Mill sharpening operations support the technical and physical characteristics of parts, thereby extending their working life. There are many approaches to the implementation of such events, the choice among which is determined by the nature of operation and the design of the element. The wear rate of the cutter 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 oriented towards the wear of the front surface. On the other hand, sharpening cutters on the rear surface is more suitable for shaped elements. Therefore, it is important to consider as many operational factors as possible that will 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 with metal workpieces. Cutters differ in size, shape and purpose.
In general, there are two categories of elements - end and mounted. The first are characterized by the presence of a shank, which is fixed in a special spindle niche. The products of the second group have a central hole that allows them to be mounted on the working spindle and securely fixed. Accordingly, such sharpening of mills has a higher level of quality, not to mention the ease of handling parts for the operator. Mounted elements can be composite, integral 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 integral. Elements are also divided according to the quality of the execution of the backed processing. So, sharpening mills with backed surfaces is performed along the front face in order to maintain basic angular indicators.
Milling Maintenance
Despite the use of high-strength alloys in the manufacture of mills, a long operating time leads to abrasion, as well as deformation of the faces. Over time, the worn out elements are disposed of, but before the expiration of the working resource, the master can restore the characteristics of the part using maintenance measures. It is important to consider that sharpening cutters allows not only to endow them with the previous geometry, which ensures high-quality work. This procedure also increases the durability of the element, reducing tool consumption. But this does not mean that any cutter can be restored in this way.
Technologists do not recommend bringing the tool to a state of complete wear. In the markers manufacturers indicate 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
For milling, special milling machines are used, equipped with spindles with an average rotation speed of up to 24,000 rpm. Before starting work on them, the master balances the milling cutters. It can be implemented in two ways - dynamic and static. In the first case, the procedure is performed on a special machine, which provides not only balancing the force, but also the moment acting on the mill during rotation. This technique is especially relevant for cases when sharpening a milling cutter for metal.
Static balancing machines only require 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 carried out directly on special high-precision equipment.
Machines are available in various 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 structural solution allows to achieve high accuracy of movement of the element, as a rule, with an error of 0.005 mm.
equipment requirements
To ensure high-quality sharpening of mills, you should not only use the equipment suitable for this task, but also prepare it correctly. First of all, equipment spindles should have sufficient vibration resistance, rotate freely and have minimal runout indicators. Further, the feed mechanism should work stably in all directions provided by the design without delays and with minimal gaps. Of great importance are the settings of the angle of elevation - this parameter should also have high accuracy. For example, sharpening a worm cutter, which is performed on automatic machines, involves the installation of a certain angle of elevation and the pitch of the helical groove. If grinding wheels are used, it is important to ensure a reliable fit of interchangeable washers and spindles, due to which an exact fit of the working element is made.
End Mill Processing
The processing of the end elements is most often done manually on universal grinding equipment. Typically, this technique updates the performance of a helical tooth tool. In many ways, the sharpening of end mills resembles a similar updating of cylindrical mills through a cup circle. This applies to operations that involve the installation of an end mill in the center of the footprint. Also, similar sharpening is performed on semi-automatic models. In this case, end mills with a diameter of 14 to 50 mm can be serviced. Moreover, the treatment is suitable for both the rear and front surfaces.
End Mill Sharpening
Mills made of high speed steel, as well as some elements equipped with carbide inserts, are grinded in assembled form. The main rear surface of the face mill is sharpened by a grinding cup wheel. Before performing the same operation on the plane of the auxiliary rear side, the element is first mounted so 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 the vertical plane. In contrast to the scheme according to which the end mills are sharpened, in this case, the position of the workpiece is changed several times. Work with the front surface of the tooth can be carried out by the end part of the grinding dish wheel or by the disk wheel from the peripheral side.
Work with disk cutters
On the rear main surface, the processing of disk elements is carried out in a cup circle. The auxiliary rear surface is made by analogy with end mills, that is, by horizontally turning the cutting edges. In this case, features of the machining of the front teeth of such a tool are noted. In this case, the grinding of disk cutters is performed on the front surface so that the teeth being machined are directed upward. The mill itself at this moment should occupy a vertical position. The vertical angle of the axis of the element must correspond to the position of the main cutting edge.
Features sharpening milling cutters on wood
The end fittings are sharpened without special tools, usually with a thin diamond bar. This element either lies on the edge of the desktop, or, if the cutter has a deep notch, is fixed with an additional tool. The input of the cutter is made on 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 grind, the edge becomes sharper, but the diameter of the tool decreases. If the cutter has a guide bearing, it must first be removed and then continue with the operation. The fact is that sharpening a mill on a tree together with a ruined bearing can lead to damage to the element. It is also necessary to clean the tool from the residues of wood resins using a special solvent.
Features of sharpening milling for metal
Such elements are less common and at the same time require less effort in the preparation process. Processing is carried out using suitable grinding wheels. The materials may be different, in particular, the use of diamond wheels, as well as parts made of ordinary or white electrocorundum, is common. If it is planned to sharpen end mills for metal made of tool steel, it is recommended to choose electrocorundum disks. For products with higher characteristics, it is advisable 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, since high temperature loads during the operation can adversely affect the structure of the circle.
Backing Milling
Backed elements are used in those cases when it is required to increase the stability of the cutting part and reduce the surface roughness. The teeth of the backed milling 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 used. Sharpening of such mills is also carried out in compliance with a strictly established rake angle. In the case of sharpened elements, a constant sharpening angle must be observed.
Milling cutters
In essence, this is an operation designed to correct the result obtained during the main sharpening. As a rule, fine-tuning is carried out in order to ensure optimal roughness indices or in those cases when it is necessary to adjust the angle of sharpening of the mill with working faces. Abrasive and diamond finishing techniques are quite common. In the first case, it is proposed to use fine-grained circles made of silicon carbide, and in the second case, diamond disks with a bakelite bond. Both techniques allow you to handle, among other things, carbide tools.
Sharpening quality control
During the verification process, the master evaluates the geometric characteristics 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 brought or sharpened planes. Auxiliary devices can be used directly in the workplace to control parameters. For example, if the end mill was sharpened on wood material, then a specialist can measure the angles along the working faces. 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 remains even in the age of high technology. The only change in this regard has occurred with milling equipment control systems. Automatic devices have appeared to optimize the handling of workpieces. However, the sharpening of drills, milling 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 we can’t talk about their wide distribution. This applies to laser technology, hydrodynamic machines, as well as installations that have a thermal effect. At this stage of their development, for economic reasons, many enterprises still prefer traditional sharpening methods.