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Design Points of Sheet Metal Structure—2

by: Jun 14,2022 2363 Views 0 Comments Posted in Sheet Metal

Sheet Metal

Design Points of Screw Hole

There are generally three ways to fix the screw:

1.Directly punch or draw holes on the plane of the iron piece. and the use self-tapping screw. For self-tapping screw, triangular self-tapping screw is better, which are less prone to get stripped, and the locking force will be a little heavier than non-triangular self-tapping screws.

If it is screwed with a diameter of 3mm, the hole diameter d should be between 2.4 and 2.5mm.

If it is screwed with a diameter of 4mm, the hole diameter d should be between 3.4 and 3.5mm.


2.Punch through holes or draw holes on the plane of the iron piece, and then tap the threads with screws.

Generally, the mechanical thread of M3 or M4 are attacked.

If it is screwed with a diameter of 3mm, the hole diameter d should be 2.6mm before tapping.

If it is screwed with a diameter of 4mm, the hole diameter d should be 3.6mm before tapping.


If the thickness of the material used is 1.0~1.2mm, it is recommended to use a drawing hole instead of a through hole.

Because when material with the thickness of 1.2mm taps the thread of M3, there is only 2.5 thread, which is easy to get stripped.


3.Punch holes on the plane of the iron piece, and then rivet the ready-made fixing nut.

The hole diameter d of the riveting set nut is preferably the size recommended by the manufacturer.

It will cost a lot of time and money to process the nuts one by one when riveting the nuts. Therefore, almost all processing plants use general punches for riveting. If the machine used is unfortunately a conventional punching machine, there is a possibility that the nut will fall off, because the punching speed of the conventional punching machine is too fast, and the material of the workpiece will end before filling the nut or stand-off groove. The problem is completely undetectable from the appearance, but some nuts will fall off when the finished product is assembled. Therefore, for the machine used for riveting the fixed nut, it is best to choose a machine that can adjust the stamping speed.


Design Points of Chassis Sheet Metal

In the assembly design of chassis, there are often a combination of 2 pieces, or a combination of more than 3 or 4 pieces. When spot welding, there must be positioning points, positioning pins or fixtures to ensure the correct position. But generally no more will be added if screws or pull studs are used, because there are already opposite screw holes and pull stud holes. However, in order to facilitate assembly, the hole diameter of the screw hole and the stud hole will be designed to be larger, so the relative position between the parts is also prone to errors.

In this case, it is recommended to use the positioning bumps with a small gap for positioning. When doing the T/A Loop operation, it is more accurate to use the positioning points with a small tolerance to do the benchmark calculation.


Before the chassis is opened, it is better to design the position and size of the required mark. Mark it on the instance can facilitate alignment when sticking the mark. There are two most common marks:

1.Make an "L"-shaped mark around the mark, or on the upper and lower sides of the left side, or the left and right sides of the upper side. This method is cheaper to mold, but the mark protrudes from the surface of the instance and is easily scratched.


Before the casing is opened, it is best to design the position and size of the required mark, and mark it on the instance to facilitate alignment when sticking the mark. There are two most common marks.

1. Make an "L"-shaped mark around the mark, or on the upper and lower sides of the left side, or the left and right sides of the upper side. This method is cheaper to mold, but the mark protrudes from the surface of the instance and is easily scratched.

2. Increase the size of the mark by 0.3mm, and make a dent of 0.2~0.3mm at the place to be marked.


No matter what method is used, you can choose an appropriate angle of the four to make a 45-degree lead angle, and make the same 45-degree lead corner at the opposite position of the mark on the example. To be fool-proof, which is used to avoid marking different directions at different times or different staff posted.


Don't forget to design a large R angle to avoid the occurrence of acute angles where there is a break, or when the upper cover is under heavy pressure, the acute angle will stand against the upper cover and cause a sharp bulge.

In addition to increasing the strength of the chassis, fixing the fan and the air duct, the middle wall can effectively prevent EMI if it is in perfect contact with the inside of the upper cover, which will greatly prevent the noise of the motherboard from emitting from the front, so it is better to avoid placing plastic parts on the middle wall to prevent contact with the upper cover.


The picture comes from the Internet



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