Engineering context
Secondary machining can refine bores, faces or datums after molding when the assembly needs a relationship that is difficult to hold directly from the tool.
The benefit must be weighed against extra handling, fixturing and the possibility of releasing molded-in stress. Machining also changes the datum chain if the gear tooth form remains as molded.
Secondary machining is most valuable when it controls a specific relationship that the molding process cannot hold economically. Typical candidates are precision bores, bearing seats or mounting faces. If the gear is fixtured from a cosmetic outer surface, however, machining may introduce a new eccentricity. The fixture should locate from a stable molded datum that has a known relationship to the teeth.
What the drawing needs to communicate
Identify exactly which feature is machined, which molded surface locates the part in the fixture and which dimensions are inspected afterward.
По возможности, указывайте эти данные на чертеже, в спецификации или в приложении к запросу предложений. Избегайте неформальных обсуждений, это упростит сравнение поставщиков и последующее внесение изменений.
Risk review
Adding a machined bore without a coherent tooth-to-bore datum can improve diameter size but not runout.
Sample acceptance
Use a fixture and inspection plan that references the functional gear datum structure.
For Secondary Machining of Molded Plastic Gears, close the DFM loop by updating the controlled CAD/drawing and sample plan. A recommendation that never reaches the released revision cannot be inspected consistently in production.
From design review to RFQ
Before requesting a price for secondary machining of molded plastic gears, identify the current drawing revision, production quantity, material constraint and the feature that most strongly affects function. Ask the supplier to flag any deviation from those inputs in the quotation so technical alternatives stay visible.
Практический анализ проекта для принятия данного решения.
Secondary machining can improve a final bore, datum, face or thread, but it changes the process chain. Define the datum used to locate the molded part, expected stock allowance, clamping method and how the machined feature relates to the gear teeth or molded interface.
Зафиксируйте допущения на чертеже или в запросе предложений, чтобы поставщик мог подтвердить их до составления коммерческого предложения. Если значение неизвестно, обозначьте его как незавершенную инженерную задачу, а не копируйте общий каталожный номер, который может не соответствовать сборке.
Лист проверки
- Molded datum used for setup
- Stock allowance
- Machined feature tolerance
- Clamp distortion risk
- Burr / stress / surface requirement
- Final inspection after machining
Используйте первый образец для подтверждения этих пунктов, используя как данные о размерах, так и соответствующую функциональную проверку. Любое допустимое отклонение должно быть зафиксировано в контролируемой версии перед повторным производством.
