PC Product Sheet Metal Processing Mechanism Design Several Important Parameters
The PC needs an appropriate amount of cooling holes during operation, and the safety requires that the holes are not too large, posing an unnecessary danger. UL, CSA requires that the inner diameter of the round hole should not be greater than 2mm. If it is SLOT, the width should not be greater than 1.5mm, and the length should not be greater than 20mm.
For the EMI problem, the upper cover and the lower cover are difficult to combine when in close contact. If there is no interference, the EMI cannot pass, so a shrapnel can be added at intervals to make the ground between the upper cover and the lower cover.
Draft angle
(1) Without prejudice to the appearance and shape of the case, the greater the range, the better
(2) Appropriate draft angle is approximately 1/10 to 1/30 (1° ~ 2°)
(3) The practical minimum is 1/120 (about 0.5°)
(4) The surface has a bite flower treatment, and the stripping slope is determined by the thickness of the bite flower. Generally, when the biting depth is 0.001 INCH (0.025 mm), the draft angle is at least 1°.
Thickness
The principle of uniform thickness is everywhere. It is also necessary to consider the structural strength and the ability to evenly distribute the impact force, and try to avoid the thin thickness of the sharp part to prevent insufficient filling.
In actual product design, thickness variation and shape are often required. The thickness variation of the step shape is easy to form deformation on the design surface, which can be improved by adding an R angle or a bevel angle. When there are inconsistent thicknesses, it should be gradually reduced as shown in the table below.
General practical thickness range Unit: mm
2. Inner round angle and outer corner angle
It is recommended that the minimum R is 0.5mm and the optimum rounding design is R/T=0.6. After this point, even if R is increased, only a small part can reduce the stress concentration phenomenon. Inner round angle R=0.5T , outer corner angle R=1.5T
3. Rib
Ribs or flanges can be used to increase the strength of the molded article without increasing the thickness. These designs not only increase the strength, but also avoid distortion when cooling. In order to avoid shrinkage, the height of the rib is 0.5 T, the bottom fillet is R=0.125T, the draft angle is 0.5°~1.5°, and the direction of the rib is preferably the same as GATE. The distance between the ribs is as much as twice the wall thickness.
4. Bushing
The bushing is for reinforcement of the hole and for embedding in combination or for supporting other things. The height of the bushing is limited to less than twice its diameter. Because it is too high due to air concentration, it is easy to cause pores and insufficient filling. If it is necessary to have a high bushing, the reinforcing rib should be placed on the side to make the material flow easy. In order to avoid the shrinkage of the root surface, you can steal the material around the sleeve, but it can't be cut too deeply, otherwise there will be traces on the surface.
5. Fusion line
Try not to appear on the appearance surface. You can use the gate size, shape, number or the material near the gate to determine the position of the fusion line. Because it is the place where the material finally meets, its strength is weak, and should avoid the place where the finished product is subjected to load.
When you want to add holes or openings for LEDs or other complexes, the openings should be chamfered or rounded to facilitate assembly.
If there is a front and rear shell or a combination of the upper and lower covers, try to make the back shell (lower cover) into the front shell (top cover) to prevent the user from seeing the gap.
When designing the button, avoid directly on the power switch. The floating design or indirect drive design should be adopted to avoid the keying caused by the dimensional error or the deflection of the transmission rod of the switch.
Do not expose the indicator light to avoid damage to the ESD. It is recommended to use a light panel or a lamp cover (Lens) for isolation. The cross section of the Lens should be smaller than the cross section of the lamp, and the surface of the Lens should be sprayed to make the light line evenly.
For the EMI problem, the upper cover and the lower cover are difficult to combine when in close contact. If there is no interference, the EMI cannot pass, so a shrapnel can be added at intervals to make the ground between the upper cover and the lower cover.
Draft angle
(1) Without prejudice to the appearance and shape of the case, the greater the range, the better
(2) Appropriate draft angle is approximately 1/10 to 1/30 (1° ~ 2°)
(3) The practical minimum is 1/120 (about 0.5°)
(4) The surface has a bite flower treatment, and the stripping slope is determined by the thickness of the bite flower. Generally, when the biting depth is 0.001 INCH (0.025 mm), the draft angle is at least 1°.
Thickness
The principle of uniform thickness is everywhere. It is also necessary to consider the structural strength and the ability to evenly distribute the impact force, and try to avoid the thin thickness of the sharp part to prevent insufficient filling.
In actual product design, thickness variation and shape are often required. The thickness variation of the step shape is easy to form deformation on the design surface, which can be improved by adding an R angle or a bevel angle. When there are inconsistent thicknesses, it should be gradually reduced as shown in the table below.
General practical thickness range Unit: mm
| material | Thickness | material | Thickness |
| Polyethylene | 0.9~4.0 | Acrylic resin | 1.5~5.0 |
| Polypropylene | 0.6~3.5 | Hard chlorinated polyethylene | 1.5~5.0 |
| Polyacetate | 0.6~3.0 | Polycarbonate resin | 1.5~5.0 |
| Polyethyl ester | 1.5~5.0 | Cellulose acetate | 1.0~4.0 |
| Polystyrene and acrylonitrile styrene (AS) | 1.0~4.0 | ABS | 1.5~4.5 |
2. Inner round angle and outer corner angle
It is recommended that the minimum R is 0.5mm and the optimum rounding design is R/T=0.6. After this point, even if R is increased, only a small part can reduce the stress concentration phenomenon. Inner round angle R=0.5T , outer corner angle R=1.5T
3. Rib
Ribs or flanges can be used to increase the strength of the molded article without increasing the thickness. These designs not only increase the strength, but also avoid distortion when cooling. In order to avoid shrinkage, the height of the rib is 0.5 T, the bottom fillet is R=0.125T, the draft angle is 0.5°~1.5°, and the direction of the rib is preferably the same as GATE. The distance between the ribs is as much as twice the wall thickness.
4. Bushing
The bushing is for reinforcement of the hole and for embedding in combination or for supporting other things. The height of the bushing is limited to less than twice its diameter. Because it is too high due to air concentration, it is easy to cause pores and insufficient filling. If it is necessary to have a high bushing, the reinforcing rib should be placed on the side to make the material flow easy. In order to avoid the shrinkage of the root surface, you can steal the material around the sleeve, but it can't be cut too deeply, otherwise there will be traces on the surface.
5. Fusion line
Try not to appear on the appearance surface. You can use the gate size, shape, number or the material near the gate to determine the position of the fusion line. Because it is the place where the material finally meets, its strength is weak, and should avoid the place where the finished product is subjected to load.
When you want to add holes or openings for LEDs or other complexes, the openings should be chamfered or rounded to facilitate assembly.
If there is a front and rear shell or a combination of the upper and lower covers, try to make the back shell (lower cover) into the front shell (top cover) to prevent the user from seeing the gap.
When designing the button, avoid directly on the power switch. The floating design or indirect drive design should be adopted to avoid the keying caused by the dimensional error or the deflection of the transmission rod of the switch.
Do not expose the indicator light to avoid damage to the ESD. It is recommended to use a light panel or a lamp cover (Lens) for isolation. The cross section of the Lens should be smaller than the cross section of the lamp, and the surface of the Lens should be sprayed to make the light line evenly.
