Basic knowledge of machining

Machining is the abbreviation of mechanical processing, which refers to the processing technology of accurately removing materials through processing machinery.

Mechanical processing mainly includes manual processing and numerical control processing.

Manual processing refers to the method of processing various materials by mechanical workers manually operating milling machines, lathes, drilling machines, sawing machines and other mechanical equipment. Manual processing is suitable for small batch and simple parts production.

Numerical control machining (CNC) refers to the use of CNC equipment by machinists for machining, including machining centers, turning and milling centers, wire EDM equipment, thread cutting machines, etc.

At present, the vast majority of machining workshops use CNC machining technology. Through programming, the position coordinates (X, Y, Z) of the workpiece in the Cartesian coordinate system are converted into program language. The CNC controller of the numerical control machine tool controls the axis of the numerical control machine tool by identifying and interpreting the program language, and automatically removes materials as required to obtain the finished workpiece. NC machining processes workpieces in a continuous manner, which is suitable for large quantities of parts with complex shapes.

The machining workshop can use CAD/CAM (Computer Aided Design and Computer Aided Manufacturing) system to automatically program the NC machine tool. The geometric shape of the part is automatically converted from the CAD system to the CAM system, and the mechanic selects it on the virtual display screen

Select various processing methods. When the machinist selects a certain processing method, the CAD/CAM system can automatically output CNC code, usually G code, and input the code into the controller of the NC machine tool for actual processing operation.

If the parts of the equipment needed for production, such as metal cutting machine tools (including turning, milling, planing, inserting and other equipment) at the rear of the factory are damaged, they need to be repaired, so they need to be sent to the machining workshop for repair or processing. In order to ensure the smooth production, general enterprises have set up machining workshops, which are mainly responsible for the maintenance of production equipment.

1、 Overview

This operating procedure gives detailed instructions to all operators engaged in machining to ensure the quality of each machining part.

2、 Scope of application

This procedure describes in detail the specific operations of machining personnel (including turning, milling, drilling, planing, grinding, shearing, etc.) during their work.

3、 General

Mechanical processing must be carried out in accordance with this procedure during the processing of various parts.

4、 Implementation steps

4.1 All operators engaged in various machinery must receive safety technical training and pass the examination before they can work.

4.2 Before operation

4.2.1 Before work, use protective equipment strictly according to regulations, tie the cuffs, do not wear scarves or gloves, and women workers should wear their hats. The operator must stand on the pedal.

4.2.2 The bolts, travel limits, signals, safety protection (safety) devices, mechanical transmission parts, electrical parts and lubrication points of all parts shall be strictly checked, and they can be started only after they are confirmed to be reliable.

4.2.3 The safety voltage and voltage applied to various machine tool lighting shall not be greater than 36V.

4.3 In operation

4.3.1 Tools, clamps, cutters and workpieces must be firmly clamped. All kinds of machine tools shall be idling at low speed after start-up, and formal operation can be started only after everything is normal.

4.3.2 It is prohibited to put tools and other things on the machine tool track surface and workbench. It is not allowed to remove iron filings by hand, and special tools should be used for cleaning.

4.3.3 Before starting the machine tool, observe the surrounding dynamics. After starting the machine tool, stand at a safe position to avoid moving parts of the machine tool and iron filings.

4.3.4 During the operation of all kinds of machine tools, it is not allowed to adjust the speed change mechanism or stroke, touch the working surface of the transmission part, moving workpiece, cutter, etc. in processing, measure any size during the operation, and separate the transmission part of the machine tool

Distribute or take tools and other items.

4.3.5 In case of any abnormal noise, stop the machine for maintenance immediately, do not operate it forcibly or with faults, and do not overload the machine tool.

4.3.6 During the processing of each machine part, strictly implement the process discipline, see the drawings clearly, see the control points, roughness and technical requirements of relevant parts of each part, and determine the processing procedure of the fabricated parts. 4.3.7 Stop the machine when adjusting the speed, stroke, clamping the workpiece and cutter, and wiping the machine tool. It is not allowed to leave the post when the machine tool is running. If you want to leave for some reason, you must stop the machine and cut off the power supply.

4.4 After operation

4.4.1 Raw materials to be processed, finished products, semi-finished products and waste materials must be stacked in a designated place, and all tools and cutters must be kept intact and in good condition.

4.4.2 After the operation, the power must be cut off, the tools must be removed, the handles of each part must be placed in the neutral position, and the electric switch box must be locked.

4.4.3 Clean the equipment, clean the iron filings, and inject lubricating oil into the guide rail to prevent corrosion.

The machining process specification is one of the process documents that specify the machining process and operation methods of parts. It is a process document that, under specific production conditions, writes a more reasonable process and operation method into a process document in the specified form, and is used to guide production after approval. The machining process procedure generally includes the following contents: the process route of workpiece processing, the specific contents of each process and the equipment and process equipment used, the inspection items and methods of workpiece, cutting amount, time quota, etc.

Step 1 of formulating the process procedure: calculate the annual production program and determine the production type. 2) Analyze part drawings and product assembly drawings, and analyze the process of parts. 3) Select the blank. 4) Draw up the process route. 5) Determine the machining allowance of each process, and calculate the process dimensions and tolerances. 6) Determine the equipment, tools, fixtures, measuring tools and auxiliary tools used in each process. 7) Determine cutting parameters and man hour quota. 8) Determine the technical requirements and inspection methods of main processes. 9) Fill in process documents.

In the process of formulating process procedures, it is often necessary to adjust the previously preliminarily determined contents to improve economic benefits. In the process of implementing the process specification, there may be unexpected situations, such as changes in production conditions, introduction of new technologies and processes, application of new materials and advanced equipment, etc., which require timely revision and improvement of the process specification, including five axis processing, ceramic processing, chemical processing, CNC processing, CNC milling, CNC turning, casting machining, micro machining, plastic parts machining, thread cutting, EDM forming, Swiss turning, WEDM, etc.

Machining equipment includes: lathes, milling and boring machines, drilling machines, machining centers, heavy machine tools, high-speed milling machines, other machine tools, and functional parts.

Machined products include: shafts, valves, shells, gears, turbines, fasteners, pipe fittings, rods, metal bushes, turning parts, etc.

Surface finish/roughness

In the sense of engineering, the finish is the roughness.

It is not recommended to use finish or finish

In the equipment technical annexes abroad,

Flatness refers to flatness, flatness and straightness.

Roughness refers to roughness and finish.

The flatness of the same material is greater than the roughness.

If the flatness of an aluminum plate is 0.4mm, the roughness can reach 0.4 μ m。

Flatness refers to the variation of the measured actual surface and its ideal plane. Generally speaking, it is “macroscopic surface flatness and straightness”.

Roughness refers to the arithmetic mean deviation of the profile, usually expressed in Ra. It is the arithmetic mean value of the concave convex small pits on the micro level, which is usually used for more precise measurement.

CNC lathe and machining center

After the machine tool is equipped with a numerical control system, the machine tool becomes a numerical control machine tool. Of course, the development of ordinary machine tools to numerical control machine tools is not just as simple as adding systems. For example, from milling machines to machining centers, the structure of machine tools has changed. The most important thing is to add

The tool magazine has greatly improved the accuracy. The main functions of the machining center are milling, boring and drilling.

Generally speaking, CNC equipment mainly refers to CNC lathes and machining centers.

A machining center is a CNC machine tool equipped with a tool magazine, which has the function of automatic tool change, and can perform multi process machining after the workpiece is clamped once. The machining center is a highly electromechanical product. After the workpiece is clamped, the CNC system can control the machine tool according to different work conditions

Automatic selection and replacement of tools, automatic tool setting, automatic change of spindle speed, feed rate, etc. can continuously complete drilling, boring, milling, reaming, tapping and other processes. As a result, the clamping time, measurement, machine tool adjustment and other auxiliary tools are greatly reduced

Sequence time has good economic effect for parts with complex machining shape, high precision requirements and frequent variety replacement.

Machining centers are generally classified according to the relative position of the spindle and the workbench, and are divided into horizontal, vertical and universal machining centers (multi axis linkage machining centers).

Differences in hardness, strength and stiffness

Hardness is an important performance index to measure the hardness of metal materials. It can be understood as the ability of materials to resist elastic deformation, plastic deformation or damage,

It can also be expressed as the ability of materials to resist residual deformation and anti destruction. Hardness is not a simple physical concept, but the elasticity, plasticity

Comprehensive index of mechanical properties such as strength and toughness. Hardness test can be divided into static pressure method (such as Brinell hardness, Rockwell hardness, Vickers hardness, etc.), scratch method (such as Mohs hardness), rebound method (such as Shore hardness) according to different test methods

And micro hardness, high temperature hardness and other methods.

Strength refers to the ability of parts to resist fracture or residual deformation beyond the allowable limit after bearing load.

In other words, strength is an important indicator to measure the bearing capacity (i.e., the resistance to failure) of parts. strength

It is the basic requirement that mechanical parts should first meet. The strength of mechanical parts can generally be divided into static strength and fatigue strength (bending fatigue and contact fatigue, etc.)

, breaking strength, impact strength, high temperature and low temperature strength, strength and creep under corrosive conditions, adhesive strength, etc. The strength test research is a comprehensive research, mainly through its stress state to study the stress state of parts and components

And predict the conditions and timing of failure.

Stiffness refers to the ability of parts to resist elastic deformation under load. Stiffness (or rigidity) of parts

It is usually expressed by the force or moment required for unit deformation. The stiffness depends on the geometric shape of the part and the type of material (i.e. the elastic modulus of the material)

。 Stiffness requirements are particularly important for some parts that will affect the working quality of the machine when the elastic deformation exceeds a certain value, such as the spindle, guide rail, lead screw, etc. of the machine tool.

Stiffness is the ability to resist deformation, strength is the ability to resist damage, and hardness is the ability to invade other objects (also the ability not to be invaded by other objects). Stiffness emphasizes no deformation or small deformation, such as the spindle of the machine tool. Strength is strong

Adjust the reliability, that is, it cannot fail. Hardness is the ability to emphasize invasion and anti invasion, such as cushion blocks for fixtures, jig sleeves, and tools.

Stiffness – the ability of a structure or component to resist elastic deformation. Stiffness, rigidity

Strength – the ability of metal materials to resist plastic deformation and fracture under external force, which is an important indicator to measure the bearing capacity of parts (i.e., the ability to resist failure).

Hardness – The ability of a material to resist hard objects pressing into its surface is called hardness, which is an indicator of the hardness of a material.