MIM公差・収縮チェックリスト（RFQレビュー用）

Quick Checklist Summary Before RFQ or Tooling

Before sending a MIM drawing for quotation or mold review, mark the functional dimensions and dimensional risks that must be checked by the supplier. This summary helps engineering, sourcing, and quality teams avoid treating every drawing dimension equally.

When Should You Use a MIM Tolerance & Shrinkage Checklist?

Use this checklist when the part has moved beyond general process research and the drawing needs engineering review. In practice, this usually happens before RFQ, before tooling approval, during MIMのDFM, or before approving first-article samples. It is especially useful when the drawing includes functional dimensions that cannot be judged from nominal geometry alone.

You should use this checklist when:

• the drawing includes tight tolerances on multiple dimensions;
• assembly fit, sealing, sliding, rotation, or alignment depends on specific CTQ dimensions;
• the part has long, flat, thin, asymmetric, or unsupported geometry;
• feature position, channel width, concentricity, perpendicularity, or flatness is critical;
• the part was originally designed for CNC machining, die casting, stamping, or investment casting;
• the buyer expects final dimensions without knowing which features may need post-sintering finishing;
• the project team wants to reduce tooling correction risk before mold manufacturing.

If your part has already shown design risk, also review the MIM設計におけるよくあるミス that often create avoidable tooling correction and sample approval issues. For the broader checklist library, visit MIMプロジェクトチェックリスト.

What Drawing Information Should Be Prepared Before Tolerance Review?

A supplier cannot accurately review tolerance and shrinkage risk from a 3D model alone. A 3D CAD model shows geometry, but the 2D drawing defines what must be controlled, measured, accepted, or rejected. For MIM projects, the most useful RFQ package separates functional requirements from general dimensions and explains why selected features matter to the assembly.

Tolerance Review Input Checklist

From a design review perspective, the most important input is not only nominal geometry. It is the relationship between function, tolerance, datum, material, surface condition, and inspection method. When this information is missing, the supplier may still quote the part, but the quotation may not reflect the real dimensional risk, secondary operation cost, or first-sample correction work.

For RFQ preparation, provide the drawing package through 図面レビューを提出 or follow the RFQ準備ガイド before sending a project inquiry.

Which Dimensions Are Truly Critical to Function?

Not every dimension on a MIM drawing should receive the same tolerance level. The first review step is to separate CTQ dimensions from general dimensions. This matters because unnecessary tight tolerances can increase tooling correction cycles, inspection burden, secondary finishing cost, and rejection risk without improving real part performance.

核心的な結論： Not every dimension on a MIM drawing should receive the same tolerance level. Functional dimensions should be separated from cosmetic or non-critical surfaces before RFQ.

CTQ Dimension Review Table

CTQ Risk Classification Before Supplier Review

After CTQ dimensions are identified, classify them by project risk. This helps engineering and purchasing teams decide which dimensions need supplier confirmation, which may require design adjustment, and which can remain under general drawing tolerance.

The real question is not whether MIM is precise. The real question is which dimensions must be precise for function. If a drawing applies tight tolerance to every surface, the supplier may need to add finishing or inspection steps to features that do not affect performance. That can raise cost and lengthen sample approval without improving the part.

This checklist identifies which dimensions require review before RFQ or tooling. For detailed tolerance capability, datum planning, GD&T interpretation, and inspection strategy, review the dedicated MIM公差 ガイドをご参照ください。.

Which Features Are Most Sensitive to MIM Shrinkage and Distortion?

MIM shrinkage is not only a percentage applied to the entire part. In production, dimensional stability depends on geometry, feedstock flow, wall thickness balance, green part strength, support during debinding and sintering, and how the part sits on the setter. This is why shrinkage-sensitive features should be reviewed before tooling, not only after inspection.

核心的な結論： MIM shrinkage risk is driven by geometry, wall balance, support condition, and feature location—not only by a single shrinkage percentage.

Shrinkage-Sensitive Geometry Checklist

In a checklist page, these risks should be identified, not fully solved. Detailed design decisions should be handled through dedicated reviews for MIM肉厚, holes, slots and undercuts, 焼結支持, ,および MIM焼結収縮補正.

Which Dimensions Can Remain As-Sintered and Which May Need Secondary Finishing?

Many MIM components are designed as near-net-shape or net-shape parts, but this does not mean every feature should be expected to meet the tightest tolerance as-sintered. The practical review question is: which dimensions can be controlled through MIM tooling and sintering, and which dimensions require a secondary tolerance route?

核心的な結論： Secondary finishing is not a failure of MIM. It is a tolerance strategy when functional dimensions are tighter than the as-sintered route can reliably support.

As-Sintered vs Secondary-Finished Tolerance Decision Table

In practice, secondary finishing is not a failure of MIM. It is a tolerance strategy. The problem occurs when it is discovered too late, after the buyer has expected a fully as-sintered part and the supplier has quoted without identifying the critical dimensions. That late discovery can change cost, lead time, inspection scope, and sample approval expectations.

For cost impact, compare tolerance route decisions with コストを考慮したMIM設計 before finalizing the drawing and RFQ package.

How Should Datum, GD&T, and Inspection Methods Be Reviewed?

Tolerance review is incomplete without inspection review. A dimension may appear acceptable on the drawing, but if the datum is unstable or the inspection method is unclear, the supplier and buyer may not measure the part the same way. This can create approval disputes even when the process is stable.

Datum and Inspection Review Checklist

A common mistake is treating GD&T as only a drawing language. For MIM parts, GD&T must be connected to real geometry stability, sintering behavior, support condition, and inspection access. If a critical datum is located on a surface that may warp, receive a gate mark, or contact a setter, measurement disagreement can occur even when the part appears visually acceptable.

For broader dimensional quality background, review 部品寸法が最終的なMIM部品品質に与える影響 および MIMにおける部品品質に影響を与える要因.

How Should First-Article Results Be Used to Correct Shrinkage or Tooling Risk?

First-article inspection should not be treated as a simple pass/fail step. For MIM parts, first-article data can reveal whether dimensional variation comes from tooling compensation, local geometry, sintering support, material behavior, measurement method, or process settings. The review should classify the deviation before corrective action is selected.

核心的な結論： First-article inspection is not only pass/fail; it is a feedback loop for controlling MIM dimensional stability before production ramp-up.

First-Article Dimensional Review Steps

1. Compare CTQ dimensions separately from general dimensions. Critical dimensions should be reviewed first because they affect assembly, sealing, fit, or function.
2. Identify whether deviation is local or systematic. A systematic deviation may suggest tooling compensation or shrinkage factor adjustment. A local deviation may suggest wall thickness imbalance, gate effect, support condition, or feature geometry risk.
3. Check whether the measurement datum is stable. Before modifying tooling, confirm that the inspection method and datum are valid.
4. Separate process adjustment from mold correction. Some dimensional issues may be improved through process control. Others may require mold correction. These should not be confused.
5. Confirm correction before production ramp-up. Production should not proceed until CTQ dimensions, inspection method, and correction direction are aligned.

If first-article results show shrinkage or support-related dimensional risk, the next engineering step is usually a deeper shrinkage compensation review combined with sintering, inspection, and tooling feedback. For related process effects, see how debinding and sintering affect MIM part quality.

エンジニアリングトレーニングのための複合シナリオ

What Should Buyers Include in an RFQ for Tolerance and Shrinkage Review?

A tolerance-focused RFQ should give the supplier enough information to judge manufacturability, not just quote a part number. For MIM, the supplier needs to understand which dimensions are functional, which surfaces are cosmetic, which features are shrinkage-sensitive, and which dimensions may need post-sintering control.

RFQ Input Package for Tolerance and Shrinkage Review

If the RFQ includes only a 3D model and a general tolerance note, the supplier may not identify the real project risk. A stronger RFQ makes the tolerance route visible before tooling: as-sintered, tool correction, secondary finishing, or design adjustment.

Related MIM Design Guides for Deeper Engineering Review

Use this checklist as the starting point. If a specific risk appears during review, the next step is to read the relevant engineering guide instead of expanding every issue inside this checklist page.