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 when 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 the relatively large length and curvilinearity of the cutting edges of 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.
A cutter is a type of round rotating cutter. Its cross section always contains a circle, and the shape itself can be any, including very complex ones. There are grooves (of varying depths) or denticles along the circumference. They process the material during the rotation of the cutter. – the process is complex and painstaking. It is important that not only the specialist has a certain level of skill, but also that the sharpening tool meets the highest requirements. Otherwise, chips, cracks or unsharpened areas will remain on the cutter after processing, which will directly affect the further performance of milling work.
Varieties
Incisors are the most different types– end, end, disk, slotted, cylindrical, groove. And these are not all varieties. They are also divided according to their purpose and are angular, shaped, keyed, for T-shaped grooves. Another division is based on the type of surface being processed:
- for metal;
- on wood;
- on plastic;
- on glass;
- and others.
Sharpening cutters for metal complex due to the large length of the cutting surface. Such work is only possible with the use of special tools. In some cases, you have to grind by hand, but this requires a lot of experience. Otherwise, all previous work will go down the drain. The grooves (teeth) will show nicks, gouges, chips and cracks. The part will have to be ground again, which invariably reduces its size.
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 relatively great length and uneven cutting teeth. During the sharpening process, you will need to take care of the movement of the base of the wheel along the edge. In this case, you will need 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. Target of this action is to reduce friction between the tooth and the milled workpiece. 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 reamed edge 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.
When 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.
- Plank from hard rocks wood 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-functioning 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 a flat 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, by 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.
Circle shape for sharpening the back angle of the teeth on the base cylindrical should be cup or plate-shaped. To sharpen the front corner, you need to use a disc-shaped or flat-shaped wheel.
Existing forms of grinding wheels can be seen in (Fig. 1).
A cutter can work productively only if correct operation. If the work is carried out under correctly assigned milling conditions, the cutter can process a large number of workpieces before it becomes noticeably dull. However, if you continue to work with a noticeably dull cutter, the cutting force will increase sharply, which will cause an increase in friction, rapid further dulling and even breakage of the cutter teeth.
Sharpening a normally dull cutter requires relatively little time and slightly reduces the size of the tooth. Sharpening a very dull cutter is a long, labor-intensive operation; you have to remove a fairly large layer of metal, so the cutter does not need to be made too dull.
It is especially necessary to monitor the condition of the cutting edges and timely sharpening of expensive cutters made of high-speed steel and equipped with carbide plates.
Sharpening cylindrical point cutters
Cylindrical cutters with pointed teeth are sharpened along the back surface of the tooth with a cup circle (Fig. 332), while maintaining the specified clearance angle.
When sharpening, the cutter is placed on a mandrel installed in the centers of the sharpening machine. The axis of the cup wheel is set at an angle of 1 - 2° to the axis of the cutter, so that the circle touches the cutter being sharpened on only one side (Fig. 332, c).
If the axes of the cup wheel and the cutter being sharpened are located in the same horizontal plane (Fig. 332, a), then the rear angle α at the cutter tooth will not work. To form a back angle, the cup circle is positioned below the axis of the cutter being sharpened by an amount H(Fig. 332, b), which is determined from a right triangle with side and angle α:
Angle α should be selected according to the table. 35.
The position of the cutter tooth during sharpening is fixed with a special stop (Fig. 332) in the form of an ordinary strip made of spring steel. The stop that supports the tooth being sharpened must be installed very close to the cutting edge. It also serves as a guide when sharpening cutters with helical teeth.
When sharpening the back surface of cylindrical cutters with disc wheels, a concave chamfer is obtained on the tooth, which weakens the tooth blade and accelerates their wear. When sharpened, cup wheels produce a flat chamfer (ribbon), which ensures greater durability of the cutters; For this reason, sharpening cutters with disc wheels is not recommended.
Sharpening end mills
Sharpening main cutting edge The teeth of end mills are made along the rear surface, similar to sharpening cylindrical cutters with pointed teeth (Fig. 333, a).
At sharpening the auxiliary cutting edge tooth (Fig. 333, b), the cutter is first installed so that its auxiliary cutting edge occupies a horizontal position. Then the cutter axis is rotated in the horizontal plane by the amount of the auxiliary angle in the plan φ 1 and at the same time tilted in vertical plane to the front clearance angle α 1. Sharpening of the front surface on the auxiliary cutting edge is carried out by the side surface of the disc wheel. The cutter is installed so that the auxiliary cutting edge is facing upward, and the cutter axis is tilted in the vertical plane by the amount of the rake angle of the auxiliary cutting edge.
Sharpening end mills
main cutting edge end mills (Fig. 334) are produced similarly cylindrical cutters the end surface of the cup wheel when installing the end mill in the centers.
Back surface sharpening auxiliary cutting edge It is produced similarly to face milling cutters using a cup wheel. The cutter is secured with a conical shank in the chuck socket.
Sharpening disc cutters
Back surface sharpening cylindrical edge Disc cutters are produced similarly to cylindrical cutters using a cup wheel.
Sharpening the back surface of the end teeth is carried out similarly to sharpening the teeth of the auxiliary cutting edge of end mills. The front surface of the end teeth is sharpened in the same way as end mills. The teeth to be sharpened are directed upward, and the axis of the cutter occupies the position:
a) vertical - when the cutter has simple teeth,
b) inclined - when the cutter has multi-directional teeth, and the angle of inclination of the cutter axis in the vertical plane is equal to the angle ω of inclination of the cylindrical cutting edge.
Sharpening cutters with backed teeth
The teeth of backed cutters are sharpened along the front surface. In Fig. 335, and a diagram of the installation for sharpening a tooth with a rake angle γ equal to zero (radial front surface) is given, and in Fig. 335, b - with a rake angle γ greater than zero. Magnitude N 1 shift grinding wheel from the center of the cutter is determined by the formula:
The amount of layer removed when sharpening should be the same for all teeth to avoid runout of the cutter. If a smaller layer is removed from one tooth than the others, it will turn out to be longer, will remove chips of a larger cross-section and will become dull sooner. The cutters are sharpened along the front surface using a disc wheel.
When sharpening, you must ensure that the front surface is radial, as shown in Fig. 336, a (tooth 3
). If the front surface has an undercut (tooth 1
) or, conversely, a negative rake angle (tooth 2
), the tooth profile will be distorted and will cut an irregular contour into the workpiece. The position of the cutter tooth during sharpening is fixed by a stop, which should be adjacent to the back surface of the tooth being sharpened.
So that after sharpening the cutting edges have minimal runout, it is recommended to sharpen using a copier that has the same number of teeth as the cutter being sharpened (Fig. 336, b).
Sharpening of prefabricated cutters (milling heads)
The cutter blade has larger number sharpening elements. In addition to the rear corners, it is necessary to sharpen: the main corners of the corner edge in plan φ and the transition edge φ 0, the auxiliary corner in plan φ 1 and the section of the transition edge f 0 . To ensure sharpening of each angle in the plan, the cutter takes a position corresponding to this angle (Fig. 337). Sharpening can be done on special sharpening or universal sharpening machines.
When sharpening on special machines milling cutter 1 inserted into the head using its own shank or a mounted mandrel 2 in a horizontal position (Fig. 338). Head 2 can rotate about a vertical axis. The cutter can be rotated around its axis using a handwheel 3 and is fixed in the desired position using a stop. After sharpening one tooth, the transition is made to the next by rotating the cutter around its axis.
In Fig. 339 shows the positions when sharpening a cutter on a special sharpening machine. First, the ends of the plates or knives are compared (I), then the plates are aligned along the cylindrical edges (II). To form back angles, the head with the grinding wheel is tilted and fixed in this position (III); to obtain plan angles, the head with the cutter is rotated about a vertical axis (IV, V, VI). The labor intensity of such sharpening is high and ranges from 3 to 12 hours, depending on the degree of dullness (amount of removal), the number of teeth and the diameter of the cutter.
It should be noted that the wear of the grinding wheel during sharpening is not compensated by the machine mechanism. Therefore, from sharpening one element of the first tooth to sharpening the same element of the last tooth, a certain wear of the grinding wheel accumulates. To eliminate runout of tooth elements that occurs during wear of the grinding wheel, it is necessary to introduce an additional finishing pass, which increases the complexity of the operation.
On a universal sharpening machine the cutter is sharpened in the centers (see Fig. 337). Due to the fact that the mounting holes, i.e., the mounting bases of the cutter, are not used during this installation, the error in the coaxial sharpening of the cutter cutters increases.
Since prefabricated cutters are the main tool for high-speed cutting methods, the labor intensity of sharpening cutters could be a serious obstacle to the introduction of high-speed milling. Therefore, in the process of mastering high-speed milling, the sharpening process was restructured in order to reduce its labor intensity. For this purpose, a method was developed, tested and implemented for sharpening prefabricated cutters with dismantled cutters and plates and their subsequent installation using a template.
Before sharpening, insert knives are removed from the body and usually sharpened as a set. In Fig. 340 shows a special rotary device for this purpose, which sharply reduces the labor intensity of sharpening. The device is installed in the centers of a universal sharpening machine. After sharpening one element, the device with a fixed set of teeth is turned to a given angle and begins sharpening the other element.
After sharpening is completed, the cutters are installed in the head body using various kinds templates (Fig. 341, a - d). Checking the collected milling head The runout should be checked using an indicator template (Fig. 341, e).
Finishing of carbide cutters
When sharpening with a grinding wheel, the carbide plate is heated unevenly, as a result of which tiny cracks may appear on its surface. Cracks increase during the cutting process and can cause tooth chipping during operation.
One of the purposes of finishing is to remove the defective layer with cracks. The second task of finishing is to increase the cleanliness of the surface of the cutting edge, which is necessary to reduce friction and tooth wear, as well as (increase the cleanliness of the machined surface. The third task of finishing is to eliminate blockages on the surface of the cutter teeth and give them a more correct geometry.
The finishing of cutting surfaces is carried out on special finishing machines with cast iron discs or manually with gentle pressure from a cast iron whetstone. Best results finishing is obtained at a speed of finishing disk in the range of 1.0-1.5 m/sec. For finishing, boron carbide paste with a grain size of 170 - 230 is used.
When finishing manually, it is necessary to observe correct position the whetstone in relation to the cutting edge and the correct movement of the whetstone. First, the front and rear surfaces are finished, then finishing (edging) chamfers are formed: for this, the plane of the whetstone is placed at an angle of 45° to the front surface, and several passes are made along the cutting edge with the whetstone with gentle pressure. It takes 2-3 seconds to form the edge chamfer. for each knife.
Boron carbide is a strong abrasive. Using a cast iron whetstone with boron carbide paste, you can remove wear holes on the teeth without removing the cutter from the machine, which is very important for high-speed milling of small workpieces with short cutting periods.
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We sharpen:
- incisors
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Proper sharpening of a tool reduces its consumption and accordingly increases its service life. Therefore, it is necessary to carefully monitor the condition of the cutting edges and sharpen the tool in a timely manner, avoiding excessive wear and especially breakage.
Sharpening and manufacturing of hobs
The production complex of the Spetsstanmash plant offers a full range of services for the manufacture and repair of metal parts and structures, including: production and sharpening of cutters for metal, wood, cast iron, aluminum, graphite or plastic.
The milling cutter is an important tool in industry and workshops. It is a part of different shapes, with distinctive feature sharp teeth. Its main function is mechanical processing of prepared material.
The operating principle of milling is the translational rotational movement of the cutter teeth.
Depending on the type of tool used, the result is:
- small grooves or grooves when using end mills;
- milling large surfaces;
- milling baguettes, window frames, gears, etc. using spiral cutters,
- cutting using a disc cutter (plinth, paneling, lining, wall beams, etc.).
An important characteristic of a cutter is the material it is made of, in particular the cutting part. These can be teeth made of high-speed steel, mineral-ceramic, metal-ceramic or diamond.
Diamond cutters are considered the most durable due to their natural physical characteristics. But, they are the most expensive. All other materials become dull after some time during use, especially if used incorrectly. Purchasing new tools is expensive, but our skilled craftsmen and high-precision modern equipment allow quality to perform this type of repair, such as sharpening knives for cutters of any geometry:
- sharpening hob cutters
- sharpening of disc cutters
- core cutters and other types.
Professional work on sharpening cutters increases the durability of the part and significantly reduces the consumption of cutting teeth.
Sharpening hob cutters: from 600 rub. / PC. (depending on wear)
Minimum sharpening time: from 10 working days
Minimum order amount: 3500 rub.
* The exact cost can be found using the form or by phone
