The accuracy and efficiency of CNC machining is affected by a number of factors, such as the physical properties of the material, the structure and accuracy of the machine tool, the material and shape of the cutter, and the setting of the machining parameters.
The reasonable combination and optimization of these factors can improve the precision and efficiency of CNC machining, enabling higher quality and more efficient machining.
Factors affecting the accuracy and efficiency of CNC machining
1. Reverse bias — Main influencing factor
Occurs when a cutting tool of a machine deviates from its programmed path due to excessive speed or force, which means that the cutting tool will not move as predicted and different parts of the machined workpiece may have different accuracies.
Reverse bias causes parts manufactured on CNC machines to deviate from their expected dimensions and tolerance limits, which leads to the wear of cutting tools and a significant reduction in productivity due to scrap and longer machining times.
To ensure optimum performance, operators need regular inspections and scheduled maintenance, such as lubricating linear motion guides or replacing worn spindles, which helps prevent problems at their source.
By using precise cutting paths and spindle speeds also minimizes vibration, which can lead to reverse bias with increasing time.
2. Wrong part position
It refers to the deviation of the actual surface and axis position relative to the ideal position, which is mainly caused by the transmission gap of the machine tool and the elastic deformation of the parts as well as the friction of the machine head.
These include, as examples, angular and distance errors in part positioning, uneven pressure on the part during clamping or loading, misalignment of tool holders and spindles, and incorrect part measurements.
Besides these factors, environmental conditions can also lead to wrong part location.
In an open-loop system, the effect of such positional error on machining accuracy is significant. However, in a closed-loop system, it depends mainly on the accuracy of the moving detection device and the amplification factor of the system, so the impact is generally not too great.
The accuracy of a CNC machined part will be affected when a part location error occurs. The shape of the object being machined will also be affected due to the incorrect angle or distance that prevents the part from being mounted correctly.
As a result, the efficiency of the CNC machining process is greatly reduced when there is an error in part location.To minimize part location errors, manufacturers must ensure that all parts and tools are correctly positioned before the machining process begins. It is also important to check for any environmental factors that may affect the accuracy of the process, for example, vibration or uneven temperatures in the working environment.
With proper positioning and maintenance, manufacturers can minimize part placement errors and ensure the accuracy of CNC-machined parts.
3. Thermal deformation of machine tools — An important factor
Heat distortion can affect machining accuracy in many different ways. Changes in the environmental temperature of the workshop, the heat generated by motor operation and mechanical movement, cutting heat, cooling medium will cause uneven temperatures in various parts of the machine tool, which will lead to a change in the shape accuracy and machining accuracy of the machine tool.
In an environment of constantly changing temperatures, machine tools consume energy during operation, a large portion is converted to heat, which causes physical changes in the various components of the machine tool.
Machine tool designers should be aware of the temperature distribution rules, and take measures to minimize the impact of thermal deformation on machining accuracy.
4. Positioning errors of machine tools
It has a great influence on the accuracy of the parts, and the feeding system of the machine tool is the main point that affects the positioning accuracy.It usually consists of a mechanical drive system and an electronic control system, and the positioning accuracy is related to the structural design of the mechanical drive system.
In the open-loop system, the machining accuracy of the CNC machine tool will be greatly affected due to more influencing factors and more complicated situation, which leads to the impossibility of positioning monitoring. However, in closed-loop systems, CNC machine tools can usually avoid positional deviations of the main components in the system by using positioning detection devices.
5. Fixtures deviation
The role of the fixture is to make the workpiece correctly positioned in relation to the cutters and the machine tool, so the error of the fixture will have a great impact on the machining error (especially the positional error). When selecting and designing fixtures, the structure and material properties of the fixture should be considered in order to minimize the geometric error of the fixture.
In practical application, fixture installation can also cause some deviation, so special attention should be paid to the accuracy control of the fixture in the manufacturing and installation process. In addition, the maintenance and care of the fixture is also very important, it is necessary to regularly check the working condition of the fixture. At the same time, clean and lubricate the fixture to ensure the normal operation of the fixture.
Strategies to improve the precision and efficiency of CNC machining
1. Reduce single-piece manufacturing time
1) Reduce time by increasing the amount of cut, cutting speed, feed rate and return stroke.
With the appearance of new tool materials, cutting speeds have been rapidly increased.
2) Use multi-part machining. Reducing the cut-in and cut-out times of the tool or making the
times coincide, thus shortening the time for machining each part and increasing productivity.
3) Reduce machining allowances. With precision casting, precision forging and other advanced
technologies, we can improve the blank manufacturing accuracy, reduce machining allowance, and shorten the time, which can greatly improve the production efficiency.
2. Minimize thermal deformation of process systems
Heat treatment technology is an important means of obtaining excellent properties for various metal materials. In many practical applications, the rational selection of materials and various molding processes cannot meet the various properties of metal workpieces, so the heat treatment process is essential.
The thermal error of a machine tool depends on cutting speed, feed, machining time and environmental temperature. To reduce the thermal deformation of the process system, it is necessary to control the machining process by adjusting parameters such as cutting speed and feed. At the same time, stabilize the temperature of the machine’s working environment to improve machining accuracy and the quality of the workpiece.
3. Decrease tool wear and deformation
When tools are in optimal condition, they last longer and work better. There are several ways to minimize wear.
First, choose predictive maintenance if possible.First, choose predictive maintenance if possible. Predicting when to perform maintenance tasks on CNC machining equipment reduces unnecessary maintenance and prevents unplanned downtime due to machine failures. Always check the condition of tools, filters and spindles when performing any scheduled maintenance. This is because these pieces may need to be replaced frequently if you use the unit frequently.
Another way is to choose a harder tool if possible. If the option is to machine the part with a softer tool, it will wear out faster. It is a more cost effective way to get a more accurate machining by keeping tools sharp.
Finally, improve the accuracy of parts and bearings. It requires precise machining of critical parts such as case support holes and spindle journals, as well as measuring and adjusting the radial runout range of the corresponding parts to minimize errors.
4. Control original errors in CNC machine tools
In the process of CNC machine tool machining, it is inevitable that there is an error between the machined part and the CNC machine tool, and this error is called the original error.
To control the original error of CNC machine tools, it is necessary to develop appropriate improvement measures according to the causes and types of errors. For example, minimize positioning errors by proper selection of tools and fixtures.
5. Design the core components of the machine reasonably
The core components that affect the positioning accuracy of a machine tool include the feed system, guideway, table and more. When designing a CNC machine tool, it is necessary to select the core components correctly.
The complexity of the part design and the number of sides the machine works on can affect the speed, precision and accuracy of the work, and one of the fastest ways to increase the speed and accuracy of CNC machining is to upgrade to a 5-axis machine.
Summary
Improving the accuracy and efficiency of CNC machining requires a combination of several factors. When selecting machine tools, cutting tools and materials, high quality equipment and easy-to-machine materials should be prioritized. During the machining process, cutting parameters and machining paths need to be rationally selected, and suitable cutters need to be chosen.
By comprehensively considering all these factors and adopting appropriate enhancement strategies, the precision and efficiency of CNC machining can be effectively improved, so that product quality and productivity can be enhanced.
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