What if the blower fails?
The main reason for this fault is that the fan has been used for a long time, and the dust deposition is too much, which leads to the increase of friction coefficient between the rotor and the bearing, and the rotor is blocked or even stuck, resulting in the overheating of the coil. The above phenomenon can be identified by the following methods: Switch on the power supply and press the blower shell by hand. If there is a slight vibration sensation, the coil should have no problem, because the rotor is stuck.
After power off, open the back cover of the fan, add a few drops of lubricating oil (such as sewing machine oil) to the sleeves at both ends of the rotor, and stir the leaf while dropping until the blade is flexible and the blower fault can be eliminated. If you press the fan a little movement, it may be no 220V AC input or coil is damaged, then you should cut off the power supply, the fan two lead line and the power line two lap point off, let it hang (note that the power line can not be touched at both ends together, otherwise cause short circuit).
Switch on the power supply and carefully measure both ends of the power cable with an electric pen. If one end is bright and the other end is not, it indicates that the power supply is normal. The coil of the fan may be damaged. If both ends of the electroprobe are on or off, there is a problem with the power supply. Of course, using a multimeter is more convenient. Use a multimeter to directly measure the two lead lines of the blower. The normal coil resistance is about 400ω. If the resistance is large or the needle does not move, the coil is damaged.
Two, the fan does not turn, but there is a long "buzzing" sound
This fault is most common on capacitive blower. The main reasons are: capacitor no capacity or serious leakage, or damage to the starting winding, remove the original capacitor, with a good capacitor connected to try. Capacitor use standard: 30W ~ 40W blower capacitor is usually between 1uF ~ 1.5uF; The capacitance of 80W ~ 120W blower is usually between 2uF ~ 3uF.
If the blower works normally after the new capacitor is replaced, the fault is indeed caused by capacitor damage. If the blower is not normal after the new capacitor is replaced, it is mostly caused by the damage of the internal starting coil of the blower, and the fault can only be eliminated by replacing the coil.
How to maximize tool life by analyzing tool position and tool path in milling
In the milling process, the mechanical load is affected by many factors. The influence of tool position and tool path on the mechanical load is analyzed here. In the turning process, only one cutting edge participates in the cutting and the cutting load is stable, while in the milling process, multiple cutting edges participate in the cutting and bear the intermittent load of rapid change.
Therefore, a great deal of choice and consideration is required for milling to be successful.
The most basic step in milling is to choose the type of milling cutter, cutting blade and cutting edge. Cutters suppliers can provide face milling, end milling, three-side milling and other cutters with roughing or finishing geometric grooves to meet the machining characteristics of the required parts.
Regardless of which tool is used in the process, the cutting edge of the tool repeatedly cuts in and out of the work material. The cutting load on each cutter tooth rises from zero before cutting to the peak value during cutting and then returns to zero at cutting. Minimizing intermittent loads in milling processes maximizes tool life, productivity, and process reliability.
Tool position, cut-in and cut-out strategy and chip thickness control are key factors to achieve this goal.
Cut-in workpiece strategy
In milling, the load on the tool depends largely on the way the tool and cutting edge cut into the workpiece. In conventional milling or reverse milling, the tool rotates in the opposite direction to the workpiece feed. In down milling, the tool rotation is the same as the workpiece feed direction.
In reverse milling, the cutting edge cuts into the workpiece with minimum chip thickness and cuts out with maximum chip thickness. In down milling, by contrast, the cutting edge cuts into the workpiece at maximum chip thickness, which can be reduced to zero when cutting out. In either case, the milling process produces chips of varying thickness.
In most cases, flush milling is recommended because it minimizes chip friction with the edge in conventional milling due to chip thinness. In face milling, the chip thickness is maximized when cutting and this helps transfer heat to the chip, thereby protecting the workpiece and tool. Chips will be discharged, reducing the risk of secondary cutting chips.
In some cases, reverse milling is preferred. Surface milling using the down milling method will produce a downward force, which will cause reverse clearance displacement on the old manual machine. In reverse milling the tool is pulled up from the workpiece and is therefore a better choice for less stable machine tools, especially heavy cutting. Reverse milling is also very effective when milling coarse surfaces or thin-walled materials.
When selecting tool positions and feeding strategies, machine tool operators should note that placing the tool on either side of the workpiece centerline is always preferred. Center positioning will generate the forces of both reverse milling and down milling, which can lead to machining instability and vibration. Side positioning is stable.
How the cutting edge cuts out of the workpiece is as important as how it cuts in. There is a definite relationship between the position of retracting tool and the life of the cutting edge. If the retreats are too sudden or uneven, the cutting edge will crack or break. On the other hand, careful retracting can prolong tool life by up to 10 times.
The key value is the retreat Angle, the retreat Angle refers to the Angle between the milling cutter center line and the cutting edge retreat point. The retracting Angle can be negative (above the tool centerline) or positive (below the tool centerline). The failure of the cutting edge is more obvious when the retracting Angle is between -30 ° and +30 °. (The width of the workpiece area enclosed by these retracting angles is roughly half the diameter of the milling cutter).
Another way to improve the intermittent nature of milling cutter cutting edge load is to maximize the number of cutting edges engaged with the workpiece at any one time. The use of smaller diameters, dense-toothed cutters, and greater radial cut depth will result in more teeth contacting the workpiece and more uniform cutting force distribution.
The chip thickness in milling greatly affects the cutting force, cutting temperature, tool life, chip formation and removal. If the chip is too thick, there will be too much load, resulting in the cutting edge micro-collapse or fracture. If the cutting is too thin, the cutting process is carried out on fewer cutting edges, and the increased friction will generate heat, which will accelerate wear.
Chip thickness is measured perpendicular to the effective cutting edge. As mentioned above, the chip formed during milling changes thickness as the cutting edge cuts through the workpiece. Tool manufacturers use the concept of "average chip thickness" for programming purposes. The average thickness is the average of the thickest and thinnest chip sizes.
Tool manufacturers provide average chip thickness for specific tool slots, which, when applied and maintained properly, results in optimal tool life and productivity.
This average chip thickness value is used by the machine operator to determine the tool feed rate to maintain the recommended average chip thickness. Tool radial engagement, tool diameter, tool position and main Angle of cutting edge are the factors to determine the appropriate feed rate. Radial meshing is the ratio of radial depth of cut (AE) to milling cutter diameter (Dc). The greater the radial engagement of the tool, the lower the feed rate required to produce the desired chip thickness.
Similarly, the smaller the tool engagement, the higher the feed rate required to obtain the same chip thickness. The main Angle of the cutting edge also affects the feed requirements. The chip thickness is maximum when the main deflection Angle is 90 degrees, so in order to achieve the same chip thickness, reducing the main deflection Angle requires increasing the feed rate.
A sharp cutting edge produces less cutting force than a grinding or chamfering edge, but is also more prone to fragmentation. To prevent micro-collapse and fracture, the mechanical load on the cutting edge must be limited, so a smaller average chip thickness is recommended when applying sharp cutting edges. In this case, the cutting edge groove type used determines how to select the correct average chip thickness and vice versa.
Machine operators can use these principles and methods in basic milling applications to control intermittent stresses on milling tools. However, as part requirements have become increasingly complex, manufacturers of CAM software and advanced CNC equipment have developed processing strategies such as cycloid Milling and chip peeling, as well as software programming modules such as Dynamic Milling, Volumill and Adaptive Clearing with constant radial cutting depth modules.
These advances in software and machine tool control technology represent high-tech advances in the basic concepts of tool advance and retreat and chip thickness management to facilitate control of the effectiveness of the tool intermittent milling process.
Recognizing the unique interactions between workpiece and tool in milling and processing reduces intermittent stress in the process, allowing manufacturers to achieve the almost unattainable triple goal of maximizing productivity, quality, and tool life.