The reliability of tool chip breaking has a great influence on normal production and operator safety. In the cutting process, the broken chips will splash and hurt people, and easily damage the machine tool; while the long strip chips will wind on the workpiece or tool, easily scratch the workpiece, cause tool damage, and even affect the safety of workers. For CNC machine tools ( CNC machining centers) and other automatic processing machine tools, because of the large number of tools and the close relationship between the tool holder and the tool, the chip breaking problem is more important. As long as one of the tools is not reliable, it may damage the automatic cycle of the machine tool, or even damage the normal operation of the whole automatic line. Therefore, when designing, selecting or grinding tools, the chip breaking problem must be considered.
In the process of CNC manufacturing , we should ensure:
The chip shall not be wound on the tool, workpiece and its adjacent tools and equipment;
Chips shall not splash to ensure the safety of operators and observers;
When finishing, the chip should not scratch the machined surface of the workpiece, which will affect the quality of the machined surface;
The pre-determined tool wear can not be guaranteed;
When the chip flows out, it does not hinder the injection of cutting fluid;
The chip will not scratch the guide rail or other parts of the machine tool.
On the basis of meeting the above requirements, different tools have different requirements for chip length. For example, the maximum chip length of rough turning steel is about 100 mm, while that of finish turning should be slightly longer. To avoid too fine chips, because it is easy to be embedded in some important parts of the machine tool guide rail and tool device (such as the reference plane), which not only needs additional protection device, but also brings some difficulties to remove the chips. For some cutting tools that are not easy to break, such as forming turning tools, slotting turning tools and cutting turning tools, the stable chip curling should be ensured on automatic machine tools such as CNC machine tools.
Classification of Chip Shape - Types of Cutting Chips
According to the specific conditions and materials of CNC parts , tool geometric parameters and cutting parameters, chip shapes generally include: banded chip, C-shaped chip, crumbling chip, pagoda shaped chip, spring shaped chip, long tight spiral chip, spiral chip, etc.
- Banded chip
In high-speed cutting of plastic metal materials, if chip breaking measures are not taken, it is easy to form banded chips, which are continuous and often wound on the workpiece or tool, which is easy to scratch the surface of the workpiece or damage the cutting edge of the tool, or even hurt people. Therefore, banded chips should be avoided as far as possible. But sometimes it is also desirable to get banded chips so that the chips can be discharged smoothly. For example, when boring blind holes on a vertical boring machine.
- C-shaped chip
When turning general carbon steel and alloy steel materials, C-shaped chips are easy to form if turning tool with chip breaking groove is used. C-shaped chip has no disadvantage of banded chip. However, most of the c-chips are broken when they collide with the tool flank or workpiece surface. High frequency chip breaking and breaking will affect the smoothness of the cutting process and the roughness of the machined surface. Therefore, it is generally not expected to get C-shaped chip in finishing, but rather long spiral chip to make the cutting process more stable.
- Windy curls
When turning steel parts with large cutting depth and large feed rate on heavy lathe, the chip is wide and thick. If C-shaped chip is formed, it is easy to damage the cutting edge, or even cause flying crash. Therefore, the radius of the arc at the bottom of the chip breaking groove is usually increased to make the chips break on the machined surface and fall by their own weight.
- Long tight curl
The forming process of long and tight curling chip is relatively stable and easy to clean. It is a good chip shape on ordinary lathe.
- Pagoda shaped curls
In NC machining, machine tool or automatic line machining, we hope to get this chip, because such chip will not wind on the tool and workpiece. And it's easy to clean.
- Detritus
When turning brittle materials such as cast iron, brittle brass and cast bronze, it is very easy to form needle like or fragment like chippings, which are easy to splash, hurt people and damage the machine tool. If the measure of chip curling is adopted, the chips can be connected into short coils.
In short, the specific conditions of the cutting process are different, and the chip shape is different. But no matter what shape of the chip, the chip must be broken reliably.
Common Methods of Chip Breaking
- Use chip breaking grooves
The chip breaking groove not only has the function of additional deformation to the chip, but also can control the curling and breaking of the chip. As long as the shape and size of chip breaking groove and the inclination angle between chip breaking groove and main cutting edge are suitable, chip breaking is reliable. No matter it is welding tool or clamp tool, regrinding tool or no regrinding tool can be used. In order to apply to different range of cutting parameters. There are many kinds of chip breaking grooves with different shapes and sizes pressed on the indexable cemented carbide inserts, which are easy to select, economical and convenient. This method is the first choice and the most widely used method in machining. The disadvantage is that the determination of the reasonable geometric parameters of the cutting tool is restricted by the chip breaking requirements.
- Using chip breaking devices
There are many types of chip breaking device, which can be divided into mechanical type, hydraulic type and electrical type. The cost of chip breaking device is high, but the chip breaking device is stable and reliable, which is generally only used in automatic line.
- Pre-slot on the surface of workpiece
According to the diameter of the workpiece, one or more grooves are cut along the axial direction of the workpiece on the surface to be machined in advance, and the depth is slightly less than the cutting depth, so that the chips cut out form a weak section and break. In this way, the reliable chip breaking is ensured, and the roughness of the machined surface of the workpiece is not affected. The chip breaking effect is very good even when machining the material with high toughness. For example, when the workpiece material with high toughness (such as 40Cr, etc.) is precisely bored and it is difficult to break chips by other methods, the longitudinal groove can be broached on the machined surface and then boring. This method can show its unique advantages.
- Changing tool geometry parameters and adjusting cutting parameters
According to the chip breaking principle mentioned above, reducing the rake angle of the tool, increasing the main deflection angle, grinding the negative chamfering on the main cutting edge, reducing the cutting speed, increasing the feed rate and changing the shape of the main cutting edge can promote the chip breaking. However, taking these methods to chip breaking will often bring some adverse consequences, such as the decline of productivity , the deterioration of workpiece surface quality, the increase of cutting force, etc. this method is rarely used in automatic line, sometimes only as an auxiliary means of chip breaking.
In addition, the use of cutting fluid can reduce the plasticity and toughness of the chip, but also conducive to chip breaking. Increasing the cutting fluid pressure can make the chip break. This method is sometimes used in hole machiningm
Hassan Awan