Several Methods to Control Chip Breaking in Turning in Machining

In the turning in machining, when the continuous band-shaped chips are produced, it is not only easy to scratch the surface of the workpiece and damage the cutting edge, but in serious cases also threatens the safety of the operator. Therefore, necessary process measures are taken to control the chip shape and breakage. Chips have always been an extremely important processing problem in the machining industry. Buying coil spring, you must dissatisfied with these annoying things.

Since the chip is the product of the deformation of the chip layer, changing the cutting conditions is an effective way to change the types of chips and achieve chip breaking. The factors that affect the chip processing conditions mainly include the workpiece material, the geometric angle of the tool, and the amount of chips. Metal springs suppliers will pay much attention on these conditions.

Generally, chips need to meet the following basic conditions: chips must not be entangled on tools, workpieces, adjacent tools and equipment; chips must not splash to ensure the safety of operators and observers; chips must not scratch the workpiece during finished surface of workpieces which will affects the quality of the finished surface; guarantee the predetermined durability of the tool and do not wear prematurely and tries to prevent its damage; when the chips flow out, it does not hinder the injection of cutting fluid; the chips will not scratch the machine tool rail or other parts, etc.

1. Classification of chip shapes in turning

Due to different degrees of plastic deformation, different types of chips may be produced. When processing plastic materials, mainly, band-shaped chips, nodular chips or granular chips are produced. When processing brittle materials, chip-shaped chips are generally produced.

1. Band-shaped chips: Band-shaped chips are continuous chips with a smooth bottom surface and a fluffy back surface. When a tool with a larger rake angle is used to process plastic metal materials at a higher cutting speed, this type of chip is likely to be produced. It is the product of insufficient deformation of the cutting layer. When band-shaped chips are produced, the cutting process is smooth and the surface roughness of the workpiece is small, but the chips are not easy to break, which often causes entanglement, roughening of the workpiece, and even affects the operation, so its chip breaking problem cannot be ignored.

2. Nodal chips: Nodal chips are chips with a smooth bottom surface, obvious cracks on the back, and deep cracks. When a tool with a reduced rake angle is used to process plastic materials at a lower cutting speed, this type of chip is likely to be produced. It is the product of more fully deformed chip layer, which has reached the degree of shear cracking. When nodular chips are produced, the chip work is not stable and the surface roughness of the workpiece is relatively large.

3. Granular chips: Granular chips are a kind of uniform granular chips. When a small rake angle tool is used to process plastic metal materials at a very low cutting speed, this kind of chip is easy to produce.

4. Shattered chips: Shattered chips are irregular fine-grained chips. When cutting brittle materials, the cutting layer hardly undergoes the plastic deformation stage and suddenly cracks and forms chips after elastic deformation. When the chipped chips are produced, the cutting work is unstable, the cutting edge is subjected to a larger impact force, and the machined surface is rough and uneven.

It can be seen from the above that the types of chips vary with the workpiece material and cutting conditions. Therefore, in the machining process, you can judge whether the chip condition is appropriate by observing the chip shape, and you can also change the chip shape by transforming the cutting conditions to transform it in a direction conducive to production.

2. The cutting method of turning processing

The fundamental cause of chip breaking and continuous is the deformation and stress in the chip formation process. When the chip is in an unstable deformed state or the chip stress reaches its strength limit, the chip will break. Usually the chip is broken after curling.

Plastic cnc services require fine craftsmanship. Reasonable choice of tool geometry angle, cutting amount, and grinding chip breaker are commonly used chip breaking methods：  

1. Reduce the rake angle and increase the entering angle: The rake angle and the entering angle are the tool geometric angles that have a greater impact on chip breaking. Reduce the rake angle, aggravate chip deformation and chip breaking will be easy. Since the rake angle is ground to a small size, the cutting force will be increased, and the increase in the cutting amount will be limited. In severe cases, the tool will be damaged, or even "stuffy". Generally, reducing the rake angle is not simply used to break chips. Increase of the entering angle can increase the cutting thickness and facilitate chip breaking. For example, a 90° tool is easier to break chips than a 45° tool under the same conditions. In addition, increase of the entering angle will help reduce vibration during processing. Therefore, increasing the entering angle is an effective chip breaking method.

2. Reducing the cutting speed, increasing the feed rate to change the cutting parameters is another measure for chip breaking. Increase the cutting speed, the underlying metal of the chip will become soft and the chip deformation will be insufficient, which is not conducive to chip breaking; reducing the cutting speed, on the contrary, is easy to break the chip. Therefore, during turning in machining, you can reduce the spindle speed to reduce the cutting speed to break the chips. Increasing the feed rate can increase the cutting thickness and facilitate chip breaking. This is a chip breaking method often used in machining, but it should be noted that as the feed rate increases, the surface roughness value of the workpiece will increase significantly.

3. Open chip breaker: Chip breaker refers to the groove made on the rake face of the tool. The shape, width and oblique angle of the chip breaker are all factors that affect chip breaking.

(1) Shape of chip breaker

The commonly used chip breakers have three types of grooves: broken line, straight arc, and full arc.

(2) Width of chip breaker

The width of the chip breaker has a great influence on chip breaking. Generally speaking, the smaller the groove width, the smaller the curl radius of the chip, the greater the bending stress on the chip, and the easier it is to break. Therefore, using a smaller chip breaker groove width is beneficial to chip breaking. However, the width of the chip breaker must be considered in connection with the feed depth of cut.

If the width of the chip breaker and the feed amount are basically appropriate, C-shaped chips can be formed. If the chip flute is too narrow, it is easy to cause chip blocking, which will increase the load of the turning tool and even damage the cutting edge; if the chip flute is too wide and the cutting curl radius is too large, the cutting deformation is not enough, it is not easy to break, and often forms a continuous band-shaped chip without flowing through the bottom of the groove.

The width of the chip groove should also be appropriate to the depth of cut. Otherwise, when the groove is too narrow, the chip appears wide and it is not easy to curl in the groove. Often, the chips do not flow through the groove bottom and form strip-shaped chips. When the groove is too wide, the chips appear to be narrow, the flow is relatively free, the deformation is not sufficient, and it does not break.

In order to obtain a satisfactory chip breaking effect, the appropriate chip breaker width should be selected according to the specific processing conditions. For workpiece materials, if the materials are of lower hardness, the groove should be narrower. If not, the groove should be wider.