Design for Manufacturing (DFM) Guidelines

Introduction

Design for Manufacturing (DFM) is a systematic approach to optimizing product design for ease of production. By adhering to these guidelines, you can reduce part cost by 20–40%, decrease lead times, and improve overall quality and reliability.

General Design Principles

• Minimize Part Count: Combine components where possible to reduce assembly time and fasteners.
• Symmetry & Alignment: Align features to standard tool axes. Avoid tilted or angled surfaces unless necessary.
• Standard Components: Use off-the-shelf bearings, seals, and fasteners to reduce cost and sourcing delays.
• Design for Assembly: Prioritize snap-fit, push-in, or self-aligning features over screws and adhesives.

CNC Machining Guidelines

Geometry & Tool Access

• Avoid sharp internal corners. Use a minimum fillet radius equal to 50% of the expected tool diameter.
• Keep pocket depths to ≤ 4x tool diameter for stability and surface finish.
• Design features that align with standard tool axes (X, Y, Z) to minimize multi-axis setups.

Holes & Threads

• Prefer drilled holes over milled slots. Use standard drill bit sizes where possible.
• Include drill point relief (0.2–0.5mm) at pocket bottoms unless specified otherwise.
• Tapped holes: ensure minimum thread depth of 1.5x nominal diameter. Use tap drills per ISO/ASME standards.

Sheet Metal Fabrication

Bends & K-Factors

• Minimum internal bend radius: 1x material thickness for mild steel/aluminum.
• Relief cut length: 1.5x material thickness unless bend extends to edge.
• Allow 0.5mm gap between bend and nearest hole/feature.

Flat Pattern Design

• Provide flat patterns with bend lines and K-factor specified (default K=0.44 for 0.5–2.0mm sheet).
• Uniform wall thickness improves forming predictability and reduces springback.
• Use standard sheet sizes to minimize waste (e.g., 1219×2438mm, 1000×2000mm).

Injection Molding Guidelines

Wall Thickness & Draft

• Maintain uniform wall thickness (typically 1.5–3.0mm). Avoid sudden transitions.
• Minimum draft angle: 1° for shallow pulls, 2–3° for deeper features.
• Rib thickness should not exceed 60% of nominal wall thickness to prevent sink marks.

Parting Lines & Ejection

• Design for single-parting line where possible. Avoid undercuts; use side-actions only if necessary.
• Provide ejector pin locations or design for sleeve ejector on external faces.
• Gate locations should not intersect cosmetic surfaces unless post-processing is acceptable.

Die Casting Guidelines

Wall & Section Design

• Optimal wall thickness: 3–6mm (Aluminum/Zinc). Thinner walls risk cold shuts.
• Use generous fillets (min 0.5mm) at all internal and external corners.
• Avoid thick sections to minimize porosity and shrinkage defects.

Draft & Ejection

• Standard draft: 1.5–3° for aluminum, 1° for zinc.
• Ensure uniform pull direction. Add ribbing or gussets instead of increasing wall thickness.

Tolerances & GD&T

For critical dimensions, apply GD&T per ASME Y14.5-2018. Specify datums clearly and avoid over-constraining. Unspecified tolerances default to ISO 2768-mK.

Surface Finishes & Treatments

Note: Specify finish on critical surfaces only. Blanket specifications increase cost and risk defects in hidden areas.

DFM Review Checklist

Run this checklist before submitting your files to ensure optimal manufacturability.