Design for Manufacturing in China: What to Check Before Sending Files

Overview

Design for Manufacturing (DFM) is the practice of designing products in a way that makes them easier, cheaper, and more reliable to manufacture. Before sending design files to a factory in China, completing a structured DFM review can prevent costly rework, delays, and quality issues during production.

This guide outlines the key checks to complete before releasing files. It is based on general mechanical engineering experience—specific requirements will vary by product type, manufacturing process, and factory capability.

What Is DFM?

DFM (Design for Manufacturing) is the process of optimizing a product design so that it can be manufactured efficiently and reliably. Key objectives include:

• Reducing part count and assembly complexity
• Selecting materials and processes that match the factory's capabilities
• Designing within achievable tolerances
• Minimizing tooling complexity and NRE (Non-Recurring Engineering) cost
• Ensuring consistent quality in mass production

File Preparation Checklist

Before sending files, verify:

• 3D CAD files: Export in a format the factory can use (STEP, IGES, or native format). STL is for 3D printing, not machining or molding.
• 2D drawings: Include critical dimensions, tolerances, surface finish, and material specifications. PDF is widely accepted.
• Bill of Materials (BOM): Include part numbers, quantities, materials, and suppliers for purchased components.
• Assembly drawings: Show how parts fit together, including fastener callouts and torque values.
• Surface finish specification: Define color, texture (e.g., SPI mold finish, Ra roughness), and coating requirements.
• Version control: Use clear version numbers and a revision table. Send the factory a single authoritative set of files.

Material and Process Alignment

Ensure the specified material is compatible with the chosen manufacturing process and is readily available from the factory's supply chain:

• For injection molding: verify the resin is available locally and the mold design matches the material's shrinkage rate
• For CNC machining: confirm the material grade, hardness, and heat treatment requirements
• For sheet metal: specify the grade, thickness, and bend radius limits
• For PCB assembly: confirm component availability and preferred package sizes

Material availability can differ between China and other regions. If you specify a material that is uncommon in the Chinese supply chain, the factory may propose an equivalent—evaluate this carefully.

Tolerance Review

Overly tight tolerances increase cost and may be unachievable in volume production. Review:

• Which dimensions are actually critical to function? Loosen non-critical tolerances.
• Are tolerances achievable with the specified process? (e.g., injection molding typically achieves +/- 0.1mm for dimensions under 100mm; CNC can achieve tighter but at higher cost)
• Are GD&T (Geometric Dimensioning and Tolerancing) callouts used correctly?
• Does the factory have the measurement equipment to verify critical tolerances?

Wall Thickness and Draft

For injection-molded parts, common DFM issues include:

• Uneven wall thickness: Can cause warping, sink marks, and internal stress. Design for uniform walls where possible.
• Excessive wall thickness: Increases cycle time, material usage, and can cause sink marks.
• Insufficient draft angle: Parts may not eject cleanly from the mold, causing damage. Typically 1-3 degrees per side, depending on texture and depth.
• Sharp corners: Add fillets to reduce stress concentrations and improve mold flow.
• Undercuts: Require side actions or lifters in the mold, increasing tooling cost. Minimize or eliminate where possible.

See our Plastic Material Selection Guide for material-specific guidance.

Assembly and DFM

Design for efficient assembly:

• Minimize part count—combine functions where possible
• Use standard fasteners rather than custom hardware
• Design for top-down assembly to simplify fixtures
• Include features for self-locating parts (pins, tabs, alignment features)
• Avoid awkward assembly positions that slow down production
• Consider testability—can the product be tested at intermediate assembly stages?

Communicating with the Factory

When sending DFM-reviewed files:

• Request the factory's DFM feedback before starting tooling
• Discuss any proposed design changes and evaluate trade-offs
• Document all agreed changes and update the files with clear version control
• Confirm the factory understands critical-to-function dimensions and inspection requirements
• Agree on first-article inspection (FAI) criteria before production

Common DFM Issues

Recurring DFM problems in hardware projects include:

• Tolerances specified tighter than the process can reliably achieve
• Material specified without verifying local availability
• Undercuts or side actions that significantly increase tooling cost
• Missing surface finish or color specifications
• Inconsistent file versions causing confusion
• Assembly sequences that require rework or complex fixturing

Most of these issues are preventable with a structured DFM review before releasing files. The time invested in DFM typically saves multiples of that time in avoided rework and delays.