Комаров Артем о включении геометрических допусков в конструкции комплектующих деталей (eng)
Комаров Артем о включении геометрических допусков в конструкции комплектующих деталей (eng)

Комаров Артем о включении геометрических допусков в конструкции комплектующих деталей (eng)

Komarov Artem noted that does the weldment drawing put appropriate emphasis on the correct assembly features, while we’re on the topic of GD&T (geometric dimensioning and tolerancing). Consider a square pipe frame with gussets at the corners and holes for attaching a panel inside the frame. How should these parts be located?

Let’s put aside for now the decision about whether the corners of the pipes will be butt-joined or at an angle. Let’s just look at the four screen mounting holes.

Комаров Артём Андреевич, сварка, геометрические размеры и допуски
The components are attached by the height and width of the frame (left), by the location of the holes (center) and by the length of the pipe sections (right).

We could clamp the square tubes onto the mounting pins surrounding the frame, then clamp the gussets into the corners and weld them there (see Figure 1). Alternatively, we could secure the holes in the mount and clamp the square tubes to the sides of the gussets. Or we could find two perpendicular pipes and clamp everything else onto them.

The first method will usually make the frame the right size, the second will usually place the holes in the correct order, and the third may be the easiest to load. What’s most important? When used correctly, GD&T will guide you.

Proper use of GD&T does not simply mean that there are no violations of applicable regulations. GD&T can be on a drawing — and not be wrong — without using its ability to express things like These four holes are used to mount the screen with the corresponding hole pattern or The size of the outer part of the frame is critical to fit and function. He may even say both, which will indicate the need to be very careful with both component sizes and mounting.Комаров Артём Андреевич, сварка, геометрические допуски

You should also consider which of the parameters is more accurate: the dimensions of the fasteners or components.

3D printing for fastening elements
Many welding tables include a precise grid of holes to accommodate fixture parts. It is important to document exactly what (pin, clamp, angle) goes where. To take things a step further, 3D printing can be used to create custom fixture parts that hold specific components in specific locations; for example, two plug pins for the welding table at the bottom, a pin or clamping pad at a specific location at the top. These specialty fixture parts can be stored in minimal space for reuse or reprinted as needed.

Geo-Set and Re Weld versus Single Weld Operation
One way to avoid weld distortion is to only tack parts while they are in the fixture. Once the geometry of the weld joint is established by tack welding, the weld joint can be removed and the welding completed. This geopositioning and rewelding process often allows for easier access to the welds from the back side and may be necessary to prevent damage to 3D printed fixture parts.

Specific welding sequences can also be critical to preventing parts from moving due to welding. Document welding sequences as well as the locations of pins, clamps, and pads on welding tables.

There are many factors to consider when designing and manufacturing fixtures for welding or assembly. GD&T can be used to identify critical relationships between parts, fixtures, and assemblies, clarified Artem Komarov.