In CNC Machining, you often encounter problems such as CNC bouncing tool, hitting tool, overcut, etc. This article talks about the solutions to these common problems, hoping to draw inferences from one another.
Bullet knife
Flick knife refers to the relatively large vibration of the tool due to excessive force. The hazard caused by spring knives is to cause over-cutting of the workpiece and damage to the tool. When the tool diameter is small and the tool bar is too long or the force is too large, the phenomenon of spring knives will occur. If a reasonable tool and processing method are used, the chance of flicking the knife can be reduced.
There are three main factors affecting tool deformation:
1) Length of knife
2) Tool diameter
3) The force of the tool
1. Length of knife
For a tool of the same diameter, when the length of the tool is doubled, its deformation will increase by 3 times. When processing, shorten the length of the knife as much as possible to reduce the risk of flicking the knife.
2. Tool diameter
For the tool of the same length, when the tool diameter is reduced by one time, its deformation will increase by 4 times. When processing, if possible, choose large-diameter tools or use reinforced tools for processing as much as possible to reduce the risk of snapping tools. (As shown in the figure below: A uses hot wire and tapered neck knives, and B uses a tool with a strengthened shank for processing)
3. The force of the tool
The deformation of the tool is directly proportional to the force it receives during processing. Reducing the force of the tool can reduce the chance of snapping the knife. To reduce the force on the tool, it is necessary to reduce the contact area between the tool and the workpiece.
Reduce force example 1:
Use the tool path corner function or increase the R position to reduce the load of the tool at the corner position, thereby reducing the probability of snapping the knife.
Reduce force example 2:
When processing deeper positions, a smaller feed and fine R-angle tool can be used to reduce the force on the tool during processing, so as to reduce the risk of snapping the knife.
The following figure shows the comparison of the contact position with the mold material when the D50R6 tool and the D50R0.8 tool are used to process the same depth. It can be seen that the use of a fine R-angle tool to process a deep workpiece can reduce the cutting force more than a large R-angle tool.
Reduce the amount of cutting tool (that is, the global depth of each tool). When the machining depth is greater than 120mm, the tool must be installed twice, that is, first install a short toolholder to process to a depth of 100mm, and then install an extended toolholder to process below 100mm Part, and set a small amount of knife.
02
Hit the knife
Knife hit means that the cutting amount of the tool is too large. In addition to the cutting edge, the tool bar also hits the workpiece. The main reasons for the tool collision are the unreasonable safety height setting or the safety height not set at all, the improper processing method selected, the improper use of the tool, and the margin setting for the second roughing is smaller than the margin for the first roughing setting, etc. .
1. Take too much knife
Solution:
Reduce the amount of knives taken. The smaller the diameter of the tool, the smaller the amount of the tool. Under normal circumstances, the amount of the tool for each rough opening of the mold is not more than 0.5mm, and the amount of the tool for semi-finishing and finishing is smaller.
2. Choosing an improper processing method
Solution:
Change the mode of contour milling to the mode of cavity milling. When the machining allowance is greater than the tool diameter, the contour processing method cannot be selected.
3. Improper safety height setting
Hit the fixture while lifting the knife
Solution:
(1) The safety height should be greater than the clamping height
(2) In most cases, it is not possible to select the "direct" tool advance and retreat mode, except for special workpieces
4. Improper setting of secondary opening coarse margin
Solution:
The margin for the second roughing should be slightly larger than the margin for the first roughing, generally 0.05mm larger. If the margin for the first opening is 0.3mm, the margin for the second opening should be 0.35mm. Otherwise, the tool bar will easily hit the upper side wall.
In addition to the above-mentioned reasons, knife collisions may occur when repairing scissors roads, so try not to repair scissors roads. The most direct consequence of tool collision is damage to the tool and workpiece, and more serious damage to the spindle of the machine tool.
03
Overcut
Overcut means that the tool also cuts the parts that cannot be cut, causing the workpiece to be damaged. There are many reasons for the over-cutting of the workpiece, mainly including low precision of the machine tool, tool collision, spring tool, small tool selected in programming but large tool used in actual processing. In addition, if the operator is not accurate in setting the knife, it may also cause overcutting.
The situation shown in the figure below is an overcut caused by improper safety height setting.
When programming, you must be careful and meticulous. After completing the programming, you need to check the tool path in detail to avoid over-cutting, otherwise the mold will be scrapped or the machine tool will be damaged.
