Tier-1 Playbook: Plastic Part Design for Injection Molding

For 10+ years I was a senior design engineer at a U.S. Tier-1 automotive supplier, owning high-volume OEM and accessory programs for Ford, General Motors, Toyota, Subaru, and Land Rover, and more. These programs included Class-A painted exteriors, structural components, multi-material overmolds, and complex assemblies spanning multiple tools and materials. Automotive is uniquely unforgiving: perfection is non-negotiable, schedules never allow enough time, and cost targets squeeze every penny, while a single defective part can stop an assembly line at $15k per minute.

This guide is the distilled result of that experience — 59 pages of practical rules, tables, and ratios with simple explanations of why they work. No academic theory, no endless standards — just the design practices that consistently delivered first-shot approval and eliminated expensive rework.

The rules in this guide were forged and tested in the crucible of high-volume manufacturing — a brutal proving ground — and became the gold standard for headache-free plastic part design. They will serve you well across every industry and application.

Who this is for:

This guide is for anyone who designs, reviews, or approves injection-molded plastic parts — regardless of industry or experience level.

• Entry-level designers and recent graduates: Get clear "what to do and why" explanations, tables, and rules to avoid common mistakes and build confidence fast.
• Experienced engineers: Use the printable reference tables for quick checks on walls, ribs, draft, tolerances, and features during design reviews.
• Startup founders and product developers: Avoid $50k–$200k mold rework on your first (or only) tooling run.
• Freelancers and consultants: Deliver Tier-1 quality to clients and justify your rates with proven rules.
• Procurement and program managers: Understand DFM to push back on risky designs and keep programs on schedule/budget.
• Teams in any industry: Automotive, medical devices, consumer electronics, industrial equipment — the rules were tested in high-volume environments, so they work reliably everywhere.

If you touch plastic parts and want to ship them flawless, first shot, this guide is your shortcut.

What you'll get:

• The 14 resins that dominate production (and why others fail)
• Nominal wall, rib, boss, and gusset ratios that eliminate sink and warp
• Draft tables by texture depth
• Gate selection and vestige rules for cosmetic surfaces
• Commercial block tolerances per ISO 20457/DIN 16901
• Common design features with dimensions that pass first-shot sampling
• Steel-safe philosophy that prevents most post-tooling nightmares
• Printable reference tables for daily use
• And much more...

Engineers, designers, startup founders, and procurement teams — from entry-level to senior — will find this the reference they keep open on their second monitor.

Lifetime updates included. Instant download.

If you've ever lost sleep over a mold rework or hesitated to press send on your tooling kick-off package, this guide is your shortcut to confidence.

-The Tier-1 Engineer