Since the introduction of computer-controlled CNC machines, machining processes have become much better and more manageable. Manufacturers use these subtractive tools to produce various customized results with less tolerance for error.
In fact, CNC machines meet the two most important quality standards in production machining – precision and accuracy. However, most people use these terms interchangeably, although there are important differences. Therefore, this article investigates the difference between accuracy and precision in production machining in detail.
What is the definition of precision?
Precision is a metric that defines how close two or more results or measurements are to each other. This term is one of the most important terms in machining. In simple terms, machining precision refers to the reproducibility or repeatability of multiple components with similar dimensions during manufacturing.
The importance of precision
Precision machines are of central importance in modern industries, as they directly influence the reproducibility, precision and efficiency of machining. Today, the demand for manufacturing microproducts or components with microfeatures continues to increase rapidly.
Meanwhile, machining these parts in large quantities requires more precise design methods and machining dynamics to meet specified requirements. Therefore, precision in machining operations is important because it reflects the ability of a manufacturing process or machine to consistently reproduce the nearly exact dimensions of the parts produced.
Precision in machining
CNC machines provide a high level of repeatability of measured dimensions while removing excess material, producing parts with tolerances within a small range. However, precision measurements for these parts must be made under the same conditions to avoid unwanted deviations or errors. The higher the precision of the machining tools, the more precise the components produced.
Accuracy vs. tolerances
At the same time, machinists establish standard tolerance limits to account for small variations between parts manufactured on the same machine. More specifically, tolerance refers to the range of deviation allowed between corresponding dimensions of machined parts. In design and manufacturing, standard tolerance limits are often small numbers set by manufacturers based on the function, form, and fit of a part.
Standard tolerances in CNC machining are generally +/- 0.127 mm. Experienced operators set the tightest machining tolerances, even in the range of +/- 0.0254 mm, which is approximately the thickness of a human hair. Maintaining these tight tolerance limits ensures that small differences do not affect the accuracy or functionality of the part.
What is the definition of precision?
This is another common term used for editing. Precision is a metric that defines how close a measured value is to the reference or standard value. To explain this concept in the context of machining: Precision refers to the degree of proximity with which a manufactured part meets the general requirements specified in the design.
In machining, accuracy depends on the tools, the kinematic structure and the type of material or part. A precision machine performs a specific machining process or combination of instructions, such as cutting, drilling, grinding and punching, as intended by the manufacturer or operator.
The importance of precision
For example, if an experienced machinist enters the code into a machine to cut a part with a length of 50 mm, an accurate device will make the exact 50 mm cut without errors. However, it is extremely difficult to obtain or produce the same parts without small differences in certain dimensions such as diameter, width and length of the machined parts.
For this reason, experts use precision-based measurement data to reflect faults in a machine or manufacturing process. Therefore, the smaller the difference between the measurement result of the manufactured part and the required standard, the more accurate the machine tool or manufacturing process will be.
Machining precision
Modern CNC machines are highly accurate for most projects, as some tools, such as CNC mills and lathes, can produce parts with an accuracy of +/- 0.0025 mm. This is equivalent to producing parts as small as a quarter of a human hair. Amazing, right?
In addition, machinists or designers determine the permissible range of deviations of the dimensions of the machined part from the standard. This is particularly important for maintaining the functionality of machined parts that conflict with other components.
Accuracy vs. Tolerances
However, not all parts require maximum precision and tight tolerances as the machining process requires additional costs, setup, inspections and time. For example, manufacturing the parts for a car engine requires a higher tolerance than that of a door handle. In other words, the latter has fewer characteristics in combination with other components of the car, therefore requiring greater tolerance.
In addition to length, width, hole size and other dimensions, surface roughness remains a crucial tolerance factor. Experts define and maintain the tolerance limit of 0.001635 mm for flat and vertical surfaces and 0.003175 mm for curved surfaces. Therefore, precision and tolerance are crucial. It is best when machining processes provide accurate and precise products.
Differences between accuracy and precision in machining
The precision and accuracy of a tool or manufacturing process determine the success of manufacturing machining. However, these two terms are often contrasted or confused when used as a measure of observation error.
Failure to recognize the differences between precision and accuracy can have a significant negative impact on the processing of collected measurement data or the conclusions drawn about the results of various manufacturing processes. Check out the differences between accuracy and precision in editing below:
1. Other description
Precision means the exact agreement of the deviations between the dimensions of the machined parts. Machining accuracy, on the other hand, refers to the closeness of the dimensions of manufactured components to standard specifications.
In simpler terms, good machining accuracy ensures that you can repeatedly produce nearly exact dimensions of machined parts without introducing random errors. On the other hand, good machining precision ensures that manufactured parts meet theoretical standards.
2. Type of error displayed
Accuracy reflects the error of a manufacturing system or tool, while precision measurements help to randomly indicate the error among manufactured components.
3. Number of measurements
To determine machining accuracy, multiple measurements under the same conditions are required. This way you can guarantee the compliance of your results. On the other hand, a single measurement is necessary for machining accuracy. This is because precision measurements only require you to compare the dimensions of the manufactured components with the standard value.
Examples of Accuracy vs. Precision
Accuracy and precision remain largely independent parameters that engineers use to determine the success of a manufacturing operation. Most CNC machines use computer software to maintain programmed dimensions when designing and manufacturing a part. Regardless, the outcome of a manufacturing process can occur in different ways:
- Precise and accurate
- Not necessary, but necessary
- Accurate but not exact
- Not precise and not accurate
Therefore, it is important to differentiate these parameters and collect measurements separately to ensure high-quality machining. Below are some analogies or practical examples to help you better understand the concept of precision and accuracy in machining parts:
1. Precise and accurate
In general, all manufacturing industries want to produce accurate and accurate parts for their customers. For example, let's say a manufacturer gives instructions to drill a hole in a bar, 70mm from the edge, with a tolerance of +/- 1mm. When the CNC machine drills holes in varying lengths between 69mm and 71mm for all batches of bars, this manufacturing process is precise and exact.
2. Not necessary, but necessary
Some parts are precision machined, but not all manufactured components are precision products. For example, an engineer wants to make a piston compression with a height of 1.2 inches and a tolerance of +/- 0.005 inches.
Suppose that some pistons are manufactured with heights between 1.195 and 1.205 inches, while other pistons in this production batch have heights below or above the tolerance limit. It can be concluded that this manufacturing process is accurate, but its quality controls are not accurate.
3. Accurate but not exact
In this case, the machine parts have similar dimensions, but do not come close to the required dimensions. From the previous analogy, the manufactured piston parts have heights of 1.21, 1.22, 1.21, and 1.215 inches. So, quality checks show that this manufacturing process is precise, but not exact, as the allowable tolerance limit is +/- 0.005 inches.
4. It is not necessary and not necessary
Errors can occur in some manufacturing processes, causing finished parts to be considered inaccurate and inaccurate. For example, if a mechanic wants to produce a plastic part with a length of 20 mm and a tolerance of +/- 0.5 mm, the plastic parts produced can have different lengths of 18 mm, 22 mm, 19 mm, 17 mm and 21 mm . mm.
This measurement result shows that the dimensions of the plastic parts manufactured in this batch do not exactly match and also deviate significantly from the required dimensions. It can be concluded that this production batch is inaccurate and inaccurate.
Benefits of accuracy and precision in parts production
The success of any manufacturing industry depends on its ability to consistently produce accurate and accurate parts. Therefore, CNC machines are now used in various manufacturing industries due to their relatively high precision and accuracy. This includes automotive, medical, construction, electrical, aerospace, oil and gas, marine, etc. Here are some benefits of accuracy and precision in part manufacturing:
1. Security considerations
Without a doubt, safety remains one of the most important factors to consider when manufacturing parts. This is especially true for aerospace and medical devices that require highly precise and precise components. If these components are defective or not manufactured to industry standards, it could put users in danger. Therefore, producing accurate and precise parts attracts customers and at the same time ensures their safety.
2. Smooth Testing and Prototyping
High machining accuracy and precision enable easier prototyping of various designs and parts, including complex titanium machining operations. Additionally, automated machining helps reduce the cost of labor-intensive work while ensuring high-quality parts. Furthermore, precision and accuracy in machining help ensure continuous performance testing of the machined part.
3. Easier Device Calibration
CNC machines consist of high-precision, high-precision computer-controlled devices that allow manufacturers to easily adjust or calibrate various tools. Machines also store manufacturing instructions until machinists enter new codes to make a different part or make certain changes.
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Concluding
High precision does not necessarily mean high accuracy, so a distinction must be made between these two parameters. Therefore, we are sure that you now better understand the differences between the terms accuracy and precision in CNC machining. Understanding these terms will help you identify important specifications and compare them to your requirements to get the best results.
Common questions
Why are accuracy and precision important in machined parts?
Accuracy and precision are critical aspects of machining operations, especially for prototypes and end-use parts. Precision is important to ensure that machined parts have the required dimensions and designs without errors affecting mechanical function. Likewise, precision machining ensures that the parts produced have consistent production values.
Which manufacturing process has the highest machining precision?
In short, the CNC micromilling process has higher machining precision than other traditional CNC machine operations. This micromilling process uses computer programs to control and direct multipoint rotary cutting tools to remove excess material. These automated processes deliver precisely customized products or parts, but they are expensive and time-consuming.
What is precision tolerance?
Precision tolerance is the allowable degree of variability that limits or controls measurement error. During manufacturing machining, manufacturers set precision tolerances for each batch of components manufactured to ensure that variations do not affect key specifications.
