CNC Precision Machining: Tolerances, Processes, Types, and Applications
Automotive parts, medical implants, defense equipment parts, and many other applications require tight functional tolerances, often as low as ±0.001 inch. Standard machining methods cannot achieve this level of accuracy. This is where the power of CNC precision machining comes into play. For those of you unfamiliar with manufacturing, CNC precision machining is a manufacturing process that utilizes computer programs to create any product to precise specifications.
So this article aims to introduce the process, equipment, materials, advantages and applications of precision CNC machining. If you are interested in learning more about CNC precision machining, read to the end.
1.What is CNC precision processing?
CNC precision machining involves shaping raw materials into finished products by cutting away excess portions specified by computer-aided design (CAD) or computer-aided manufacturing (CAM) blueprints. Automation of tool movement provides tighter tolerances than traditional machining methods, with precision machining typically involving ±0.1 to 0.2 mm tolerances.
2.Common types of tolerances in CNC processing
(1)Standard tolerance
Machinists often adhere to standard CNC tolerances for commonly manufactured parts. This includes specific accuracy for elements such as threads, pins and pipes, with many milling services offering international standards of around +/-0.1mm. For a full explanation, see the detailed CNC machining chart.
(2) Bilateral Tolerances
When bilateral tolerances are used, the deviation from a given dimension can be negative or positive, allowing the part to be slightly larger or smaller than specified. For example, +/- 0.06mm means that the machined part can be 0.06mm shorter or longer than the specified measurement. Such specifications usually apply to external dimensions.
(3) Geometric Dimensioning and Tolerancing
GD&T tolerances are more thorough than other machining tolerance systems. It highlights the measured value and the allowable deviation. It also outlines the specific geometric features of the machined part, such as its flatness, concentricity and true position. GD&T tolerances are often used for parts with extremely precise dimensions.
(4) Unilateral Tolerances
Unilateral tolerances allow deviation in only one direction, either positive or negative. For example, a tolerance specified as +0.00/-0.06mm means that the finished part can be up to 0.06mm smaller than the specified measurement, but no larger. This tolerance is often used in designs where a part must be installed into another component, and it is critical to ensure that the part does not exceed the specified size.
(5) Limit tolerance
The limit tolerance is expressed as a range of values, and as long as the measurement falls within this range, the part is good. For example, 13 – 13.5mm is the limit tolerance for CNC machining, indicating that the size of the part must be between the upper and lower limits (13mm is the upper limit and 13.5mm is the lower limit).
3.CNC Precision Machining Process Guide
(1) Design and CAD Modeling
CAD software is one of the most basic software in CNC machining, used to draw and design three-dimensional models or two-dimensional drawings of parts. After determining the final requirements, engineers or designers will create a detailed 3D engineering design that contains dimensions, tolerances, features, proportions and other information. Provides a basis for subsequent processing and manufacturing.
(2) CAM and CNC programming
CAM software is another important software in CNC machining, which is used to convert CAD models into command codes (G-code) that machine tools can recognize and execute. CAM software generates cutting paths, tool paths, cutting parameters and other information based on the geometric information of the part and the machining requirements. This process is also called CNC programming, and these codes can be read by CNC precision machines.
(3) CNC machine tool setting
Accurate CNC machine tool setting involves two main tasks: tool setting and workpiece clamping. First, the operator installs the tool in the collet or tool holder and mounts the workpiece on the machine tool bed or chuck. At this stage, the correct tool selection (end mill, face mill, drill, etc.) and stable clamping of the workpiece and tool are crucial to the final accuracy.
(4) Machining parts
The machine establishes a connection with the control system to process the operating instructions. This is the actual machining stage, and the operator can manually adjust parameters such as spindle speed, cutting speed, depth, feed rate, and set various machining instructions and process parameters. At the same time, fine-tuning parameters through testing can help produce parts that meet precision requirements.
(5) Post-processing and finishing
This is the last and most important step in CNC precision machining. The post-processing process includes cleaning, deburring, polishing, surface treatment and other links, each of which directly affects the final quality and service life of the parts. The selection of post-processing methods should be based on different metal materials, part shapes and usage requirements.
For example, for aluminum alloy parts, anodizing, sandblasting, spraying and other methods can be used for surface treatment to enhance their corrosion resistance and aesthetics; for stainless steel parts, electroplating, polishing and other processes can be selected to improve their surface finish and hardness. Different combinations of post-processing methods can achieve different effects and meet customers’ different requirements for part quality.
4.Types of precision CNC machining equipment
Due to the different processes involved in CNC precision machining, different equipment is required to make it work.
(1) CNC milling machine
Milling is a precise machining process that involves using a rotating tool to remove excess material from a workpiece. It involves several types of factories. Examples of such milling cutters include end mills, chamfer mills, and spiral mills. CNC-enabled milling machines also include manual milling machines, surface milling machines, universal milling machines, and universal milling machines.
(2) CNC lathes
Turning is a precision CNC machining process that involves rotating a workpiece next to a rotating single-point cutting tool. The most popular tools used for turning are lathes, such as turret lathes, engine lathes, and engine-specific lathes. Other turning equipment includes straight turning, taper turning, external grooving, threading, etc.
(3) CNC drilling equipment
Drilling is a precision machining process that uses a rotating multi-point drill bit to form a cylindrical hole in the raw material/workpiece. In addition, the drill bit is designed to keep the chips off the workpiece, leaving the drilled hole clean.
(4) CNC discharge mining equipment
Discharge mining is a precision machining process that uses electrical discharge (sparks) to obtain a finished product.
The device consists of a tool electrode (tool) and a workpiece electrode (workpiece) separated by a dielectric fluid and subjected to a voltage. The process is also known as spark machining, spark erosion, burning, die sinking or wire erosion.
5.Main Applications and Industries of CNC Precision Parts
Due to its versatility, cost and time efficient process, precision machining has gradually taken a leading position in the manufacturing industry. Precision machining processes are used in the following industries:
6.Conclusion
CNC precision machining can be said to be the most effective way to manufacture custom parts. In addition to saving you money, it takes very little time and allows little room for error. Incorporate this manufacturing process into your production today!