How Should Buyers Build a Micro Injection Molding RFQ?

01

H2: Start with the manufacturing decision the RFQ must support

State whether the request is for feasibility, prototype parts, bridge supply, or repeat production. A feasibility request can invite alternatives and identify unknowns. A production request needs a clearer part revision, material status, forecast, approval route and change-control expectation. Put this decision on page one so a supplier does not price a development tool while the buyer assumes a production solution.

Define what makes the component micro-critical. Size alone is not enough. Identify narrow channels, thin sections, small gates, fine surface replication, mating pitch, optical surfaces, insert interfaces, or a feature whose small error prevents assembly or flow. Include function and the consequence of failure. A feature that merely looks small may be lower risk than a micro-channel that controls fluid movement. This context helps the supplier focus its DFM review and metrology proposal on the real risk.

02

H2: Issue CAD and drawing data that can be reviewed together

Use the injection molding 3D CAD quote package to communicate the nominal shape, including hidden features. Supply the revision, file format, unit system, assembly interfaces and necessary mating geometry. Mark confidential files and define access. Missing revision control or units creates avoidable ambiguity where millimetres and micrometres are used together.

The injection molding technical drawing should not apply a tight limit to every model dimension. Define datums, functional dimensions, needed geometric controls, surface or flash restrictions and inspection state. State whether measurement is after conditioning, assembly or another defined condition. Ask the supplier to identify conflicts between model, drawing and specification rather than choose an interpretation silently.

Use a CTQ register beside the drawing. Record the nominal, allowable variation, datum, function, risk and measurement method. Ask whether each feature is directly measurable, needs a fixture, needs non-contact metrology, or is better verified with a functional gauge.

03

H3: Describe micro-features in functional terms

For each micro-feature, provide section views and the permissible gate vestige, parting-line witness, ejector-mark location or burr limit where these affect use. If the feature must remain open, seal, transmit light, mate to another part, or retain a fluid, write that requirement explicitly. Photographs of an existing acceptable part can help clarify a visual condition, but they do not replace dimensional and functional requirements.

Avoid a blanket micrometre tolerance. Tolerance depends on geometry, resin behaviour, shrinkage, tooling, process control and measurement. Industry guidance likewise links part design, material selection and tool design (Reference 2). Discuss supplier-specific capability after DFM, then tighten only features that need it.

04

H2: Make material and dimensional-stability assumptions visible

Name the resin grade if fixed, including supplier, colour, additives, filler, recycled-content restriction and needed compliance documents. If selection is open, state priorities such as chemical exposure, electrical performance, stiffness, temperature or transparency. A resin family name alone does not control shrinkage, flow or moisture sensitivity; review the proposed grade and data sheet with the geometry.

Ask bidders to identify how material preparation, shot size, gate and runner design, cavity temperature control, packing, cooling and ejection could affect fill and stability. For micro injection molding, small changes in viscosity or air evacuation can matter disproportionately because the flow path and features are small. The supplier should state which assumptions remain to be confirmed during trials instead of presenting an early quote as a guarantee of final dimensional performance.

05

H2: Request a tooling concept, not an unsupported tool-life promise

A useful injection molding quote distinguishes part-production pricing from tool scope. Request the proposed cavity count, family-versus-dedicated tool decision, runner concept, gate approach, parting-line and ejection concept, inserts or side actions, expected tool steel or insert strategy, and anticipated maintenance items. Ask which choices are preliminary and which need a DFM decision. Fine cavities may need dedicated insert, venting and demolding solutions; their suitability depends on the actual geometry rather than the word micro.

Give the annual forecast, batch-size range, ramp profile, service horizon, destination and packaging or traceability constraints. Request a capacity explanation based on the proposed tool and process, not a general assurance. Ask for the basis of any tool-life expectation, including resin, filler, maintenance and approved operating conditions.

06

H2: Specify evidence before asking for a committed quotation

List the evidence needed at DFM, trial and production stages. A proportionate package can include a DFM report with open items, material identification, trial record, first-article dimensional report, photographs or magnified images for defined cosmetic areas, and a control plan. Define which revision the report represents and who approves it. If cavity-to-cavity variation matters, state whether the results must be traceable by cavity. If a functional check is more meaningful than a single dimension, describe the test fixture, mating part or acceptance result.

Match the metrology method to the feature. Research on micro injection molded products cautions that contact tools can be difficult to use on extremely narrow features and notes that optical approaches may be more suitable for dimensional and surface evaluation in those cases (Reference 1). That does not make one instrument correct for every part. Require the supplier to state measurement resolution, datum setup, magnification or scan strategy, calibration status where applicable, and limits of the proposed method. A measured number without this context is weak evidence.

07

H2: Compare quotations by technical closure as well as price

Use the same RFQ package and response template for every bidder. Separate non-recurring tooling, sampling or validation work, unit price at stated volume bands, secondary operations, packaging, inspection, freight basis and exclusions. Require assumptions to be visible: resin grade, colour, number of cavities, cycle-time basis if quoted, yield assumption, packaging unit and Incoterm if cross-border delivery is involved. Do not compare unit prices where suppliers have priced different technical baselines.

Score responses for completeness and risk closure. Strong responses identify missing information, explain CTQ measurement and separate preliminary feasibility from approved capability. Treat certainty carefully if it lacks a tool concept or validation route. A clarification request is often more useful than an attractive number built on unstated assumptions.

08

H2: Keep the supplier collaboration open through DFM and trials

Invite suppliers to challenge geometry before award. Ask them to rank risks such as incomplete fill, venting, flash, gate vestige, ejection damage, shrinkage variation, distortion and difficult measurement. Require each proposal to separate a must-change issue from an option that improves robustness or cost. Freeze the part revision only after the buyer has documented decisions on functional trade-offs. This discipline protects both sides from treating a quote-stage concept as a released tool design.

Close with a technical review, agreed DFM output, revised quote after design closure and sample-approval plan. Send any baseline-changing clarification to all bidders. This creates a traceable path to an approved tool concept and helps control later engineering changes.