Precautions for Structural Design of Machined Parts
Most metal parts are machined before they are officially used in order to meet the standards for use. This is also the last step before the assembly of mechanical parts. Therefore, the quality and cost of machining have a great impact on the quality and cost of mechanical parts and the entire machine. Therefore, in the design process, we must consider the problem of mechanical processing technology.
Especially for some special mechanical parts, the manufacturing process is often very special, and special consideration should be given to the design. Whether a part can be manufactured can be a decisive factor in whether a design can be adopted. Therefore, when designing the structure of these machined parts, the following issues need to be noted.
1. Structure design of parts for saving materials
Pay attention to reduce the size of the blank. The flange is made of round steel. If the maximum diameter is 100mm, it should be processed with round steel of 105mm or 110mm. If the design has a maximum diameter of 98mm, it can be processed with 100mm steel, which can save a lot of steel.
2. Structural design to reduce the amount of machining work
(1) Take into account the influence of casting error
The error of cast parts is relatively large and must be fully considered when designing the casting surface.
For example, the bearing end cover matches the boss on the box body, but the position of the boss on the box body is difficult to be very accurate.
If the end cap flange and the boss diameter are designed to be exactly equal, the end cap may protrude out of the boss due to the influence of the casting error.
Therefore, the diameter of the cast boss should be larger.
(2) Different processing precision surfaces should be separated
When the two surface roughness requirements are different, there must be a clear boundary between the two surfaces. This is not only easy to process, but also beautiful in shape.
3. Reduce the structural design of manual processing or supplementary processing
(1) Replace the manual grinding guide with a surface grinder
The guideway of the omnipotent tool microscope of large optical metrology instrument was originally designed as a circular guideway. It is used for manual grinding, then modified to flat V guide, and processed by surface grinder. The productivity has been greatly improved.
(2) Replacing Scraping and Grinding Decelerator with Plane Grinding or Fine Planing
The split surface of the split type gearbox case requires a high degree of flatness. It turns out that some production units use manual scraping, which has a large workload and low productivity. In the future, it will be changed to a surface grinder to process live fine planers.
4. Simplify the shape and requirements of the machined surface
(1) Must avoid the fitting of non-circular parts
There is a flange on the surface of the box part to match it.
In order to make the positioning of the cover accurate, in addition to fixing with a screw, the design has a stop fit, and the matching hole should be round, and it is not suitable to use other shapes such as a rectangle, a square, an ellipse or the like.
(2) must be full of complex shape parts chamfering
Chamfering of complex shaped parts is difficult. Such as elliptical complex shapes, it is difficult to chamfer by mechanical processing, chamfering by hand, it is difficult to guarantee the quality of processing.
5. Structure design of parts for easy clamping and measurement
Avoid parts structures that cannot be clamped. Mechanical parts must be clamped to the machine during machining. Therefore, there must be a part on the mechanical part that is easy to clamp. In addition, the clamping parts must have sufficient support to ensure that the parts do not shake under the action of cutting forces. Therefore, the part has sufficient rigidity to avoid clamping deformation.
6, to avoid cutting tools in the unfavorable conditions
The tool can easily enter or exit the machined surface. When the tool enters or exits the machined surface, it requires a certain amount of movement space. The design should retain enough clearance.
7. Correctly handle the structure of the shaft and the hole (inner and outer surfaces)
Complex machining surfaces are designed on the outer surface rather than on the inner surface, and shaft parts are easier to machine than holes.
Therefore, when the two shafts, the hole-shaped parts are matched together, and there are some complicated structures among them, it is often better to design these structures on the shaft than to design the inner surface of the holes.
Especially for some special mechanical parts, the manufacturing process is often very special, and special consideration should be given to the design. Whether a part can be manufactured can be a decisive factor in whether a design can be adopted. Therefore, when designing the structure of these machined parts, the following issues need to be noted.
1. Structure design of parts for saving materials
Pay attention to reduce the size of the blank. The flange is made of round steel. If the maximum diameter is 100mm, it should be processed with round steel of 105mm or 110mm. If the design has a maximum diameter of 98mm, it can be processed with 100mm steel, which can save a lot of steel.
2. Structural design to reduce the amount of machining work
(1) Take into account the influence of casting error
The error of cast parts is relatively large and must be fully considered when designing the casting surface.
For example, the bearing end cover matches the boss on the box body, but the position of the boss on the box body is difficult to be very accurate.
If the end cap flange and the boss diameter are designed to be exactly equal, the end cap may protrude out of the boss due to the influence of the casting error.
Therefore, the diameter of the cast boss should be larger.
(2) Different processing precision surfaces should be separated
When the two surface roughness requirements are different, there must be a clear boundary between the two surfaces. This is not only easy to process, but also beautiful in shape.
3. Reduce the structural design of manual processing or supplementary processing
(1) Replace the manual grinding guide with a surface grinder
The guideway of the omnipotent tool microscope of large optical metrology instrument was originally designed as a circular guideway. It is used for manual grinding, then modified to flat V guide, and processed by surface grinder. The productivity has been greatly improved.
(2) Replacing Scraping and Grinding Decelerator with Plane Grinding or Fine Planing
The split surface of the split type gearbox case requires a high degree of flatness. It turns out that some production units use manual scraping, which has a large workload and low productivity. In the future, it will be changed to a surface grinder to process live fine planers.
4. Simplify the shape and requirements of the machined surface
(1) Must avoid the fitting of non-circular parts
There is a flange on the surface of the box part to match it.
In order to make the positioning of the cover accurate, in addition to fixing with a screw, the design has a stop fit, and the matching hole should be round, and it is not suitable to use other shapes such as a rectangle, a square, an ellipse or the like.
(2) must be full of complex shape parts chamfering
Chamfering of complex shaped parts is difficult. Such as elliptical complex shapes, it is difficult to chamfer by mechanical processing, chamfering by hand, it is difficult to guarantee the quality of processing.
5. Structure design of parts for easy clamping and measurement
Avoid parts structures that cannot be clamped. Mechanical parts must be clamped to the machine during machining. Therefore, there must be a part on the mechanical part that is easy to clamp. In addition, the clamping parts must have sufficient support to ensure that the parts do not shake under the action of cutting forces. Therefore, the part has sufficient rigidity to avoid clamping deformation.
6, to avoid cutting tools in the unfavorable conditions
The tool can easily enter or exit the machined surface. When the tool enters or exits the machined surface, it requires a certain amount of movement space. The design should retain enough clearance.
7. Correctly handle the structure of the shaft and the hole (inner and outer surfaces)
Complex machining surfaces are designed on the outer surface rather than on the inner surface, and shaft parts are easier to machine than holes.
Therefore, when the two shafts, the hole-shaped parts are matched together, and there are some complicated structures among them, it is often better to design these structures on the shaft than to design the inner surface of the holes.
