CNC Machining vs. Vacuum Casting: How to Choose? A Guide to Process Decisions for Prototyping and Small-Batch Production
In different stages of product development, the needs for prototyping and small-batch production vary. When faced with two mainstream processes, CNC machining and vacuum casting, many R&D personnel may feel confused: when should CNC be used? When should casting be used? This article will compare them from multiple dimensions to help you make the right choice.
CNC Machining: Leading in Precision, Widest Material Selection
CNC machining is a subtractive process that removes material through computer-controlled machine tools. Its core advantages include:
- Material Diversity: It can process engineering plastics such as ABS, PC, POM, PEEK, as well as metal materials like aluminum alloy, stainless steel, magnesium alloy, and brass.
- High Precision: The standard tolerance can reach ±0.05mm, and precision parts can be controlled within ±0.01mm, meeting the needs of functional testing and assembly verification.
- No Mold Investment: Orders can start from 1 piece, without the need to bear mold costs, which is suitable for the stage with frequent design iterations.
The limitations of CNC machining mainly lie in the higher unit cost for small batches (more than 20 pieces), because the programming and setup time needs to be amortized.
Vacuum Casting: An Economical Choice for Small-Batch Production
Vacuum casting is a replication process based on silicone molds: first, a high-precision master model is made, then a silicone mold is created, and finally, PU resin is poured to obtain the replica. Its core advantages include:
- Cost Advantage: The cost of a silicone mold is only 1/10 to 1/5 of that of a formal steel mold, and the unit cost is extremely low within the range of 10 to 100 pieces.
- Close to Injection Molding Quality: The surface quality of the cast parts is excellent, and they can be painted, screen-printed, or electroplated, almost indistinguishable from mass-produced products.
- Fast Delivery: From confirming the drawings to the first batch of finished products, the standard delivery time is only 5-7 days.
The limitation of vacuum casting lies in the fact that although PU resin can simulate common plastics such as ABS, PC, PP, and soft rubber, it cannot completely replace all engineering plastics; also, the lifespan of a silicone mold is about 15-25 pieces, and multiple molds need to be made if the quantity exceeds this.
How to Choose Based on Quantity?
| Quantity Required | Recommended Process | Reason |
|---|---|---|
| 1-10 Pieces | CNC Machining | High precision, real material, no mold cost |
| 10-50 Pieces | CNC or Vacuum Casting | Choose CNC if the material requirements are high; choose casting if cost-sensitive and appearance is the main concern |
| 50-200 Pieces | Vacuum Casting | Significant cost advantage, surface close to injection molding |
| More than 200 Pieces | Simple Mold or Formal Mold | Casting is no longer economical, consider aluminum mold or steel mold |
Practical Decision Case: A medical equipment company needed 20 sets of casing for detection instruments for clinical testing. The unit cost of CNC machining was high; after using vacuum casting, not only was the cost significantly reduced, but the casing's texture fully met the doctors' trial requirements. The customer saved a considerable prototyping cost and accelerated the project schedule.
If you have prototyping or small-batch production needs, we recommend sending your drawings to Yiruida Technology. We provide free DFM analysis (Design for Manufacturability) and process recommendations to help you make the optimal decision.