration damping sleeve must be checked and adjusted, and wear and tear must be replaced promptly.
In roughing, the workpiece can use a chicken-shaped chuck to increase the amount of cutting to improve productivity. But the chicken-shaped chuck may cause the forged cylinder outlet roundness to be too poor in finishing. Finishing can use taper positioning and friction clamping. To ensure reliable clamping, you need to increase the clamping force of the oil receiver; if the friction force is insufficient, you can change the press and the workpiece’s positioning taper to smaller.
2.4 Rough Boring
2.4.1 Sharpening of rough boring tools
Because of the deep hole boring chip removal difficulties, tool sharpening to cutter head at the chip breakage groove opens deeper, narrower, to increase the effect of chip breakage and convenient chip removal. Cutting edge tilt angle should pay attention to the form of chip removal using boring compatibility.
2.4.2 Adjustment of a rough boring head
The structure of the rough boring head is shown in Figure 2; the front guide block is carbide, and the back guide block is a plastic wood strip; the adjustment principle of the rough boring head is: to ensure that the tip of the cutter and the position of the front carbide guide block is compatible; the size of the front carbide guide block and the back plastic wood guide strip are consistent; the radial dimensions of the plastic wood guide strip are consistent with each other.
Figure.2 Rough boring head structure schematic diagram
1-Boring tool; 2-Compression screw; 3-Carbide guide block; 4-Adjustment screw; 5-Glued wood guide bar; 6-Boring head; 7-Counterbore gauge.
The tip of the tool should be more than the front carbide guide block ahead of the tip of the tool ahead of the amount of machining allowance and feed related, generally between 1mm-2mm. At the same time, the tool’s tip in the radial dimension should be slightly higher than the carbide guide block, about 0.02mm. In order to ensure that the above dimensions must use a special tool gauge for the knife, the inner diameter of the tool gauge, according to the size requirements of each process, was produced. If the gap between the front carbide guide block and the tool setting gauge is large, after replacing the new carbide guide block, it is necessary to re-grind the rough boring head; if the tip of the cutter is not suitable for the amount of excess, it is necessary to re-sharpen the rough boring tool. After the size adjustment of the guiding block of the wood bar, to ensure that the size of the front carbide guide block with the same size, it is best to adjust each time after the outer diameter of the re-processing of the wood bar to ensure that the radial dimensions of each guiding bar are the same.
2.5 Fine Boring
Currently, the most widely used fine boring is the form of a floating boring tool, as shown in Figure 3. The fine boring tool can slide in the rectangular hole of the fine boring head, automatically adjusting the cutting volume of the two cutting edges to reduce the error caused by the bending of the shank and inaccurate clamping.
Figure.3 Schematic structure of the fine boring head
1-finish boring head; 2-finish boring tool; 3-guide bar; 4-wedge plate; 5-adjustment nut; 6-lock nut; 7-connector
2.5.1 Sharpening of fine boring tools
The floating boring cutting process is similar to reaming; the machining allowance is not easy to be too large, in Figure 1 shows the structure of the forged cylinder barrel processing, fine boring allowance of 0.08mm-0.15mm, cutter head grinding a longer calibrated edge, to play a role in extrusion, the primary and secondary deflection angle is taken 1.5 °-2.5 °, cutter head sharpening, surface roughness should be in the Ra3.2 or less, and at the same time to check the quality of cutting edge, there should be no serration phenomenon, the two sides of the cutting edge must be cut, and the cutting edge must be cut, and the cutting edge should be cut, and the cutting edge should be cut, the cutting edge should be cut. Both sides of the cutting edge must be symmetrical; two cutting and calibration edges must be in the same plane.
2.5.2 Adjustment of fine boring head
The principle of fine boring head adjustment is that the font size of the guide bar ϕ2 is consistent with the diameter of the bottom hole before fine boring, the back side of the guide bar ϕ1 is consistent with the diameter of the hole after fine boring, and the radial dimensions of each guide bar are consistent with each other. Chip removal is a problem that requires special attention in fine boring; the coolant flow should be increased appropriately in fine boring. Otherwise, the iron chips are likely to scratch the surface of the processed bore.
Rolling can improve the surface quality of the forged cylinder bore but cannot improve the geometric accuracy of the bore and positional tolerance; the workpiece in the rolling before the accuracy and roughness of the higher, the higher the surface quality after rolling. The surface roughness of the bottom hole before rolling is generally controlled at Ra1.6 or so.
2.6.1 Adjustment of rolling head
Different rolling heads are used in deep-hole machining, but the adjustment principle is the same. Roller head rollers need to be grouped to ensure that the same roller head with a row of roller diameters is consistent with each other, with a maximum difference of no more than 0.002mm. If a double row of rollers of the roller head, the front and back of the two rows of rollers of the outside diameter can be inconsistent. The edges of the rollers should be rounded to 1mm or 2mm, and the surface should be polished with a surface roughness of Ra0.2-0.4μm. The rounded corners of the rollers in the same row should be consistent. For double rows of rollers of the rolling head after the row of rollers, the outer diameter needs to be larger than the front row of the outer diameter of 0.01 mm-0.02 mm.
2.6.2 Selection of rolling parameters
Rolling dosage should be selected according to the hardness of the material, wall thickness, and other conditions from the test. Rolling the smaller the amount of walking knife surface quality is better. The rolling allowance is too small rolling effect not good; it cannot improve the surface quality of the bottom hole effectively, the amount of interference is too large, the forged cylinder barrel will roll hair, resulting in “peeling” and even the rolling head stuck in the middle of the forged cylinder barrel, resulting in damage to the rolling head and forged cylinder scrapped. Thin-walled forged cylinder barrel rolling overload will also destroy the straightness of the forged cylinder barrel. Rolling processing as far as possible to complete a knife. In the forged cylinder shown in Figure 1, forged cylinder processing is 0.25-0.35mm/r. Rolling the amount of interference to take 0.08mm-0.12mm, the actual size of the forged cylinder after rolling increased by about 0.02mm.
2.7 Combined boring
In mass production, to improve productivity, you can use a combination of boring, that is, boring and rolling composite processing, the rough boring tool, floating boring tool, and roller mounted on a tool body, in a tool in the completion of the rough boring, fine boring and rolling. The combination of boring of the principle of the knife with the previously mentioned process is separate from the principle of the knife is the same; the difference is that the combination of the boring tool body is more difficult to guide some of the requirements of the knife precision is higher.
2.8 Honing and Power Honing
Honing is also a commonly used means of processing the bore and can improve the forged cylinder bore geometric accuracy and surface roughness; honing adaptability than the deep hole rolling good, honing forged cylinder roundness is generally better than after rolling, but the efficiency of honing is much lower than rolling. Power honing is a forged cylinder with another process; it is larger than ordinary honing, with high grinding efficiency.
In honing and power honing according to the forged cylinder material, choose the oil stone abrasive and particle size. The coarser the grain size of the oil stone, the higher the cutting efficiency, but the worse the surface roughness; the finer the grain size of the oil stone, the lower the cutting efficiency, but the better the surface roughness. Under the premise of meeting the requirements of workpiece roughness, try to choose a coarse particle size to improve productivity. The hardness of the oil stone and forged cylinder diameter, the hardness of the workpiece, the form of honing machine, honing head of the form of tensioning, honing head of the tensioning force have a relationship and need to be based on the specific circumstances of the comprehensive choice, honing and power honing grinding parameters in the general cutting manuals can be found in the need to determine the optimal process parameters through trial processing.
3. Process comparison
The use of precision cold-drawn seamless steel tube directly for honing or directly buying a high-precision cold honing tube, the forged cylinder plant only needs to process the forged cylinder barrel ends can be, the process of the scrap rate is almost zero, the material utilization rate is also very high, is a relatively advanced process. However, the current high-precision cold-drawn honed tube specifications, the supply of varieties is less rich than forged cylinder, and internal stress is greater in some important forged cylinders and ultra-high-pressure forged cylinders when applying certain restrictions. With the development of the cold-drawn seamless steel tube industry, this process will be more and more applications in the forged cylinder manufacturing industry.
Rolling process production efficiency is much higher than honing and power honing, and stable quality in mass production has obvious advantages. However, for the technical quality of workers, machine tools and tools honing requirements in mass production have obvious advantages.
Honing and power honing flexibility and adaptability are better in single-piece production. Special forged cylinder production has more advantages, and honing can repair part of the rolling failure of the workpiece. Rolling and honing can be used jointly to avoid shortcomings and reduce the scrap rate of forged cylinder barrel machining.
Cylinder barrel machining process development should comprehensively consider drawing requirements, batch, machine tools, cutting tools, blank quality and technical quality of workers, etc., and the development of process parameters to be amended in the actual production. To process high-quality workpieces, in addition to the process and parameters to be reasonable, but also a set of practical process management systems.
Author: Yang Zhensheng