Disposable cutting insert for boring cutter

A disposable cutting insert for a boring cutter can reduce the roughness of a cut surface and achieve a mirror-like surface effect. The disposable cutting insert has a long curved blade edge, and the radius vertex of the long blade edge is deviated slightly from an external side of a vertex of the radius of cutting edge. A short curved blade edge is formed between the radius arc vertex and the radius arc vertex of the cutting edge. The vertical distance of the short curved blade edge is greater than the feed rate. The cutting edge cuts the work piece and the short curved blade edge can scrape a small size of material precisely for scraping the peak cut by the cutting edge and lower the height of the peak, so as to lower the surface roughness, and produce a mirror-like surface for an internal periphery of a bored hole.

FIELD OF THE INVENTION

The present invention relates to a disposable cutting insert for a boring cutter, and more particularly to a disposable cutting insert used for the precision boring manufacture of a metal work piece that requires a mirror-like surface for a bored surface.

BACKGROUND OF THE INVENTION

In general, a conventional internal boring manufacture that requires a mirror-like surface effect on the surface roughness has to go through three cutting tools: a coarse boring cutter, a fine boring cutter and an internal microller burnishing tool. The coarse boring cutter carries out a coarse boring operation and reserves ψ0.2˜0.3 mm for a fine boring manufacture, and the fine boring cutter completes a fine boring operation by a feed rate of f=0.04˜0.1 mm/rev and reserves ψ0.02˜0.04 mm for the polish by the internal microller burnishing tool, such that a mirror-like surface effect with a surface roughness up to Rmax=0.04˜1.2 μm can be achieved. This manufacturing method is used extensively for a high precision having a strict requirement on the diameter of a hole including the hole of a bearing of a device with relative movements such as a cylinder hole.

The aforementioned internal boring manufacture for achieving a surface roughness with a mirror-like surface effect needs to employ three cutting tools mainly because a general boring cutter cannot complete the mirror-like surface manufacture directly, and thus it is necessary to use an internal microller burnishing tool to complete the mirror-like surface manufacture. The main reasons and their drawbacks are described as follows:

Referring toFIG. 6for a conventional disposable cutting insert for a boring cutter50, a side cut angle θ1is defined between a side blade edge51and a vertical line of the disposable cutting insert50, and an end cutting edge angle θ2is defined between a front blade edge52and a horizontal line, and the side blade edge51is linear to the front blade edge52and connected to a cutting edge53. If the disposable cutting insert50performs a boring or cutting operation as shown inFIG. 7, then the boring cutter500will remove the material of a work piece60by the front blade edge52and the cutting edge53. After a surface61of the internal periphery of the work piece60is cut, the surface roughness is correlated with the radius R of the cutting edge53and the feed rate f. Referring toFIG. 8for the surface roughness of a cut surface, the manufacture conditions include (a) The radius of cutting edge R=0.4 mm; and (b) The feed width f=0.07 (mm/rev). According to the equation for calculating the manufacturing roughness Rmax≈(f2)*1000/(8R) μm, and the foregoing manufacture conditions, the roughness Rmax=(0.072)*1000/(8*0.4)=1.53 μm can be obtained, and it belongs to the category of a fine manufacture. Although the surface is smooth and bright, the requirement for a mirror-like surface manufacture (Rmax=0.1 μm) cannot be met, and thus it is necessary to use other surface manufacture cutters to achieve the roughness (Rmax smaller than or equal to 0.1 μm) for the mirror-like surface manufacture.

Referring toFIG. 9for a schematic view of a general internal microller burnishing tool, the internal microller burnishing tool60is applied to the internal periphery of a work piece that requires a mirror-like surface manufacture and enhance the surface roughness. InFIG. 10, an internal microller burnishing tool60press a surface peak of the work piece surface by an extrusion method. Although such method can achieve the mirror-like surface effect and lower the surface roughness, its application still has the following drawbacks:

1. During the manufacture, it is necessary to change the internal microller burnishing tool, and thus this method incurs a longer manufacturing time and a higher cost.

2. The cost of the internal microller burnishing tool is high, and thus the manufacturing cost is naturally high as well.

3. After the internal microller burnishing tool has been used for many times, bits produced by the extrusion will be accumulated in the roll beads (cylinder), and it is necessary to clean the tool from time to time. However, a small amount of bits will remain, and the remained bits will be extruded and adhered onto the surface of the work piece and produces a friction with the surface that may blacken the manufacturing surface.

SUMMARY OF THE INVENTION

In view of the foregoing shortcomings of the prior art, the inventor of the present invention based on years of experience in the related field to conduct extensive researches and experiments, and finally developed a disposable cutting insert for a boring cutter in accordance with the present invention.

Therefore, it is a primary objective of the present invention to provide a disposable cutting insert for a boring cutter to overcome the foregoing shortcomings of the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIGS. 1 and 2for the present invention, a disposable cutting insert10for a boring process is comprised of a polygonal body, and defined by an upper plane11, a lower plane12and a plurality of side surfaces13,14,15,16, wherein a stepped hole17penetrates a center position of the disposable cutting insert10, and each side surface13,14,15,16has an appropriate inclination α, β, and the inclination α of the side surface13,14is approximately equal to 11°, and the inclination β of the side surface15,16is approximately equal to 7°, and the upper plane11is a cut plane of a cut work piece that produces iron bits, and the lower plane12is provided for supporting, and a long blade edge181(or the long cutting edge) is formed between the upper plane11and the side surface14, and a cutting edge (the corner radius cutting edge)19is formed between two adjacent side surfaces13,14, and the long blade edge18is substantially a large arc blade edge. Referring toFIG. 3, the radius arc vertex P of the long blade edge181is deviated from a small distance d1and a small angle β at an external side of the radius arc vertex Q1of the cutting edge19(as depicted in a schematic enlarged view of a portion shown inFIG. 3A, and distance d1is approximately equal to 3˜4 μm in this embodiment. In other words, the radius arc vertex P of the long blade edge181is protruded slightly from the radius arc vertex Q1of the cutting edge19, and thus a short curved blade edge180is formed between this radius arc vertex P and the radius arc vertex Q1of the cutting edge18. The central position C1of the arc radius of the long blade edge18must be limited, which means that the position of the radius arc vertex P must be limited, because it will affect the distance g between the radius arc vertex P and the radius arc vertex Q1of the cutting edge18. Being the vertical length of the short curved blade edge180, the distance g must be greater than the manufacturing cutting feed f, in order to lower the surface roughness. In general, the distance d2between two points PQ2is approximately equal to 0.5˜1.5 mm, such that the of the vertical length g of the short curved blade edge180falls within 0.2˜1.0 mm, and thus it is applicable whenever the cutting feed f falls within 0.15˜0.8 mm.

InFIGS. 1 and 2, a rear oblique surface111inclined downward to the rear side is disposed between the upper plane11and the long blade edge181and the front blade edge182and the short curved blade edge180of the disposable cutting insert10for improving the sharpness of the cutting edges.

The disposable cutting insert10in accordance with the present invention is used for an internal boring manufacture, and it only needs to go through two cutting tools: a coarse boring cutter and a boring cutter with a disposable cutting insert10for the boring cutter in order to achieve the required surface roughness for a mirror-like surface effect, and it no longer requires the internal microller burnishing tool, and thus the invention can save the manufacturing manpower, time and cost.

After the manufacture conducted by the coarse boring cutter, a reserved space of Ψ0.02˜0.30 mm is reserved and the manufacture conditions including a feed rate of f=0.1˜0.3 mm/revand a rotation speed of VC=100˜300M/mim are adopted to complete the mirror-like surface manufacture.

Referring toFIGS. 3 and 4, the cutting edge19is a position for producing a cut for the internal hole diameter, and the radius arc vertex P of the arc blade edge181is protruded slightly from the radius arc vertex Q1of the cutting edge19by approximately 3˜4 μm, and thus the short curved blade edge180will scrape the material slightly, and the included angle between the radius (which is 50 mm in this embodiment) of the long blade edge181and the vertical axis (which is the side cut angle γ as shown inFIG. 3A) is very small. Even if the feed rate is fast, the roughness will remain very low. For example, the feed rate f=0.3 mm/rev in accordance with this embodiment, and the vertical length g (which is the distance between two points PQ1) of the short curved blade edge180is approximately equal to 0.6˜0.8 mm and greater than the feed rate f=0.3 mm. After the hole is bored, the maximum surface roughness Rmax=0.04 μm, which can achieve the mirror-like surface effect directly without the need of using the internal microller burnishing tool, so as to save manufacturing manpower, time and cost.

Referring toFIG. 5for an enlarged view of the surface roughness, a short curved blade edge180will scrape the wave peak20of a cutting path Pn produced by the cutting edge16and lower the surface roughness, so as to lower the Rmax and achieve the mirror-like surface effect.

In summation of the description above, the present invention has the following advantages:

1. The design of the short curved blade edge can achieve the cutting function for scraping the peak of the cutting edge. In the same cutting conditions, the present invention can effectively lower the roughness, and achieve the mirror-like surface effect.

2. The disposable cutting insert of the invention is applicable for the present existing disposable cutters, and thus users need not to expend additional expenses. The disposable cutting insert fits a cutter, a boring cutter and other types of cutters.

3. A reserved space of 0.02˜0.30 mm is reserved after an internal hole is bored for a work piece that requires a low roughness and a mirror-like surface effect, and thus the present invention can meet the requirements for the mirror-like surface manufacture without using additional cutting tools (such as the internal microller burnishing tool), and thus the invention can lower the cost of cutting tools and the manufacturing time effectively.

In summation of the description above, the disposable cutting insert of the invention comes with a short curved blade edge for reducing the roughness and achieve the mirror-like surface effect, and the work piece can be manufactured directly by the disposable cutter without using additional cutting tools, and thus such cutting insert can be applied extensively for cutting, milling, boring operations. The present invention breaks through the bottleneck of cutter designs, and enhances the performance over the conventional structure and further complies with the patent application requirements and is duly filed for patent application.