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1. Material Specifications
1. Material Specifications
The material type and grade stated on the Fractory platform is what should be followed even if alternative materials are shown on the production drawings attached. If anything is unclear please ask the account manager associated with the job.
The material thickness shown on the Fractory platform should also be followed and any alternative thicknesses (eg. 0.9mm instead of 1mm) should be agreed with the account manager for the job up front and Fractory platform updated to show what is actually being delivered.
Unless otherwise specified the surface condition and visual appearance of both sides of the finished sheet metal part should be in line with class B Finish as specified in the "General Appearance" section of this handbook.
If a pre-polished material has been requested we would require a class B+ Finish on the polished side and a class B Finish on the non polished side as specified in the "General Appearance" section of this handbook.
Please see below section of the General Appearance Class table that relates to tooling marks along with example images for each.
Class A finish (polished)
Class B+ finish (pre-polished)
Class B finish
Class C finish
2. Dimensional and Geometrical Tolerances
2. Dimensional and Geometrical Tolerances
Unless otherwise specified on the Fractory platform the dimensional tolerances for sheet metal bending/folding should fall within the Class B tolerance range as shown on the Tolerance Classifications page. The tolerance classifications for bending/folding sheet metal parts can be seen below :
Please note that these tolerances apply to the overall part dimension regardless of the number of folds.
*NOTE* Some parts may require dimensional tolerances that are tighter than Class A. In these cases it will be identified on the Fractory Platform and would need to be agreed up front.
3. Sheetmetal bending defects
3. Sheetmetal bending defects
The following section outlines common sheet metal bending defects. Apart from tooling marks, none of the defects listed below are permissible. Fractory requires all components to be delivered free of these imperfections. If there is a risk of any of these defects, it is mandatory to inform Fractory before proceeding with production.
3.1 Dimensional & Angular Defects
3.1 Dimensional & Angular Defects
Springback - The most common defect. After the punch releases, the metal slightly "unbends" toward its original shape due to elastic recovery.
Off-Center Bend - Occurs when the blank slips or isn't properly squared against the backgauges, resulting in asymmetrical flange lengths.
Angular Variation - The bend angle is inconsistent across the length of the part (e.g., 91 degrees at one end and 89 degrees at the other), often caused by "crowning" issues in the press brake.
3.2 Material Integrity Defects
3.2 Material Integrity Defects
Cracking - Small cracks appearing on the outer radius of the bend. This usually happens if the bend radius is too sharp for the material thickness or if you are bending "against the grain" of the metal.
Thinning - The material at the bend radius becomes significantly thinner than the rest of the sheet, weakening the part. The maximum allowable cross sectional reduction is 10% of the material thickness.
3.3 Surface & Cosmetic defects
3.3 Surface & Cosmetic defects
Die Marking (Tooling Marks) - Visible indentations or "scratches" left by the shoulders of the V-die. While often purely cosmetic, they can be rejected in high-finish industries. Acceptability criteria for tooling marks is shown at the top of this page and in the "General Appearance" page.
3.4 Geometrical Deformations
3.4 Geometrical Deformations
Hole Distortion - If a pre-drilled hole or slot is too close to the bend line, it will stretch into an oval shape during the bending process.
Bowing - The flat surfaces of the part become wavy or warped because of internal stresses being "locked in" during the bend.
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