Adding an insert to a molded silicone part can combine a flexible sealing, cushioning or handling feature with a rigid component. The insert may be metal, plastic or another project-reviewed material. However, an insert shown inside a silicone body is not enough information for a supplier to judge tooling, handling, interface risk or inspection.
A useful RFQ separates what the insert must do, what the silicone must do and how the combined part will be assembled and verified. This guide describes drawing and sample inputs that help engineering and procurement teams start that review without assuming a particular bond result or process capability.
Define the insert and its function
Identify the insert material, grade or existing part number, and state whether it is buyer-supplied or supplier-sourced. Provide its controlled drawing and available three-dimensional data. Mark coatings, plating, surface finishes, heat treatment and areas that must remain free of silicone. If the insert is an existing purchased component, include the revision and supplier variation that the overmolder should expect.
Explain whether the insert transfers load, locates the part, provides a thread, carries an electrical path, supports assembly or only creates a rigid mounting feature. This functional context helps the supplier distinguish critical interfaces from cosmetic surfaces.
Show the complete overmolded geometry
Provide a drawing of the finished component as well as the insert alone. Dimension the insert position relative to functional silicone features and assembly datums. Mark the intended silicone coverage, exposed areas, transition edges, holes and shutoff regions. Cross-sections are especially useful where the insert is buried or where silicone thickness changes around it.
Identify thin silicone sections, deep pockets and sharp insert edges that may affect flow, venting, tearing or removal. Ask the supplier to review whether local radii, edge breaks or section changes are needed. Do not rely on a rendered image to communicate controlled dimensions.
The Molded Silicone Parts page provides a starting point for geometry, tooling and sample discussions.
Separate mechanical retention from interface adhesion
State whether the design expects mechanical retention, adhesion at the material interface or both. Mechanical concepts can include holes, grooves, undercuts, ribs or captured geometry, but each feature must be reviewed for insert strength, silicone flow, demolding and inspection. An interface that appears large in a model does not by itself establish a reliable bond.
If adhesion matters, describe the load direction, environment and acceptance question. Provide any approved surface preparation, primer or cleanliness restrictions, but keep every material pairing subject to project review. Compatibility can depend on the exact insert material, finish, contamination, storage, silicone system, processing and test method. Supplier review and representative samples are required.
Describe insert orientation and tooling access
Show how the insert may be located in the mold and which surfaces can act as supports or shutoffs. Mark features that cannot accept clamp marks, witness lines or temporary contact. If orientation is easy to reverse, add a poka-yoke feature or a clear inspection method rather than relying only on operator memory.
Explain whether inserts arrive loose, on a carrier, in trays or as a connected subassembly. Include realistic insert dimensional variation because tooling must locate actual parts, not only nominal CAD. Ask how the supplier plans to control movement during mold closing and material flow.
Identify sensitive and keep-clear areas
Threads, connector faces, electrical contacts, sealing surfaces and identification marks may need protection. Highlight these regions on the drawing and state the acceptable condition after molding. Where masking or secondary cleaning might be considered, ask the supplier to describe the method and its effect on inspection and handling.
Also identify insert edges that could damage mating components or become exposed if silicone shifts. The drawing should make clear whether a small witness of insert material is acceptable or whether full coverage is functionally necessary.
Plan samples around specific questions
Define what early samples must answer: insert position, silicone coverage, fit, appearance, handling, retention or an application-specific test. If prototype tooling or manually prepared inserts differ from the intended production route, record those differences. A prototype can help review geometry without proving the outcome of a later process.
Supply representative inserts from the expected production source and include the full range of relevant finishes or variants. If destructive sectioning or pull testing is requested, agree on specimen preparation, direction, rate, conditioning and reporting before samples are made. A test value is meaningful only when the method and failure mode are recorded.
Set practical inspection inputs
List dimensions that control insert location, silicone thickness and assembly. Agree on datums, fixtures and measurement conditions for the flexible finished part. State how exposed insert areas, flash, parting lines, silicone coverage and surface marks will be classified. Reference photographs or approved samples can support appearance review when used with a controlled revision.
For hidden interfaces, discuss indirect controls such as insert verification before molding, process records, weight checks or project-specific sampling. Do not demand inspection of an inaccessible feature without agreeing on a realistic method.
Address handling and traceability
Describe how inserts should be stored and presented to limit damage, mixing or contamination. Define labels for insert lot, silicone lot, drawing revision and finished-part lot when those records are needed. Packaging should protect exposed insert surfaces and prevent flexible sections from taking an unwanted set during shipment.
If the buyer supplies inserts, state the incoming quantity, acceptable surplus, damaged-part handling and reconciliation expectations. Keep commercial and timing assumptions project-specific because insert availability, preparation, tooling and sample scope can change the route.
Build the RFQ package
Include the finished-part drawing, insert drawing, 3D data, material and finish details, functional description, assembly context, quantity stages, sample objectives, inspection priorities and packaging needs. Mark required coverage, keep-clear areas, interface expectations and any approved preparation restrictions. Identify open questions instead of hiding them in general notes.
Ask the supplier to return assumptions, proposed retention approach, tooling questions, sample plan and verification method. Bond strength and material compatibility must remain project-specific until the exact construction and test context are reviewed.
To request a project-specific review, submit the controlled drawings, insert information, application context and sample questions through the Forvard Tech RFQ form.