CNC machining

The term CNC stands for “computer numerical control,” and CNC processing is defined as the subtraction manufacturing process, which typically uses computer control and machine tools to remove layers of material from inventory pieces (called blanks or workpieces) and produce custom-designed parts.

This process is applicable to various materials, including metal, plastic, wood, glass, foam and composite materials, and has been applied in various industries, such as large-scale CNC machining and CNC finishing aerospace parts

CNC machining features

01

High degree of automation and very high production efficiency. Except for blank clamping, all other processing procedures can be completed by CNC machine tools. If the automatic loading and unloading mode is combined, it is a basic part of the unmanned factory.

CNC processing reduces the labor of the operator, improves the working conditions, eliminates the marking, multiple clamping and positioning, detection and other processes and auxiliary operations, and effectively improves the production efficiency.

02

Adaptability to CNC machining objects. When changing the processing object, in addition to changing the tool and solving the blank clamping method, only reprogramming is required without other complex adjustments, which shortens the production preparation cycle.

03

High processing precision and stable quality. The machining dimension accuracy is between d0.005-0.01mm, which is not affected by the complexity of the parts. Because most

operations are automatically completed by the machine, the size of the batch of parts is improved. The position detection device is also used on the precision controlled machine tool, which further improves the precision of precision CNC machining.

04

CNC machining has two main characteristics: one is that it can greatly improve the machining accuracy, including the machining quality accuracy and machining time error accuracy; The second is the repeatability of processing quality, which can stabilize the processing quality and maintain the quality of processed parts

CNC processing technology and scope of application

Different machining methods can be selected according to the materials and requirements of machined workpieces. Understanding the common machining methods and their scope of application can help us find the most suitable machining method for parts.

Turning 

The method of using a lathe to process parts is generally called turning. With formed turning tool, the rotary surface can also be machined during cross feed. Turning can also process thread surface, end plane and eccentric shaft.

The turning accuracy is generally IT11-IT6, and the surface roughness is 12.5-0.8 μ m。 In fine turning, it can reach IT6-IT5, and the roughness can reach 0.4-0.1 μ m。 The productivity of turning is high, the cutting process is relatively stable, and the tools are relatively simple.

Scope of application: drilling center hole, drilling, reaming, tapping, turning excircle, boring, turning end face, turning groove, turning forming surface, turning cone surface, knurling, turning thread

Gangmilling 

Milling is a method of machining the workpiece on a milling machine using a rotating multi edge tool (milling cutter). The main cutting motion is the rotation of the tool. According to the same or opposite direction of the main movement speed and the workpiece feed direction during milling, it can be divided into forward milling and reverse milling.

(1) Forward milling

The horizontal component of the milling force is the same as the feed direction of the workpiece. There is usually a gap between the feed screw of the worktable and the fixed nut. Therefore, the cutting force is easy to cause the work-piece and the worktable to move forward together, causing a sudden increase in the feed rate, causing a tool strike.

(2) Up milling

It can avoid the phenomenon of shifting during milling. In up milling, the cutting thickness gradually increases from zero, so the cutting edge begins to experience a stage of squeezing and sliding on the hardened machined surface, which accelerates the tool wear.

Scope of application: plane milling, step milling, groove milling, forming surface milling, spiral groove milling, gear milling, cutting

Planing

Planing generally refers to the processing method of removing excess materials on the planer by using the planer to make reciprocating linear motion relative to the workpiece.

The precision of planing can generally reach IT8-IT7, and the surface roughness is Ra6.3-1.6 μ m. The planeness of finish planing can reach 0.02/1000, and the surface roughness is 0.8-0.4 μ m. It has advantages for processing large castings.

Scope of application: plane planing, vertical plane planing, stepped plane planing, right angle groove planing, inclined plane planing, dovetail groove planing, T-shaped groove planing, V-shaped groove planing, curved surface planing, keyway in the planing hole, gear bar planing, and composite surface planing

Grinding

Grinding is a method of using high hardness artificial grinding wheel (grinding wheel) as a tool to cut the workpiece surface on the grinder. Its main motion is the rotation of the grinding wheel.

The grinding accuracy can reach IT6-IT4, and the surface roughness Ra can reach 1.25-0.01 μ m. It can even reach 0.1-0.008 μ m。 Another feature of grinding is that it can process hardened metal materials, which belongs to the scope of finishing, so it is often used as the final processing procedure. According to different functions, grinding can also be divided into cylindrical grinding, internal hole grinding, flat grinding, etc.

Scope of application: cylindrical grinding, internal grinding, surface grinding, form grinding, screw grinding, gear grinding

Drilling

The process of machining various internal holes on a drilling machine is called drilling, which is the most commonly used method of hole processing.

The drilling accuracy is relatively low, generally IT12~IT11, and the surface roughness is generally Ra5.0~6.3um. After drilling, reaming and reaming are often used for semi finishing and finishing. Reaming accuracy is generally IT9-IT6, and surface roughness is Ra1.6-0.4 μ m。

Scope of application: drilling, reaming, reaming, tapping, strontium hole, scraping

Boring

Boring is a processing method that uses a boring machine to enlarge the hole diameter and improve the quality of the existing hole. Boring is mainly based on the rotary motion of the boring cutter.

The precision of boring is high, generally IT9-IT7, and the surface roughness is Ra6.3-0.8mm, but the productivity of boring is low.

Scope of application: machining high-precision holes and finishing of multiple holes

Grinding

Gear tooth surface machining methods can be divided into two categories: forming method and generating method.

The machine tool used for machining the tooth surface by the forming method is generally an ordinary milling machine, and the cutter is a forming milling cutter, which requires two simple forming movements, namely, the rotary movement and the linear movement of the cutter. The commonly used machine tools for generating tooth surfaces are gear hobbing machines, gear shapers, etc.

Scope of application: gear, etc

Complex Surface

The method of copying milling and numerical control milling or special machining method is mainly used for the cutting of three-dimensional surfaces.

Scope of application: components of complex surfaces

Spark-erosion

Electrical discharge machining (EDM) is realized by melting the surface material of the workpiece at high temperature produced by the instantaneous spark discharge between the tool electrode and the workpiece electrode.

Scope of application:

① Processing hard, brittle, tough, soft and high melting point conductive materials;

② Processing semiconductor materials and non-conductive materials;

③ Machining various shaped holes, curved holes and micro holes;

④ Processing various solid surface cavities, such as forging die, die-casting die, plastic die chamber;

⑤ It is used for cutting, cutting, surface strengthening, engraving, nameplate printing and marking.

electrochemical machining

Electrolytic

Electrochemical machining (ECM) is a method of forming workpiece based on the electrochemical principle of metal anodic dissolution in electrolyte.

The workpiece is connected to the positive pole of the DC power supply, and the tool is connected to the negative pole. A narrow gap (0.1mm-0.8mm) is maintained between the two poles. The electrolyte with a certain pressure (0.5MPa~2.5MPa) flows through the gap between the two electrodes at a high speed of 15m/s~60m/s).

Scope of application: machining of molded holes, cavities, complex surfaces, small diameter deep holes, rifling, deburring, engraving, etc.

laser processing

The laser processing of the workpiece is completed by the laser processing machine. Laser processing machine is usually composed of laser, power supply, optical system and mechanical system.

Scope of application: small hole machining of diamond wire drawing dies, watch and clock jewel bearings, porous skin of divergent air cooled stamping sheets, engine fuel injection nozzles, aeroengine blades, etc., and cutting of various metal and non-metallic materials.

Ultrasonic machining

Ultrasonic machining is a method of machining workpieces by using ultrasonic frequency (16KHz~25KHz) to vibrate the end face of the tool to impact the suspended abrasive in the working fluid.

Scope of application: difficult to cut materials

Main application industries

Generally, CNC machined parts have high accuracy, so CNC machined parts are mainly used in the following industries

Aerospace

Aerospace needs components with high precision and repeatability, including turbine blades in engines, tooling for making other components, and even combustion chambers used in rocket engines.

Automobile and machine manufacturing

The automotive industry needs to manufacture high-precision molds for casting parts (such as engine seats) or machining high tolerance parts (such as pistons). Gantry type machines can cast clay modules, which are used in the design phase of automobiles.

military project

The military industry uses high-precision components with strict tolerance requirements, including missile components, gun barrels, etc. All machined parts in the military industry can benefit from the accuracy and speed of CNC machines.

medical care

Medical implants are usually designed to fit the shape of human organs and must be made of high-grade alloys. Since no manual machine can generate such shapes, CNC machines become a necessity.

energy

The energy industry covers all engineering fields, from steam turbines to nuclear fusion and other cutting-edge technologies. The steam turbine needs high-precision turbine blades to maintain the balance in the turbine. The shape of the R&D plasma suppression cavity in nuclear fusion is very complex. It is made of advanced materials and needs the support of CNC machines

Today, with the development of machining, following the improvement of market requirements, a variety of machining processes have been derived. When choosing the machining process, you can consider many aspects, including the surface shape, dimension accuracy, position accuracy, surface roughness, etc. of the workpiece to be machined

Select the most appropriate process to ensure the quality and processing efficiency of the workpiece with minimum input, and maximize the benefits generated