We often see rounded - edge designs in many products. This design is called edge rounding. In the quality inspection department of justway, many parts can be seen to have used this process.
Edge rounding includes chamfers and fillets. They play a very important role in the manufacturing, assembly, and use of products and cannot be ignored. So much so that many engineers want to add a chamfer, and it must be a fillet, when they see an edge in product design. However, they don't realize that adding chamfers and fillets randomly may greatly increase the product manufacturing cost.
The design of chamfers and fillets is mainly for safety, process, and aesthetic decoration purposes.
After parts are processed by milling, the edges are often very sharp. Chamfers and fillets are commonly used to remove sharp corners and burrs to avoid scratches. Chamfering and rounding in these areas can also relieve the stress at the sharp parts of the product, reducing damage and failure caused by bumps, fatigue, and other reasons.
For some parts, appropriate chamfers and fillets must be designed due to process requirements. Designing chamfers for shaft - hole - fitting parts makes assembly easier; chamfering the tooth tips of gears can not only prevent the tooth tips from warping due to heat - treatment deformation but also prevent the tooth tips from cracking due to through - hardening, avoiding affecting the meshing quality.
Designing draft angles for powder - metallurgy parts facilitates product demolding and reduces wear; designing chamfers or fillets at the corners of the product structure makes it easier for liquids to flow smoothly in the mold, be evenly pressurized, and be demolded.
Chamfers and fillets also have a decorative effect. Rounded chamfers make products look more friendly and attractive. There are 4 common types of chamfering methods in product design: parallel - type chamfer, related - type chamfer, reverse - type chamfer, and planar - transition - type chamfer.
The parallel - type chamfer is characterized by parallel horizontal lines and perpendicular cross - section contour edges. When the chamfer radius is small, it forms a sharp and delicate "line", which can reflect the exquisite and integral sense of the product process.
The related - type chamfer creates virtual space outside the component, making the overall volume of the product appear significantly smaller. It "shaves" the product visually, not only weakening the rigid and cold image of the rectangle but also making the overall shape simple and enhancing the integrity of the product. It is widely used in electronic products.
The reverse - type chamfer has changes in broken lines, curves, angles, and virtual spaces. Compared with the parallel - type chamfer, the reverse - type chamfer has changes in the rhythm of body - surface transitions and three - dimensional spaces, creating a dynamic hint and having a strong independent effect in shape segmentation. The most typical applications are on mobile phone buttons and computer keyboards. The opening and closing cover designs of some electronic products also often use this type of chamfer.
The planar - transition - type chamfer is the most common type of chamfer, with no obvious parting line. Its smooth - transition body feeling and rich and diverse shapes enhance the overall aesthetic feeling of the product.
The transition part of a fillet is smooth, without sharp points and edges; while a chamfer forms an inclined plane. No matter how the inclination angle changes, the two sides of the inclined plane will form sharp corners with the part contour line, but these sharp corners are obtuse angles and not sharp. Therefore, fillets are more suitable for reducing stress concentration than chamfers, and the protective performance of fillets is better than that of chamfers.
In the assembly relationship, chamfer design often plays a guiding role to facilitate assembly, but interference must be avoided. Take the chamfers and fillets in the following figure as an example. To ensure no interference, when an outer chamfer is matched with an inner fillet, the outer chamfer needs to be larger than the inner fillet. Similarly, when an outer fillet is matched with an inner chamfer, the outer fillet needs to be larger than the inner chamfer.
In machining, both fillets and chamfers can be processed by methods such as cutting and grinding. However, the processing range of chamfers is wider than that of fillets, and chamfers are easier to process.
For example, when processing a shaft - type part, using an ordinary lathe, a chamfer can be processed with an ordinary turning tool, while a fillet requires a special forming tool; when using a CNC machine tool, the processing efficiency of chamfers is higher than that of fillets.
So, in terms of economy, chamfers are superior to fillets. When there are no special requirements, chamfers are preferred for outer surfaces and planes. Fillets should be selected as much as possible for the corners of the inner - cavity side walls because when the tool uses the side edge for cutting, a circular arc with the radius of the tool will be left at the corner. If the inner - cavity side wall is processed into a chamfer or a right - angle, auxiliary processing equipment such as electrical - discharge machining is required, which will incur relatively high costs.
The tool cost generated by chamfers will increase proportionally with the increase of the edge radius. Rounding corners without considering the situation will cause unnecessary processing costs.
Before adding chamfers or fillets to the design, you can first think about the following 4 questions:
If it is just for prototyping, the cost of each part is already high, and adding chamfer or fillet designs is not cost - effective. However, if it is for mass production, the cost increase for each part is not much, and it is cost - effective. For parts that require casting or forging processes, fillets are not only cost - effective but also necessary.
The smaller the tolerance, the higher the processing cost. If the size is determined to be unimportant, the chamfer can be removed from the solid model, and a note can be added to the drawing stating, "Deburr sharp edges and specify the range value of the chamfer or arc for deburring."
Therefore, a necessary principle for saving costs when designing chamfers and fillets is to add as few strictly - toleranced, large - sized fillets and chamfers as possible while meeting the requirements.
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