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Technical CommunicationIn the first two articles, we introduced the application background and manufacturing method of gradient chamfering. In this article, we will introduce the grinding quality inspection and cutting performance comparison of gradient chamfering.
04 Gradient chamfering PCBN tool grinding accuracy detection
4.1 Tool nose arc radius and edge defect detection
In order to characterize the precision of cutting edge preparation, the R value of the tool arc radius and the Rk value of the cutting edge projection curve are selected to evaluate the edge quality.
The parameters were measured using a Japanese Meiji MT7530 microscope. The test results of the three sets of tools are shown in Figure 15, where the design value of the radius of the tool nose arc is 0.8mm.
It can be seen from the figure that the radius error of the tool nose arc of each group of tools is within ±20μm; as the grinding times increase from 6 times to 8 times, the Rk value gradually decreases, and from 8 times to 10 times, the Rk value gradually decreases. Increase.
Observed under 200x scanning electron microscope (as shown in Figure 16), the first group of tools and the third group of tools have micro chipping individually, and the second group of tools has no obvious chipping. In comparison, the number of grinding times When it is 8 times, the cutting edge quality is the most ideal....
4.2. Gradient chamfering width and angle detection
It is difficult to detect the angle change of the gradient chamfered structure by conventional methods. Here, the gradient chamfered structure is detected in segments, and the detection positions refer to the five sections in FIG. 12 .
Due to the small area of the measured section, it is difficult to directly mark the detected position on the tool. In order to ensure that the detected section is vertical or parallel to the right edge of the table, as shown in Figure 17, first align it horizontally on the white light interference microscope table. Place a rectangular stop, and then place the tool at the focal point of the lens. The arc area of the tool tip is tangent to the stop. Since the interval angle λ and the cut angle K are equal, the measured section can be controlled by fine-tuning the angle K. At this time, the contact point between the detection section and the stop will coincide with the tangent point between the arc area of the tool nose and the stop.
The process of detecting the width and angle of the gradient chamfer by using the white light interferometer microscope to extract the section function is shown in Figure 18.
Taking a certain section of the detection blade as an example, first determine the longitudinal scale of the tangent point (Figure 18a), and then determine the position of the measured section through the longitudinal scale (Figure 18b), and then extract the profile of the detection section (Figure 18c), and then complete the corresponding parameter values. measurement (Fig. 18d).
Table 2 shows the test results of the chamfering width and angle of the sample knife. It can be seen that the chamfering width after sharpening fluctuates around the design value of 0.151mm, which shows that the sharpening process is relatively stable; mm, 0.149mm, 0.152mm, the maximum error is 16μm.
In comparison, the 6th and 8th grinding width errors are small, and the 10th grinding error is large; the grinding times have little influence on the measurement error of the chamfering angle of each section, which can be ignored; the actual chamfering angle and the theoretical Compared with the angle, the error does not exceed ±0.6°, which meets the grinding accuracy tolerance requirements.
05 Cutting performance test
In order to verify the cutting performance of the gradient chamfering tool, a comparative test of the constant value and the gradient chamfering tool was carried out.
The test is carried out on a CK6150 CNC machine tool. The workpiece adopts a GCr15 bearing outer ring with a hardness of (60±2) HRC, an outer diameter of 62 mm and a width of 17 mm.
Gradient chamfering tool is selected for grinding times of 8 times, chamfering width is 0.1mm, and the angle variation range is 15°~30°. The material and specifications of the comparative tool are the same as that of the gradient chamfering tool, the chamfering width is 0.1mm, and the angle is 30°. °.
The cutting parameters selected for the test are fixed, the cutting speed is 150 m/min, the feed rate is 0.1 mm/r, and the cutting depth is 0.1 mm. The test system is shown in Figure 19.
In the test, the KISTLER 9257B dynamometer was used to collect the cutting force, and the VHX-1000 ultra-depth-of-field microscope was used to measure the tool wear. The subsequent measurement also included the three-dimensional topography of the workpiece surface and the chip shape. The cutting force measurement data are shown in Table 3.
It can be seen from Table 3 that when the tool flank is not worn, compared with the constant value chamfering tool, the radial force and cutting force of the gradient chamfering tool are reduced by 16% and 11% respectively, but the tangential force is slightly increased. , about 8%, which is the result of the decomposition of the cutting force in all directions by the spiral edge of the progressive chamfering tool.
As the cutting progresses, the flank wear of the progressive chamfering tool is relatively small, and its radial force and tangential force increase slowly.
Further comparison of the rake face wear morphology and chip morphology of the two types of tools after cutting for 14 minutes, as shown in Figures 20a and 20b, it is found that the wear area of the rake face of the gradually chamfered tool has a larger area and a shallower depth, and the generated chips The distortion is small and straight, these characteristics reflect the reduced friction between the chips and the ideal chip evacuation.
Comparing the flank wear profiles of the two structures shown in Figures 20c and 20d, it can be seen that the flank wear of the gradient chamfering tool is relatively uniform, while the flank face of the constant value chamfering tool has obvious boundary groove wear bands. This is because the gradual chamfering tool has good chip evacuation performance. During the cutting process, the material is rarely accumulated in the cutting edge area and is shunted to the flank face, thereby reducing the frictional effect on the flank face, and the conduction of cutting heat is obvious. Reduced, eventually resulting in a relatively low degree of wear, the quality of the workpiece surface is more ideal at this time.
06Comprehensive evaluation
1. The edge structure of gradient chamfering cutting is proposed, the PCBN tool with gradient chamfering is designed, the mathematical model of the edge line of the gradually chamfering tool is established, and the numerical simulation of the established edge line model is carried out.
2. According to the PCBN tool structure of gradient chamfering, combined with the face grinding method and the reduction idea, the approximate envelope grinding trajectory planning is proposed. The trajectory simulation shows that when the number of grinding is greater than or equal to 8, the grinding effect is not very different.
3. Carry out the grinding test of PCBN tool with gradient chamfering, put forward the detection method of the cutting edge defect, chamfering width and angle and other parameters of the precision, and complete the quantitative evaluation of the grinding precision of the developed tool.
4. Combining the grinding simulation optimization and tool preparation accuracy detection results, it can be seen that the number of grindings has a greater impact on the tool preparation accuracy. When the number of grinding is 8, the tool quality is optimal.
5. Compared with the fixed value chamfering tool, the gradient chamfering tool has better cutting performance, and its chip removal and tool wear resistance have been significantly improved.
Excerpts from this article: Teacher Chen Tao from Harbin University of Science and Technology, "Design, Manufacture and Grinding Accuracy Testing of PCBN Tools with Gradient Chamfers"
Crankshaft Processing Technology - Rolling
rolling
Process principle
Rolling
It is a plastic processing method that brings a roller with high hardness and smooth surface into rolling frictional contact with the metal surface, so that the surface layer of the processed metal undergoes a small amount of plastic deformation and improves the surface roughness and the comprehensive mechanical properties of the material.
Unlike machining, rolling is a plastic working method that does not remove material.
The workpiece processed by rolling can not only improve the surface quality instantly, but also improve the wear resistance after the machined surface is hardened, and the fatigue strength will also increase by about 30%, which has the advantage that cannot be obtained in cutting.
Because it can perform ultra-precision machining of parts easily and at low cost, it is increasingly widely used in industries such as precision machinery, chemicals, and home appliances, including the automotive industry, and has played a great advantage.
Crankshaft rolling process
The content of crankshaft rolling is all journals (all main journals and connecting rod journals) groove fillets.
Why does the crankshaft need to be rolled?
The crankshaft is subjected to alternating loads during operation. The transition between the main journal and the connecting rod journal fillet is a weak link in the strength of the crankshaft. The transition fillet between the journal and the crank arm has stress concentration after cutting or grinding. The high-speed rotation and large alternating load stress may cause cracks or fractures at the crankshaft fillet.
This will result in an increase in the crankshaft structure and weight, which not only reduces the utilization rate of materials, but also increases the weight of the engine, resulting in poor engine fuel economy.
In view of the above problems, rolling technology can be perfectly solved.
After rolling, a surface hardened layer can be left on the surface of the crankshaft journal, which can not only improve the surface quality, but also form residual compressive stress and improve the fatigue resistance of the crankshaft.
Rolling process parameters
The main parameter of the rolling process is the rolling force.
The setting of the rolling force mainly depends on the material of the workpiece, the size of the fillet and the maximum burst pressure of the engine.
If the rolling force is too small, the strengthening effect of the crankshaft will be weakened. If the rolling force is too large, the surface of the crankshaft will be crushed and the fatigue strength of the crankshaft will be reduced.
Product requirements for rolling force are a range that can be verified by fatigue testing for optimum rolling force.
Fatigue test usually includes two parts: single-step test and step test.
single step test
The main purpose is to analyze and verify the dynamic durability of the crankshaft through a small number of crankshaft workpieces and the number of cycles (usually more than 200,000 times) in a specific working state.
Ladder test
It is to analyze the performance of crankshaft products for many crankshaft workpieces (with statistical significance, such as more than 30 pieces) and the number of cycles in a specific working state (the number is slightly less than the single-step test).
The rolling force requirement of the product drawing is the rolling force required for a single groove and an angle.
1. The rolling force set on the equipment is the force value converted according to the requirements of the product drawing, as shown in the figure below.
2. Equipment calibration pressure: the set pressure used when maintaining and calibrating the pressure sensor, and use an external dynamometer to check whether the pressure sensor is accurate.
rolling
crafting process
1. Workpiece positioning
Axial positioning is performed with the central holes of the crankshaft end and flange end, and angular positioning is to use laser detection (as shown in the figure below) the top of 1# connecting rod journal P1 (the connecting rod journal closest to the crankshaft mandrel end).
2. Clamping drive
To clamp the outer circle of the flange end, use a floating chuck with two-point clamping.
3. Pre-clamping
The rolling arms are closed and the crankshaft workpiece is pre-clamped at low pressure.
4. Measurement before rolling
Measure the runout of the incoming spindle diameter of the workpiece. If the runout warning value is exceeded, the machine tool will alarm and not roll the workpiece.
5. "A-B-C" completes rolling
The A ring is boosted to the final rolling pressure, the B ring maintains the final rolling pressure, and the C ring is depressurized to the pre-clamping pressure.
6. Measurement after rolling
Measure the runout of the workpiece spindle diameter after rolling.
7. Alignment
If the runout exceeds the set requirements, straightening is required. After straightening, measure the runout value again, and the straightening can be repeated, but the number of times is limited. Generally, it is set to 3-5 times, and the equipment alarms for more than 5 times.
8. Marking
Qualified workpieces are specifically marked.
Common equipment brands
The monitoring functions of rolling equipment mainly include rolling force monitoring and tool monitoring.
1. Rolling pressure monitoring:
The force value change in the rolling process is recorded in real time through the pressure sensor, and the difference from the set pressure cannot be greater than the alarm value, otherwise the device will alarm.
The TD/PD files corresponding to all workpieces can be opened in the resource manager on the device. The TD records the tracking graph of the rolling force, and the PD records the beating and other data, which is convenient for inspection and analysis of problems.
2. Tool monitoring
Tool monitoring is divided into three dimensions (methods):
Method 1: Frequency and amplitude, focusing on tool state.
Method 2: Position and Vibration, focusing on the state of the workpiece.
Method 3: Diameter, which mainly monitors the difference in diameter of incoming materials.
Common Tool Types