Tolerance tables provided by the Rubber Manufacturer’s Association (RMA) come with ranges to illicit communication between the user and provider over a wide array of industries. It can be noted that precision tolerance can be achieved by utilizing the manufacturing process. In contrast, some mis-specified tolerances more often than not lead to irrelevant expenses.
As engineers and product designers, it is vital to understand the strict implementations that involve dimensional tolerances in silicone molded parts. Considerations affecting dimensions and tolerances in the design stage include the process in part volume, reduced shrinkage from bonded inserts, shrinkage after cure, and fixed vs. closure dimensions.
Some guidelines to acquire the right dimensional tolerances for silicone molded parts include the following:
1. Be guided with the Rubber Manufacturer’s Association manual when pinning down tolerances.
The RMA manual provides necessary guidelines for extracting the right tolerances for silicone molded parts. It is observed from the manual that medical line tolerances can be classified under the RMA’s A1 (high precision tolerance) section. The reason for this is the variety of tolerance ranges depending on a product’s design and need.
Using the RMA manual as a reference for product designers and engineers alike would help keep tolerance requirements feasible and more cost-efficient. Tolerances outside this limit may be hard to meet, and may lead to unwanted delays and extra cost.
2. Proper tooling maintenance.
Determining proper tooling results in consistent tolerance requirement. To widen the use of the tool, one must determine the right type of tooling alongside the manufacturing needs. The following might serve as a guide for choosing the appropriate tooling for silicone molded parts:
• Soft-Tooling- The ductile nature of a soft tool lets the engineer test different casting objects without changing drafts. Hence, the resultant prototype parts are accurate within a few thousandths of an inch. It is -24RC; typically used for prototype products, with 1,000 cycle guarantee.
• Pre-Hard Tooling- This tooling involves a 33RC-50RC (depending on the steel grade); and is often used for production tooling. In addition, it has a 10,000- 100,000 cycle guarantee.
• High-Precision Tooling- This tooling is pre-hard base of 33RC-50RC, with 250,000+ cycle guarantee. It has a single cavity bridge tooling for pre-production launch.
3. Review the design and manufacturing process.
In depth knowledge about the design and manufacturing process of silicone parts will prevent unnecessary expenses and dissatisfaction to both parties. Processes such as the molding technique, material shrink rate, geometry and impact of the component are factors to closely look at.
Using proper dimensional tolerances permits engineers and product designers to direct their attention to the key design features. These features may actually be the vital ones that would interact within the final assembly. Thus, the engineering challenge is to come up with a more functional silicone rubber parts.
With this, companies ought to be aware of the available processes, and have a clear understanding of each strengths and weaknesses together with the relative merits of the different materials they employ.