The first part is always a millimetre out
A new part is drawn in CAD and unfolded. The flat pattern is cut on the laser and bent on the brake. The flange is short by a millimetre, or the overall width is long. The bender adjusts the backgauge and gets a good part by bending it slightly differently, which is fine for this batch. Next time the same material and tooling are used on a different part, the same thing happens.
The senior bender has a notebook of what really works for each thickness and die. The CAD software uses a default table from years ago.
Why flat patterns and brakes disagree
The allowance a bend needs depends on material, grade, thickness, grain direction, punch radius and die opening. Default tables in CAD are a starting point. Your actual combination of stockholder material and tooling is what counts, and that knowledge is collected on the shop floor, then kept there.
- CAD uses default bend tables or one K factor for everything.
- Corrections found at the brake are not sent back to the drawing office.
- The senior bender's notebook is the real bend table.
- Different brakes and tool sets behave differently.
- Material from a new stockholder bends differently and nobody records it.
What mismatched bend data costs
Scrapped first offs on every new part. Setups that take longer because the bender is correcting the pattern by adjusting the bend. Parts that pass individually but do not fit when assembled, because small errors add up. And a quiet dependence on one person, whose notebook leaves when they do.
The bend data library we build
- A simple test bend routine on a tablet at the brake records material, grade, thickness, punch, die, V opening, brake and the measured result of a test piece.
- First off measurements on real jobs are recorded the same way, so the library grows from normal work as well as tests.
- From these, the library works out the bend deduction or allowance for each combination, and flags where results vary widely.
- The library is exported in the format your CAD software uses for bend tables, so flat patterns are unfolded with your own data.
- When a part is drawn with a combination the library has no data for, the drafter is warned so a test bend can be done first.
- The senior bender's notebook values can be entered to start, and checked against new results over time.
| Recorded per bend | Why |
|---|---|
| Material, grade and thickness | Allowance changes with each |
| Punch radius and die V opening | Tooling changes the result |
| Brake used | Machines differ |
| Measured flange lengths | Actual result, not theory |
| Stockholder and batch | Spot changes when supply changes |
When CAD and the brake agree
Flat patterns come off the laser closer to right, so first offs pass more often and setups are quicker. The drafter knows when a part uses a combination that has not been tested. New benders work from the same data as the senior one. And when a new stockholder's material bends differently, the change is seen in the results, not discovered through a run of scrap.
The knowledge that used to sit in one notebook becomes a shared asset of the business.
Quoting benefits in a small way too. When the estimator prices a part in a material or thickness with little bend data, the library shows it, and the quote can allow for a test bend and a slower first off rather than assuming it will go like the familiar work.
Are your flat patterns a guess?
- First offs are routinely adjusted at the brake.
- CAD uses a default bend table or one K factor.
- One person's notebook holds the real bend data.
- Assemblies do not fit even when parts pass.
- Changing material supplier caused a run of problems.