In mechanical transmission, rotary motion becomes reciprocating linear motion or linear motion becomes rotary motion, which is usually completed by eccentric shaft or crankshaft. For example, the lubrication pump driven by the eccentric workpiece in the lathe headstock, the crankshaft in an automobile engine, etc. Their processing principle: mainly takes measures in clamping, that is to find the axis of the eccentric part to be processed to coincide with the rotation axis of the lathe spindle.
The method of eccentric turning should adopt different clamping methods according to the different quantity, shape and accuracy requirements of workpieces, but the axis of the eccentric part to be machined should coincide with the rotation axis of the lathe spindle. There are seven common clamping methods for CNC turning eccentric parts.
Turning eccentric workpiece with four jaw single action chuck
This method is suitable for the eccentric workpieces with small eccentricity, low precision, short length and small quantity.
The alignment steps are as follows:
① Put the finished work piece on the four jaw chuck. During clamping, first adjust the two claws of the chuck to make them in an asymmetric position, the other two claws in a symmetric position, and the eccentric circle line of the workpiece is in the center of the chuck (see right of figure B below)
② Place the small flat plate and needle plate on the bed surface, align the needle tip with the eccentric circle line, and correct the eccentric circle. Then, align the tip of the needle with the horizontal line of the outer circle, as shown in the left of figure B above, and check whether the horizontal line is horizontal from left to right. Turn the workpiece 90 ° and check another horizontal line with the same method, then tighten the clamp and recheck the clamping condition of the workpiece.
③ After the workpiece is calibrated, tighten the four claws again to cut. In the initial cutting, the feed rate should be small and the cutting depth should be shallow. After the workpiece is rounded, the cutting amount can be appropriately increased, otherwise the turning tool will be damaged or the workpiece will be displaced. (c) left:
Turning eccentric workpiece with three jaw self centering chuck
This method is suitable for machining eccentric workpieces with large quantity, short length, small eccentricity and low precision. When clamping the workpiece, first turn the outer circle of the non eccentric part of the eccentric workpiece, then pad a pre selected thickness gasket between any claw of the chuck and the joint surface of the workpiece, correct the generatrix and eccentricity, and clamp the workpiece before turning.
Measurement and inspection of eccentric workpieces: when adjusting and correcting the side bus and eccentricity of workpieces, it is mainly carried out on the lathe with a dial indicator with a magnetic meter seat (right in the figure above (c)). Turning can only be carried out after meeting the requirements. After the workpiece is finished, the final inspection is needed to determine whether the eccentricity meets the requirements. The method is to put the workpiece into the V-shaped iron, measure it at the eccentric circle with a dial indicator, rotate the workpiece slowly and observe its runout.
Turning eccentric workpiece with double chuck
This method is suitable for machining eccentric workpieces with short length, small eccentricity and large quantity. The eccentricity should be adjusted before machining. The tube thread lathe is first clamped on the three jaw self centering chuck with a well processed mandrel. I Masa; the pipe thread lathe then adjusts the four jaw single acting chuck, which shifts the center of the spindle center to the eccentricity of a workpiece; the tube thread lathe dismantling the mandrel can clamp the workpiece to process. The advantage of this method is that the eccentricity of a batch of workpieces only needs to be corrected once, but the disadvantage is that two chucks overlap and the rigidity is poor.
Turning eccentric workpiece with flower disc
This method is suitable for machining the workpiece with short length, large eccentricity and low precision. Before machining the eccentric hole, first process the outer circle and both ends of the workpiece to the required position, and then draw the position of the eccentric hole on the end face. Then use the pressing plate to evenly clamp the workpiece on the flower plate, and use the eight pin plate to correct and then press it tightly, then the workpiece can be turned.
Turning eccentric workpiece with eccentric chuck
This method is suitable for machining short shaft, disc, sleeve and other precision partial L-I parts. The pipe thread lathe has the advantages of convenient clamping, guaranteed processing quality, high precision and strong universality.
Turning eccentric workpiece with two centers
This method is suitable for machining long eccentric workpiece. Before machining, the main center hole of the center point and the center hole of the eccentric point should be drawn at both ends of the workpiece, and the center hole should be machined with the pipe thread lathe, and then the turning can be carried out with the front and rear centers. If the eccentricity of the eccentric shaft is small, it may interfere with the main center bar when drilling the eccentric center hole. At this time, the process table can be added, that is, the length of the workpiece is extended to the depth of the two center holes. When the pipe thread is processed by lathe, the blank can be turned into a smooth shaft first, then the center hole at both ends can be turned to the length of the workpiece, and then the eccentric center hole line can be drawn, the eccentric center hole can be drilled, and the eccentric shaft can be turned.
Turning eccentric workpiece with special fixture
This method is suitable for eccentric workpieces with high precision and large batch. Before machining, the corresponding eccentric shaft or eccentric sleeve should be machined according to the eccentricity of the workpiece, and then the workpiece should be centered on the eccentric sleeve or eccentric shaft for turning.