What factors will affect the accuracy in machine tool processing?

 What factors will affect the accuracy in machine tool processing?

On the road of machine tool processing, all companies are committed to making their products infinitely close to zero error, but the ideal is full, the reality is always very skinny, in the actual processing process, the accuracy of the machine tool will be more or less The impact of various internal and external factors. The forming motion of the tool relative to the workpiece during machining is generally done by the machine tool. Therefore, the machining accuracy of the workpiece depends to a large extent on the accuracy of the machine tool. Machine tool manufacturing errors have a great influence on the machining accuracy of the workpiece: spindle rotation error, guide rail error and drive chain error. And if the machine tool is worn, it will further reduce the working accuracy of the machine.

The first thing to mention is the spindle rotation error. Anyone who is engaged in machining knows that the machine tool spindle is the reference for clamping workpieces or tools, and transmits motion and power to the workpiece or tool. Therefore, the spindle rotation error will directly affect the accuracy of the workpiece being machined. The spindle rotation error refers to the amount of variation of the actual rotation axis of the spindle at each instant relative to its average rotation axis. It can be decomposed into three basic forms: radial circular runout, axial turbulence and angular swing.

What factors will affect the accuracy in machine tool processing?

The main reasons for the spindle radial rotation error are: the coaxiality error of the spindles of the spindle, various errors of the bearing itself, the coaxiality error between the bearings, and the spindle winding. However, their influence on the radial rotation accuracy of the spindle varies with the processing method.

For example, when turning the outer circle on a lathe with a sliding bearing structure as the main shaft, the direction of action of the cutting force F can be considered to be substantially constant. Under the action of the cutting force F, the main journal has different parts and the inner diameter of the bearing. When a certain fixed part is in contact, the roundness error of the main journal has a great influence on the radial rotation precision of the main shaft, and the roundness error of the inner diameter of the bearing has little effect on the radial rotation accuracy of the main shaft; Since the direction of action of the cutting force F rotates with the rotation of the main shaft, under the action of the cutting force F, the main shaft always contacts a different part of the inner surface of the bearing with a certain fixed portion of the journal, and therefore, the inner surface of the bearing The roundness error has a great influence on the spindle radial rotation accuracy, while the spindle neck roundness error has little effect.

Different machining methods, the machining error caused by the spindle rotation error is also different. When the outer circle and the inner hole are machined on a lathe, the radial rotation error of the spindle can cause roundness and cylindricity error of the workpiece, but there is no direct influence on the end face of the workpiece. The axial rotation error of the spindle has little effect on the machining of the outer circle and the inner hole, but it has a great influence on the perpendicularity and flatness of the machined end face. In the case of a thread, the main axial rotation error can cause a periodic error in the lead of the thread being machined. Appropriately improve the manufacturing precision of the spindle and the box, select high-precision bearings, improve the assembly accuracy of the spindle components, balance the high-speed spindle components, and pre-tension the rolling bearings to improve the rotation accuracy of the machine tool spindle.

What factors will affect the accuracy in machine tool processing?

Followed by the guide rail error, the guide rail is the benchmark for determining the relative positional relationship of each machine tool component on the machine tool, and is also the benchmark for machine tool motion. The accuracy requirements of the lathe guide mainly have the following three aspects: straightness in the horizontal plane, straightness in the vertical plane, and parallelism of the front and rear rails (twist).

In addition to the manufacturing tolerances of the guide rail itself, the uneven wear and installation quality of the guide rail is also an important factor in the guide rail error. Rail wear is one of the main reasons for the decline in machine accuracy. In addition, the transmission chain error refers to the error of the relative motion between the transmission components at the beginning and the end of the transmission chain, which is generally measured by the angular error of the end components of the transmission chain.

It is worth mentioning that the geometric error of the tool has a great influence on the machining accuracy. The influence of the tool error on the machining accuracy varies with the type of the tool. When the tool is formed by a fixed-size tool, the manufacturing error of the tool is changed. It will directly affect the machining accuracy of the workpiece; for general tools (such as turning tools), the manufacturing error has no direct influence on the machining accuracy of the workpiece.

Any tool in the cutting process inevitably wears out, and thus causes the size and shape of the workpiece to change. Proper selection of tool materials and selection of new wear-resistant tool materials, reasonable selection of tool geometry parameters and cutting amount, correct sharpening of the tool, correct use of coolant, etc., can effectively reduce tool size wear. If necessary, compensation devices can also be used to automatically compensate for tool size wear.

Last but not least, the geometric error of the fixture will also affect the accuracy of the machine. The function of the fixture is to make the workpiece have the correct position corresponding to the tool and the machine tool. Therefore, the manufacturing error of the fixture has a great influence on the machining accuracy of the workpiece (especially the positional accuracy).

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