How to make the cutting plan of metal parts(2)

When manufacturing parts on CNC machine tools, there are generally two kinds of situations. The first one is that there are parts drawings and blanks. The CNC machine tools suitable for the parts should be selected. The second situation: there is already a CNC machine tool, to choose parts suitable for the machine tool. In either case, the main factors to be considered are the material and type of the blank, the complexity of the part contour, size, accuracy, number of parts, heat treatment requirements and so on. Following is a brief introduction of how to choose the manufacturing process of parts:

(1) Determining the type of blank

The type of blank shall be determined according to the material, shape and size of the part and the number of workpieces placed.

(2) Procedures for determining parts

The process of parts shall be determined according to all technical requirements such as dimensional accuracy, surface roughness and heat treatment, as well as the type, structure and size of blanks.

(3) Determining the manufacturing process

That is to determine the machine tool, workpiece clamping method, processing method, measurement method and processing size (including the processing allowance for the next process).

II. Principles for Formulating Parts Processing

(1) Precision base plane principle

The part must choose the suitable surface as the base surface of the machine tool or fixture. As the first process to locate the base surface, the rough surface is called the rough base surface, and the processed surface is called the fine base surface. The main base surface should be processed first.

(2) The principle of separation of roughness and precision

For the surface with high precision, it is generally necessary to finish the workpiece after all rough processing. In this way, the deformation of workpiece caused by clamping force, cutting heat and internal stress during rough machining can be eliminated, and the arrangement of heat treatment process can be facilitated. In mass production, rough and finish processing are often carried out on different machine tools, which is also conducive to the rational use of high-precision machine tools.

(3) One-time clamping principle

In the production of single piece and small batch, the surface with position accuracy requirement should be finished in one clamp as far as possible.

3. Programmes to Improve Cutting Efficiency

(1) High Speed Cutting

Milling is the main technology of high-speed cutting, and milling cutter is the main tool of high-speed cutting. This kind of tool bears a great centrifugal force when it rotates at high speed. Because its function far exceeds that of cutting force, it becomes the main load of the tool. At very high speed, besides the balance of the tool and fixture itself is the necessary prerequisite, the overall balance of the tool after installation is still needed.

(2) High feed cutting

In the traditional way of finishing, because there are certain requirements for the surface roughness of the workpiece, the feed of the tool is small. In theory, the surface roughness of the workpiece is only affected by the grain size of the workpiece material as long as the feed rate does not exceed the width of the tool’s polishing edge without considering the stiffness and the micro-defects of the polishing edge itself.

(3) Large margin cutting

Large margin cutting is generally called heavy cutting, and large margin cutting is also one aspect of high efficiency cutting. By using impact-resistant and high wear-resistant heavy cutting milling cutters, the parts of the original process that need multiple cutting can be completed at one time, but because of poor accuracy, they are usually only used for rough work.

Selection of High Speed Cutting Oils

(1) Non-ferrous metal cutting oil

Cutting force and temperature are not high when cutting copper, aluminium alloy and non-ferrous and light metals. Special cutting oil for copper and aluminium alloy, which has good corrosion resistance and low proportion of anti-wear agent, can be selected.

(2) Cast iron cutting oil

It is necessary to select cutting oil with strong rust-proof function when processing cast iron. When cast iron and bronze are brittle materials, crushing chips often form in cutting, which easily flow with cutting oil everywhere and cause parts damage between machine tool guideways. Cutting oil with good cooling and cleaning performance can be used and filtering work can be done well.

(3) Alloy steel cutting oil

When cutting alloy steel and titanium alloy, if the cutting quantity is low and the surface roughness requirement is small, such as broaching and thread cutting, the cutting oil with excellent extreme pressure performance is needed, sulfurized fatty acid ester can be chosen as the main additive of extreme pressure cutting oil.

The above is a common classification method of cutting technology. In actual cutting, it is necessary to constantly combine various factors such as workpiece, working condition, cutting tool, equipment and so on to analyze and optimize comprehensively, in order to get a suitable process with stable quality, economy and high efficiency.