Metal drilling

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Depending on the required quality and number of workpieces, holes are drilled according to markings or the workpiece surface. The following basic rules should be observed during the operation:

  • when drilling through holes in workpieces it is necessary to pay attention to the way of their fastening; if the workpiece is fastened on the table, it is necessary to set it on the pad to ensure free exit of the drill after finishing machining;
  • the drill bit should be brought to the workpiece only after turning the spindle so that when it touches the workpiece surface there is little load on it, otherwise the cutting edges of the drill bit could be damaged;
  • Do not stop turning the spindle while the drill is in the hole to be drilled. First you must take the drill out and then stop turning the spindle or stop the machine, otherwise the drill may be damaged;
  • If during drilling you hear grinding, vibrations caused by seizing, skewing or wear of the drill bit, you should immediately remove it from the workpiece and then stop the machine;
  • when drilling deep holes (l5d, where l is hole depth, mm; d is hole diameter, mm) it is necessary to periodically withdraw the drill from the machined hole to remove chips, as well as to lubricate the drill. This significantly reduces the probability of drill breakage and premature blunting;
  • It is advisable to drill a hole more than 25 mm in solid material in two passes (with reaming or countersinking);
  • Drilling should be carried out only in accordance with the modes specified in the process charts or tables of reference books, as well as the recommendations of the master (technologist);
  • when drilling holes in workpieces made of steel or ductile materials it is mandatory to use coolant to protect cutting tools from premature wear and increase cutting conditions.

Drilling along the marking is used in individual and small-scale production, when production of conductors is economically unjustified due to the small number of processed parts. In this case, the driller receives marked workpieces with control circles marked on them and the center of the future hole (Fig. 6.21, а). In some cases, the hole marking is made by the driller.

Drilling on the marking is carried out in two stages: firstly, pre-drilling, and then the final drilling. The pre-drilling is done by hand, drilling a small hole (0,25d). Then turn back the spindle and drill bit, remove the shavings, check the alignment of the circle of the drilled hole with the marked circle.

If the pre-drilled hole is correctly drilled (Fig. 6.21, b), drilling should be continued and finished, and if the hole has gone sideways (Fig. 6.21, c), then make an appropriate correction: cut through with a narrow chisel (cross cutter) two or three grooves 2 from the side of the center where the drill needs to be displaced (Pic. 6.21, г). The grooves guide the drill bit into the designated spot with the core cutter. After correcting the offset, continue drilling all the way through.

A few words about deep drilling

With this short note we would like to start talking about deep hole drilling. The deep drilling operation is one of the most difficult from the point of view of people who do not encounter it on a daily basis, and for some it even causes some fear. We will try to show that with the right choice of tools, equipment, and processing conditions, deep drilling is not as difficult as it seems.

According to the commonly accepted terminology, holes of depth greater than 10xD are considered “deep”, where D is the diameter of the hole. Mention of deep drilling is traditionally associated with the need for specialized deep drilling tools (single-blade cannon drills or ejector drills). However, this is not entirely true. Let’s try to show briefly, without going into design features, what other tools can be used for deep hole machining. The production program of the companies that produce modern high-speed tools (Fette, Guehring, Titex Plus) includes drills of extra long series with steep angle of approach of the spiral of the chip groove. As a rule, these drills are produced in diameter range up to 12 mm with cylindrical shank with possible drilling depths up to 25-30 diameters. Drills of larger diameters are made with a conical shank, for depths up to 10-12 diameters. For chip removal, these drills are used in deep hole drilling cycles with drill out of the hole. In addition to HSSD drills, more recently there have been solid carbide drills that allow processing up to a depth of 12 diameters. Usually they are drills with straight chisel grooves and internal coolant channels. The diameter range (as with all solid carbide drills) is limited to 3 to 20 mm. Such drills can be seen in the program of Fette, Biax, NAM. Another alternative option are drills with inserts. Here we can highlight the construction of drills KSEM by Kennametal Hertel, which allows in the range of 16-32 mm to drill to 10 diameters, as a drill from solid tungsten carbide. Well, and for big diameters (up to 300 mm) systems with replaceable multifaceted inserts and pilot drill bits (like HTS by Kennametal Hertel) are used. Drilling depth with such drills is limited only by technological conditions of processing. There are other options for processing deep holes, but, nevertheless, the main technological technique remains drilling with deep drills. The advantages of this type of processing manifest themselves in high accuracy, optimum straightness and good surface quality. The leaders in production of such drills on European market are companies Botek, Guehering, Tiefbohrtechnik, Sandvik. The main technical and design features of each company are described in detail in their catalogs. This article will outline the most general aspects of such drills. Most of the deep-hole drills used today are structurally of the two groups:

  • for diameters from 1 to 40 mm single-blade drills (single-edged drills) with a carbide core bit soldered to the drill stem with a shank;
  • for diameters from 14 to 250 mm, ejector drills consisting of a head with carbide plates and two tubes that act as a stem, coolant supply and chip drain.

Here are two basic preconditions for using any drill bit for deep hole drilling

  • The machine coolant delivery system must provide enough pressure and coolant flow to remove chips from the hole without the drill being pulled out; the machine spindle must be designed to deliver coolant internally through the tool. Coolant flow and pressure values necessary for normal drill bit performance are given in tables and graphs below. At the same time, a high degree of purification of coolant from impurities and chips is required, since the internal channels of coolant supply in the drills have a fairly small diameter. As a coolant for specialized deep hole drilling machines oil for deep hole drilling is used, while different emulsions are used for universal machines.
  • The machine design and set up must ensure that the orientation and centering of the drill bit is sufficient to guarantee straightness of movement.

The particular characteristics of deep hole drilling operations led to the development of a special machine type for deep hole drilling. These machines provide high pressure coolant supply and high flow through the tool, and are also equipped with a system of guiding sleeves and rests for drill bit guidance. This is the drilling diagram shown in the following illustration. The appearance on the market of machining centers with effective systems of coolant supply through the spindle and tools made it possible to implement drilling of deep holes directly in the cycle of complete machining of the part. The pilot hole serves as the conductor bushings. The schematic of such machining is shown in the figure, and the technology looks like this:

  • making a pilot hole to a depth of typically about 1.5 diameters with the highest possible accuracy. In general, pilot drilling is carried out with a solid carbide drill bit;
  • the tool feed to the pilot hole without turning the spindle, turning the spindle and the coolant on;
  • Continuous drilling with simultaneous removal (flushing out) of chips;
  • After reaching the target depth, the coolant supply is switched off;
  • accelerated drill exit from the hole when the spindle is stationary.

The few diagrams in this article are made to show what we can achieve with the deep hole drills. Of course, if the equipment is in proper condition and, most importantly, if all processing parameters are observed. The graphs shown describe single-sided drills.

The user can expect IT7-IT9 tolerance when using such drills. Sufficiently high accuracy is achieved due to the fact that cutting forces are redistributed on the lateral surfaces of the carbide head (in contrast to twist drills, where the load is transferred to the bands). The lateral surfaces under the influence of this force polish the inner wall of the hole, resulting in very good roughness results. The final roughness is also influenced by the quality of the coolant which acts as a polishing agent. Such drills also show good results for such parameters as straightness of holes and deviation from the axis. The straightness can be negatively affected by inclusions or changes in the material structure (bleaching, sinks, etc.). д.). In terms of deviation from the axis, redistribution of cutting forces again plays a positive role (unbalanced helical drills lead to unbalanced forces and consequently to the drift of the drill from the hole axis). When choosing a particular drill bit type it is obligatory to check whether for the given type and diameter the pressure and flow of coolant provided by the machine is sufficient. Examples of such diagrams (for single-sided drills) are given below. Of course, each manufacturing firm gives refined data based on the design features of its products. When ordering drills it is also necessary to specify correctly the type of shank for fastening the tool. Leading companies produce products both with special shanks for deep hole drills, and with shanks according to DIN1835, DIN6535 and other standards. Correctly resharpened deep-hole drills naturally contribute to a long service life and good results. Some companies offer their own appliances or small machines already adapted specifically for resharpening such drills.

Drilling techniques

A distinction is made between through, blind and incomplete holes (fig. 9.44). Through holes drilled to the full thickness of the component. Blank holes Have a given depth that is less than the thickness of the product in a given location. Incomplete holes do not have a full circle at the base.

1. through; 2. blind; 3. incomplete

Depending on the number of workpieces to be machined, drilling is carried out by marking or by the guideway.

When drilling from the markings (Fig. 9.45, а) Pre-drill the workpiece with axial marks, circle of the future hole, punch the center of the hole to guide the drill bit and the circle. Experienced locksmiths only cross the circle with the axial marks. If necessary, a pilot circle with a diameter that is slightly larger than the future hole diameter is made and then tapped.

а. Hole marking; б. Correcting a misaligned hole

Drilling on the markings is carried out in two stages: firstly, the test drilling, and then the final. Carry out pilot drilling with hand feed to a depth of 1/4 of the drill bit diameter to check if the drill bit is correctly guided. If the contours of the hole are offset in relation to the future hole markings (fig. 9.45, б), The workpiece is fastened firmly and reliably in the reamer, which reduces the risk of the operator being unable to move the center of the hole. Then the hole is drilled again and, having ensured that it is correct, the final drilling is carried out using a mechanical feed.

Drilling in the conductor hole (see “Drilling in the conductor hole” on page 31). Fig. 9.27) are produced in cases where a higher accuracy of the hole is required, as well as when a sufficiently large batch of identical parts. This method is much more productive than drilling on a marking, as there is no need for marking, alignment of the workpiece before drilling. The workpiece is securely and quickly clamped in the cradle, reducing the fatigue of the worker. Availability of permanent installation bases and drill guide sleeves increases the accuracy of machining. Drilling by marking and by conductor is carried out with COTS.

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Drilling blind holes to a predetermined depth is carried out by bushing stop (Fig. 9.46, a), measuring ruler fixed on the machine tool (fig. 9.46, б), or at the limb of the automatic feeder.

Fig. 9.46. Drilling blind holes: а. on the bushing stop; б. According to the machine tool ruler (1. stop; 2. ruler)

The drilling depth is read off from the beginning of the calibrating part of the drill bit (the size of the cutting part is not taken into account). The drill is brought up to contact with the workpiece surface, drilled to the depth of the taper of the cutting part of the drill, and the initial position of the drill on the ruler or limb of the machine is fixed by a pointer. Then the desired drilling depth is added to this value and the drilling. Some drilling machines are fitted with a stop on the measuring ruler (Fig. 9.46, б), which is fixed with a screw. While drilling, the drill bit is lowered to the set depth and the stop reaches the stop and stops with the machine tool spindle.

When drilling blind holes it is necessary to periodically remove the drill bit from the hole, clean the hole from shavings and measure the depth with a caliper.

Drilling incomplete holes is shown in Fig. 9.47, a, b. In this case, a second workpiece or spacer of the same material is applied to the workpiece to be machined, clamped in a vise, and drilled, and then the spacer is discarded.

Fig. 9.47. Hole drilling techniques: a, b. incomplete; в. side; г. in hollow parts; 1. Item; 2. gasket; 3. plug

When drilling lateral holes (Fig. 9.47, в) The drill face must be machined beforehand (e.g. by milling) so that the drill bit is perpendicular to the face.

In through lateral drilling of tube-type products (Fig. 9.47, г) a wooden or metal plug must be hammered into the hole.

Drilling step holes is done in two ways:

  • 1) first drill the hole to the smallest diameter, then drill it out to one or two larger diameters within the depth of each step (Fig. 9.48, а);
  • 2) First use the largest diameter drill bit, and then use drills with smaller diameters for the number of stages (Fig. 9.48, б).

Exact holes are drilled in two passes. The first pass is made with a drill with a diameter of 1m. 3 mm less than dia-

Fig. 9.48. drilling options for step holes

meter hole. Then the hole is drilled out with a drill of the desired diameter.

It is often necessary to drill holes with intersecting axes. When the holes intersect at right angles, first drill a longer hole, then a shorter one. If the holes are not crossed at right angles, after drilling a longer hole, they are plugged and a second hole is drilled.

Deep hole drilling (deep holes are holes 6 to 8 times the diameter of the hole) is carried out with deep drills. The drill is often taken out of the hole to cool it down and remove swarf.

The drilling of holes of large diameters is carried out by reaming, i.e.е. First, the hole is drilled with a drill with a diameter of 1/3 of the nominal size, and then the hole is drilled through. You can use annular drilling with cutter heads (Fig. 9.49), having a hollow body with fixed cutters on it. Circular drilling in the workpiece 2

1. cutters; 2. part; 3. core

How to drill metal products correctly

One of the most important parameters when drilling a hole is the sharpness of the drill bit. If you buy one of the cheapest drills, it may be dull or even a soft metal drill bit that will not give you a couple of holes.

How quickly the drill bit tip will shear and dull depends on the drilling speed, the hardness of the metal, the force applied to the drill bit, and the cooling.

  • When drilling large holes, smaller hole diameters must first be drilled. So the process will be much faster, and the drills will not blunt so quickly.
  • For exact alignment of the hole, use a core bit and punch the center of the hole before drilling.
  • To cool the working part of the drill bit, you need to use machine oil. Simply dip the tip of the drill bit into a container with oil. Repeat this operation from time to time. Soapy water can be used to cool it down (by reducing friction).
  • When drilling deep holes, periodically remove the core bit and remove the shavings.

How to drill sheet metal

When working with sheet metal should not have any special difficulties, even when drilling holes of large diameter. The only thing to do is to put a block of wood under the drill bit to help get the shavings out. When you feel you have almost drilled through a sheet of metal reduce the pressure on the drill bit, this will also help reduce the chance of burrs forming.

How to properly make holes in pipes

The main problem when drilling holes in round tubes, is the difficulty of perpendicular drilling. This means that the hole from which you started drilling does not match the exit hole. To solve this problem, you need to use a drilling machine, or special guides, which you can make yourself or buy ready-made.

drilling, deep, holes, lathe

How to drill aluminum

Anyone who has worked with aluminum parts knows that it is a soft metal. The main problem when drilling aluminum, is the abundant chip wrapping of the drill bit. This causes the drill bit to stop drilling and get stuck in the metal. To avoid this, you need to often take the drill out of the hole and remove shavings.

How to drill stainless steel (stainless steel)

Stainless steel is an alloy steel, which is not easy to drill. In order to make the drilling process comfortable, it is advisable to choose drill bits with a cobalt tip. It is necessary to drill stainless steel at minimum speed, namely 100-200 rpm. Such revolutions give the required cutting speed of stainless steel and good quality. If your tool does not have RPM control, it is worth to press the button periodically for a second or two, which will not let the drill quickly accelerate.

If you want to make a hole of large diameter, you should use drill bits for metal, which allow you to drill only the outer diameter of the hole.

Characteristics of the deep hole drilling process

When deep processing, the basic principles of the manufacturing process are followed.

Initially carry out the selection of rotational speed of the drilling part of the equipment or the maximum possible cutting speed (drill feed).

Take care of ensuring normal crushing of chips, the withdrawal of the contents from the recess completely.

An important nuance at the time of waste dissection is considered to be the safety of the tool cutter. Make sure the drill bit is undamaged in this area, as well as free of burrs and other imperfections. Another key criterion for efficient processing of metal surfaces is the supply of cooling and lubricating fluid according to the following rules.

As the parts are drilled while the cooling and lubricating liquid is supplied with a certain pressure and flow, pumping devices. oil pumps or pumps for pumping viscous substances. are introduced into the system.

The power of the system is selected on the basis of the fluid consumption and the required pressure for the lubricant.

Liquid supply is an indispensable technology item:

drilling, deep, holes, lathe
  • Chips are properly guided out of the working area through the outlet channels.
  • The frictional force between the contacting elements is reduced.
  • Release excessive heat generated by long drilling procedures to protect the drill bit.
  • Additional machining of the recess is performed.

Cylindrical hole machining technology

Hole machining on lathe is made depending on the type of workpiece, required accuracy and surface roughness: by drilling, reaming, countersinking, reaming, reaming.

Holes are divided into through (machined per stroke) and blind (machined to a specific depth). According to shape they can be: a) Profiling; b) Reaming; c) Reaming; d) Reaming smooth, stepped, with grooves (fig. 3.31). Holes whose length exceeds 5 diameters are called deep.

The choice of finish depends on the purpose for which the hole is intended. The designer on the drawing indicates the accuracy of machining and surface roughness in accordance with the service purpose of parts with a hole.

Fig. 3.31. Shapes of cylindrical holes; а. through smooth; 6. through steps; в. Through-hole with groove; d. dull smooth; д. step-deep holes

In table 3.2. Shows the machining accuracy and surface roughness achieved by the various hole machining methods.

Table 3.2. Accuracy and surface roughness achieved by hole machining with various methods

Drilling. the basic technological method of creating holes in a solid material of the workpiece.

Spiral, cannon, shotgun drills are used for twist drillings. By drilling it is possible to obtain holes with accuracy of 11-12th quality and roughness Ja 12,5. 25 microns. Reboring increases the diameter of the previously drilled hole and, under certain conditions, improves the accuracy of the hole by about 1 grade.

Spiral drills are mainly used as cutting tools for drilling and reaming.

Spiral drill (fig. 3.32) is a two-tooth cutting tool consisting of a working part, a neck and a shank. The working part includes the cutting and guide part.

the working section of the drill has two chisel grooves in the helical shape to make it easier for the chips to leave the hole. For the same purpose, the guide part has a small reverse taper (0,03. 0.12 mm for every 100 mm of length). In order to increase the strength of the drill bit, the depth of the chip grooves gradually decreases towards the shank.

The cutting part has two cutting edges, which are connected in the center by a bridge (cross edge). The front face of the tooth is part of the helical surface of the chisel groove and the back face is part of the chisel groove. by the surface of the cone formed by sharpening the drill.

Figure. 3.32. Elements and geometry of twist drill bits

The shanks are made conical (for drills with diameter of 6 mm). 80 mm) according to the dimensions of the standard Morse cones or cylindrical. for drills with small diameters up to 20 mm. Tapered shank ends in a foot. The foot is designed for knocking the drill out of the spindle seat or the adapter sleeve, and the neck is designed for firing the drill from the seat of the spindle. for the exit of the grinding wheel when grinding the shank and the working part.

Drills are made of high-speed steel P6M5 and equipped with BK8 hard alloy. Drill bits equipped with tungsten carbide are designed for drilling cast iron and hard-to-machine steels.

To create favorable cutting conditions, the drill bit teeth are given a wedge shape, which is determined by the main angles: front, sharpening angle and back. The rake angle has the greatest value (20°-30°) due to the helical shape of the chip groove. Rear grinding angle also has variable value to compensate its reduction in work: from 10-15° at the periphery to 20-25° near the axis.

The angle at the apex of the drill has a significant influence on the cutting resistance. As this angle decreases, the total cutting resistance increases, and the feed force acting along the drill axis decreases (tab. 3.3). For general purpose drills, the angle at the apex is within 116-118°.

Table 3.3. Angle value 2. drill diameter, mm; ?/-diameter of the hole in the workpiece, mm.

The elements of cutting conditions for drilling are as follows. Cutting depth I during drilling is half of the drill bit diameter:

Feed rate B during drilling and reaming corresponds to the axial movement of the drill bit per one revolution of the workpiece and is expressed in millimeters per revolution.

Cutting speed g, m/min, for drilling depends on the drill diameter ? and rotation speed of the workpiece п, min 1 :

Values of feed and cutting speed are taken from the reference book depending on specific drilling conditions.

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Spindle speed n, min.1. is determined by formula

The drill feed is most often done by hand on the lathe. When working with mechanical feed for holes 5 to 30 mm in diameter in steel workpieces it can be selected within 0,1. 0,4 mm/rev.

Cutting speed for high-speed drills when processing holes in steel and iron workpieces is selected in the range of 20. 40 m/min, for drill bits equipped with tungsten carbide plates it can be increased by 2-3 times. Drills with smaller diameters take a higher value of cutting speed.

Deep holes Processed with gun drills and shotgun drills. Characteristic feature of their design. one tooth and a large guiding surface.

During deep hole drilling with a drill bit of conventional design, “drift” of the drill bit is inevitable due to the difference in radial forces on the cutting edges, which can lead to “splitting” of the hole (increase in diameter), although the axis of the hole remains straight. In order to prevent “sinking”, for deep hole drilling special single flute drills (so called gun drills) with straight chisel grooves and quadrilateral drills are used.

Description of the presentation on the individual slides:

Education Department of the City of Moscow Western District Educational Board of Education of the City of Moscow Secondary General Education School 23 We study lathe work Drilling Hole Drilling on a lathe TV-6 (TV-7) 7-8 grade Part 5 Teacher of technology SBEE Secondary General Education School 23 Seliverstov Yu.И., honored teacher R.Ф. Moscow 2015

The aims of the lesson: 1.To introduce: 1.1. With the elements and geometry of a drill bit; 1.2. With the methods of installing the drill bit in the tailstock quill; 1.3. With the technology of drilling holes on a screw-cutting lathe. 1.4. Possible defects when drilling holes on a lathe 1.5. Learning about the safety rules of drilling holes on the lathe. 2. To teach: 2.1. Techniques of drilling and reaming holes on a lathe. 3. Nurture: 3.1 Careful attitude to the machine, tools and their contents. 3.2. Willingness to master certain technical knowledge and skills when learning turning. 3.3. Respect and diligence, diligence, self-discipline and sociability. 4. To develop: cognitive activity and technical thinking of students.

DRILLING HOLES ON A CENTRE TURNING MACHINE Drilling work can be carried out on a Swiss-type lathe in the same way as on a boring mill and a wood-turning lathe. The main motion is rotation of the workpiece clamped in the three-jaw self-centering turning chuck, and the feed motion is translational movement of the drill bit by means of the screw mechanism of the tailstock.

A drill is used as a cutting tool. A twist drill bit consists of a core piece, a neck and a shank. The end of the work piece where the two cutting edges are located is called the cutting portion of the drill. The angle between the cutting edges is 2φ (angle at the apex). 118-120⁰ When machining steel and cast iron, the drill bit has two helical quills connected by a bridge. Narrow guide strips are ground on the outside surface of the quills. There are two spiral grooves between the quills: one of the walls of the groove forms the front surface of the drill bit’s cutting wedge.

Drill bits with a cylindrical shank are inserted into a drill chuck, and then the chuck is inserted and secured in the hole of the tailstock quill (a). Drills with a tapered shank are placed in the hole of the tailstock quill (b). If the taper size of the drill shank is smaller than the tapered hole in the quill, an adapter sleeve is used (c).

The drill is positioned strictly in line with the centers. In order to prevent the drill from shifting relative to the axis of the hole, the workpiece is centered at the beginning of drilling with a short, large-diameter spiral drill. Using a bent chisel or a special pilot drill. Prior to drilling, the face of the workpiece is trimmed to bring it perpendicular

To prevent shifting of the drill bit during drilling, a support pin (5) is to be installed in the toolholder and brought close to the drill bit. It supports the drill bit at the beginning of drilling and prevents it from wobbling. as soon as the tips of the cutting edges of the drill bit go deeper into the hole to be drilled, the stop is withdrawn from the drill bit. This support is especially necessary for long drill bits and small diameters. At the beginning the drill bit is fed in very slowly, but when it penetrates the metal to a depth greater than the cutting edge length the feed is increased.

While drilling deep holes, chips accumulate in the drill grooves. Therefore, you should periodically remove the drill bit from the hole and use a brush or hook to clean it when the machine is off. Never use your finger to remove chips. On no account may the drill bit be supported with the hands during drilling. Before the drill comes out of the through hole, the drill feed must be reduced sharply. When the drill comes out of the workpiece, the cut layer of metal unequally loads the cutting edges of the drill, which can cause the drill to twist and break.

If it is necessary to obtain a hole with a diameter greater than 12 mm, it is recommended first to drill the workpiece with a drill bit of a smaller diameter, and then to re-drill the obtained hole to the required size. This makes drilling easier and protects the drill bit from premature wear. Sometimes a characteristic metallic squeal is heard during drilling. It is usually a sign that the hole is skewed or the drill bit is blunt. If this happens stop the feed immediately, take the drill out, stop the machine and change the drill. Do not stop the machine while the drill bit is in the hole. this could cause the drill bit to jam and break.

Possible drilling faults: 1. The diameter of the drilled hole is much larger than the diameter of the drill bit (a). Cause: drills not properly sharpened (cutting edges of unequal length). Resharpen drill bit. 2. Hole axis does not coincide with the workpiece axis (b). Reason. the drill bit is sideways at the beginning of drilling. Resharpen drill bit, center hole precentering with center drill bit or short drill bit. 3. Diameter of the hole is larger than the drill bit’s diameter and the tapered bottom is stepped (c). Cause. unequal length and inclination of cutting edges to the drill bit axis. Resharpen the drill bit. 4.Hole axis does not coincide with the workpiece axis at the end of drilling (d). Cause: drill bit retraction at the beginning of infeeding because there is no center dimple in the workpiece. 5.Diameter of the hole is larger on the edges than in the middle (e). Reason: Drill is not centered because the tailstock housing is pointing toward or away from the machine. Set the tailstock in the center line of the machine.

Roughing out deep holes

In deep hole machining, boring is a secondary finishing operation performed after deep drilling in the workpiece. Shafts, or as a forming operation in parts. Pre-drilled pipes. Counterboreings are carried out on special machines, with special tools and according to various process patterns. Depending on the application, there are three main types of deep boring. Rough boring conforms to hole axis location and straightness requirements. Finishing boring ensures the requirements of the accuracy of diameter dimensions and roughness of the treated surface. Combined boring allows the functions of roughing and finishing to be performed in one working stroke. Rough boring is used when it is impossible to meet the requirements of the location of the hole axis and its straightness during drilling, and if necessary to remove a large amount of allowance left after drilling. Depending on the scheme, a distinction is made between deep compression boring (Fig. 1, a) and deep tensile boring (Fig. 1, б). According to the scheme on compression, reaming starts from the end B of the workpiece 5, located closer to the feed carriage 4. In this case the axial component of cutting force Px creates compression stresses in the stem 3. According to the scheme of tensile reaming starts from the opposite face A of the workpiece 5. The axial component of cutting force Px causes tensile stress in the stem. Both types are used for both roughing and finishing boring. To coordinate and guide the tool at the beginning of boring, usually a conductor bushing 2 is used, which is installed in the guide post 1. In the squeezing arrangement, the conductor bushing 2 is an accessory to an oil reservoir, chip collector or specially designed guide that is housed in the guide post 1. In both arrangements the boring head is guided in the conductor sleeve by its guiding elements. With tensile boring the outside diameter of the stem has to be selected from the diameter of the drilled hole, and not from the diameter of the bored hole as with the compression boring scheme. Consequently the stem has less stiffness. Despite this, the final results for axis location accuracy are better for tensile roughing as the stem works under more favorable conditions and therefore errors towards the end of the process are reduced. Tensile roughing results in less deviation from straightness of the bore axis than the compression turning pattern. However, in practice, tensile boring (especially roughing) causes certain difficulties, in particular when working on machines with fixing the left part of the workpiece in the chuck (pot), in the presence of a bushing. plugs for supplied coolant (see fig. Fig. 2, a, b), etc. At deep boring, as well as at deep drilling, supply of cooling lubricant (Coolant) to the cutting zone of the boring head is obligatory, used as a means for removal of chips formed at cutting. Methods of coolant supply and chip removal during deep boring are different. At external supply of coolant with internal chip outlet (fig. 2, a) coolant is supplied through the oil receiver along the external channel H (in the gap) between the surface of the stem of the tool 2 and the walls of the hole in the workpiece 1. Coolant is drained off together with swarf through the window C in the boring head and then along the internal channel B of the tool stem. As in the workpiece there is already a through hole, this hole has to be closed by a blind plug 4 with the seal 3 pressed tightly to the end of the workpiece. Before switching on the working feed of the tool the cavity D in the workpiece is completely filled with coolant thanks to which conditions for chip evacuation are created that are close to conditions of drilling. External supply of liquid coolant into hole D of the workpiece (fig. 2, b) is conducted through the blind plug 4 against the tool feed. Chips together with cutting oil get into the window C of the boring head and are removed (by internal drain) through the hole of the stem. There should be a seal on the tool body that prevents coolant from entering the gap between the stem and the surface of the machined hole. External supply of coolant through the oil receiver along the external channel H (in a gap) is carried out to the boring head against the tool feed (fig. 2, в). Then through a window in the boring head coolant together with swarf goes to the internal cavity of the head and is flushed out through a hole in the workpiece. Seal 3 is required on the tool body that blocks the passage of coolant into the workpiece hole bypassing the head. Internal supply of coolant through the hole B of the stem to the cutting elements of the boring head through the window C allows an external discharge of chips in the direction of the tool supply through the hole of the workpiece (fig. 2, г). The advantages and disadvantages of these boring methods are determined by the chip evacuation technique applied and the technological equipment used. In schemes with external coolant supply (Fig. 2, a and c) it is necessary to use an oil receiver, which complicates the boring process. With coolant supply through the bore hole (Fig. 2, b) the use of a blind stopper is obligatory, the tool becomes more complicated (sealing is required) and swarf may enter under the guide heads, which is highly undesirable. Boring with coolant supply through the bore hole (internal supply) with external chip removal through the bore hole (fig. 2, d) does not require any complex technological equipment, moreover, chips are taken away through the unworked hole and the possibility of them getting under the tool guides is almost completely eliminated. Thanks to this method is widely used in practice. Tools for deep hole roughing can be divided into two main groups: boring heads with certainty of basing and boring heads without certainty of basing, and in each group for a compressive or tensile working pattern. Naturally, the tools in each group differ in terms of structural design of its individual elements. By design of guiding elements, there are boring heads with rigid, resilient, adjustable and sliding guiding elements. By design of cutting elements there are boring heads with replaceable cutters, with boring blocks, with mechanical attachment of multifaceted carbide plates. Boring heads are noted according to the number of guides, their location on the head body, the structural design and the material used for these guides, etc. A feature of rough boring (as opposed to drilling) is unevenness of the allowance, removed along the circle. Therefore, for roughing, special attention is paid to the development of tool designs that reliably ensure the required accuracy and productivity under the changing cutting forces during the revolution. The periodic unevenness of the forces acting on the tool leads to a certain degree of vibration during cutting, to axis misalignment, etc. Boring heads with a certain basement are the most reliable in roughing the holes with minimal bias and minimal deviations from the straightness of the axis. Their disadvantage is the limited productivity determined by the fact that these tools are basically single bladed and if they are multi-blade tools then work with a division of the width of cut and therefore the feed rate is selected as for single-blade tools. Boring heads for roughing are usually designed for compression work. And only in special cases where high demands are made on the drill hole in terms of axis misalignment and deviation from straightness are the heads made for tensile work. Single-blade heads as tools with defined base are widespread and can be produced for work with external and internal supply of coolant. multi-blade heads are less frequently used and most of them are designed for work with internal supply of coolant. Consider the design of some boring heads used for roughing. Single-blade boring heads with permanent base are used for reaming bores with diameter 50 mm or 50 mm. 250 mm. The head works in compression with internal coolant supply (through the hole in the stem) with coolant output to the cutting elements through window B. Chips are fed on ahead of the head along the bore (see tooling table). Fig. 2, г). Head has replaceable cutting element in the form of cylindrical cutter 5 with soldered-on inserts. The cutter is fixed in the head body and controlled in diameter by the screw placed in the end face of the cutter. Head has double-row guiding elements. The first row. guiding elements without tension, are made in the form of two rigid fixed bars 1, which are interchangeable. The second row. guiding elements with interference, made in the form of three elastic guides 3 of caprolon, under which plates 4 of polyurethane are put in the head groove to increase the elastic properties. The guides are evenly spaced around the circumference. The second row of guiding elements is designed to reduce the possible rotation angle of the head axis in the hole and to reduce vibrations. The overlap should be set at approximately 0.1. 0.15 mm. The head has a shank, on the outer surface of which there are seating journals B and tap threads for connection with the stem. Up to 90 mm diameter, right-angle threads are two threads in heads with a diameter of up to 90 mm and three threads in heads with a larger diameter. On the front end of the head is a hole A, coaxial with the axis of the head and has a threaded section. centering pin is screwed into this hole to control cutter adjustment accuracy to required head diameter. Double-blade head with permanent base has cutting elements in the form of replaceable prismatic cutters 5 with tungsten carbide inserts set in the slots of the head housing 1. Adjustment of the sections by diameter is performed by screws 6, and their fastening is performed by screws 2. Guiding elements with interference fit are made as three rigid stationary guides 4 and one independent limited movable guide 3. Replaceable guides on a steel backing are fastened to the body of the head with screws. The head has a shank with B outer mounting surfaces under the stem. Coolant is brought to the blade through hole B. In the front of the body there is a sleeve with a hole L for the instrument used for setting the cutters to the required diameter. The rails are sanded together with the body. Before grinding, the spring guide is removed from the spring-loaded guide and a measuring spacer is inserted in its place. After grinding the spacers are replaced by the spring. The working tension and spring stiffness are selected so that the spring force to the surface of the hole is 400. 1200 N for bore diameters of 60. 180 mm. Boring heads for deep single hole machining with certainty are designed for boring of deep bores with diameter of 45. 250 mm. Cutting element of the head is made in the form of cassette 4 with a longitudinal key entering into the relative groove on the body 5 of the head. The cassette is fastened in the housing with a screw 7. On it by means of wedge 6 fixed carbide plate I rhombic shape, which has two cutting edges. Adjustment of the head to the diameter is made by changing the guides 2 and adjusting the cassette extension. the three carbide guides 2 are pressed against the machined hole surface by the radial forces of cutting and friction, thus ensuring the tool’s lateral stability. Three plastic (polyamide) guides 3 serve to damp the vibrations of the boring head. Boring heads with single cutter with certainty of basing from Sandvik Coromant are possible to use for reaming after drilling with ejector drills as they use ejector system for chip removal during cutting (fig. 6, а). The heads present several designs, two of which (fig.6, b) the polyhedral inserts used in the heads are fixed in special cassettes with a device for adjustment of the outreach of the cutting insert by diameter. These heads have two hard tungsten carbide and one textolite guide and are available in diameters from 43.01 to 183.9 mm. Boring heads with a diameter range of 20 to 43 mm have a screw base in the housing slot. Clamping of the insert (adjustment of departure) is carried out by a special screw located in the center of the head. Boring of cylindrical holes by double-sided cutting heads with cutting thickness division is performed by heads without basic orientation. They have special boring blocks with diametrically symmetrically located cutting blades. To reliably base the heads, their guiding elements are restricted in their mobility. In one design of such a head as a cutting element is used rigidly fixed in the body 2 boring block 1. The unit is installed in the housing in a special end slot, secured from displacement along the slot by a cut pin 4 and fixed by screws 3. Guides in the form of pads 10 with screws 9 fixed on them with hard alloy wear plates 8 enter the windows of head housing 2 and with their bevels rest on inclined surfaces of bushing 7. The sleeve is moved along the axis by means of a slotted spring 6 compressed by nuts 5, which determine the tension of the guides. The excess of the guideways over the diameter of the cutting blades is usually taken as 0,4. 0.6 mm. The constant contact between the guideways and the bushing is maintained by leaf springs 11. To prevent the tool-holders from jamming in the housing windows, their face surfaces are made on a cylindrical surface. It is indicated that the head has high vibration resistance and productivity. It should be noted that heads with limited movable guideways can also be executed with a single cutter, as heads with a certain basicization (see “The head with a limited movable guideway”). Fig. 8, а). There are quite a few designed boring heads without fixed boring head boring heads, and all of them differ in design of mechanisms for extending the guides. There are designs with two rows of guides and with two springs acting on them (fig. 8, b) etc. Boring head with independent guideway separation has a simpler design than the spring type. The head has as a resilient element polyurethane plates 4, which are installed in the slots in the body 1 under each guide 2. The guides are held back from falling out of the slot by screws 3. The tension is adjusted by selecting the thickness of the shims 5. The cutter block 6 is set in the face groove of the body and secured from moving along the groove with the key 7 and screws 8. Coolant supply to blades through stem hole and head through A holes. Guides are ground to head diameter directly in the housing or on a special mandrel, for which purpose steel plates with thickness less than polyurethane ones are installed to the size equal to the half of diametrical interference before grinding. This interference is taken within a range of 0.4. 1,4 mm per diameter. The head is highly resistant to vibrations and has high efficiency (7). 9 m/h and more); when working with it, no surface rim is formed, and the drift does not exceed 0.3 mm/rpm. м. Analysis of designs and results of boring heads of double-sided cutting with thickness division with limited movable guides allows to note their advantages. Higher productivity in comparison with single-blade as well as multiple-blade heads with shear width division, as they work with shear thickness division; higher vibration resistance, which allows getting a bored hole without cutting. The disadvantages are: complexity of design, higher cost in comparison with single-blade heads; difficult maintenance and adjustment; greater axis deviation in comparison with heads with definite basic setting. Controlled boring heads are used for the purpose of ensuring minimal deviation from straightness of the machined hole or for boring of holes to achieve specified (defined by the designer) deviations from straightness of the axis at some part. The process of controlled boring consists in the fact that the position of the top of the cutter (which forms the surface of the hole) is continuously controlled relative to the geometric axis of the machined hole, defined by any method, and the position of this top is corrected if necessary. One of the variants of boring heads for controlled boring is the one in which the role of the reference (geometrical) axis of the machined hole is performed by the laser beam. Its working principle (Fig.10) may be as follows. The geometrical axis of the boring hole is defined by the laser 1. The spot of its beam hits the four quadrant photodiode located on the axis of the boring head. In case of irregular illumination by the beam of the photodiode sectors, the electrical signals are emitted in the adders 8 and 9, which are amplified by the amplifiers 10 and 11. The amplified signals are fed into the electrohydrovalves 12 and 13, which in accordance with the signal supply working fluid under pressure into the drive cylinders of the head guides until it coincides with the center of the spot light. Naturally, at realization of the considered scheme it is necessary to take into account that the laser beam at free passage in aperture of the part can be distorted as a stream of a coolant with a chip, and air disturbance from a hot chip that will lead to big errors of rotation of a geometrical axis set by a beam. Therefore, in a boring head realizing the principle of controlled boring, the photodiode was placed inside the head and the laser beam passed inside the boring bar.

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