Friends who do non-standard mechanical design basically draw every day, and there will be some design problems more or less. Today I will share with you some common design problems, and also for your reference when designing to avoid similar problems.
PART 1 The rounded corner design is unreasonable. As shown in Figure 1 (left), the rounded corner design of the part is unreasonable. Some engineers who have just started working often make this mistake. They may draw the step transition position into a rounded corner for aesthetic reasons. In this way, they need to perform milling as shown in Figure 1 (right) during processing, but the rounded corner of the part is too long, and the cutting edge length of the tool is not enough during processing, which will easily cause the tool to give up. Therefore, the reasonable design should be as shown in Figure 2, and it can be directly designed into a right angle, so that the above processing problems will not occur.
Figure 1 The rounded corner design is unreasonable
Figure 2
Comment: When we judge the rationality of the structure, the essence is to consider the convenience and cost of processing. If an ordinary milling machine is used for processing, right angles are more convenient than arc angles. If it is fast wire or CNC processing, there is no such problem. With the development of processing technology, the processing technology has also changed greatly. Laser cutting or fast wire cutting is a very common process. PART 2 The hole design is unreasonable. In Figure 3 below, the punching position is close to the bending position of the sheet metal. In this way, the drilling position is not guaranteed. If it is a threaded hole, the thread will be easily deformed. Therefore, when designing, the hole position needs to be far away from the bending position.
Figure 3 The hole position is close to the bending position of the sheet metal
For example, in the figure below, the part is a rack welded by a welded square tube, and the punching position is close to the welding area. The hardness near the welding position is high, and it is difficult to process and easy to break the drill bit and tap. Therefore, when designing, it is reasonable to keep the punching position away from the welding area.
Figure 4 The hole position is close to the welding area
Comment: After the 3D design of the sheet metal structure is completed, the holes on the bending or welding edge should be adjusted appropriately according to the specific structure.
PART 3 The design of the shaft parts is unreasonable. As shown in Figure 5 below, a simple schematic structure is drawn in this figure for expression. In the middle is a shaft part connected in the middle of the two parts. The shaft parts in the figure are designed to be two small and large in the middle. This requires secondary clamping during processing, which is complex and difficult to guarantee the size. It can be designed to be large at one end and small at the other without affecting the function. This shape is easier to process.
Figure 5 Unreasonable design of shaft parts
Comment: Not all shafts designed to be small at both ends and large in the middle are unreasonable. In fact, most structures with two bearing positions have such characteristics.
Figure 6 Reducer shaft PART 4 One-piece part design problem As shown in Figure 7, the left side is made of two parts spliced together. In fact, this spliced structure is not large in size, and it is better to process it directly from one part. Dividing it into two parts will make the processing complicated, the size difficult to control, and waste installation time. The right side is a one-piece part, which is simpler to process, does not have so many holes to be processed, and the size is better guaranteed.
Figure 7 It is more reasonable to design small parts into one
As shown in Figure 8, the part is large in size. If it is designed as an integrated part, it will lead to problems such as large processing cutting, complex processing, and increased costs.
Figure 8 Large parts are better designed in separate parts
In short, when considering whether to design as separate parts or one-piece parts, processing, cost, installation and debugging should be considered comprehensively. Generally, when the length, width and height of the structure are less than 80*80*80mm, we generally design it as a one-piece part, and when the length, width and height of the structure are greater than 80*80*80mm, we design it as a separate part.
Comment: Whether to design as a whole or separate parts, in addition to considering the size, the focus is on whether the processing technology is the simplest, the easiest to ensure the accuracy requirements of the parts, and whether the overall cost is the lowest.
