A Complete User Guide to Cnc Machining
CNC Machining Introduction
The CNC Machining usually refers to precision machining under digital control with a computer, including CNC machining lathes, CNC machining millers and CNC machining borers. A Cnc Machine tool, also known as computer-controlled machine tool, is an automatic machine tool controlled by programs.
This control system can logically process programs that have control programming or other symbolic instruction regulations, and uses a computer to decode them, so as to make the machine tool operate and conduct part machining.
Turning or milling with tools are carried out to machine blank materials into semi-finished or finished products.
CNC machining or numerical control machining refers to the machining by using numerically-controlled machining tools. CNC means that the numerically-controlled machine tool is controlled by programming with the numerical control machining language, which is often called G codes.
With G codes for numerical control machining, the machining tool of the numerically-controlled machine tool is told which Cartesian position coordinates are used, the tool’s feed speed and the spindle speed are controlled, and the tool convertor and coolant functions are achieved.
The numerical control machining has great advantages over manual machining. For example, parts can be produced by numerical control machining with high precision and repeatability, and parts with complex outlines which cannot be produced by manual machining can be produced by numerical control machining.
The technologies of numerical control machining have been so popular nowadays that most machining workshops have the capability of numerical control machining.
Typically, in a machining workshop, the most common numerical control machining methods are CNC milling, CNC turning and CNC EDM wire cutting (Electrical Discharge Machining). The tool used for numerical control milling is called a numerical control miller or CNC machining center. The lathe used for CNC turning is called a CNC turning center.
Although manual programming can be carried out with the G codes for CNC machining, usually in a machining workshop the CAD (Computer Aided Design) file is automatically read by the CAM (Computer Aided Manufacturing) software and the G code program is generated to control the CNC machine tool.
How Does the CNC Machining Work?
Modeling and programming are required before CNC machining. The difficulty of 3D modeling depends on the product structure. The modeling of a product with a more complicated structure is more difficult and requires more programming processes that are more complicated.
The programming includes machining process setting, tool selection, rotational speed setting, and the distance of each tool feed. In addition, different clamping methods are used for different products, so the clamp should be well designed before machining.
For some products with complicated structures, special clamps need to be made.
The programming includes the whole product machining process. Although CNC automation is used later, the programming at the early stage must be done by the personnel with rich practical experience, so as to avoid increased cost due to repeated trials.
CNC Machining Process
1）Read the drawing and the program sheet.
2）Transfer corresponding program to the machine tool
3）Check the program heading and cutting parameters.
4）Determine the size and margin for workpiece machining.
5）Clamp the workpiece in a reasonable way.
6）Align the workpiece accurately.
7）Establish the workpiece coordinates accurately.
8）Choose the tool and cutting parameters reasonably.
9）Clamp the tool in a reasonable way.
10）Use a safe method of trial cutting.
11）Observe the machining process.
12）Adjust the cutting parameters.
13）Feed issues back to related personnel timely during machining.
14）Check the workpiece quality after machining.
The History of CNC Machining
The CNC machining center derives from the CNC milling center.
In the late 1940s, the CNC machine tool started to be discussed in USA. The first CNC milling machine was successfully developed in the Servomechanism Lab of Massachusetts Institute of Technology (MIT) in 1952 and put into service in 1957.
The first machining center was successfully developed by a US company Carny-Terek in 1958. It added an active tool change device to a CNC horizontal boring and milling machine and achieved compound machining, including several processes such as milling, drilling, boring, reaming and tapping, with just one-time workpiece clamping. This is a big breakthrough in the development of manufacturing technologies, marking the start of a CNC machining era in manufacturing.
Since CNC machining is the basis of modern manufacturing technologies, this creation has epochal significance and far-reaching influences in the manufacturing industry. Major countries with developed industries all over the world have attached importance to the discussion and development of CNC machining technologies.
Since 1970s, the CNC machining center has developed rapidly and the machining center with replaceable spindle boxes showed up. It has several multi-shaft spindle boxes with tools and the ability of active replacement, so as for multiple hole machining on a workpiece at the same time.
In 1958, China started the research and development of CNC machine tools and successfully manufactured a CNC lathe equipped with vacuum tube CNC system. In 1965, China started mass production of three-coordinate CNC milling machines equipped with transistor CNC system.
After development for dozens of years, computerized control has been achieved on the CNC machine tools nowadays which are widely used in various fields especially including mould making, aerospace accessories, and workpieces with high precision requirements.
In 2001, China Hardware introduced high-precision CNC machining equipment of Hass and DMG from the USA and Germany and has been using it for workpiece machining entrusted by customers from the high-precision industry. By far, China Hardware has provided CNC machining of parts and accessories for companies in most countries with high industrial standards and requirements around the world.
CNC Machining Materials
There are a lot of materials for CNC machining. Different materials are required in different industries and different materials have different performance levels and ranges of application.
The known materials for machining currently include stainless steel such as SUS201, SUS202, SUS304, SUS303, SUS316L, SUS430, SUS310, SUS410, SUS434, super duplex steel, carbon steel, aluminum, titanium alloy, ABS, brass and carbon fiber, as well as plastics such as PVC, POM, PEEK, bakelite plate, ceramic, wood, acrylic, gold, silver, mould steel, rose copper, bronze, tempered glass, tungsten steel and stone.
The above materials have a wide range of application, generally suitable for industries covering aerospace, navigation and shipping, military, intelligent device, electronics, intelligent wear, foundation construction, household appliances, industrial supplies, communications, literature and art, sports equipment, automation equipment, automobile parts, and home building materials.
With 20 years of rich experience on machining of the above materials, China Hardware is capable of carrying out the precision and material level requirement tests for all high-end customers in a very good way.
CNC Machining Procedure
The machining procedure planning is for the whole technological process and cannot be determined based on the nature of a single process or the process of a single surface.
If there is a reference plane problem in positioning, high precision machining is required at the semi-finish machining and full rough machining stage. Sometimes in order to reduce conversion of the dimensional chain, semi-finish machining is possibly required for some minor surfaces at the finish machining stage.
Only after the main process methods and machining stages are determined for part surfaces, the main procedure for each surface can be combined into several steps at a process stage.
How to classify the machining procedures? For the parts machined on a CNC machine tool, the machining procedures are classified by the principle of high process concentration. The following shows several ways of specific dividing.
1. Division by used tool.
The technological processes carried out with the same tool are classified into the same process. This classifying method is especially suitable for the workpiece with a lot of surfaces to be machined. The machining center usually takes this method.
2. Division by the times required for batch assembly of a kind of workpieces.
An assembly procedure is a technological process that can be finished after a part is clamped once. This machining method is also especially applicable to the parts for a minicar without a lot machining with once clamping. On the necessary premise that the quality of finished automobile parts after once machining, the machining of automobile parts can be finished with once clamping.
3. Division by rough machining and finish machining
Take some technological processes completed in the rough machining as one procedure, and some technological processes completed in the fine machining as another. This classification is more suitable for the parts with strength and hardness requirements.
The thermal treatment must be carried out with high precision the requirement for the parts, and the inner stress must be effectively eliminated. Besides, the part changes a lot after machining, so the part machining must be classified based on rough machining and semi-fine machining stages.
4. Division by process position.
Take the technological processes for completing the same model surface as the same procedure.
In order to machine the automobile parts with a lot of complex surfaces, the order of CNC machining, thermal treatment and auxiliary processes should be arranged in a reasonable way, and the connection between processes should also be well handled.
5. Division by manufacturing procedure.
A part has a lot of surfaces, each of which has its own precision requirements. And related precision requirements between surfaces are also needed.
To meet the design precision needs for the parts, necessary principles of proportionality should be followed in arrangement of the process order.
1)Principle of rough machining before fine machining.
Arrange the order of processes for all surfaces as rough machining, semi-fine machining, fine machining and then surface finish machining, so as to improve the precision and surface quality of part machining step by step.
If CNC lathe machining is used for all part surfaces, the process order is rough machining, semi-fine machining and then fine machining. That is, semi-fine machining and then fine machining are carried out after rough machining is all done.
During rough machining, most machining allowances can be removed rapidly, and then fine machining is carried out for different surfaces in proper order. This can greatly improve manufacturing efficiency as well as machining precision and surface roughness for the parts. This method is especially suitable for the workpiece surfaces with high position precision requirements.
Although this is not absolute, if a higher level machining surface is required for some specifications and precision and part characteristics including intensity, shape and size precision are fully considered, the order of rough machining, semi-fine machining and then fine machining can be followed.
For a surface with high precision requirements, it is better to leave the part alone for a long time before fine machining and after rough machining, so that the part surface stress generated after rough machining can be fully relieved. This is to reduce the degree of change of the part surface stress and thus further improve the machining precision of the part.
2)Principle of Reference Plane First
The machining starts with the machining of the surface originally acting as the fine machining basis. Because fine machining was carried out for the surface originally set as the basis with minor clamping errors, during automobile part machining, rough machining and semi-fine machining are required for the datum reference surface first of all.
If necessary, fine machining needs to be done. Therefore, for a axle part, rough machining and semi-fine machining should be carried out on the datum reference surface, and then fine machining is carried out.
For example, for a axle part, the central hole is always made first of all, and then its surface or the fine standard of the positioning hole is followed for a series of holes or other surfaces. If the fine height datum surface is more than once, the datum shift order and the principle of gradual improvement of machining precision must be followed for height datum surface machining.
3)The principle of surfaces before holes is mainly for machining of important mechanical parts such as box structure parts, support structure parts, and frame structure parts.
The outline positioning dimensions on the box plane changes greatly and it is stable and safe for the user to conduct flat outline positioning, so it is more suitable for post-machining of the box’s flat surface and then pre-machining of the box’s hole.
In this way, not only the user’s subsequent positioning workpiece operations can have a stable and safe circle plane structure as the datum plane for workpiece positioning and machining, but also a big group of small holes are unnecessary to make on flat part surfaces.
This allows the process to be simpler and even greatly improves the accuracy of positioning and machining for a small group of big holes. Usually, you can divide the machining processes by a part’s main positions to be machined.
For example, a simple columnar shape of solid geometry is machined before a complicated one, a position with low accuracy requirements is machined before one with high accuracy requirements, and a rectangular flat surface is machined before an elliptical hole.
4)The principle of inside machining before outside machining is for the precision socket spanner which has high requirements of coaxiality between the outer circle and the hole diameter.
Therefore, the machining principle of holes before out circles is usually applied. That is, take the outer circle as the datum reference for inner hole machining and then take the hole diameter with high precision as the datum reference for outer circle machining. Only in this way, high requirements of coaxiality between the outer circle and the hole diameter can be guaranteed, and the clamping structure used can be concise.
Advantages and Disadvantages of CNC Machining
CNC machining has the following advantages
①The times of clamping with tooling are significantly reduced, and no complex tooling is required to machine parts in complicated shape. If you need to change the size and dimensions of a part, just modify the part machining program to fit the new product development and remodeling.
②It has stable machining quality, high machining precision, and high precision repeatability and meets the machining requirements of high precision and exact dimensions.
③For multiple variety and small scale production, it has high production efficiency and can reduce the time for production preparation, machine tool adjustment and process inspection. Besides, the cutting time is also reduced because of the best cutting.
④It can cover complicated surfaces that are too difficult for conventional machining and even some unobservable positions.
Disadvantages of CNC Machining
The CNC machine tool costs a lot and needs high level maintenance which has high requirements of programming and debugging abilities for the CNC technicians. Plus, CNC machining costs more than ordinary manual machining.
3D Printing vs CNC Machining
- The 3D printing is suitable for prototype machining and has advantages for early R&D and samples, while CNC machining has certain limitations. With very low limitations, 3D printing can be used for various prototypes no matter how complicated they are, but the high precision requirement is difficult to guarantee.
- The 3D printing is not for mass production, and CNC machining has a price advantage over the 3D printing.
- Actually, the 3D print is no match for CNC machining as to overall printing, especially the ultra-large structural parts which are difficult to achieve by 3D printing. CNC machining does not have this problem.
- The 3D printing is no match for CNC machining as to surface finishment. CNC machining is a better choice for the parts with high requirements of surface finishment. The surface of the part made by 3D printing feels rough, just like the surface treated with abrasive blasting.
- The 3D printing is no match for CNC machining as to material selection. You don’t have many material choices for 3D printing to cover various industries, while it is different for CNC machining. CNC machining has a larger range of materials for you to choose, and this is good for later finish machining and surface treatment.
A reminder of how to choose the best CNC machining manufacturer
A good CNC machining manufacturer should have the following characteristics.
- The CNC machining company has been operating for more than ten years. Because the machining experience of a CNC machining manufacturer accumulates over time, the company with a short history usually does not have enough experience on CNC machining.
- The CNC machining manufacturer has more than 15 CNC machine tools of world-famous brands. Only a company of a certain scale is able to better carry out part machining as required by the customer and guarantee on-time delivery. Besides, production precision and surface smoothness can be ensured only with world-famous CNC machine tools.
- The CNC machining manufacturer has an independent quality department, complete quality system, and perfect testing tools such as 2D optical tester, three-coordinate tester, angle gauge, outer diameter calliper with digital display, inner diameter calliper with digital display, depthometer with digital display, salt spray tester, hardness tester, and optical screening machine. Conforming hardware products can be manufactured only with sound quality assurance.
- The CNC machining manufacturer has a team of production technicians with rich experience. Customized CNC machining parts with high precision and high requirements cannot be manufactured without excellent technicians.
To sum up, we have understood the whole process of CNC machining, how CNC machining works, the materials for CNC machining as well as advantages and disadvantages of CNC machining, compared 3D printing with CNC machining and known how to choose the best CNC machining manufacturer.
As one of the best CNC machining manufacturer on the earth, China Hardware provides CNC machining services for a lot of customers all over the world every year, and has been recognized and praised by lots of well-known companies.
Featuring high precision, high requirements, high quality, fast delivery and reasonable price, China Hardware has become a world-leading CNC machining manufacturer.
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