Workpiece positioning and clamping scheme
The workpiece positioning and benchmarks should be consistent with the design basis, and should be prevented with a workpiece positioning, and the best choice.\" \"one-two sales as a positioning benchmarks in CNC machine tools, benchmarks, and the positioning is carefully to find.
On the CNC lathe workpiece positioning installed with basic principles of ordinary machine tools. The Install method workpiece workpiece impact the processing accuracy and efficiency in order to give full play to the characteristics of their work, and the CNC machine tools folder installed workpiece should take into account the following factors:
1. as far as possible common fixture, only when you must design and manufacture of special fixture;
2. structural design to meet the accuracy requirements; 3. ease of positioning and clamping; 4. cleanup for ease of cutting;
5. resist cutting forces by sufficient rigidity; ·Determine order passes and passes route
The cutting line is the index of controlled processing tool relative to the workpiece and the direction of the trajectory. Reasonable choice of processing route is very important, because it is part of the machining accuracy and surface quality are closely related. In determining the cutting line is the main consideration the following points:
1） Ensure that parts of the request processing accuracy.
2) convenient numerical computation, reduce the programming effort. 3) find the shortest route to reduce processing time in order to improve processing efficiency air knife.
4) minimize procedures paragraph number.
5) Ensure that workpiece contours of the surface roughness after processing the request should be final, ultimate contours go straight sword processing.
6) The dilemma knives knife (entry with all the routes have to seriously consider in order to minimize the contours on the cutting edge knife (elastic deformation caused by sudden changes) and left a knife marks, also need to avoid the contours on surface vertical cutter and workpiece scratch.
Processing arrangements should be based on parts of the structure of the order and stock status and orientation clamp needed to take into account, with a focus on the rigidity of the job is not compromised. Order should be carried out by the following principles:
( 1) the process of processing cannot affect next process among the positioning and Clamping, punctuated by a universal machine tool manufacturing processes should also be integrated into account.
( 2) First-shaped cavity in the process, and then shape processes.
( 3) In the same location, gripping manner or with a knife processing processes, with a view to reducing duplication best connect with positioning, number changer number number plates and sift.
( 4) At the same time that you install in the process, many road arrangements should be first-come-first-served basis to the workpiece rigid undermine small processes. ·Cutting sequence of arrangements:
① first rough after finishing first roughing, semi-finishing intermediate arrangements, final arrangements finishing and polishing.
② After hsien Chu at the first part of the Assembly base and work surfaces, and other major surface processing, arrangements such as keyways, after light and threaded holes for fastening and other minor surface processing. Due to minor surface processing workload small and often has a position with major surface accuracy requirements, it is generally placed after the main surface of the half-finished, done prior to finishing.
③ After the first hole for parts such as box, frame, link, base, machining end surface of the plane and hole used as a location, and then machining holes. This allows the positioning of workpiece clamping is stable and reliable, which guarantees the position accuracy of hole and plane, reducing tool wear and bring convenience to the hole.
④ base to serve as a precision base surface, would be the first to process. So, the first operation is usually positioned surface roughing and semi-finishing (sometimes including finishing), and then to finish the base of location machining other surfaces. For example, the top hole machining of shaft parts.
工件的定位与装夹方案：
工件的定位与基准应与设计基准保持一致，应防止过定位，对与箱体工件最好选择“一面两销”作为定位基准，定位基准在数控机床上要仔细找正。
在数控车床上工件定位安装的基本原则与普通机床相同。工件的装夹方法影响工件的加工精度和效率，为了充分发挥数控机床的工作特点，在装夹工件时，应考虑以下几种因素：
1.尽可能采用通用夹具，必须时才设计制造专用夹具； 2.结构设计要满足精度要求； 3.易于定位和装夹； 4.易于切削的清理； 5.抵抗切削力由足够的刚度； 3.确定走刀顺序及走刀路线：
走刀路线是指数控加工过程中刀具相对于被加工件的运动轨迹和方向。加工路线的合理选择是非常重要的，因为它与零件的加工精度和表面质量密却相关。在确定走刀路线是主要考虑下列几点:
1） 保证零件的加工精度要求。 2） 方便数值计算，减少编程工作量。
3） 寻求最短加工路线，减少空刀时间以提高加工效率。 4） 尽量减少程序段数。
5）保证工件轮廓表面加工后的粗糙度的要求，最终轮廓应安排最后一走刀连续加工出来。
6） 刀具的进退刀（切入与切出）路线也要认真考虑，以尽量减少在轮廓处停刀（切削力突然变化造成弹性变形）而留下刀痕，也要避免在轮廓面上垂直下刀而划伤工件。
加工顺序的安排应根据零件的结构和毛坯状况，以及定位夹紧的需要来考虑，重点是工件的刚性不被破坏。顺序一般应按下列原则进行：
(1)上道工序的加工不能影响下道工序的定位与夹紧，中间穿插有通用机床加工工序的也要综合考虑。
(2)先进行内形内腔加工序，后进行外形加工工序。
(3)以相同定位、夹紧方式或同一把刀加工的工序最好连接进行，以减少重复定位次数，换刀次数与挪动压板次数。
(4)在同一次安装中进行的多道工序，应先安排对工件刚性破坏小的工序。
4.切削加工顺序的安排：
①先粗后精 先安排粗加工，中间安排半精加工，最后安排精加工和光整加工。 ②先主后次 先安排零件的装配基面和工作表面等主要表面的加工，后安排如键槽、紧 固用的光孔和螺纹孔等次要表面的加工。由于次要表面加工工作量小，又常与主要表面有位 置精度要求，所以一般放在主要表面的半精加工之后，精加工之前进行。
③先面后孔 对于箱体、支架、连杆、底座等零件，先加工用作定位的平面和孔的端面，然后再加工孔。这样可使工件定位夹紧稳定可靠，利于保证孔与平面的位置精度，减小刀具的磨损，同时也给孔加工带来方便。
④基面先行 用作精基准的表面，要首先加工出来。所以，第一道工序一般是进行定位面的粗加工和半精加工(有时包括精加工)，然后再以精基面定位加工其它表面。例如，轴类零件顶尖孔的加工。
Workpiece positioning and clamping scheme
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