Checklist: DfM Review Before Sending Sheet Metal Drawings

Sending sheet metal drawings to a fabricator without a DfM review often leads to the same pattern: the shop finds a bend radius the press cannot hold, a hole too close to a bend, or a flat pattern that does not match the folded part. The cost is not just a revised drawing. It is expedited changes, material reorders, and a later delivery date.

This checklist is built for that moment before submission. It groups checks by theme so you can audit material, bending, cutting, and finishing without skipping steps. Each item includes the reason it matters and a red flag to watch for.

1. Material Selection and Stock Thickness

Start with the material. A DFM sheet metal review fails early if the material and thickness do not match the function, the bend radius, and the process. The drawing should state the material grade, thickness, finish, and whether the material is mill finished or prefinished.

Check	What to Verify	Red Flag
Material grade	Correct alloy and temper for the application	Generic “steel” with no grade or finish
Thickness	Matches bend radius and springback requirements	Thickness changed without updating bend deductions
Surface finish	Prefinish or mill finish is specified	No finish note on a painted or plated part
Edge condition	Deburring or burr control is defined	No note for thin gauge or cosmetic edges
Tolerance	General and critical tolerances are separated	All features listed at the same tolerance

A red flag is a drawing that assumes a material behavior the shop must guess. If the part is a bracket for a vibration load, the material and temper should be explicit. If the part is visible, the finish note belongs on the drawing, not in an email chain.

2. Bend Radii and Bend Lines

Bend lines are where most DFM sheet metal errors begin. Every bend line needs a direction, a radius, and a note on which side is the inside or outside of the bend. The radius must be achievable by the die and tooling, and it must account for material springback.

1. Confirm every bend line has a radius callout.
2. State whether the radius is inside, outside, or the neutral axis.
3. Mark the bend direction with arrows or bend letters.
4. Add a note for minimum radius if the design uses a sharp corner.
5. Flag any bend where the radius changes mid-line.

A zero bend radius on a thick sheet is a common red flag. Sharp corners crack in bending, especially on thicker material. If the design requires a tight corner, the drawing should say whether a break line, a small radius, or a cut line is intended.

A second red flag is a bend line that crosses a hole, slot, or edge. The shop must interpret the priority. The drawing should show which feature is cut first and whether the hole remains at its original position after bending.

3. Bend Deductions, K-Factors, and Flat Pattern

The flat pattern must match the folded part. If the flat pattern is generated from a CAD system, the K-factor and bend deduction settings matter. A mismatch between the flat pattern and the intended part length causes cumulative errors.

Check that the flat pattern includes:

• Bend deductions or K-factor values.
• A note on whether the flat pattern is the manufacturing pattern.
• Feature lengths after bending, not just the unfolded length.
• A tolerance on critical bend lengths.

A red flag is a flat pattern that uses generic K-factors without a note. If the part has multiple bends of different radii, the flat pattern may drift. The drawing should state whether the shop is allowed to adjust the flat pattern within tolerance or whether the pattern is fixed.

Another red flag is a part with many small bends and no tolerance stack-up note. The shop may produce each bend correctly, but the final part length may be off. State the critical dimension and the acceptable range.

4. Holes, Slots, and Clearance

Holes and slots must be clear of bend lines, edges, and other features. The minimum distance depends on thickness, material, and process, but the drawing should make it explicit. A hole too close to a bend can shift, tear, or crack. A slot too close to an edge can break off during cutting or bending.

1. Check hole-to-bend-line clearance.
2. Check hole-to-edge clearance.
3. Check hole-to-hole clearance.
4. Verify slot width and end radius.
5. Add a note for any feature that must be punched before bending.

A red flag is a hole directly on a bend line. If the design requires a hole to cross a bend, the shop must know whether to punch before bending or after. The drawing should state the operation order.

A second red flag is a slot with no end radius. Sharp slot ends crack, especially on thin gauge. If the slot is a clearance feature, the end radius should be at least as large as the tool radius used to cut it.

5. Cutting, Perforation, and Edge Preparation

The cutting process affects what the drawing can promise. Laser, plasma, waterjet, and mechanical shearing all have different edge quality and kerf behavior. The DFM sheet metal review should state the intended cutting method or at least the edge condition required.

• Laser cutting: good for fine features, but small holes and tight slots need minimum sizes.
• Plasma cutting: acceptable edge quality for thicker stock, but not ideal for fine detail.
• Waterjet cutting: good for thick material and non-ferrous alloys, but edge burr may require deburring.
• Mechanical shearing: fast for straight lines, but not for complex contours.

A red flag is a drawing that specifies a feature size without a process note. A 1 mm hole in 3 mm aluminum is a different question than a 1 mm hole in 1 mm mild steel. The process and material together determine feasibility.

Another red flag is a drawing that assumes a perfectly square edge. If the part will be welded, mated, or painted, the edge condition matters. State whether the edge is to be deburred, chamfered, or left as cut.

6. Fit, Fasteners, and Assembly

Sheet metal parts rarely live alone. The DfM review should verify that the part fits the assembly and that fasteners can be installed. A hole that is the wrong diameter, a slot that is too narrow, or a bend that interferes with a mating part will cause assembly rework.

Check these items:

• Fastener hole diameter and depth.
• Counterbore or countersink depth.
• Slot width for sliding or adjusting features.
• Clearance between the part and the mating surface.
• Access for tool heads and fasteners.

A red flag is a drawing that shows a fastener hole but no depth. If the fastener is a screw, the hole depth determines the thread engagement. If the fastener is a rivet, the hole and backing plate must align.

A second red flag is a slot that is too narrow for the fastener or tool. If the slot is used for adjustment, the tool head must fit. If it is used for sliding, the width must account for paint, plating, or finish thickness.

7. Finishing, Coating, and Surface Requirements

Finishing changes the part after it is formed. Paint, plating, powder coating, and anodizing all add thickness, change surface texture, and affect fit. The DfM sheet metal checklist must confirm that the finish is compatible with the features.

1. Specify the finish type and thickness.
2. State whether the finish is inside, outside, or both.
3. Add a note for areas that must be masked.
4. Confirm that the finish does not interfere with bends, holes, or mating surfaces.
5. Add a note for corrosion protection if the part is exposed.

A red flag is a drawing that specifies a plating thickness but does not adjust the hole diameter. If a 6 mm hole is plated, the hole may close. The drawing should state whether the hole is machined after plating or whether the hole diameter already includes the plating allowance.

A second red flag is a finish note on a drawing with no mask note. If the part has a painted area and a bare area, the shop must know which area is bare. The drawing should show the mask boundary.

8. Documentation, Tolerances, and Revision Control

The last DFM sheet metal check is the document itself. A drawing that is technically correct but poorly documented creates the same errors as a bad design. The shop needs to know what to check first, what is critical, and what can be adjusted.

• Add a title block with material, thickness, finish, and quantity.
• State general tolerances.
• Identify critical dimensions with a symbol or note.
• Add a bend direction note.
• Include a revision history.
• State the drawing scale and units.

A red flag is a drawing with no general tolerance note. If every dimension is unmarked, the shop must guess. The drawing should state the default tolerance and then mark the exceptions.

A second red flag is a drawing that changes the material without a new revision. If the material changes, the bend behavior changes. The flat pattern may still work, but the bend angle and springback may not. A revision note protects both sides.

9. Final Pre-Submission Audit

Run this short audit before the drawings leave your office. It takes minutes and catches the errors that cost the most later.

1. All bend lines have radius, direction, and inside/outside callouts.
2. All flat pattern features match the folded part length.
3. All holes and slots have edge and bend clearance.
4. Material, thickness, and finish are stated in the title block.
5. Cutting process or edge condition is specified.
6. Fastener holes and slots have depth and tool clearance.
7. Finishing does not interfere with fit or function.
8. General tolerances and critical dimensions are marked.
9. Revision history is current.
10. The drawing is readable at the scale shown.

If any item fails, fix it before sending. A small change now is cheaper than a rework later. The goal of the DFM sheet metal review is not to make the drawing perfect on paper. It is to make the drawing executable in the shop.

The part you are trying to make is not just a set of lines. It is a physical object that must bend, hold a fastener, fit a mating surface, and survive the finish process. The checklist above forces those questions to be answered before the shop has to guess.