Today, a fairly large number of milling cutters of various sizes are produced. They can be classified according to functional and design qualities.
Sharpening of end mills is carried out using special devices for such tools. In some cases, sharpening can be done manually.
The cutters have a relatively large length and uneven teeth for cutting. During the sharpening process, you will need to take care of the movement of the base of the wheel along the edge. IN in this case It will be necessary to sharpen shaped cutters that have a backed corner. You should know that sharpening is quite difficult. To preserve the profile of the structure and facilitate the sharpening process, the backed teeth will need to be sharpened exclusively along the front base. Sharp teeth, which have a straight or curved shape, must be sharpened exclusively along the rear base. Slotting and parting cutters can be sharpened along the front and back bases of the teeth.
Geometry of cutter teeth
Geometry of the cutter teeth: a - sharpened tooth, b - backed tooth.
To sharpen correctly, you will need to know the geometry of the cutter teeth. The design of the teeth distinguishes between cutters with backed and sharp teeth. In the latter, the part of the rear base, which is adjacent to the cutting edge, is a plane. Teeth with sharp ends are in most cases sharpened along the back base, but they can also be sharpened along the front base of the tooth.
The backed teeth that come with the end mills have a back base that follows an Archimedes spiral. It is quite difficult to process a shaped base technologically, so you can sharpen cutters with backed teeth exclusively on the front base.
Regardless of the number of teeth in the cutter, each of them can be considered as a separate tooth, which is characterized by typical parameters for the tooth - the angles of the front and back, the size of the sharpening area, and the angle of inclination of the teeth.
The sharpening platform is an element of the rear base of the tooth, which is subjected to grinding during the sharpening process along the rear base. The maximum wear of the teeth will occur along this base. Its size affects the magnitude of the friction force between the tool and the workpiece, so the base must be maintained in a specific range.
Scheme for sharpening prefabricated cutters on a universal sharpening machine.
The main rake angle is the angle between the tangent to the front base and the base of the axis. It can be measured in a plane that will pass through a given point perpendicular to the main cutting edge.
The main relief angle is the angle between the tangent to the rear base at a given point of the main cutting edge and the tangent to the plane of rotation of this point. This angle helps reduce friction between the tool and the workpiece.
Using the auxiliary relief angle, you can characterize the large gap between the milled base and the body of the tooth. It is necessary to sharpen a tool at an additional angle when there is a specific amount of damage to the tool and an increase in the sharpening area. The purpose of this action is to reduce friction between the tooth and the workpiece being milled. You should be aware that not all tools of this type have this angle.
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How to sharpen end mills for woodworking?
The shape of the teeth can be straight or helical. The inclination of the tool teeth can be characterized as the angle between the developed edge of the screw type and the axial part of the tool.
The values of the tooth angles will depend on the type of tool, the grade of alloy and steel from which it is made, as well as the type of material for which the tool is intended for milling.
During milling viscous materials the main rake angle should be selected in the range of 15-20° or more. Carbide tools for milling steel will have an angle of 0° or -5°. The clearance angle varies over a wide range.
Items you will need:
- Diamond beam.
- Table.
- Water or soap and water.
- Solvent.
- Abrasive paper.
- Hardwood plank or steel strip.
- Abrasive wheel.
It is possible to sharpen shaped end mills without special sharpening devices, along the front base, with a diamond bar of small thickness. The beam must be installed on the extreme part of the table. If the tool has a large recess, then the tool must be secured along the table.
Heat resistance table various materials, °C.
When sharpening, the beam will need to be wetted clean water or a solution with soap. After sharpening, the tool will need to be washed and dried.
As the front base is sharpened, the edge will become sharper, but the diameter of the tool will not decrease much.
If a bearing is installed on the tool, then the first step is to dismantle it and then sharpen it. An attempt to save time in this case may result in a damaged bearing and a non-functional cutter.
It is imperative to clean the cutter from excess resin from the trees. It is best to use a solvent for this.
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In the process of sharpening tools, you will need to use bars of different grain sizes. The grain size will depend on the thickness of the layer of material being removed and the required cleanliness of the base. Before sharpening, you will need to make sure that the beam has the appropriate shape.
Figure 1. Shapes of grinding wheels.
If the cutter teeth are made of relatively soft material, instead of timber, you can use abrasive paper, which is glued to level base. As a base, you can use a hardwood plank or a steel strip.
End mills for milling wood are sharpened to special device with a low speed of rotation of the circle. In this case, you will need to use a suitable abrasive wheel.
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Sharpening wheels
Sharpening of modular cutters can be done with wheels made of white or ordinary electrocorundum, diamond and others. For example, using electrocorundum wheels, you can perform high-quality sharpening of cutters for working with metal and wood, which are made from tool steel or other steel of standard performance. CBN wheels make it possible to sharpen steel structures high performance. Silicon carbide and diamond wheels are used for sharpening cutters made of hard metals.
By increasing the temperature, the hardness of such a device decreases. A temperature of 1000°C can reduce the hardness by almost 2 times. At a temperature of 1300°C, this indicator will decrease by about 6 times.
Figure 2. Sharpening the end mill: a - the main cutting edge, b - the auxiliary cutting edge, c - installation diagram of the cutter for sharpening the teeth of the auxiliary cutting edge.
Using water to reduce the temperature in most cases leads to rust on the workpieces and corners of the machine. To eliminate corrosion, you need to add soap and some electrolytes to the water, which can form films for protection. When sanding, a solution with soap or soda is almost always used. If fine grinding is performed, a low-concentration emulsion should be used.
To increase the quality of grinding with an abrasive wheel and reduce significant damage, it is recommended to select the maximum grain size that can provide the required cleanliness class for the base of the cutter used.
The peripheral speed of the wheel when sharpening hard metal teeth should be approximately 15-18 m/s. For example, when using a wheel with a diameter of 12.5 cm, the engine rotation speed should be approximately 1600-2700 rpm. If you need to sharpen more brittle materials, the actions need to be performed at a lower speed. When using hard metal tools, harsh conditions result in high stresses and cracks, and in some cases, damage to the cutting edges. In this case, wheel wear will increase.
The shape of the wheel for sharpening the back angle of teeth on a cylindrical base should be cup or disc-shaped. To sharpen the front corner, you need to use a disc-shaped or flat-shaped wheel.
Existing shapes of grinding wheels can be seen in (Fig. 1).
A milling cutter is a tool used to process various products. Milling cutters of various types are used, which make it possible to change the external and internal surfaces with the required accuracy. To achieve high productivity, the cutter must be of high quality - be sharply sharpened. Sharpening of ends, wood, plastic, glass is carried out using special machines and equipment.
Tool sharpening
Sharpening is carried out to restore cutting ability, with operations performed contour-wise and separately.
Cutters received for sharpening are usually pre-ground on a cylindrical surface using a cylindrical grinding machine to eliminate damage, followed by further sharpening of the back or front of the teeth.
End mills with pointed teeth are sharpened along the back surface with a special disk- or cup-shaped wheel. To do this, the circle is installed with respect to the axis at an angle of 89°, which makes it possible to achieve the required contact between the contacting surfaces.
When sharpening the back surfaces of end mills, 2 main methods are used:
- polyelement;
- contour.
When using the multi-element method, the cutting edges are sharpened separately. First, the main surfaces of all teeth are sharpened, then the auxiliary and transitional ones.
With the contour method, sharpening is performed sequentially on each tooth in one operation. A single-turn sharpening method is also used, when the cutting edges are processed in one operation. All teeth are sharpened in one revolution and the allowance is removed using a grinding operation.
Types of Tools Used
On industrial enterprises apply Various types tool:
- Cylindrical - for processing workpieces using machines equipped with a horizontal spindle.
- Face - for milling workpieces on machines with a vertical spindle.
- End - for driving ledges, recesses, contours (curvilinear). Used on installations for vertical milling.
- Disc - for driving grooves and grooves on horizontal machines.
- Keyed – for making grooves on machines with a vertical spindle.
- Angular – for milling planes (inclined), grooves, bevels.
- Shaped – when processing shaped surfaces.
To process workpieces, equipment is used that is designed for the following work:
- for metal;
- on wood.
Milling cutters with appropriate equipment are usually produced as sets with mounting dimensions for the fastening part different diameters. In order for the cutter to be used for a long period, it must always be sharpened, and when carrying out a working operation it is necessary temperature regime, preventing overheating, which reduces their strength characteristics.
Using hob sharpening equipment
When processing workpieces, hobs are most often used.
The characteristics of hob cutters are strictly regulated by GOST 9324-60 and are produced:
- whole;
- prefabricated (welded, plug-in).
Prefabricated hobs (for modules from 10 to 16) are used with insert combs, which are made of high-speed cast steel or forged.
Hobs (for modules 18 to 30) are manufactured by welding and mounting carbon steel teeth on a base.
When using hobs for cutting cylindrical gear wheels the working parts of the tooth wear unevenly.
To increase the service life of hob cutters, a height correction method is proposed by changing the shape of the spatial curve characterizing the working process. The method of axial displacement of the tool is also used, which increases the speed of operations with an increase in the service life of hob cutters.
The process of sharpening backed hob cutters is performed along the front surface, and sharpened ones along the back surface of the tooth. After finishing the sharpening process, measurements are taken:
- front surface profile;
- circumferential pitch;
- compliance of chip flutes.
Types of equipment used for fixing tools
The equipment used to fasten the tool is divided into 2 types:
- nozzle;
- end
The end equipment is attached using a collet and a chuck, and the attachment equipment is used by installing it on a spindle using a special mandrel.
To fasten the tool, 2 types of mandrels are produced:
- center;
- terminal
Center mandrels are produced with a conical shank, which has dimensions corresponding to the hole in the spindle, and are produced in 2 types 7:24 and Morse taper.
When using this type of mandrel, it is allowed to install several cutting tools secured with special rings.
When using a cylindrical end mill, a chuck with a collet is required. Typically, the equipment includes 7-11 collets allowing you to select required size for secure fixation.
Equipment for fixing the workpiece
To carry out the milling process, it is necessary to fix the workpiece, for which the following are used:
- rotary tables;
- vice;
- clamps.
Round rotary tables are used for milling operations on workpieces with a curved surface.
This type of table has a wide range of offsets:
- rotation;
- changing the angle of the table plane;
- Possibility of processing products in a vertical position.
Clamps or clamps allow you to fix products using special elements, which in turn are attached to the table using bolts and nuts. To fix small-sized workpieces, a simple vice with a rotating mechanism is used.
Using Accessories
To fix cylindrical parts, a three-jaw chuck and special centers are used, which, with the help of clamps and steady rests, carry out fixation, as well as the use of dividing heads. These devices are used to process parts at a given angle during rotation.
The dividing head consists of the following elements:
- housings;
- rotary pads;
- spindle.
A three-jaw chuck is attached to the spindle, designed to fix the workpiece; the other end rests against the headstock. The block can rotate and lock at the required angle. When processing a long workpiece, steady rests are used for fixation.
How to sharpen a milling cutter for metal 11.09.2017 21:16
The industry produces a huge number of cutters for metal, and sharpening them is often a problem for those who work with them. Design features tool and a large number of teeth causes difficulties during sharpening.
How to sharpen a cutter for metal correctly?
As a rule, sharpening of cutters for metal is carried out using special equipment. Improper sharpening leads to breakage of teeth and failure of the cutter. Correct sharpening milling cutters allows you to use the tool much longer and reduce wear. To do this, you also need to carefully monitor the cutting surface of the cutter teeth.
To sharpen cutters for metal, special machines and special equipment are used. Therefore, it is better to entrust this matter to professionals.
The peculiarity of sharpening cutters is their relatively large length and curvilinearity. cutting edges their teeth. When sharpening, it is necessary to ensure that the surface of the wheel moves exactly along the edge.
What types of cutters are there?
- Cylindrical cutters are used for processing workpieces using machines equipped with a horizontal spindle.
- End mills - for milling workpieces on machines with a vertical spindle.
- End mills - for driving ledges, recesses, contours (curvilinear). Used on installations for vertical milling.
- Disc cutters - for driving grooves and grooves on horizontal machines.
- Key cutters- for making grooves on machines with a vertical spindle.
- Angle cutters - for milling planes (inclined), grooves, bevels.
- Shaped cutters - when processing shaped surfaces.
In the metalworking industry, the use of cutters as cutting tool has a wide distribution. Almost all parts of various engines, both electric and internal combustion, are manufactured using milling. Lots of details for household appliances, machines and fixtures are also processed using milling cutters.
Milling cutter sharpening operations maintain the technical and physical characteristics of parts, thereby extending their working life. There are many approaches to performing such activities, the choice among which is determined by the nature of operation and the design of the element. The wear rate of a cutter largely depends on its design, based on which the technician selects maintenance regimes.
For example, the selection of a method for regrinding high-speed parts is based on the wear of the front surface. On the other hand, flank sharpening of cutters is more suitable for shaped elements. Therefore, it is important to take into account as many operational factors as possible, which will allow you to make the right choice of processing technology.
Types of cutters
Such elements are widely used in the processing of parts on copying, moulding, tenoning, milling and other machines. As a rule, this is woodworking equipment, although there are also parts for working with metal blanks. Milling cutters vary in size, shape and purpose.
In general, there are two categories of elements - end and mounted. The first ones are distinguished by the presence of a shank, which is fixed in a special spindle niche. 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 differs more high level quality, not to mention ease of handling of parts for the operator. Attachment elements can be composite, solid or prefabricated.
A feature of this group is the ability to form a cutting tool from several milling parts. It is also worth noting the category of end mills, which can be prefabricated or solid. Elements are also divided according to the quality of the backed processing. Thus, sharpening of cutters with backed surfaces is carried out along the front edge in order to maintain the basic angular parameters.
Milling cutter maintenance
Despite the use of high-strength alloys in the manufacture of cutters, long periods of operation lead to abrasion and deformation of the edges. Over time, worn-out elements are disposed of, but before the working life expires, the master can restore the characteristics of the part with the help of measures Maintenance. It is important to consider that sharpening cutters allows not only to give them the same geometry, which ensures 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. Manufacturers of cutters indicate in the markings technical and operational values that are limiting for a specific element, and after they are overcome, the cutting edges cannot be restored.
sharpening process
To perform sharpening, special milling machines, equipped with spindles with an average rotation speed of up to 24,000 rpm. Before starting work on them, the master balances the cutters. It can be carried out in two ways - dynamic and static. In the first case, the procedure is performed on a special machine, which provides not only balancing of the force, but also the moment acting on the cutter during rotation. This technique is especially relevant for cases when sharpening a cutter for metal.
Balancing machines using the static method 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. Direct sharpening is carried out on special high-precision equipment.
The machines are available in different configurations, providing both manual and automatic control. Common to all units of this type is the presence on the guides work surface. This design solution makes it possible to achieve high accuracy of element movement, usually with an error of 0.005 mm.
equipment requirements
To ensure high-quality sharpening of cutters, you should not only use equipment suitable for this task, but also prepare it correctly. First of all, equipment spindles must have sufficient vibration resistance, rotate freely and have minimal runout. Next, the feed mechanism must operate stably in all directions provided for by the design without delays and with minimal gaps. Great importance have elevation angle settings - this parameter should also have high accuracy. For example, sharpening hob cutter, which is performed on automatic machines, involves setting both a certain lifting angle and the pitch of the helical groove. If grinding wheels are used, it is important to ensure a reliable fit of the replaceable washers and spindles, due to which the working element is accurately seated.
End mill machining
Processing of end elements is most often done manually using universal sharpening equipment. Typically, this technique is used to update the performance of a helical tooth tool. In many ways, sharpening end mills resembles similar updating of cylindrical cutters using a cup wheel. This applies to operations that involve installing the end mill in the center of the seat. 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. In this case, the treatment is suitable for both the back and front surfaces.
Sharpening end mills
Mills made of and some elements equipped with carbide plates are sharpened in assembled form. The main flank surface of the end mill is sharpened with a grinding cup wheel. Before performing the same operation on the plane of the auxiliary rear side, the element is first installed so that its cutting edge is in a horizontal position. After this, the cutter axis rotates horizontally and at the same time tilts in vertical plane. Unlike the scheme for sharpening end mills, in this case the position of the workpiece is changed several times. Work with the front surface of the tooth can be carried out with the end part of a grinding disc wheel or with a disk wheel from the peripheral side.
Working with disc cutters
On the rear main surface, the processing of the disk elements is carried out using a cup circle. The auxiliary back surface is made by analogy with end mills, that is, by turning the cutting edges horizontally. At the same time, the peculiarities of processing the end teeth of such a tool are noted. In this case, sharpening of disk cutters is performed along the front surface so that the teeth being processed are directed upward. The cutter itself at this moment should occupy a vertical position. The vertical inclination angle of the element axis must correspond to the position of the main cutting edge.
Features of sharpening wood cutters
End shaped parts are sharpened without special devices usually using a thin diamond stone. This item or lies on the edge of the work table, or, if the cutter has a deep recess, is fixed additional tool. The cutter is inserted along a fixed block. During processing, the block is periodically moistened with water. When the procedure is completed, the master thoroughly washes and dries the product. As the front surfaces grind down, 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 the operation can be continued. The fact is that sharpening a wood cutter together with a ruined bearing can lead to damage to the element. It is also necessary to clean the tool from any remaining wood resins using a special solvent.
Features of sharpening cutters for metal
Such elements are less common and at the same time require less effort in the preparation process. Processing is done using grinding wheels suitable grain size. The materials may be different, in particular, it is common to use parts made of ordinary or white electrocorundum. If you plan to sharpen end mills for metal made from tool steel, then it is recommended to choose electrocorundum discs. For products with more high performance It is advisable to use CBN wheels. 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 negatively affect the structure of the wheel.
Processing of backed cutters
Relief elements are used in cases where it is necessary to increase the stability of the cutting part and reduce surface roughness. The teeth of the backed cutter are processed along the front surface in such a way that after regrinding in the radial section, the profile of the functional edge retains its original parameters until the part is fully used. Sharpening of such cutters is also carried out in compliance with a strictly established rake angle. When processing sharpened elements, it is necessary to maintain a constant sharpening angle.
Finishing of cutters
In essence, this is an operation designed to correct the result obtained during the main sharpening process. As a rule, finishing is carried out in order to ensure optimal roughness indicators or in cases where it is necessary to adjust the sharpening angle of a cutter with working edges. Abrasive and diamond finishing techniques are quite common. In the first case, it is assumed that fine-grained silicon carbide wheels will be used, and in the second case, diamond blades on a bakelite bond. Both techniques allow you to handle, among other things, carbide tools.
Sharpening quality control
During the inspection process, the master evaluates the geometric parameters 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 to control parameters directly at the workplace. For example, if you sharpened an end mill according to wood material, then the specialist can measure the angles along the working edges. For this purpose, a protractor is used, the scale of which is presented in the shape of an arc. Special ones are also used to evaluate other parameters; again, most of them are focused on checking the geometric data of the cutter.
Conclusion
Need in machining cutting tool is preserved even in centuries high technology. The only change in this regard has been with the milling equipment control systems. Appeared automatic devices, allowing you to optimize the process of handling workpieces. However, cutters, bits and other processing metal elements still done with abrasives. Of course there is also alternative technologies, which make it possible to restore the geometry of parts, but there is no talk of their widespread use yet. 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, many enterprises still give preference traditional methods sharpening.
