Metal Work

What is Metal working？

Metal processing is referred to as metalworking, also known as: metal working, metalwork, metal processing, working of metals, refers to the production activities of human beings to process materials with metal characteristics composed of metal elements or mainly composed of metal elements. It is a process technology that processes metal materials into objects, parts and components of specific shape, size and precision, including large-scale machined parts such as bridges and ships, and even small components of engines, jewelry and watches. It is widely used in different fields such as science, industry, art, handicraft and so on.

Classification of Metal working.

1. Deformation processing:

• Plastic forming : forging, rolling, extrusion, impact extrusion, wire drawing
• Solid forming : spinning, bending, stamping forming, punching, punching, cutting forming, no cutting forming
• Press working (forging, sheet stamping)
• Powder metallurgy

2. Cutting:

• Lathes, milling machines, drilling machines, boring machines, WEDM(Wire cut Electrical Discharge Machining)

3. Grinding:

• Constant pressure grinding, constant feed grinding

4. Welding:

• Gas shielded welding, carbon dioxide gas shielded welding, furnace welding, laser welding, laser spot welding

5. Heat treatment:

• Annealing, normalizing, quenching, tempering, solution, aging, chemical heat treatment, nitriding treatment

6. Surface treatment:

• Mechanical surface treatment: sandblasting, shot blasting, polishing, rolling, polishing, brushing, spraying, painting, oiling, etc.
• Chemical surface treatment: blue and blackening, phosphating, pickling, electroless plating of various metals and alloys, TD treatment, QPQ treatment, chemical oxidation, pickling and passivation treatment, etc.
• Electrochemical surface treatment: anodizing, electrochemical polishing/electropolishing treatment, electroplating and other sprayed surfaces, etc.
• Modern surface treatment: chemical vapor deposition CVD, physical vapor deposition PVD, ion implantation, ion plating, laser surface treatment, etc.

Among them, the laser cutting machine can complete the cutting and hole cutting of solid forming parts, and can replace various cutting tools such as milling machines, drilling machines, boring machines, and wire electric discharge machining. A laser cutting machine can simultaneously replace a variety of traditional processing.

• Laser cutting: high workpiece precision, one-time forming, high efficiency and wide processing range.
• Traditional machining: The workpiece is rough, the efficiency is low, and the processing range is not wide.

Definition of Metalworking Accuracy

We deal with machining every day, and we often mention precision, but is the precision you say right? Or strict? Let’s take a look at it together!

Machining accuracy is the degree to which the actual size, shape, position of the surface of the machined part conforms to the ideal geometric parameters required by the drawing. The ideal geometric parameter is the average size for the size; for the shape, it is the absolute circle, cylinder, plane, cone and straight line, etc.; for the mutual position, it is the absolute parallel, vertical, coaxial, Symmetry etc.

1. Dimensional accuracy

The degree of conformity between the actual size of the processed part and the center of the tolerance zone of the part size.

2. Shape accuracy

Refers to the degree of conformity between the actual geometry of the surface of the machined part and the ideal geometry.

3. Position accuracy

Refers to the actual position accuracy difference between the relevant surfaces of the parts after machining.

4. Interrelationships

Usually, when designing machine parts and specifying the machining accuracy of parts, attention should be paid to controlling the shape error within the position tolerance, and the position error should be smaller than the dimensional tolerance. That is to say, for precision parts or important surfaces of parts, the shape accuracy requirements should be higher than the position accuracy requirements, and the position accuracy requirements should be higher than the dimensional accuracy requirements.

The deviation of the actual geometric parameters of the part from the ideal geometric parameters is called the machining error. The size of the machining error reflects the level of machining accuracy. The larger the error, the lower the machining accuracy, and the smaller the error, the higher the machining accuracy.

Introduction to machining accuracy

Machining accuracy is mainly used to produce products, and machining accuracy and machining error are terms used to evaluate the geometric parameters of the machined surface. The machining accuracy is measured by the tolerance level. The smaller the level value is, the higher the precision is; the machining error is represented by a numerical value, and the larger the numerical value is, the greater the error is. High machining accuracy means small machining errors, and vice versa.

There are 20 tolerance grades from IT01, IT0, IT1, IT2, IT3 to IT18. IT01 indicates the highest machining accuracy of the part, and IT18 indicates that the machining accuracy of the part is the lowest. Generally speaking, IT7 and IT8 have medium machining accuracy. level.

The actual parameters obtained by any machining method will not be absolutely accurate. From the function of the part, as long as the machining error is within the tolerance range required by the part drawing, it is considered that the machining accuracy is guaranteed.

The difference between accuracy and precision:

1. Accuracy

Refers to the closeness of the obtained measurement result to the true value. The measurement accuracy is high, which means that the systematic error is small. At this time, the average value of the measured data deviates less from the true value, but the data is scattered, that is, the size of the accidental error is not clear.

2. Precision

Refers to the reproducibility and consistency between the results obtained by repeating the determination using the same spare sample. It is possible to have high precision, but precision is inexact. For example, three results obtained by using a length of 1 mm are 1.051 mm, 1.053 mm, and 1.052 mm, respectively. Although they have high precision, they are inaccurate.

Accuracy means the correctness of the measurement results, and precision means the repeatability and reproducibility of the measurement results. Precision is the precondition for accuracy.

Methods to improve machining accuracy

1. Adjust the process system

(1) Trial cutting method adjustment

By trial cutting – measuring the size – adjusting the amount of the tool’s bite – cutting by cutting – try cutting again, and so on until the desired size is achieved. This method has low production efficiency and is mainly used for single-piece small batch production.

(2) Adjustment method

The required dimensions are obtained by pre-adjusting the relative positions of the machine, fixture, workpiece and tool. This method has high productivity and is mainly used for mass production.

2. Reduce machine tool error

(1) Improve the manufacturing accuracy of spindle components

The rotation accuracy of the bearing should be improved: use high-precision rolling bearings; use high-precision multi-oil wedge dynamic pressure bearings; use high-precision static pressure bearings. The accuracy of the accessories with the bearing should be improved: the machining accuracy of the box support hole and the spindle journal should be improved; the machining accuracy of the matching surface with the bearing should be improved; the radial runout range of the corresponding parts should be measured and adjusted to compensate or offset the errors.

(2) Appropriately preload the rolling bearing

Can eliminate clearance; increase bearing stiffness; homogenize rolling element errors.

3. Reduce the transmission error of the transmission chain

(1) The number of transmission parts is small, the transmission chain is short, and the transmission precision is high.

(2) The use of deceleration transmission is an important principle to ensure the transmission accuracy, and the closer the transmission pair is to the end, the smaller the transmission ratio should be.

(3) The precision of the end piece should be higher than that of other transmission parts.

4. Reduce tool wear

The tool must be re-sharpened before the dimensional wear of the tool reaches the stage of severe wear.