Cutter sharpening operations maintain the technical and physical characteristics of parts, thereby extending their working life. There are many approaches to the implementation of such activities, the choice among which is determined by the nature of operation and the design of the element. The intensity of cutter wear largely depends on its design, based on which the master selects maintenance modes.
For example, the selection of the method of regrinding high-speed parts is guided by the wear of the front surface. On the other hand, sharpening cutters on the back surface is more suitable for shaped elements. Therefore, it is important to take into account as many operational factors as possible in order to make the right choice of processing technique.
Varieties of cutters
Such elements are widely used in the processing of parts on copying, molding and tenoning, milling and other machines. As a rule, this is woodworking equipment, although there are also parts for working withmetal blanks. Cutters differ in size, shape and purpose.
In general, there are two categories of elements - end and mounted. The former are distinguished by the presence of a shank, which is fixed in a special niche of the spindle. Products of the second group have a central hole, which allows them to be mounted on the working spindle and securely fixed. Accordingly, such sharpening of cutters is distinguished by a higher level of quality, not to mention the ease of handling parts for the operator. Push-on elements can be composite, solid and prefabricated.
A feature of this group is the possibility of forming a cutting tool from several milling parts. It is also worth noting the category of end mills, which can be prefabricated and solid. The elements are also divided according to the quality of the backed processing. So, sharpening of cutters with relief surfaces is carried out along the front edge in order to maintain the basic angular indicators.
Cutter maintenance
Despite the use of high-strength alloys in the manufacture of milling cutters, a long time of operation leads to abrasion and deformation of the edges. Over time, worn parts are disposed of, but before the expiration of the working life, the master can restore the characteristics of the part through maintenance activities. It is important to bear in mind that sharpening cutters allows not only to endow them with the same geometry, which ensures high-quality work. This procedure also increases the life of the element, reducing tool consumption. But this does not mean that any cutter can berestored in this way.
Technologists do not recommend bringing the tool to a state of complete wear. Manufacturers of cutters indicate in the markings technical and operational values that are limiting for a particular element, and after overcoming them, the cutting edges cannot be restored.
Technical support for the sharpening process
To perform sharpening, special milling machines are used, equipped with spindles with an average speed of up to 24,000 rpm. Before starting work on them, the master balances the cutters. It can be done in two ways - dynamic and static. In the first case, the procedure is performed on a special machine, which not only balances the force, but also the moment acting on the cutter during rotation. This technique is especially relevant for cases where the cutter is sharpened for metal.
Static balancing machines only involves balancing the force acting on the cutter. The element is fixed in the frame, after which it is balanced through a device consisting of two horizontal guide knives. Sharpening is performed on special high-precision equipment.
Machines are available in different configurations, involving both manual and automatic control. Common to all units of this type is the presence of linear bearings on the guides of the working surface. This design solution allows to achieve high accuracy of movementelement, usually with an error of 0.005mm.
Hardware requirements
To ensure high-quality sharpening of cutters, you should not only use the equipment suitable for this task, but also properly prepare it. First of all, the equipment spindles must have sufficient vibration resistance, rotate freely and have minimal runout. Further, the feed mechanism must work stably in all directions provided for by the design without delays and with minimal gaps. The elevation angle settings are of great importance - this parameter should also have high accuracy. For example, sharpening a worm cutter, which is performed on automatic machines, involves setting both a certain angle of elevation and a helical groove pitch. If grinding wheels are used, then it is important to ensure a secure fit of the interchangeable washers and spindles, due to which the working element is precisely fitted.
Machining end mills
The processing of end elements is most often done manually on universal grinding equipment. Typically, this technique is used to update the performance of a helical tool. In many ways, sharpening end mills is similar to updating cylindrical cutters with a cup wheel. This applies to operations that require the end mill to be placed in the center of the seat. Also, similar sharpening is performed on semi-automatic models. In this case, end mills can be serviceddiameter from 14 to 50 mm. The processing is suitable for both the back and the front surface.
Sharpening end mills
Milling cutters made of high-speed steel, as well as some elements equipped with carbide inserts, are sharpened assembled. The main back surface of the face mill is sharpened with a grinding cup wheel. Before performing the same operation on the plane of the secondary rear side, the element is first set in such a way that its cutting edge is in a horizontal position. After that, the axis of the cutter rotates horizontally and at the same time tilts in a vertical plane. In contrast to the scheme, according to which end mills are sharpened, in this case, the position of the workpiece is changed several times. The front surface of the tooth can be worked with the end part of the grinding pad wheel or with the disk wheel from the peripheral side.
Working with disc cutters
On the rear main surface, the processing of disk elements is carried out with a cup wheel. The auxiliary back surface is made by analogy with end mills, that is, by turning the cutting edges horizontally. At the same time, the features of processing the end teeth of such a tool are noted. In this case, the grinding of disk cutters is carried out along the front surface so that the processed teeth are directed upwards. The cutter itself at this moment should occupy a vertical position. Angle of inclination of the element axis verticallymust match the position of the main cutting edge.
Features of sharpening cutters for wood
End shaped parts are sharpened without special tools, usually with a thin diamond stone. This element either lies on the edge of the desktop, or, if the cutter has a deep recess, it is fixed with an additional tool. The cutter is inserted along a fixed bar. During processing, the bar is periodically wetted with water. When the procedure is completed, the master thoroughly washes and dries the product. As the front surfaces are ground down, the edge becomes sharper, but the diameter of the tool will decrease. If the cutter has a guide bearing, it must be removed first and then the operation can be continued. The fact is that sharpening a cutter on a tree along with a ruined bearing can lead to damage to the element. It is also necessary to clean the tool from the remnants of wood resins with a special solvent.
Features of sharpening cutters for metal
These elements are less common and at the same time require less effort in the preparation process. Processing is carried out using grinding wheels of suitable grit size. In this case, the materials can be different, in particular, the use of diamond wheels, as well as parts made of ordinary or white electrocorundum, is common. If you plan to sharpen end mills for metal, made from tool steel, then it is recommended to choose electrocorundum discs. For products with highercharacteristics, it is desirable to use elbor circles. The most productive and efficient sharpening parts are made of silicon carbide. They are used to service cutters made of hard alloys. Before work, the abrasive is cooled, as high temperature loads during the operation can adversely affect the structure of the circle.
Processing of relief cutters
Reinforced elements are used in cases where it is required to increase the stability of the cutting part and reduce surface roughness. The teeth of a relief cutter are processed along the front surface in such a way that after regrinding in a radial section, the profile of the functional edge retains its original parameters until the part is fully exploited. Sharpening of such cutters is also carried out in compliance with a strictly established rake angle. In the case of sharpened elements, a constant pointing angle must be observed.
Cutters finishing
In essence, this is an operation designed to correct the result obtained during the main sharpening process. As a rule, finishing is performed in order to ensure optimal roughness or in cases where it is necessary to correct the sharpening angle of the cutter with working edges. The techniques of abrasive and diamond finishing are quite common. In the first case, the use of fine-grained silicon carbide wheels is assumed, and in the second case, diamond discs on a bakelite bond are supposed to be used. Both techniques make it possible to handle, among other things, carbideinstrument.
Sharpening quality control
During the verification process, the master evaluates the geometric parameters of the cutting surfaces for compliance with technical requirements. In particular, the runout of the cutter is determined, as well as the degree of roughness of the finished or sharpened planes. Auxiliary devices can be used in the control of parameters directly at the workplace. For example, if the end mill was sharpened on wood material, then the specialist can measure the angles along the working edges. For this, a goniometer is used, in which the scale is presented in the form of an arc. Special measuring tools are also used to evaluate other parameters, again, most of them are focused on checking the geometric data of the cutter.
Conclusion
The need for machining cutting tools persists even in the age of high technology. The only change in this regard has been with the milling equipment control systems. Automatic devices have appeared to optimize the handling of workpieces. However, sharpening of drills, cutters, bits and other processing metal elements is still carried out using abrasives. Of course, there are alternative technologies that allow you to restore the geometry of parts, but so far there is no need to talk about their wide distribution. This applies to laser technologies, hydrodynamic machines, as well as installations that have a thermal effect. At this stage of their development, for economic reasons, manyenterprises still prefer traditional sharpening methods.
