With the rapid development of modern science and technology, by a polycrystalline diamond (PCD), polycrystalline cubic boron nitride (PCBN) and other superhard material tools and more abundant species, and its performance has been continuously developed and enhanced. Abrasive blade size from tens of microns to a few microns nanometer; diamond, cubic boron nitride content of the content into low, medium and high levels of content; binding agents both metal and non-metallic composite material have; PCD layer thickness ranging from millimeters to microns; PCD and cemented carbide substrate binding mode of a flat, corrugated surfaces; PCD layer has a high wear resistance, high toughness, high heat, such as different properties. Currently PCD, PCBN cutting tool to expand the scope of application to the automotive, aerospace, precision machinery, household appliances, wood, electrical and electronic industries for the production of turning, boring, milling cutters and drills, reamers, countersinks, knives, saws, Lou knives, razors, etc.
Although PCD, PCBN cutting tools is growing so fast, but due to its high hardness tool sharpening has been plagued by difficulties most users, blade resharpening also mainly accomplished by the original manufacturer of cutting tools. Tool not only high prices, long delivery, but also takes up corporate liquidity. Therefore, it is necessary to seriously study the characteristics and grinding of PCD PCD tool sharpening techniques.
2 PCD cutting tool manufacturing process
PCD cutting tool production process generally includes polishing, cutting, solid pick, sharpening, quality and so on. PCD blanks superhard materials usually have a diameter of 1/2, 3, 4 inches, and its surface is usually rougher (Ra2 ~ 10μm), can not be directly used for production of tools, to the surface to be ground and polished to a mirror (Ra ≤ 0.01μm), or by laser cutting and EDM wire cutting into a certain geometric shape and size requirements of the blade, and further on the blade and the base junction to be solid mechanical and chemical treatment, and use of silver-based brazing the blade fixed on a substrate, the final grinding diamond wheel.
PCD cutting tool manufacturing technology is one of the key sharpening the cutting edge quality. Lack of good quality material blade sharpening techniques and technologies will result in a waste of resources, the use of a good tool sharpening process will improve product quality, reduce tool cost.
3 PCD grinding characteristics of the material
PCD is specially treated with a small amount of binder diamond under high pressure at high temperature sintering. Disordered arrangement of the PCD diamond grains having a uniform, high hardness and wear resistance. PCD can be used for cutting tools, grinding wheel dressing, geological drilling, measuring probe, touch with brushed, sandblasted touch with the other. But the PCD high hardness and high wear resistance but also to its processing has brought great difficulties.
Domestic and foreign scholars PCD materials of high hardness and high wear resistance processing problems caused a great deal of research and testing, including electrical discharge machining, ultrasonic machining, electrochemical machining, laser processing, etc., and achieved certain results . However, a comprehensive analysis found that the current multi-processing technology for PCD material roughing applications. PCD cutting edge in order to get good quality, the best method is still working with diamond grinding wheel or grinding.
Grinding of PCD mainly mechanical and thermal chemical mixing both results. Mechanical action is achieved by grit diamond wheel for PCD materials continue to impact the formation of diamond micro-crushing, wear, loss or cleavage; thermal chemistry is PCD diamond grinding wheel the diamond formation temperature oxidation or graphitization. The result of mixture of the two resulting PCD material is removed. Grinding its main characteristics are:
(1) a large grinding force
Diamond is the hardest known mineral substances, with a variety of metals, non-metallic materials, the amount of wear of friction pairs only carbide 1/50 ~ 1/800; PCD hardness (HV) of 80 ~ 120KN / mm2 , second only to single crystal diamond, much higher than the carbide. PCD diamond grinding wheel used when starting the cutting strength is high at approximately carbide (0.4MPa) more than 10 times; specific grinding energy of 1.2 × 104 ~ 1.4 × 105J/mm3; therefore far higher grinding force for grinding carbide.
(2) grinding ratio is small
Since high hardness and wear resistance of PCD (relative wear resistance of tungsten carbide 16 to 199 times), when grinding the grinding ratio PCD only 0.005 ~ 0.033, about carbide 1/1000 ~ 1/100000; grinding efficiency is only 0.4 ~ 4.8mm3/min. Therefore, to ensure the quality of the cutting edge of the tool and the removal, grinding for a long time, the processing efficiency is very low. In addition, when the PCD hardness, content, particle size is not the same, the grinding time disparities.
(3) a great influence on particle size
PCD cutting tool materials are used mainly divided into three categories according to size: coarse-grained (20 ~ 50μm), medium size (10μm or so) and fine-grained (~ 5μm), its grinding force, grinding ratio difference of several to tens of times. Coarse-grained PCD grinding than the maximum, the grinding is also the most difficult and the most severe jagged edge grinding, quality is the worst, but wear the strongest; grained PCD grinding ratio is relatively low, grinding easier, After grinding blade best quality.
4 PCD cutting tool sharpening requirements for tooling
Based on the grinding characteristics of PCD, PCD grinding wheel with diamond grinding equipment when the requirements are much higher than the average tool grinder. Are:
(A) the machine has good rigidity of process systems
The PCD material hardness is high, so there must be a higher grinding resistance to deformation, particularly clamping system and tool spindle system. PCD cutting tool sharpening grinding force when generally up to 100 ~ 500N. Thus requiring a large machine shaft, bearing axial stiffness and strength must be high.
(2) the machine has adjustable stroke and speed adjustable short-swing mechanism
PCD grinding ratio is very low, PCD grinding process mainly through the mechanism of diamond grinding wheel for PCD materials continue to impact the formation of micro-crushing, wear, loss, cleavage and other mechanical and oxidation of graphite thermal chemical mixed results . So a short swing mechanism is conducive to improve the grinding efficiency, improve the quality of tool edge. Average swing from 0 ~ 50mm, swing speed of 20 to 60 beats / min.
(3) high-precision machine tool holder swivel function and online detection device
Since brittle, wear-resistant PCD material, typically designed to be arc-shaped tip to reduce tool and workpiece relative to the amplitude of vibration. In order to achieve rounded corners, and the machine's precision rotary tool holder should have the functionality and nose radius size and quality on-line detection devices. This can avoid positioning errors caused by multiple setups, while improving processing efficiency can be doubled.
5 PCD, PCBN cutting tool sharpening process
5.1 Sharpening the selection process
An object of the cutting tool sharpening is to obtain cost-effective cutting edge quality, but the quality is good or bad lies in the choice of grinding wheel size. Wheel finer granularity, the smaller the cutting edge chipping and grinding efficiency is lower. This could be based on the cutting edge of precision, purpose (see Table 1) or a failure level (see Table 2), the PCD cutting tool sharpening process is divided into coarse, fine, fine three processing stages. Depending on the circumstances establish a reasonable grinding process can greatly improve the processing efficiency.
Table 1 at the cutting edge of precision, use classification
No - the cutting edge precision - Optional grinding wheel size - Uses
a coarse -0.05mm-230/270 # ~ 320/400 # - roughing
b fine-0.02mm-W20 ~ W40-semi-finishing
c fine-0.005mm-W1 ~ W10-finishing
Table 2 blade failure degree classification (re-grinding tool)
No - Failure degree - Optional grinding wheel size - Remarks
a coarse - cutting edge breakage 0.5mm-230/270 # ~ 320/400 # - or EDM
b fine - cutting edge chipping 0.3mm-W20 ~ W40
c fine - cutting edge wear 0.1mm-W1 ~ W10
Roughing less demanding on the cutting edge, the optional electric processing or grinding. Processing power, high efficiency, suitable for machining complex tools, such as a printed circuit board with a drill, cutting laminate flooring with a milling cutter and so on. When the optional coarse grinding wheel, grinding the contact area, grinding force (300 ~ 400N), can quickly remove excess allowance; fine grained grinding wheel selection processing, the contact area is small sharpening , grinding force low (100 ~ 200N), grinding, less heat, but the material removal rate. This stage is mainly by grinding and polishing, to further improve the quality of the cutting edge. Finishing among the living in both.
5.2 Grinding Process points
(A) better precision spindle, general grinding wheel face runout should be ≤ 0.02mm. Wheel runout is too large, the impact of intermittent grinding wheel cutting edge, easy to make cutting edge chipping occurs, it is difficult to obtain high-precision cutting edges.
(2) grinding wheel should have good dynamic balance. The unbalance wheel vibration will cause the machine to, in turn affect the quality of the cutting tool edge and precision.
(3) grinding wheel should be preferred vitrified diamond grinding wheel. Because vitrified grinding process prone to microcracks that are updated self-sharpening abrasive that steady grinding process, help to improve the accuracy and efficiency of the machined surface; followed by an optional high heat resistance resin bond diamond grinding wheel.
(4) Timely attention to wheel the blade, and the blade Whetstone granularity to the right. PCD cutting tools with diamond grinding wheel, the wheel will be blocked, passivation, high temperatures and rapid wear, resulting in reduced processing speed and chatter, noise, burns generation. Normally select used wheel fine granularity than 1 to No. 2 soft silicon carbide as the blade Whetstone Whetstone.
(5) due to an iron-based alloy diamond easy and chemical diffusion, accelerated wheel wear, and should therefore be avoided as much as possible while grinding metal and PCD.
(6) Be sure to wheel rotation direction from the tool rake face flank rotation. From grinding PCD cutting edge of the force shows that when the tool rake face grinding wheel from turning the flank, its grinding force (tangential and normal force of) acting on the cutting edge inward, that tool by compressive stress, easy to collapse knife; contrary, compared with tensile stress, the cutting edge chipping easily. If for structural reasons must be reversed sharpening tool, then the choice of resin bonded grinding wheel is superior to metal and ceramic bonded grinding wheel.
(7) In order to ensure the quality of the cutting edge while increasing grinding efficiency, the posterior horn of the tool can be divided into large and small rear corner after corner. Coarse-grained grinding wheel with a large rear corner first, because a large contact surface grinding force, grinding efficiency is high; Then fine-grained grinding wheel small rear corner after corner edge of the small width of about 0.1 ~ 0.3mm control , small contact surface grinding good quality.
(8) as far as possible in one clamping the cutting edge of the tool to complete processing.
(9) PCD grinding coolant should preferably water-based grinding fluid. PCD material as high hardness and heat resistance, water-based grinding fluid cooling effect than oil-based grinding fluid, to improve processing efficiency and edge quality. In addition to fully cool the grinding process can not stop to avoid a small amount of grinding fluid or intermittent supply resulting diamond (grinding wheel, tool) for mass consumption (oxidation, graphite) and tool edge breakage.
