since the process of pulling the chips are formed as a rule in very difficult conditions, so the durability of the engine is influenced by the size and shape of the grooves for chip removal. Longitudinal section of the groove should be of such size that the groove could easily accommodate all of the resulting chips. If chip does not fit in the groove, it is pressed, which can lead to broken teeth and even to break the broach. The geometric parameters of the flute is determined by the length and thickness of the shear layer when pulling. Furthermore, the grooves should not be overly weaken the cross section of the broach.
characteristics of the material significantly affect the shear chips and form. When cutting ductile metals it is usually in spiral curls roller, which is placed in the active or working part of the grooves, and the processing of brittle materials, cast iron, bronze and other chip fracture is cut by separate elements, filling the entire space of the groove, not including the working volume. Based on these features currently use the following profiles of grooves:
— Dvokrevetna shape provides good chip formation in dense cushion, economical filling of the grooves with a chip and its removal in the processing of plastic materials, even with large thickness of the slice (up to 0.4 mm).
— Odnaleziona form with a flat back of the tooth is easy to manufacture, but the shaving it is wedged, so use a profile broaches, having a relatively small climbs on the tooth when machining steels, and also at broaches and other cutting schemes in the processing of materials such as cast iron.
— Dvokrevetna special shape with the protrusions of the grooves ensures good chip evacuation when machining with high cutting speeds.
-. Durationa an elongated shape with a straight section at the bottom of the grooves applied in the processing of very long parts. Cushions formed here one after another are placed in the groove of the broach.
— odnaleziona elongated form with a flat back is easy to manufacture, well proven platform used in the processing of long parts of a brittle metal.
Step roughing teeth and other geometrical parameters of the chip grooves of the broach are selected based on the conditions of the normal process of filling chips in the groove of the broach. Cutting chips when machining ductile materials rolls up into a flat spiral and placed in the active part of the groove, the groove depth and pitch are calculated from the values of fill factor, the value of which is determined from the ratio of areas or volumes of the active part of a groove to area or volume stratum.
the Value of the fill factor is usually set empirically. The value of the coefficient depends on the properties of the material, thickness of cut, size and shape of the groove . Profile broaches, when the cut chips is obtained stiffener from stroiarsenal previous tooth, it prevents the clotting of the chips in the roller, the fill factor is 25% more than for group h-frame where it changes from 2.5 to 3.3. In addition, in the processing of steels with increasing slice thickness k-factor for relevant h-frame increases, and for the group decreases. For cast iron, bronze and other brittle metals it affects slightly the value of k varies from 1.8 to 2.5.
in determining the pitch of the broach, in addition to the recommendations related to the selection of the size and shape of the grooves, note the following requirements.
1. Geometrical parameters of cutting elements of the tooth needs to provide the maximum resistance of the pull.
2. The tooth should have the maximum amount of regrinding.
3. The tooth must be strong enough not to collapse under the influence of the bending tangential cutting forces.
the Geometric parameters of the teeth of broaches. The magnitude of rake angle y = 5-25° is set depending on properties of the processed material, also material in the pullback, although currently the majority of broaches photomosaics of high-speed steels P9, P12, P18, R6M5 and other brands.
the Increase in rake angle from 5 to 15° when pulling steels increases the resistance high speed broaches, according CTZ, 20-25%, and when the values rise on the tooth more than 0.05 mm reduces the cutting forces. The corner also affects the slope of the bonded cylinders. Rear corner of the inner teeth of broaches are accepted regardless of the properties of the hauled material, Here the determining factor is the need to preserve their working size when perekachivanie teeth.
the Presence of ribbons with a zero clearance angle on the teeth of the broach has a significant effect on increasing the friction of the tooth on the treated surface and increase the cutting forces. Therefore, it is recommended that the cutting teeth are sharpened to the tip and to facilitate the process of sharpening it is recommended to leave a chamfer of a width not exceeding 0,02—0,03 mm On the control teeth, the amount of chamfer should be no more than 0.2 mm.
external broaches, which are installed on a specific size can easily be adjusted to increase the resistance of the rear corners on the cutting teeth can be increased to b—10 degrees.
cutting Diagrams when pulling
the Design of the working end of the broach and its performance depend on the size of the shear layers of metal, and to prioritize removing various sections of the processed profile, i.e. taken from a single or group of cutting schemes.
currently, when pulling are two types of single scheme of cutting this profile, and the generator of the group (progressive) cutting diagrams.
universal profile cutting diagrams all the teeth-like profile cap in detail and are cut by thin parallel layers of metal by a height of a subsequent tooth but the previous.
Generator cutting scheme provides for the formation of predetermined contour extending surface gradual transition from blades simple shapes to complex. Cutting the basic allowance is usually made teeth with rectilinear or in the form of a circle arc profile, which greatly simplifies the manufacture of broaches. A simple profile of the individual teeth of broaches allows you to change the thickness of the slice to teeth with short blades have more lift, causing the length of the broach can be reduced. In addition, simplifies the sharpening of broach and increases the strength of individual sections of the blade. Desired profile on the product is formed by the auxiliary cutting blades, and the final cleaning of the surface is made fine teeth, with the profile of the machined surface. Thus, the finishing of the gauge and the teeth of broaches are executed as if profile cutting. Generator cutting scheme are square and regular sliianie internal drive, as well as the usual flat and profiled external drive.
the Disadvantage of generating second operation is often reduced vitality of their unfavourable geometry of the corners of the teeth, and in some cases give a lower accuracy of the machined part profile. Generator drive find application mainly in the processing of shaped surfaces when the application of group broaches unprofitable.
universal group schemes of cutting. Group cutting scheme is characterized in that the layers of metal around the profile of the cut is not every tooth, and group or section 2-5 of the teeth. The first (Welt) teeth sections are cut in the metal groove, and the last (zachistki) tooth cut off the remaining tabs. Truecristian here is achieved through the relief fillets, chamfers, flats and other structural elements of the adopted option scheme the group cutting, so there is no need of making special stroiarsenal grooves as required at bench top profile cutting diagrams. The use of broaches group schemes cutting reduces the number of cutting teeth and the length of the broach as a whole due to a sharp increase in the thickness of the cutting layer section of teeth.
In the processing of holes of relatively small diameters, and also when machining holes of great length, when due to the lack of traction of the machine or the strength of pulling the magnitude of the rise per section is limited, it is better to apply the multifaceted broach cutting diagrams. Roughing teeth of these broaches are also made of sections. Education of individual sections of the cutting blades is made with flat satyavani that PA Welt the teeth of each section are staggered. The presence of less deep relief instead of flat fillets with the same length of the cutting sections of the tooth allows reducing the complexity of manufacture of broaches as the formation of flats can be made not only grinding, but also more efficient pre-milling with transverse flow. In addition, the final grinding of the flats due to the small allowance reduced burn marks and blades increases the resistance of the broaches. When machining slotted surfaces of various shapes pulling is the best process. The most wide application have the spline broach group cutting diagrams, and Vice versa, spline broach generating schemes are very rare. This is due to the fact. that generator spline broaches are small (up to 0.15 mm) rise on each tooth and the teeth cut chips across the width of the slot. However, the processing because of the small climbs on the tooth is usually a set of broaches. In addition, the lack of support back angle causes increased wear of the corners of the teeth receiving surface of a low cleanliness class.
In the processing of slotted holes have proven themselves broach made on the various options for a group cutting diagrams — the presence of two teeth in the section. The first, or slit, of the tooth, the length of the main blade which is more than half the width of the slot, cut the main part of the allowance. Cutting areas created by relief chamfers, fillets or flat. The second (zachistki) tooth cuts the metal with the two sides just at the corners, i.e. at narrow sections with a width of 0.5—2 mm and are formed completely .slots in width. For protection from cutting shavings zachistil tooth across the width of the slot, its diameter is typically 0.04 mm smaller than the diameter Welt of the tooth. In addition, the corners of the slit teeth have a favorable geometry. Besides not cutting across the width of the slot the chip has no friction on the sides of the slots and scrolls freely in the groove durational form. Also facilitated the withdrawal of the narrow shavings cut by the corners of the cleanup of the tooth, having a very small lateral chamfer (to 0.6—0.8 mm). Therefore, it is possible to significantly increase the thickness of the cutting layer of each tooth, resulting in a reduced length of pull.
Despite some similarity in the constructive design of the cutting elements of the teeth and the nature of the shear layer, the foregoing options group schemes spline broaches it is advisable to apply the following guidelines.
Some of the options group schemes cutting (alternating cut and trapezoidal) are also widely used in the processing of the planes and open the outer surfaces. Due to the fact that the outer pulling is done most often when removing large allowances for the crust, reducing the length of the set of broaches due to the choice of the rational scheme becomes of particular interest. Scheme variable cutting should be used only for those broaches, which should pereuchivatsya on the front surface, as when sharpening on the back surface decreases the depth of the filets and a few of regrinding requires recovery. Broach, a certain size can be easily secured, it is advisable reface as the front and rear surfaces.
Broach of the trapezoidal cutting diagrams usually consists of two sections (parts) that are installed on a common tool plate. In each section the rise of s> = 0,l and 1.0 mm is carried out on each tooth. The teeth on the two sections have the same height and only the last tooth of the second section is underestimated by 0.02—0.04 mm in comparison with the last tooth of the first section of the broach. The first section, which is like a short splined broach, cut to remove the stock narrow trapezoidal grooves, and the second, with straight or circular blades, are cut the remaining protrusions of the metal to form a plane or cylindrical surface.
In connection with the big climbs on the tooth length of each section does not exceed 250 mm. Durability of this pullback are much higher than of profile broaches. This is facilitated by the increased angle at the vertex and a positive rear corners; lateral blades of trapezoidal teeth, which are formed by grinding and sharpening trapezoidal slots on the back surface of the passage when the raised rear end of the broach PA 1 to 1.5 mm. Broach trapezoidal cutting scheme is very simple to manufacture, allows a large amount of regrinding, however, it can be used with large margins, and work in black.
materials: Gigalo N. I., Kiselev V. V. design and manufacture of cutting tools.