Design for Manufacturing (L25)

“Over-the-Wall” Design Method

Leads to increased production costs and reduced part quality

Design for Manufacturing (DFM)

Leads to increased production costs and reduced part quality

The practice of designing products to make them easier and cheaper to manufacture while improving quality and reliability.

Product Development Lifecycle

• DFM: designing parts, components or products for ease of manufacturing with an end goal of making a better product at a lower cost.

• This is done by simplifying, optimizing and refining the product design.

• Stakeholders: engineers, designers, sales & marketing, manufacturing, quality control, regulatory, supply chain & logistics, etc.

DFMA (Design for Manufacturing and Assembly)

seeks to improve the final product by considering manufacturing and assembly constraints early on.

DFM Injection Molding Constraints

Constraint #1: Uniform wall thicknesses

Constraint #2: Draft angles

Constraint #3: Avoid undercuts

Constraint #4: Account for material specific shrinkage rates

Constraint #5: Avoid sharp corners

Constraint #6: Parting line, gate(s), and ejector pin locations

Constraint #7: Thin slots/features

Constraint #8: Shut-offs

Constraint #9: Text/Engraving

Constraint #10: Boss/rib/gusset design

Constraint #11: Holes

DFM CNC Machining Constraints

• Constraint #1: Limit cavity depth to no more than 4x the tool diameter to avoid tool deflection

  • Deep pockets -> include a 1-3 degree draft angle to minimize tool wear

• Constraint #2: Avoid sharp corners by filleting them to a radius of at least 1/3 the cavity depth

• Constraint #3: Thin wall vibrate & deflect

  • Keep wall thickness to 0.8mm for metals and 1.5mm for plastics

• Constraints #4: Standard CNC tools cannot create undercuts

  • T-slot and dove tail tools can be used

• Constraint #5: Nonstandard hole sizes need custom tools

  • Stick to standard drill and tap sizes

• Constraint #6: Tighter tolerances increase time and cost

  • Apply tight tolerances only to critical features

  • Noncritical dimensions, use standard tolerance +/- 0.005 in or greater

• Constraint #7: Small features are difficult to machine (requires small tools that can break)

• Constraint #8: Complex geometries are difficult to clamp

  • Ensure there are flat surfaces or bosses for clamping

DFM Sheet Metal Forming Constraints

• Key parameters: Bend radius, material thickness, tooling clearance, forming speed, forming pressure

• Constraint #1: Bend radius – minimum radius the sheet can be bent without cracking

  • No less than the sheet thickness

• Constraint #2: Spring back

  • Difficult to account for, must rely on expertise of sheet metal manufacturer

• Constraint #3: Material thickness – thicker sheet material is more challenging to work with, but create stronger parts

• Constraint #4: Hole placement

  • Keep holes 2-3xs’s the material thickness away from any edge

• Constraint #5: Deep drawing – to avoid tearing or wrinkling

  • Limit the draw ratio (height/diameter) to less than 2:1

• Constraint #6: Flanges and tabs

  • The length should be at least 2x’s the sheet thickness

DFM Casting Constraints

• Constraint #1: Shrinkage

  • Design parts to be slightly larger

• Constraint #2: Wall thickness

  • Nonuniform wall thickness can lead to uneven cooling and defects (warping/cracks)

• Constraint #3: Draft angles

  • Drafting the walls 1-3 degrees enables mold release

• Constraint #4: Sharp corners

  • Sharp internal corners can cause cracking during cooling

• Constraint #6: Undercuts

  • Avoid undercuts whenever possible