2 product design skills 2.1 adopt the principle of "three modernizations"

(1) Standard parts shall be selected as far as possible, or standard parts shall be used for modification or purchased parts.

(2) When designing splines and threads, it should be easy to use standard tools and measuring tools for processing and testing, especially the existing tools and measuring tools of the enterprise should be given priority.

(3) For the design of large structural parts and steel castings, fasteners that do not need to be tapped shall be used as far as possible, such as welding nut plates instead of screw holes. When designing large workpieces, it should be considered to weld the nut plate using the ballasted hole as the benchmark.

(4) Try to select the existing mature parts, or mature structure and process methods to make the products serialized and universal. This "building block" method can speed up the design speed, shorten the trial production cycle of new product prototype and occupy the market as soon as possible.

(5) Establish the enterprise's own "standard parts library" to speed up the progress of design and trial production. The author's enterprise has established and gradually improved the "factory standard parts" system and the "factory standard parts library", and selected all the same or similar parts used in more than three main products as factory standard parts.

(6) Steel castings with uniform taper, consistent plate thickness, size and brand shall be selected as far as possible. 2.2 improve the design from the shape and structure (1) minimize the number of parts. Combine several parts into one part, such as changing welded parts into stamping parts, so as to reduce the number of parts. (2) The parts are designed into a symmetrical structure. (3) The parts with similar shapes used in several products are designed into universal parts. (4) Simplify the shape of each part, improve the shape of the part, reduce the bending shape, and sometimes change the parts that are difficult to ensure the dimensional accuracy during pressing into weldments. 2.3 improve the process scheme (L) avoid unnecessary cutting, especially unnecessary cutting of clamping datum surface. When welding parts are prepared to be welded by a welding robot with a high degree of automation, the pre welding processing of the constituent parts shall be considered to ensure the mutual position and size between the constituent parts of the weldment, otherwise the error is too large, and the robot will not be able to automatically track the welding. (2) On the premise of ensuring that the parts can be used * and reasonably, reduce the machining accuracy grade requirements such as dimensional tolerance, surface roughness and geometric tolerance. (3) Reduce the bending shape and complexity of parts, and reduce the scrap rate and manufacturing cost. (4) When cutting the length of section steel, try to change the flame cutting into section steel cutting; Generally, the flame cutting of sheet metal is changed to cutting and blanking with plate shears; The cutting of rectangular strip workpiece is changed from four sides to strip steel, which is only cutting and blanking in length. Carry out necessary value engineering analysis on the main parts.

Principles and techniques of product design - continued 2.4 adopt resource-saving and pollution reducing technology (1) change steel castings into weldments. It is difficult for the foundry industry to completely solve the problem of environmental pollution, and it is easy to produce casting defects, which can be easily solved by using welding technology and weldments. (2) On the premise of ensuring the strength of parts and optimizing the plate thickness, the weight of parts shall be reduced as much as possible. In the design of structural weldments, the rib plate must be stressed to avoid the stress on the weld. When the welding stiffness or deformation of the thick plate is small, it is often not required to weld the thick plate. Some individual thick plates can often be replaced by thinner plates and appropriate stiffened plates, which not only reduces the total weight, but also increases the bearing capacity. (3) Select reasonable parameters such as weld length and fillet size. A considerable number of designers often confuse "strength weld" with "connection weld". In design, it is often required that all welds in weldments should be fully welded, and the larger the weld angle, the better. In fact, the designer should carefully consider whether to choose penetration or not. The stress state of the weldment shall be carefully studied, and then the fillet size and weld length to be adopted shall be determined. Those who can use intermittent welds do not require full welding in the full-length direction, which can not only save the welding processing cost, but also reduce the welding deformation; If fillet weld can be used, try not to weld after beveling on the parts, so as to reduce one beveling process. (4) Adopt the process method of less cutting or no cutting to improve the workpiece strength and reduce the manufacturing cost. For gear processing, the methods of integral roll forging and precision forging have been widely used in the automotive industry to reduce or even cancel the processing of tooth profile. Precision forged gears have also been used in the drive axle differential gears of construction machinery. Precision forging makes the metal fiber form an envelope along the tooth shape direction, which is different from cutting the metal fiber when cutting the tooth shape of general gears. Precision forging gears greatly improve the bearing strength of gears, reduce the cutting amount, and even eliminate the need for tooth shape processing and reduce the manufacturing cost. (5) Try to replace some free forged forgings with weldments. (6) Unify the technical requirements and process specifications of heat treatment of parts, so that different parts can be heat treated simultaneously in the same furnace to improve the utilization rate of electric furnace; Save power consumption. (7) Make full use of the waste heat of forgings, continue heating after forging, and directly carry out heat treatment such as normalizing after forging. (8) Formulate reasonable technical requirements for heat treatment according to the specific conditions of parts. Medium carbon steel or alloy medium carbon steel parts are quenched and tempered, which can effectively improve and give full play to the mechanical strength and other properties of the material. However, for shaft parts with relatively large shaft diameter, the effective layer of quenching during quenching and tempering is only a few millimeters, which is left after quenching and tempering and machining, while the state of the heart has not been well improved. So according to the author's experience, φ For solid shaft parts above 70, the process flow of normalizing + machining or normalizing + quenching + grinding of outer circle can be considered. Because shaft parts are often quenched with high frequency or medium frequency, heating only occurs on the surface of the outer circle, and the core fabric can not be quenched. If the salt bath furnace is used for heating, the core can be heated, but the hardenability of the material is limited, and the quenching during quenching and tempering is actually not hardenable in the core. Normalizing can effectively improve the overall structure of parts and refine the metallographic structure of the heart, which is enough for some parts. (9) When designing the hydraulic system, the overall layout of the machine shall be fully considered. The volume of the hydraulic oil tank shall be sufficient to minimize the amount of hydraulic oil; The pipeline route is simple and compact, and the length is as short as possible. Similarly, when designing electrical system and braking pipeline system, the direction of cable or braking pipeline shall be reasonable and the length shall be the shortest.

Conclusion product design is a complex process of comprehensive information processing. Its final result is to draw lines, symbols and numbers into reasonable design drawings. Designers should comprehensively consider the following aspects; (1) Simplify the shape of each part and make the machine structure simple; (2) Combine the functions of parts and reduce the type or quantity of parts; (3) Apply new structure, new process, new material and new principle to simplify product structure and improve product reliability; (4) Decompose components and study the simplest structure of assembly and assembly; (5) Group similar parts; (6) Analyze the serialization of similar products according to the standard number sequence; (7) Realize the generalization and standardization of product parts. The key for product designers to improve design quality lies in consciously and actively learning the knowledge related to production and processing process and processing technology, and mastering design skills.