Product of chengdu meisherui new material co., LTD. -- boring tool

Cutting tool is an important part of machining, including drill, reaming drill, boring cutter, reamer and inner surface broach. Compared with other mechanical processing, boring processing is a kind of more difficult processing. It only by adjusting a blade (or blade holder) to process such as H7, H6 micron scale holes.
 
Boring cutter is a kind of boring tool, commonly used occasions are inner hole processing, reaming, inner hole profiling, etc. A cutting tool with one or two cutting sections specially used for roughing, semi-finishing, or finishing existing holes. Boring cutter can be used on boring machine, lathe or milling machine.

The shape of the cutting part of a single-edge boring cutter is similar to that of a turning tool. In order to make the hole to obtain high dimensional accuracy, fine boring cutter can accurately adjust the size of the boring hole on the machine tool, it has a precision vernier engraved line indicating plate, indicating plate with the boring head of the core bar composed of a pair of precision screw nut pair mechanism. When the nut is turned, the core rod equipped with the tool head can be moved in a straight line along the directional key, with the help of a vernier scale reading accuracy up to 0.001 mm.
 
Double-edged boring cutter has two distributed on both sides of the center at the same time cutting cutter teeth, because the radial forces produced during cutting balance each other, can increase the cutting amount, high production efficiency. Double-edged boring cutter is divided into floating boring cutter and fixed boring cutter according to whether the blade is floating on the boring bar. Floating boring cutter is suitable for hole finishing. In fact, it is equivalent to a reamer and can boring holes with high dimensional accuracy and smooth surface.
 
Choice of boring cutter
Boring processing characteristics
1). Tool rotation: in the machining center machining tool rotation, boring tool has fine-tuning mechanism or automatic compensation function, can be adjusted according to the tolerance requirements of micron level, because the chip outflow direction in constant change, so the tip, workpiece cooling and chip discharge is more difficult than the lathe processing.

2), tool vibration:
(1) the rigidity of the tool system: including the rigidity of the tool handle, boring bar, and the middle connecting part. Because of the cantilever processing, especially when small hole, deep hole and hard workpiece processing, the rigidity of the tool system is particularly important.
(2) the influence of dynamic balance of the tool system: relative to the rotation axis of the tool system, if there is an unbalanced mass of the tool itself, the vibration will occur due to the centrifugal force during rotation. Especially in the high speed machining tool dynamic balance has a great impact.
(3) the fixed rigidity of the workpiece itself or the workpiece: some smaller, thinner parts due to their own lack of rigidity, or because of the shape of the workpiece and other reasons can not use a reasonable fixture for full fixation.
(4) the influence of blade tip shape: the cutting resistance is different due to the different blade rake Angle, tip radius and chip breaking groove shape.
(5) The influence of cutting conditions: including cutting speed, feed, feed, and the way and type of cutting oil, etc.
(6) the influence of the machine spindle system: the rigidity of the machine spindle itself, the performance of bearings and gears, and the connection rigidity between the spindle and the tool handle.
 
3) the tool clamping
In boring holes, the most important thing is to clamp the tool correctly. The center height of the tool is an important factor leading to tool failure.
(1) the cutting edge relative to the main back Angle of the workpiece decreases, resulting in the tool surface and the workpiece contact, the friction between the blade and the workpiece, when the blade rotates, this friction will further make the tool tip deviation, resulting in deeper cutting tool into the workpiece. Increasing the rackangle can reduce the plastic deformation of the rackface when squeezing the cutting layer, reduce the frictional resistance of the chip flowing through the front, and thus reduce the cutting force and cutting heat. However, increasing the rake Angle will reduce the intensity of the cutting edge and reduce the heat dissipation volume of the tool head
(2) when the tool back Angle is reduced, the front Angle of the blade relative to the workpiece is increased, which causes the tool to scrape the workpiece, causes the vibration of the tool and damages the tool. This situation is more serious when boring holes.
 
For this purpose the tool should be mounted slightly above the center height (but as close as possible to the center height). In this way, the normal backward Angle of the tool relative to the workpiece is increased, and the cutting conditions are improved. If vibration occurs during machining, the tool tip will be deflated downward and toward the center, so as to approach the ideal center height. The tool can also be slightly withdrawn, reducing the possibility of cutting the workpiece. Cutting tool rake Angle decreases, can stabilize the working pressure. If the rake Angle is reduced to 0°, it will produce too much working pressure, resulting in tool failure, so the boring tool with positive rake Angle should be selected.
 
4). Dust discharge
When processing, because the tool is in the hole, the cutting fluid is difficult to reach the cutting edge, resulting in difficult chip discharge, affecting the tool life.
The choice of boring tool is greatly limited by the aperture and length of the part (the depth and overhang of the hole). The general rule is to choose the shortest overhang and the largest tool size possible. Selecting the right tool and properly applied and reliably clamped minimizes tool deflection and vibration.
While the tool is cutting, tangential and radial cutting forces attempt to deflect the tool away from the workpiece. Any radial deviation means reduced cutting depth and chip thickness, which leads to a vibration trend. Radial skew affects the diameter of the machined hole, while tangential skew means that the cutting edge of the blade moves downward away from the centerline. The factors that must be considered when boring are: blade groove shape, chip removal problem, cutting tool requirements.
The main deflection Angle of the boring tool affects the direction and magnitude of the axial and radial forces. Tip radius and tip Angle are important to reduce radial and tangential forces. The rule of thumb for choosing a tip radius is that it should be slightly less than the depth of cut. In inner hole turning, it is best to use a positive rake basic shape blade, which produces less cutting force than the use of negative rake tool. Can reduce the cutting force such as the selection of low friction coefficient of cermet blades, thin coated blades or non-coated blades than thick coated blades generally produce a lower cutting force, can be preferred.
Chip removal is very important to the performance and safety of inner hole machining. Too short scrap iron will consume higher power during the machining process and will increase vibration and cause blade crescent depression wear. Longer iron chips can cause chip removal problems. Shorter spiral chips are the ideal chip shape in cutting because they are easier to discharge and do not cause large pressure on the cutting edge during chip breaking.
Centrifugal force forces the chip out. Usually the chip stays in the hole, and the tool presses the chip onto the machined surface, damaging the part and tool. Therefore, a series of measures should be taken to improve the chip removal performance as follows: the use of internal cutting fluid to help chip removal or the use of compressed air to use through holes through the spindle chip blowing out. Boring is turned upside down to keep the chip away from the cutting edge. Reduce cutting speed. Use small cutting head to maximize chip storage space.
The selection of the tool for inner hole processing shall comply with the following principles: a. The diameter of the boring bar shall be selected as large as possible under the premise of ensuring that there is enough space for chip removal between the boring bar and the hole. B, ensure that the cutting parameters and chip shape to ensure smooth chip removal. C. Ensure that the length of boring bar is selected as small as possible. The clamping length shall not be less than three times the diameter of the boring bar. D, choose >75° as close as possible to 90° close to 90 degrees of the main Angle, BBB> degrees, so that the cutting force towards the boring bar. C. Select the basic shape of the positive rake Angle of the blade and the groove shape of the positive rake Angle of the blade to minimize the cutter deviation. D. Select the blade with the tip radius less than the cutting depth. E. Vibration due to friction (not real cutting effect) should be avoided during cutting due to lack of cutting edge. And vibration caused by tool deflection when the cutting edge is overloaded (large cutting depth and/or feed). F. Choose cermet or thin-coated blades and uncoated blades to provide lower cutting forces. This is especially important when the length and diameter are large. Sharp cutting edges generally improve hole quality by minimizing the vibration tendency. G. The groove shape with open chip breaking groove is more favorable for boring. H. In some cases, blade grades with higher strength are required to deal with chip clogging or vibration trends. To improve the chip shape, consider changing the tool path.
 
Material of boring blade
Boring blade can be made of hard alloy, metal ceramic, ceramic, PCD\PCBN and other materials.
Cemented carbide boring tools mostly use PVD or CVD coating. Suitable for processing most steel, titanium alloy, cast iron and non-ferrous metal alloy, processing high temperature alloy and austenitic stainless steel. Ceramic blade brand includes alumina (Al2O3) base and silicon nitride (Si3N4) base two categories. Used for boring alloy steel, tool steel, martensitic steel with hardness greater than HRC60, and fine boring of hardened steel, cast iron (hardness HRC45 or higher), nickel base and cobalt base alloy. Silicon nitride based ceramic blades include coated and uncoated grades. Used for boring gray cast iron and ductile cast iron. Boring of high temperature alloy. Cermets are composite materials composed of titanium carbide or titanium carbon nitride and metal (nickel, cobalt) binder. With a good anti - chip accumulation and plastic deformation ability, used for finish requirements than the workpiece fine boring process. It can be used for high speed fine boring and semi - fine boring of most carbon steel, alloy steel and stainless steel. Long tool life and good surface finish can also be obtained when used in processing gray cast iron and ductile cast iron. Polycrystalline diamond (PCD) blade is made by welding PCD tip on hard alloy matrix. The cutting edge of PCD tool can keep sharp for a long time, and it is also suitable for high speed cutting. The hardness of polycrystalline cubic boron nitride (PCBN)R is second only to PCD. PCBN blade grade is usually used for fine boring of hardened steel, tool steel, high speed steel (HRC45~60), gray hard cast iron and powder metallurgy materials. In high speed machining, it can obtain longer tool life than other types of tools processing the same workpiece