The selection of the right custom silicone tips for your product can be simple – until you make a small mistake which leads to a costly mistake, a waste of parts or a product launch failure. The vast majority of issues associated with custom silicone tip projects are not uncommon problems that would arise from unusual technical issues but rather predictable errors that would be committed during the initial specification and supplier selection process. Advanced OEM engineers get into these pitfalls because silicone is different than rigid plastics or metals.
This guide is based on actual production experience with a variety of brands in medical, food service and industrial applications. It covers the most frequently and expensively made errors in custom silicone tips orders and how to avoid them to keep your project on track and on budget.
Mistake 1 – Submitting Drawings That Are Not Ready for Silicone Molding
OEM teams typically begin with a drawing designed for injection-molded plastic or machined metal and pass it on to a silicone manufacturer. Molding tolerances and ultra-tight tolerances, as well as sharp corners and vertical walls, are difficult molding challenges for flexible silicone that are easy to handle for rigid parts.
The result? Changes to the tooling which occur after the mould has been cut, longer sampling periods, or parts which seem acceptable but do not work in use. For instance, a common requirement is to set the tolerance for an inner bore of a dispensing tip to ±0.05 mm. This is easily done for metal parts, but challenging and expensive for silicone without design modifications.
The answer to these concerns is simple: Just ask for a formal Design for Manufacturability (DFM) review before approving tooling. Include 2D drawings and 3D CAD files. If your team doesn’t have extensive silicone experience, solicit the supplier for annotated feedback on draft angles, parting lines, and wall thickness.
The discipline of getting drawings and requirements right before tooling begins is the single biggest factor separating teams that succeed at sourcing high-quality custom silicone products from those that spend months cycling through costly revisions.
Mistake 2 – Specifying Material Only as “Food-Grade” or “Medical-Grade” Without Further Detail
The term “food-grade silicone” or “medical-grade” on an RFQ may seem like enough but these are general terms. Even at a general grade, there are differences in hardness (durometer), cure system (platinum vs. peroxide), pigment compliance, extractables and sterilization compatibility.
Food-grade tips have come to us with pigments that weren’t properly documented, and medical tips that worked in their first few autoclave cycles but failed later on.
The best way to prevent it: Ensure that your RFQ is specific. Wrote the exact use, contact media, ways of sterilizing and necessary certificates such as FDA CFR 21, LFGB, ISO 10993, etc. Before approving, always ask for material datasheets, compliance statements and test summaries. If in any doubt, ask the supplier to suggest formulations in line with your requirements and validate with documentation.
Mistake 3 – Setting Tolerances Without Understanding Silicone Process Capability
A tolerance is usually determined in the same way as with rigid parts and applied to silicone tips. An intensive sort operation or a part that is close to impossible to produce consistently could significantly increase costs due to a tolerance of ±0.05 mm on the flexible wall or non-critical feature.
On the other hand, if tolerances are too large on critical sealing surfaces, then the assembly will fail later on.
The Costly Assumption That Silicone Behaves Like Rigid Plastic
Silicone deflects, recovers and changes dimension according to temperature, compression and measuring conditions. Parts can measure differently immediately after demolding, and hours later or at different temperatures.
Smart approach: Inquire from suppliers about their process capability data for similar features (Cpk). Tolerance should be based on RMA/ARPM guidelines and only reduced when required by function. Indicate critical versus non-critical dimensions and for critical dimensions and/or features, specify measurement conditions (e.g., temperature, fixturing, time since molding).
Mistake 4 – Choosing a Supplier on Unit Price Alone
The lowest per-piece pricing can end up costing more than it saves. The lowest cost supplier might be able to provide the first samples that are acceptable, but they have problems with the manufacturing process and end up with dimensional drift, color variation or material problems occurring after thousands of parts are delivered.
Better way: Assess suppliers’ ability, not just cost. Seek internal tooling, quality systems in documentation, material traceability and application experience. Compute total landed cost including tooling amortization, inspection and re-sourcing risk.
Questions to Ask a Supplier Before Placing a Tooling Order
- Make your own tooling? Which grades of steel do you use?
- Do you have a Cpk from similar parts that are now being produced?
- How are you going to let people know about your material changes?
- What are your actions when you have a non-conforming lot?
- Have you ever made silicone tips for other applications?
Good suppliers will know the answer to these questions and be able to give it to you confidently and specifically.
Mistake 5 – Providing Incomplete or Verbal Application Requirements
Any text, such as “we need a soft food-safe tip for a nozzle” is too vague. The resulting parts can be similar in size, but different in hardness, color, or compliance.
Prevention: Deliver a full written technical brief with drawings and tolerances, material and compliance requirements, colour specifications, surface finish, expected volumes, and documentation requirements. Ensure that all points have been accepted by the supplier formally before issuing purchase order.
Mistake 6 – Skipping or Rushing the Sampling Stage
In the process of project pressure, it is sometimes necessary to approve the first sample or to shorten the sampling rounds. When sampling, the problems can be addressed at a relatively low cost, but when scaled up to production level, the cost becomes very high.
Best practice: Include at least two sampling points in the timeline and have clear pass/fail criteria for each. Use real mating hardware and real environment to test the samples. Think of sampling as insurance and not an expense.
What a Proper Sample Approval Looks Like
A complete approval involves two sets of documents: dimensional reports of critical features, functional fit testing, material and durometer testing, visual inspection against agreed documents and signed-off golden samples that remain with both parties.
Mistake 7 – Ignoring Total Cost of Tooling Ownership
The cost of the first tool quote does not take into consideration tool life, cavity count, maintenance and replacement expenses. For high volume programs, a low cost single-cavity tool could have to be replaced often, adding up to a high overall cost.
Solution: Talk about tool life in shots and compare to your volume and product life. Avoid using multi-cavity hardened tools if you do not need a large quantity. Specify in the supply contract who is responsible for ownership, maintaining and replacing the equipment.
Mistake 8 – Neglecting Packaging and Handling Requirements
Bulk bags shipped en masse to various companies may contain silicone tips that are contaminated, distorted, or cavity-mixed, causing incoming inspection issues or assembly problems, particularly in medical and food industries.
Fix: Be specific in the purchase order about the bagging – individual, tray and/or clean room if necessary, lot and traceability labeling. For regulated products add these requirements to supplier quality agreement.
A Pre-Order Checklist for Custom Silicone Tips
When placing a tooling order, make sure you have:
- Fill in drawings with DFM feedback taken into account
- Specifications of the materials, and compliance paperwork.
- Silicone process capability based realistic tolerances
- Multiple rounds of sampling planned using functional testing.
- Supplier’s ability proven outside of cost.
- Ensure clear packaging and labelling and documentation requirements.
- The tooling life and overall cost expectations were in line with volume.
The following are common pitfalls that need to be avoided in silicone projects to make them successful and not painful. Doing the work in the beginning to obtain the correct specification and choose the right supplier can save hours, dollars and aggravation down the road.
