Machined parts (ductile iron)

Machined parts refer to the process of altering the external dimensions or properties of a workpiece using mechanical equipment. Based on differences in processing methods, they can be categorized into cutting processes and pressure processing.

The production process of machinery encompasses the entire journey from raw materials (or semi-finished products) to finished goods. For machinery production, this includes raw material transportation and storage, production preparation, blank fabrication, component machining and heat treatment, product assembly and debugging, painting, and packaging. The scope of production processes is extensive. Modern enterprises organize and direct production using systems engineering principles and methods, viewing the production process as a production system with inputs and outputs.

In the production of machined parts, any process that alters the shape, dimensions, position, or properties of the production object to transform it into a finished or semi-finished product is termed a manufacturing process. This constitutes the primary component of the production process. Processes can be further categorized into casting, forging, stamping, welding, machining, assembly, and others. In mechanical manufacturing, the manufacturing process generally refers to the combined machining processes for parts and the assembly processes for machines. Other activities, such as transportation, storage, power supply, and equipment maintenance, are termed auxiliary processes. A manufacturing process consists of one or more sequentially arranged operations, and each operation comprises several work steps.

The operation of a machined part is the fundamental unit constituting the mechanical processing process. An operation refers to the portion of the process continuously completed by one (or a group of) workers on a single machine tool (or at a single workstation) on the same workpiece (or simultaneously on several workpieces). The primary characteristics defining an operation are that the workpiece, equipment, and operator remain unchanged, and the operation's content is completed continuously.

An operation step is defined as a sequence completed under conditions where the machined surface, cutting tool, and cutting parameters remain unchanged.

A pass, also known as a working stroke, is the operation step completed during a single pass of the cutting tool over the machined surface.

When establishing a machining process, it is essential to determine the number of operations the workpiece will undergo and their sequential order. A simplified process flow listing only the names of major operations and their sequence is termed the process route.

The formulation of the process route establishes the overall layout of the machining process. Its primary tasks include selecting the machining methods for each surface, determining the machining sequence for each surface, and establishing the total number of operations in the entire process. The formulation of the process route must adhere to certain principles.

The basic characteristic of high-density molding sand for gray iron castings is that the amount of coal powder added is also relatively low. Therefore, the following points should be taken into account when preparing sand.

1. Clay content and mud content. The strength of sand with high clay content increases with the increase of specific pressure, and the effective bentonite is usually controlled at 7% to 10%. The sum of effective clay and dead clay in molding sand is equivalent to the mud content, which is generally controlled between 12% and 16%. Excessive or insufficient clay content can affect the various performance indicators of the molding sand.

2. Moisture. The moisture content in the molding sand used in the production of lost foam castings is the main factor determining the plasticity and bonding strength of clay. When the moisture content is too high, it can easily cause the deterioration of clay adhesion, decrease the flowability of molding sand, and result in uneven mold density. When the moisture content is too low, the molding sand is difficult to mix evenly, the strength of the molding sand is low, the brittleness is high, the demolding performance is poor, and it is easy to cause sand sticking defects in castings. The general moisture content should be controlled to be 10% to 20% higher than the moisture content at which the peak wet compressive strength is obtained.

3. Original sand particle size. When molding with high density, the sand mold has a high density and expands greatly during pouring. Therefore, the original sand particle size should not be overly concentrated. The original sand particles are circular or polygonal, and generally three or four screen sand is selected.