Welded Press and Load Bearing Frames
A press frame is a structure that gets loaded, unloaded and loaded again, several million times. That single fact changes how it should be specified more than any material choice.
Frames like this very rarely fail by being overloaded once. They fail at a weld toe, at a stress raiser that a static calculation said was fine, after a number of cycles nobody counted.
What this application demands
- Fatigue, not static strengthCyclically loaded joints are assessed differently from statically loaded ones, and the relevant standards say so explicitly. Weld profile, undercut and toe angle stop being cosmetic and become the thing that decides the life of the structure.
- Weld quality where the load isThis is the part type where ISO 5817 level B genuinely earns its place, on the joints that carry the cyclic load. Applying it to the guarding as well is what makes the quote unnecessarily painful.
- Full penetration where the section must carry throughA partial penetration joint in a primary load path is a designed in crack starter. Where the section has to carry, the joint is prepared and fused through, and it gets inspected.
- Volumetric inspectionUltrasonic testing finds the planar defects that matter structurally, such as lack of fusion. Radiography is better at porosity and worse at tight planar defects. On a press frame the method is chosen for what you are actually looking for.
- Deflection under loadA press that flexes produces parts that vary. Frame stiffness is a process capability requirement, not just a structural one.
What goes wrong
In roughly the order we see it on drawings.
Static thinking on a cyclic part
Sizing the frame for the peak load and stopping there. The fatigue assessment is a separate exercise and it drives the weld details.
Blanket quality level
Level B everywhere raises cost and rework on joints nobody was worried about, and it distracts attention from the joints that matter.
No weld map
On a fatigue loaded frame, which weld gets which treatment is the most important information on the drawing. A numbered weld map is not optional here.
Sharp geometry at the weld toe
A steep toe angle concentrates stress. Dressing the toe on critical welds is a recognised way to extend fatigue life, and it has to be specified to happen.
What to put on the drawing
Every line here removes an assumption a shop would otherwise price as risk. Risk is always priced against you.
The full package is on the RFQ checklist, which is printable and remembers your ticks in your own browser.
- Loading stated as cyclic, with the expected number of cycles.
- A numbered weld map showing quality level and inspection per joint.
- Full penetration specified explicitly where the section carries through.
- Inspection method and extent per weld, with the acceptance standard.
- Toe dressing or profile requirements on fatigue critical welds.
- Deflection limit under working load.
- Stress relief called out where the frame is heavily restrained and carries machined features.
Questions on this part type
Why does fatigue change the weld specification?
Because a joint that is perfectly adequate under a static load can fail under millions of cycles at a stress raiser. Acceptance standards distinguish between predominantly static and fatigue loading for exactly this reason, and some imperfection limits differ between the two.
Should every weld on a press frame be level B?
No. Level B on the joints carrying the cyclic load, and a lower level on secondary structure and guarding. A blanket note is expensive and it hides which joints actually matter.
Ultrasonic or radiographic testing?
For the planar defects that drive fatigue failure, such as lack of fusion, ultrasonic testing is generally the better tool. Radiography shows porosity and slag very clearly and produces a permanent record, and it is poor at tight planar defects lying in the wrong plane. Pick the method for the defect you care about.
Go deeper
- Which Weld Quality Level to Put on Your DrawingWhat ISO 5817 quality levels B, C and D actually accept, how the level changes welding cost and rework, and how to apply different levels to different joints.
- Which Weld Inspection Method to Specify, and on Which WeldsVisual, dye penetrant, magnetic particle, ultrasonic and radiographic testing on weldments: what each method finds, what it misses and what it adds to the quote.
- AWS D1.1, ISO 3834 and EN 1090 Explained for People Who Buy WeldmentsWhat AWS D1.1, ISO 3834 and EN 1090 each cover, which one applies to your part and market, and what to ask a supplier to show you for each.
- Why Your Frame Came Out Bowed, and What a Shop Does About ItThe six causes of weld distortion in large weldments and the controls fabricators use: joint design, weld sequence, heat input, fixturing, prebending and balanced welding.
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