Practical exercises refer to instruction books.
Yantai Nanshan college machinery engineering training center
Metalworking teaching and research section
Training lathe basic operation
First, the purpose of training:
1. Understand the safety operation procedures of ordinary lathes.
2. Master the basic operation and steps of ordinary lathe.
3. Relevant requirements for operators
4. Master the basic operating skills of turning.
5. Cultivate good professional ethics
2. Training content:
1. security technology
2. Familiar with the structure and function of ordinary lathe.
3. Familiar with the basic operation of ordinary lathe.
(1) Start and stop of lathe.
(2) Lathe speed, feed rate, feed direction and smooth screw conversion.
③ Manual feed control of lathe.
3. Training equipment:
C6 16- 1D lathe 18 sets.
4. Training steps:
(a) familiar with the basic concept of lathe work and its processing scope.
Turning is a cutting method to change the shape and size of the blank on the lathe and process it into the required parts by using the rotary motion of the workpiece and the motion of the tool. Among them, the rotation of the workpiece is the main movement, and the movement of the cutter is the feed movement (Figure 1- 1).
Fig. 1- 1 Lathe is mainly used to process the surface of the revolving body (fig. 1-2). The tolerance grade of machining dimension is IT 1 1 ~ IT6, and the surface roughness Ra value is 12.5 ~ 0.8 micron ... There are many kinds of lathes, including horizontal lathes.
Bed is the most widely used.
Figure 1-2 Typical surfaces that can be machined by ordinary lathes
A) excircle b) end face c) conical surface d) slotting and cutting e) cutting inner groove f) drilling center hole.
G) drilling h) drilling I) reaming j) turning forming surface k) turning external thread l) knurling.
(2) Understand the model and structure of horizontal lathe.
Ⅰ. Model of machine tool
C 6 1 32
Main parameter code (110 of the maximum turning diameter, i.e. 320mm)
Machine tool type code (general lathe type)
Machine tool group code (common lathe group)
Machine tool category code (lathe category)
C 6 16
The main parameters are110, that is, the dimension from the lathe spindle axis to the guide rail surface is 160mm,
(Maximum diameter of turning workpiece is 320mm).
Group (common lathe)
Category (Lathe)
Ⅱ. Structure of Horizontal Lathe
1. Horizontal lathe model
Horizontal lathe is represented by C6 1×××, where c is the machine tool classification number, which means lathe machine tool; 6 1 is the system code, indicating the level. Others indicate the relevant parameters and improvement numbers of the lathe.
2. The name and purpose of each part of the horizontal lathe
The appearance of C6 132 common lathe is shown in figure 1-3.
Figure 1-3 C6 132 Ordinary Lathe
1- headbox; 2- Feed box; 3- gearbox; 4- Front bed foot; 5- sliding box; 6- tool rest; 7- tailstock; 8 lead screw; 9- naked strip; 10- bed; 1 1- rear bed foot; 12- intermediate tool rest; 13- square tool rest; 14- turntable; 15- small tool rest; 16- big tool rest
1. The headstock, also known as the headstock, includes the spindle and the transmission mechanism. Variable speed means that the spindle can get 12 different rotational speeds (45 ~ 1980 r/min) by changing the position of the handle outside the headstock. The spindle is a hollow structure and can pass through a long rod. The maximum diameter of the spindle hole through which the bar can pass is 29 mm ... The right end of the spindle has external threads for connecting chucks, dials and other accessories. The inner surface of the right end of the spindle is a Morse No.5 taper hole, into which the taper sleeve and the tip can be inserted. When the center is used to install the shaft workpiece together with the center in the tailstock, the maximum distance between the two centers is 750 mm ... Another important function of the headstock is to transfer the motion to the feed box and change the feed direction.
2. The feed box, also known as the feed box, is a speed-changing mechanism of feed movement. It is fixed on the front side of the bed at the lower part of the headstock. By changing the position of the handle outside the feed box, the motion transmitted by the spindle in the spindle box can be converted into a polished rod or a screw rod output by the feed box, and different rotational speeds can be obtained, so as to change the feed rate or turn threads with different pitches. Its longitudinal feed is 0.06 ~ 0.83 mm/revolution; The transverse feed speed is 0.04-0.78 mm/revolution; Rotatable 17 metric thread (pitch 0.5~9mm) and 32 inch thread (2 ~ 38 threads per inch).
3. The gear box is installed in the inner cavity of the front foot of the lathe, and the gear transmission shaft in the gear box is directly driven by the motor through the coupling. There are two long handles outside the gearbox, namely, the double sliding gear and the three sliding gear that move the transmission shaft, which can obtain six kinds of rotation speeds and transmit them to the front of the car through the belt.
4. The drag box, also called the drag box, is the control mechanism of the feed movement. It drives the turning tool to feed through the rotation of the polished rod or the lead screw and the opening and closing nut. There are three layers of skateboards on the trunk. When the polished rod is connected, the bed saddle can drive the middle slide plate, the small slide plate and the tool rest to move longitudinally along the guide rail of the bed. The middle slide plate can drive the small slide plate and the tool rest to move laterally along the guide rail on the saddle. Therefore, the tool holder can move vertically or horizontally. When the lead screw is opened and the opening and closing nut is closed, the thread can rotate. There is an interlocking mechanism in the carriage, so that the polished rod and the lead screw cannot be used at the same time.
5. The tool rest is used to clamp the turning tool and can move vertically, horizontally and obliquely. The tool rest is a multi-layer structure, which consists of the following parts. (see figure 1-4)
(1) The bed saddle is firmly connected with the carriage and can move longitudinally along the guide rail of the bed.
(2) The sliding plate is installed on the transverse guide rail on the top surface of the bed saddle and can move transversely.
(3) The turntable is fixed on the middle sliding plate. After loosening the fastening nut, you can rotate the turntable to make it form the required angle with the guide rail of the lathe bed, and then tighten the nut to process the conical surface.
(4) The small slide plate is installed in the dovetail groove on the turntable, which can make short-distance feeding movement.
5] Square tool rest It is fixed on a small slide plate and can clamp four turning tools at the same time. Loosen the locking handle, you can turn the square tool rest and change the required turning tool to the working position.
6. The tailstock is used to install the rear center to support the processing of long workpieces, or to install tools such as drills and reamers for hole processing. Offset tailstock can turn the conical surface of long workpiece. The structure of the tailstock consists of the following parts. (see figure 1-5)
(1) There is a tapered hole at the left end of the sleeve, which is used to install a pointed or tapered shank tool. The axial position of the sleeve in the tailstock can be adjusted by handwheel and fixed by locking handle. When the sleeve is retracted to the rightmost position, the tip or tool can be unloaded.
⑵ The tailstock body is connected with the base. When the fixing screw is loosened, the screw can make the tailstock body move slightly laterally on the bottom plate, so that the front and rear centers are aligned with the center or offset by a certain distance to turn the long conical surface.
(3) The base is directly installed on the guide rail of the lathe bed to support the tailstock body.
7. The polished rod and the lead screw transfer the movement of the feed box to the sliding box. The polished rod is used for general turning, and the lead screw is used for turning threads.
8. The lathe bed is the basic part of the lathe, which is used to connect the main parts and ensure the correct relative position of the parts during the movement. On the bed, there are guide rails for moving the carriage and tailstock.
9 Joystick Joystick is the control mechanism of lathe. There is a handle at the left end of the joystick and the right side of the carriage box, and the operator can easily manipulate the handle to control the lathe spindle to rotate forward, reverse or stop.
10 joystick is the control mechanism of lathe. The left end of the joystick and the right side of the carriage box are respectively equipped with handles, which can be easily manipulated by the operator to control the lathe spindle to rotate forward, reverse or stop.
Figure 1-4 tool rest
Photo 1-5 tailstock
1 center 2 sleeve locking handle 3 center sleeve 4 screw 5 nut 6 tailstock locking handle 7 handwheel 8 tailstock 9 base
(3) Transmission system of horizontal lathe
The power output by the motor is transmitted to the spindle through the gearbox and belt drive, which changes the position of the handle outside the gearbox and the spindle box to get different gear sets engaged, thus getting different spindle speeds. The spindle drives the workpiece to rotate through the chuck. At the same time, the rotary motion of the spindle is transmitted to the carriage box through the reversing gear, the exchange gear, the feed box and the polished rod (or lead screw), so that the carriage box drives the tool rest to do linear feed motion along the lathe bed.
(4) Various handles and basic operations of horizontal lathe
1. Adjustment of horizontal lathe and use of handle
The adjustment of C6 132 lathe is mainly carried out by changing the position of their respective handles. See figure 1-6 for details.
Figure 1-6 C6 132 Lathe Adjusting Handle
1, 2, 6— Main motion speed-changing handle 3, 4— Feed motion speed-changing handle 5— Tool rest moving left and right reversing handle 7— Tool rest transverse manual handle 8— Square tool rest locking handle 9— Small tool rest moving handle 10— Tailstock sleeve locking handle1—Tailstock sleeve locking. Handle 15 —— transverse automatic handle 16 —— longitudinal automatic handle 17 —— longitudinal manual wheel 18 —— Replace the clutch of polished rod and lead screw.
2. The basic operation of horizontal lathe
(1) parking practice (the spindle rotates forward and backward, and the stop handle 13 is in the stop position)
1) change the spindle speed correctly. By changing the speed change handle 1, 2 or 6 outside the gearbox and headstock, various corresponding spindle speeds can be obtained. When the handle does not rotate smoothly, you can turn the chuck gently by hand.
2) Correctly change the feeding speed. Check the marks on the feed box according to the selected feed amount, and then change the positions of handles 3 and 4 according to the positions of the handles on the marks to obtain the selected feed amount.
3) Be familiar with the rotation direction of longitudinal and transverse manual feed handles. Hold the longitudinal feed manual wheel 17 in the left hand and the transverse feed manual handle 7 in the right hand. Rotate the handwheel clockwise and counterclockwise respectively to control the moving direction of the tool rest and the tool rest.
4) Familiar with the operation of longitudinal or transverse motorized feed. The polished rod or screw closing handle 18 is located in the polished rod closing position. Lift the longitudinal electric feed handle 16 for longitudinal feed, and lift the transverse electric feed handle 15 for transverse feed. Pull down respectively to stop the longitudinal and transverse electric feed.
5) Operation of tailstock. The tailstock is moved by hand and fixed by fastening bolts and nuts. Turn the tailstock moving sleeve handwheel 12, move the sleeve in the tailstock, and turn the tailstock locking handle 1 1 to fix the sleeve in the tailstock.
(2) Before low-speed driving practice, check whether each handle position is in the correct position, and then start driving practice.
1) Spindle start-motor start-control spindle rotation-stop spindle rotation-turn off the motor.
2) Motor feed-motor start-control spindle rotation-manual vertical and horizontal feed-motor vertical and horizontal feed-manual return-motor horizontal feed-manual return-stop spindle rotation-turn off the motor.
Please pay special attention to:
1) Before the machine tool comes to a complete stop, it is forbidden to change the spindle speed, otherwise there will be serious gear jumping in the spindle box and even a machine tool accident. Check whether the handle is in the correct position before driving.
2) Don't shake the longitudinal and transverse handles in the wrong direction, especially pay attention to fast advance and retreat, otherwise the workpiece will be scrapped and safety accidents will occur.
3) For each rotation of the manual handle with transverse feed, the transverse cutting amount of the cutter is 0.02 mm, and the cutting amount in the diameter direction of the cylinder is 0.04 mm. ..
5. Review thinking questions
1. When turning, what movements do the workpiece and tool need to make? What are the names, symbols and units of turning elements? Explain the meaning of C6 132A.
2. What are the main components of horizontal lathe? What is the role of each?
3. What are the characteristics of the structure of horizontal lathe? What are the main applications?
Training 2 Basic operation of turning
First, the purpose of training:
1. Master the type, composition and basic angle of the cutter.
2. Master cutting methods such as end face and excircle.
3. Master the basic operating skills of turning.
2. Training content:
1. Safe operation
2. The structure, type, basic angle and function of the cutter.
3. The basic cutting operation of ordinary lathe
① Clamping of parts
② Installation of cutting tools
(3) Turning method of end face and excircle.
④ Turning method of knurling.
⑤ Turning method of slotting cutting.
⑥ Turning method of cone
3. Training equipment:
C6 16- 1D lathe 18 sets.
4. Training steps:
(1) Turning tools
I. Tool materials
1, the properties of tool materials.
(1) High hardness and good wear resistance. Before cutting metal, the hardness of the tool material must be higher than that of the material to be machined. The hardness of general tool materials should be above 60HRC. The harder the tool material, the better the wear resistance.
(2) Sufficient strength and impact toughness. Strength means that under the action of cutting force, the blade will not break and the arbor will not break. Impact toughness refers to the ability of tool materials to ensure no edge collapse under the working conditions of impact or intermittent cutting.
(3) High heat resistance. Heat resistance, also known as red hardness, is the main index to measure the performance of tool materials, which comprehensively reflects the ability of tool materials to maintain high hardness, wear resistance, strength, oxidation resistance, adhesion resistance and diffusion resistance at high temperature.
(4) Good manufacturability and economy
2, commonly used tool materials
At present, cemented carbide tool materials are widely used in turning tools, and high-speed steel tool materials are also used in some cases.
(1) High speed steel High speed steel is a kind of high alloy steel, commonly known as Bai Gang, Fenggang and Fenggang. Its strength, impact toughness and manufacturability are very good, and it is the main material for manufacturing tools with complex shapes. Such as: forming turning tools, twist drills, milling cutters, gear cutters, etc. The heat resistance of high speed steel is not high, and the hardness decreases around 640℃, so it cannot be cut at high speed.
(2) Carbide and cobalt with high heat resistance and good wear resistance are used as binders, pressed into blades of various shapes by powder metallurgy, and then brazed on the blades with copper as cutting tool materials. The wear resistance and hardness of cemented carbide are much higher than that of high speed steel, but the plasticity and impact toughness are not as good as that of high speed steel.
Ⅱ. Composition and angle of turning tool
Turning tool is the single-edged tool with the simplest shape, and other complex tools can be regarded as the combination and evolution of turning tools. The definition of turning tool angle is also applicable to other tools.
1, composition of turning tool
Turning tool consists of cutter head (cutting part) and cutter body (clamping part). The cutting part of turning tool is composed of three sides, two edges and one tip, namely one point, two lines and three sides. (Figure 2- 1)
(a) (b) (c)
2. Turning tool angle
The main angles of turning tool are rake angle, rake angle, main deflection angle, auxiliary deflection angle and blade inclination angle.
1) The included angle between the rake face and the rake face base surface indicates the rake face inclination. The front angle can be divided into positive, negative and zero. When the rake face is below the base surface, the rake angle is positive, otherwise it is negative and the coincidence degree is zero.
The function of rake angle: increasing rake angle can make the blade sharp, reduce cutting force, reduce cutting temperature, reduce tool wear and improve surface processing quality. However, too large rake angle will reduce the strength of the cutting edge and easily damage the cutting edge.
Selection principle: when processing steel parts (plastic materials, etc.). ) with carbide turning tool, generally choose = 10? ~20 ; When processing gray cast iron (brittle materials, etc.). ), generally choose = 5o ~ 15. The rake angle should be larger when finishing and smaller when roughing. When the strength and hardness of the workpiece material are large, the rake angle is small, sometimes even negative.
2) The included angle between the main side of the relief angle and the cutting plane indicates the inclination of the main side.
The function of the relief angle is to reduce the friction between the main relief surface and the workpiece and affect the strength and sharpness of the cutting edge. Selection principle: general back angle is desirable =6? ~8? .
3) The included angle between the main cutting edge of the main deflection angle and the projection of the feed direction on the base surface.
The function of the main deflection angle: it affects the working length, cutting depth resistance, tip strength and heat dissipation of the cutting edge. The smaller the main deflection angle, the longer the working length of the cutting edge and the better the heat dissipation condition, but the greater the cutting depth resistance.
Selection principle: The main deflection angles commonly used for turning tools are 45, 60, 75 and 90. When the workpiece is thick and hard, a smaller value can be taken. When turning slender shaft, in order to reduce the bending deformation of workpiece caused by radial force, a larger value should be selected.
4) The included angle between the cutting edge of the auxiliary deflection angle pair and the projection of the feed direction on the base surface.
Function: It affects the surface roughness of the machined surface, and reducing the auxiliary deflection angle can make the machined surface smooth.
Selection principle: generally = 5o ~ 15, fine turning 5o ~ 10, rough turning 10o ~ 15.
5) Angle of inclination When the tip of the knife is the highest point of the cutting edge, the angle between the main cutting edge and the base surface is positive and negative.
The role of edge inclination angle: it mainly affects the strength of the main cutting edge and controls the chip removal direction. Based on the bottom surface of the tool holder, the tip of the tool is positive when it is at the highest point of the main cutting edge, and the chips flow to the surface to be machined; When the main cutting edge is parallel to the bottom surface of the tool holder =0o, the chips flow out in the direction perpendicular to the main cutting edge; When the tip is the lowest point of the main cutting edge, it is negative, and the chips flow to the machining surface.
Selection principle: generally choose between 0o and 5. In rough machining, negative values are often taken. Although the chips flow to the machined surface, the strength of the main cutting edge is guaranteed. Finishing often takes a positive value to make the chips flow to the surface to be machined, so as not to scratch the quality of the machined surface.
Ⅲ. Installing turning tool
The turning tool must be correctly and firmly installed on the tool rest, as shown in Figure 2-3.
Pay attention to the following points when installing turning tools:
1) The cutter head should not extend too long, otherwise it will easily generate vibration during cutting, which will affect the machining accuracy and surface roughness of the workpiece. Generally, the extension length of the cutter head is not more than twice the thickness of the cutter bar, and it is enough to see the tip turning.
2) The tip of the tool should be equal to the center line of the lathe spindle. If the lathe tool is installed too high and the rake angle decreases, the main back of the lathe tool will have strong friction with the workpiece; If the installation is too low, the rake angle will be reduced, the cutting will not be smooth, and the tip will collapse. The height of the top can be adjusted according to the height of the top of the tailstock. The installation of turning tool is shown in Figure 2-3a).
Figure 2-3 Installation of turning tool A) Correct B) Wrong
3) The gasket at the bottom of the turning tool should be flat and thick to reduce the number of gaskets. After adjusting the height of the cutter head, tighten the turning tool alternately with at least two screws.
(2) The excircle, end face and steps of the vehicle
Ⅰ. Install the workpiece with a three-jaw self-centering chuck
1. Install the workpiece with a three-jaw self-centering chuck.
Figure 2-4 Three-jaw Self-centering Chuck Structure and Workpiece Installation
The structure of the three-jaw self-centering chuck is shown in Figure 2-4a. When the small bevel gear is rotated by the chuck wrench, the large bevel gear also rotates. Under the action of the plane thread on the back of the large bevel gear, the three claws move or retract centripetally at the same time, clamping or loosening the workpiece. Its characteristic is good centering, and the automatic centering accuracy can reach 0.05 ~ 0. 1.5 ㎜. As shown in Figure 2-4b, workpieces with smaller diameters can be clamped. When clamping a cylindrical workpiece with a large diameter, three opposite claws can be used, as shown in Figure 2-4c. However, the three-jaw self-centering chuck is generally only suitable for lighter workpieces because of its low clamping force. When clamping heavy workpieces, it is advisable to use a four-jaw single-acting chuck or other special fixtures.
2. Install the workpiece with a clamp and a top.
Generally speaking, it is more suitable to clamp short rotating workpieces with three-jaw self-centering chuck, but the rigidity is poor for long rotating workpieces. Therefore, generally long workpieces, especially important workpieces, cannot be directly clamped by a three-jaw self-centering chuck, but should be clamped at one end and supported by a rear center at the other end.
Ⅱ. Vehicle excircle
1. Adjust the lathe
The adjustment of lathe includes spindle speed and turning tool feed.
Calculate and select the spindle speed according to the cutting speed. The choice of cutting speed is related to workpiece material, tool material and workpiece machining accuracy. V = 0.3 ~ 1m/s when turning with high-speed steel turning tool, and v = 1 ~ 3m/s when turning with cemented carbide turning tool. The rotation speed of high hardness steel is lower than that of low hardness steel.
For example, if a cast iron pulley with a diameter of d = 200mm is machined with a carbide turning tool, the selected cutting speed v = 0.9m/s, and the spindle speed is calculated as follows:
(rotational speed)
The feed speed is determined according to the requirements of workpiece processing. When rough turning, generally take 0.2 ~ 0.3 mm/r; The finish depends on the required surface roughness. For example, when the surface roughness is Ra3.2, choose 0.1~ 0.2 mm/r; Ra 1.6, choose 0.06 ~ 0. 1.2 mm/r, and so on. The feed rate can be adjusted according to the position of the pull handle of the lathe feed table, and the specific method is similar to adjusting the spindle speed.
2. Rough turning and fine turning
The purpose of rough turning is to remove the redundant metal layer as soon as possible, so that the workpiece is close to the final shape and size. After rough turning, a machining allowance of 0.5 ~ 1mm should be left.
Finishing is to remove the remaining small amount of metal layer to obtain the required precision and surface roughness of the part, so the back cutting amount is small, about 0. 1 ~ 0.2 mm, and the cutting speed can be high or low, so beginners can use a lower speed. In order to improve the surface roughness of the workpiece, the front and rear surfaces of the turning tool for finishing should be polished with oilstone and engine oil, and sometimes the tip of the tool will be ground into a small arc.
In order to ensure the dimensional accuracy of machining, the trial cutting method should be adopted in turning. The steps of trial cutting method are shown in Figure 2-5.
Figure 2-5 Trial Cutting Steps
3. The quality analysis of the car when it is cylindrical.
1) The size is wrong: the reason is carelessness, and the size is wrong when turning; Dialing calculation error or operation error; Due to carelessness and inaccurate measurement.
2) The surface roughness does not meet the requirements: the reason is that the grinding angle of the cutting edge is wrong; Incorrect tool installation or tool wear, improper selection of cutting parameters; This is due to the excessive clearance between lathe parts.
3) Taper outer diameter: the reason is that the cutting depth is too large and the tool is worn; Loose knives or trays; When turning with a small carriage, the lower reference line of the turntable is not aligned with the "0" line; When turning two centers, the "0" line at the end of the bed is not on the axis; It is caused by insufficient machining allowance during finishing.
Ⅲ. End face of automobile
Face turning method: when turning the face, the main cutting edge of the tool should form a certain angle with the face. The part of the workpiece protruding from the chuck should be as short as possible. When turning, the middle carriage should be used for horizontal feed, and the number of feeds depends on the machining allowance. The feed can be from the outside to the middle or from the center of the circle to the outside.
Figure 2-6 shows several common face turning situations.
Figure 2-6 Common Turning Tools for Automobile Tail
When turning end face, pay attention to the following points:
1) The turning tool tip should be aimed at the center of the workpiece, so as to avoid leaving a boss at the center of the end face.
2) It is easy to prick the knife if it deviates from the end face of the lathe. Selection of back feed ap: AP = 0.2 mm ~ 1 mm rough turning and 0.05 mm ~ 0.2 mm fine turning.
3) When the diameter of the end face changes from the outside to the center, the cutting speed is also changing. When calculating the cutting speed, it must be calculated according to the maximum diameter of the end face.
4) If the end face of the large-diameter lathe is concave or convex, check whether the turning tool, square tool rest and large carriage are locked.
Quality analysis of automobile end face;
1) The end face is uneven, resulting in convex-concave phenomenon or "small head" in the center of the end face; The reason is that the cutting edge of the lathe is polished or improperly installed, the tip of the lathe is not aligned with the center of the workpiece, the depth of lateness is too large, the lathe has a gap, and the carriage moves.
2) Poor surface roughness. The reason is that the turning tool is not sharp, the manual feed is uneven or too fast, and the cutting parameters of the automatic feed are not selected properly.
Ⅳ, car steps
The method of turning steps is basically the same as turning excircle, but the dimension requirements of excircle diameter and step length should be considered when turning, and the verticality between the step plane and the workpiece axis must be ensured.
Control method of step size:
1) When the length and size of the steps are low, it can be directly controlled by a large tray.
2) The length of the steps can be determined by steel ruler or template, as shown in Figures 2-7a and 2-7b. When turning, take the notch slightly shorter than the step length as the processing limit, and measure the exact length of the step with vernier caliper or depth vernier caliper.
Figure 2-7 Control Method of Step Size and Size
3) When the length and size of the steps are very high and the length is very short, a small sliding dial can be used to control the length.
(3) knurling
There are two patterns: straight and net. The knurling knives are also divided into straight knurling knives (Figure 2-8a) and net knurling knives (Figure 2-8b, c). Knurling is to squeeze the workpiece with a knurling knife, so that its surface is plastically deformed and patterns are formed. The radial extrusion force of knurling is very large, so the rotation speed of the workpiece is low during machining. Sufficient cooling lubricant must be supplied to avoid grinding the knurling knife and prevent fine chips from getting stuck in the knurling knife and generating random lines.
Figure 2-8 Knurling Knife
(4) grooving and cutting
Me, grooving.
The method of turning grooves on the surface of workpiece is called grooving, which has outer grooves, inner grooves and end grooves. As shown in Figure 2-9.
Figure 2-9 Common grooving methods Figure 2- 10 high-speed steel grooving knife
1. Selection of grooving knife
High-speed steel grooving knives are often used for grooving. The geometry and angle of the slotting knife are shown in Figure 2- 10.
2. Slotting method
When turning a rectangular groove with low precision and narrow width, you can use a slotting knife with the same width as the groove to turn it at one time by the straight-forward method. If the accuracy requirement is high, it is generally divided into two cars.
When turning a wide groove, the straight cutting method can be used for many times (see Figure 2- 1 1), and a certain finish turning allowance is left on both sides of the groove, and then finish turning to size according to the groove depth and width.
Figure 2- 1 1 width-cutting groove
Ⅱ. Cut off
Cut with a cutting knife. The shape of the cutting knife is similar to that of the grooving knife, but it is easy to break because the blade is narrow and long. There are two common cutting methods: straight cutting method and left-right knife borrowing method, as shown in Figure 2- 1 1. Direct method is often used to cut brittle materials such as cast iron; The left-right knife borrowing method is often used to cut plastic materials such as steel.
Please pay attention to the following points when cutting:
1) cutting is generally carried out on the chuck, as shown in figure 2- 12. The cutting part of the workpiece should be close to the chuck to avoid cutting the workpiece installed at the top.
Figure 2- 12 Cutting on the chuck Figure 2- 13 The tip of the tool must be equal to the center of the workpiece.
2) The tip of the cutter must be at the same height as the center of the workpiece, otherwise there will be a boss at the cutting place, which will easily damage the cutter head (Figure 2- 13).
3) The length of the cutter extending out of the tool rest should not be too long, and the feed should be slow and even. When cutting, the feed speed must be slowed down to avoid the cutter head breaking.
5) When cutting two top workpieces, it is not allowed to cut directly to the center, in case the turning tool breaks and the workpieces fly out.
(5) turning the conical surface
The method of turning workpieces into conical surfaces is called turning conical surfaces. The common methods of turning conical surface are wide knife method, small rotary tool rest method, copying method, tailstock offset method and so on. This paper introduces the rotary small tool rest method and tailstock offset method.
ⅰ, rotating small tool rest method
When machining a short conical workpiece, you can turn it by turning a small tool holder. When turning, loosen the nut on the turntable below the small slide plate, turn the turntable to the scribe line of the required cone half angle α/2, align it with the reference zero line, and then fix the nut on the turntable. If the cone angle is not an integer, estimate a value close to the cone and align it gradually after trial operation, as shown in Figure 2- 14.
Figure 2- 14 Cone of Small Scooter Figure 2- 15 Cone of Offset Position Method
Ⅱ. Tailstock migration method
When turning the conical surface of small taper and long taper parts, the method of moving tailstock can be adopted. This method can feed automatically, but the disadvantage is that it can't turn the whole conical surface and inner conical surface, and the workpiece with large taper. The slide plate on the tailstock is laterally offset by a distance s, so that the connecting line between the two offset centers intersects with the original center lines of the two centers at an angle α/2, and the deviation of the tailstock depends on the machining position of the workpiece head between the workpiece head and the two centers. The tailstock offset is related to the total length of the workpiece, as shown in Figure 2- 15. Tailstock offset can be calculated by the following formula:
Where s- tailstock offset;
L—— the length of the cone part of the workpiece;
L0-the total length of the workpiece;
D, d—— Diameter of cone big head and diameter of cone small head.
The offset direction of the bed end is determined by the conical direction of the workpiece. When the small end of the workpiece is close to the bed end, the bed end should move inward, otherwise, the bed end should move outward.
Quality analysis of turning cone;
1. The taper is inaccurate, resulting in calculation error; The rotation angle and bed end deviation of the small carriage are inaccurate; Or the lathe tool, carriage and bed end are not fixed properly and move during turning. Even because the surface roughness of the workpiece is too poor, the gauge or the workpiece has burrs or is not cleaned, resulting in errors in inspection and measurement.
3. The conic generatrix is not straight, indicating that the conic surface is not a straight line, and there is a concave-convex phenomenon on the conic surface, or the middle is low and the two ends are high. The main reason is that the lathe tool installation is not aligned with the center.
4. The surface roughness can't meet the requirements. Due to improper selection of cutting parameters, tool wear or wrong grinding angle, the surface roughness is poor. No surface polishing or insufficient polishing allowance. When cutting a conical surface with a small carriage lathe, uneven manual feed, large machine gap and poor workpiece rigidity will also affect the surface roughness of the workpiece.
5. Review thinking questions
1. How are the five main marking angles of cylindrical turning tools defined? What are their respective roles?
2. What are the requirements when installing turning tools?
3. What is the purpose of trial cutting? Combined with the actual operation method, explain the trial cutting steps.
4. What turning tools are commonly used for turning cylindrical surfaces? Why are 90 offset tools commonly used in turning the outer surface of long shafts?
5. What are the machining cones? What are their characteristics? What types of production are they suitable for?
6. What are the geometric features of grooving knives and cutting knives?