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畢業(yè)設(shè)計(jì)（論文）報(bào)告用紙
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畢業(yè)設(shè)計(jì)外文翻譯
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學(xué) 院： 機(jī)電工程學(xué)院
專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化
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年6月3日
第 23 頁(yè) 共 43 頁(yè)
畢業(yè)設(shè)計(jì)（外文翻譯）報(bào)告用紙
(一)BORING AND BORING MACHINES
As carried out on a lathe, boring produces circular internal profiles in hollow work-pieces or on a hole made by drilling or another process, Boring is done with cutting tools that are similar to those used in turning. Because the boring bar has to reach the full length of the bore, tool deflection and, therefore, maintainance of dimensional accuracy can be a significant problem.
The boring bar must be sufficiently stiff—that is, made of a material with high elastic modulus, such as tungsten carbide –to minimize deflection and avoid vibration and chatter. Boring bars have been designed with capabilities for damping vibration.
Although boring operations on relatively small work-pieces. Can be carried out on a lathe, boring mills are used for large work-pieces. These machines are either vertical or horizontal, and are capable of performing operations such as turning, facing, grooving, and chamfering. A vertical boring machine is similar to a lathe but has a vertical axis of work-piece rotation.
The cutting tool (usually a single point made of M-2 and M-3 high-speed steel and C-7 and C-8 carbide) is mounted on the tool head, which is capable of vertical movement (for boring and turning) and radial movement (for facing), guided by the cross-rail. The head can be swiveled to produce conical (tapered) surfaces.
In horizontal boring machine, the work-piece is mounted on a table that can move horizontally in both the axial and radial directions. The cutting tool is mounted on a spindle that rotates in the headstock, which is capable of both vertical and longitudinal movements. Drills, reamer, taps, and milling cutters can also be mounted on the machine spindle.
Boring machine are available with a variety of features. Although work-piece diameters are generally 1 m-4 m(3ft-12ft),work-piece as large as 20 m(60ft) can be machined in some vertical boring machines. Machine capacities range up to 150 kw (200hp).these machines are also available with computer numerical controls, which allow all movements to be programmed. With such controls, little operaror involvement is required and consistency and productivity are improved. Cutting speeds and feeds for boring are similar to those for turning.(For capabilities of boring operations)
Jig borers are vertical boring machines with high –precision bearings. Although they are available in various sizes and used in tool rooms for making jigs and fixtures, they are now being replaced by more versatile numerical control machines.
Design considerations for boring. Guidelines for efficient and economical boring operations are similar to those for turning. Additionally, the following factors should be considered：
A.Whenever possible, through holes rather than blind holes should be specified.(The term blind hole refers to a hole that does not go though the thickness of the work-piece )
B.The greater the length –to –bore-diameter ratio, the more difficult it is to hold dimensions because of the deflections of the boring bar due to cutting forces.
C.Interrupted internal surfaces should be avoided.
（2）Fundamentals of Machine Tools
In many cases products form the primary forming processes must undergo further refinements in size and surface finish to meet their design specifications. To meet such precise tolerances the removal of small amounts of material is needed. Usually machine tools are used for such operation.
In the United States material removal is a big business-in excess of $ per year, including material, labor, overhead, and machine-tool shipments, is spent. Since 60 percent of the mechanical and industrial engineering and technology graduates have something connection with the machining industry either through sale, design, or operation of machine shops, or working in related industry, it is wise for an engineering student to devote some time in his curriculum to studying material removal and machine tools.
A machine tool provides the means for cutting tools to shape a workpiece to required dimensions; the machine supports the tool and the workpiece in a controlled relationship through the functioning of its basic members, which are as follow:
(a) Bed, Structure or Frame. This is the main member which provides a basis for, and a connection between, the spindles and slides; the distortion and vibration under load must be kept to a minimum.
(b) Slides and Sideways. The translation of a machine element (e.g. the slide) is normally achieved by straight-line motion under the constraint of accurate guiding surfaces (the slideway).
(c) Spindles and Bearings. Angular displacements take place about an axis of rotation; the position of this axis must be constant within extremely fine limits in machine tools, and is ensured by the provision of precision spindles and bearings.
(d) Power Unit. The electric motor is the universally adopted power unit for machine tools. By suitably positioning individual motors, belt and gear transmissions are reduced to a minimum.
(e) Transmission Linkage. Linkage is the general term used to denote the mechanical, hydraulic, pneumatic or electric mechanisms which connect angular and linear displacements in defined relationship.
There are two broad divisions of machining operations:
(a) Roughing, for which the metal removal rate, and consequently the cutting force, is high ,but the required dimensional accuracy relatively low .
(b) Finishing, for which the metal removal rate, and consequently the cutting force, is low, but the required dimensional accuracy and surface finish relatively high .
It follows that static loads and dynamic loads, such as result form an unbalanced grindingwheel, are more significant in finishing operations than in roughing operations, The degree of precision achieved in any machining process will usually be influenced by the magnitude of the deflections, which occur as a result of the force acting.
Machine tool frames are generally made in cast iron, although some may be steel casting or mild-steel fabrications. Cast iron is chosen because of its cheapness, rigidity, compressive strength and capacity for damping the vibrations set-up in machine operations, To avoid massive sections in castings, carefully designed systems of ribbing are used to offer the maximum resistance to bending and torsional stresses. Two basic types of ribbing are box and diagonal. The box formation is convenient to produce, apertures in walls permitting the positioning and extraction of cores. Diagonal ribbing provides greater torsional stiffness and yet permits swarf to fall between the sections; it is frequently used for lathe beds.
The slides and slideways of a machine tool locate and guide members which move relative to each other, usually changing the position of the tool relative to workpiece .The movement generally takes the form of translation in a straight line, but is sometimes angular rotation, e.g. tilting the wheel-head of a universal thread-grinding machine to an angle corresponding which the helix angle of the workpiece thread. The basic geometric elements of slides are flat, vee, dovetail and cylinder. These elements may be used separately or combined in various ways according to the applications . Features of slideways are as follows :
(a) Accuracy of Movement. Where a slide is to be displaced in a straight line, this line must lie in two mutually perpendicular planes and there must be no slide rotation. The general tolerance for straightness of machine tool slideways is 0~0.02mm per 1000mm; on horizontal surfaces this tolerance may be disposed so that a convex surface results, thus countering the effect of "sag" of the slideway.
(b) Means of Adjustment. To facilitate assembly, maintain accuracy and eliminate "play" between sliding members after wear has taken place, a strip is sometimes inserted in slides. This is called a gibstrip. Usually, the gib is retained by socket-head screws passing through elongated slots；and is adjusted by grub-screws secured by lock nuts.
(c) Lubrication. Slideways may be lubricated by either of the following systems：1)Intermittently through grease or oil nipples, a method suitable where movements are infrequent and speed low．
2) Continuously e.g. by pumping through a metering valve and pipe-work to the point of application; the film of oil introduced between surfaces by these means must be extremely thin to avoid the slide “floating”．If sliding surfaces were optically flat oil would be squeezed out，resulting in the surfaces sticking. Hence in practice slide Sill"faces are either grourld using the edge of a cup wheel，or scraped. Both processes produee minulte surface depressions，which retain‘‘pocket” of oil, and complete separation of the parts may not occur at all points.
(d) Protection．To maintain slideways in good order, the following conditions must be met：
1) Ingress of foreign matter，e．g．swarf，must be prevented. Where this is no possible，it is desirable to have a form of slideway，which does not retain swarf，e.g. the inverted vee.
2) Lubricating oil must be retained．The adhesive property of oil for use on vertical or inclined slide surface is important; oils are available which have been specially developed for this purpose. The adhesiveness of oil also preverts it being washed away by cutting fluids．
3) Accidental damage must be prevented by protective guards．
(二) Boring fixture
Boring fixture is to rough up the side facing hole, because dimensional requirements and location requires more so need to limit the five degrees of freedom in. Because of the typical case accessories side two pins localization way can also meet the above two kinds of positioning requirement, so for the boring fixture choose a two way of positioning pin completely. Positioning of components of the design of , including positioning structure, its size and layout mode, etc. Also the positioning of the main decision and the design requirements of the processing and the part of the shape of the locating datum size precision, so factors such as in the design should be analyzed the locating datum form. Plate figure shows is the type B slides with the plate for horizontal direction, decorate in the groove of the positioning, can prevent tiny chip stay in positioning surface. The main specifications plate thickness H take 10 mm. Plate with carbon tool, the heat treatment to 55 T8 HRC-60. 6 piece of plate used at the same time, need to try to make thickness H equal. Plate with bolt in the clip in the concrete tighten. It can limit 3 dof . Two pin location that is with cylindrical holes position. The In essence the benchmark hole positioning, pins choose fixed location pins, it is the combination of the components used in positioning positioning of one. Figure 2.1 shows is the type A location pins, can limit the two degrees of freedom. Fixed location pins (GB/T2203-91) main specifications D take 12 mm. Positioning pin material to use carbon tool, the heat treatment to 55 T8 HRC-6 Working principle: by way of positioning fixture is a two pins, surface, as is processing components to fine benchmark plane positioning. The benchmark by cutting plane, can be directly on the plane positioning. After scraping, grinding p`lane with smaller surface roughness and plane degree error, we can get a precise positioning of. Some of the commonly used location components have plate surface nail etc. Supporting peace This class is a surface with the positioning of the components. This design jigs choose plate as positioning components. This fixture using single homonymous linkage clamping institutions, through the compressive bar linkage connected pin shaft lever pressure clamping claw realize and relax, press the piston rod external fixture structure realize sports. The DuoGe positioning in the benchmark portfolio fixed position is very common. They can is flat, and YuanZhuMian outside, inside the YuanZhuMian, cone face all kinds of combination. The combination should be the choice of reasonable positioning positioning component; According to the principle of superposition benchmark selecting position datum; Combination of some positioning components, orientation, when used alone, limit freedom, direction along the coordinate transformation and combination is converted to limit when positioning coordinate direction around the degrees of freedom. This design processing speed reducer, the case accessories two holes, in order to make the benchmark side position is unified. The localization way the positioning components as the plate, pins and diamond pin. Below will focus on the introduction of the diamond pin design and decorate, to prevent a location. The diamond pin as waterproof supporting turn, the arrangement should make long axis and the center of the two pins, and should be vertical attachment to choose the right diamond pin the diameter of the basic size and the cutting edge after the width of the cylindrical part as shown in figure 2.4. The diamond pin design procedure is as follows: 1. Sure two pins the center distance of two pins center distance should be equal to the size of the basic orientation of two pitch, the size of the average tolerance is commonly 2. Select pins on table take pins of standard code for A 12 h7x14GB/T2203 3. Choose diamond pin width b according to table take b = 4 mm 4. Sure the diamond pin diameter (1) for compensation amount. A(2) the positioning of the smallest diamond. Calculation clearance (3) the diameter of the diamond pin. Calculation Take tolerance zone, namely the diamond pin for h6 the standard code for B12 h6x 14 . Add the fixture workpiece machining errors by the working hours of four aspects:
(1) the fixture position errors, namely, the cutting machine element positioning relative position error of the movement of the forming. (2)-positioning error caused by positioning, namely the working procedure of the position of the benchmark error. (3) the position of the tool relative fixture that knife orientation error error. (4)and process of some factors processing error. Because the two sets of fixture use the locating datum and scheme, in which do exactly the same position error analysis are as follows:
(1) the perpendicular tolerance 0.08 (2) the known:Figure 2.5 diamond pin perpendicularity errors were (3) the parallel degree of tolerance 0.04 mm. As shown in figure 2.4 shows, when the workpiece will influence the parallel degree tolerance skewed by the figure 2.5 can get the corner error formula. Type of work pieces positioning the diameter of holes-tolerance (mm); -the diameter of the cylinder pins tolerance (mm); -the diameter of the diamond pins tolerance (mm); cylindrical pins and the minimum clearance between hole(mm); L-centre distance (mm).
Chapter 6
Form
?Flatness
?Straightness
?Cylindricity
?Circularity
Chapter Objectives
Readers will learn:
1.Flatness of a surface, flatness on a unit basis and flatness of a derived median plane; what they mean, the tolerance zone configurations and how they are measured.
2.Straightness of a surface, straightness of a derived median line; what they mean, the tolerance zone configurations and how they are measured.
3.Cylindricity of a surface; what it means, the tolerance zone configuration, what it controls and to within how much, how it is measured and how it relates to flatness.
4.Circularity, what it means, the tolerance zone configuration, what it controls and to within how much and how it is measured.
Chapter Six
Form
There are four geometric characteristic symbols in the category called form. They are:
Flatness
Straightness
Cylindricity
Circularity
These symbols are used in feature control frames to tolerance defined 2-D and 3-D elements of part feature configurations. They are not related to datums, but are often used to tolerance the shape of primary datum features.
Two of the most common geometric characteristics used on primary datum features are flatness (for planar seating surfaces) and cylindricity (for cylindrical mating, alignment features). These are 3-dimensional form controls. Let’s begin by examining flatness.
Form
Flatness
Flatness used as a 3-D surface control, constructs a tolerance zone that consists of two parallel planes separated by the geometric tolerance. The entire surface being toleranced must have all its elements between these two planes. For example:
FIGURE 6-1 [Flatness of a Surface]
Chapter Six
In this type of surface control, no datums are referenced. It is a 3-D form control that doesn’t try to relate the orientation or location of the zone to datums. Since the surface is planar (not a diameter), no diameter symbol is appropriate in the feature control frame. It is a surface control, not an axis control. The use of a diameter symbol in a feature control frame denotes the control of an axis. Since this flatness control is just trying to tolerance the shape of a single surface, it is not a feature of size. It has no maximum or least material condition. Therefore, no material condition symbol is appropriate to use in the feature control frame. So, the only items to be found in the feature control frame are the flatness geometric characteristic and a geometric tolerance.
Measurement can be done by scanning the surface to determine if all points on the surface are within the tolerance zone. This can be done by manually orienting the surface to obtain optimal results as shown in FIGURE 6-2, or by allowing a computer program to merge the tolerance zone with the variables data collected by a machine like the coordinate measurement machine (CMM).
FIGURE 6-2 [Measuring flatness on a surface plate with a dial indicator and stand]
Form
Sometimes, flatness is applied on a per unit basis. This would allow a tolerance that is so much per the unit specified. This type of constraint is generally used to refine an overall control of the entire surface. For example:
0.5
0.1 / 20 X 20
This means the entire surface must have all its elements capable of fitting between 2 parallel planes that are 0.5mm apart. The refinement requirement tells us that every 20x20mm square on the surface must be flat to within 0.1mm. This prevents any abrupt surface variations within these 20x20mm squares. The entire surface could have a uniform curvature of 0.5mm, but no pits or bumps greater than 0.1mm.
FIGURE 6-3 [Flatness on a Unit Basis or Rate Basis]
In the ASME Y14.5-2009 standard on Dimensioning and Tolerancing, flatness of the derived median plane has replaced straightness of the derived median plane. It appears as shown in FIGURE 6-4.
Chapter Six
FIGURE 6-4 [Flatness of the Derived Median Plane]
FIGURE 6-5 [Measurement of Flatness of the Derived Median Plane]
The tolerance zone for the flatness of the derived median plane control shown in FIGURE 6-4 and being verified in FIGURE 6-5 consists of two parallel planes that are 0.1 apart. It must contain the derived median plane. The maximum material condition symbol allows the flatness tolerance zone to grow locally as the part shrinks (is produced smaller than the MMC) locally.
As FIGURE 6-4 shows, the flatness tolerance zone may grow
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