工业夹紧技术(中英文)
1 基本原理 / Basic principles
1.1 简单的液压夹紧机构(图1)。
A simple hydraulic clamping mechanism (Figure 1).
1.2 术语和定义 / Terms and definitions
1.2.1 夹紧柱塞 / Clamping Plunger
对工件施加夹紧力的装置。
A device that applies clamping force to the workpiece.
1.2.2 工件 / Workpiece
需要固定到位的零件或材料。
The part or material that is to be held in place.
1.2.3 压力活塞 / Pressure Piston
用于向液压介质施加压力的装置。
A device used to apply pressure to a hydraulic medium.
1.2.4 液压介质 / Hydraulic Medium
用于传输通过向压力活塞施加力而产生的压力的流体
A fluid used to transmit the pressure created by applying a force to the pressure piston
1.3 液压夹紧过程 / Hydraulic clamping process
液压夹紧过程包括正确应用液压夹紧系统产生的力来固定工件。液压夹紧系统由图1所示的组件组成,该图显示了使用液压介质的基本布置和工作原理。
使用液压流体用于夹紧目的的任何此类过程可被称为液压夹紧系统。夹紧系统中液压油提供的工作压力最大可达 5000 psi (350 bar),即使在使用紧凑型夹紧缸时也能施加相当大的夹紧力。
如果设计和控制得当,液压夹紧机构将防止工件在加工或施加其他力时移动(滑动、扭曲等),但不会导致工件发生意外的永久变形。
The hydraulic clamping process consists of properly applying the forces created by a hydraulic clamping system to secure a workpiece. A hydraulic clamping system consists of the components illustrated in Figure 1, which shows the basic arrangement and operating principle of the use of hydraulic media.
Any such process using hydraulic fluids for clamping purposes may be referred to as a hydraulic clamping system. The operating pressure provided by hydraulic fluids in clamping systems can reach a maximum of 5000 psi (350 bar), allowing the application of considerable clamping forces even when using compact clamping cylinders.
When properly designed and controlled, the hydraulic clamping mechanism will prevent the workpiece from moving (sliding, twisting, etc.) when machining or other forces are applied, yet will not cause an unexpected permanent distortion to occur in the workpiece.
2 液压夹紧装置的装配 / Assembly of hydraulic clamping devices
2.1 工件的定位、夹紧和支撑 / Locating, clamping, and supporting workpieces
2.1.1 本体的定位 / Locating a Body
术语“定位”是指将工件定位在夹紧装置内,并将其固定到位以进行必要的加工的过程。只有正确固定的工件才能在规定的公差范围内一致地进行加工。
The term “locating” refers to the process of positioning the workpiece inside the clamping device, and holding it in position for the necessary machining. Only workpieces that are correctly held can be consistently machined within specified tolerances.
2.1.2 限制自由度 / Limiting the degrees of freedom
定位和固定工件的过程可以称为“限制自由度”。工件在任何可能方向上的任何运动都被认为代表一个自由度。
因此,三维工件具有六个自由度,如图 2 所示。这六个自由度由 x、y 和 z 方向上的平移运动“T”以及绕工件转动的旋转运动“R”组成。 x、y 和 z 轴。
可以通过引入穿过任意两个轴的参考平面来降低给定工件或物体所拥有的自由度。
例如,图 3a 中的平面限制了沿 x 和 z 方向行进的运动以及绕 y 轴的旋转。通过限定该固定平面,工件因此可以被限制或约束到三个自由度。
另外两个自由度可以通过引入第二参考平面来约束,如图 3b 所示。该参考平面将运动限制为 x 方向上的平移运动。
约束最后一个自由度可以通过定义第三个参考平面来完成,如图 3c 所示。
The process of locating and holding a workpiece may be referred to as “limiting the degrees of freedom.” Any motion of a workpiece in any possible direction is considered to represent one degree of freedom.
A three-dimensional workpiece therefore possesses six degrees of freedom, as shown in Figure 2. These six degrees of freedom consist of the translational motions “T” in x, y, and z direction, and the rotational motions “R” turning about the x, y, and z axes.
The degrees of freedom that a given workpiece or body possesses may be reduced by introducing reference planes that pass through any two axes.
For example, the plane in Figure 3a limits movement to travel in x and z directions and rotation about the y-axis. By defining this fixed plane, the workpiece can thus be limited or constrained to three degrees of freedom.
Another two degrees of freedom may be constrained by introducing a second reference plane, as shown in Figure 3b. This reference plane limits movement to translational motion in the x direction.
Constraining the last degree of freedom can be accomplished by defi ning a third reference plane as shown in Figure 3c.
2.1.3 确定工作地点 / Locating a workplace
定位和保持的过程必然需要消除所有六个自由度的运动,实际应用中采用以下三种定位技术。
图 4a:半约束工件。工件仅固定在一个平面上(消除三个自由度)。
图 4b:受约束的工件。工件由两个平面固定(消除五个自由度)。
图 4c:完全约束的工件。工件由三个平面固定(消除六个自由度)。
The process of locating and holding a necessarily require the elimination of movement in all six degrees of freedom, the following three locating techniques are used in actual practice.
Figure 4a: Semi-constrained Workpiece. The workpiece is held in one plane only (elimination of three degrees of freedom).
Figure 4b: Constrained Workpiece. The workpiece is held by two planes (elimination of fi ve degrees of freedom).
Figure 4c: Fully-constrained Workpiece. The workpiece is held by three planes (elimination of six degrees of freedom).
2.1.4 避免过度定位 / Avoiding over-location
A. 带定位平面的工件
b. 工件定位不正确
C. 正确定位工件
当对于任何给定的自由度存在多个定位平面或点时,就会发生工件的过度定位。
a. Workpiece with locating planes
b. Incorrectly located workpiece
c. Correctly located workpiece
Over-location of the workpiece occurs when there is more than one locating plane or point for any given degree of freedom.
为了防止在加工工件时弯曲 bc 肋,引入了第三参考平面 (3)。将工件 (6) 放置在夹紧装置 (4) 内会导致过度定位。由于在该装置中定位面(1)和(3)之间的距离是恒定的,因此各个工件之间的尺寸c不同。因此,这种过度定位会引起加工误差。
To prevent bending the b-c rib while machining the piece, a third reference plane (3) is introduced. Placing a workpiece (6) inside the clamping device (4) causes over-location. Since the distance between the locating planes (1) and (3) is constant in this device, the dimension c differs between individual workpieces. This over-location therefore gives rise to machining error.
图 5c:显示如何正确定位工件。为了避免工件倾斜,从工件 (5) 传递到待加工主体 (6) 的扭矩“M”必须通过适当的反扭矩来平衡。该反扭矩由夹紧力“F”产生。
Figure 5c: Shows how to locate a workpiece correctly. To avoid tilting the workpiece, the torque “M” transferred from the workpiece (5) to the body to be machined (6) must be balanced by an appropriate counter-torque. This counter-torque is created by the clamping force “F.”
如果工件(图 5)受到太多定位点的限制,也可能会发生过度定位。沿承载表面引入多于三个定位点、或在引导平面中引入多于两点、或在支撑平面中引入多于一点可能会导致不期望的工件运动,从而对最终产品的精度产生不利影响。任何额外的支撑点都必须是可调节的。
Over-location may also occur if a workpiece (Figure 5) is limited by too many locating points. The introduction of more than three locating points along the bearing surface, or more than two points in the guide plane, or more than one point in the supporting plane may lead to undesirable workpiece motion, and thus adversely affect the precision of the resulting product. Any additional support points must be adjustable.
如果必须支撑待加工的工件以避免偏转,则所有其他支撑点必须定义为变量,并且必须根据正在加工的工件来确定。
If the workpiece to be machined must be supported to avoid deflection, then all other bearing points must be defined as variables and must be determined in relationship to the workpiece being machined.
选点过程须遵守许多设计准则,但也可能有例外。
• 务必根据工件的预加工情况安排定位点。先前加工的点优先作为所需的定位点。
• 定位平面上的定位点应尽可能远离。
• 布置夹紧点,以便在夹紧过程中保留定义的位置。
• 定位点应与夹紧点一致,以缩短工件内部的力矢量。可以使用三个、两个甚至一个夹紧来将工件夹紧在定位平面上。
• 精密表面不应保持在连续表面上,这样可以避免“无限”数量的接触点。
The location process is subject to a number of design guidelines, but exceptions are possible.
• Always arrange the location points according to the pre-machined condition of the workpiece. Previously machined points have priority as desirable locating points.
• The locating points on the locating plane should be as far away from each other as possible.
• Arrange the clamping points such that the defined position is retained during clamping.
• The locating points should be in line with the clamping points to shorten the force vectors inside the workpiece. Three, two, or even one clamping point may be used to clamp a workpiece against the locating plane.
• Precision surfaces should not be held on a continuous surface, so that an “infinite” number of contact points can be avoided.
3 夹紧 / Clamping
术语“夹紧”是指将已定位的工件牢固地紧固在夹紧装置中以用于加工目的。定位和夹紧可以被视为组合操作。
夹紧总是与通过装置的力传递相关。力矢量应尽可能描述从夹紧力的施加点穿过工件到支承点的直线。
The term “clamping” refers to the secure fastening of an already positioned workpiece in a clamping device for machining purposes. Locating and clamping may be viewed as a combined operation.
Clamping is invariably associated with force transmission through the device. The force vector should, as far as possible, describe a straight line from the application point of the clamping force through the workpiece to the bearing points.
与夹紧一样,定位也遵循许多设计准则,但也可能有例外:
• 保持夹紧力矢量远离工件上的关键公差区域。
• 应避免或尽量减少由于夹紧力造成的工件变形和划痕。
• 应选择工件上的夹紧点,以便无需重新夹紧即可加工工件,或者,如果不可行,则应尽量减少重新夹紧。
• 所需的夹紧力应通过粗略估计得出。
• 由于加工时产生的热膨胀和振动,工件的夹紧尺寸可能会发生变化。
• 仅当工件由坚固的支撑点适当支撑时,才应承受夹紧力,如图 6 所示。
As with clamping, locating is subject to a number of design guidelines, although exceptions are possible:
• Keep the clamping force vector away from the critical tolerance zones on the workpiece.
• Workpiece deformation and marking due to clamping forces should be avoided or minimized.
• The clamping points on the workpiece should be selected so that the piece can be machined without reclamping or, if this is not feasible, with a minimum of reclamping.
• The required clamping forces should be approximated by rough estimations.
• The clamping dimensions of the workpiece may change due to thermal expansion and vibration resulting from machining.
• The workpiece should only be exposed to a clamping force if it is appropriately supported by a solid bearing point, as illustrated in Figure 6.
由于振动和热膨胀的影响,夹紧工件的尺寸可能会发生变化。两种类型的夹紧可以补偿这些变化。
• 机械夹紧
• 液压夹紧
The dimensions of clamped workpieces may change due to vibrations and the effects of thermal expansion. Two types of clamping may compensate for these changes.
• Mechanical Clamping
• Hydraulic Clamping
图 7(机械夹紧)中的插图表明,随着夹紧区域中工件尺寸的变化,张力会得到缓解。
在液压夹紧中,夹紧工件的夹紧元件会根据变化进行调整,同时保持恒定的夹紧力。如图 8 所示,其中工件由于加工过程中温度升高而被拉长。
The illustration in Figure 7 (mechanical clamping) demonstrates that tension is relieved as the dimensions of the workpiece in the clamping area change.
In hydraulic clamping, the clamping elements gripping the workpiece adjust to changes while maintaining a constant clamping force. This is illustrated in Figure 8, where the workpiece is elongated due to temperature increases during machining.
机械夹紧是通过使用以下机械夹紧元件来完成的:
• 夹紧杆
• 夹紧弹簧
• 夹紧螺母
• 夹紧螺栓(图 7)
Mechanical clamping is accomplished by using the following mechanical clamping elements:
• Clamping Bars
• Clamping Springs
• Clamping Nuts
• Clamping Bolts (Figure 7)
液压夹紧是通过以下方式实现的:
• 弹性介质
• 空气夹紧(气动夹紧)
• 液体夹紧(液压夹紧)
Hydraulic clamping is achieved by:
• Elastometric media
• Clamping with air (pneumatic clamping)
• Clamping with liquids (hydraulic clamping)
机械夹紧元件通常用于简单的夹紧装置。然而,通过在夹紧元件和工件之间插入气缸,可以将机械夹紧元件转换为液压夹紧元件。此外,机械元件也可以与液压夹紧元件相结合。
夹紧可能会出现误差,导致被夹紧的工件变形。由于此类变形不得影响工件的功能,因此应考虑所有可想到的定位和支撑技术,以及夹紧力通过工件的最佳可能定向传递。
建议估算夹紧力,以防止夹紧力过高和工件可能变形。还可以通过为夹紧点和定位点选择合适的形状(例如球形)来避免工件的变形。
Mechanical clamping elements are usually used for simple clamping devices. However, mechanical clamping elements may be converted to hydraulic ones by inserting cylinders between the clamping element and the workpiece. In addition, mechanical elements may also be combined with hydraulic clamping elements.
Clamping may be subject to errors that cause deformation of the clamped workpiece. Since such deformations must not affect the function of the workpiece, all conceivable locating and supporting techniques, as well as the best possible directed transmission of the clamping force through the workpiece, should be considered.
It is recommended that clamping forces be estimated to prevent excessively high clamping forces and possible deformation of the workpiece. Deformation of the workpiece may also be avoided by selecting a suitable shape (for example, a sphere) for the clamping points and the locating points.
4 支撑工件 / Supporting the workpiece
4.1 支撑工件 / Supported workpiece
工件需要支撑以确保刀具、工件和夹紧装置之间的功能性力传递,和/或保护工件免受由于加工力、重力而变形(例如在薄横截面的点处的偏转)和夹紧力。工件支撑还可以消除由此产生的加工误差(图 9)。
此外,通过使用更佳的支撑机构,可以提高表面质量并延长工具的使用寿命。然而,工件的三维位置不应由其支撑来定义。它依次位于定位进程之前,并且优先级也较低。
The workpiece requires support to ensure functional force transmission between the tool, the workpiece, and the clamping device, and/or to protect the workpiece from deformation (such as deflection at points with a thin cross-section) due to machining forces, gravitational forces, and clamping forces. Workpiece support also acts to eliminate the resulting machining errors (Figure 9).
In addition, surface quality may be improved and the service life of the tool prolonged with the use of an optimum supporting mechanism. The three-dimensional position of a workpiece, however, should not be defined by its support. It is preceded sequentially by the locating process and also has a lower priority.
4.2 弯曲工件的支撑选项 / Supporting options for bent workpieces
a. 未夹紧的工件
b. 夹紧工件
c. 加工工件
a. Unclamped workpiece
b. Clamped workpiece
c. Machined workpiece
即使工件必须由超过理论定位点数量的频繁移动和可变元件支撑,工件也被认为是受到支撑的。一个例子是容易振动的不稳定工件。
当变形工件必须在所有三个平面上保持和夹紧而不改变其形状时,可以使用涉及自调节球面的技术。在这种情况下,轴承表面、紧公差螺栓、限位器以及可垂直调节的支撑和夹紧元件必须配备球面。
A workpiece is considered to be supported even if it must be supported by frequently mobile and variable elements surpassing the theoretical maximum number of locating points. An example of this would be an unstable workpiece that easily vibrates.
When a deformed workpiece must be held and clamped in all three planes without altering its shape, it is possible to use a technique involving selfadjusting spherical surfaces. In this case the bearing surfaces, the close-tolerance bolts, the limit stops, and the vertically adjustable supporting and clamping elements must be equipped with spherical surfaces.
图 10 中的图示说明了两种不同的夹紧方法。它显示了传统夹紧引起的工件变形(图 10a)。由于这种变形,工件的表面区域在松开时表现出更大程度的变形。
The illustrations in Figure 10 illustrate two different clamping methods. It shows deformation of a workpiece caused by conventional clamping (Figure 10a). As a result of this deformation, the surface area of the workpiece exhibits a greater degree of deformation when unclamped.
这种凸形变形可能是由于一旦夹紧压力释放,工件就呈现其原始变形形状(c)。
This deformation, which is convex in shape, may be attributed to the fact that the workpiece assumes its original, deformed shape (c), as soon as the clamping pressure is released.
图 10b 所示的夹紧点呈球形,因此可以很大程度上适应工件曲率 (b)。因此,加工表面是平坦的,工件仅承受可能通过加工释放的内应力。
The clamping points illustrated in Figure 10b are spherically shaped, and can therefore largely adapt to the workpiece curvatures (b). The machined surface is therefore fl at, and the workpiece is only exposed to possible internal stresses that may be released by machining.
4.3 锁模力的确定 / Determination of the clamping force
重要的是要确保夹紧在设备内的工件不会因夹紧力和随后的切削力作用而从其位置移动。通过向设备的实心轴承表面施加夹紧力,可以较大限度地减少这种移动风险(图 11)。
It is important to ensure that a workpiece that is clamped inside a device is not moved from its position by the clamping force and the subsequent action of the cutting force. This risk of movement may be minimized by applying the clamping force to the solid bearing surfaces of the device (Figure 11).
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