Super-Ingenuity (SPI)

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Standard & Inspection Protocol

Injection Molding Tolerance Standards: ISO 20457 (TG4/TG6) & DIN 16742 — Drawing Callouts + Inspection Conditions

This page shows how to select ISO 20457 TG grades (TG6 baseline, TG4 for CTQs), what to write on the drawing, and how to set inspection conditions (23°C/50%RH, CMM vs fixture). You’ll also get PPAP-ready dimensional reporting rules to avoid supplier/customer disputes. Injection Molding services

Isometric 3D CAD render of a multi-cavity injection mold illustrating ISO 20457 and DIN 16742 tolerance requirements
ISO 20457 / TG4-TG6 VALIDATED

What Tolerances Can Injection Molding Realistically Hold?

Baseline answer: Injection molding typically holds ±0.05–±0.15 mm on mold-fixed CTQ features for small/medium parts; large envelopes and flatness-critical surfaces need wider bands due to shrinkage/warpage—final acceptance must define conditioning, datums, and the fixture/CMM method.

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3D CAD view of a multi-cavity injection mold highlighting CTQ features and mold-fixed datums for tolerance capability and inspection planning at Super-Ingenuity

Typical capability ranges by part size

Tolerance capability tracks the part envelope and how shrink/warpage accumulates across distance. Small precision components (< 50 mm) often target ±0.05 mm on mold-fixed CTQs; mid-sized parts (100–300 mm) typically plan ±0.15–±0.30 mm; large envelopes (> 500 mm) may require ±0.50 mm+ depending on resin, gating, and cooling balance.

For RFQs, always specify conditioning + measurement method + datums; otherwise a “±0.05 mm target” is not enforceable across resins, cavity counts, and part sizes.

Capability by feature type

Mold-fixed CTQs (hole diameters Ø, boss spacing, sealing land widths) can be controlled tighter than free-form cosmetic surfaces. Use GD&T (position/profile) tied to functional datums; relax non-functional surfaces to prevent unnecessary tooling and process cost escalation.

Ranges below assume stable process + agreed conditioning (23°C / 50%RH) + mold-fixed features. Non-mold-fixed areas and large flatness surfaces generally require wider tolerance bands and/or restrained inspection conditions.
Feature TypeTypical Achievable RangeHigh-Risk DriversRecommended GD&TInspection Method
Hole / Boss Diameters±0.05 mm to ±0.10 mmCore pin deflection, resin viscosity driftSize / Position (datum-controlled)Plug gauge + CMM correlation
Flatness (large areas)0.1 mm per 25 mm length (typ.)Cooling asymmetry, differential shrinkFlatness ⏥ (restrained condition if needed)Surface plate + CMM / optical scan (validated)
Snap-fit Clearance±0.08 mm to ±0.12 mmMaterial stiffness, gate location sensitivityProfile of Surface ⌒ (functional datums)Functional fixture + go/no-go
Sealing Surfaces±0.05 mm (CTQ zones)Parting line flash, warpage near shutoffsProfile ⌒ / Cylindricity (as applicable)Vision system (validated) + fixture check

The “Tolerance Killers”: Factors that Degrade Precision

  • Semi-crystalline shrink variation: PP / PA66 shrink is higher and more non-linear than amorphous PC/ABS—capability depends on moisture control and consistent melt/pack.
  • Wall thickness imbalance: Thickness variation drives sink + residual stress, pulling features out of spec; apply rib/wall rules from CNC design guidelines for wall thickness & rib rules.
  • Fiber orientation: Glass fiber aligns with flow, often causing anisotropic shrink (perpendicular > parallel), especially across large planes.
  • Cooling asymmetry: Temperature gradients and unbalanced channels create post-mold warpage; address early in Injection molding design decisions.
Expert insight: Injection molding holds tight tolerances on mold-fixed, symmetric CTQ features—and looser tolerances on large flat areas prone to warpage. Capability is dominated by resin shrink behavior, wall uniformity, thermal balance, and repeatable measurement. Next: choose a tolerance grade and write the exact drawing callout + acceptance method to make the tolerance enforceable.

Standards Map: ISO 20457, DIN 16742, SPI, and Automotive PPAP

Use this map to decide what standard to cite, what to write on the drawing, and what inspection/PPAP evidence to submit—so tolerance disputes are preventable, not negotiable.

ISO 20457: Global Molded-Part Precision

Replacing the older ISO 8062, ISO 20457 is the definitive global standard. It’s not just a list of numbers; it defines tolerance grades (TG) based on material groups and manufacturing conditions. Specifying "ISO 20457" without a Grade is insufficient—you must define the acceptance temperature (typically 23°C) and measurement humidity to ensure repeatable Quality Assurance results.

Minimum enforceable callout: “ISO 20457–TGx + conditioning (23°C/50%RH) + datum scheme + inspection method (CMM/fixture)”.

DIN 16742: The European Supply Chain Benchmark

Widely used by German Tier 1 suppliers, DIN 16742 provides general tolerances for plastic parts. It focuses on the relationship between mold-fixed and non-mold-fixed dimensions. If your drawing references this, it implies a strict adherence to European engineering rigor often required in Export Mold Production.

When DIN 16742 is cited, always state whether the feature is mold-fixed or non-mold-fixed—otherwise the tolerance expectation is ambiguous by design.

SPI: Surface Aesthetics, Not Dimensions

The SPI (Society of Plastics Industry) standard exclusively controls surface finish. From SPI-A1 (Mirror Polish) to SPI-D3 (Textured/Matte), this defines "how it looks and feels," not its size. For dimensional control, SPI must be paired with ISO standards. See our Surface Finishing Guide for visual samples.

Correct pairing example: “Surface finish: SPI-A2; General tolerances: ISO 20457–TG6.”

Automotive PPAP: IATF 16949 Compliance

Automotive standards demand more than just "in-spec" parts. Under the IATF 16949 system, PPAP (Production Part Approval Process) requires evidence of process stability (Cpk > 1.33), Gauge R&R (MSA), and full Dimensional Results for every cavity.

For PPAP, dimensional results should be cavity-identified + ballooned drawing aligned + MSA (Gauge R&R) referenced—otherwise the dataset is not actionable.

Standard What it Controls Where it Appears What to put on Drawing What to submit to Customer
ISO 20457 Dimensional tolerances, deformation, and tolerance grades (TG). Global/International RFQs. "ISO 20457-TG6" Full Dimensional Inspection Report.
DIN 16742 General tolerances for plastic molded parts. European / German engineering projects. "DIN 16742-TG5" Deviation analysis vs. CAD model.
SPI Surface roughness, polish levels, and texture depth. Cosmetic and optical components. "Surface Finish: SPI-A2" Surface plaque samples or RA measurements.
Automotive PPAP Process Capability (Cpk), MSA, Control Plans, and PSW. Automotive Tier 1 & 2 supply chains. "Critical Characteristic (CC/SC)" PPAP Level 3 Dossier (18 Elements).

ISO 20457: How to Choose a Tolerance Grade (TG6 Baseline / TG4 for CTQ) Without Over-Constraining the Mold

Grade Selection Logic

Choosing a Tolerance Grade (TG) requires a balance between functionality and cost. For precision injection molding, TG6 is the standard benchmark for industrial parts, while TG4 represents the extreme limit of tool-room capability.

Decision order: define CTQ → lock datums → pick TG grade → define conditioning & inspection method. Without this order, ‘tight tolerance’ is not measurable.

  • Function: Use tight TGs for snap-fits and bearing housings.
  • Material Family: Amorphous resins (PC, ABS) support tighter grades than semi-crystalline (PA66, POM).
  • Cosmetic Zones: Relax tolerances on non-mating surfaces to reduce scrap rates.

ISO vs. GD&T: When to Step Up

ISO 20457 handles general plus/minus dimensions well. However, for complex assemblies, Geometric Dimensioning and Tolerancing (GD&T) is mandatory. If a feature's orientation or position relative to a datum affects performance, linear tolerances are insufficient. Step up to GD&T when orientation/position to a datum drives function (sealing, bearing, alignment); linear ± tolerances alone will not control assembly risk. Refer to our Manufacturing tolerances & quality standards (GD&T-ready acceptance) for further guidance.

Industrial Acceptance Protocol: Avoiding Supplier Disputes

A tolerance is meaningless without a defined measurement context. At Super-Ingenuity, we follow strict Quality Assurance protocols to ensure data alignment between our factory and your lab.

Measurement Timing Dimensions must not be measured "hot" off the press. We enforce a 24-48 hour conditioning period at 23°C to allow for post-mold shrinkage stabilization.

Acceptance note: "Final dimensional report is valid only after 24–48h conditioning at 23°C (unless otherwise agreed)."

Environment Control Hygroscopic materials (like Nylon) change size with humidity. Measurement must occur in a climate-controlled room (50% ±10% RH) to meet ISO 20457 standards.

Acceptance note: "Measurement environment: 23°C ±1°C, 50% ±10% RH; hygroscopic resins require recorded conditioning log."

Fixture & Orientation For flexible parts, the use of a "Restrained Condition" fixture must be agreed upon. We define the part orientation and probe points in the early DFM stage to prevent MSA (Measurement Systems Analysis) failures.

Acceptance note: "If ‘restrained condition’ is required, fixture design + probing points must be approved before PPAP layout."

Need a professional evaluation of your part's tolerance capability? Send CAD + CTQ list — get TG grade recommendation + inspection plan (DFM/Moldflow included) →

DIN 16742: Fast Translation Guide for Global RFQs (Mold-Fixed vs Non-Mold-Fixed)

DIN Tolerance Class Selection Logic

If your RFQ references DIN 16742, you are dealing with a standard that categorizes tolerances based on material properties (Groups 1-4) and manufacturing accuracy. Unlike simple linear offsets, DIN accounts for the mold-fixed vs. non-mold-fixed (moving parts) dimensions. Rule of use: Start with TG6 for general housing/enclosure dimensions, and step up to TG4 only for CTQs (sealing interfaces, bearing seats, precision inserts). For large cosmetic covers, use TG8 to prevent scrap escalation from warpage and anisotropic shrink.

Mapping DIN Expectations to Inspection Plans

To ensure a smooth Quality Assurance cycle, your inspection plan must balloon dimensions based on their functional impact. Drawing/inspection note: Report Group A (mold-fixed) dimensions by cavity ID first; treat non-mold-fixed features as process-dependent and control them with functional fixtures or GD&T tied to datums.

Precision mold design complying with DIN 16742 standards for German automotive Tier-1
DIN 16742 Class Typical Dimension Range Notes Recommended Usage
TG4 (Precision) ±0.03mm to ±0.07mm (Small features) Medical device fluid connectors, high-speed gears.
TG6 (Standard) ±0.10mm to ±0.25mm (Medium parts) Automotive interior trim, electronic enclosures, consumer tech.
TG8 (Loose) ±0.40mm to ±0.80mm (Large parts) Heavy industrial covers, structural frames, non-mating surfaces.

Common Pitfalls in DIN Compliance

Multi-Cavity Variation: DIN tolerances are often calculated for a single cavity. In high-volume production with 16+ cavities, the "cavity-to-cavity" delta can consume 30-50% of your tolerance band. We address this through precision multi-cavity mold balancing (why cavities still vary) techniques that equalize gate pressure.

Anisotropic Shrink: Materials like glass-filled PA66 shrink differently along the flow vs. across the flow. A single DIN value may not cover the elliptical deformation of large circular features.

SPI Finish Callouts (A/B/C/D): Impact on Fit, Draft, and Acceptance (SPI Controls Appearance—Not Dimensions)

Grade A: Polish

Diamond buffed (A-1 to A-3). Mirror-like finish for lenses or high-gloss consumer electronics. Requires high-grade tool steel (S136).

Impact: Best for optical/cosmetic, but increases tool steel requirement and polishing time; verify shutoff sealing edges.

Grade B: Paper

Sandpaper finish (B-1 to B-3). Removes machining marks. Ideal for semi-gloss parts that need to hide minor mold defects.

Impact: Low risk to dimensions; typical draft ~1° is often sufficient for most cosmetics.

Grade C: Stone

Grit stone finish (C-1 to C-3). Common for non-cosmetic industrial parts or as a base for heavy textures.

Impact: Adds measurable texture depth—reserve for non-mating surfaces or allow extra clearance.

Grade D: Blast

Glass bead or sand blast. Provides a matte, non-reflective "stippled" look. High friction—requires significant draft angles.

Impact: High friction; plan 3–5° draft and avoid tight fits near textured walls.

How Texture Changes Real Dimensions

Surface requirements are not just aesthetic; they dictate Draft Angles. A standard SPI B-2 finish may only need 1° of draft, whereas a heavy SPI D-3 or VDI texture may require 3° to 5° to prevent "drag marks" during ejection.

Rule: Texture is physical depth. Heavy SPI-D / VDI can add ~0.05–0.15 mm per side, consuming clearance and causing assembly interference unless offset is modeled or fit is redefined.

Writing Appearance-Only Callouts

To avoid unnecessary costs, define visible vs. non-visible faces. At Super-Ingenuity, we recommend "Texture Exclusion Zones" on your drawings for shutoffs and sealing surfaces where flash or bypass leakage is a concern. Always exclude texture on: shutoffs, sealing lands, datum features, and any CTQ mating interface—otherwise inspection and leakage criteria become unmeasurable.

Check our Surface Finishing Guide for more.

SPI Surface finish comparison plaques showing A, B, and C grades
📋 DRAWING NOTE TEMPLATES (COPY & PASTE)
“SPI B-2 on cosmetic surfaces only (refer to View A). Non-cosmetic surfaces: mold finish at supplier discretion.” “Texture not allowed on shutoff, sealing surfaces, and critical datum features.”

Pro Tip: Specifying the "supplier discretion" on internal ribs can significantly reduce mold production lead times.

Automotive Programs: PPAP Dimensional Results (Level 3, Cavity-Identified) for Injection Molded Parts

Dimensional Results: The OEM Blueprint

In Tier-1 automotive supply chains, dimensional approval is the gateway to SOP. We provide a Ballooned Drawing where every dimension is indexed to a corresponding line item in the measurement report. For IATF 16949 compliance, samples must be identified by cavity number to isolate tool-driven variations from process-driven ones.

CTQ & Stability Strategy

Not all dimensions are equal. Critical-to-Quality (CTQ) features—typically marked with a "C" or diamond—require a Cpk study (Process Capability Index) on at least 30 samples per cavity. Non-critical dimensions are verified via a "Layout" (usually 1-5 samples) to ensure the entire part geometry meets the CAD master.

MSA Basics for Molded Parts

The biggest pitfall in automotive molding is Measurement System Analysis (MSA). If your Gauge R&R (GR&R) exceeds 10%, the customer will reject your results. At Super-Ingenuity, we design custom CMM fixtures to ensure part orientation is identical across every measurement cycle, eliminating operator bias. See our Quality Assurance protocols for more details.

Quality Engineer performing CMM dimensional layout for automotive PPAP approval
PPAP Item What it means for Molding Typical Evidence Common Rejection Reasons
Dimensional Results Verification of every single feature on the drawing. Ballooned drawing + 100% Layout Report (by cavity). Incomplete data; measuring "hot" parts without conditioning.
Process Capability (Cpk) Evidence that CTQs remain in spec over time. Statistical analysis (Cpk > 1.33 or 1.67). Process drift; high cavity-to-cavity variation.
MSA / Gauge R&R Validation that the measurement system is reliable. GR&R study (< 10% preferred). Poor fixture design; non-repeatable datums on flexible parts.
Appearance Approval (AAR) Validation of color, grain, and SPI finish. AAR Form + Colorimeter readings. Grain "stretch" or wash-out on steep draft walls.
Expert Quality Summary: For automotive injection molded parts, PPAP dimensional approval typically requires a ballooned drawing, dimensional layout results from representative samples (often by cavity), and evidence that CTQ characteristics are controlled. Clear datums, consistent conditioning, and a stable measurement method (fixture + MSA/GR&R) prevent disputes and resubmissions.

Preparing for an Automotive Audit? Consult with our Quality Director →

How to Tolerance a Molded Part Drawing: The Professional Workflow (Reduce PPAP Rejections & Quote Risk)

01

Define Functional Datums

Establish datums based on how the part fits into the assembly. Prioritize mating features over cosmetic ones to ensure a repeatable alignment system during CMM measurement.

Output: Datum scheme + measurement setup (CMM alignment or fixture concept).

02

Tag CTQ vs Non-CTQ

Do not "Critical-to-Quality" everything. Focus on 5-10 key dimensions that drive performance. Excessive CTQs lead to high tooling costs and unnecessary scrap rates.

Output: CTQ list (≤10–15 items) with target Cpk/Ppk requirement.

03

Use Profile Tolerances

For complex surfaces, use Profile of a Surface (⌒) GD&T. This avoids cluttered drawings with hundreds of ± dimensions and allows for efficient 3D color-map scanning.

Output: GD&T profile tied to datums for complex surfaces (avoid hundreds of ± dimensions).

04

Molding-Specific Notes

Always specify:
• Specific material grade and manufacturer.
• Shrinkage reference (e.g., 0.5% as-designed).
• Parting line and flash allowance zones.

Output: 2D note block including resin grade, conditioning, and texture exclusion zones.

05

Align with Capability

Ensure your tolerances can be measured. A ±0.01mm tolerance on a flexible, fiber-filled molded part is physically unverifiable without expensive gauging.

Output: Capability confirmation: inspection method + gauge strategy agreed before tooling.

🚨 5 Drawing Mistakes That Will Inflate Your Quote

If our engineers see these on your RFQ, the mold production costs will spike due to the high risk of rejection.

Large Flat Cosmetics Tight tolerances on large, thin flat surfaces. Risk: Post-mold warpage is unavoidable.

Fix: Define cosmetic zones and relax flatness; control function with datums + fixture.

Texture without Draft Heavy SPI-D3 texture with less than 3° draft. Risk: Guaranteed drag marks and scrap.

Fix: State SPI/VDI grade + minimum draft (e.g., ≥3° for heavy texture) on visible faces only.

Un-datum'd Flexible Parts Measuring a soft part "in free state" without fixtures. Risk: Impossible to get repeatable MSA.

Fix: Define restrained condition fixture and datum targets before GR&R/MSA.

Metal-like Resins Specifying ±0.02mm on Nylon (PA66). Risk: Moisture absorption makes this dimension dynamic.

Fix: Tighten only CTQ interfaces; for hygroscopic resins require conditioning and wider non-CTQ bands.

Unspecified Conditioning Measuring parts right after injection. Risk: Dimensions will change 48 hours later.

Fix: Add conditioning note: 24–48h @ 23°C / 50%RH before final layout.

Get your drawings reviewed by our DFM team: Request Professional Drawing Review →

Shrinkage & Warpage: How to Avoid Tolerance Failures (Prevent Drift, Bowing, and PPAP Rejections)

Material Physics: The Foundation of Shrinkage

Tolerance failures often stem from a fundamental mismatch between material choice and geometry. Amorphous resins (like ABS, PC) exhibit low, isotropic shrinkage (approx. 0.4-0.7%), making them ideal for tight-tolerance enclosures. Conversely, Semi-crystalline resins (like PA66, POM) undergo significant volumetric change (1.5-2.5%) during cooling. Failure to account for this result in "under-sized" features and dimensional drift.

Rule: Use tighter TG grades mainly on mold-fixed CTQs with amorphous resins; for semi-crystalline or glass-filled materials, control function with datums/fixtures and allow wider non-CTQ bands to absorb anisotropic shrink.

1. Geometry Levers
  • Wall Uniformity: Thick sections shrink more than thin ones, pulling the part into a "bow" shape.
  • Ribs & Bosses: Must be 40-60% of wall thickness to prevent sink marks and internal stress.
  • Coring Strategy: Eliminate heavy mass areas to ensure linear cooling.

Output: Define a wall-thickness map; keep ribs at 40–60% wall and avoid >2:1 thickness transitions.

2. Tooling Levers
  • Gate Location: Defines the flow front; improper placement causes "end-of-fill" shrink variation.
  • Cooling Balance: Delta-T between cavity and core must be < 5°C to prevent differential contraction.
  • Venting: Trapped gas increases local pressure and disrupts packing.

Output: Cooling plan with measured ΔT target (≤5°C) and vent depth specification to avoid trapped-gas packing variation.

3. Process Levers
  • Pack/Hold Pressure: Compacting the melt compensates for volumetric shrinkage.
  • Mold Temp: High temps improve surface but increase cooling time and shrink risk.
  • Material Drying: Moisture in Nylon (PA) leads to hydrolytic degradation and inconsistent dimensions.

Output: Validated process window (pack/hold and mold-temp limits) + drying spec recorded for each lot (esp. PA/PEEK/PPS).

Predictive Engineering: When to Request Moldflow & DFM?

If your design includes glass-fiber reinforcement, wall thickness ratios exceeding 2:1, or tolerances tighter than ISO 20457 Grade 6, empirical "guessing" is a high-risk strategy. Moldflow analysis identifies warpage vectors before tool steel is cut.

Get Free DFM & Moldflow Simulation

Required for: Automotive PPAP | Medical Devices | High-Cavitation Tooling

Measurement Setup: CMM vs Optical vs Gauges (Make Tolerances Repeatable, Not Debatable)

Fixturing Flexible Parts

Plastic parts are rarely rigid. If you measure a thin-walled housing without a Functional Fixture, you aren't measuring the part—you are measuring "gravity deformation" or "operator handling error." We use 3D-printed or machined nests to hold parts in their "as-assembled" state to ensure valid Quality Standard compliance.

Acceptance note: If the part is flexible, inspection is valid only in an agreed restrained-condition fixture with defined datums.

Optical Scanning Pitfalls

While fast, 3D laser scanning struggles with high-gloss (SPI A-1) or translucent resins. Light scatter leads to "surface noise," often misinterpreted as roughness or deviation. For these scenarios, a tactile CMM (Coordinate Measuring Machine) is the mandatory gold standard for precision.

Acceptance note: For glossy/transparent resins, optical scan results are for trend only unless validated against tactile CMM on CTQs.

Cavity-to-Cavity Reporting

In a 16-cavity mold, a single "representative sample" is a major risk. We provide Multi-Cavity Reports to identify if specific cavities are drifting due to imbalanced hot runner temps or gate wear, crucial for IATF 16949 programs.

Acceptance note: For ≥8 cavities, reports must be cavity-ID separated (no pooled “representative sample”).

Timing & Conditioning: The Dimensional Drift Curve

Dimensions of an injection molded part are dynamic. A part measured 5 minutes after ejection (0h) will be significantly larger than it is 48 hours later. ISO 20457 requires a stabilized state. We enforce a 24-48h conditioning period in a controlled 23°C / 50% RH environment to prevent false "Out of Spec" rejections.

Drawing note template: “FINAL DIMENSIONAL INSPECTION AFTER 24–48h CONDITIONING @ 23°C / 50%RH; MEASURE PER AGREED DATUM SCHEME.”

CMM Specialist checking measurement repeatability on molded components
Measurement Method Best For Weakness Setup Tips Reporting Format
Contact CMM High-precision CTQs, Datums. Slow cycle time per part. Use ruby tips; avoid high-force probes. AS9102 / PPAP Table
Optical Scanner Complex freeform surfaces. Shiny/Clear material interference. Use matte spray if allowed; align to CAD. Color-map deviation + CMM correlation on CTQs
Custom Gauges High-volume go/no-go checks. No quantitative data (just pass/fail). Check for wear/calibration monthly. Pass/Fail Log
Vision System Small 2D features, Flash check. No Z-axis depth precision. Backlighting is key for edge contrast. Statistical histogram

Ensure your measurement plan is aligned with factory capability: Consult Our Metrology Team →

Acceptance Rules: Pass/Fail for Injection Molded Parts (Windows, Conditioning, and PPAP Evidence)

Acceptance Windows vs. Points

Unlike CNC parts, injection molded components are dynamic. We define Acceptance Windows that account for batch-to-batch material viscosity changes. A single-point "fail" at +0.02mm may be functionally irrelevant if the Statistical Process Control (SPC) shows the mean is stable.

Acceptance rule: CTQs are judged by a stable mean with SPC evidence under agreed conditioning; a single-point fail without context is not a valid rejection trigger.

Temporary Out-of-Spec (TOS)

During initial T1/T2 trials, dimensions may drift as the tool reaches thermal equilibrium. We manage TOS through process tuning rather than tool steel changes, ensuring Rapid Tooling projects stay on schedule without premature machining.

TOS rule: During T1/T2, treat drift as process/thermal stabilization unless cavity-ID data proves a steel-driven issue.

Engineering Concessions

When a non-functional dimension falls outside the drawing limit, we issue an Engineering Concession Note (ECN). This documents the deviation, risk assessment, and customer approval, forming a vital part of the PPAP Level 3 dossier.

ECN rule: Concessions apply only to non-functional dimensions and must include risk assessment + customer sign-off + expiry/lot scope.

Functional Acceptance

Focuses on CTQ (Critical to Quality) features: Assembly interfaces, snap-fit tension, and sealing surfaces. Strict Pass/Fail based on CMM data and functional gauge testing.

  • Zero tolerance for flash on shut-offs.
  • Cpk > 1.33 for critical diameters.

Must define: datums + fixture/restraint condition + measurement method (CMM/gauge) before first layout.

Cosmetic Acceptance

Based on Limit Samples (Golden Samples). Defines acceptable levels of weld lines, gate vestige, and texture uniformity under specific lighting (D65).

  • Defined viewing distance (typically 500mm).
  • SPI grade compliance on visible "Class A" surfaces.

Must define: limit samples (golden) + lighting (D65) + viewing distance + defect class map (A/B zones).

Standard Deviation Protocol (If Parts Are Out of Spec)

  1. Root Cause Analysis: Determine if the error is Tool-based (Steel), Process-based (Settings), or Material-based (Shrink).
  2. Risk Assessment: Does the deviation affect safety, fit, or function?
  3. Correction vs. Concession: Low risk → ECN concession with defined scope; high risk → steel-safe correction + re-layout, archived into PPAP dossier.

Seeking an expert partner to manage your complex molding tolerances? Start Your Quality Consultation →

Quick Checklist: RFQ Package for Tight-Tolerance Molded Parts (Faster Quote, Fewer Assumptions)

What to Send (Input Data)

To receive an accurate quote from our Export Mold Production team, your RFQ package should include:

  • Required: CAD models (STEP/IGES)
  • Required: 2D drawing (PDF/DWG) with CTQs ballooned
  • Required: Material spec (resin grade + supplier; glass content if any)
  • Preferred: Annual volume + cosmetic zone map (Class A/B/C surfaces)

What to Request Back (Output Expectations)

Ensure your supplier’s technical proposal addresses the following Quality Standards:

  • Tolerance proposal: ISO 20457–TGx / DIN 16742 class + CTQ list
  • Inspection plan: datums + fixture/restraint condition + method (CMM/gauge/optical)
  • Cavity traceability: cavity-ID layout report plan (no pooled samples)
  • FAIR format: sample first-article layout template
📋 PROJECT REQUIREMENT TEMPLATE (COPY-PASTE)
PROJECT SCOPE: High-Precision Electronic Enclosure
STANDARD: ISO 20457 - TG6 (General) / TG4 (Critical Features)
MATERIAL: PC/ABS (Low Shrink Amorphous)
COSMETIC: SPI B-2 on View A; SPI C-1 on internal ribs
PPAP LEVEL: Level 3 required (include Cpk study on 32 pcs per cavity)
CONDITIONING: 48h @ 23°C / 50% RH before final CMM layout

Note: For automotive programs, please include your IATF 16949 specific requirements for Cavity-specific Dimensional Results.

Downloadable Quality & Tolerance Templates

Download field-tested templates to standardize drawing callouts, CTQ mapping, and PPAP-ready dimensional reporting. These templates reduce RFQ ambiguity and prevent avoidable rejections caused by missing conditioning, datums, or cavity-ID evidence. Align your project with IATF 16949 and global quality standards.

TXT Engineering Snippet

2D Tolerance Note Block

Ready-to-use drawing notes covering ISO 20457/DIN 16742, conditioning time, and SPI surface finish callouts.

GENERAL TOLERANCES: ISO 20457-TG6 SURFACE FINISH: SPI B-2 (COSMETIC) CONDITIONING: 48H @ 23°C / 50% RH DATUMS: REF. 3D STEP MASTER
Copy ISO/DIN Note Block Text
XLS 45 KB Excel

CTQ & Critical Feature Table

Standardized table for mapping characteristics, target dimensions, tolerances, measurement methods, and sample sizes. Includes CTQ priority, target dimension, datum/method (CMM/fixture), sample size, and cavity-ID reporting fields.

Download Excel Template
PDF 1.2 MB Template

PPAP Dimensional Report (Ballooned + Cavity-ID)

Professional layout template for ballooned drawings, cavity-specific results, and summary reports for Quality Assurance approval.

Download PDF Sample

Need a customized Measurement System Analysis (MSA)?
Our metrology team can design specific fixtures and reporting formats for your high-precision Export Mold programs.

Consult Our Quality Director →

Frequently Asked Questions: Injection Molding Tolerance Standards

What is ISO 20457 and when should I use it?
**Use ISO 20457** as the default global tolerance standard for molded plastic parts, but it is enforceable only when you specify the TG grade plus conditioning and measurement method (datums/CMM or fixture). It is mandatory for export mold production projects.
Is SPI a dimensional tolerance standard or surface finish only?
SPI (Society of Plastics Industry) is exclusively a surface finish standard. It defines the visual appearance and roughness (A-mirror, B-paper, C-stone, D-blast). It does NOT control dimensions. For size control, you must pair SPI finish callouts with ISO 20457 or DIN 16742 tolerances. Check our Surface Finishing Guide for visual samples.
What tolerances are realistic for injection molded parts?
Those ranges apply mainly to mold-fixed CTQs; flatness and large freeform areas must be looser due to warpage and post-mold drift. Generally, ±0.1mm is realistic for small, high-precision features in amorphous resins. However, for glass-filled or semi-crystalline resins, ±0.2mm to ±0.5mm is more common for mid-to-large parts. "Metal-like" tolerances (< ±0.02mm) are rarely achievable or stable in injection molding due to post-mold shrinkage and thermal expansion.
How do I mark CTQ tolerances for automotive PPAP?
Critical-to-Quality (CTQ) dimensions should be highlighted on your 2D ballooned drawing with a diamond or "C" symbol. These features require process capability evidence (Cpk > 1.33) and must follow IATF 16949 measurement protocols, including Gauge R&R validation of the inspection fixture.
How does texture (SPI/VDI) affect dimensional acceptance?
Textures have physical depth (typically 0.05mm to 0.15mm). If the 3D model doesn't account for texture depth, the part may measure "oversized" in textured areas. Additionally, heavy textures require 3° to 5° of draft, which can shift the location of parting line features. Always specify if dimensions include or exclude texture depth.
When should I use GD&T instead of ± tolerances on plastic parts?
Use Geometric Dimensioning and Tolerancing (GD&T) when feature orientation or position relative to a datum is critical for assembly. GD&T is superior for plastic parts because it allows for "profile of a surface" control, which better manages the organic, warped nature of precision molded parts compared to rigid linear offsets.
How do conditioning time and humidity change dimensions?
Plastic parts shrink over time as they cool and reach internal stress equilibrium. Hygroscopic resins (like PA66) also swell as they absorb moisture. ISO 20457 requires measurement after 24-48 hours of conditioning in a climate-controlled room (23°C/50%RH) to ensure stable and repeatable data.
How to report cavity-to-cavity variation in multi-cavity molds?
For multi-cavity tools, reporting must be cavity-specific. Use a Cavity Identification Plan where samples are numbered. The report should show the min/max/mean for each cavity separately to identify if specific gates are imbalanced or if specific cores are wearing prematurely. This is a core requirement for Quality Assurance in high-volume production.
ISO 20457 tolerance grade chart for different material groups

Still have questions about tolerance compliance? Ask our Metrology Specialists directly.

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Send CAD + ballooned CTQ list. We return an enforceable tolerance package: ISO 20457/DIN 16742 TG recommendation, drawing callouts (conditioning + datums), and a measurement plan (CMM/fixture + report format) aligned to your program.

  • Tolerance Review Output: ISO 20457/DIN 16742 TG grade proposal + 2D note block (conditioning/datums/texture exclusion) + measurement plan (CMM/fixture).
  • Automotive (PPAP) Output: Ballooned drawing alignment + cavity-ID layout plan + CTQ capability targets (Cpk/Ppk) + MSA/GR&R checklist.
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Super-Ingenuity engineering team performing DFM and moldflow analysis for precision parts