Dec 30, 2019
In the processing of turning pins, knurling of parts is often encountered. The knurling process seems simple, but often the pattern is disordered due to improper operation. The following briefly describes the bit of knowledge of the knurling operation.
There are many types of knurling patterns, which are roughly straight, twill, and reticulated. Among them, there are diamonds and squares, that is, 30 degrees and 45 degrees. According to the Chinese national standard GB6403.3-84, the knurling pattern is calculated by the modulus, there are four kinds of 0.2, 0.3, 0.4, 0.5, and its P value (distance of the number of pattern teeth, unit mm) is 0.2 = 0.628, 0.3 = 0.942,0.4 = 1.257,0.5 = 0.571. Usually the pattern has metric and imperial system. The P value of the imperial system is calculated according to the number of teeth per inch; the metric P value is a specification per 0.1, that is, 0.3,0.4,0.5,0.6 , 0.7, 0.8, 1.0, 1.2, 1.4, 1.6, etc.
2. Specifications of the knurled wheel
According to different diameters, widths and patterns, knurling wheels have many specifications. Domestically produced series have diameters of ф15, ф20, ф25, ф30, etc .; widths include 6, 8, 10, 12, 15, 20 and other series. The pattern has straight and twill, and the net is formed by the combination of two opposite twill knurling wheels. The imported knurling is now mostly German, and there are many specifications. There are ф10, ф15, ф20, ф25 and other specifications according to the diameter. According to different widths, there are specifications such as 4/6/8/10/15/20, and according to different patterns, there are specifications such as straight, twill, and net. In addition, there are special anilox wheels in foreign countries. As long as the part pattern is within the width of the wheel, it can be directly embossed with a single wheel. If the part anilox exceeds the width of the flower wheel, it is still necessary to use the upper and lower twill wheels for walking and pressing.
3. Type of knurled knife
The knurling operation requires a knurling knife, that is, a shank equipped with a knurling wheel. Knurled knives can be purchased directly, or you can buy knurled wheels and make them yourself. Generally there are single wheel type, multiple wheel type and six wheel type. Single wheel type is to install a flower wheel on a knurling tool holder; double wheel type is to install two flower wheels on a knurling tool handle, usually two pairs of opposite twill wheels are formed; six wheel type That is, there are three sets of compound wheels to be mounted on the handle, which can directly convert different pattern combinations. Knurling knives used on our automatic lathes are usually made by buying imported knurling wheels.
4. Knurling operation
Knurling on a lathe is subject to considerable stress. The workpiece must be clamped securely. The knurling tool must be installed at an angle of 3 ° -5 °. The initial contact surface between the roller and the workpiece is narrow, which makes rolling cutting smooth. The beginning of knurling is very important. It is necessary to press directly into the workpiece without any pause, so that the workpiece can be pressed out of the pattern at once. Wait for the pattern to roll clearly before cutting. Otherwise, it is easy to produce broken heads, that is, the pattern is chaotic. When knurling, ensure that there is sufficient lubricating fluid to prevent chips from accumulating in the knurling sipe, which will stick to the tool and the workpiece, and will damage the pattern when knurling. The clearance of the rollers should not be too large, otherwise radial swing and shaft movement will occur. When rolling straight grains, the circumferential length (π * D) of the workpiece may not be an integer multiple of the pitch (t) of the knurling knife, otherwise, the rolling tracks may not overlap after one revolution, causing the pattern to be chaotic. Then the rolling rule pressure should be large (under the condition of the rigidity of the machine tool and the workpiece), so that the workpiece circle can form a deeper and wider pattern at the beginning, and the knurling teeth can fall at the beginning of the second circle. In the groove of the workpiece, continuous rolling can disperse non-coincidence errors into deeper and wider tooth grooves. The machine tool is not easy to run too fast. Generally, the speed is 185r / min-230r / min, and the feed rate is 0.22mm / r-0.24mm / r. The same is true for knurling on automatic lathes. When designing the cam, it is required that after the knurling knife contacts the surface of the workpiece, it is directly cut into the specified pattern bottom diameter, and then stays for about 10 ° -15 ° and then retracts immediately. If it is a flower, cut into the bottom diameter of the pattern and immediately let the knurling knife walk horizontally. After reaching a prescribed distance, also retreat the knife immediately, otherwise after a long stay, a knife mark will be generated, which will damage the surface shape of the pattern. Pressing the anilox on the automatic lathe exceeds the length of the flower wheel, it is necessary to use the compound wheel for flowering.